JP2005203241A - Electrically-charged particle beam observation method and electrically-charged particle beam device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an electrically charged particle beam observation method and an electrically charged particle beam device in which, even if an observed sample is or includes an insulator and its surface material is a sample composed of the insulator and a conductive material, a charged particle beam image of a high picture quality which is not influenced by electrostatic charge is obtained. <P>SOLUTION: The region on the sample 4 that should be observed is scanned two-dimensionally with an electron beam from an electron gun 1, and a secondary electron image in the observation is displayed in a display device 34 by a signal based on a secondary electron from the observation region inspected at a secondary electron inspection device 31 by this scanning. In this kind of observation, before the secondary electron beam image in the observation region is obtained, it is pre-irradiated with the electron beam at least to the region including the observation region so that the electrostatic charge does not occur. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

  The present invention relates to a charged particle beam observation method and a charged particle beam apparatus suitable for observing a sample in a manufacturing process of a semiconductor device such as an IC or LSI.

  A semiconductor device has, for example, a multilayer structure formed on a silicon wafer (silicon substrate). In this multilayer structure, an insulating layer is formed between specific layers, and a contact hole or a via hole is formed in the insulating layer. Then, electrical connection between specific layers is performed by embedding wiring (conductive material) in the contact hole or via hole. In the following description, contact holes are taken as an example.

  Such contact holes are formed by applying a resist to the insulating layer in the process of manufacturing a semiconductor device, exposing the contact hole pattern thereon, and then performing development processing, etching processing, and the like.

  In the formation of such a contact hole, a contact hole having a predetermined diameter is not formed, or a contact hole CH in which a part of the insulating layer A remains at the boundary with the conductive layer D as shown in FIG. It may be formed.

  Therefore, inspecting the formation state of the contact hole after forming the contact hole is important in determining whether or not to perform a subsequent manufacturing process. Also, depending on the contact hole formation state obtained by this inspection, it is possible to determine whether the development process or etching process performed in the previous process is appropriate, and the contact hole formation process is defective. Cause analysis can also be performed.

  Such a contact hole formation state inspection is performed non-destructively by, for example, electron beam irradiation of a scanning electron microscope (SEM). That is, the contact hole is scanned with an electron beam, and for example, a secondary electron image of the contact hole detected on the basis of the secondary electron is displayed on a screen on a display device, and the image of the contact hole is displayed. By observing the above, the contact hole formation state is inspected.

  When a secondary electron image of a contact hole is obtained by such electron beam scanning, charging is generated by electron beam irradiation of the insulating layer.

  That is, in the insulator sample, the ratio δ of the emission amount of secondary electrons to the incident electron amount δ (hereinafter referred to as the energy determined from the acceleration voltage of the electron beam and the voltage applied to the sample) E (hereinafter, (Referred to as a curve in FIG. 2), δ> 1 in a certain energy region (between Ea and Eb where δ = 1 in FIG. 2), and other energy regions In this case, δ <1, and it is known that the sample surface is positively charged in the former case and negatively charged in the latter case (the energy values Ea and Eb at which δ = 1 differ depending on the substance). .

  If the sample is charged positively or negatively, the S / N ratio during SEM observation may be deteriorated and the observed image may be distorted due to charged contrast (abnormal contrast).

  In order to solve such problems, for example, the following image quality improvement methods have been proposed.

  In order to improve the potential contrast of the image, the region including the image acquisition region is irradiated with an electron beam before the image acquisition to charge the region positively or negatively (Patent Document 1).

  An area including an image acquisition area is irradiated with an electron beam on a sample having large irregularities such as a contact hole bottom and a side wall after dry etching, and the area is positively charged (Patent Document 2).

  Prior to image acquisition, the area including the image acquisition area is scanned with an electron beam to charge the area positively or negatively. When positively charged, an image is acquired under the condition that the area is negatively charged. In the case of charging the image, an image is acquired under the condition of positively charging the region (Patent Document 3).

Japanese Patent Laid-Open No. 2000-208085 JP 2002-270665 A Japanese translation of PCT publication No. 2002-524827

  However, any of the image quality improvement methods has the following problems.

  When the sample to be observed has a structure in which a plug is embedded in an insulator and the plug is connected to the ground of the substrate (eg, formed on an insulating layer having a multilayer structure formed on the silicon substrate). Semiconductor devices with a structure that allows electrical connection between specific layers by embedding wiring (corresponding to plugs) in the contact holes), the insulator part must be positive or negative during precharge before image acquisition It is charged, but the plug part is not charged. In this way, when a charged part and an uncharged part occur in the observation area (image acquisition area) during precharge before image acquisition, the image is distorted during image acquisition, and the image quality is not improved. Become.

