JP2018010714A - Wien filter - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a wien filter capable of simply achieving convergence in two directions.SOLUTION: A wien filter comprises: a plurality of electromagnetic poles 90 of which eight or more are arranged at regular angle intervals as a center of an optical axis of a secondary beam, and is formed by a conductive material and a soft magnetic material; a coil wound to the circumference of each of the plurality of electromagnetic poles 90; and a shield member 91 arranged so as to cover the circumference of the plurality of electromagnetic poles 90. A uniform parallel electric field is applied to the plurality of electromagnetic poles 90 to a direction where a primary beam is deflected so as to be generated in an optical axis vicinity of a secondary beam. Different currents are applied to the coil to the direction where the primary beam is deflected so as to generate a uniform parallel magnetic field in the optical axis vicinity. A first beam hole 92 in which the primary beam makes incident from an oblique upper direction, a second beam hole 93 in which the primary beam is emitted and in which a secondary beam makes incident, and a third beam hole 94 in which the secondary beam is emitted are provided in the shield member 91, and an output surface 92b of the first beam hole 92 is not horizontal.SELECTED DRAWING: Figure 8

Description

  The present invention relates to a Wien filter which is composed of orthogonal electric and magnetic fields and is an energy separator for an electron beam.

  As a conventional semiconductor inspection apparatus, the movement of the sample accompanying the continuous movement of the stage is synchronized with the deflection of the trajectory of the electron beam (hereinafter referred to as secondary beam) emitted from the sample by electron irradiation to the sample by the deflecting means. The secondary image is stopped on the two-dimensional CCD sensor, and the image of the same detection area of the sample is projected on the same part of the two-dimensional CCD sensor during the synchronization period. 2. Description of the Related Art An electron beam inspection apparatus using a type of electron optical device is known (see, for example, Patent Document 1).

  Further, when the energy of the electron beam irradiated to the sample (hereinafter referred to as the primary beam) reaches several eV, not only the current density in the irradiation region is uniform, but also the uniformity of the incident angle distribution on the sample is obtained. Therefore, it is necessary to design an electron optical system that takes this into consideration.

  In the primary beam whose optical axis is bent by the Wien filter, the difference in the focusing characteristics between the electric field direction and the magnetic field direction is described in Patent Document 2, but when the bending angle of the primary beam is about 45 °, There is a significant difference that can no longer be called aberration.

Japanese Patent No. 4332922 Japanese Patent No. 3014210

  In designing the primary beam electron optical system, it is preferable that there is no difference in focusing characteristics between the electric field direction and the magnetic field direction as described in paragraph 0004. Furthermore, it is preferable that it can be realized by a Wien filter alone. In Patent Document 2, this is realized by changing the angle of the electrode. However, such a configuration is difficult to employ in a Wien filter including multipole electromagnetic poles.

  The present invention has been devised to pay attention to the above problems and to effectively solve them. An object of the present invention is to provide a Wien filter which is composed of multipole electromagnetic poles and hardly causes a difference in focusing characteristics between an electric field direction and a magnetic field direction of a primary beam.

According to an aspect of the present invention, the primary beam incident on the sample is irradiated from a diagonally upper direction, and is used in an inspection apparatus that inspects the sample based on the secondary beam generated from the sample. Is a Wien filter that emits with the direction of the substantially vertical downward direction emitted and changes the direction of the secondary beam incident vertically upward, with the optical axis of the secondary beam as the center, etc. Eight or more electromagnetic poles arranged at angular intervals and made of a conductive material and a soft magnetic material, a coil wound around each of the electromagnetic poles, and a shield member arranged to cover the periphery of the electromagnetic poles And different potentials can be applied to the electromagnetic poles so that a uniform parallel electric field is generated in the vicinity of the optical axis of the secondary beam in the direction in which the primary beam is deflected. Different currents can be applied to the shield member so that a uniform parallel magnetic field is generated in the vicinity of the optical axis of the secondary beam in the direction in which the primary beam is deflected, and the primary beam is applied to the shield member obliquely from above. An incident first beam hole, a first beam deflected by the electromagnetic pole is emitted, a second beam hole from which the secondary beam generated from the sample is incident, and a second beam emitted from the secondary beam. A Wien filter is provided, wherein three beam holes are provided, and an exit surface of the first beam hole is non-horizontal.
Since the exit surface of the first beam hole is non-horizontal, it is possible to improve the focusing characteristics of the primary beam incident from obliquely above.

  Preferably, the angle between the exit surface of the first beam hole and the horizontal plane is set according to a focusing characteristic in the electric field direction and a focusing characteristic in the magnetic field direction of the primary beam.

  The angle between the exit surface of the first beam hole and the horizontal plane may be set to an angle that reduces a deviation between the focusing characteristic in the electric field direction and the focusing characteristic in the magnetic field direction of the primary beam.

  The angle between the exit surface of the first beam hole and the horizontal plane may be set to an angle that reduces the deviation between the focusing position of the primary beam in the electric field direction and the focusing position in the magnetic field direction.

  The primary beam may be incident on the first beam hole from 45 degrees obliquely above, and an angle between the exit surface of the first beam hole and a horizontal plane may be approximately 90 degrees.

  The electromagnetic pole may superimpose a quadrupole electric field or a quadrupole magnetic field in addition to the uniform parallel electric field and the uniform parallel magnetic field.

  According to the present invention, bi-directional focusing of the primary beam can be achieved without adding a new optical element. Further, since only the shape of the shield member is changed, there is no need to change the shape of the electrodes and magnetic poles asymmetrically as in Patent Document 2, so that bi-directional focusing can be realized more easily, and the secondary beam advances at the same time. There are no factors that tend to impair sex.

It is an elevation view which shows the main components of the inspection apparatus which concerns on one Embodiment of this invention. It is the top view of the main components of the inspection apparatus shown in FIG. 1, Comprising: It is the figure seen along line BB of FIG. It is a figure which shows the structure of the electron optical apparatus which concerns on one Embodiment of this invention. It is a figure for demonstrating the beam path | route in the electron optical apparatus shown in FIG. (A) It is a figure explaining operation | movement of the high-speed deflector which deflects a secondary beam so that the secondary beam which concerns on one Embodiment of this invention follows the movement of a wafer. (B) It is a figure which shows the relationship between the irradiation area | region which concerns on one Embodiment of this invention, and a visual field area | region. (C) It is a figure which shows the relationship between the irradiation area | region and visual field area | region which concern on one Embodiment of this invention. It is a figure which shows the structure of the combination unit of the high-speed deflector, imaging lens, and intermediate electrode which concerns on one Embodiment of this invention. It is a flowchart which shows operation | movement of the simulation apparatus which concerns on one Embodiment of this invention. (A) It is sectional drawing of the Wien filter 726 which concerns on this embodiment. (B) It is a figure which shows the radiation | emission position of primary beam B1-B4 in the Wien filter 726 which concerns on this embodiment. 4 is a perspective view schematically showing a plurality of electromagnetic poles 90. FIG. It is a figure which shows typically the figure which looked at the cross section of the shield member 91 from diagonally. It is a figure which shows the focusing characteristic of the electric field direction of the primary beams B1-B4 in the Wien filter 726 which concerns on this embodiment, and a magnetic field direction. It is sectional drawing of the Wien filter 726 which concerns on a modification. (A) It is sectional drawing of Wien filter 726 'which concerns on a comparative example. (B) It is a figure which shows the radiation | emission position of primary beam B1-B4 in Wien filter 726 'which concerns on this embodiment. It is a figure which shows the focusing characteristic of the electric field direction of the primary beams B1-B4 in the Wien filter 726 'which concerns on a comparative example, and a magnetic field direction. The figure which shows schematic structure of the electron gun 721, the primary optical system 72, the secondary optical system 74, and the detector 761 as an electron generation source. The figure which shows typically the orbit of the secondary emission electron in the secondary optical system. The figure explaining an image tracking function. The figure explaining an image tracking function. The figure explaining an image tracking function. The figure explaining an image tracking function. FIG. 6 is a schematic cross-sectional view of an E × B filter 1022. FIG. 6 is a schematic top view of an E × B filter 1022. The typical sectional view of the electromagnetic pole in ExB filter 1022. FIG. The figure which shows typically the electric field and magnetic field which normalized the broken-line part in FIG. 18A. The figure which shows typically the electric field and magnetic field which normalized the broken-line part in FIG. 18A. The simulation result which calculated the distortion of the electronic image projected on the detector 761. FIG. The simulation result which calculated the distortion of the electronic image projected on the detector 761. FIG.

  Hereinafter, an inspection apparatus according to an embodiment of the present invention will be described with reference to the drawings. The embodiment described below shows an example when the present invention is implemented, and the present invention is not limited to the specific configuration described below. In carrying out the present invention, a specific configuration according to the embodiment may be adopted as appropriate.

In FIG.1 and FIG.2, the main component of the inspection apparatus 1 by this embodiment is shown by the elevation and the plane.
The inspection apparatus 1 according to the present embodiment includes a cassette holder 10 that holds a cassette that stores a plurality of samples, a mini-environment device 20, a main housing 30 that defines a working chamber, a mini-environment device 20, and a main A loader housing 40 disposed between the housing 30 and defining two loading chambers; a loader 60 for loading a sample from the cassette holder 10 onto a stage device 50 disposed in the main housing 30; An electron optical device 70 attached to the housing 30, an optical microscope 3000, and a scanning electron microscope (SEM) 3002 are provided and are arranged in a positional relationship as shown in FIGS. 1 and 2. The inspection apparatus 1 further includes a precharge unit 81 disposed in the vacuum main housing 30, a potential application mechanism that applies a potential to the sample, an electron beam calibration mechanism, and positioning of the sample on the stage device 50. And an optical microscope 871 constituting an alignment control device 87 for performing the above.

  Here, the sample is an exposure mask, EUV mask, nanoimprint mask (and template), semiconductor wafer, optical element substrate, optical circuit substrate, or the like. Some of these have a pattern and some have no pattern. Some of them have a pattern and some do not. Patterns with no irregularities are formed with different materials. Those without a pattern include those coated with an oxide film and those not coated with an oxide film.

<Cassette holder>
The cassette holder 10 includes a plurality of cassettes c (for example, closed cassettes such as SMIF and FOUP manufactured by Assist) in which a plurality of samples (for example, 25 sheets) are stored in a state of being arranged in parallel in the vertical direction. 2 in this embodiment). As this cassette holder, a cassette having a structure suitable for the case where the cassette is transported by a robot or the like and automatically loaded into the cassette holder 10, or an open cassette having a structure suitable for the manual loading is used. Each can be selected and installed. In this embodiment, the cassette holder 10 is of a type in which the cassette c is automatically loaded. For example, the cassette holder 10 includes an elevating table 11 and an elevating mechanism 12 that moves the elevating table 11 up and down. 2 can be automatically set in the state shown by the chain line in FIG. 2, and after the setting, the first transport unit 61 in the mini-environment apparatus 20 is automatically rotated to the state shown in the solid line in FIG. Directed to the pivot axis. Further, the lifting table 11 is lowered to the state shown by the chain line in FIG. As described above, the cassette holder used for automatic loading or the cassette holder used for manual loading may be a known structure as appropriate. Description is omitted.

  The sample stored in the cassette c is a sample to be inspected, and such inspection is performed after or during the process of processing the sample in the semiconductor manufacturing process. Specifically, a sample subjected to a film forming process, CMP, ion implantation, or the like, a sample having a pattern formed on the surface, or a sample in which a pattern has not yet been formed is stored in a cassette. Since a large number of samples accommodated in the cassette c are arranged side by side in parallel in the vertical direction, the first transport unit 61 can hold the sample at an arbitrary position by the first transport unit 61. The arm 612 can be moved up and down.

<Mini-environment device>
1 and 2, a mini-environment device 20 includes a housing 22 that defines a mini-environment space 21 that is controlled in atmosphere, and a gas such as clean air in the mini-environment space 21. A gas circulation device 23 for circulating and controlling the atmosphere, a discharge device 24 for collecting and discharging a part of the air supplied into the mini-environment space 21, and a mini-environment space 21 are provided. And a pre-aligner 25 for roughly positioning a sample to be inspected.

