Scanning electron microscope and image generation method

Abstract

The present invention relates to a scanning electron microscope for generating an image of a workpiece such as a wafer, a mask, a panel, or a substrate by scanning an electron beam. The scanning electron microscope of the present invention comprises: deflectors (17, 18) for deflecting an electron beam to scan a target area (T) on a workpiece (W) with the electron beam; and a deflection control unit (22) for applying a scanning voltage and an offset voltage to the deflectors (17, 18), wherein the scanning voltage causes the electron beam to scan the target area (T), and the offset voltage causes the electron beam to move from the center of an optical axis (O) to the target area (T).

Description

Technical Field

[0001] The present invention relates to a scanning electron microscope which generates an image of a workpiece such as a wafer, a mask, a panel, a substrate, etc. by scanning the workpiece with an electron beam. Background Art

[0002] A scanning electron microscope is used to inspect the pattern formed on the wafer. The scanning electron microscope is configured to move a stage holding the wafer so that a target area on the wafer moves to a predetermined imaging position, and after the stage moves, the target area is scanned with an electron beam to generate an image of the target area.

[0003] Usually, a large number of target areas are set in one wafer. Therefore, when the image of one target area is generated, the workbench is moved to move other target areas to a specified imaging position. Then, after the workbench is moved, the electron beam is used to scan the other target areas, thereby generating images of the target areas. The scanning electron microscope generates images of multiple target areas on one wafer by repeating such actions.

[0004] Prior art literature

[0005] Patent Literature

[0006] Patent Document 1: Japanese Patent Application Publication No. 2008-84626 Summary of the invention

[0007] Problem that the invention aims to solve

[0008] Usually, the stage movement time includes the time from when the stage starts to move to when the stage stops and the minute vibration of the stage stops below the allowable level. Therefore, the movement of the stage takes a certain amount of time, resulting in a decrease in processing throughput. In particular, when a large number of target areas are set on a single wafer, the stage must be moved multiple times, and it takes a lot of time to complete the generation of images of all target areas.

[0009] Therefore, the present invention provides a scanning electron microscope that can increase the throughput by reducing the number of stage movements.

[0010] Technical means of solving problems

[0011] In one form, a scanning electron microscope is provided, comprising: a deflector that deflects an electron beam to scan a target area on a workpiece with the electron beam; a deflection control unit that applies a scanning voltage and an offset voltage to the deflector, the scanning voltage causing the electron beam to scan the target area, and the offset voltage moving the electron beam from the center of an optical axis to the target area; and an electron detector that detects electrons emitted from the workpiece, the deflection control unit being configured to correct the scanning voltage by multiplying an instruction value of the scanning voltage by an aberration correction coefficient, and applying the corrected scanning voltage and the offset voltage to the deflector.

[0012] In one aspect, the deflection control unit is configured to store a plurality of aberration correction coefficients, select one aberration correction coefficient from the plurality of aberration correction coefficients according to the position of the target area, and correct the scanning voltage by multiplying a command value of the scanning voltage by the selected aberration correction coefficient.

[0013] In one form, the plurality of aberration correction coefficients are respectively associated with positions of a plurality of divided regions defined within a maximum field of view of the scanning electron microscope, and the target region is smaller than each of the plurality of divided regions.

[0014] In one aspect, the deflection control unit is configured to store a plurality of aberration correction coefficients, interpolate an aberration correction coefficient using the plurality of aberration correction coefficients according to a position of the target area, and correct the scanning voltage by multiplying a command value of the scanning voltage by the interpolated aberration correction coefficient.

[0015] In one form, the deflection control unit is configured to store a plurality of aberration correction coefficients, sequentially change an aberration correction coefficient to be selected from the plurality of aberration correction coefficients according to an incident position of the electron beam, and correct the scanning voltage by multiplying a command value of the scanning voltage by the selected aberration correction coefficient.

[0016] In one form, a scanning electron microscope is provided, comprising: a deflector that deflects an electron beam to scan a target area on a workpiece with the electron beam; a deflection control unit that applies a scanning voltage and an offset voltage to the deflector, the scanning voltage causing the electron beam to scan the target area, and the offset voltage moving the electron beam from the center of an optical axis to the target area; and an electron detector that detects electrons emitted from the workpiece, the deflection control unit being configured to correct the scanning voltage by adding a focus correction coefficient to or subtracting a focus correction coefficient from a command value of the scanning voltage, and applying the corrected scanning voltage and the offset voltage to the deflector.

[0017] In one form, the deflection control unit is configured to store a plurality of focus correction coefficients, select one focus correction coefficient from the plurality of focus correction coefficients according to the position of the target area, and correct the scanning voltage by adding or subtracting the selected focus correction coefficient from the command value of the scanning voltage.

[0018] In one form, the plurality of focus correction coefficients are respectively associated with positions of a plurality of divided regions defined within a maximum field of view of the scanning electron microscope, and the target region is smaller than each of the plurality of divided regions.

[0019] In one form, the deflection control unit is configured to store a plurality of focus correction coefficients, interpolate a focus correction coefficient using the plurality of focus correction coefficients according to the position of the target area, and correct the scanning voltage by adding or subtracting the interpolated focus correction coefficient from the command value of the scanning voltage.

[0020] In one form, the deflection control unit is configured to store a plurality of focus correction coefficients, sequentially change a focus correction coefficient to be selected from the plurality of focus correction coefficients according to an incident position of the electron beam, and correct the scanning voltage by adding or subtracting the selected focus correction coefficient from the command value of the scanning voltage.