  Further, since the method of Patent Document 3 performs precharging by electron beam scanning, it takes time for precharging, and the image acquisition throughput is reduced.

  It is an object of the present invention to provide a novel charged particle beam observation method and charged particle beam apparatus that solve such problems.

  In the charged particle beam observation method of the present invention, a region to be observed on a sample is two-dimensionally scanned with a charged particle beam, and the display device observes the signal based on the charged particle beam from the observation region detected by the scanning. In a charged particle beam observation method configured to display a charged particle beam image of an area, before obtaining the charged particle beam image of the observation area, the charging is performed so that at least the area including the observation area is not charged. It is characterized by pre-irradiation with a particle beam.

  The charged particle beam apparatus according to the present invention comprises a charged particle beam generating means, a scanning means for two-dimensionally scanning an area to be observed on a sample with a charged particle beam from the charged particle beam generating means, and observation by the scanning. Means for detecting a charged particle beam generated from a region, a display device for displaying a charged particle beam image of the observation region based on the detected charged particle beam from the observation region, and a charged particle beam from the charged particle beam generation unit Accelerating means comprising an accelerating power source for generating a voltage for accelerating the sample in the direction of the sample, electric field forming means for forming an electric field on the sample surface, and sample voltage applying means for applying a voltage to the sample Before the charged particle beam image of the observation area is obtained, pre-irradiation with the charged particle beam is performed so that at least the area including the observation area is not charged. The form to so that.

  According to the charged particle beam observation method of the present invention, even if the sample to be observed contains an insulator or an insulator, and the surface material is a sample made of an insulator and a conductor, the image quality is not affected by charging. A charged particle beam image is obtained.

  In the present invention, before image acquisition (imaging) of a scanning region by electron beam scanning on a predetermined region of a sample, pre-irradiation with an electron beam is performed so that the surface of the sample is not charged. This is so that an image with good image quality can be acquired, and is based on the principle described below.

  When a sample having a uniform sample surface material (sample whose sample surface is made only of an insulator) is precharged (eg, positively charged) using a conventional method, the surface charge of the sample Sa is as shown in FIG. As shown in FIG. In this way, when the charge distribution on the sample surface is uniform, secondary electrons are emitted uniformly from the sample surface even if the sample Sa is scanned on the sample Sa during observation, so the image quality of the acquired image is affected by the charge-up. It is good without receiving. However, a sample whose surface material is not uniform using a conventional method, for example, a sample in which a conductor (eg, a plug) is embedded in an insulator, and the plug is connected to the ground of the substrate. When Sb is precharged (for example, positively or negatively charged), as shown in FIGS. 3B and 3C, the insulator portion is charged positively or negatively, but the plug portions Pa, Pb, Pc are charged. , Pd, Pe, and Pf are not charged, and the charge on the sample surface is non-uniform. When such a sample surface is scanned with an electron beam at the time of observation, the energy of electrons emitted from the sample surface is different at locations where the charge distribution on the sample surface is non-uniform, so there is uneven brightness in the secondary electron image. Occur. In addition, since the electric field above the sample surface is not uniform, the charged state of the sample surface changes due to the return of emitted electrons to the sample surface. Therefore, abnormal contrast due to charge-up occurs in the acquired image, and image quality cannot be improved.

  Therefore, the present invention pre-irradiates with an electron beam so that the surface of the sample is not charged before the electron beam is scanned on the sample for image acquisition during observation, so that the potential of the sample surface is made uniform. As a result, it has been found that the image quality can be improved even in samples having different sample surface materials (samples whose surface is made of an insulator and a conductive material).

  In order to prevent the sample surface from being charged by pre-irradiation with an electron beam, the electron landing energy, the electric field above the sample, the beam current, and the beam diameter were controlled. To confirm whether pre-irradiation is not charged, immediately after performing pre-irradiation, scan an area narrower than the pre-irradiation area with an electron beam, acquire an image of the scanning area, and brightness of the image of the scanning area, This is performed by comparison with the brightness of the peripheral area of the scanning area in the pre-irradiation area. That is, if the brightness of the former and the latter area does not change, the battery is not charged. If the former area is black with respect to the latter area, the positive charging is progressing. If the brightness is white, the charging is negative. To do.

  In the present invention, after pre-irradiation that does not cause such charging, a part of the pre-irradiation area is scanned with a charged particle beam, and an image of the area is observed based on the charged particles obtained from the area. I found that there was no charge effect.