  The housing 22 has a top wall 221, a bottom wall 222, and a peripheral wall 223 that surrounds the four circumferences, and has a structure that blocks the mini-environment space 21 from the outside. In order to control the atmosphere of the mini-environment space, the gas circulation device 23 is attached to the top wall 221 in the mini-environment space 21 to clean the gas (in this embodiment, air) and / or A gas supply unit 231 for flowing clean air in a laminar flow through the above gas outlet (not shown) and a bottom wall 222 in the mini-environment space 21 are arranged on the bottom wall 222 and directed toward the bottom. A recovery duct 232 for recovering the air that has flowed down, and a conduit 233 for connecting the recovery duct 232 and the gas supply unit 231 and returning the recovered air to the gas supply unit 231. In this embodiment, the gas supply unit 231 takes about 20% of the supplied air from the outside of the housing 22 and cleans it. However, the ratio of the gas taken in from the outside can be arbitrarily selected. . The gas supply unit 231 includes a HEPA or ULPA filter having a known structure for producing clean air. The laminar flow of the clean air, that is, the downward flow, that is, the downflow is mainly supplied to flow through the transport surface by the first transport unit 61 disposed in the mini-environment space 21 and is generated by the transport unit. This prevents dust having a possibility of adhering to the sample. Therefore, it is not always necessary that the downflow jet outlet is located close to the top wall as shown in the drawing, and it is sufficient if it is above the transport surface of the transport unit. Moreover, there is no need to flow over the entire mini-environment space. In some cases, cleanliness can be ensured by using ion wind as clean air. Further, a sensor for observing the cleanliness can be provided in the mini-environment space, and the apparatus can be shut down when the cleanliness deteriorates. An entrance / exit 225 is formed in a portion of the peripheral wall 223 of the housing 22 adjacent to the cassette holder 10. A shutter device having a known structure may be provided in the vicinity of the doorway 225 so that the doorway 225 is closed from the mini-environment device side. The laminar flow downflow created in the vicinity of the sample may be, for example, a flow rate of 0.3 to 0.4 m / sec. The gas supply unit may be provided outside the mini-environment space 21 instead of inside it.

  The discharge device 24 includes a suction duct 241 disposed below the first transport unit 61 at a position below the sample transport surface of the first transport unit 61, and a blower (not shown) disposed outside the housing 22. And a conduit (not shown) connecting the suction duct 241 and the blower. The discharge device 24 flows down around the first transport unit 61, sucks in gas containing dust that may be generated by the first transport unit 61 by the suction duct 241, and passes through the conduit and the blower. To the outside of the housing 22. In this case, the air may be discharged into an exhaust pipe (not shown) drawn near the housing 22.

  The pre-aligner 25 disposed in the mini-environment space 21 is formed on an orientation flat formed on the sample (referred to as a flat portion formed on the outer periphery of a circular sample, hereinafter referred to as an orientation flat) or on the outer periphery of the sample. One or more V-shaped notches or notches are detected optically or mechanically to pre-position the rotational position around the specimen axis OO with an accuracy of about ± 1 degree. It is supposed to keep. The pre-aligner 25 constitutes a part of the mechanism for determining the coordinates of the inspection object and is responsible for the rough positioning of the inspection object. Since the pre-aligner 25 itself may have a known structure, the description of the structure and operation is omitted.

  Although not shown, a recovery duct for a discharge device may be provided below the pre-aligner 25 so that air containing dust discharged from the pre-aligner 25 may be discharged to the outside.

<Main housing>
1 and 2, a main housing 30 that defines a working chamber 31 includes a housing main body 32, and the housing main body 32 is placed on a vibration isolating device, that is, a vibration isolating device 37 disposed on a base frame 36. It is supported by the mounted housing support device 33. The housing support device 33 includes a frame structure 331 assembled in a rectangular shape. The housing main body 32 is disposed and fixed on the frame structure 331, and is connected to the bottom wall 321 mounted on the frame structure, the top wall 322, the bottom wall 321 and the top wall 322, and surrounds the circumference. 323 to isolate the working chamber 31 from the outside. In this embodiment, the bottom wall 321 is composed of a relatively thick steel plate so as not to be distorted by weighting by equipment such as the stage device 50 placed on the bottom wall 321. Also good. In this embodiment, the housing body 32 and the housing support device 33 are assembled in a rigid structure, and vibration from the floor on which the base frame 36 is installed is transmitted to the rigid structure by the vibration isolator 37. It comes to stop. An entrance / exit 325 for taking in and out the sample is formed in the peripheral wall 323 of the housing body 32 adjacent to the loader housing described later.

  The vibration isolator 37 may be an active type having an air spring, a magnetic bearing or the like, or a passive type having these. Since any of them may have a known structure, description of its own structure and function is omitted. The working chamber 31 is maintained in a vacuum atmosphere by a known vacuum device (not shown). A control device 2 that controls the operation of the entire apparatus is disposed under the base frame 36.

<Loader housing>
1 and 2, the loader housing 40 includes a housing body 43 that defines a first loading chamber 41 and a second loading chamber 42. The housing main body 43 includes a bottom wall 431, a top wall 432, a peripheral wall 433 that surrounds the four circumferences, and a partition wall 434 that partitions the first loading chamber 41 and the second loading chamber 42. Can be isolated from the outside. The partition wall 434 is formed with an opening, that is, an entrance / exit 435 for exchanging samples between both loading chambers. In addition, entrances 436 and 437 are formed in a portion of the peripheral wall 433 adjacent to the mini-environment device and the main housing. The housing main body 43 of the loader housing 40 is placed on and supported by the frame structure 331 of the housing support device 33. Therefore, the floor vibration is not transmitted to the loader housing 40. The entrance / exit 436 of the loader housing 40 and the entrance / exit 226 of the housing 22 of the mini-environment device 20 are aligned with each other, and there is a shutter that selectively blocks communication between the mini-environment space 21 and the first loading chamber 41. A device 27 is provided. The shutter device 27 surrounds the entrances 226 and 436 and seals 271 fixed in close contact with the peripheral wall 433, and a door 272 that prevents air from flowing through the entrances in cooperation with the seal 271. And a driving device 273 for moving the door. Further, the entrance / exit 437 of the loader housing 40 and the entrance / exit 325 of the housing main body 32 are aligned with each other, and there is a shutter device 45 that selectively blocks the communication between the second loading chamber 42 and the working chamber 31. Is provided. The shutter device 45 surrounds the entrances and exits 437 and 325 and in close contact with the peripheral walls 433 and 323 and cooperates with the sealing material 451 and the sealing material 451 fixed to them, and allows air to flow through the entrance and exit. It has a door 452 for blocking and a driving device 453 for moving the door. Further, the opening formed in the partition wall 434 is provided with a shutter device 46 which is closed by a door 461 and selectively prevents communication between the first and second loading chambers. These shutter devices 27, 45 and 46 are adapted to hermetically seal each chamber when in the closed state. Since these shutter devices may be known ones, detailed description of their structure and operation will be omitted. The support method of the housing 22 of the mini-environment device 20 and the support method of the loader housing are different, and vibrations from the floor are prevented from being transmitted to the loader housing 40 and the main housing 30 via the mini-environment device 20. Therefore, an anti-vibration cushion material may be disposed between the housing 22 and the loader housing 40 so as to airtightly surround the doorway.

  In the first loading chamber 41, a sample rack 47 is disposed that supports a plurality (two in this embodiment) of samples in a horizontal state with a vertical separation. The sample rack 47 includes support columns fixed in an upright state at four corners of a rectangular substrate 471, and each support column 472 has a two-stage support portion formed on the support portion. Is placed and held. The tips of the arms of the first and second transfer units described later are brought close to the sample from between the adjacent columns, and the sample is held by the arm.

The loading chambers 41 and 42 can be controlled in a high vacuum state (the degree of vacuum is 10 ⁻⁵ to 10 ⁻⁶ Pa) by an evacuation apparatus (not shown) having a known structure including a vacuum pump (not shown). It has become. In this case, the first loading chamber 41 can be maintained as a low vacuum chamber in a low vacuum atmosphere, and the second loading chamber 42 can be maintained as a high vacuum chamber in a high vacuum atmosphere to effectively prevent sample contamination. By adopting such a structure, the sample accommodated in the loading chambers 41 and 42 and to be inspected next can be transported into the working chamber 31 without delay. By adopting such loading chambers 41 and 42, the throughput of defect inspection is improved, and the degree of vacuum around the laser light source that is required to be stored in a high vacuum state is as high as possible. Can be.

  A vacuum exhaust pipe and a vent pipe (not shown) for an inert gas (for example, dry pure nitrogen) are connected to the first and second loading chambers 41 and 42, respectively. Thereby, the atmospheric pressure state in each loading chamber is achieved by an inert gas vent (injecting an inert gas to prevent oxygen gas other than the inert gas from adhering to the surface). Since the apparatus for performing such an inert gas vent itself may have a known structure, a detailed description thereof will be omitted.

<Stage device>
The stage device 50 includes a fixed table 51 disposed on the bottom wall 321 of the main housing 30, a Y table 52 that moves in the Y direction (a direction perpendicular to the paper surface in FIG. 1) on the fixed table, and a Y table. An X table 53 that moves in the X direction (left-right direction in FIG. 1), a rotary table 54 that can rotate on the X table, and a holder 55 that is arranged on the rotary table 54 are provided. The sample is releasably held on the sample placement surface 551 of the holder 55. The holder may have a known structure capable of releasably gripping the sample mechanically or by an electrostatic chuck method. The stage device 50 operates a plurality of tables as described above by using a servo motor, an encoder, and various sensors (not shown), thereby causing the sample held by the holder on the mounting surface 551 to be electro-optically. Positioning can be performed with high accuracy in the X direction, Y direction, and Z direction (up and down direction in FIG. 1) with respect to the electron beam emitted from the apparatus 70, and further in the direction around the vertical axis (θ direction) on the sample support surface. It is like that. For positioning in the Z direction, for example, the position of the mounting surface on the holder may be finely adjusted in the Z direction. In this case, the reference position of the mounting surface is detected by a position measuring device (laser interference distance measuring device using the principle of an interferometer) using a fine-diameter laser, and the position is controlled by a feedback circuit (not shown). Instead, the position of the notch or orientation flat of the sample is measured to detect the planar position and rotation position of the sample with respect to the electron beam, and the rotation table is rotated by a stepping motor capable of controlling a minute angle or the like. Servo motors 521 and 531 for the stage device 50 and encoders 522 and 532 are disposed outside the main housing 30 in order to prevent dust from being generated in the working chamber as much as possible. Note that the stage device 50 may have a known structure used in, for example, a stepper and the like, and a detailed description of the structure and operation will be omitted. Also, since the laser interference distance measuring device may have a known structure, detailed description of the structure and operation is omitted.

  Standardization of the signal indicating the rotation position and X and Y position of the sample obtained during inspection by inputting the rotation position and X and Y position of the sample with respect to the electron beam in advance to a signal detection system or image processing system described later. Can also be planned. Further, the sample chuck mechanism provided in the holder is adapted to apply a voltage for chucking the sample to the electrode of the electrostatic chuck, and is provided at three points (preferably equally spaced in the circumferential direction) of the outer periphery of the sample. It is designed to press and hold (separated). The sample chuck mechanism includes two fixed positioning pins and one pressing clamp pin. The clamp pin can realize automatic chucking and automatic release, and constitutes a conduction point for voltage application.

  In this embodiment, the table that moves in the left-right direction in FIG. 2 is the X table and the table that moves in the up-down direction is the Y table. However, the table that moves in the left-right direction in FIG. The moving table may be an X table.

  As shown in FIGS. 1 and 2, the stage apparatus 1 of the present embodiment places the first and second samples W and moves continuously, and the primary optical system of the first electron optical apparatus 701. While 76 is irradiating the first sample W with the primary beam, the primary optical system of the second electron optical device 702 irradiates the second sample with the primary beam. According to such an aspect, the time required for the inspection of the plurality of samples W can be significantly shortened.