[0021] Effects of the Invention

[0022] According to the present invention, in addition to the scanning voltage, an offset voltage is also applied to the deflector. The offset voltage can move the entire scanning area of ​​the electron beam away from the center of the optical axis. Therefore, the scanning electron microscope can scan the target area away from the center of the optical axis with the electron beam without moving the worktable. As a result, the number of times the worktable is moved is reduced, thereby significantly increasing the processing volume. BRIEF DESCRIPTION OF THE DRAWINGS

[0023] Figure 1 It is a schematic diagram showing one embodiment of a scanning electron microscope.

[0024] Figure 2 FIG. 1 is a side view schematically showing an X deflector, a Y deflector, and a wafer on a worktable.

[0025] Figure 3 A top view showing the target area on the wafer.

[0026] Figure 4 It is a top view showing an example of a plurality of target areas located within the maximum field of view.

[0027] Figure 5 It is a schematic diagram showing an example of an aberration correction table.

[0028] Figure 6 A diagram for explaining one embodiment of interpolating aberration correction coefficients.

[0029] Figure 7 A schematic diagram showing an example of a focus correction table.

[0030] Figure 8 A diagram illustrating an embodiment of interpolating focus correction coefficients.

[0031] Fig. 9 It is a schematic diagram showing another example of the aberration correction table.

[0032] Fig.10 It is a schematic diagram showing another example of the focus correction table. DETAILED DESCRIPTION

[0033] Hereinafter, embodiments of the present invention will be described with reference to the accompanying drawings.

[0034] Figure 1 Schematic diagram showing an embodiment of a scanning electron microscope. The scanning electron microscope 1 is an image generating device for generating an image of a workpiece. Examples of the workpiece include wafers, masks, panels, substrates, etc. used in the manufacture of semiconductor devices. In the embodiments described below, a wafer is used as an example of a workpiece, but the present invention is not limited to the following embodiments.

[0035] The scanning electron microscope 1 includes an electron gun 15 that emits an electron beam, a condenser lens 16, an X deflector 17, a Y deflector 18, an objective lens 20, and a workbench 31. The electron gun 15 emits an electron beam, the condenser lens 16 converges the electron beam emitted from the electron gun 15, the X deflector 17 deflects the electron beam in the X direction, the Y deflector 18 deflects the electron beam in the Y direction, the objective lens 20 focuses the electron beam on a wafer W as an example of a workpiece, and the workbench 31 supports the wafer W. The structure of the electron gun 15 is not particularly limited. For example, a field emission type electron gun or a semiconductor photocathode type electron gun can be used as the electron gun 15.

[0036] The X direction and the Y direction are perpendicular to each other. The X deflector 17 and the Y deflector 18 are deflectors for deflecting the electron beam. The worktable 31 has an actuator (not shown) built in that can move the wafer W independently in the X direction and the Y direction. Such a worktable 31 is also called an XY worktable.

[0037] The scanning electron microscope 1 further includes a stage displacement measuring device 23 for measuring the displacement of the stage 31. The stage displacement measuring device 23 is configured to measure the displacements in the X direction and the Y direction of the stage 31. As an example of such a stage displacement measuring device 23, two laser interferometers for measuring the displacements in the X direction and the Y direction of the stage 31 can be cited.

[0038] The condenser lens 16 and the objective lens 20 are connected to a lens control device 21, and the movements of the condenser lens 16 and the objective lens 20 are controlled by the lens control device 21. The X deflector 17 and the Y deflector 18 are connected to a deflection control unit 22, and the deflection movements of the X deflector 17 and the Y deflector 18 are controlled by the deflection control unit 22. The stage displacement measuring device 23 is also connected to the deflection control unit 22, and the measured value of the displacement of the stage 31 is sent to the deflection control unit 22. The stage 31 disposed in the chamber 30 is connected to the stage control device 32, and the movement and position of the stage 31 are controlled by the stage control device 32.

[0039] The secondary electron detector 25 and the reflected electron detector 26 are connected to the image acquisition device 28. The image acquisition device 28 is configured to convert the electron detection signals output from the secondary electron detector 25 and the reflected electron detector 26 into an image. The secondary electron detector 25 and the reflected electron detector 26 are each an electron detector that detects electrons emitted from the wafer W. The conveying device 34 has a conveying robot (not shown) equipped with a manipulator to place the wafer W on the workbench 31 in the chamber 30 and take the wafer W out of the workbench 31.

[0040] The electron beam emitted from the electron gun 15 is converged by the focusing lens 16, deflected by the X deflector 17 and the Y deflector 18, and converged by the objective lens 20 to irradiate the surface of the wafer W. When the primary electrons of the electron beam are irradiated to the wafer W, secondary electrons and reflected electrons are emitted from the wafer W. The secondary electrons are detected by the secondary electron detector 25, and the reflected electrons are detected by the reflected electron detector 26. The electron detection signals of the secondary electron detector 25 and the reflected electron detector 26, that is, the detection signals of the secondary electrons and the detection signals of the reflected electrons, are input to the image acquisition device 28 and converted into an image. The scanning electron microscope 1 generates an image of the surface of the wafer W in this way.