  FIG. 4A schematically shows the charge distribution state on the surface of the sample Sc pre-irradiated so as not to be charged. If the sample surface is set in an uncharged state and charges are uniformly deposited, it is considered that negative charges are trapped on the sample surface with very weak energy to positive charges in the vicinity of the surface. This negative charge can easily move on the surface of the sample via positively charged sites.

  When a sample pre-irradiated so as not to be charged in this way is irradiated with an electron beam based on electron beam scanning on the image acquisition region Rp at the time of image acquisition (during observation), secondary electrons es are emitted from the sample surface, and the sample The surface is charged positively or negatively depending on the landing energy. For example, as shown in FIG. 4B, when the image acquisition region Rp is charged negatively, the surface of the image acquisition region Rp and the vicinity of the surface have excessive negative charges. 4), the negative charge moves to the surface of the image acquisition region Rp and the peripheral portion of the surface, the positive charge around the surface of the image acquisition region Rp to which the negative charge has moved moves, As shown in (d), the state when pre-irradiation is returned, that is, the sample surface returns to an uncharged state.

  On the other hand, as shown in (e) of FIG. 4, when the image acquisition region Rp is positively charged at the time of image acquisition (observation), the surface of the image acquisition region Rp lacks negative charges. As shown in FIG. 4 (f), the negative charge trapped on the surface of the peripheral portion with weak energy moves to the image acquisition region Rp on the surface of the sample, and pre-irradiation as shown in FIG. 4 (g). The state at the time when the sample is taken, that is, the sample surface returns to the uncharged state.

  In this way, prior to electron beam scanning on the image acquisition region for image acquisition during observation, pre-irradiation with an electron beam is performed so that the sample surface including the image acquisition region is not charged, and the potential of the sample surface is set. If uniform, even when an image is acquired by scanning the image acquisition area with an electron beam and observing the image of the area based on the secondary electrons obtained from the area, the image is not affected by charging.

  The actual effect of the present invention was verified as follows.

  First, an image is formed by scanning the sample with an electron beam without pre-irradiation. Further, immediately after that, a wider area is scanned than the scanning area, thereby imaging a wide area. The time from the first image acquisition to the second image acquisition was set between 0.5 and 5 sec. Information regarding charging of the first image acquisition region can be obtained from the luminance difference between the first image acquisition region and the second image acquisition region. As a result of the experiment, it was found that the first image acquisition region had a tendency of whiteness in brightness as compared with the peripheral portion, so that the charging progressed negatively. At this time, even if the time from the first image acquisition to the second image acquisition was changed, the charged state of the first image acquisition region in the second image did not change.

  On the other hand, as in the present invention, after pre-irradiation of the sample surface including the image acquisition region so as not to be charged, an image is formed by scanning a part of the pre-irradiation region with an electron beam. After pre-irradiation, imaging in the second region was performed immediately after imaging in the first region in the same manner as described above. The luminance difference between the first region and the surrounding area in the second image was small even when the image acquisition interval was 0.5 sec compared to the case where pre-irradiation without charging was not performed. This means that when pre-irradiation without charging is performed, there is little charging in the first image acquisition. In addition, it was found that when pre-irradiation without charging was performed, the luminance difference between the first region in the second image and its surroundings became smaller as the image acquisition interval became longer. This is because, as described above, the charge trapped on the surface can be easily moved, so that the charge due to the first imaging is relaxed.

  As described above, the pre-irradiation for preventing the sample surface from being charged is a negative charge deposited on the sample surface to make the charge state uniform, and the charge at the time of observing the image is acquired by the movement of the deposited charge. It suppresses.

  In this way, the present invention can improve image quality by performing pre-irradiation so that the surface of the sample is not charged even if it is a sample with a different sample surface material (sample consisting of an insulator and a conductor). It is a thing. As a result, fine details of the sample can be observed.

  Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings.

  FIG. 5 shows one schematic example of an electron beam inspection apparatus which is an example of the charged particle beam apparatus of the present invention.

  In the figure, reference numeral 1 denotes an electron gun, and an electron beam from the electron gun is appropriately focused on a sample 4 by a condenser lens 2 and an objective lens 3. Reference numerals 5X and 5Y denote X-direction and Y-direction deflection coils for scanning the sample with an electron beam. The sample 4 is placed on a stage 7 whose movement is controlled by a stage drive mechanism 6.

  8 is a current limiting diaphragm, 9 is an open-angle lens, 10 is an upper electrode disposed between the sample 4 and the objective lens 3, and 11 is an insulating substrate mounted on the stage 7, and a substrate electrode on which the sample is directly placed It is.