<Loader>
The loader 60 includes a robot-type first transfer unit 61 arranged in the housing 22 of the mini-environment device 20 and a robot-type second transfer unit 63 arranged in the second loading chamber 42. I have.

The first transport unit 61 has a multi-node arm 612 that is rotatable about the axis O ₁ -O ₁ with respect to the drive unit 611. As the multi-node arm, an arbitrary structure can be used, but in this embodiment, the multi-node arm has three portions which are rotatably attached to each other. One portion of the arm 612 of the first transport unit 61, that is, the first portion closest to the drive unit 611 is a shaft that can be rotated by a drive mechanism (not shown) having a known structure provided in the drive unit 611. 613 is attached. The arm 612 can be rotated around the axis O ₁ -O ₁ by the shaft 613, and can expand and contract in the radial direction with respect to the axis O ₁ -O ₁ as a whole by relative rotation between the parts. A gripping device 616 for gripping a sample such as a mechanical chuck or an electrostatic chuck having a known structure is provided at the tip of the third portion farthest from the shaft 613 of the arm 612. The drive unit 611 can be moved in the vertical direction by an elevating mechanism 615 having a known structure.

  The first transport unit 61 has an arm extending in one direction M1 or M2 of the two cassettes c in which the arm 612 is held by the cassette holder 10, and the sample stored in the cassette c is armed. On the top of the arm or gripped by a chuck (not shown) attached to the tip of the arm. Thereafter, the arm contracts (as shown in FIG. 2), and the arm rotates to a position where it can extend in the direction M3 of the pre-aligner 25 and stops at that position. Then, the arm 612 extends again and the sample held by the arm 612 is placed on the pre-aligner 25. After receiving the sample from the pre-aligner 25 in the reverse direction, the arm 612 further rotates and stops at a position where the arm 612 can extend toward the second loading chamber 41 (direction M4), and the sample in the second loading chamber 41 is stopped. The sample is delivered to the rack 47. Note that when the sample is mechanically gripped, the periphery of the sample (in the range of about 5 mm from the periphery) is gripped. This is because a device (circuit wiring) is formed on the entire surface excluding the peripheral portion of the sample, and if this portion is gripped, the device is broken or a defect is generated.

  The second transport unit 63 is basically the same in structure as the first transport unit 61, and only differs in that the sample is transported between the sample rack 47 and the stage device 50 mounting surface. Therefore, detailed description is omitted.

  In the loader 60, the first and second transport units 61 and 63 substantially transport the sample from the cassette held in the cassette holder 10 onto the stage device 50 disposed in the working chamber 31 and vice versa. The arm of the transfer unit moves up and down while keeping it in a horizontal state, simply taking out the sample from the cassette and inserting it into the cassette, placing the sample on the sample rack and taking it out from it, and taking the sample This is only at the time of mounting on the stage device 50 and taking it out from the stage device 50. Therefore, a large sample, for example, a sample having a diameter of 30 cm or 45 cm can be moved smoothly.

<Sample transport>
Next, the conveyance of the sample from the cassette c supported by the cassette holder 10 to the stage device 50 disposed in the working chamber 31 will be described in order.

  As described above, the cassette holder 10 has a structure suitable for manually setting a cassette, and has a structure suitable for automatically setting a cassette. In this embodiment, when the cassette c is set on the lifting table 11 of the cassette holder 10, the lifting table 11 is lowered by the lifting mechanism 12 and the cassette c is aligned with the entrance / exit 225.

  When the cassette is aligned with the entrance / exit 225, a cover (not shown) provided in the cassette c is opened, and a cylindrical cover is disposed between the cassette c and the entrance / exit 225 of the mini-environment. The inside of c and the mini environment space 21 is shut off from the outside. Since these structures are publicly known, detailed description of the structure and operation is omitted. When a shutter device that opens and closes the entrance / exit 225 is provided on the mini-environment device 20 side, the shutter device operates to open the entrance / exit 225.

  On the other hand, the arm 612 of the first transport unit 61 is stopped in a state facing in either the direction M1 or M2 (in this description, the direction of M2). One of the samples stored in the container is received. In this embodiment, the vertical position adjustment between the arm 612 and the sample to be taken out from the cassette c is performed by the vertical movement of the drive unit 611 and the arm 612 of the first transport unit 61. You may carry out by the up-and-down movement of the raising / lowering table 11, or you may perform both.

When the reception of the sample by the arm 612 is completed, the arm 612 is contracted, the shutter device is operated to close the entrance / exit (when the shutter device is present), and then the arm 612 is rotated around the axis O ₁ -O _1. It will be in the state which can expand | extend toward the direction M3. Then, the arm 612 extends, the sample placed on the tip or held by the chuck is placed on the pre-aligner 25, and the pre-aligner 25 changes the direction of rotation of the sample (direction around the central axis perpendicular to the sample surface). Position within a predetermined range. When the positioning is completed, the first transport unit 61 receives the sample from the pre-aligner 25 at the tip of the arm 612 and then contracts the arm 612 so that the arm 612 can be extended in the direction M4. Then, the door 272 of the shutter device 27 moves to open the entrances 226 and 436 and the arm 612 extends to place the sample on the upper stage side or the lower stage side of the sample rack 47 in the first loading chamber 41. Note that the opening 435 formed in the partition wall 434 is closed in an airtight state by the door 461 of the shutter device 46 before the shutter device 27 is opened and the sample is delivered to the sample rack 47 as described above.

  In the process of transporting the sample by the first transport unit 61, clean air flows in a laminar flow (as a downflow) from the gas supply unit 231 provided on the housing 22 of the mini-environment device 20. Prevents dust from adhering to the upper surface of the sample. Part of the air around the transport unit 61 (in this embodiment, air that is mainly dirty with about 20% of the air supplied from the supply unit) is sucked from the suction duct 241 of the discharge device 24 and discharged out of the housing. . The remaining air is recovered via a recovery duct 232 provided at the bottom of the housing 22 and returned to the gas supply unit 231 again.

  When a sample is placed on the sample rack 47 in the first loading chamber 41 of the loader housing 40 by the first transport unit 61, the shutter device 27 is closed and the loading chamber 41 is sealed. Then, after the inert gas is expelled in the first loading chamber 41 and the air is expelled, the inert gas is also discharged and the inside of the loading chamber 41 is made a vacuum atmosphere. The vacuum atmosphere in the first loading chamber 41 may be a low degree of vacuum. When the degree of vacuum in the loading chamber 41 is obtained to some extent, the shutter device 46 operates to open the entrance / exit 435 sealed by the door 461, the arm 632 of the second transport unit 63 extends, and the sample is held by the gripping device at the tip. One sample is received from the rack 47 (mounted on the tip or held by a chuck attached to the tip). When the reception of the sample is completed, the arm 632 contracts and the shutter device 46 operates again to close the entrance / exit 435 with the door 461. Note that before the shutter device 46 is opened, the arm 632 is in a posture capable of extending in the direction N1 of the sample rack 47 in advance. In addition, as described above, the doors 437 and 325 are closed by the door 452 of the shutter device 45 before the shutter device 46 is opened, thereby preventing communication between the second loading chamber 42 and the working chamber 31 in an airtight state. The inside of the second loading chamber 42 is evacuated.

When the shutter device 46 closes the entrance / exit 435, the inside of the second loading chamber 42 is evacuated again, and is evacuated at a higher degree of vacuum than in the first loading chamber 41. Meanwhile, the arm 632 of the second transfer unit 63 is rotated to a position where it can extend toward the stage device 50 in the working chamber 31. On the other hand, in the stage apparatus 50 in the working chamber 31, the Y table 52 has an X axis line X ₁ − that passes through the rotation axis O ₂ −O ₂ of the second transport unit 63 with the center line X ₀ -X ₀ of the X table 53. X ₁ and up to approximately match the position, moves upward in FIG. 2, Further, X table 53 is moved to a position close to the leftmost position in FIG. 2, is waiting in this state. When the second loading chamber 42 becomes substantially the same as the vacuum state of the working chamber 31, the door 452 of the shutter device 45 moves to open the entrances 437 and 325 and the arm 632 extends to hold the sample, and the tip of the arm 632 holds the sample. The stage device 50 in the chamber 31 is approached. Then, the sample is placed on the placement surface 551 of the stage device 50. When the placement of the sample is completed, the arm 632 contracts and the shutter device 45 closes the entrances 437 and 325.

  The operation until the sample in the cassette c is transported onto the stage device 50 has been described above. To return the sample placed on the stage device 50 and completed processing from the stage device 50 to the cassette c, The reverse operation is performed. Further, in order to place a plurality of samples on the sample rack 47, the first transport unit 61 performs the transport of the sample between the sample rack 47 and the stage device 50 by the second transport unit 63. The sample can be transported between the cassette c and the sample rack 47, and the inspection process can be performed efficiently.

  Specifically, in the case where there are already processed sample A and unprocessed sample B in the sample rack 47, (1) First, the unprocessed sample B is moved to the stage device 50, the processing is started, 2) During this processing, the processed sample A is moved from the stage device 50 to the sample rack 47 by the arm 632, and the unprocessed sample C is similarly extracted from the sample rack 47 by the arm 632 and positioned by the pre-aligner 25. Move to the sample rack 47 of the loading chamber 41. In this way, in the sample rack 47, the processed sample A can be replaced with the unprocessed sample C while the sample B is being processed.

Further, depending on how to use such an apparatus for performing inspection or evaluation, a plurality of stage apparatuses 50 are placed in parallel, and a plurality of specimens are transferred by moving specimens from one sample rack 47 to each apparatus. Simultaneous processing is also possible.
According to the above embodiment, the following effects can be obtained.

(A) An overall configuration of a mapping projection type inspection apparatus using an electron beam is obtained, and an inspection object can be processed with high throughput.
(B) Inspecting the inspection object while monitoring the dust in the space by providing a sensor for observing the cleanliness by supplying a clean gas to the inspection object in the mini-environment space to prevent the adhesion of dust. Can do.
(C) Since the loading chamber and the working chamber are integrally supported via the vibration preventing device, it is possible to supply and inspect the inspection target to the stage device 50 without being affected by the external environment.

<Electronic optical device>
FIG. 3 is a diagram illustrating a configuration of the electro-optical device 70. FIG. 4 is a diagram for explaining a beam path in the electron optical device 70. The inspection target (sample) of the electron optical device 70 is the sample W. The sample W is a silicon wafer, a glass mask, a semiconductor substrate, a semiconductor pattern substrate, a substrate having a metal film, or the like. The electron beam inspection apparatus according to the present embodiment detects the presence of foreign matter on the surface of the sample W made of these substrates. The foreign material is an insulator, a conductive material, a semiconductor material, or a complex thereof. The types of foreign substances are particles, cleaning residues (organic substances), reaction products on the surface, and the like.

  As shown in FIGS. 3 and 4, the electron optical device 70 includes a primary optical system 72 that generates an electron beam and a secondary optical system 74 that forms an enlarged image of secondary emission electrons or mirror electrons from the sample W. And a detector 761 for detecting these electrons. An image processing unit 763 that processes a signal from the detector 761 is connected to the detector 761.

  The primary optical system 72 is configured to generate an electron beam and collectively irradiate the sample W with an area covering the detection size of the detector 761. The primary optical system 72 includes an electron gun 721, a lens 722, an aperture 723, a Wien filter 726, and a lens 727. The electron gun 721 has a laser light source 7211 and a light emitting surface cathode 7212, and an electron beam is generated by the electron gun 721. The generated electron beam is accelerated and shaped by the lens 722 and the aperture 723. In the Wien filter 726, the electron beam is affected by the Lorentz force due to the magnetic field and the Coulomb force due to the electric field, is incident obliquely from above, is deflected vertically downward, and travels toward the sample W. The lens 727 projects an intermediate image formed in the vicinity of the Wien filter 726 onto the sample W. The primary beam is decelerated near the sample W and is incident on the sample W or reflected near the sample W.

