JP5178781B2 - Sensor output data correction device and sensor output data correction method - Google Patents

Description

  Embodiments described herein relate generally to a sensor output data correction apparatus and a sensor output data correction method.

  In recent years, the circuit line width required for a semiconductor element has been increasingly narrowed as a large scale integrated circuit (LSI) is highly integrated and has a large capacity. These semiconductor elements use an original pattern pattern (also referred to as a mask or a reticle, hereinafter referred to as a mask) on which a circuit pattern is formed, and the pattern is exposed and transferred onto a wafer by a reduction projection exposure apparatus called a stepper. It is manufactured by forming a circuit. Therefore, a pattern drawing apparatus capable of drawing a fine circuit pattern is used for manufacturing a mask for transferring such a fine circuit pattern onto a wafer. A pattern circuit may be directly drawn on a wafer using such a pattern drawing apparatus. Alternatively, development of a laser beam drawing apparatus for drawing using a laser beam in addition to an electron beam has been attempted.

  In addition, improvement in yield is indispensable for manufacturing an LSI that requires a large amount of manufacturing cost. However, as represented by a 1 gigabit class DRAM (Random Access Memory), the pattern constituting the LSI is about to be in the order of submicron to nanometer. One of the major factors that reduce the yield is a pattern defect of a mask used when an ultrafine pattern is exposed and transferred onto a semiconductor wafer by a photolithography technique. In recent years, with the miniaturization of LSI pattern dimensions formed on semiconductor wafers, the dimensions that must be detected as pattern defects have become extremely small. Therefore, it is necessary to improve the accuracy of a pattern inspection apparatus that inspects defects in a transfer mask used in LSI manufacturing.

  On the other hand, with the development of multimedia, LCDs (Liquid Crystal Display) are increasing in size of the liquid crystal substrate to 500 mm × 600 mm or more, and TFTs (Thin Film Transistors) formed on the liquid crystal substrate. : Thin film transistors) and the like are being miniaturized. Therefore, it is required to inspect a very small pattern defect over a wide range. For this reason, there is an urgent need to develop a sample inspection apparatus for efficiently inspecting defects of a photomask used in manufacturing such a large area LCD pattern and a large area LCD in a short time.

  Here, in a conventional pattern inspection apparatus, an optical image obtained by imaging a pattern formed on a sample such as a lithography mask using a magnifying optical system at a predetermined magnification and an identical pattern on the sample are captured. It is known to perform an inspection by comparing with an optical image. For example, as a pattern inspection method, a “die to die inspection” that compares optical image data obtained by imaging the same pattern at different locations on the same mask, or a drawing apparatus that draws a pattern using pattern-designed CAD data as a mask Drawing data (design pattern data) converted into a device input format for input to the inspection device is input to the inspection device, design image data (reference image) is generated based on the drawing data, and measurement data obtained by imaging the pattern There is a “die to database test” that compares an optical image. In the inspection method in such an inspection apparatus, the sample is placed on the stage, and the stage is moved so that the light beam scans on the sample and the inspection is performed. The sample is irradiated with a light beam by a light source and an illumination optical system. The light transmitted or reflected by the sample is imaged on the sensor via the optical system. The image picked up by the sensor is sent to the comparison circuit as measurement data. The comparison circuit compares the measurement data and the reference data according to an appropriate algorithm after the alignment of the images, and determines that there is a pattern defect if the shape and the output signal level do not match.

  Here, the output data of the sensor that captures an image of the pattern formed on the sample is corrected for the output offset of the sensor by offset correction after AD conversion, and the gain is corrected by gain correction. Offset and gain correction is performed for each pixel to be imaged. The offset and gain correction coefficients are calculated for each pixel corresponding to the image capture width of the sensor from the sensor output data collected in advance in the white and black areas of the object to be measured before measurement. Then, the calculated correction coefficient is set in the apparatus, and thereafter correction is performed using the correction coefficient. However, in the conventional offset correction and gain correction methods, the output level and pattern of the defect are caused by the change in the output level of the sensor due to the change in the light amount with time of the light source and the change in sensitivity of each light receiving element of the sensor with time. Therefore, it is difficult to cope with demands for detecting fine defects and detecting differences in pattern line widths.

JP 2007-071630 A

  Embodiments of the present invention provide an apparatus and method for overcoming the above-described problems and correcting a change in sensor output level due to a change in light quantity with time and a change in sensitivity with time of each light receiving element of the sensor itself. The purpose is to do.