[0041] The deflection control unit 22 includes at least one computer and a power supply 22c. More specifically, the deflection control unit 22 includes a storage device 22a storing a program, a processing device 22b executing a calculation according to a command included in the program, and a power supply 22c generating a voltage to be applied to the X deflector 17 and the Y deflector 18. The storage device 22a includes a main storage device such as a RAM and an auxiliary storage device such as a hard disk drive (HDD) and a solid state drive (SSD). Examples of the processing device 22b include a CPU (central processing unit), a GPU (graphics processing unit), and an FPGA (field programmable gate array). However, the specific configuration of the deflection control unit 22 is not limited to these examples.

[0042] The processing device 22b generates a command value of a scanning voltage and a command value of an offset voltage, and sends these command values ​​to the power supply 22c. The power supply 22c is configured to generate a scanning voltage and an offset voltage according to the command value from the processing device 22b, and simultaneously apply these scanning voltages and offset voltages to the X deflector 17 and the Y deflector 18. The scanning voltage is a voltage for deflecting the electron beam to scan the target area on the wafer W with the electron beam. The offset voltage is a voltage for moving the electron beam from the center of the optical axis to the target area.

[0043] Figure 2 1 is a side view schematically showing the X deflector 17, the Y deflector 18 and the wafer W on the worktable 31. Figure 3 1 is a top view showing a target area T on a wafer W. The optical axis center O corresponds to the trajectory of the electron beam when no voltage is applied to the X deflector 17 and the Y deflector 18. The deflection control unit 22 can shift the scanning area of ​​the electron beam from the optical axis center O by applying an offset voltage to the X deflector 17 and the Y deflector 18.

[0044] like Figure 3 As shown, the target area T is located at a position deviated from the optical axis center O. Usually, the worktable 31 is moved so that the optical axis center O is located within the target area T. In this embodiment, an offset voltage is applied to the X deflector 17 and the Y deflector 18 in addition to the scanning voltage without moving the worktable 31, so that the electron beam can scan the entire target area T deviated from the optical axis center O.

[0045] The offset voltage is a voltage for moving the electron beam from the optical axis center O to the target area T, and is determined according to the distance and direction from the optical axis center O to the target area T. More specifically, the processing device 22b of the deflection control unit 22 calculates the distance and direction from the optical axis center O to a predetermined point in the target area T (for example, the center point of the target area T), and determines the command value of the offset voltage required to move the electron beam from the optical axis center O to the target area T according to the calculated distance and direction. Then, the processing device 22b sends the command value of the offset voltage to the power supply 22c. The power supply 22c generates the offset voltage according to the command value of the offset voltage, and applies the offset voltage to the X deflector 17 and the Y deflector 18.

[0046] Figure 4 It is a top view showing an example of a plurality of target areas located within the maximum field of view. Figure 4 The maximum field of view MX shown is the maximum range in which the electron beam can be deflected by means of the X deflector 17 and the Y deflector 18. In other words, as long as the target area is within the maximum field of view MX, the scanning electron microscope 1 can generate an image of the target area without moving the worktable 31. Figure 4 As shown, the optical axis center O is located at the center of the maximum field of view MX.

[0047] The scanning electron microscope 1 generates images of the first target area T1 and the second target area T2 at positions offset from the optical axis center O in the following manner. First, the worktable 31 supporting the wafer W is moved to a predetermined imaging position in such a manner that the first target area T1 and the second target area T2 are located within the maximum field of view MX. The electron gun 15 emits an electron beam, and at the same time, the deflection control unit 22 applies a scanning voltage and a first offset voltage for moving the electron beam from the optical axis center O to the first target area T1 to the X deflector 17 and the Y deflector 18, thereby scanning the first target area T1 with the electron beam. While the electron beam is scanning the first target area T1, the scanning voltage changes, whereas the first offset voltage is fixed.

[0048] By irradiating the first target area T1 with an electron beam, secondary electrons and reflected electrons are emitted from the wafer W. The secondary electrons and reflected electrons are detected by electron detectors, namely, a secondary electron detector 25 and a reflected electron detector 26. The electron detection signals, namely, the detection signals of the secondary electrons and the detection signals of the reflected electrons, are sent to the image acquisition device 28, and the image acquisition device 28 generates an image of the first target area T1 using the detection signals of the secondary electrons and the detection signals of the reflected electrons.

[0049] Next, while the stage 31 is maintained at the above-mentioned predetermined imaging position (that is, without moving the stage 31), the deflection control unit 22 applies a scanning voltage and a second offset voltage for moving the electron beam from the optical axis center O to the second target area T2 to the X deflector 17 and the Y deflector 18, thereby scanning the second target area T2 with the electron beam. While the scanning voltage changes while the electron beam scans the second target area T2, the second offset voltage is fixed.

[0050] By irradiating the second target area T2 with an electron beam, secondary electrons and reflected electrons are emitted from the wafer W. The secondary electrons and reflected electrons are detected by an electron detector, namely, a secondary electron detector 25 and a reflected electron detector 26. The electron detection signal, namely, the detection signal of the secondary electrons and the detection signal of the reflected electrons are sent to the image acquisition device 28, and the image acquisition device 28 generates an image of the second target area T2 using the detection signal of the secondary electrons and the detection signal of the reflected electrons.

[0051] In this way, the scanning electron microscope 1 can scan multiple target areas T1 and T2 away from the optical axis center O with an electron beam without moving the stage 31. As a result, the number of times the stage 31 is moved can be reduced, thereby greatly improving the processing throughput. As long as the target area is within the maximum field of view MX, the scanning electron microscope 1 can generate an image of another target area without moving the stage 31.