  The primary optical system 72 irradiates both a precharged electron beam for charging and an imaging electron beam. The incident energy (landing energy) of the primary beam to the sample W is defined by the difference between the sample potential and the acceleration potential of the electron gun. The experimental results show that the precharge landing energy LE1 and the landing energy of the imaging electron beam The difference from LE2 is preferably 5 to 20 [eV].

  In this regard, when there is a potential difference between the foreign matter on the surface 21 of the sample W and the surroundings, it is assumed that the precharge landing energy LE1 is irradiated in the negatively charged region. The charge-up voltage varies depending on the value of LE1. This is because the relative ratio of LE1 and LE2 changes (LE2 is the landing energy of the imaging electron beam as described above). When LE1 is large, the charge-up voltage becomes high, whereby a reflection point is formed at a position above the foreign substance (position closer to the detector 761). Depending on the position of this reflection point, the trajectory and transmittance of the mirror electrons change. Therefore, an optimum charge-up voltage condition is determined according to the reflection point. On the other hand, if LE1 is too low, the efficiency of forming mirror electrons decreases. The difference between LE1 and LE2 is preferably 5 to 20 [eV]. The value of LE1 is preferably 0 to 40 [eV], more preferably 5 to 20 [eV].

  By adjusting the conditions of the electric field and magnetic field of the Wien filter 726, the incident angle of the primary electron beam on the sample W can be determined. For example, the conditions of the Wien filter 726 can be set so that the primary beam is incident on the sample W perpendicularly. In order to further increase the sensitivity, for example, it is effective to slightly tilt the incident angle of the electron beam of the primary optical system with respect to the sample W. An appropriate inclination angle is 0.05 to 10 degrees, preferably about 0.1 to 3 degrees.

  In this way, by irradiating the foreign object with an electron beam with a slight incident angle, the signal from the foreign object is strengthened, and at the same time, the condition that the mirror electron trajectory does not deviate from the center of the optical axis of the secondary optical system. Since it can be formed, the transmittance of mirror electrons can be increased. Therefore, the tilted electron beam is very advantageously used when the foreign particles are charged up to guide the mirror electrons.

  There is a sample W on the stage device 50, and there is a foreign substance on the sample W. The primary beam is applied to the surface 21 of the sample W with landing energy LE5 to 10 [eV]. Electrons of the primary beam are bounced back without contacting the foreign matter by the foreign matter charged up in advance. The mirror electrons thus generated are guided to the detector 761 by the secondary optical system 74. At the same time, secondary emission electrons by the primary beam irradiated on the surface 21 of the sample W that is not charged up are also generated. However, the secondary electron emission efficiency by electron irradiation with landing energy LE of about 5 to 10 [eV] is close to 0, and secondary electrons are emitted from the surface 21 of the sample W with an angular distribution close to Lambert's cos law. Most of the secondary electrons are cut by the aperture 742 of the secondary electron optical system, and the proportion of secondary electrons reaching the detector 761 is a low value, for example, about 0.5 to 4.0%. . On the other hand, since the ratio of the mirror electrons to the primary electrons is approximately 1, and the scattering is smaller than the angular distribution of the secondary electrons, the mirror electrons reach the detector 761 with high transmittance. Therefore, a signal derived from a foreign object is detected with high contrast.

  Further, the image of the mirror electrons derived from the foreign matter is projected onto the detector 761 larger than the actual size due to the effect of the local electric field formed by the charged-up foreign matter. The enlargement ratio ranges from 5 to 50 times. Under typical conditions, the magnification is often 20 to 30 times. If the size of the expanded foreign matter is 3 times or more the pixel size of the detector 761, it can be detected as a foreign matter. Therefore, the projection magnification of the secondary optical system 74 is reduced to increase the pixel size of the detector 761. By increasing the area that can be detected at once, high-speed and high-throughput inspection can be realized.

  For example, when the size of the foreign matter is 20 [nm] in diameter, the pixel size of the detector 761 may be 60 [nm], 100 [nm], 500 [nm], or the like. As in this example, it is possible to image and inspect a foreign object using a pixel size of the detector 761 that is three times or more that of the foreign object. This is a feature that is remarkably superior for increasing the throughput as compared with the SEM method or the like.

  The secondary optical system 74 is means for enlarging and projecting the distribution of the electrons reflected from the sample W or the secondary electrons emitted from the surface 21 of the sample W onto the detector 761. The secondary optical system 74 includes lenses 727, 740 and 741, an NA aperture 742, and a detector 761. The electrons are reflected from the sample W and pass through the objective lens 727 and the Wien filter 726 again. Then, the electrons are guided to the secondary optical system 74. In the secondary optical system 74, an electron signal derived from the sample W is imaged on the detector 761 through the lens 740, the NA aperture 742, and the lens 741.

  The NA aperture 742 has a function of defining the transmittance and aberration of the secondary system. The size and position of the NA aperture 742 are selected so that the difference between a signal from a foreign object (such as mirror electrons) and a signal from the surrounding (normal part) becomes large. Alternatively, the size and position of the NA aperture 742 are selected so that the ratio of the signal from the foreign object to the surrounding signal is increased. Thereby, S / N can be made high.

  For example, it is assumed that the NA aperture 742 can be selected in the range of φ50 to φ3000 [μm]. It is assumed that mirror electrons and secondary emission electrons are mixed in the detected electrons. In order to improve the S / N of the mirror electron image in such a situation, the selection of the aperture size is advantageous. In this case, it is preferable to select the size of the NA aperture 742 so that the transmittance of secondary emission electrons can be reduced and the transmittance of mirror electrons can be maintained.

  For example, when the incident angle of the primary electron beam is 3 °, the reflection angle of the mirror electrons is approximately 3 °. In this case, it is preferable to select a size of the NA aperture 742 that allows the trajectory of mirror electrons to pass. For example, a suitable size is φ250 [μm]. Since it is limited to the NA aperture (diameter φ250 [μm]), the transmittance of secondary emission electrons is reduced. Therefore, the S / N of the mirror electron image can be improved. For example, when the aperture diameter is changed from φ2000 to φ250 [μm], the background gradation (noise level) can be reduced to ½ or less.

  The foreign material may be composed of any kind of material, for example, a semiconductor, an insulator, a metal, or the like, or a mixture thereof. Since a natural oxide film or the like is formed on the surface of the foreign matter, the foreign matter is covered with an insulating material. Therefore, even if the foreign material is a metal, charge-up occurs in the oxide film. This charge-up is preferably used in this example.

  The detector 761 is means for detecting electrons guided by the secondary optical system 74. The detector 761 includes a two-dimensional image sensor 7611. The two-dimensional image sensor 7611 has a plurality of pixels arranged in a two-dimensional direction.

  An EB (Electron Bombardment) semiconductor sensor can be applied to the two-dimensional image sensor 7611. For example, an EB-CMOS sensor may be applied to the two-dimensional image sensor 7611. The EB-CMOS sensor can directly make an electron beam (secondary beam) incident on it. Therefore, there is no deterioration in resolution due to the photoelectric conversion mechanism or the light transmission mechanism, and a high MTF (Modulation Transfer Function) and contrast can be obtained. In addition, when EB-CMOS is used, it is possible to increase the S / N of a weak signal of a small foreign matter. Therefore, higher sensitivity can be obtained. The improvement in S / N reaches 1.2 to 2 times. As the two-dimensional image sensor, an EB-CCD sensor or an EB-TDI sensor may be used.

  In addition, a CCD (Charge Coupled Device) or a TDI (Time Delay Integration) -CCD may be applied to the two-dimensional image sensor 7611. These are sensors that detect signals after converting electrons to light. Therefore, means such as photoelectric conversion are necessary. Therefore, electrons are converted into light by using photoelectric conversion or scintillator. The image information of light is transmitted to TDI that detects light. In this way, electrons are detected.

  Note that the number of pixels of the two-dimensional image sensor 7611 can be 2 k × 2 k to 10 k × 10 k. Further, the data rate of the two-dimensional image sensor 7611 can be set to 10 GPPS or less. Furthermore, the pixel size of the two-dimensional image sensor 7611 can be set to 1 to 15 μm.

  The image processing unit 763 performs image processing such as noise reduction processing, integration processing, and sub-pixel alignment on the secondary beam image obtained by the detector 761. The processing speed of the image processing unit 763 can be 10 GPPS or less.

  The electron optical device 70 will be further described. The sample W is placed on a stage device 50 that can move in the x, y, z, and θ directions. High-precision alignment is performed by the stage apparatus 50 and the optical microscope 871. Then, the mapping projection optical system performs foreign matter inspection and pattern defect inspection of the sample W using the electron beam. Here, the potential of the surface 21 of the sample W is important. In order to measure the surface potential, a surface potential measuring device capable of measuring in vacuum is attached to the main chamber 160. This surface potential measuring device measures a two-dimensional surface potential distribution on the sample W. Based on the measurement result, focus control is performed in the secondary optical system 74 that forms an electronic image. A focus map of the two-dimensional position of the sample W is produced based on the potential distribution. Using this map, the inspection is performed while changing and controlling the focus during the inspection. As a result, blurring and distortion of the image due to changes in the surface potential depending on the location can be reduced, and accurate and stable image acquisition and inspection can be performed.

  Further, in the inspection of foreign matter, it is important to efficiently acquire a mirror signal from the foreign matter. The position of the NA aperture 742 is very important because it defines signal transmission and aberrations. Secondary emission electrons emitted from one point of the surface 21 of the sample W are generally emitted in accordance with Lambert's cosine law and reach a uniformly wide region (for example, φ3 [mm]) at the NA position. Therefore, secondary emission electrons are insensitive to the position of the NA aperture 742. On the other hand, in the case of mirror electrons, the reflection angle on the surface 21 of the sample W is approximately the same as the incident angle of the primary electron beam. Therefore, the mirror electrons show a small spread and reach the NA aperture 742 with a small beam diameter. For example, the spreading region of the mirror electrons is 1/20 or less of the spreading region of the secondary emission electrons. Therefore, the mirror electrons are very sensitive to the position of the NA aperture 742. The spreading region of the mirror electrons at the NA position is usually a region of φ10 to 100 [μm]. Therefore, it is very advantageous to obtain the position where the mirror electron intensity is the highest and arrange the center position of the NA aperture 742 at the obtained position.

  In order to realize the installation of the NA aperture 742 at such an appropriate position, in the preferred embodiment, the NA aperture 742 is in the x and y directions with an accuracy of about 1 μm in the vacuum of the electron column. Moved to. The signal intensity is measured while moving the NA aperture 742. Then, the position with the highest signal intensity is obtained, and the center of the NA aperture 742 is set at the obtained coordinate position.

  The EB-CCD 745 is very advantageously used for signal intensity measurement. Thereby, two-dimensional information of the beam can be known, and the number of electrons incident on the detector 761 can be obtained, so that quantitative signal intensity evaluation can be performed.

  Alternatively, the condition of the lens 741 may be set so that the position of the NA aperture 742 and the position of the detection surface of the detector 761 realize a conjugate relationship. This configuration is also very advantageous. As a result, an image of the beam at the position of the NA aperture 742 is formed on the detection surface of the detector 761. Therefore, the beam profile at the position of the NA aperture 742 can be observed using the detector 761.

  The NA size (aperture diameter) of the NA aperture 742 is also important. Since the signal region of the mirror electrons is small as described above, the effective NA size is about 10 to 200 [μm].

  In this regard, an electron image is formed by mirror electrons and secondary emission electrons. By setting the aperture size, the ratio of mirror electrons can be further increased. Thereby, the contrast of mirror electrons can be increased, that is, the contrast of foreign matter can be increased.

  More specifically, when the aperture hole is made smaller, secondary emission electrons decrease in inverse proportion to the aperture area. Therefore, the gradation of the normal part becomes small. However, the mirror signal does not change and the gradation of the foreign matter does not change. Accordingly, the contrast of the foreign matter can be increased by the amount of reduction in the surrounding gradation, and a higher S / N can be obtained.