According to the embodiment, the sensor output data correction apparatus includes an offset circuit, a gain correction circuit, an average value calculation circuit, and a gain correction coefficient calculation circuit. The offset circuit illuminates the patterned sample, receives light obtained by transmission or reflection, receives output data from a sensor that outputs image data, and performs offset correction of the output data. The gain correction circuit performs gain correction by inputting a gain correction coefficient and multiplying the output data by the input gain correction coefficient. The average value calculation circuit is a position where light is transmitted from the pattern when it is obtained by transmission out of the output data of the sensor subjected to the offset correction and gain correction, and from the pattern when it is obtained by reflection. The average value of the pixel values of the output data of the sensor is calculated using the output data of the sensor acquired at the position where the light is reflected. The gain correction coefficient calculation circuit corrects the gain correction coefficient used for the gain correction using the rate of change of the average value from the set reference value, and feeds back to the gain correction circuit. The position where light is transmitted from the pattern when obtained by the transmission is a position where there is no influence from the surroundings and the pattern does not exist in the target pixel, and the light from the pattern when obtained by the reflection is used. The position where is reflected is a position that is not affected by the surroundings, and is a position where the pattern occupies the entire target pixel.
Input the output data of the sensor that has been subjected to the offset correction and gain correction, from the input output data, if obtained by transmission, the output data of the sensor acquired at the position where the light is transmitted from the pattern, An identification circuit for identifying the output data of the sensor obtained at a position where light is reflected from the pattern when obtained by reflection;
The identification circuit, for each pixel of interest, if the pixel of interest and a plurality of pixels in the pixel region surrounding the pixel of interest are all equal to or greater than a threshold value, As output data of the sensor acquired at a position where light is transmitted from a pattern, if obtained by reflection, it is identified as output data of the sensor acquired at a position where light is reflected from the pattern,
The average value calculation circuit calculates an average value of the pixel values of the output data of the sensor acquired at the position identified by the identification circuit.

In addition, according to the embodiment, the sensor output data correction method includes inputting output data from a sensor that illuminates a patterned sample, receives light obtained by transmission or reflection, and outputs image data. The offset correction of the output data, the step of performing gain correction by inputting the gain correction coefficient and multiplying the output data by the input gain correction coefficient, and the offset correction and gain correction are performed. If the sensor output data is obtained by transmission, the sensor output data acquired at a position where light is transmitted from the pattern, and if obtained by reflection, the sensor is acquired at a position where light is reflected from the pattern. A step of calculating an average value of each pixel value of the output data of the sensor using the output data of the sensor, and the above-described reference value from the set reference value Using the rate of change of the average value by correcting the gain correction coefficient used for the gain correction, and a step of feedback for the gain correction. The position where light is transmitted from the pattern when obtained by the transmission is a position where there is no influence from the surroundings and the pattern does not exist in the target pixel, and the light from the pattern when obtained by the reflection is used. The position where is reflected is a position that is not affected by the surroundings, and is a position where the pattern occupies the entire target pixel.
Input the output data of the sensor that has been subjected to the offset correction and gain correction, from the input output data, if obtained by transmission, the output data of the sensor acquired at the position where the light is transmitted from the pattern, If obtained by reflection, identify the output data of the sensor acquired at the position where light is reflected from the pattern,
When identifying, for each target pixel, if the target pixel and a plurality of pixels in the pixel region surrounding the target pixel are all equal to or greater than the threshold value, As output data of the sensor acquired at a position where light is transmitted from a pattern, if obtained by reflection, it is identified as output data of the sensor acquired at a position where light is reflected from the pattern,
An average value of each pixel value of the output data of the sensor acquired at the identified position is calculated.

It is a conceptual diagram which shows the structure of the pattern inspection apparatus in 1st Embodiment. It is a figure for demonstrating the acquisition procedure of the optical image in 1st Embodiment. It is a conceptual diagram which shows the internal structure of the sensor output correction circuit in 1st Embodiment. It is an example of the graph for demonstrating the method of the offset correction in 1st Embodiment. It is an example of the graph for demonstrating the method of the gain correction in 1st Embodiment. It is a conceptual diagram which shows the internal structure of the white part average output level calculation circuit in 1st Embodiment. It is a figure which shows an example of the order of the sensor output in 1st Embodiment, and the data output order after a data conversion circuit. It is a conceptual diagram which shows the internal structure of the gain correction coefficient calculation circuit in 1st Embodiment. It is a conceptual diagram which shows the internal structure of the sensor output correction circuit in 2nd Embodiment. It is a conceptual diagram which shows the internal structure of the white part identification circuit and white part average output level calculation circuit in 2nd Embodiment. It is a figure which shows an example of the order of the sensor output in 2nd Embodiment, and the data output order after a data conversion circuit. It is a conceptual diagram which shows the internal structure of the white part determination circuit in 2nd Embodiment. It is a figure which shows an example of the pixel area | region centering on the attention pixel in 2nd Embodiment. It is a figure which shows an example of the white part template in 2nd Embodiment. It is a figure for demonstrating another optical image acquisition method.

