WO2022209936A1 - ワークピース上のパターンの画像を生成する方法 - Google Patents
ワークピース上のパターンの画像を生成する方法 Download PDFInfo
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- WO2022209936A1 WO2022209936A1 PCT/JP2022/012175 JP2022012175W WO2022209936A1 WO 2022209936 A1 WO2022209936 A1 WO 2022209936A1 JP 2022012175 W JP2022012175 W JP 2022012175W WO 2022209936 A1 WO2022209936 A1 WO 2022209936A1
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- image
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- adjustment
- electron microscope
- scanning electron
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- 238000000034 method Methods 0.000 title claims abstract description 20
- 238000013461 design Methods 0.000 claims abstract description 15
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- 238000005259 measurement Methods 0.000 description 8
- 238000007689 inspection Methods 0.000 description 7
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Classifications
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- H—ELECTRICITY
- H04—ELECTRIC COMMUNICATION TECHNIQUE
- H04N—PICTORIAL COMMUNICATION, e.g. TELEVISION
- H04N23/00—Cameras or camera modules comprising electronic image sensors; Control thereof
- H04N23/70—Circuitry for compensating brightness variation in the scene
- H04N23/76—Circuitry for compensating brightness variation in the scene by influencing the image signals
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- H—ELECTRICITY
- H01—ELECTRIC ELEMENTS
- H01J—ELECTRIC DISCHARGE TUBES OR DISCHARGE LAMPS
- H01J37/00—Discharge tubes with provision for introducing objects or material to be exposed to the discharge, e.g. for the purpose of examination or processing thereof
- H01J37/02—Details
- H01J37/22—Optical or photographic arrangements associated with the tube
- H01J37/222—Image processing arrangements associated with the tube
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- G—PHYSICS
- G06—COMPUTING; CALCULATING OR COUNTING
- G06T—IMAGE DATA PROCESSING OR GENERATION, IN GENERAL
- G06T7/00—Image analysis
- G06T7/60—Analysis of geometric attributes
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- H—ELECTRICITY
- H01—ELECTRIC ELEMENTS
- H01J—ELECTRIC DISCHARGE TUBES OR DISCHARGE LAMPS
- H01J37/00—Discharge tubes with provision for introducing objects or material to be exposed to the discharge, e.g. for the purpose of examination or processing thereof
- H01J37/02—Details
- H01J37/22—Optical or photographic arrangements associated with the tube
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- H—ELECTRICITY
- H01—ELECTRIC ELEMENTS
- H01J—ELECTRIC DISCHARGE TUBES OR DISCHARGE LAMPS
- H01J37/00—Discharge tubes with provision for introducing objects or material to be exposed to the discharge, e.g. for the purpose of examination or processing thereof
- H01J37/26—Electron or ion microscopes; Electron or ion diffraction tubes
- H01J37/28—Electron or ion microscopes; Electron or ion diffraction tubes with scanning beams
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- G—PHYSICS
- G06—COMPUTING; CALCULATING OR COUNTING
- G06T—IMAGE DATA PROCESSING OR GENERATION, IN GENERAL
- G06T2207/00—Indexing scheme for image analysis or image enhancement
- G06T2207/10—Image acquisition modality
- G06T2207/10056—Microscopic image
- G06T2207/10061—Microscopic image from scanning electron microscope
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- G—PHYSICS
- G06—COMPUTING; CALCULATING OR COUNTING
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- G—PHYSICS
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- G06T—IMAGE DATA PROCESSING OR GENERATION, IN GENERAL
- G06T2207/00—Indexing scheme for image analysis or image enhancement
- G06T2207/30—Subject of image; Context of image processing
- G06T2207/30108—Industrial image inspection
- G06T2207/30164—Workpiece; Machine component
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- H—ELECTRICITY
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- H01J—ELECTRIC DISCHARGE TUBES OR DISCHARGE LAMPS
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- H01J2237/26—Electron or ion microscopes
- H01J2237/28—Scanning microscopes
- H01J2237/2813—Scanning microscopes characterised by the application
- H01J2237/2817—Pattern inspection
Definitions
- the present invention relates to a method for generating images of patterns on workpieces such as wafers, substrates, panels, masks, etc. with a scanning electron microscope, and more particularly to a technique for continuously generating multiple images while adjusting the brightness of the images. .