  Further, an aperture or the like may be configured so that the position of the aperture can be adjusted not only in the x and y directions but also in the z axis direction. This configuration is also advantageous. The aperture is preferably installed at a position where the mirror electrons are most narrowed. Thereby, the reduction of the aberration of the mirror electrons and the reduction of the secondary emission electrons can be performed very effectively. Therefore, higher S / N can be obtained.

<Electronic image tracking method>
The electron optical device 70 will be further described. As shown in FIG. 3, the primary optical system 72 includes a first high-pressure reference tube 701 provided along the path of the primary beam so as to surround the path. In the primary optical system 72, the emission current can be set to 10 μA to 10 mA, the transmittance can be set to 20 to 50%, the spot size can be set to φ1 to φ100 μm, and the size of the irradiation region ( The illumination field size) can be φ10 to φ1000 μm, and the optical system magnification can be 10 to 1/10.

  A high-speed deflector 749 is provided in the middle of the path of the secondary beam in the secondary optical system 74. Specifically, the high-speed deflector 749 is provided closer to the detector 761 than the NA aperture 742. This high-speed deflector 749 is composed of multipole elements (12 poles in the present embodiment), deflects the secondary beam in an arbitrary direction, and simultaneously superimposes the quadrupole field, hexapole field, and octupole field. By applying this, it is possible to reduce aberrations that occur with deflection. This deflection direction (deflection amount) is controlled by the control device 2 that functions as the deflection control device 90. The configuration of the high-speed deflector 749 will be further described later. The multipole used in the high-speed deflector 749 may be a multipole such as an 8-pole or 4-pole.

  Note that the imaging magnification of the secondary optical system 74 can be 10 to 10000 times, and the size of the sample captured by one pixel of the two-dimensional image sensor 7611 is 1 to 1000 nm (1 to 1000 nm / pixel). The transmittance of the NA aperture 742 can be 10 to 50%, and the minimum defect sensitivity can be 1 to 200 nm.

  The control device 2 functions as a deflection control device that controls the deflection direction of the high-speed deflector 749 as described above, and also controls the other operations of the electro-optical device 70 and the stage that controls the stage device 50. It also functions as a control device, a transport control device that controls the configuration for transporting the sample W, an imaging control device that controls the imaging of the two-dimensional image sensor 7611, and the like. In particular, in the present embodiment, the sample W is moved at a constant speed by the stage device 50 during the inspection, but the control device 2 controls the movement of the sample W by controlling the stage device 50. In FIG. 3, the set 56 of the fixed table 51, Y table 52, X table 53, and rotating table 54 in FIGS.

  FIG. 5A is a diagram for explaining the operation of the high-speed deflector 749 that deflects the secondary beam so that the secondary beam follows the movement of the sample W. FIG. As shown in FIG. 5A, when the sample W is continuously moving in the right direction, the high-speed deflector 749 causes the secondary beam from the position A1 on the sample W to the two-dimensional image sensor 7611. The secondary beam is deflected so as to form a secondary beam image, and while the sample W is moving in the right direction, the secondary beam image of the portion of the sample W at the position A1 is accompanied by the movement. So that the image is always formed at the same position on the two-dimensional image sensor 7611, the deflection direction and the deflection amount of the secondary beam are changed at each time step dt. That is, the high-speed deflector 749 is operated so that the secondary beam image is stationary for a predetermined time when viewed from the two-dimensional image sensor 7611. The time step dt is the difference between the moving speed (image surface moving speed) on the two-dimensional image sensor 7611 obtained by integrating the moving speed v of the sample W and the absolute value M of the imaging magnification of the secondary optical system 74, and dt. It is desirable that the product does not exceed the size of one pixel of the two-dimensional image sensor 7611, and the operation cycle is preferably 100 kHz to 100 MHz.

  By such change (follow-up) of the deflection direction and deflection amount of the secondary beam, the two-dimensional image sensor 7611 holds until the portion of the sample W at the position A1 reaches the position A2 by movement. The secondary beam from the portion of the sample W that was initially at the position A1 is always incident, and during this period (one period), the two-dimensional image sensor 7611 performs the secondary beam image for the same region of the sample W. Will be imaged. When the portion of the sample W that has been at the position A1 reaches the position A2, the high-speed deflector 749 returns the visual field region to the position A1 again. As a result, a secondary beam image of an area adjacent to the previous imaging area of the sample W at the current position A1 is captured. Similarly, after the field of view of the two-dimensional image sensor 7611 returns from the position A2 to the position A1, the secondary beam image of the portion of the sample W is always on the two-dimensional image sensor 7611 following the movement of the sample W. The high-speed deflector 749 changes the deflection direction and the deflection amount of the secondary beam every time step dt so as to form an image at the same position.

  As described above, the field area of the two-dimensional image sensor 7611 reciprocates between the position A1 and the position A2, but the field area must always be irradiated with the primary beam. In order to realize this, as shown in FIG. 5B, the primary beam is irradiated on the sample so that the irradiation region EF of the primary beam covers all of the visual field region VF1 at the position A1 and the visual field region VF2 at the position A2. What is necessary is just to irradiate W, ie, the irradiation area | region EF should just have the magnitude | size for two visual field areas. In this case, the irradiation region EF of the primary beam can always be fixed at this position.

  Further, as shown in FIG. 5C, the irradiation region of the primary beam may be moved from the irradiation region EF1 at the position A1 to the irradiation region EF2 at the position A2 by following the movement of the sample W and the visual field region. At this time, the irradiation region of the primary beam can be changed by changing the deflection direction and the deflection amount of the primary beam by a high-speed deflector (not shown) arranged on the electron gun 721 side from the Wien filter 726.

  The secondary optical system 74 includes a second high-pressure reference tube 702, a third high-pressure reference tube 703, and a fourth high-pressure reference tube 704 in order from the side closer to the sample W, which is a sample, respectively. Is provided so as to surround this route. The second high-pressure reference tube 702 is provided between the sample W and the Wien filter 726 as a beam separator, and the third high-pressure reference tube 703 is provided on the two-dimensional image sensor 7611 side of the Wien filter 726. The fourth high-pressure reference tube 704 is provided between the third high-pressure reference tube 703 and the detector 761. The NA aperture 742 is provided inside the third high-pressure reference tube 703, and the high-speed deflector 749 is provided inside the fourth high-pressure reference tube 704.

  The first high-voltage reference tube 701, the second high-pressure reference tube 702, the third high-pressure reference tube 703, and the fourth high-pressure reference tube 704 have a first voltage V1, a second voltage V2, and a third voltage, respectively. A voltage V3 and a fourth voltage V4 are applied. In the embodiment, assuming that the sample W is a ground potential and the detection voltage in the detector 761 is V5, these voltages have a relationship of V1 = V2 = V3, V3> V4, and V4 = V5. The suitable incident energy of the electron beam to the detector 761 is determined in advance at the design stage. For example, if it is 5 keV, V5 is 5 kV. V1 (= V2 = V3) is determined from the influence of the space charge effect of the primary beam and the secondary beam and ease of handling, and is preferably 20 to 50 kV. In addition, since the majority of the secondary beam is cut in the NA aperture 742, the influence of the space charge effect in the optical path from the NA aperture 742 to the detector 761 is negligible, so that the third high-pressure reference tube 703 The connecting portion of the fourth high-pressure reference tube 704 is provided closer to the detector 761 than NA. This is also suitable for ensuring the high-speed response of the voltage power supply of the high-speed deflector 749 disposed in the fourth high-pressure reference tube 704.

  On the other hand, a bipotential lens is formed by the contact of two different potentials. Since this potential difference causes a strong lens action and is a fixed focal length because it is determined by the potential difference between two high-pressure reference tubes in contact with each other, it is very difficult to handle this lens element in the electron optical design.

  Therefore, in the present embodiment, an intermediate electrode 750 is provided between the third high-pressure reference tube 703 and the fourth high-pressure reference tube 704, and a potential different from V3 and V4 is applied to the intermediate electrode. Most of the potentials are smaller than V3 and larger than V4, but may be larger than V3 or smaller than V4. Further, it may be the same potential as V3 or V4. This makes it possible to adjust the lens action that occurs when different potentials are in contact. Further, the intermediate electrode 750 is disposed near the object surface of the projection lens 741 and used as a field lens of the projection lens 741.

  FIG. 6 is a diagram illustrating a configuration of a combination unit of a high-speed deflector, an imaging lens, and an intermediate electrode. The intermediate electrode 750 includes a third high voltage reference tube 703 to which a third voltage of 40 kV, for example, is applied, and a fourth high voltage reference tube 704 to which a fourth voltage of, for example, 5 kV is applied. The high-voltage reference tube 703 and the fourth high-pressure reference tube 704 are arranged in contact with each other, and an intermediate voltage of, for example, 5 kV to 20 kV is applied.

  The high-speed deflector 749 uses a 12-pole structure as described above in order to deflect the secondary beam with high accuracy. The 12 poles are arranged at equiangular intervals in the circumferential direction with respect to the optical axis, and can be individually applied with voltage by the control device 2. The voltage accuracy of the high-speed deflector 749 is improved by using the power source and the amplifier for high-speed deflection superimposed on the fourth voltage V4 by the fourth high-voltage reference tube.

  The projection lens 741 employs a double gap type magnetic lens. By reversing the magnetic flux directions of the upper coil 7411 and the lower coil 7412, the image of the secondary beam can be projected almost without rotation. Further, by changing the ratio of the magnetic flux between the upper coil 7411 and the lower coil 7412, the rotation of the image can be finely adjusted, and the distortion unique to the magnetic lens called S-shaped distortion can be reduced. Further, the magnetic lens coils 7411 and 7412 are of a two-wiring method, whereby the temperature can be stabilized with a constant power.

  The high-speed deflector 749 is desirably disposed in the vicinity of the image side focal position of the projection lens 741.

  The high-speed deflector 749 performs not only the deflection for following the movement of the sample W but also the distortion correction of the secondary beam image as described above and the position fluctuation correction described later. This is realized by superimposing and applying a deflection field calculated based on a deviation from the original position.

  Returning to FIG. 3, the position variation correction will be described. As described above, the sample W is continuously moved at a constant speed by the stage device 50, and the high-speed deflector 749 changes the deflection direction of the secondary beam so that the visual field region moves following the movement of the sample W. At this time, an unintended position change may be added to the movement of the sample W by the stage device 50 at this time. As described above, the two-dimensional image sensor 7611 always captures a secondary beam image of the same part of the sample W during one cycle of the movement of the visual field region. When added, the contamination that the secondary beam from the other part of the sample W enters each pixel of the two-dimensional image sensor 7611 occurs.

  As described above, the stage apparatus 50 moves the sample W held by the holder 55 in the X direction and the Y direction by operating a plurality of tables using a servo motor, an encoder, and various sensors (not shown). And in the Z direction (vertical direction in FIG. 1) and further in the direction around the axis perpendicular to the sample support surface (θ direction) with high accuracy. As a configuration for this purpose, a mirror 571 is fixed to the holder 55, a laser beam is irradiated onto the inner wall of the main housing 30, and a laser beam reflected from the mirror 571 is incident thereon. 572 is provided.

  In the inspection apparatus 1 of the present embodiment, position fluctuation correction is performed using the mirror 571 and the laser interferometer 572 fixed to the holder 55 as position fluctuation detection means. Unintended position fluctuations of the sample W detected by the laser interferometer 572 are input to the control device 2. The control device 2 is instructed to change the deflection direction of the secondary beam by the high-speed deflector 749 when the sample W moves without unintentional position change. In consideration of not only the movement of the sample W but also the unintended position fluctuation of the sample W detected by the laser interferometer 572, the deflection direction of the secondary beam by the high-speed deflector 749 is determined to control the high-speed deflector 749. . The control device 2 may not be instructed to change the deflection direction of the secondary beam by the high-speed deflector 749 when the sample W moves without unintentional position change. The apparatus 2 detects the position of the sample W (the holder 55 that holds the sample W) including the unintended position variation of the sample W, which is detected by the laser interferometer 572, and based on this position, the high-speed deflector 749 The high-speed deflector 749 may be controlled by determining the deflection direction of the next beam.