(First embodiment)
FIG. 1 is a conceptual diagram showing a configuration of a pattern inspection apparatus according to the first embodiment. In FIG. 1, a pattern inspection apparatus 100 that samples a substrate such as a mask or wafer on which a pattern is formed and inspects defects in the pattern on the sample includes an optical image acquisition unit 150 and a control system circuit 160. . The optical image acquisition unit 150 includes an XYθ table 102, a light source 103, an enlargement optical system 104, a photodiode array 105, a sensor circuit 106, a laser length measurement system 122, an autoloader 130, and an illumination optical system 170. In the control system circuit 160, a control computer 110 serving as a computer is connected to a position circuit 107, a comparison circuit 108, a development circuit 111, a reference circuit 112, a sensor output correction circuit 140, and an autoloader control circuit via a bus 120 serving as a data transmission path. 113, a table control circuit 114, a magnetic disk device 109, a magnetic tape device 115, a flexible disk device (FD) 116, a CRT 117, a pattern monitor 118, and a printer 119. The XYθ table 102 is driven by an X-axis motor, a Y-axis motor, and a θ-axis motor. The sensor output correction circuit 140 is an example of a sensor output data correction device. In FIG. 1, description of components other than those necessary for describing the first embodiment is omitted. It goes without saying that the pattern inspection apparatus 100 usually includes other necessary configurations.

  As an optical image acquisition step, the optical image acquisition unit 150 acquires an optical image on the photomask 101 that is a sample on which a graphic indicated by graphic data included in the design data is drawn based on the design data. Specifically, the optical image is acquired as follows.

  A photomask 101 to be inspected is placed on an XYθ table 102 provided so as to be movable in a horizontal direction and a rotation direction by motors of XYθ axes, and the pattern formed on the photomask 101 includes an XYθ table. Light is emitted by a suitable light source 103 disposed above 102. The light beam emitted from the light source 103 irradiates the photomask 101 serving as a sample via the illumination optical system 170. A magnifying optical system 104, a photodiode array 105, and a sensor circuit 106 are disposed below the photomask 101, and light that has passed through the photomask 101 that is a sample such as an exposure mask passes through the magnifying optical system 104. Then, an image is formed as an optical image on the photodiode array 105 and is incident thereon.

FIG. 2 is a diagram for explaining an optical image acquisition procedure according to the first embodiment.
As shown in FIG. 2, the inspection area is virtually divided into a plurality of strip-shaped inspection stripes having a scan width W in the Y direction, and each of the divided inspection stripes is continuously scanned. Thus, the operation of the XYθ table 102 is controlled, and an optical image is acquired while moving in the X direction. In the photodiode array 105, images having a scan width W as shown in FIG. 2 are continuously input. Then, after acquiring the image of the first inspection stripe, the image of the scan width W is continuously input in the same manner while moving the image of the second inspection stripe in the opposite direction. When an image in the third inspection stripe is acquired, the image moves while moving in the direction opposite to the direction in which the image in the second inspection stripe is acquired, that is, in the direction in which the image in the first inspection stripe is acquired. To get. In this way, it is possible to shorten a useless processing time by continuously acquiring images.

  The pattern image formed on the photodiode array 105 is photoelectrically converted by the photodiode array 105 and further A / D (analog-digital) converted by the sensor circuit 106. In this way, light is converted into an image by photoelectric conversion. The photodiode array 105 is provided with a sensor in which a plurality of pixel columns are arranged, such as a TDI (time delay integration) sensor or a line sensor. By continuously moving the XYθ table 102 serving as a stage in the X-axis direction, the TDI sensor images the pattern of the photomask 101 serving as a sample. These light source 103, magnifying optical system 104, photodiode array 105, and sensor circuit 106 constitute a high-magnification inspection optical system.

  The XYθ table 102 is driven by the table control circuit 114 under the control of the control computer 110. It can be moved by a drive system such as a three-axis (XY-θ) motor that drives in the X, Y, and θ directions.

  Measurement data (optical image) output from the sensor circuit 106 is subjected to offset correction and gain correction by the sensor output correction circuit 140. Here, as described above, when the offset correction or gain correction is performed only with a preset correction coefficient as in the prior art, as described above, the change in light quantity with time and the sensitivity over time of each light receiving element of the sensor itself. It is difficult to correct the change in the output level of the sensor due to the change. Therefore, in the first embodiment, the correction coefficient used when performing the gain correction is corrected and fed back, so that the sensor caused by the change in light quantity with time and the change in sensitivity with time of each light receiving element of the sensor itself. Correct the output level change.

