JP4295748B2 - Method for scanning an object comprising a plurality of critical regions using a scanning beam array - Google Patents

Description

Cross-reference of related applications

  [001] This application claims priority to US Provisional Application No. 60 / 581,817, filed June 21, 2004, entitled "Scanning Critical Areas Using Multiple Beam Systems". The entirety of which is incorporated herein by reference.

Field of Invention

  [002] It relates to scanning an object including a plurality of critical regions using a scanning beam array, in particular, an object such as a wafer or reticle using a charged particle beam array.

Background of the Invention

  [003] Inspection of objects such as wafers and reticles using scanning electron beam inspection tools is known in the art. A single beam inspection tool scans a wafer or reticle with a single beam. The relative size differences between wafer size and beam cross-sectional area limit the throughput of such systems.

  [004] Various techniques have been suggested to increase the throughput of inspection and metrology systems. The first technique involves scanning only a portion of the wafer. This portion typically includes a plurality of critical areas positioned at various locations.

  [005] Other techniques involve using a multiple beam scanning array. Some multi-beam systems include a fixed beam array that starts from a line array to a two-dimensional grating array.

  [006] The following US patents and US patent applications are incorporated herein by reference in their entirety, which provide a summarized overview of the state of the art of a multiple beam scanning system. US Patent No. 6,465,783 entitled "High-throughput specimen-inspection apparatus and methods utilizing multiple parallel charged particle beams and an array of multiple secondary-electron-detectors", "Multi-beam multi-column electron beam inspection" Parker's US Patent No. 6,734,428 entitled "system", Rho's US Patent No. 6,750,455 entitled "Methods and Apparatus for Multiple Charged Particle Beams", "Apparatus andmethods for secondary electron emission microscope with" US Pat. No. 6,803,572 to Venekrasen et al. entitled “dual beam”, and US patent application 2002/0015143 to Yin et al. entitled “Multi-Beam Multi-Column Electron Beam Inspection System”.

  [007] There is a need to provide an effective system and method for scanning objects using multiple beam arrays.

Summary of the Invention

  [008] The present invention comprises (i) a beam array generator adapted to generate a beam array characterized by a beam array axis; and (ii) positioning the object under the beam array. At least one mechanism adapted, wherein at least two beams positioned along a beam array axis scan at least two critical areas of the object substantially simultaneously, the first axis being The mechanism being oriented with respect to the beam array axis.

  [009] Conveniently, the system further includes a controller adapted to define a first spatial relationship between the at least two important regions along the important region axis. Conveniently, the at least one mechanism is adapted to rotate the object relative to the beam array. Conveniently, at least one mechanism is adapted to rotate the beam array relative to the object. Conveniently, the system is adapted to define the spatial relationship by applying image processing.

  [010] Conveniently, the system is adapted to scan at least two critical areas after the object to be inspected is positioned under the beam array.

  [011] A method for inspecting an object includes the steps of defining a first spatial relationship between at least two critical regions positioned along an axis of the critical region; and at least responsive to the first spatial relationship. Positioning an object under a plurality of beams of the beam array, wherein at least two beams of the beam array positioned along a beam array axis substantially define the at least two critical regions. Scanning at the same time, the first axis being oriented to the beam array axis.

  [012] Conveniently, the positioning step comprises rotating the object relative to the beam array. Conveniently, the positioning step comprises rotating the beam array relative to the object. Conveniently, the defining step comprises image processing. Conveniently, the method further comprises scanning at least two important areas.

  [013] Conveniently, the total area of the plurality of important regions is relatively small with respect to the size of the surface of the object. Conveniently, the object is a wafer or a reticle. Conveniently, the beam array includes a beam grating.

  [014] Conveniently, the beam is a charged particle beam. Conveniently, the orientation angle between the initial axis and the beam array axis is responsive to the ratio of the beam array spacing to the critical area spacing.

  [015] In order to understand how the present invention is implemented in practice, preferred embodiments of the present invention will now be described by way of non-limiting examples with reference to the accompanying drawings.

Detailed Description of the Invention

  [023] In the detailed description of the preferred and other embodiments of the present invention, reference is made to the accompanying drawings. It will be appreciated by those skilled in the art that other embodiments and variations are readily apparent without departing from the scope of the invention.