  As described above, in the inspection apparatus 1 including the electron optical device 70 of the present embodiment, the secondary beam of the same portion of the sample W is synchronized with the movement of the sample W while the sample W is moving. Since the high-speed deflector 749 that deflects the secondary beam so as to be incident on the same part of the two-dimensional image sensor 7611 also functions as a position variation corrector that corrects contamination due to unintended position variation of the sample W. The two-dimensional image sensor 7611 can obtain a secondary beam image with high accuracy.

  The first voltage V1, the second voltage V2, the third voltage V3, the fourth voltage V4, and the detection voltage V5 are not limited to the above example. For example, V1 <V2, V2 = V3, V3> The relationship may be V4, V4 = V5, that is, the first voltage V1 may be smaller than the second voltage V2 and the third voltage V3. If the voltage V1 applied to the first high-pressure reference tube 701 in the primary optical system 72 is reduced, the discharge risk in the first high-pressure reference tube 701 can be reduced. That is, the primary optical system has an aperture 723 in the first high-pressure reference tube 701, and the aperture 723 absorbs 50% or more of the emission from the electron gun 721. The amount of variation is also large. In contrast, by reducing the first voltage V1 applied to the first high-pressure reference tube 701, the risk of discharge can be reduced or eliminated.

  In the inspection apparatus 1, a voltage control device that adjusts the fourth voltage V4 applied to the fourth high-voltage reference tube 704 may be provided, and the fourth voltage V4 may be variable in synchronization with V5. At this time, the fourth voltage V4 (and V5) may be adjustable in a range of ± 1 kV, for example. Thus, by adjusting the fourth voltage V4 (and V5), the electron energy (incident energy) of the secondary beam incident on the detector 761 can be adjusted. Thereby, the gain (that is, the brightness of the secondary beam image) of the two-dimensional image sensor 7611 can be adjusted.

<Re-inspection simulation by software>
Returning to FIG. 3, as described above, the electron optical device 70 irradiates the sample W, which is the sample held by the stage device 50, with the primary beam, which is the surface beam, and thereby the secondary generated from the sample W. The beam is directed to detector 761. The detector 761 captures the secondary beam with a two-dimensional image sensor (not shown), generates an image of the secondary beam image, and outputs the image to the image processing unit 763.

  As an inspection processing apparatus, the image processing unit 763 applies an image processing filter (an average value (Mean) filter, a Gaussian filter, a median (Median) filter, etc.) to the secondary beam image input from the detector 761. ), And after performing shading correction, inspection is performed by comparison processing such as cell-cell comparison, die-die comparison, die-database comparison, and the like. Specifically, the image processing unit 763 detects a portion where the difference exceeds a predetermined threshold in the comparison process as a defect, and generates a defect image.

  The image processing unit 763 performs inspection according to the set inspection condition parameter. The inspection condition parameters include cell period for cell-cell comparison, edge tolerance value for die-die comparison, threshold for detecting defects, image processing filter, shading correction value, and die-database comparison parameters. , Classification information of defects that are not desired to be detected are included. It should be noted that this defect classification information that is not desired to be detected is obtained as a result of classification by imaging with an SEM after inspection.

  By the way, in an inspection apparatus for inspecting a defect occurring in a sample, in order to reliably detect a true defect and not to detect a non-defect portion (pseudo defect), an inspection condition such as a detection threshold is set. It is necessary to repeat the inspection many times while changing and to determine the optimum inspection conditions.

  However, when inspection is repeated, there is a problem that optimization of inspection conditions takes time. In addition, by repeating the inspection, there is a problem that damage is accumulated in the sample or the sample is contaminated.

  Therefore, in order to determine the inspection condition with a small number of inspections while avoiding damage to the sample and contamination of the sample, the simulation apparatus 200 is provided in the inspection apparatus 1 of the present embodiment. The image processing unit 763 outputs a defect image and an unprocessed image (secondary beam image) used to generate the defect image to the simulation apparatus 200.

  The simulation apparatus 200 includes a simulation processing unit 201, an input unit 202, and a monitor 203. For example, a general-purpose computer including an input unit, a monitor, an arithmetic processing unit, a memory, a storage device, an input / output port, and the like. Consists of. The simulation processing unit 201 is realized by the inspection result review program according to the present embodiment being executed by the arithmetic processing unit. This inspection result review program may be provided to the simulation apparatus 200 through a network, or may be provided to the simulation apparatus 200 by reading out the search result review program stored in the storage medium. The search result review program provided in this way is stored in the storage device of the simulation apparatus 200, and is read out and executed from there to constitute the simulation processing unit 201.

  The simulation processing unit 201 performs a re-inspection simulation on the secondary beam image input from the inspection apparatus 100 while changing the inspection condition parameter, and determines an optimal inspection condition parameter. The inspection condition parameters that the simulation processing unit 201 changes for the re-inspection simulation include a cell period in the case of cell-cell comparison, an edge tolerance value in the case of die-to-die comparison, a threshold value for detecting defects, and image processing. Filters, shading correction values, die-database comparison parameters, defect classification information that should not be detected, and the like are included.

  FIG. 17 is a flowchart showing the operation of the simulation apparatus 200. First, the electro-optical device 70 performs inspection, and the image processing unit 763 outputs the inspection result to the simulation device 200 (step S331). At this time, the image processing unit 763 also outputs the unprocessed image (secondary beam image) used to obtain the inspection result and the classification information of the defect not to be detected to the simulation apparatus 200 together with the inspection result. In the simulation apparatus 200, the simulation processing unit 201 reads this inspection result, generates a defect image, and displays it on the monitor 203 (step S332).

  Next, the simulation processing unit 201 changes the inspection condition, executes re-inspection simulation (step S333), and outputs the re-inspection result obtained thereby (step S334). In this re-inspection simulation, as in the inspection in the electron optical device 70, the defect in the defect classification information that is not to be detected is not detected. The simulation processing unit 201 reads the reinspection result obtained in step S334, generates a defect image, and outputs the defect image to the monitor 203 (step S335).

  Next, by evaluating the defect image obtained by this re-inspection, it is determined whether the inspection condition is optimal (step S336). If the inspection condition is not optimal (NO in step S336), the process proceeds to step S333. Returning, the inspection condition is changed, and the re-inspection simulation is executed (step S333). In this way, when the re-inspection simulation is repeated while changing the inspection condition parameters, and the inspection conditions become optimal (YES in step S336), the inspection conditions for adopting the optimal inspection conditions in the electron optical device 70 are used. (Step S337), and the process ends. The simulation processing unit 201 may determine whether the search condition is optimal based on an input from the input unit 202, for example.

  As described above, according to the present embodiment, after the actual inspection is performed in the electron optical device 70, the inspection is performed using the defect image and the unprocessed image output from the electron optical device 70 by the simulation device 200. Since the reinspection simulation is performed by the inspection result review software while changing the conditions, the inspection conditions can be optimized with a small number of inspections, and the time for optimizing the inspection conditions can be shortened. Further, since it is not necessary to repeat the actual inspection by the electron optical device 70, damage to the sample can be reduced, and contamination of the sample can be reduced.

(First embodiment)
Next, the Wien filter 726 shown in FIGS. 3 and 4 will be described in detail. The Wien filter 726 deflects the primary beam from the primary optical system 72 and guides it to the lower sample W due to the effects of the orthogonal parallel magnetic field and parallel electric field generated there, and the secondary beam generated in the sample W is moved upward. This is led to the detector 761. First, a comparative example will be described.

  FIG. 13 is a cross-sectional view of a Wien filter 726 'according to a comparative example. A Wien filter 726 ′ shown in FIG. 13A includes a plurality of electromagnetic poles 90 ′, coils (not shown) wound around the individual electromagnetic poles 90 ′, and a shield member 91 ′.

  The shield member 91 ′ is disposed so as to cover the electromagnetic pole 90 ′ and the coil, and confines a magnetic field and an electric field in the shield member 91 ′. The shield member 91 'is formed with an incident hole 92', an intermediate hole 93 ', and an exit hole 94'. The primary beam enters the entrance hole 92 '. This primary beam is deflected by the action of the magnetic field and electric field generated by the electromagnetic pole 90 ', and is emitted from the intermediate hole 93'. Further, the secondary beam generated from the sample W enters the intermediate hole 93 ', travels straight, and exits from the exit hole 94'.

  Here, as shown in FIGS. 3 and 4, since the primary beam is incident obliquely from above (more precisely, from an angle deviating from the vertical direction), the entrance hole 92 ′ is aligned with the incident angle of the primary beam. It is an oblique hole. In the comparative example, the exit surface 92b 'of the entrance hole 92' is on a horizontal plane.

  As shown in FIG. 13B, the primary beam incident on the incident hole 92 'has a spatial spread. Here, a state in which the beams B1 to B4 arranged at a pitch of 30 ° with the primary beam optical axis as the center is incident on the inside of the Wien filter 726 'through the incident hole 92' in parallel with the primary beam optical axis is shown.

  FIG. 14 is a diagram illustrating a transition of a relative distance with respect to the optical axis of the primary optical system in the electric field direction and the magnetic field direction of the primary beams B1 to B4 illustrated in FIG. 13B in the Wien filter 726 ′ according to the comparative example. is there. The horizontal axis in the figure is the traveling direction distance of the optical axis of the primary optical system. Moreover, the vertical axis | shaft of the figure is a relative position with the optical axis of a primary optical system.

As shown in the figure, with respect to the electric field direction, the primary beams B1 to B4 incident in parallel to the optical axis of the primary optical system from a position off the center of the incident hole 92 ′ pass through the incident hole 92 ′ and then become primary. It approaches the optical axis of the optical system and eventually converges to a single point at a specific distance zo. However, with respect to the direction of the magnetic field, the primary beams B1 to B4 incident in parallel to the optical axis of the primary optical system from a position off the center of the incident hole 92 ′ pass through the incident hole 92 ′ and then temporarily enter the light of the primary optical system. The distance from the axis approaches the optical axis of the first-order primary optical system from near the intermediate hole 93 ′. Although it is not yet clear why such a primary beam trajectory is generated, the potential of the electromagnetic pole 90 'positioned on the primary beam incidence side and the shield member 91' It seems that this is the result of a difference in the deflection characteristics depending on the position of the orbit due to the electric field (potential change) generated between them. In any case, such extreme non-stigmatic focusing characteristics increase the difficulty of optical design, and it is necessary to add new optical elements for correcting the non-stigmatic focusing characteristics.
Therefore, in the present embodiment, the following is performed.

  FIG. 8 is a cross-sectional view of the Wien filter 726 according to the present embodiment. As shown in FIG. 8A, the Wien filter 726 includes a plurality (eight or more) of electromagnetic poles 90 and a shield member 91 arranged so as to cover the electromagnetic poles 90. The electromagnetic pole 90 deflects the primary beam and generates a magnetic field and an electric field for causing the secondary beam to travel straight. The shield member 91 is made of a soft magnetic material such as Permalloy C, for example. The shield member 91 is provided with an incident hole 92 having an entrance surface 92a and an exit surface 92b, an intermediate hole 93, and an exit hole 94. In addition, although the physical entrance surface 92a and the exit surface 92b do not necessarily exist in the incident hole 92, they are called in this way assuming a virtual surface. There may be only one incident hole 92 for the purpose of allowing the primary beam to pass therethrough. However, in consideration of the symmetry of the electric and magnetic fields, a plurality of incident holes 92 may be opened in rotational symmetry with respect to the optical axis of the secondary beam. good.