  FIG. 3 is a conceptual diagram illustrating an internal configuration of the sensor output correction circuit according to the first embodiment. In FIG. 3, the sensor output correction circuit 140 includes an offset correction circuit 10, a gain correction circuit 12, a white average output level calculation circuit 14, and a gain correction coefficient calculation circuit 16. The output of the photodiode array 105 A / D converted by the sensor circuit 106 is offset corrected by the offset correction circuit 10. Here, as an example, the case where the photodiode array 105 receives light obtained by illuminating and transmitting the patterned photomask 101 is shown.

  FIG. 4 is an example of a graph for explaining a method of offset correction in the first embodiment. In FIG. 4, the horizontal axis indicates the light amount, and the vertical axis indicates the sensor output (pixel value). The offset correction circuit 10 inputs a preset offset correction coefficient and adds the offset correction coefficient to each output (data after digitization) of the photodiode array 105 to offset the output data.

  FIG. 5 is an example of a graph for explaining a method of gain correction in the first embodiment. In FIG. 5, the horizontal axis indicates the light amount, and the vertical axis indicates the sensor output (pixel value). The gain correction circuit 12 inputs a preset gain correction coefficient and performs gain correction by multiplying the output data by the input gain correction coefficient.

  Here, in the sensor output data, when it is obtained by transmission, which is a white portion, data obtained from a position that is not affected by the surroundings and does not have a pattern in the target pixel is originally a pixel value. Is maximized. On the other hand, in the case of a transmissive type that becomes a black portion, light does not transmit from the position where the pattern occupies the entire target pixel, that is, the position filled with the pattern, so the pixel value becomes the minimum value “0”. The pixel value received from the position where the pattern exists in a part of the area, the position affected by the surrounding pattern while being a white part, or the position affected by the surrounding white part while being a black part Become. Therefore, the change in the output level of the sensor due to the change in the amount of light over time or the change in sensitivity of each light receiving element of the sensor over time is the output level (pixel) of the signal from the white part that is not affected by the surroundings. It can be grasped by calculating how the (value) has changed with respect to the reference output level (pixel value). Therefore, in the first embodiment, the sensor output coefficient is corrected by correcting the gain coefficient of the sensor by the white portion average output level calculation circuit 14 and the gain correction coefficient calculation circuit 16 attached after the offset correction and the gain correction.

  In the first embodiment, the gain coefficient is corrected using a correction white pattern. The correction white patterns 20 and 22 are preferably formed outside the inspection area of the photomask 101 shown in FIG. The optical image acquisition unit 150 captures the correction white patterns 20 and 22 by temporarily interrupting imaging of the inspection stripe before or during the inspection. The correction white patterns 20 and 22 are formed in white areas that are not affected by the surroundings. For example, after acquiring an optical image of a plurality of inspection stripes, before the next inspection stripe is imaged, the position of the stage is moved so that illumination light is irradiated to the correction white patterns 20 and 22. Then, the correction white patterns 20 and 22 are imaged while moving the stage. Thereby, a plurality of pixel values in the white portion can be acquired from the correction white patterns 20 and 22. If there is a change in light quantity over time or a change in sensitivity of each light receiving element of the sensor over time, the output level of the obtained sensor also changes. Here, the correction white patterns 20 and 22 are divided into two regions, but the present invention is not limited to this. There may be one or three or more. Then, the gain coefficient is corrected using the imaging data of the correction white patterns 20 and 22.

  FIG. 6 is a conceptual diagram showing an internal configuration of the white portion average output level calculation circuit according to the first embodiment. The white portion average output level calculation circuit 14 includes a data conversion circuit 40, a pixel output integration circuit 42, and a pixel average value averaging circuit 44. In the TDI sensor, a plurality of photodiode elements are arranged side by side so that a plurality of pixel columns can be imaged simultaneously. Therefore, for example, images of L pixels (L ≧ 2, for example, 1024) can be simultaneously acquired by simultaneously imaging a plurality of photodiode elements corresponding to the image capture width. Furthermore, a plurality of photodiode elements are arranged in each column. Then, while moving, a plurality of photodiode elements in the same column continuously image the same pixel position while shifting the time. Therefore, a plurality of pixel data is obtained for the same position on the photomask 101. For example, m (m ≧ 2, for example, 1024) data can be acquired for each pixel position. The data conversion circuit 40 converts the data output order so as to continuously output a plurality of obtained pixel data for each pixel.