[0052] When the electron beam is greatly shifted from the optical axis center O by application of an offset voltage, aberration may occur. Therefore, in one embodiment, the scanning electron microscope 1 is configured to correct aberration as follows.

[0053] The deflection control unit 22 stores a plurality of aberration correction coefficients for correcting aberrations in the storage device 22a. The deflection control unit 22 is configured to select one aberration correction coefficient from the plurality of aberration correction coefficients, correct the scanning voltage by multiplying the command value of the scanning voltage by the selected aberration correction coefficient, and apply the corrected scanning voltage and offset voltage to the X deflector 17 and the Y deflector 18. More specifically, the processing device 22b selects one aberration correction coefficient from the plurality of aberration correction coefficients stored in the storage device 22a, corrects the command value of the scanning voltage by multiplying the command value of the scanning voltage by the selected aberration correction coefficient, and sends the corrected command value to the power supply 22c. The power supply 22c generates a corrected scanning voltage according to the corrected command value, and applies the corrected scanning voltage and offset voltage to the X deflector 17 and the Y deflector 18. In one embodiment, the deflection control unit 22 may select one aberration correction coefficient from a plurality of aberration correction coefficients, and correct the scanning voltage by adding or subtracting the selected aberration correction coefficient from the command value of the scanning voltage.

[0054] Aberration occurs due to the deflection of the electron beam from the optical axis center O. Therefore, the degree of aberration may vary depending on the position of the target area relative to the optical axis center O. Therefore, in one embodiment, the deflection control unit 22 is configured to select an aberration correction coefficient according to the position of the target area. More specifically, the deflection control unit 22 is configured to select one aberration correction coefficient from a plurality of aberration correction coefficients stored in the storage device 22a according to the position of the target area.

[0055] The storage device 22 a stores an aberration correction table indicating the relationship between a plurality of aberration correction coefficients and positions within the maximum field of view MX. Figure 5 Schematic diagram showing an example of an aberration correction table. Figure 5 As shown, the aberration correction table includes a plurality of aberration correction coefficients C00 to C33 arranged in the maximum field of view MX. These aberration correction coefficients C00 to C33 are respectively associated with the positions of a plurality of segmented areas R1 to R16 defined in the maximum field of view MX. The plurality of segmented areas R1 to R16 have the same shape and the same size and are distributed in the entire maximum field of view MX. In the present embodiment, the plurality of aberration correction coefficients C00 to C33 arranged in a matrix in the maximum field of view MX are respectively assigned to the plurality of segmented areas R1 to R16 distributed in a matrix in the maximum field of view MX. The plurality of aberration correction coefficients C00 to C33 are predetermined based on the distance from the optical axis center O and other factors.

[0056] The target areas T1 and T2 are located within the maximum visual field MX. The size of each of the target areas T1 and T2 is limited to a predetermined size. More specifically, each of the target areas T1 and T2 is smaller than each divided area defined within the maximum visual field MX.

[0057] The deflection control unit 22 selects one aberration correction coefficient from a plurality of aberration correction coefficients in the aberration correction table according to the position of the target area T1. Figure 5 In the example shown, the aberration correction coefficient corresponding to the position of the target area T1 is C30. The deflection control unit 22 selects one aberration correction coefficient C30 from the aberration correction coefficients C00 to C33 according to the position of the target area T1. The deflection control unit 22 corrects the scanning voltage by multiplying the command value of the scanning voltage by the selected aberration correction coefficient C30, and applies the corrected scanning voltage and offset voltage to the X deflector 17 and the Y deflector 18.

[0058] According to this embodiment, since the scanning voltage is corrected according to the position of the target area T1, the aberration can be reduced or eliminated. Figure 5 The number of matrix-shaped aberration correction coefficients included in the aberration correction table may also be greater than Figure 5The embodiments shown may be fewer or more.

[0059] exist Figure 5 In the other target area T2 shown in FIG. 1 , an aberration correction coefficient C13 different from the aberration correction coefficient C30 in the target area T1 is used. Thus, according to the present embodiment, the deflection control unit 22 can correct the aberration using different aberration correction coefficients for each target area. In particular, according to the present embodiment, during the period of scanning one target area with an electron beam, only one fixed aberration correction coefficient is used to correct the scanning voltage, so the deflection control unit 22 does not need to read other aberration correction coefficients from the storage device 22a during scanning, and as a result, the throughput can be improved.

[0060] like Figure 6 As shown in FIG. 1 , when the target region T spans across a plurality of divided regions, the deflection control unit 22 interpolates the aberration correction coefficient using a plurality of aberration correction coefficients assigned to a plurality of divided regions overlapping the target region T. Figure 6 In the example shown, the segmented regions overlapping the target region T are R3, R4, R7, and R8, and the aberration correction coefficients corresponding to the segmented regions R3, R4, R7, and R8 are C20, C30, C21, and C31. The deflection control unit 22 interpolates the aberration correction coefficients using the aberration correction coefficients C20, C30, C21, and C31. Examples of specific methods for interpolating the aberration correction coefficients include a weighted interpolation method and a triangle segmentation interpolation method.

[0061] When the electron beam is greatly moved away from the optical axis center O by application of an offset voltage, defocus may occur. Therefore, in one embodiment, the scanning electron microscope 1 is configured to correct the focus as follows.