- the brightness may change due to factors such as sample charging, changes in the state of the laminated film, and charging of the electron microscope itself. Therefore, brightness is adjusted at a preset time or at a preset location within the sample to suppress the influence of changes in brightness on inspection and measurement results.
- the brightness of the image changes greatly depending on the line width and density of the target pattern. For example, an image with a low pattern density has a high brightness, while an image with a high pattern density has a low brightness. Therefore, it is not possible to perform stable brightness adjustment by performing brightness adjustment in areas with different pattern densities.
- the time to irradiate the beam for purposes other than inspection and measurement is additional time other than inspection and measurement, which reduces throughput. Especially in the case of electron microscopes that scan large areas, the throughput is greatly reduced.
- the present invention provides an image generation method capable of appropriately adjusting brightness without lowering throughput.
- a method of generating an image of a workpiece having a patterned surface while adjusting the brightness of the image comprising: determining a reference area within the surface of the workpiece; A pattern density is calculated from pattern design data in the reference area, a plurality of adjustment areas having pattern densities similar to the calculated pattern density within a predetermined range are determined, and the image of the reference area is scanned. An image of one of the plurality of adjustment regions is generated by the scanning electron microscope, and a histogram of brightness of the image of the one adjustment region and a histogram of brightness of the image of the reference region.
- a method for generating is provided.
- the parameters include analog parameters for determining the electron detection sensitivity of the scanning electron microscope and digital parameters for adjusting brightness by image processing, and the method adjusts the setting values of the analog parameters. subsequently applying the adjusted settings of the analog parameters to the scanning electron microscope and applying the adjusted settings of the digital parameters in image processing of a plurality of images of the plurality of intermediate regions; and adjusting brightness of the plurality of images.
- the steps of generating an image of one of the plurality of adjustment regions with the scanning electron microscope and adjusting the brightness of the plurality of images of the plurality of intermediate regions are repeated.
- the pattern density is defined by the relationship between the width and length of the corresponding CAD pattern.
- the adjustment areas are selected so that the pattern density in each adjustment area approximates the pattern density in the reference area. Therefore, parameter adjustment in each adjustment region can be substituted for parameter adjustment in the reference region. According to the present invention, it is not necessary to generate an image of the reference area every time the luminance is adjusted. In other words, the brightness can be adjusted in multiple adjustment areas included in the target area while generating images of multiple target areas including adjustment areas and intermediate areas. As a result, it is possible to generate images of target areas with stable brightness without reducing the throughput of image generation of a large number of target areas including adjustment areas and intermediate areas.
- FIG. 1 is a schematic diagram showing an embodiment of an image generation device
- FIG. FIG. 4 is a schematic diagram illustrating an embodiment for calculating pattern density in a reference area
- FIG. 10 is a schematic diagram illustrating another embodiment for calculating the pattern density of the reference area
- 4 is a flow chart describing an embodiment of a method for setting a reference area and a plurality of adjustment areas
- 4 is a flow chart describing one embodiment of an operation for generating an image
- FIG. 4 is a diagram showing an example of a luminance histogram
- FIG. 7A is a histogram showing an example in which the entire mountain is biased toward the low luminance side.
- FIG. 7B is a histogram showing an example in which the entire mountain is biased toward the high brightness side.
- FIG. 7A is a histogram showing an example in which the entire mountain is biased toward the low luminance side
- FIG. 7B is a histogram showing an example in which the entire mountain is biased toward the high brightness side.
- FIG. 8A is a histogram of luminance to illustrate one embodiment of adjusting analog and digital parameters.
- FIG. 8B is a histogram of luminance to illustrate one embodiment of adjusting analog and digital parameters.
- FIG. 8C is a histogram of luminance to illustrate one embodiment of adjusting analog and digital parameters.
- FIG. 1 is a schematic diagram showing an embodiment of an image generation device.