  FIG. 7 is a diagram illustrating an example of the sensor output order and the data output order after the data conversion circuit in the first embodiment. For example, a case is shown in which L photodiode elements are arranged in one direction so that 1 to L pixels can be imaged simultaneously. As shown in FIG. 7A, the data conversion circuit 40 receives the first pixel data, the second pixel data,. Then, the first pixel data, the second pixel data,... The L pixel data, which are simultaneously imaged at different times, are input in order. In this way, data of the same pixel is not continuously input. Therefore, as shown in FIG. 7B, the data conversion circuit 40 continuously outputs a plurality of obtained pixel data for each pixel. That is, the first data, the second data,..., The mth data are continuously output for the first pixel, and then the first data and the second data are similarly output for the second pixel. ,..., The m-th data is output continuously, then the same is output for the third pixel, and the same is output for the L pixel. As described above, the sensor output data obtained by continuously capturing the correction white patterns 20 and 22 is converted, and a plurality of pixel data obtained from the correction white patterns 20 and 22 are continuously obtained for each pixel. Output.

  The pixel output integration circuit 42 integrates pixel values of every N pieces of data for each pixel, and divides the integrated value by N to calculate an average value of the pixel values for every N pieces of data. However, N <m. That is, for the first pixel, the pixel output integration circuit 42a calculates an average value of pixel values for every N pieces of data. For the second pixel, the pixel output integration circuit 42b calculates an average value of pixel values for every N pieces of data. For the third pixel, the pixel output integration circuit 42c calculates an average value of pixel values for every N pieces of data. Thereafter, similarly, the pixel output integration circuit 42 corresponding to each pixel calculates an average value of the pixel values for each N pieces of data. As described above, an average value of pixel values is calculated for each of N pieces of data for a plurality of pieces of pixel data obtained from the correction white patterns 20 and 22.

  Further, the pixel average value averaging circuit 44 inputs a plurality of average values for each of N pieces of data and calculates the average value of the average values. The capacity of the data memory can be reduced by calculating the overall average value from a plurality of average values without calculating the average value of all the pixel values at once. That is, for the first pixel, the pixel average value averaging circuit 44a calculates the average value of the average values. For the second pixel, the pixel average value averaging circuit 44b calculates an average value of the average values. Thereafter, similarly, the pixel average value averaging circuit 44 corresponding to each pixel calculates the average value of the average values. As described above, the average value of the average values of the plurality of pixel data obtained from the correction white patterns 20 and 22 is calculated.

  As described above, the white portion average output level calculation circuit 14 calculates an average value of a plurality of pixel values obtained from the position of the white portion among the output data of the sensor subjected to the offset correction and the gain correction. The white portion average output level calculation circuit 14 is an example of an average value calculation circuit.

  FIG. 8 is a conceptual diagram showing the internal configuration of the gain correction coefficient calculation circuit according to the first embodiment. In the gain correction coefficient calculation circuit 16, a memory 51, a change rate calculation circuit 50, and a correction circuit 52 are arranged for each pixel. Each memory 51 stores, for each pixel, a white reference output value captured at a stage before a change in light quantity with time and a change in sensitivity with time of each light receiving element of the sensor itself occur. .

  First, the change rate calculation circuit 50 calculates a change rate C obtained by dividing the pixel average value A obtained from the position of the white part by the reference output value B in the memory 51 for each pixel. That is, the change rate calculation circuit 50a for the first pixel calculates a change rate C obtained by dividing the pixel average value A of the first pixel obtained from the position of the white portion by the reference output value B in the memory 51a. For the second pixel, the change rate calculation circuit 50b calculates a change rate C obtained by dividing the pixel average value A of the first pixel obtained from the position of the white portion by the reference output value B in the memory 51b. Thereafter, similarly, the change rate calculation circuit 50 corresponding to each pixel calculates the change rate C. As described above, the change rate C is calculated for each pixel for the sensor output data obtained from the correction white patterns 20 and 22.

  Next, the correction circuit 52 inputs a gain coefficient before correction for each pixel, and outputs a value obtained by dividing the gain coefficient before correction by the change rate C to the gain correction circuit 12 as a corrected gain coefficient. give feedback. The gain correction circuit 12 that has received the feedback subsequently performs gain correction using the fed back gain coefficient.

  As described above, the gain correction coefficient calculation circuit 16 corrects the gain coefficient used for gain correction using the rate of change of the pixel average value in the correction white patterns 20 and 22 from the set reference value, and the gain correction circuit. 14 to feed back. With such a configuration, it is possible to correct the change in the output level of the sensor due to the change in light quantity with time and the change in sensitivity with time of each light receiving element of the sensor by gain correction.

  Thereafter, the pattern in each inspection stripe is imaged with the corrected gain coefficient. In this way, the optical image data (measurement data) in which the change in the output level of the sensor due to the change in the light amount with time and the change in sensitivity with time of each light receiving element itself is corrected is output from the position circuit 107. The data indicating the position of the photomask 101 on the XYθ table 102 is sent to the comparison circuit 108. The measurement data is, for example, 8-bit unsigned data, and represents the brightness gradation of each pixel.