[0062] The deflection control unit 22 stores a plurality of focus correction coefficients for correcting the focus in the storage device 22a. The deflection control unit 22 is configured to select one focus correction coefficient from the plurality of focus correction coefficients, correct the scanning voltage by adding or subtracting the selected focus correction coefficient from the command value of the scanning voltage, and apply the corrected scanning voltage and offset voltage to the X deflector 17 and the Y deflector 18. More specifically, the processing unit 22b selects one focus correction coefficient from the plurality of focus correction coefficients stored in the storage device 22a, corrects the command value of the scanning voltage by adding or subtracting the selected focus correction coefficient from the command value of the scanning voltage, and sends the corrected command value to the power supply 22c. The power supply 22c generates a corrected scanning voltage according to the corrected command value, and applies the corrected scanning voltage and offset voltage to the X deflector 17 and the Y deflector 18.

[0063] Defocusing occurs due to the deflection of the electron beam from the optical axis center O. Therefore, the degree of defocusing may vary depending on the position of the target area relative to the optical axis center O. Therefore, in one embodiment, the deflection control unit 22 is configured to select a focus correction coefficient according to the position of the target area. More specifically, the deflection control unit 22 is configured to select one focus correction coefficient from a plurality of focus correction coefficients stored in the storage device 22a according to the position of the target area.

[0064] The storage device 22 a stores a focus correction table indicating the relationship between a plurality of focus correction coefficients and positions within the maximum field of view MX. Figure 7 FIG. 1 is a schematic diagram showing an example of a focus correction table. Figure 7 As shown, the focus correction table includes a plurality of focus correction coefficients D00 to D33 arranged within the maximum field of view MX. These focus correction coefficients D00 to D33 are respectively associated with the positions of a plurality of segmented areas S1 to S16 defined within the maximum field of view MX. The plurality of segmented areas S1 to S16 have the same shape and the same size and are distributed within the entire maximum field of view MX. In the present embodiment, the plurality of focus correction coefficients D00 to D33 arranged in a matrix within the maximum field of view MX are respectively assigned to the plurality of segmented areas S1 to S16 distributed in a matrix within the maximum field of view MX. The plurality of focus correction coefficients D00 to D33 are predetermined based on the distance from the optical axis center O and other factors.

[0065] The target areas T1 and T2 are located within the maximum visual field MX. The size of each of the target areas T1 and T2 is limited to a predetermined size. More specifically, each of the target areas T1 and T2 is smaller than each divided area defined within the maximum visual field MX.

[0066] The deflection control unit 22 selects one focus correction coefficient from a plurality of focus correction coefficients in the focus correction table according to the position of the target area T1. Figure 7 In the example shown, the focus correction coefficient corresponding to the position of the target area T1 is D30. The deflection control unit 22 selects one focus correction coefficient D30 from the focus correction coefficients D00 to D33 according to the position of the target area T1. The deflection control unit 22 corrects the scanning voltage by adding or subtracting the selected focus correction coefficient D30 from the command value of the scanning voltage, and applies the corrected scanning voltage and offset voltage to the X deflector 17 and the Y deflector 18.

[0067] According to this embodiment, since the scanning voltage is corrected according to the position of the target area T1, defocusing can be reduced or eliminated. Figure 7 The number of multiple focus correction coefficients in a matrix form contained in the focus correction table can also be compared Figure 7 The embodiments shown may be fewer or more.

[0068] exist Figure 7 In the other target area T2 shown in FIG. 1 , a focus correction coefficient D13 different from the focus correction coefficient D30 in the target area T1 is used. In this way, according to the present embodiment, the deflection control unit 22 can correct the focus using different focus correction coefficients for each target area. In particular, according to the present embodiment, during the period of scanning one target area with an electron beam, only one fixed focus correction coefficient is used to correct the scanning voltage, so the deflection control unit 22 does not need to read other focus correction coefficients from the storage device 22a during scanning, and as a result, the throughput can be improved.

[0069] like Figure 8 As shown in FIG. 1 , when the target area T spans across a plurality of divided areas, the deflection control unit 22 interpolates the focus correction coefficient using a plurality of focus correction coefficients assigned to a plurality of divided areas overlapping the target area T. Figure 8 In the example shown, the segmented areas overlapping the target area T are S3, S4, S7, and S8, and the focus correction coefficients assigned to these segmented areas S3, S4, S7, and S8 are D20, D30, D21, and D31. The deflection control unit 22 interpolates the focus correction coefficient using these focus correction coefficients D20, D30, D21, and D31. Examples of specific methods for interpolating the focus correction coefficient include a weighted interpolation method and a triangle segmentation interpolation method.

[0070] The deflection control unit 22 may also Figure 5 The aberration correction table shown and Figure 7 The focus correction table shown is stored in the storage device 22a. The deflection control unit 22 selects one aberration correction coefficient from a plurality of aberration correction coefficients according to the position of the target area or interpolates one aberration correction coefficient using a plurality of aberration correction coefficients. Furthermore, the deflection control unit 22 selects one focus correction coefficient from a plurality of focus correction coefficients according to the position of the target area or interpolates one focus correction coefficient using a plurality of focus correction coefficients. Subsequently, the deflection control unit 22 multiplies the command value of the scanning voltage by the selected or interpolated aberration correction coefficient to correct the command value, corrects the scanning voltage by adding (or subtracting) the selected or interpolated focus correction coefficient from the corrected command value, and applies the corrected scanning voltage and the offset voltage to the X deflector 17 and the Y deflector 18.