  Reference numerals 12, 13, and 14 denote lens control circuits for controlling the excitation intensity of the condenser lens 2, objective lens 3, and aperture angle lens 9, respectively. Reference numeral 15 denotes a deflection control circuit that supplies a deflection signal to the deflection coils 5X and 5Y. is there. 16 is an acceleration voltage control circuit for supplying an acceleration voltage to the electron gun 1, and 17 is a stage control circuit for supplying a stage movement control signal to the stage drive mechanism 6. Reference numerals 18 and 19 denote voltage sources for applying a voltage to the upper electrode 10 and the substrate electrode 11, respectively. Reference numerals 20 and 21 denote control circuits for the respective voltage sources.

  The lens control circuits 12, 13, 14, the deflection control circuit 15, the acceleration voltage control circuit 16, the stage control circuit 17, and the voltage source control circuits 20, 21 have DA converters 22, 23, 24, 25, 26, respectively. 27, 28, and 29, a lens control command, a deflection control command, an acceleration voltage control command, a stage movement command, and a voltage control command are sent from the control device 30 that performs various commands and various data processing.

  In the figure, reference numeral 31 denotes a secondary electron detector for detecting secondary electrons from the sample 4, and the detected secondary electron signal is sent to the control device 30 via an amplifier 32 and an AD converter 33. Reference numeral 34 denotes a display device (for example, a cathode ray tube or a liquid crystal display device), and reference numeral 35 denotes a storage device including a plurality of frame memories.

  An absorption current detector 36 detects an absorption current flowing through the sample 4. The absorption current detected by the absorption current detector 36 is sent to the control device 30 via an AD converter 37.

  The stage 7 is movable in the two-dimensional horizontal direction of X and Y, can be tilted around either X or Y axis, and can be rotated around the electron optical axis (Z axis). Yes.

  The control device 30 incorporates a sample inspection recipe. In the inspection recipe, landing energy, sample substrate voltage, sample upper part electric field, beam current, and beam diameter are registered as observation positions, pre-irradiation conditions, and image acquisition conditions.

  The landing energy is obtained based on the sum of the acceleration voltage of the electron gun 1 and the voltage of the substrate electrode 11 (voltage applied to the sample 4). The pre-irradiation and image acquisition conditions can be selected from a group of conditions stored in a database based on the surface material information of the sample.

  In the apparatus having such a configuration, an area to be observed is scanned with an electron beam, and an image of the area to be observed is acquired on the basis of the secondary electrons detected by the scanning. Pre-irradiate the area.

  This pre-irradiation is performed as follows.

The stage control circuit 17 sends a movement drive signal to the stage drive mechanism 6 based on a stage movement command from the control device 30, and the center of the region to be observed of the sample 4 registered in the inspection recipe is on the electron optical axis. Move stage 7 in the same way. While moving to this observation position, the lens control circuits 12, 13, 14, the deflection control circuit 15 and the voltage source control circuits 20, 21 set various lenses as pre-irradiation conditions. Pre-irradiation is large without scanning the electron beam. This is done by electron beam irradiation of the cross section. As shown in FIG. 6, as the pre-irradiated electron beam, the beam diameter Da is set so that the cross section Bd includes the image acquisition region Rp at the time of observation, and a region where the beam current density is broad is used. . The area of the pre-irradiation area is set such that DA ≧ Db, where Da is the diameter of the pre-irradiation area of the electron beam and Db is the larger dimension of the image acquisition area Rp at the time of observation.

  Since the pre-irradiated sample surface is irradiated with a beam having a uniform density so as not to charge the sample surface with such an electron beam, the charge on the sample surface can be uniformly distributed. Further, since pre-irradiation is not scanned, an extra time for scanning at least one frame is not required. Therefore, a decrease in throughput can be prevented.

  The lens control circuit 12 controls the excitation of the condenser lens 2 and sets the beam current of the electron beam from the electron gun 1. The lens control circuit 14 controls the excitation of the opening angle control lens 19 and sets the beam diameter of the electron beam. The beam diameter can be set by controlling the excitation of the objective lens 3 by the lens control circuit 13.

  Further, the beam current density and beam diameter of the electron beam may be determined by combining the settings of the condenser lens 2, the opening angle control lens 9, and the objective lens 3. During pre-irradiation, the deflection control circuit 15 controls the excitation of the X and Y deflection coils 5X and 5Y so that the electron beam does not scan the sample.

  As a method of pre-irradiating with an electron beam so as not to charge the sample surface, for example, the following four methods can be considered.