- the image generation device includes a scanning electron microscope 1 that generates an image of the workpiece W and an operation control section 5 that controls the operation of the scanning electron microscope 1 .
- workpieces W include wafers, masks, panels, substrates, etc. used in the manufacture of semiconductor devices.
- the operation control unit 5 is composed of at least one computer.
- the operation control unit 5 includes a storage device 5a in which programs are stored, and a processing device 5b that executes operations according to instructions included in the programs.
- the storage device 5a includes a main storage device such as a random access memory (RAM) and an auxiliary storage device such as a hard disk drive (HDD) and solid state drive (SSD).
- Examples of the processing device 5b include a CPU (central processing unit) and a GPU (graphic processing unit).
- the specific configuration of the operation control unit 5 is not limited to these examples.
- the scanning electron microscope 1 includes an electron gun 15 for emitting an electron beam, a focusing lens 16 for converging the electron beam emitted from the electron gun 15, an X deflector 17 for deflecting the electron beam in the X direction, and an electron beam in the Y direction. It has a Y deflector 18 for deflection, an objective lens 20 for focusing the electron beam on the work piece W, and a stage 31 for supporting the work piece W.
- Electron gun 15 , focusing lens 16 , X deflector 17 , Y deflector 18 and objective lens 20 are arranged in column 30 .
- the electron beam emitted from the electron gun 15 is focused by the focusing lens 16, then deflected by the X deflector 17 and the Y deflector 18, and is focused by the objective lens 20 to irradiate the surface of the workpiece W.
- the workpiece W When the workpiece W is irradiated with the primary electrons of the electron beam, the workpiece W emits electrons such as secondary electrons and reflected electrons. Electrons emitted from the workpiece W are detected by an electron detector 26 .
- the electron detector 26 includes a scintillator 27 that converts electrons (secondary electrons or reflected electrons) emitted from the workpiece W into light, and a photomultiplier tube (PMT) that converts the light converted by the scintillator 27 into an electrical signal. 28 and an analog amplifier 29 for amplifying the electrical signal output from the photoelectron amplifier tube 28 . Electrons (secondary electrons or reflected electrons) emitted from the workpiece W are detected by an electron detector 26 including a scintillator 27 , a photoelectron multiplier tube 28 and an analog amplifier 29 . An electrical signal output from the electron detector 26 is input to an image acquisition device 32 and converted into an image. The scanning electron microscope 1 thus produces an image of the surface of the workpiece W. FIG. The image acquisition device 32 is connected to the operation control section 5 .
- the image generation device has a function for adjusting the brightness of the image generated by the scanning electron microscope 1. Brightness adjustment will be described in detail below.
- Parameters for adjusting the brightness of an image include analog parameters and digital parameters.
- Analog parameters are applied to the electron detector 26 which detects electrons (secondary electrons or backscattered electrons) emitted from the workpiece W, and digital parameters are performed on the image produced by the scanning electron microscope 1. Applies to digital processing. The analog parameters are applied when the scanning electron microscope 1 produces images, and the digital parameters are applied for the image processing of the images produced by the scanning electron microscope 1 .
- the analog parameter is a parameter that determines the electron detection sensitivity of the scanning electron microscope 1. More specifically, a plurality of analog parameters for adjusting the electrical signal output from electron detector 26 . These analog parameters include the PMT gain for adjusting the level of the electrical signal output from the photoelectron amplifier tube 28, the analog gain for adjusting the level of the electrical signal output from the analog amplifier 29, and the analog amplifier 29 includes an analog offset that shifts the position of the peaks of the electrical signal output from along the luminance value.
- the PMT gain is a parameter for changing the amplification ratio when converting incident light into an electrical signal. Increasing the PMT gain converts the incident light into a stronger electrical signal.
- Analog gain and analog offset are parameters for adjusting the operation of analog amplifier 29 . Increasing the analog gain lowers the electrical signal peaks, but makes the electrical signal strength more uniform over the entire luminance range. When the analog offset is increased, the position of the peak of the electrical signal moves to the high luminance side.
- a digital parameter is a parameter for adjusting brightness by image processing.
- Digital parameters include digital gain and digital offset.
- Image processing is performed on the image by the motion control unit 5 .