  FIG. 9 is a perspective view schematically showing a plurality of electromagnetic poles 90. The Wien filter 726 is composed of electromagnetic poles 90 made of eight conductive materials and soft magnetic materials arranged at equal intervals in the circumferential direction with respect to the optical axis of the secondary beam. A coil 90a is wound around each electromagnetic pole 90. Different electric potentials can be applied to the individual electromagnetic poles 90. A potential obtained by applying a voltage VE to the cosine of the arrangement phase angle of the individual electromagnetic poles 90 with respect to the direction in which the primary beam is incident is applied to the respective electromagnetic poles 90. When applied, a uniform parallel electric field is generated near the optical axis of the secondary beam surrounded by the electromagnetic pole 90. In addition, different currents can be applied to the individual coils 90a, and currents obtained by multiplying the sine of the arrangement phase angle of the individual electromagnetic poles 90 by the current IB with respect to the direction in which the primary beam is incident on each coil 90a. By applying the coil 90a, a uniform parallel magnetic field orthogonal to the above-described uniform parallel electric field is generated in the vicinity of the optical axis of the secondary beam. By the electric and magnetic fields, the primary beam passing through the space inside the eight electromagnetic poles 90 (hereinafter referred to as a beam passage hole 90b) is deflected. Further, by adjusting the voltage VE and the current IB, the primary beam incident from the incident hole 92 is deflected and emitted from the intermediate hole 93, and the secondary beam incident from the intermediate hole 93 goes straight, and the emission hole 94 Exits from.

  FIG. 10 is a diagram schematically showing a cross-sectional view of the shield member 91 as viewed obliquely. With reference to Fig.8 (a) and FIG. 10, the shape of the shield member 91 is demonstrated. In the present embodiment, it is assumed that the primary beam is incident from above 45 degrees obliquely (more specifically, an angle inclined by 45 degrees from the vertical direction).

  The shield member 91 is designed in consideration of thickness and arrangement so that the magnetic flux density in the shield member 91 is used at, for example, half or less of the saturation magnetic flux density of the material. Further, in order to ensure that the uniform parallel electric field and the uniform parallel magnetic field generated by the electromagnetic pole 90 exist only in a limited region, the electron entrance / exit hole of the shield member 91 has a certain degree along the electron trajectory. It is important to make the shield shape with a length of.

  The lower part of the shield member 91 is bent vertically upward at the center, and an intermediate hole 93 is formed by the bent surface 91a. The same intermediate hole 93 shape can be realized by bending the center of the lower part of the shield member 91 vertically downward or by increasing the plate thickness of the lower part of the shield member 91, but both of them reduce the distance from the electromagnetic pole 90, This configuration is desirable because the magnetic flux density in the shield member 91 increases.

  On the upper surface of the upper part of the shield member 91, a surface 91b substantially perpendicular to the trajectory of the primary beam is formed, and an incident hole 92 is formed there. Furthermore, the center of the upper surface of the upper part of the shield member 91 is bent vertically downward, and an emission hole 94 is formed in the bent surface 91c. If the length of the shield along the trajectory of the primary beam of the surface 91b is, for example, 5 times or more the diameter of the entrance hole 92, the crossing angle with the primary beam may not be substantially a right angle.

  The lower surface of the upper part of the shield member 91 forms a substantially vertical surface 91d, on which an exit surface 92b of the incident hole is provided. The upper end of the vertical surface bends and extends in the horizontal direction, and then extends vertically downward.

  The entrance surface 92a of the incident hole 92 is orthogonal to the primary beam, and more specifically, is inclined by 45 degrees from the horizontal direction. Further, the incident hole 92 is inclined at 45 degrees in accordance with the incident angle of the primary beam. In the present embodiment, unlike the comparative example, the exit surface 92b of the entrance hole 92 is non-horizontal, and more specifically vertical. The primary beam emitted from the exit surface 92b enters the electric and magnetic fields generated by the electromagnetic pole 90.

  The intermediate hole 93 is below the beam passage hole 90 b in the electromagnetic pole 90, and the primary beam deflected by the electromagnetic pole 90 is emitted toward the sample W placed below the Wien filter 726. Further, the secondary beam generated from the sample W is incident on the intermediate hole 93. The secondary beam travels vertically upward without being deflected by the balance between the Coulomb force generated by the parallel electric field generated by the electromagnetic pole 90 and the Lorentz force generated by the parallel magnetic field.

  The exit hole 94 is located above the beam passage hole 90 b in the electromagnetic pole 90, and the secondary beam exits toward a detector disposed above the Wien filter 726.

  As shown in FIG. 8B, the primary beam incident on the incident hole 92 has a spatial spread. Here, a state in which the beams B1 to B4 arranged at a pitch of 30 ° around the primary beam optical axis are incident on the inside of the Wien filter 726 from the entrance surface 92a of the incident hole 92 in parallel with the primary beam optical axis.

  FIG. 11 is a diagram illustrating a transition of the relative distance of the primary beam B1 to B4 in the electric field direction and the magnetic field direction with respect to the optical axis of the primary optical system in the Wien filter 726 according to the present embodiment. The vertical axis and horizontal axis in FIG. According to this embodiment, all of the beams B1 to B4 are focused at a specific distance zo in both the electric field direction and the magnetic field direction.

  As described above, the reason why the focusing characteristics are different between the comparative example (FIGS. 13 and 14) and the present embodiment (FIGS. 8 to 11) is that the shape of the shield member 91 is different, and therefore, the shield member 91 is formed in the shield member 91. This is because the potential distribution, the electric field, the magnetic field, and the incident angle to the end face are different. This will be described in more detail.

  Katsumi Ura, “Nano Electron Optics” (Kyoritsu Shuppan), pages 163 to 165, when an electron beam is incident non-perpendicularly on the end face of a magnetic field, a force is applied to the electron beam in a focusing direction according to the incident angle. It acts, or force acts in the direction of divergence. The same thing can happen at the electric field end face. However, in the comparative example, the force generated by the oblique incidence of the end face is the diverging direction in the electric field direction and the converging direction in the magnetic field direction, which is the opposite direction to the result of the trajectory calculation. Therefore, another effect, for example, the force generated by the difference between the potential of the electron beam and the space potential around the orbit in the Wien filter may be dominant.

  In any case, the shape of the shield member 91, particularly the angle of the exit surface 92 b in the incident hole 92 (that is, the incident angle to the electric field and magnetic field generated by the electromagnetic pole 90) is entered using the numerical analysis. What is necessary is just to determine suitably according to the focusing characteristic of the electric field direction of a beam, and the focusing characteristic of a magnetic field direction. More specifically, the angle of the exit surface 92b is set to an angle that reduces (preferably matches) the deviation between the focusing characteristic in the electric field direction and the focusing characteristic in the magnetic field direction. In other words, the angle of the exit surface 92b is set to an angle that reduces (preferably matches) the shift between the focusing position in the electric field direction and the focusing position in the magnetic field direction.

  FIG. 12 is a cross-sectional view of a Wien filter 726 according to a modified example, and the difference from FIG. 8 will be mainly described. In this modification, it is assumed that the primary beam is incident obliquely from above 35 degrees. Also in the Wien filter 726, the exit surface 92b in the entrance hole 92 is non-horizontal.

  The shape of the lower surface of the upper portion of the shield member 91 and the shape of the upper surface of the upper portion of the shield member 91 are substantially the same as in FIG. 8, but the inclination angle of the surface 91b is different.

  The lower surface of the upper part of the shield member 91 forms a surface 91d inclined substantially at 55 °, and an exit surface 92b of the incident hole is provided there. The upper end of the inclined surface 91d extends in the horizontal direction and then bends vertically downward.

  The entrance surface 92a of the incident hole 92 is provided so as to be inclined so as to be substantially orthogonal to the primary beam incident angle. Further, the incident hole 92 is inclined at 35 degrees in accordance with the incident angle of the primary beam. The exit surface 92b of the entrance hole 92 is also inclined, and the primary beam emitted from the exit surface 92b is incident on the electric field and magnetic field generated by the electromagnetic pole 90.

  Thus, even when the primary beam is incident at an angle other than 45, the shape of the shield member 91, particularly the angle of the exit surface 92b in the incident hole 92, may be appropriately determined as described above according to the incident angle. .

  Thus, in this embodiment, the exit surface 92b of the incident hole 92 is not horizontal and is set to an appropriate angle according to the incident angle of the primary beam. Then, the primary beam incident from the incident hole 92 in parallel with the optical axis of the primary beam is converged to one point with substantially the same traveling distance in the magnetic field direction and the electric field direction. Thus, bi-directional focusing of the primary beam can be achieved without adding new optical elements. In addition, it is only necessary to change the shape of the shield member, and it is not necessary to change the shape of the electrodes and magnetic poles asymmetrically. Therefore, the two-way focusing can be realized more easily, and at the same time, the straight beam tends to be impaired. There is no.

  In the present embodiment, the reason why the electromagnetic pole 90 is composed of eight or more poles is not simply that a uniform parallel electric field and a uniform parallel magnetic field are formed over a wide range over the beam passage hole 90b. By simply providing a uniform parallel electric field and a uniform parallel magnetic field that are orthogonal to each other, a focusing action is generated only in the direction of the electric field even if the secondary beam is adjusted to the straight beam condition and allowed to pass through the beam. This is an effect caused by the difference between the potential of the passing beam and the potential distribution of the space, and cannot be eliminated. As a result, when the aperture aperture is arranged on the downstream side of the Wien filter in the direction of travel of the electron beam, the optimum position differs between the electric field direction and the magnetic field direction.

  With the electromagnetic pole 90 of the present embodiment, a quadrupole electric field or a quadrupole magnetic field can be generated by being superimposed on the beam passage hole 90b. The generated quadrupole electric field or quadrupole magnetic field generates a beam in the electric field direction. By relieving the focusing action and simultaneously giving a new focusing action in the magnetic field direction, the bi-directional focusing of the straight-passing beam can be achieved, and the aperture aperture can be arranged at the optimum position.

  Both the quadrupole electric field and the quadrupole magnetic field generated in a superimposed manner may be generated, but bi-directional focusing can be achieved with either one.

(Second Embodiment)
The second embodiment to be described next is a more specific example.
FIG. 15 is a diagram showing a schematic configuration of an electron gun 721, a primary optical system 72, a secondary optical system 74, and a detector 761 as electron generation sources.

  The primary optical system 72 is an irradiation system, which includes a gun lens 1021 (corresponding to the lens 722 in FIG. 3), an E × B filter 1022 (beam separator, corresponding to the Wien filter 726 in FIG. 3), and an objective lens 1023 (lens in FIG. 3). 727), a cathode lens 1024, and the like.

  The gun lens 1021 expands the shape of photoelectrons (hereinafter referred to as a primary beam) from the electron gun 721 to about 5 times and accelerates the primary beam to 20 to 30 kV. The E × B filter 1022 deflects the photoelectrons by 45 degrees and directs the primary beam toward the sample W such as an EUV mask. The objective lens 1023 reduces the photoelectron shape to about 1/5 times. Cathode lens 1024 decelerates the primary beam. As described above, the surface of the sample W is irradiated with the primary beam at the landing voltage of 0 to 1 kV.

  The secondary optical system 74 is a projection system, and includes a cathode lens 1024, an objective lens 1023, an E × B filter 1022, a transfer lens 1031 (corresponding to the lens 740 in FIG. 3), and an aperture stop 1032 (corresponding to the NA aperture 742 in FIG. 3). ), Zoom lens 1033 (corresponding to lens 741 in FIG. 3), projection lens 1034, electrostatic deflector 1035 (corresponding to high-speed deflector 749 in FIG. 3), and the like. The cathode lens 1024, the objective lens 1023 and the E × B filter 1022 are shared with the primary optical system 72.

  The cathode lens 1024 accelerates electrons (hereinafter referred to as secondary emission electrons) emitted from the sample W to 20 to 30 kV. The objective lens 1023 enlarges an image by secondary emission electrons (hereinafter referred to as an electronic image) to about 5 times. The E × B filter 1022 advances secondary emission electrons straight. The transfer lens 1031 enlarges the electronic image by about twice. The zoom lens 1033 enlarges the electronic image by 2.29 to 5 times (variable) at a constant rotation angle. The projection lens 1034 enlarges the electronic image by about 10 times. The electrostatic deflector 1035 deflects the electronic image. As described above, the secondary emission electrons are imaged on the detector 761, and the electron image of the sample W is detected.