  As described above, the charged state of the sample surface changes depending on the landing energy. A curve Qa in FIG. 7 is a partially enlarged view of the relationship between the landing energy and the secondary electron emission rate shown in FIG. At the landing energy Ea, Eb where the secondary electron emission rate δ = 1, the sample surface is not charged because the amount of incident electrons is equal to the amount of emitted electrons. On the other hand, the secondary electron emission rate δ> 1 (the landing energy between Ea and Eb is positively charged because the amount of emission is larger than the amount of incident electrons. Also, the secondary electron emission rate δ <1. If the landing energy is less than Ea and greater than Eb, the amount of emitted electrons is less than the amount of incident electrons, and thus the surface is negatively charged. Now, the charged state of the sample surface changes depending on the electric field above the sample surface, so that secondary electrons emitted from the sample do not return to the sample above the sample surface. When an electric field is applied, the secondary electron emission rate curve becomes Qb. When the electron beam is irradiated with the landing energy of Ec and Ed where the secondary electron emission rate δ = 1, the sample surface is not charged.

  Based on such a theory, landing energy (determined by the electron acceleration voltage and the sample applied voltage (substrate electrode voltage)), the electric field above the sample surface, and the substrate electrode voltage are controlled in order to perform pre-irradiation without charging.

  In the first method, electrons are applied to the surface of the sample with landing energy Ec or Ed that gives an emission rate δ = 1 in the secondary electron emission rate curve Qb when a voltage is applied in a direction in which the secondary electrons do not return to the sample 4. Pre-irradiate with a beam. In this case, the voltage of the upper electrode 10 is set so that the electric field above the sample surface does not return secondary electrons to the sample. The landing energy is controlled by the acceleration voltage of the electron gun 1 and the voltage of the substrate electrode 11.

  In the second method, a voltage is applied in the direction in which the emitted secondary electrons return to the sample (the secondary electron emission rate curve in this case is Qa), and the landing energy Ea or the secondary electron emission rate δ = 1 or Eb is pre-irradiated with an electron beam. In this case, the voltage of the upper electrode 10 is set so that the electric field above the sample surface returns secondary electrons to the sample. The landing energy is controlled by the acceleration voltage of the electron gun 1 and the voltage of the substrate electrode 11.

  In the third method, a voltage is applied in a direction in which the secondary electrons do not return to the sample (in this case, the secondary electron emission rate curve is Qb), the landing energy is set to an arbitrary value, and the landing energy with respect to the set landing energy is set. The electric field above the sample surface is controlled by the voltage of the upper electrode 10 so that the secondary electron emission rate δ becomes 1, and in this state, pre-irradiation is performed with the electron beam having the set landing energy.

  In the fourth method, a voltage is applied in the direction in which the emitted secondary electrons return to the sample (the secondary electron emission rate curve in this case is Qa), the landing energy is set to an arbitrary value, and the set landing is set. The electric field above the sample surface is controlled by controlling the voltage of the upper electrode 10 so that the secondary electron emission rate δ with respect to energy becomes 1, and in this state, pre-irradiation is performed with the electron beam having the set landing energy.

  When the sample surface material is different (sample surface is made of an insulating material and a conductive material), pre-irradiation without charging is performed as follows.

  Curves QAa and QAb shown in FIG. 8 are secondary electron emission rates when the secondary electrons emitted from the material A return to the sample and do not return, respectively. On the other hand, the secondary electron emission rate curves QBa and QBb are secondary electron emission rates when the secondary electrons emitted from the material B return to the sample and do not return, respectively. In this way, when the sample surface material is different, even if only the landing energy is adjusted, it is difficult to set the secondary electron emission rate σ = 1 for different substances. Do.

  Even when a voltage is applied to the substrate electrode 11 or the upper electrode 10 so that the emitted secondary electrons return to the sample 4 (secondary electron emission rate curves at this time are QAa and QAb), or the secondary electrons Even when a voltage is applied to the substrate electrode 11 or the upper electrode 10 (secondary electron emission rate curves at this time are QBa and QBb) so as not to return to the sample 4, the landing corresponding to each of the intersections C1 and C2 The electron beam is set to have an energy value, and the voltage of the substrate electrode 11, the acceleration voltage of the electron beam, and the voltage of the upper electrode 10 are controlled so that the secondary electron emission rate δ becomes 1. In this state, pre-irradiation is performed with an electron beam having the set landing energy value.

  As described above, the pre-irradiation is performed so as not to be charged under the condition that the secondary electron emission rate = 1 by controlling the landing energy, the substrate electrode voltage, and the sample upper electric field.