  In addition, as a reference data creation step, reference data for comparison with measurement data based on design data of a photomask 101 that is a reference image creation unit constituted by the development circuit 111, the reference circuit 112, and the like to be inspected. Reference image). The design data is stored in the magnetic disk device 109 or the like.

  As a comparison process, the comparison circuit 108 (comparison unit) inputs the measurement data and the reference data, and then performs alignment after comparing them. Comparison is made according to a predetermined algorithm, and the presence or absence of a defect is determined for each pixel. The comparison result is output to the pattern monitor 118 or the like.

  As described above, it is possible to suppress erroneous detection of defects by performing comparison with data corrected for changes in sensor output level due to changes in light intensity over time and changes in sensitivity of each light receiving element of the sensor itself over time. Thus, pseudo defects can be reduced and high-precision inspection can be performed.

(Second Embodiment)
In the first embodiment, the correction white patterns 20 and 22 formed on the photomask 101 are imaged as necessary, and the gain coefficient is corrected each time the image is captured. However, the present invention is not limited to this. In the second embodiment, a configuration will be described in which the correction white patterns 20 and 22 are purposely corrected using pixel data imaged in the inspection area. The configuration of the pattern inspection apparatus is the same as that shown in FIG. Except for the internal configuration of the sensor output correction circuit 140, the configuration is the same as that of the first embodiment. The following is the same as the first embodiment except for the contents to be specifically described.

  FIG. 9 is a conceptual diagram showing the internal configuration of the sensor output correction circuit according to the second embodiment. In FIG. 9, the sensor output correction circuit 140 is a white portion average output level calculation circuit 15 instead of the white portion average output level calculation circuit 14, and the white portion average output level calculation circuit 15 is connected between the gain correction circuit 12 and the white portion average output level calculation circuit 15. 3 is the same as FIG. 3 except that the unit identification circuit 13 is provided. The white part identifying circuit 13 automatically identifies a pixel position that becomes a white part from the sensor output data of the inspection area under inspection.

  FIG. 10 is a conceptual diagram showing the internal configuration of the white part identifying circuit and the white part average output level calculating circuit in the second embodiment. The white part identifying circuit 13 receives the output data of the sensor that has been subjected to offset correction and gain correction. And the pixel position of a white part is identified among the input output data. The white part identifying circuit 13 includes a data conversion circuit 60, a memory 61, and a white part determining circuit 62 for each pixel. A white portion template is stored in the memory 61.

  FIG. 11 is a diagram illustrating an example of the sensor output order and the data output order after the data conversion circuit according to the second embodiment. Here, as described above, for example, a case where L photodiode elements are arranged in one direction so that 1 to L pixels can be simultaneously imaged is shown. As shown in FIG. 11A, the data conversion circuit 60 receives the first pixel data, the second pixel data,. Then, the first pixel data, the second pixel data,... The L pixel data, which are simultaneously imaged at different times, are input in order. Here, as shown in FIG. 11B, the data conversion circuit 60 continuously outputs the pixel of interest and a plurality of surrounding pixel data surrounding the pixel of interest for each pixel of interest. For example, the data of k × k (k ≧ 3) pixel regions centered on the pixel of interest are output continuously. Next, the target pixel is shifted to the Lth pixel side, and similarly, each data of k × k pixel regions is continuously output. That is, for the first pixel, each data of a pixel region constituted by the pixel of interest of the first pixel, the front and back surrounding the pixel of interest, and the pixel on the side where the pixel exists is output. When k × k pixel regions centered on the target pixel cannot be selected, the pixel region may be configured with effective pixels. The same applies hereinafter. Next, the pixel of interest is shifted to the Lth pixel side, and each data of a pixel region composed of the pixel of interest of the second pixel, the front and back surrounding the pixel of interest, and the pixel on the side where the pixel exists is output. Similarly, after the third pixel, each data of the pixel region is output while sequentially shifting the target pixel. When the target pixel is shifted to the Lth pixel, the second pixel of the first pixel is set as the target pixel, and the same process is repeated. As described above, the data conversion circuit 60 converts the data output order so that each data of the pixel area surrounding the target pixel and the target pixel is continuously output while shifting the target pixel.

  FIG. 12 is a conceptual diagram illustrating an internal configuration of the white portion determination circuit according to the second embodiment. A threshold value determination circuit 64 and a template matching circuit 66 are arranged in the white portion determination circuit 62 of each pixel. The threshold value determination circuit 64 for the pixel of interest receives each data of the pixel of interest surrounding the pixel of interest and the pixel of interest from the data conversion circuit 60.