- Digital gain is a parameter for changing the overall distribution of luminance of all pixels forming an image. When the digital gain is increased, the peak luminance of the image is lowered, but the luminance of all pixels forming the image is made more uniform.
- the digital offset is a parameter for shifting the position of the luminance peak of the entire image along the luminance value. When the digital offset is increased, the position of the luminance peak of the entire image moves to the high luminance side.
- five luminance parameters ie, PMT parameter, analog gain, analog offset, digital gain, and digital offset are used to adjust the luminance of the image.
- PMT parameter analog gain, analog offset, digital gain, and digital offset
- the present invention is not limited to this embodiment, and only one of the five luminance parameters described above may be used, or parameters other than the five luminance parameters described above may be used.
- a plurality of electron detectors or different detection methods may be combined and independent parameters may be used.
- the image generating device adjusts the brightness of the images while continuously generating images of each of the plurality of target regions on the workpiece W.
- the image generator adjusts the brightness at intervals while generating images of multiple target areas on the workpiece W.
- the brightness adjustment interval is either a time interval or a distance interval on the workpiece W.
- Brightness adjustment is performed in multiple regions with the same or similar pattern density. These multiple regions include one reference region and multiple adjustment regions.
- the reference area is the area used to determine the initial values of the above luminance parameters (ie, PMT parameters, analog gain, analog offset, digital gain, and digital offset) used for luminance adjustment.
- Each adjustment area is an area having a pattern density similar to the pattern density in the reference area within a predetermined range. Pattern density will be described later.
- a reference area and a plurality of adjustment areas where luminance adjustment is performed are included in a plurality of target areas that are targets for image generation.
- the reference area and the plurality of adjustment areas are predetermined prior to generating images of the plurality of target areas on the workpiece W.
- the reference region and the plurality of adjustment regions may be determined while generating images of the plurality of target regions on the workpiece W.
- the motion control unit 5 saves the determined positions and sizes of the reference region and the plurality of adjustment regions in its storage device 5a.
- Each adjustment area is an area having a pattern density that approximates the pattern density of the reference area.
- Pattern density is defined by the relationship between the width and length of the CAD pattern corresponding to the pattern within each region. More specifically, the pattern density is calculated from the width and length of the corresponding CAD pattern.
- the CAD pattern is a virtual pattern defined by pattern design information included in pattern design data formed on the workpiece W, and has a polygonal shape.
- the pattern formed on the workpiece W is formed according to the CAD pattern on the design data.
- the design data of the pattern formed on the work piece W is stored in advance in the storage device 5a of the operation control section 5.
- the operation control unit 5 calculates the pattern density of the reference area from the pattern design data in the reference area. Similarly, the operation control unit 5 calculates the pattern density of each of a plurality of target areas on the workpiece W to be imaged from the pattern design data in each target area.
- FIG. 2 is a schematic diagram illustrating an embodiment for calculating the pattern density of the reference area on the workpiece W.
- the three patterns shown in FIG. 2 are CAD patterns corresponding to the three patterns in the reference area.
- the motion control unit 5 calculates the pattern density of the reference area from the design data. More specifically, the operation control unit 5 calculates the pattern density of the reference area from the dimension of the corresponding CAD pattern on the design data.
- the dimension along the scanning direction of the electron beam is defined as width
- the dimension along the direction perpendicular to the scanning direction of the electron beam is defined as length.
- the three CAD patterns include portions with three widths W1, W2, W3.
- the total length of the width W1 portion is L1
- the total length of the width W2 portion is L2+L3
- the total length of the width W3 portion is L4+L5+L6.
- the pattern density of the reference area is expressed as the relationship between the widths W1, W2, W3 of the three CAD patterns corresponding to the patterns in the reference area and the corresponding lengths L1, L2+L3, L4+L5+L6.
- FIG. 3 is a schematic diagram illustrating another embodiment for calculating the pattern density of the reference area on the workpiece W.
- the three CAD patterns shown in FIG. 3 are the same as the three CAD patterns shown in FIG. 2, but the scanning direction of the electron beam is different from that in FIG. 2 by 90°.