[0071] As described above, according to the present embodiment, the deflection control unit 22 can reduce or eliminate both aberration and defocus using both the aberration correction coefficient and the focus correction coefficient.

[0072] The degree of aberration may vary according to the incident position of the electron beam toward the target area. Therefore, in one embodiment, the deflection control unit 22 is configured to change the aberration correction coefficient according to the incident position of the electron beam in the target area. More specifically, the deflection control unit 22 is configured to select one aberration correction coefficient from a plurality of aberration correction coefficients stored in the storage device 22a according to the incident position of the electron beam in the target area.

[0073] The storage device 22 a stores an aberration correction table indicating the relationship between a plurality of aberration correction coefficients and positions within the maximum field of view MX. Fig. 9 Schematic diagram showing an example of an aberration correction table. Fig. 9 As shown, the aberration correction table includes a plurality of aberration correction coefficients C00 to C99 arranged in the maximum field of view MX. These aberration correction coefficients C00 to C99 are respectively associated with a plurality of positions defined in the maximum field of view MX. In the present embodiment, the plurality of aberration correction coefficients C00 to C99 arranged in a matrix in the maximum field of view MX correspond to a plurality of positions distributed in a matrix in the maximum field of view MX. The plurality of aberration correction coefficients C00 to C99 are predetermined based on the distance from the optical axis center O and other factors.

[0074] The target area T1 is located within the maximum field of view MX. The deflection control unit 22 selects one aberration correction coefficient from a plurality of aberration correction coefficients in the aberration correction table according to the incident position of the electron beam within the target area T1. Fig. 9 In the example shown, the aberration correction coefficients corresponding to the respective positions in the target area T1 are C61 to C83. The deflection control unit 22 selects one aberration correction coefficient from the aberration correction coefficients C61 to C83 according to the incident position of the electron beam in the target area T1. That is, during the period in which the electron beam scans the target area T1, the deflection control unit 22 successively changes the aberration correction coefficient according to the incident position of the electron beam. Then, the deflection control unit 22 corrects the scanning voltage by multiplying the command value of the scanning voltage by the selected aberration correction coefficient, and applies the corrected scanning voltage and offset voltage to the X deflector 17 and the Y deflector 18.

[0075] According to the present embodiment, the deflection control unit 22 sequentially changes the aberration correction coefficient to be selected from a plurality of aberration correction coefficients according to the incident position of the electron beam, and corrects the scanning voltage by multiplying the command value of the scanning voltage by the selected aberration correction coefficient. Since the scanning voltage is corrected according to the incident position of the electron beam, the aberration can be reduced or eliminated. The aberration correction table is not limited to Fig. 9 The number of matrix-shaped aberration correction coefficients included in the aberration correction table may also be greater than Fig. 9There are many embodiments shown. Generally speaking, the greater the number of aberration correction coefficients included in the aberration correction table, the more finely the aberration can be corrected.

[0076] exist Fig. 9 In another target region T2 shown in FIG. 1 , aberration correction coefficients C47 to C58 different from aberration correction coefficients C61 to C83 in the target region T1 are used. In this way, according to the present embodiment, the deflection control unit 22 can correct aberrations using a different set of aberration correction coefficients for each target region.

[0077] In one embodiment, the deflection control unit 22 is configured to change the focus correction coefficient according to the incident position of the electron beam in the target area. More specifically, the deflection control unit 22 is configured to select one focus correction coefficient from a plurality of focus correction coefficients stored in the storage device 22a according to the incident position of the electron beam in the target area.

[0078] The storage device 22 a stores a focus correction table indicating the relationship between a plurality of focus correction coefficients and positions within the maximum field of view MX. Fig.10 FIG. 1 is a schematic diagram showing an example of a focus correction table. Fig.10 As shown, the focus correction table includes a plurality of focus correction coefficients D00 to D99 arranged in the maximum field of view MX. These focus correction coefficients D00 to D99 are respectively associated with a plurality of positions defined in the maximum field of view MX. In the present embodiment, the plurality of focus correction coefficients D00 to D99 arranged in a matrix in the maximum field of view MX correspond to a plurality of positions distributed in a matrix in the maximum field of view MX. The plurality of focus correction coefficients D00 to D99 are predetermined based on the distance from the optical axis center O and other factors.

[0079] The target area T1 is located within the maximum field of view MX. The deflection control unit 22 selects one focus correction coefficient from a plurality of focus correction coefficients in the focus correction table according to the incident position of the electron beam within the target area T1. Fig.10 In the example shown, the focus correction coefficients corresponding to the respective positions in the target area T1 are D61 to D83. The deflection control unit 22 selects one focus correction coefficient from the focus correction coefficients D61 to D83 according to the incident position of the electron beam in the target area T1. That is, during the period in which the electron beam scans the target area T1, the deflection control unit 22 changes the focus correction coefficient successively according to the incident position of the electron beam. Then, the deflection control unit 22 corrects the scanning voltage by adding or subtracting the selected focus correction coefficient from the command value of the scanning voltage, and applies the corrected scanning voltage and the offset voltage to the X deflector 17 and the Y deflector 18.