  FIG. 16 is a diagram schematically showing the trajectory of secondary emission electrons in the secondary optical system 74. As shown in the drawing, the secondary emission electrons on the axis form an image at the center of the detector 761 regardless of the magnification of the zoom lens 1033. On the other hand, off-axis secondary emission electrons form an image at a position corresponding to the magnification of the zoom lens 1033 on the detector 761. More specifically, an image is formed at a position farther from the center of the detector 761 as the magnification is larger.

  Here, as the sensor in the detector 761, a CMOS sensor is suitable for high inspection throughput. In this case, it is necessary to image secondary emission electrons on the CMOS sensor continuously for a predetermined time. Therefore, this inspection apparatus is equipped with an image tracking function described below.

  17A to 17D are diagrams for explaining the image tracking function. The sample W is held by the stage device 50 (more precisely, a holder on the stage device 50), and in the figure, an example in which the stage device 50 moves to the left is shown. However, the irradiation area 50a is stationary. Further, it is assumed that a part of the detector 761 is a projection region 761a.

  As shown in FIG. 17A, at the start of imaging of the image acquisition region W1 on the sample W, the image acquisition region W1 is located on the lower right side of the projection region 761a in the detector 761 (more precisely, the image acquisition region W1). Is located at the lower right side of the center of the projection region 761a). Therefore, a positive voltage (for example, 60V) is applied to the left electrode 35a of the electrostatic deflector 1035 and a negative voltage (for example, −60V) is applied to the right electrode 35b so that the secondary emission electrons are deflected to the left. As a result, secondary emission electrons from the image acquisition region W1 form an image at the center of the detector 761.

  As the stage device 50 moves to the left, the absolute value of the voltage applied to the electrodes 35a and 35b is decreased. This is to reduce the deflection amount of the secondary emission electrons.

  As shown in FIG. 17B, when the stage device 50 further moves to the left and the image acquisition region W1 is located immediately below the projection region 761a, the voltage applied to the electrodes 35a and 35b is set to 0V. This is because there is no need to deflect secondary emission electrons.

  As the stage device 50 further moves to the left, a negative voltage is applied to the left electrode 35a and a positive voltage is applied to the right voltage 35b, and the absolute value is gradually increased. This is because the secondary emission electrons are deflected to the right.

  As shown in FIG. 17C, at the end of imaging of the image acquisition region W1, the absolute value of the voltage applied to the electrodes 35a and 35b is maximized. For example, −60V is applied to the left voltage and 60V is applied to the right voltage.

  As described above, even when the stage apparatus 50 moves, the image acquisition region W1 in the sample W is imaged fixed on the projection region 761a of the detector 761.

  When the imaging of the image acquisition area W1 is completed in FIG. 17C, the imaging of the adjacent image acquisition area W2 is started. Therefore, as shown in FIG. 17D, the sign of the voltage applied to the electrodes 35a and 35b is switched at high speed to obtain the same voltage as in FIG. 17D.

  As described above, the voltage applied to the electrodes 35a and 35b of the electrostatic deflector 1035 is controlled in accordance with the movement of the stage device 50, thereby deflecting the electronic image and continuing at a certain position on the detector 761 for a predetermined period. Thus, an electronic image can be formed. Note that the relationship between the amount of movement of the stage device 50 and the voltage to be applied to the electrodes 35a and 35b is known in advance by experiments and calculations. The apparatus 2 in FIG. 1 may perform the movement of the stage apparatus 50 and the voltage control in conjunction with each other.

  In such image tracking, in order to prevent distortion from being formed in the formed electron image, not only the voltage applied to the electrodes 35a and 35b of the electrostatic deflector 1035 but also the secondary emission electrons are E ×. It is also important to go straight through the B filter 1022, and for that purpose it is necessary to establish a Wien condition in the E × B filter 1022.

  18A and 18B are a schematic sectional view and a schematic top view of the E × B filter 1022, respectively. FIG. 8C is a schematic cross-sectional view of electromagnetic poles in the E × B filter 1022.

  The E × B filter 1022 includes, for example, eight electromagnetic poles 1221a to 1221g arranged at equal intervals, and a yoke 1222 made of, for example, pure iron covering these. A hole 1223 is formed on the upper and lower surfaces of the yoke 1222, and the primary beam passes through the hole 1223 on the upper surface of the yoke 1222, the electromagnetic poles 1221a to 1221g, and the hole 1223 on the lower surface of the yoke 1222 in this order. Secondary emission electrons pass through the hole 1223 on the lower surface of the yoke 1222, the electromagnetic poles 1221a to 1221g, and the hole 1223 on the upper surface of the yoke 1222 in this order.

  When a voltage is applied to the electromagnetic poles 1221a to 1221g, an electric field is formed in the electron passage path. A coil 1224 is wound around the electromagnetic poles 1221a to 1221g, and a current is supplied to form a magnetic field in the electron passage path. By forming appropriate electric and magnetic fields, the primary beam can be deflected 45 degrees and the secondary emission electrons can travel straight.

  For this purpose, it is necessary to establish Wien conditions by forming equal electric and magnetic fields along the electron passage path.

  FIG. 19A and FIG. 19B are diagrams schematically showing the normalized electric field and magnetic field of the broken line part (the center A to the lower end B of the E × B filter 1022) in FIG. 18A. As shown in FIG. 19A, when the electric field and the magnetic field do not match, the Wien condition is not established, and the secondary emission electrons do not travel straight. On the other hand, as shown in FIG. 19B, the Wien condition is established by matching the electric field and the magnetic field as much as possible, and the secondary emission electrons can be made to travel straight.

  For this purpose, the shape of the E × B filter 1022, for example, the shape of the yoke 1222 may be appropriately designed. More specifically, as shown in FIG. 18A, the shape of the yoke 1222 includes the diameter D of the hole 1223 on the upper surface and the lower surface, the thickness t on the upper surface and the lower surface, and the distance L from the electromagnetic poles 1221a to 1221g on the upper surface or the lower surface. At least one of can be adjusted. The vicinity of the hole 1223 in the yoke 1222 is also called a shield flange, and it can be said that the shield flange may be designed appropriately.

Actually, these can be optimized by trial and error of the thickness t and the distance L while measuring or simulating the diameter D, electric field, and magnetic field of the hole 1223. For example, since the distance L cannot be reduced so much by the voltage applied to the electromagnetic poles 1221a to 1221g, the distance L may be fixed and the optimum hole diameter D and thickness t may be searched.
It is desirable that the electric field and the magnetic field completely coincide with each other, but it is sufficient that the electric field and the magnetic field substantially coincide with each other. The integrated value of the difference between the magnetic field and the magnetic field may be set to a predetermined value or less.

  As described above, in this embodiment, the shape of the E × B filter 1022, particularly the shape of the yoke 1222, can be designed to accurately deflect the primary beam by 45 degrees and cause the secondary emission electrons to travel straight. it can. As a result, distortion of the electron image formed on the detector 761 can be suppressed. By using such an E × B filter 1022, a CMOS sensor can be applied as the detector 761, and the inspection throughput can be improved.

  20A and 20B are simulation results obtained by calculating the distortion of the electronic image projected on the detector 761. FIG. FIG. 20A shows a case where the image acquisition area W1 is located immediately below the projection area 761a and there is no deflection by the electrostatic deflector 1035, as shown in FIG. 17B. As shown, there is almost no distortion. FIG. 20B shows a case where the image acquisition region W1 is located on the lower right side of the projection region 761a and the secondary emission electrons are deflected to the left by the electrostatic deflector 1035, as shown in FIG. 17A. As shown in the figure, even when the image acquisition area W1 is not directly below the projection area 761a, the distortion can be reduced.

Based on the present embodiment, the following deflectors (E × B filter, Wien filter), more specifically, the direction of the primary beam incident obliquely from above is changed to a substantially vertical downward direction, and is emitted, and A deflector that emits the secondary beam incident vertically upward is almost conceivable.
[1]
A plurality of electromagnetic poles (1221a to 1221g) around which a coil (1224) is wound;
A yoke (1222) provided with a hole (1223) and covering the plurality of electromagnetic poles (1221a to 1221g),
A deflector (1022) through which electrons pass between the plurality of electromagnetic poles (1221a to 1221g) and through a hole (1223) of the yoke (1222);
A deflector (1022) having a shape in which an electric field generated by a voltage applied to the electromagnetic poles (1221a to 1221g) and a magnetic field generated by a current flowing through the coil (1224) substantially coincide with each other along the passage path of the electrons. ).

[2]
The yoke (1222) is configured such that an electric field generated by a voltage applied to the electromagnetic poles (1221a to 1221g) and a magnetic field generated by a current flowing through the coil (1224) substantially coincide with each other along the passage path of the electrons. The deflector (1022) according to [1], wherein the diameter of the hole (1223), the distance between the yoke (1222) and the electromagnetic poles (1221a to 1221g), and the thickness of the yoke (1222) are designed.

  The embodiment described above is described for the purpose of enabling the person having ordinary knowledge in the technical field to which the present invention belongs to implement the present invention. Various modifications of the above embodiment can be naturally made by those skilled in the art, and the technical idea of the present invention can be applied to other embodiments. Therefore, the present invention should not be limited to the described embodiments, but should be the widest scope according to the technical idea defined by the claims.

  90: electromagnetic pole, 90a: coil, 90b: beam passage hole, 91: shield member, 91a to 91d: surface, 92: entrance hole, 92a: entrance surface, 92b: exit surface, 93: intermediate hole, 94: exit hole 1022: E × B filter, 1221a to 1221g: Electromagnetic pole, 1222: Yoke, 1223: Hole

Claims (6)

Used in an inspection apparatus that inspects the sample based on the secondary beam generated from the sample by irradiating the sample with the primary beam, and changes the direction of the primary beam incident from obliquely upward to a substantially downward vertical direction. A Wien filter that emits the secondary beam incident vertically upward with almost no change in the direction of the secondary beam,
8 or more electromagnetic poles arranged at equiangular intervals around the optical axis of the secondary beam, and made of a conductive material and a soft magnetic material;
A coil wound around each said electromagnetic pole;
A shield member arranged to cover the periphery of the electromagnetic pole,
Different potentials can be applied to the electromagnetic poles so as to generate a uniform parallel electric field in the vicinity of the optical axis of the secondary beam in the direction in which the primary beam is deflected,
Different currents can be applied to the coils so as to generate a uniform parallel magnetic field near the optical axis of the secondary beam in the direction in which the primary beam is deflected,
In the shield member,
A first beam hole into which the primary beam is incident obliquely from above;
A second beam hole from which the primary beam deflected by the electromagnetic pole is emitted and the secondary beam generated from the sample is incident;
A third beam hole from which the secondary beam is emitted,
A Wien filter, wherein an exit surface of the first beam hole is non-horizontal.   2. The Wien filter according to claim 1, wherein an angle between an exit surface of the first beam hole and a horizontal plane is set according to a focusing characteristic in an electric field direction and a focusing characteristic in a magnetic field direction of the primary beam. .   The angle between an exit surface of the first beam hole and a horizontal plane is set to an angle that reduces a deviation between a focusing characteristic in an electric field direction and a focusing characteristic in a magnetic field direction of the primary beam. The Wien filter according to 2.   The angle between the exit surface of the first beam hole and a horizontal plane is set to an angle that reduces a deviation between a focusing position in the electric field direction and a focusing position in the magnetic field direction of the primary beam. The Vienna filter according to any one of 3 above. The primary beam is incident on the first beam hole from 45 degrees obliquely above,
The Wien filter according to any one of claims 1 to 4, wherein an angle between an exit surface of the first beam hole and a horizontal plane is approximately 90 degrees.   The Wien filter according to claim 1, wherein the electromagnetic pole superimposes a quadrupole electric field or a quadrupole magnetic field in addition to the uniform parallel electric field and the uniform parallel magnetic field.

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