- the three CAD patterns include portions with three widths W1, W2, W3, W4, W5.
- the total length of the width W1 portion is L1, the total length of the width W2 portion is L2+L3+L4, the total length of the width W3 portion is L5, and the length of the width W4 portion is L5.
- the total is L6 and the total length of the portion of width W5 is L7.
- the pattern density of the reference area is expressed as three CAD pattern widths W1, W2, W3, W4, W5 and corresponding lengths L1, L2+L3+L4, L5, L6, L7 of the three CAD patterns corresponding to the patterns in the reference area.
- the operation control unit 5 similarly calculates pattern densities of areas other than the reference area in the target area. Furthermore, the operation control unit 5 determines a plurality of adjustment areas having pattern densities similar to the pattern density of the reference area within a predetermined range. More specifically, the operation control unit 5 compares the pattern density of the reference area with the pattern density of each of the target areas, and determines a plurality of areas having pattern densities that approximate the pattern density of the reference area within a predetermined range. is selected from the target area, and the selected area is determined as the adjustment area.
- the adjustment area is an area where luminance adjustment is performed.
- the predetermined range used to determine similarity is a numerical range centered on the pattern density of the reference area (ie, the width and length of the CAD pattern within the reference area).
- FIG. 4 is a flow chart describing an embodiment of a method for setting a reference area and a plurality of adjustment areas.
- a reference area within the surface of workpiece W is determined. Determination of the reference area may be performed by the user or may be performed by the operation control section 5 .
- the motion control unit 5 saves the determined position and size of the reference area in its storage device 5a. The position and size of the reference area can be specified from the pattern design data.
- the operation control section 5 calculates the pattern density of the reference area.
- the operation control unit 5 calculates pattern densities of areas other than the reference area in the target area.
- step 1-4 the operation control unit 5 compares the pattern density of the reference area with the pattern densities of the other areas, and selects a plurality of pattern densities that are similar to the pattern density of the reference area within a predetermined range. determine the adjustment region of The operation control unit 5 saves the determined positions and sizes of the plurality of adjustment regions in the storage device 5a. The positions and sizes of the plurality of adjustment regions can be specified from the pattern design data.
- the operation control unit 5 issues a command to the scanning electron microscope 1 to instruct the reference region, the plurality of adjustment regions, and the intermediate region ( Scanning electron microscope 1 is caused to generate images of a plurality of target areas, including (discussed below).
- motion controller 5 may determine the reference area and multiple adjustment areas.
- the operation control unit 5 issues a command to the scanning electron microscope 1 to cause the scanning electron microscope 1 to generate an image of the reference area.
- the operation control unit 5 receives the image of the reference area from the scanning electron microscope 1, and adjusts the set values of the parameters for adjusting the brightness of the image of the reference area.
- the parameters are the five luminance parameters described above (ie, PMT parameter, analog gain, analog offset, digital gain, and digital offset).
- the set values of the parameters adjusted in step 2-2 are the initial values of the parameters.
- the parameter settings for adjusting the brightness of the image of the reference region may be adjusted by the user.
- a luminance histogram is a graph having a horizontal axis representing luminance and a vertical axis representing the number of pixels having each luminance.
- FIG. 6 is a diagram showing an example of a luminance histogram.
- the luminance on the horizontal axis is a number from 0 to 255, for example. This numerical range of luminance from 0 to 255 is an example, and other numerical ranges may be used.
- brightness adjustment is such that one end of the histogram mountain foot is at the minimum value of brightness (0 in the example of FIG. 6) and the other end is the maximum value of brightness (0 in the example of FIG. 6), as shown in FIG. 255).
- FIG. 7A when the entire peak of the histogram is biased toward the low-luminance side and the left end of the foot of the peak does not appear on the histogram, the image is dark and many blackouts appear in the image.
- FIG. 7B when the entire peak of the histogram is biased toward the high brightness side and the right end of the foot of the peak does not appear on the histogram, the image is bright and has many blown-out highlights. appear. Therefore, luminance adjustment is performed so that the histogram has a mountain shape as shown in FIG.