  In any method, landing energy (determined by electron acceleration voltage and sample applied voltage (substrate electrode voltage)), electric field above the sample surface, and substrate electrode for performing pre-irradiation that is not charged depending on the sample. The voltage is obtained in advance by experiments or the like, and is stored as a pre-irradiation condition in the inspection recipe of the control device 30. At the time of pre-irradiation, the pre-irradiation condition is read and pre-irradiation is performed. That is, the electron acceleration voltage data satisfying the pre-irradiation condition is sent to the acceleration voltage control circuit 16 via the DA converter 26 to control the acceleration energy of the electron beam from the electron gun 1, and the sample applied voltage satisfying the pre-irradiation condition. Data is sent to the voltage source control circuit 20 via the DA converter 28 to control the voltage applied from the voltage source 19 to the substrate electrode 11, and the electric field data above the sample surface that constitutes pre-irradiation conditions passes through the DA converter 29. To the voltage source control circuit 21 to control the voltage applied from the voltage source 18 to the upper electrode 14.

  The extraction of the pre-irradiation conditions is performed as follows, for example.

  The charged state of the sample surface is controlled by the electric field above the sample surface, the landing energy and beam diameter of the electron beam, and the absorption current is detected in synchronization with the electron beam irradiation. It can be judged that it is not charged. That is, when the incident current is Ip, the secondary electron current is Ise, and the absorption current is Iae, the relationship of Ip = Ise + Iae is established. Since the incident current Ip is fixed and pre-irradiation is performed, the secondary electron current Ise can be calculated by measuring the absorption current Iae. Since Ip = Ise is satisfied under the condition of Iae = 0, the incident and outgoing electron flows are balanced, that is, the secondary electron emission rate δ = 1. In this case, it is determined that the sample surface is not charged. it can.

  Based on such a theory, pre-irradiation condition extraction is performed.

  The landing energy, the upper electric field on the sample surface, and the sample substrate voltage are controlled in various ways, the pre-irradiation as described above is performed, and a condition for Iae = 0 is searched. When the condition is determined, an image is acquired, and the image signal processing unit of the control device 30 performs image quality determination by luminance comparison as described above. As a result, when it is determined as normal, the landing energy, the sample surface upper field, and the sample substrate voltage at that time are determined as pre-irradiation conditions.

  The processing procedure for the pre-irradiation conditions is incorporated in the control device 30 and may be automatically searched or the conditions may be determined manually.

  Such extraction of pre-irradiation conditions is performed for each of different types of samples, and the determined pre-irradiation conditions are stored in a table in the storage device of the control device 30.

  After pre-irradiation as described above, an operation for acquiring an observation image starts based on an inspection start command from the control device 30.

The electron beam from the electron gun 1 is focused in a spot shape on the sample by the condenser lens 2 and the objective lens 3. At the same time, the electron beam scans the observation region by the X direction deflection coil 5X and the Y direction deflection coil 5Y. As described above, this observation region is a part of the pre-irradiation region.
By such scanning, secondary electrons generated from the observation region are detected by the secondary electron detector 31, and the output of the secondary electron detector is sent to the control device 30 via the amplifier 32 and the AD converter 33. It is done. The control device temporarily stores it in the storage device 35 and then calls it to display it as a secondary electron image of the observation region on the screen of the display device 34.

  Next, the operation moves to an inspection (observation) operation for another region. At that time, if the inspection region is outside the pre-irradiation region previously performed, the scanning region is scanned as described above. Perform pre-irradiation.

  In addition, pre-irradiation is performed before image acquisition by electron beam scanning in the inspection area. This pre-irradiation is performed by moving the stage so that the center of the inspection area (area to be observed) is on the electron beam optical axis. It may be possible to increase the throughput by performing it while it is being performed. At this time, the pre-irradiation is more accurately performed when the center of the inspection region is as close as possible to the electron beam optical axis. Therefore, for example, if the pre-irradiation area is 100 μm × 100 μm and the inspection area is 10 μm × 10 μm, the pre-irradiation is started when the center of the inspection area reaches about 80 μm of the electron beam optical axis.

  In the above example, in order to improve the throughput, the pre-irradiation is not performed by the electron beam scanning but is performed by one irradiation with the electron beam cross section enlarged. However, if the throughput does not need to be improved, Alternatively, electron beam scanning may be performed.

  According to the present invention, by performing pre-irradiation without charging, the image quality of the image acquisition region obtained at the time of observation (inspection) is improved. Therefore, the present invention is also applied to various detections and corrections. (For example, pre-irradiation in which charging is not generated is performed before vibration correction or temperature correction in vibration correction or temperature correction by detecting vibration displacement, etc.), and a new effect can be obtained.