  [024] For illustrative purposes, the following description relates to a system for inspecting a wafer with an electron beam array. According to other embodiments of the present invention, the described systems and methods are applicable for metrology, lithography, and the like. The object to be inspected may be a reticle, a flat display, a MEMS device, or the like. The array shape may be different from the two-dimensional grating, and the beam may include an ion beam or a light beam.

  [025] FIG. 1 illustrates an inspection system 10 of one embodiment of the present invention. The system 10 includes a beam generator 20 that can generate an array of charged particle beams 202. The beam generator 20 can be implemented in various ways. The plurality of tip portions of the first embodiment generate a plurality of beams. In another embodiment, a single tip generates a beam that is a laser that is converted into multiple beams.

  [026] The beam generator 20 also includes optical components that focus the beam array onto an object to be inspected, such as the wafer 100. The wafer 100 is usually placed on the XY stages 30 and 31 and the optional θ stage 32.

  [027] Even though the wafer 100 is inspected inside the vacuum chamber 40, the wafer 100 is inserted into the system 10 by a cassette 50 having a pre-alignment function. These functions allow the wafer to be inserted at a fixed tilt angle with respect to the imaginary XY axes of the stage. Note that components other than cassette 50 have a pre-alignment function. For example, the robot or the pre-alignment apparatus can perform a predetermined rotation before the wafer is placed on the XY stage 30-31.

  [028] The system 10 includes one or more detection devices 60, a processor capable of receiving the detection device signals, and finding defects. The processor 70 can also be used in the initial process of finding critical areas. The finding step may include obtaining an image of the wafer portion until a weight region is found.

  [029] The processor 70 can also be used to determine the orientation angle between the beam array and the wafer to be inspected. Note that the processor 70 includes multiple components and may include multiple components that can be located at various locations or integrated with each other. For simplicity of explanation, various components, including optical components, have been omitted.

  [030] It should be noted that the configuration illustrated in FIG. 1 is only one of many possible configurations of the inspection system 10, and may have a different architecture than the illustrated architecture.

  [031] FIG. 2 illustrates a wafer 100 that includes a plurality of dies 102. Each die 102 has at least one critical area, such as at least the reference number “8”. For convenience of explanation, assume that each die includes one critical area, all of which are located at substantially the same location within the die. Further, it is assumed that the important regions 8 are parallel to each other and arranged in a lattice corresponding to the arrangement of a plurality of dies.

  [032] The distance between adjacent critical regions along a first axis, such as the imaginary X axis, is defined as a critical region spacing (ROID) 111. Note that other definitions can be used, the imaginary X-axis is used only for ease of explanation.

  [033] The dies are usually ideally identical to each other. Thus, the critical area is located at substantially the same location within each die. When a single critical area is included within each die, rather than within multiple dies, they are advantageously identical in shape and are usually parallel to each other. This is not necessary, but is essential when the method is applied to inspect objects other than wafers. Note that when the die has more than one critical region, they may differ in shape, orientation, size, etc.

  [034] FIG. 3 illustrates multiple spots corresponding to multiple beams 202, in accordance with an embodiment of the present invention. The beam 202 in FIG. 2 forms a regular lattice. 1 and 2 illustrate an array of critical regions and a beam array having the same shape (although adjacent members of the grid may vary in distance), it should be noted that this is not necessary.

  [035] The beams 202 of the beam array 200 form a plurality of rows along an imaginary beam array axis, such as the X 'axis. The distance between two adjacent beams along the X ′ axis is called the beam array distance (BAD) 222.

  [036] If the BAD 222 is equal to the ROID 111, then the wafer 100 can be positioned below the beam generator such that the first axis X is parallel to the first beam array axis X '. In such cases, multiple critical regions can be placed under multiple beams of the array. The amount of simultaneously scanned critical region depends on the amount of critical region and the amount of beam, assuming that the beam array has substantially the same shape as the imaginary grating formed by the critical region.

  [037] If the BAD 222 is different from the ROID 111, the beam array needs to be oriented with respect to the wafer. Orientation can be achieved in a variety of ways, including rotating the wafer 100, rotating the beam 202, or both. The rotation can be applied after the wafer 100 is placed in the inspection system or before the wafer is placed under the beam array.