- step 2-3 among the above five parameters, the adjusted setting values of the PMT parameter, analog gain, and analog offset, which are analog parameters, are applied to the scanning electron microscope 1.
- FIG. At step 2-4 the operation control section 5 issues a command to the scanning electron microscope 1 to cause the scanning electron microscope 1 to continuously generate a plurality of images of a plurality of intermediate regions.
- the plurality of intermediate regions are regions included in the target region and regions other than the reference region and the plurality of adjustment regions.
- the number of intermediate regions may be determined based on the time interval or distance interval required for brightness adjustment.
- step 2-5 the operation control unit 5 sets the adjusted setting values of the digital parameters, ie, the digital gain and the digital offset, among the five brightness parameters, to the plurality of intermediate regions generated in step 2-4.
- the digital parameter is a parameter for adjusting the brightness of the image through image processing, so the operation control section 5 can adjust the brightness of the generated image using the digital parameter.
- the image whose luminance has been adjusted by the digital parameters is stored in the storage device 5a of the operation control section 5.
- the operation control unit 5 issues a command to the scanning electron microscope 1 to cause the scanning electron microscope 1 to generate an image of one of the plurality of adjustment regions.
- the operation control section 5 receives the image of the one adjustment area from the scanning electron microscope 1, and compares the luminance histogram of the image of the one adjustment area with the luminance histogram of the image of the reference area.
- the setting value of the parameter for adjusting the brightness of the image of the one adjustment area is adjusted so that the difference becomes small.
- the operation control unit 5 adjusts the setting values of the parameters so that the mountain shape of the luminance histogram of the image of the one adjustment region approaches the mountain shape of the luminance histogram of the reference region image.
- the parameters are the five luminance parameters described above (ie, PMT parameter, analog gain, analog offset, digital gain, and digital offset).
- the scanning electron microscope 1 repeatedly images the same area of the workpiece W to generate a plurality of images
- the motion control unit 5 integrates these images, and furthermore, each pixel of the integrated image It is configured to generate an average image by dividing the luminance value by the cumulative number of sheets.
- FIG. 8A is a diagram showing a luminance histogram of one image out of a plurality of images before integration.
- the analog parameter is applied to each of the multiple images before being integrated. Specifically, as indicated by the dotted line in FIG. 8A, the operation control unit 5 widens the luminance range (that is, increases the contrast) as long as the luminance does not saturate on the low luminance side and the high luminance side. Adjust analog parameters.
- FIG. 8B is a diagram showing a luminance histogram of an average image obtained by integrating a plurality of images of the same region and further dividing the luminance value of each pixel of the integrated image by the number of integrated images.
- the integrated luminance value of each pixel is divided by the integrated number of pixels, random noise is removed from the average image and an average image with an improved SN ratio is obtained.
- the luminance range of the average image is narrowed (ie the contrast is reduced).
- the operation control unit 5 applies the digital parameter among the five luminance parameters described above to the average image to widen the luminance range (increase the contrast). That is, the operation control unit 5 adjusts the set values of the digital parameters so that the shape of the histogram in FIG. 8C approaches the luminance histogram of the image of the reference area indicated by the dotted line.
- step 2-8 the operation control unit 5 adjusts the adjusted set values of the digital parameters, the digital gain and the digital offset, among the above five parameters to the adjustment values generated in step 2-5 above. Applies to image processing of region images. The image whose luminance has been adjusted by the digital parameters is stored in the storage device 5a of the operation control section 5. FIG.
- the operation control unit 5 applies the adjusted set values of the PMT parameter, analog gain, and analog offset, which are analog parameters, to the scanning electron microscope 1 among the above five parameters. These analog parameters are then applied to scanning electron microscope 1 before generating an image.
- the operation control unit 5 issues a command to the scanning electron microscope 1 to cause the scanning electron microscope 1 to continuously generate a plurality of images of the other plurality of intermediate regions.
- the plurality of intermediate areas in step 2-10 are also included in the target area.
- the number of intermediate regions may be determined based on the time interval or distance interval required for brightness adjustment.