  Also, for example, when extracting a shape from an image including a defect and an image not including a defect and automatically detecting a defect from the degree of coincidence, if an image not including a pre-irradiated defect is used, Since the image quality is improved and minute defects can be recognized, it contributes to the improvement of automatic defect detection accuracy.

  In addition, in the automatic defect detection, the S / N ratio must be good so that noise is not recognized as a defect. For this reason, the image signal is averaged by increasing the number of times of image integration, but the throughput is reduced. Therefore, if the pre-irradiation method without charging of the present invention is applied to improve the image quality, the normal operation has been performed up to about 1/100000 to 1/1000000 coulomb / square centimeter with an incident current and beam irradiation amount approximately five times that of the conventional method. Therefore, the number of integrations can be reduced to about 1/4 of the conventional number, and the throughput can be improved by about 4 times.

  Moreover, the defect extracted in the automatic defect detection is transferred to the automatic defect classification computer, and therefore, in the automatic defect classification for discriminating the type of defect, since the image quality is poor in the past, the fine defect classification is impossible. However, since the automatic defect classification can be performed using the image improved by the pre-irradiation without charging according to the present invention, the fine defect is shown in detail, so that the automatic defect classification accuracy is improved.

  The present invention is not limited to the embodiments described so far. For example, the present invention may be applied to a semiconductor inspection apparatus configured with a plurality of columns including an electron microscope.

  In the above example, as a power source for generating a voltage for accelerating electrons, a power source for generating a voltage for forming an electric field above the sample surface, and a power source for generating a voltage to be applied to the sample, the pre-irradiation is used. And scanning for observing the observation area may be provided separately and switched at high speed at each time.

  In the above example, an example in which an insulating sample is observed by scanning with an electron beam has been described. However, the present invention is also effective when an insulating sample is observed by scanning with an ion beam.

  In the above example, the observation of the secondary electron image of the sample has been described. However, the present invention is also effective for detecting the reflected electron from the sample and observing the reflected electron image.

The example of the formation state of a contact hole is shown. The relationship between landing energy and secondary electron emission ratio is shown. The charged state of the sample surface by the conventional precharge method is represented. The charged state of the sample surface used for explanation of the principle of the present invention is shown. 1 shows a schematic example of a charged particle beam apparatus according to the present invention. FIG. 6 shows a relationship between an electron beam cross section used in the apparatus shown in FIG. 5 and an image acquisition region. The relationship between the landing energy and the secondary electron emission ratio when the sample surface material is uniform is shown. This shows the relationship between the landing energy and the secondary electron emission ratio when the sample surface materials are different (samples whose surface is made of an insulator and a conductive material).

Explanation of symbols

A ... Insulating layer D ... Conductive layer CH ... Contact hole Sa, Sb, Sc ... Sample Pa, Pb, Pc, Pd, Pe, Pf ... Plug part Rp ... Image acquisition region 1 ... Electron gun 2 ... Condenser lens 3 ... Objective lens DESCRIPTION OF SYMBOLS 4 ... Sample 5X ... X direction deflection coil 5Y ... Y direction deflection coil 6 ... Stage drive mechanism 7 ... Stage 8 ... Current limiting aperture 9 ... Opening angle lens 10 ... Upper electrode 11 ... Substrate electrode 12, 13, 14 ... Lens control circuit DESCRIPTION OF SYMBOLS 15 ... Deflection control circuit 16 ... Acceleration voltage control circuit 17 ... Stage control circuit 18, 19 ... Voltage source 20, 21 ... Voltage source control circuit 22, 23, 24, 25, 26, 27, 28, 29 ... DA converter 30 ... Control device 31 ... Secondary electron detector 32 ... Amplifier 33 ... AD converter 34 ... Display device 35 ... Storage device 36 ... Absorption current detector 37 ... AD converter

Claims (23)