[0080] According to the present embodiment, the deflection control unit 22 sequentially changes the focus correction coefficient to be selected from a plurality of focus correction coefficients according to the incident position of the electron beam, and corrects the scanning voltage by adding or subtracting the selected focus correction coefficient from the command value of the scanning voltage. Since the scanning voltage is corrected according to the incident position of the electron beam, defocusing can be reduced or eliminated. Fig.10 This is an example of a focus correction table. The focus correction table is not limited to Fig.10 The number of multiple focus correction coefficients in a matrix form included in the focus correction table may also be greater than Fig.10 There are many embodiments shown. Generally speaking, the greater the number of focus correction coefficients included in the focus correction table, the more detailed the focus can be corrected.

[0081] exist Fig.10 In the target region T2 shown in FIG. 1 , focus correction coefficients D47 to D58 are used, which are different from the focus correction coefficients D61 to D83 in the target region T1 . In this way, according to the present embodiment, the deflection control unit 22 can correct the focus using a different set of focus correction coefficients for each target region.

[0082] The deflection control unit 22 may also Fig. 9 The aberration correction table shown and Fig.10 The focus correction tables shown are both stored in the storage device 22a. Fig. 9 and Fig.10 In the example shown, the deflection control unit 22 selects one aberration correction coefficient from the aberration correction coefficients C61 to C83 according to the incident position of the electron beam in the target area T1, and further selects one focus correction coefficient from the plurality of focus correction coefficients D61 to D83. Then, the deflection control unit 22 multiplies the command value of the scanning voltage by the selected aberration correction coefficient to correct the command value, and further corrects the scanning voltage by adding (or subtracting) the selected focus correction coefficient to the corrected command value, and applies the corrected scanning voltage and the offset voltage to the X deflector 17 and the Y deflector 18.

[0083] In the target area T2, the deflection control unit 22 selects one aberration correction coefficient from the aberration correction coefficients C47 to C58 according to the incident position of the electron beam in the target area T2, and further selects one focus correction coefficient from the plurality of focus correction coefficients D47 to D58. Then, the deflection control unit 22 multiplies the command value of the scanning voltage by the selected aberration correction coefficient to correct the command value, and further corrects the scanning voltage by adding (or subtracting) the selected focus correction coefficient from the corrected command value, and applies the corrected scanning voltage and the offset voltage to the X deflector 17 and the Y deflector 18.

[0084] As described above, according to the present embodiment, the deflection control unit 22 can reduce or eliminate both aberration and defocus using both the aberration correction coefficient and the focus correction coefficient.

[0085] In one embodiment, the deflection control unit 22 may be configured to determine a correction voltage based on the measured value of the displacement of the stage 31 and to apply the correction voltage to the X deflector 17 and the Y deflector 18. This embodiment will be described below.

[0086] Figure 1 The workbench 31 shown is mainly made of metal. A vacuum is formed in the chamber 30, so the temperature in the chamber 30 is easy to rise. In particular, the workbench 31 has built-in actuators (not shown) for moving in the X direction and the Y direction, so the workbench 31 itself may become a heat source. When the temperature of the workbench 31 rises, the workbench 31 itself undergoes thermal expansion, and there is a possibility that the position of the target area of ​​the wafer W on the workbench 31 changes.

[0087] Therefore, in the present embodiment, the deflection control unit 22 is configured to determine the correction voltage based on the measured value of the displacement of the worktable 31 sent from the worktable displacement measuring device 23, and apply the correction voltage to the X deflector 17 and the Y deflector 18 together with the above-mentioned scanning voltage (or the corrected scanning voltage) and the offset voltage. The correction voltage changes according to the displacement amount of the worktable 31. Generally speaking, the larger the displacement amount of the worktable 31, the larger the correction voltage. The deflection control unit 22 stores correlation data (such as a correlation equation or a correlation table) indicating the relationship between the displacement amount of the worktable 31 and the correction voltage in the storage device 22a. The deflection control unit 22 determines the correction voltage using the measured value of the displacement of the worktable 31 sent from the worktable displacement measuring device 23 and the above-mentioned correlation data.

[0088] According to the present embodiment, the scanning electron microscope 1 can generate an image of the target region based on the correct position of the target region on the wafer W.

[0089] The purpose of recording the above-mentioned embodiments is to enable a person with common knowledge in the technical field to which the present invention belongs to implement the present invention. As long as a person skilled in the art can certainly achieve various variations of the above-mentioned embodiments, the technical idea of ​​the present invention can also be applied to other embodiments. Therefore, the present invention is not limited to the described embodiments, but is interpreted in the broadest scope of the technical idea defined by the claims.

[0090] Industrial Applicability

[0091] The present invention can be used in a scanning electron microscope that generates an image of a workpiece by scanning a workpiece such as a wafer, a mask, a panel, or a substrate with an electron beam.

[0092] Explanation of symbols

[0093] 1…Scanning electron microscopy

[0094] 15…Electron gun

[0095] 16…Collector lens

[0096] 17…X deflector

[0097] 18…Y deflector

[0098] 20…Objective lens

[0099] 21…Lens control device

[0100] 22…Deflection control unit

[0101] 22a… Storage device

[0102] 22b…Processing device

[0103] 22c...Power supply

[0104] 23…Workbench displacement measuring device

[0105] 25…Secondary electron detector

[0106] 26…Reflected electron detector

[0107] 28…Image acquisition device

[0108] 30…Chamber

[0109] 31…Workbench

[0110] 32…Workbench control device

[0111] 34…Conveying device.