- the operation control unit 5 sets the set values of the digital gain and digital offset, which are the digital parameters adjusted in step 2-7, to the plurality of intermediate regions generated in step 2-10. Applies to image processing of images.
- the brightness of each image of the plurality of intermediate regions is adjusted by digital parameters.
- the image whose luminance has been adjusted by the digital parameters is stored in the storage device 5a of the operation control section 5.
- the operation control unit 5 determines whether images of all target areas have been generated. If images of all the target areas have not been generated, the operation control section 5 repeats steps 2-6 and after. When the images of all the target areas have been generated, the operation control section 5 issues a command to the scanning electron microscope 1 to terminate the generation of the images of the target areas.
- the pattern density within each adjustment region approximates the pattern density within the reference region. Therefore, parameter adjustment in each adjustment region can be substituted for parameter adjustment in the reference region. According to this embodiment, it is not necessary to generate an image of the reference area every time the luminance is adjusted. In other words, while the scanning electron microscope 1 generates images of multiple target regions including adjustment regions and intermediate regions, the motion control unit 5 can adjust the brightness in a plurality of adjustment regions included in the target regions. . As a result, the throughput of imaging multiple target regions, including adjustment regions and intermediate regions, can be increased.
- the pattern of the workpiece is an image in which only one layer on the surface is resolved.
- a similar brightness adjustment technique can be used using layer design data. For example, if fewer electrons reach the detector in lower layers and the effect of brightness on the detected image decreases, the pattern density for each layer calculated from the design value is multiplied by a certain ratio to match the actual detected image.
- the present invention can be used for methods of generating images of patterns on workpieces such as wafers, substrates, panels, masks, etc. with a scanning electron microscope.
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Abstract
Description
一態様では、前記複数の調整領域のうちの1つの画像を前記走査電子顕微鏡で生成する工程から、前記複数の中間領域の前記複数の画像の輝度を調整する工程までを繰り返す。
一態様では、前記パターン密度は、対応するCADパターンの幅と長さとの関係によって定義される。
図1は、画像生成装置の一実施形態を示す模式図である。画像生成装置は、ワークピースWの画像を生成する走査電子顕微鏡1と、走査電子顕微鏡1の動作を制御する動作制御部5を備えている。ワークピースWの例としては、半導体デバイスの製造に使用されるウェーハ、マスク、パネル、基板などが挙げられる。