  FIG. 13 is a diagram illustrating an example of a pixel region centered on a target pixel according to the second embodiment. In FIG. 13, a pixel region of 5 columns × 5 stages is shown as an example. The threshold determination circuit 64 inputs each data of the pixel area. Then, it is determined whether the pixel value of each obtained data is equal to or greater than a predetermined threshold value. Alternatively, each threshold value for the upper and lower limits may be prepared, and the determination may be made based on whether or not the obtained pixel value of each data falls between the upper and lower threshold values.

  The template matching circuit 66 for the target pixel matches the pixel area using the white portion template.

  FIG. 14 is a diagram illustrating an example of a white part template according to the second embodiment. The white portion template has a shape that does not include a corner portion of a pixel region of k × k as shown in FIG. 14C, or a landscape orientation shown in FIG. 14A, a portrait orientation shown in FIG. 14B. Also good. Then, the template matching circuit 66 determines whether or not the threshold value determination is ok for all pixels that overlap the white portion template. If the threshold value determination is ok for all pixels that overlap with the white part template, an effective flag is defined and output for the target pixel in the pixel region. As described above, the pixel with the valid flag is identified as the white part. Even if the pixel value of the target pixel is within the threshold value range, if the surrounding pixel value is out of the threshold value, it may be affected by the out-of-range pixel, so it is not identified as a white part. The valid flag information and the data of the target pixel are output to the white portion average output level calculation circuit 15.

  In the white portion average output level calculation circuit 15, a pixel output integration circuit 70 and a pixel average value averaging circuit 72 are arranged for each pixel.

  The pixel output integration circuit 70 integrates the pixel values of every N pieces of data with valid flags for each pixel, and divides the integrated value by N to obtain every N pieces of data extracted only from the white part. An average value of pixel values is calculated.

  Further, the pixel average value averaging circuit 44 inputs a plurality of average values for each of N pieces of data obtained by extracting only the white portion, and calculates the average value of the average values. As described above, only the white pixel is identified from the inspection sensor data, and the average value of the average values is calculated for the plurality of identified white pixel data.

  As described above, the white portion average output level calculation circuit 15 calculates an average value of a plurality of pixel values obtained from the position of the white portion among the output data of the sensor subjected to the offset correction and the gain correction. The white portion average output level calculation circuit 15 is an example of an average value calculation circuit. The subsequent steps are the same as those in the first embodiment.

  As described above, in the second embodiment, only the white pixels can be automatically recognized from the inspection sensor data. Then, the gain coefficient can be corrected using the plurality of pixel data of the identified white portion. Therefore, since it is not necessary to stop the inspection, the gain coefficient can be corrected in real time during the inspection.

  It is possible to provide a correction circuit for a change in the output level of the sensor caused by a change in the amount of light or a change in sensor sensitivity, and the fluctuation in the output level of the sensor can be reduced.

  FIG. 15 is a diagram for explaining another optical image acquisition method. In the configuration of FIG. 1, the photodiode array 105 that simultaneously enters the number of pixels of the scan width W (for example, 2048 pixels) is used. However, the present invention is not limited to this, and as shown in FIG. Each time a constant pitch movement is detected by a laser interferometer while scanning at a constant speed in the direction, a laser scanning optical device (not shown) scans the laser beam in the Y direction, detects transmitted light, A technique of acquiring a two-dimensional image for each size area may be used.

  In the above description, what is described as “˜circuit”, “˜unit”, or “˜process” can be configured by a program operable by a computer. Or you may make it implement by not only the program used as software but the combination of hardware and software. Alternatively, a combination with firmware may be used. When configured by a program, the program is recorded on a recording medium such as a magnetic disk device, a magnetic tape device, an FD, or a ROM (Read Only Memory). For example, the table control circuit 114, the expansion circuit 111, the reference circuit 112, the comparison circuit 108, and each circuit in the sensor output correction circuit 140 that constitute the arithmetic control unit may be configured by electrical circuits. You may implement | achieve as software which can be processed by the computer etc. which are arrange | positioned in the control computer 110 or each circuit. Moreover, you may implement | achieve with the combination of an electrical circuit and software.

  The embodiments have been described above with reference to specific examples. However, the present invention is not limited to these specific examples. For example, in each embodiment, transmitted light is used, but reflected light or transmitted light and reflected light may be used simultaneously. In the case of a reflective type using reflected light, light is reflected from a position that is not affected by the surroundings and the pattern occupies the entire target pixel, that is, a position that is completely filled with the pattern. Part. Then, light is transmitted at a position where there is no influence from the surroundings and there is no pattern in the target pixel, so that the black portion is not reflected. Therefore, when a reflection type inspection apparatus is used, the gain coefficient is corrected using the rate of change from the reference value of the average value of the plurality of pixel values obtained from the position where the pattern occupies the whole, and the gain correction circuit 14 Just give feedback.

  Although the reference image is generated from the design data, data of the same pattern captured by a sensor such as a photodiode array may be used. In other words, a die to die inspection or a die to database inspection may be used.