Claims

1. A scanning electron microscope, characterized in that have: a work table, which supports a workpiece; a deflector that deflects the electron beam to scan a target area on the workpiece with the electron beam; a deflection control unit for applying a scanning voltage and an offset voltage to the deflector, wherein the scanning voltage causes the electron beam to scan the target area, and the offset voltage causes the electron beam to move from the center of the optical axis to the target area; as well as an electron detector that detects electrons emitted from the workpiece, The deflection control unit is configured to correct the scanning voltage by multiplying the command value of the scanning voltage by an aberration correction coefficient, scan the target area with the electron beam by applying the corrected scanning voltage and the offset voltage to the deflector, and further, make the deflector scan another target area with the electron beam without moving the workbench by changing the aberration correction coefficient and the offset voltage.

2. The scanning electron microscope according to claim 1, characterized in that The deflection control unit is configured to store a plurality of aberration correction coefficients, select one aberration correction coefficient from the plurality of aberration correction coefficients according to the position of the target area, and correct the scanning voltage by multiplying the command value of the scanning voltage by the selected aberration correction coefficient.

3. The scanning electron microscope according to claim 2, characterized in that The plurality of aberration correction coefficients are respectively associated with the positions of a plurality of divided regions defined within the maximum field of view of the scanning electron microscope, The target region is smaller than each of the plurality of divided regions.

4. The scanning electron microscope according to claim 1, characterized in that The deflection control unit is configured to store a plurality of aberration correction coefficients, interpolate an aberration correction coefficient using the plurality of aberration correction coefficients according to the position of the target area, and correct the scanning voltage by multiplying a command value of the scanning voltage by the interpolated aberration correction coefficient.

5. The scanning electron microscope according to claim 1, characterized in that The deflection control unit is configured to store a plurality of aberration correction coefficients, sequentially change an aberration correction coefficient to be selected from the plurality of aberration correction coefficients according to an incident position of the electron beam, and correct the scanning voltage by multiplying a command value of the scanning voltage by the selected aberration correction coefficient.

6. A scanning electron microscope, characterized in that have: a work table, which supports a workpiece; a deflector that deflects the electron beam to scan a target area on the workpiece with the electron beam; a deflection control unit for applying a scanning voltage and an offset voltage to the deflector, wherein the scanning voltage causes the electron beam to scan the target area, and the offset voltage causes the electron beam to move from the center of the optical axis to the target area; as well as an electron detector that detects electrons emitted from the workpiece, The deflection control unit is configured to correct the scanning voltage by adding or subtracting a focus correction coefficient to or from the command value of the scanning voltage, scan the target area with the electron beam by applying the corrected scanning voltage and the offset voltage to the deflector, and further, cause the deflector to scan another target area with the electron beam without moving the workbench by changing the focus correction coefficient and the offset voltage.

7. The scanning electron microscope according to claim 6, characterized in that The deflection control unit is configured to store a plurality of focus correction coefficients, select one focus correction coefficient from the plurality of focus correction coefficients according to the position of the target area, and correct the scanning voltage by adding or subtracting the selected focus correction coefficient from the command value of the scanning voltage.

8. The scanning electron microscope according to claim 7, characterized in that The plurality of focus correction coefficients are respectively associated with the positions of a plurality of segmented regions defined within the maximum field of view of the scanning electron microscope, The target region is smaller than each of the plurality of divided regions.

9. The scanning electron microscope according to claim 6, characterized in that: The deflection control unit is configured to store a plurality of focus correction coefficients, interpolate focus correction coefficients using the plurality of focus correction coefficients according to the position of the target area, and correct the scanning voltage by adding or subtracting the interpolated focus correction coefficient from the command value of the scanning voltage.

10. The scanning electron microscope according to claim 6, characterized in that: The deflection control unit is configured to store a plurality of focus correction coefficients, successively change a focus correction coefficient to be selected from the plurality of focus correction coefficients according to an incident position of the electron beam, and correct the scanning voltage by adding or subtracting the selected focus correction coefficient from the command value of the scanning voltage.

11. An image generation method, characterized in that: Place the workpiece with the first target area and the second target area on the workbench. A scanning voltage corrected by multiplying a command value of the scanning voltage by a first aberration correction coefficient and a first offset voltage for shifting the electron beam from the center of the optical axis to the first target area are applied to the deflector, thereby scanning the first target area with the electron beam, The electrons emitted from the first target area are detected by an electron detector. A scanning voltage corrected by multiplying a command value of the scanning voltage by a second aberration correction coefficient and a second offset voltage for shifting the electron beam from the center of the optical axis to the second target area are applied to the deflector, thereby scanning the second target area with the electron beam without moving the workbench, The electron detector detects the electrons emitted from the second target area.

12. An image generation method, characterized in that: Place the workpiece with the first target area and the second target area on the workbench. A scanning voltage corrected by adding or subtracting a first focus correction coefficient to or from a command value of the scanning voltage and a first offset voltage for moving the electron beam from the center of the optical axis to the first target area are applied to the deflector, thereby scanning the first target area with the electron beam, The electrons emitted from the first target area are detected by an electron detector. A scanning voltage corrected by adding or subtracting a second focus correction coefficient to or from a command value of the scanning voltage and a second offset voltage for moving the electron beam from the center of the optical axis to the second target area are applied to the deflector, thereby scanning the second target area with the electron beam without moving the workbench, The electron detector detects the electrons emitted from the second target area.

Images