  [038] Rotation can also be achieved by various electric, magnetic, and / or electromagnetic fields that rotate the beam array, or by a combination of such and mechanical means. Conveniently, the wafer is placed on the XY and θ stages 30-32.

  [039] The orientation angle is responsive to the relationship between the BAD 222 and the ROID 111. In the mathematical term k * BAD = m * ROID * cos (θ), θ is defined as the orientation angle between the X axis and the X ′ axis, and m and k are defined as positive integers.

  [040] It should be noted that in certain cases, this equation can be satisfied by numerical values where m and k are not integers. If this is the case, the throughput of the system can be greater than with a single beam system. If k or m is approximately an integer, scan the first critical region with the first beam, and scan the other critical regions replaced by the ROID with a beam approximately replaced by K * BAD from the first beam; Can be partially overlapped between.

  [041] FIGS. 4-6 illustrate an exemplary relationship between the beam 202 and the plurality of critical regions 8. FIG. 4 and 5 illustrate oblique orientation angles, while FIG. 6 illustrates two rows of beams that have been rotated by 90 degrees to scan multiple critical areas. Note that these figures, like the other figures in this specification, are not a common measure. In particular, the beam is not necessarily that, but is usually much smaller than the critical area.

  [042] FIG. 4 illustrates an exemplary relationship between the beam 202 and the critical region 8. FIG.

  [043] According to embodiments of the present invention, the additional area and critical area can be scanned during the scanning process. These additional areas are usually defined according to various parameters including inaccuracies in scanning, inaccuracies in critical areas, differences in the location of critical areas within different dies, mechanical movement limitations, etc. The

  [044] While the wafer is being scanned, the wafer is typically moved along an imaginary axis (eg, the Y axis). In many cases, continuous translation of the wafer causes the beam to scan an area that expands between critical areas.

  [045] FIG. 7 illustrates a critical region 8 and a plurality of additional areas 110 scanned according to one embodiment of the present invention. The additional area 110 is slightly larger than the critical area 8. Each additional area 110 surrounds a row of important regions 8. Note that although FIG. 6 illustrates a continuous additional area, this is not necessary.

  [046] According to one embodiment of the present invention, the inspection system only processes signals from critical areas, but this is not necessary. The inspection system can apply various comparison methods including between dies and between cells.

  [047] A beam array was used that included two rows of five beams each. It should be noted that other arrays can be used, including arrays containing many beams, as well as arrays that are shaped differently.

  [048] In some cases, the critical regions were arranged in rows, and the inventor was able to increase throughput by applying a 90 degree orientation angle.

  [049] FIG. 8 is a flowchart of a method 400 for inspecting an object that includes a plurality of critical regions.

  [050] The method 400 begins with a step 410 of defining a first spatial relationship between at least two critical regions positioned along the critical region axis. Conveniently, step 410 includes rotating the object relative to the beam array. Conveniently, step 410 includes rotating the beam array with respect to the object. Conveniently, the beam is a charged particle beam.

  [051] Following the step 410 is a step 420 of positioning an object under the plurality of beams of the beam array according to at least a first spatial relationship, wherein the positioning is along the beam array axis. The at least two beams of the beam array that are scanned substantially simultaneously at least two critical regions whose first axis is oriented with respect to the beam array axis.

  [052] Conveniently, the orientation angle between the first axis and the beam array axis is responsive to the ratio between the beam array spacing and the critical region spacing. Conveniently, step 420 involves image processing.

  [053] Following step 420 is a step 430 of scanning at least two critical regions.

  [054] Conveniently, step 420 includes orienting the object relative to the beam array axis prior to inserting the object into an inspection system comprising a beam array generator.

  [055] FIG. 9 illustrates a portion of a scan path 201 shaped by a raster scan, which is generated by mechanical movement along the Y axis and deflection of a single beam along the X axis.

  [056] Conveniently, the total area of the plurality of important regions is relatively small with respect to the size of the surface of the object. Conveniently, the overall size of the scanning area. Conveniently, the object is a wafer or a reticle. Conveniently, the beam array is a beam grating.