  In addition, although descriptions are omitted for parts and the like that are not directly required for the description of the present invention, such as a device configuration and a control method, a required device configuration and a control method can be appropriately selected and used.

  In addition, all pattern inspection apparatuses, pattern inspection methods, and image alignment methods that include elements of the present invention and that can be appropriately modified by those skilled in the art are included in the scope of the present invention.

DESCRIPTION OF SYMBOLS 10 Offset correction circuit 12 Gain correction circuit 14 White part average output level calculation circuit 16 Gain correction coefficient calculation circuit 100 Pattern inspection apparatus 101 Photomask 102 XYθ table 103 Light source 104 Magnifying optical system 105 Photodiode array 106 Sensor circuit 140 Sensor output correction circuit 150 Optical Image Acquisition Unit 160 Control Circuit

Claims (4)

An offset circuit that illuminates a patterned sample, receives light obtained by transmission or reflection, and outputs output data from a sensor that outputs image data, and performs offset correction of the output data;
A gain correction circuit that performs gain correction by inputting a gain correction coefficient and multiplying the output gain by the input gain correction coefficient;
Of the output data of the sensor that has been subjected to the offset correction and gain correction, if it is obtained by transmission, it is obtained at a position where light is transmitted from the pattern, and if it is obtained by reflection, it is obtained at a position where light is reflected from the pattern. Using the output data of the sensor, an average value calculation circuit for calculating an average value of each pixel value of the output data of the sensor;
A gain correction coefficient calculation circuit that corrects a gain correction coefficient used for the gain correction using a change rate of an average value of each pixel value from a set reference value, and feeds back to the gain correction circuit;
With
The position where light is transmitted from the pattern when obtained by the transmission is a position where the pattern is not present in the target pixel without being affected by the surroundings,
The position where the light is reflected from the pattern when obtained by reflection, Ri position der occupying the whole was a pattern the target pixel at a position which is not affected by the ambient,
Input the output data of the sensor that has been subjected to the offset correction and gain correction, from the input output data, if obtained by transmission, the output data of the sensor acquired at the position where the light is transmitted from the pattern, An identification circuit for identifying the output data of the sensor obtained at a position where light is reflected from the pattern when obtained by reflection;
The identification circuit, for each pixel of interest, if the pixel of interest and a plurality of pixels in the pixel region surrounding the pixel of interest are all equal to or greater than a threshold value, if the pixel of interest of the pixel region is obtained by transmission, As output data of the sensor acquired at a position where light is transmitted from a pattern, if obtained by reflection, it is identified as output data of the sensor acquired at a position where light is reflected from the pattern,
The sensor output data correction device, wherein the average value calculation circuit calculates an average value of each pixel value of the output data of the sensor acquired at a position identified by the identification circuit . The sensor of the sensor output data of claim 1, wherein the by photoelectric conversion is a line sensor or TDI sensor, and converts the light to the image correction device. The identification circuit inputs the output data of the sensor for each predetermined area, and identifies the position by performing a threshold determination process for the input data for each input area and a matching process using a template. The sensor output data correction device according to claim 1 . Illuminating a patterned sample, receiving light obtained by transmission or reflection, inputting output data from a sensor that outputs image data, and performing offset correction of the output data; and
A step of performing gain correction by inputting a gain correction coefficient and multiplying the output data by the input gain correction coefficient;
Among the output data of the sensor subjected to the offset correction and the gain correction, a plurality of data obtained from a position where the pattern does not exist when obtained by transmission, and a position where the pattern occupies the whole when obtained by reflection. A step of calculating an average value of pixel values;
Correcting a gain correction coefficient used for the gain correction using a rate of change of the average value from a set reference value, and feeding back the gain correction coefficient;
With
The position where light is transmitted from the pattern when obtained by the transmission is a position where the pattern is not present in the target pixel without being affected by the surroundings,
The position where the light is reflected from the pattern when obtained by reflection, Ri position der occupying the whole was a pattern the target pixel at a position which is not affected by the ambient,
Input the output data of the sensor that has been subjected to the offset correction and gain correction, from the input output data, if obtained by transmission, the output data of the sensor acquired at the position where the light is transmitted from the pattern, If obtained by reflection, identify the output data of the sensor acquired at the position where light is reflected from the pattern,
When identifying, for each target pixel, if the target pixel and a plurality of pixels in the pixel region surrounding the target pixel are all equal to or greater than the threshold value, As output data of the sensor acquired at a position where light is transmitted from a pattern, if obtained by reflection, it is identified as output data of the sensor acquired at a position where light is reflected from the pattern,
A sensor output data correction method, comprising: calculating an average value of each pixel value of the sensor output data acquired at the identified position .

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