ステップ1-1では、ワークピースWの表面内の基準領域が決定される。基準領域の決定は、ユーザーによって実施されてもよいし、あるいは動作制御部5によって実施されてもよい。動作制御部5は、決定された基準領域の位置および大きさをその記憶装置5aに保存する。基準領域の位置および大きさは、パターンの設計データから特定することができる。
ステップ1-2は、動作制御部5は、基準領域のパターン密度を算定する。
ステップ1-3では、動作制御部5は、ターゲット領域のうち、基準領域以外の他の領域のパターン密度を算定する。
ステップ1-4では、動作制御部5は、基準領域のパターン密度を、上記他の領域のそれぞれのパターン密度と比較し、基準領域のパターン密度と所定の範囲内で近似するパターン密度を持つ複数の調整領域を決定する。動作制御部5は、決定された複数の調整領域の位置および大きさをその記憶装置5aに保存する。複数の調整領域の位置および大きさは、パターンの設計データから特定することができる。
ステップ2-1では、動作制御部5は走査電子顕微鏡1に指令を発して、基準領域の画像を走査電子顕微鏡1に生成させる。
ステップ2-2では、動作制御部5は、基準領域の画像を走査電子顕微鏡1から受け取り、基準領域の画像の輝度を調整するためのパラメータの設定値を調整する。本実施形態では、パラメータは、上述した5つの輝度パラメータ(すなわち、PMTパラメータ、アナログゲイン、アナログオフセット、デジタルゲイン、およびデジタルオフセット)である。このステップ2-2で調整されたパラメータの設定値は、パラメータの初期値である。一実施形態では、基準領域の画像の輝度を調整するためのパラメータの設定値は、ユーザーにより調整されてもよい。
ステップ2-4では、動作制御部5は走査電子顕微鏡1に指令を発し、複数の中間領域の複数の画像を走査電子顕微鏡1に連続して生成させる。複数の中間領域は、ターゲット領域に含まれる領域であり、基準領域および上記複数の調整領域以外の領域である。複数の中間領域の数は、輝度調整に必要な時間的間隔または距離的間隔に基づいて定められてもよい。
ステップ2-5では、動作制御部5は、上記5つの輝度パラメータのうち、デジタルパラメータであるデジタルゲインおよびデジタルオフセットの調整された設定値を、上記ステップ2-4で生成した複数の中間領域の複数の画像の画像処理に適用する。上述したように、デジタルパラメータは、画像処理により画像の輝度を調整するパラメータであるため、動作制御部5は、生成された画像の輝度をデジタルパラメータにより調整することができる。デジタルパラメータにより輝度が調整された画像は、動作制御部5の記憶装置5a内に保存される。
ステップ2-7では、動作制御部5は、上記1つの調整領域の画像を走査電子顕微鏡1から受け取り、上記1つの調整領域の画像の輝度のヒストグラムと、基準領域の画像の輝度のヒストグラムとの差が小さくなるように、上記1つの調整領域の画像の輝度を調整するためのパラメータの設定値を調整する。具体的には、動作制御部5は、上記1つの調整領域の画像の輝度のヒストグラムの山形状が、基準領域の画像の輝度のヒストグラムの山形状に近づく方向にパラメータの設定値を調整する。本実施形態では、パラメータは、上述した5つの輝度パラメータ(すなわち、PMTパラメータ、アナログゲイン、アナログオフセット、デジタルゲイン、およびデジタルオフセット)である。
ステップ2-11では、動作制御部5は、上記ステップ2-7で調整されたデジタルパラメータであるデジタルゲインおよびデジタルオフセットの設定値を、上記ステップ2-10で生成した複数の中間領域の複数の画像の画像処理に適用する。複数の中間領域の各画像の輝度はデジタルパラメータにより調整される。デジタルパラメータにより輝度が調整された画像は、動作制御部5の記憶装置5a内に保存される。
5 動作制御部
15 電子銃
16 集束レンズ
17 X偏向器
18 Y偏向器
20 対物レンズ
26 電子検出器
27 シンチレータ
28 光電子増幅管
29 アナログ増幅器
30 カラム
31 ステージ
32 画像取得装置
Claims (4)
- 表面にパターンが形成されているワークピースの画像を、該画像の輝度を調整しながら生成する方法であって、
前記ワークピースの表面内の基準領域を決定し、
前記基準領域のパターン密度を、前記基準領域内のパターンの設計データから算定し、
前記算定されたパターン密度と所定の範囲内で近似するパターン密度を持つ複数の調整領域を決定し、
前記基準領域の画像を走査電子顕微鏡で生成し、
前記複数の調整領域のうちの1つの画像を前記走査電子顕微鏡で生成し、
前記1つの調整領域の画像の輝度のヒストグラムと、前記基準領域の画像の輝度のヒストグラムとの差が小さくなるように、前記1つの調整領域の画像の輝度を調整するためのパラメータの設定値を調整し、
前記ワークピースの表面内の複数の中間領域の複数の画像を前記走査電子顕微鏡で生成する、方法。 - 前記パラメータは、前記走査電子顕微鏡の電子検出感度を決定するアナログパラメータと、画像処理によって輝度を調整するためのデジタルパラメータを含み、
前記方法は、前記アナログパラメータの設定値を調整した後に、前記アナログパラメータの前記調整された設定値を前記走査電子顕微鏡に適用し、
前記複数の中間領域の複数の画像の画像処理に、前記デジタルパラメータの前記調整された設定値を適用することで、前記複数の画像の輝度を調整する工程をさらに含む、請求項1に記載の方法。 - 前記複数の調整領域のうちの1つの画像を前記走査電子顕微鏡で生成する工程から、前記複数の中間領域の前記複数の画像の輝度を調整する工程までを繰り返す、請求項2に記載の方法。
- 前記パターン密度は、対応するCADパターンの幅と長さとの関係によって定義される、請求項1乃至3のいずれか一項に記載の方法。
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