  The region to be observed on the sample is two-dimensionally scanned with the charged particle beam, and the charged particle beam image of the observation region is displayed on the display device by a signal based on the charged particle beam from the observation region detected by the scanning. In the charged particle beam observation method, the charged particle beam observation in which the charged particle beam is pre-irradiated so that at least the region including the observation region is not charged before the charged particle beam image of the observation region is obtained. Method.   2. The charged particle beam observation method according to claim 1, wherein the pre-irradiation is performed by irradiating the electron beam with a landing energy at which the ratio of the amount of emitted secondary electrons to the amount of incident electrons on the sample surface is 1.   3. The charged particle beam observation method according to claim 2, wherein the pre-irradiation is performed in a state where the charged particles emitted from the sample do not return to the sample.   3. The charged particle beam observation method according to claim 2, wherein the pre-irradiation is performed in a state where the charged particles released from the sample return to the sample.   3. The landing energy is arbitrarily set, the ratio of the amount of secondary electrons emitted to the amount of incident electrons on the sample surface with respect to the set energy value is set to 1, and pre-irradiation is performed in that state. Charged particle beam observation method.   6. The charged particle beam observation method according to claim 5, wherein the pre-irradiation is performed in a state where the charged particles emitted from the sample do not return to the sample.   6. The charged particle beam observation method according to claim 5, wherein the pre-irradiation is performed in a state where the charged particles emitted from the sample return to the sample.   When the sample is made of an insulator and a conductor, a curve of the ratio of the amount of secondary electrons emitted to the amount of incident electrons on the sample surface with respect to the landing energy value required for the insulator and the conductor is obtained. The landing energy value corresponding to the intersection of the curve of the ratio of the amount of secondary electrons emitted to the amount of incident electrons on the sample surface with respect to the landing energy value and the amount of incident electrons on the sample surface corresponding to the set energy value is set. The charged particle beam observation method according to claim 1, wherein the ratio of secondary electron emission amounts is set to 1, and pre-irradiation is performed in that state.   The charged particle beam observation method according to claim 1, wherein the pre-irradiation is performed by irradiating a charged particle beam having a cross section larger than an observation region.   The charged particle beam observation method according to claim 1, wherein pre-irradiation is performed while the sample is moved in order to bring the observation region onto the valence electron optical axis.   3. The charged particle beam observation method according to claim 2, wherein the landing energy is controlled based on the valence electron beam acceleration voltage and the voltage applied to the sample.   The charged particle beam observation method according to claim 3 or 6, wherein the charged particles emitted from the sample are not returned to the sample by controlling an electric field formed above the sample surface.   The charged particle beam observation method according to claim 4 or 7, wherein the charged particles emitted from the sample are returned to the sample by controlling an electric field formed above the sample surface.   The charged particle beam observation method according to claim 3 or 6, wherein the charged particles emitted from the sample are not returned to the sample by controlling the voltage applied to the sample.   The charged particle beam observation method according to claim 4 or 7, wherein the charged particles emitted from the sample are returned to the sample by controlling a voltage applied to the sample.   The charged particle beam observation method according to claim 1, wherein an absorption current flowing through the sample is detected, and a charged state of the sample by pre-irradiation is determined based on the detected value.   As a power source for generating a voltage for accelerating the valence electron beam, a power source for generating a voltage to form an electric field above the sample surface, and a power source for generating a voltage to be applied to the sample, the pre-irradiation time and the observation region The charged particle beam observation method according to claim 1, wherein a scanning time for observation is provided, and switching is performed at each time.   Charged particle beam generating means, scanning means for two-dimensionally scanning the area to be observed on the sample with the charged particle beam from the charged particle beam generating means, and detecting the charged particle beam generated from the area to be observed by the scanning Means for displaying a charged particle beam image of the observation region based on the detected charged particle beam from the observation region, and a voltage for accelerating the charged particle beam from the charged particle beam generation unit in the sample direction Accelerating means including an accelerating power source for generating electric field, electric field forming means for forming an electric field on the sample surface, and sample voltage applying means for applying a voltage to the sample, and charged particles in the observation region Prior to obtaining a beam image, a charged particle beam that is pre-irradiated with a charged particle beam so that at least the region including the observation region is not charged. Location.   The charged particle beam apparatus according to claim 19, wherein the landing energy is controlled based on a voltage for accelerating the charged electron particles and a sample applied voltage.   The charged particle beam apparatus according to claim 19, wherein an electrode is provided above the sample surface, and an electric field formed above the sample surface is controlled based on a voltage applied to the electrode.   20. The charged particle beam apparatus according to claim 19, wherein an electric field formed above the sample surface is controlled based on a sample applied voltage.   20. The charged particle beam apparatus according to claim 19, wherein an electric field formed above the sample surface is controlled based on a voltage applied to an electrode provided above the sample surface and a sample applied voltage.   As a power source for generating a voltage for accelerating the electrons, a power source for generating a voltage for forming an electric field above the sample surface, and a power source for generating a voltage to be applied to the sample, pre-irradiation and observation region 20. The charged particle beam apparatus according to claim 19, wherein a scanning unit for observation is provided, and switching is performed at each time.

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