  [057] The present invention can be implemented using conventional tools, methodologies, and components. Accordingly, details of such tools, components, and methodologies are not described in detail herein. In the preceding description, numerous specific details (electro-optically effective materials and test structure shapes) are set forth in order to provide a thorough understanding of the present invention. However, it should be appreciated that the invention can be practiced without resorting to the details specifically set forth.

  [058] Only exemplary embodiments of the present invention, and a few examples of versatility, are shown and described in this disclosure. It is to be understood that the present invention can be used in various other combinations and environments, and that changes or modifications can be made within the scope of the inventive concept as expressed herein.

FIG. 1 illustrates an inspection system according to one embodiment of the present invention. FIG. 2 illustrates a wafer including a plurality of dies. FIG. 3 illustrates multiple spots corresponding to multiple beams, according to one embodiment of the present invention. FIG. 4 illustrates an exemplary relationship between a beam and a plurality of critical areas, according to one embodiment of the present invention. FIG. 5 illustrates an exemplary relationship between a beam and a plurality of critical regions, according to one embodiment of the present invention. FIG. 6 illustrates an exemplary relationship between a beam and a plurality of critical areas, according to one embodiment of the present invention. Fig. 3 illustrates an important region 8 and a plurality of additional areas scanned according to one embodiment of the present invention. FIG. 8 is a flowchart of a method according to an embodiment of the present invention. FIG. 9 illustrates a portion of a raster scan shaped scan path in accordance with one embodiment of the present invention.

Explanation of symbols

DESCRIPTION OF SYMBOLS 8 ... Critical area, 10 ... System, 20 ... Beam generator, 30 ... X stage, 31 ... Y stage, 32 ... θ stage, 40 ... Vacuum chamber, 50 ... Cassette, 60 ... Detection device, 70 ... Processor, 100 ... Wafer, 102 ... die, 110 ... additional area, 111 ... ROID, 200 ... beam array, 201 ... scanning path, 202 ... beam, 222 ... BAD.

Claims (15)

A method for inspecting an object having a plurality of important areas,
Defining a first spatial relationship by image processing between at least two important regions positioned along a first axis;
Positioning the object under a plurality of beams of a beam array having a beam array axis so that at least two beams of the beam array are scanned into the at least two critical areas substantially simultaneously. The first axis is oriented in a particular angular relationship with respect to the beam array axis, the angular relationship is selected according to at least the first spatial relationship, and the beam is a charged particle Said step being a beam;
Said method.   The method of claim 1, wherein the positioning comprises rotating the object relative to the beam array.   The method of claim 1, wherein the positioning comprises rotating the beam array relative to the object.   The method of claim 1, wherein an orientation angle between the initial axis and the beam array axis is responsive to a ratio of a beam array spacing to a critical area spacing.   The method according to claim 1, wherein a total area of the plurality of important regions is relatively small with respect to a size of a surface of the object.   The method of claim 1, wherein the object is a wafer or a reticle.   The method of claim 1, wherein the beam array is a beam grating.   The method of claim 1, wherein the positioning comprises orienting the object relative to the beam array axis prior to inserting the object into an inspection system comprising a beam array generator. A beam array generator adapted to generate a beam array having a beam array axis;
A processor adapted to define a first spatial relationship by image processing between at least two critical regions positioned along a first axis of the object;
Positioning the object under the beam array and orienting the first axis in a specific angular relationship with respect to the beam array axis, at least two beams of the beam array At least one mechanism that causes at least two critical areas to be scanned substantially simultaneously, wherein the beam is a charged particle beam;
An inspection system comprising: The system of claim 9 , wherein the at least one mechanism is adapted to rotate the object relative to the beam array. The system of claim 9 , wherein the at least one mechanism is adapted to rotate the beam array with respect to the object. The method of claim 9 , wherein an orientation angle between the first axis and the beam array axis is responsive to a ratio of a beam array spacing to a critical area spacing. The system of claim 9 , wherein the total area of the plurality of critical regions is relatively small with respect to a size of a surface of the object. The system of claim 9 , wherein the object is a wafer or a reticle. The system of claim 9 , wherein the beam array comprises a beam grating.

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