JP5684628B2 - Pattern inspection apparatus and pattern inspection method - Google Patents

Description

  The present invention relates to a pattern inspection apparatus and a pattern inspection method, and for example, relates to a pattern inspection apparatus and method for inspecting a pattern defect of an object serving as a sample by correcting a light amount fluctuation of a laser beam from a light source.

  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. For example, drawing is performed using an electron beam or a laser beam.

  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, it has become an urgent task to develop a pattern 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 the pattern inspection apparatus, the light amount fluctuation caused by the light source or the optical system becomes the gradation fluctuation of the acquired image, which affects the inspection performance. In particular, it adversely affects the CD measurement accuracy. Conventionally, in order to correct a light amount variation, a light amount is measured by a light amount sensor (for example, see Patent Document 1). However, if there is a difference between the response frequency band of the light quantity sensor output and the response frequency band of the sensor output for image acquisition, there is a problem that correction of the light quantity fluctuation is insufficient and a correction error remains. In particular, correction of high-frequency fluctuations tends to be insufficient.

JP 2005-241290 A

  As described above, if there is a difference between the response frequency band of the light quantity sensor output and the response frequency band of the sensor output for image acquisition, there is a problem that the correction of the light quantity variation becomes insufficient. Conventionally, such a point has not been dealt with.

  SUMMARY OF THE INVENTION Accordingly, an object of the present invention is to provide a pattern inspection apparatus and method capable of overcoming the above-described problems and reducing correction errors due to a difference between the response speed of the light quantity sensor output and the response speed of the sensor output for image acquisition. And

The pattern inspection apparatus according to one aspect of the present invention includes:
A light source for generating laser light;
An illumination optical system that illuminates a laser beam onto the inspected sample on which the pattern is formed;
A light amount sensor that is provided between the light source and the sample to be inspected and measures a light amount of laser light by branching a part of the light;
An imaging sensor that receives a laser beam transmitted or reflected by the sample to be inspected and captures an optical image of the pattern;
When the output timing of the imaging sensor is earlier than the output timing of the light quantity sensor, a first time period for temporarily storing output data of the imaging sensor during a time difference period between the output timing of the imaging sensor and the output timing of the light quantity sensor A storage device;
A second storage device that temporarily stores output data of the light amount sensor during a time difference period between the output timing of the image sensor and the output timing of the light amount sensor when the output timing of the light amount sensor is earlier than the output timing of the image sensor. When,
A correction unit that corrects the gradation value of the optical image captured by the imaging sensor using the light amount value output from the light amount sensor at the time when the time difference is shifted;
A comparison unit that inputs a reference image to be compared and compares the optical image with the corrected gradation value and the reference image in units of pixels;
It is provided with.

In addition, a movable stage for placing the sample to be inspected,
A third time difference information indicating a plurality of time differences between the output timing of the imaging sensor and the output timing of the light quantity sensor, obtained by varying at least one of the moving direction and moving speed of the stage, is stored. A storage device;
A selection unit that selects one of a plurality of time differences according to the conditions for imaging;
Further comprising
The correcting unit preferably corrects the gradation value of the optical image captured by the imaging sensor using the light amount value output from the light amount sensor at the time shifted by the selected time difference.

Further, the imaging sensor makes at least one of the moving direction and moving speed of the stage variable, and takes an optical image of the pattern for each condition,
The light quantity sensor measures the light quantity of the laser beam for each condition under the condition that the image sensor takes an image,
It is preferable to further include a time difference calculation unit that calculates a time difference for each condition using the captured optical image and the measured light quantity.

The pattern inspection method of one embodiment of the present invention includes:
Generating laser light from a light source;
Illuminating laser light onto the sample to be inspected on which the pattern is formed;
A step of measuring the amount of laser light before the sample to be inspected is illuminated using a light amount sensor;
A step of receiving an optical image of a pattern by receiving a laser beam transmitted or reflected by a sample to be inspected using an imaging sensor; and
Of the time difference between the output timing of the imaging sensor and the output timing of the light quantity sensor, the data with the earlier output timing out of the optical image data taken by the imaging sensor and the light quantity data measured by the light quantity sensor Temporarily storing in a storage device;
Correcting using the light amount value output from the light amount sensor at the time when the gradation value of the captured optical image is shifted by the time difference;
A step of inputting a reference image to be compared and comparing the optical image with the corrected gradation value and the reference image in units of pixels;
It is provided with.

Also, a plurality of time differences between the output timing of the imaging sensor and the output timing of the light quantity sensor obtained by varying at least one of the moving direction and moving speed of the movable stage on which the sample to be inspected is placed A step of reading a plurality of time difference information from a storage device that stores a plurality of time difference information indicating, and selecting one of the plurality of time differences according to a condition at the time of imaging,
It is preferable that the gradation value of the optical image picked up by the image pickup sensor is corrected by using the light amount value output from the light amount sensor at the time shifted by the selected time difference.

  According to the present invention, the gradation value of a captured optical image can be corrected with the light amount value output from the light amount sensor at the time when the time difference between the output timing of the imaging sensor and the output timing of the light amount sensor is shifted. Therefore, it is possible to eliminate the difference between the output timing of the light sensor output and the output timing of the imaging sensor output. Therefore, more accurate inspection can be performed.

1 is a conceptual diagram showing a configuration of a pattern inspection apparatus in Embodiment 1. FIG. 6 is a diagram for explaining an optical image acquisition procedure according to Embodiment 1. FIG. 5 is a graph showing an example of a difference between a TDI sensor output timing and a light amount sensor output timing in the first embodiment. FIG. 3 is a flowchart showing main steps of a pattern inspection pre-processing method and a pattern inspection method in the first embodiment. FIG. 6 is a conceptual diagram for explaining a change in output timing in the TDI sensor in the first embodiment. 6 is a graph showing an example of a relationship between a gradation variation of the TDI sensor and a time difference in the first embodiment. It is a figure for demonstrating another optical image acquisition method.

Embodiment 1 FIG.
FIG. 1 is a conceptual diagram showing the configuration of the pattern inspection apparatus according to the first embodiment. In FIG. 1, a pattern inspection apparatus 100 that inspects a defect of a sample using a substrate such as a mask as a sample includes an optical image acquisition unit 150 and a control circuit 160. The optical image acquisition unit 150 includes a light source 103, an illumination optical system 170, a half mirror 172, a light amount sensor 144, an XYθ table 102 (stage), an enlargement optical system 104, a time delay integrator (TDI) sensor 105, a sensor circuit 106, a laser measurement. A long system 122 and an autoloader 130 are provided. In the control circuit 160, the control computer 110 serving as a computer transmits a position circuit 107, a comparison circuit 108 serving as an example of a comparison unit, a development circuit 111, a reference circuit 112, and an autoloader control circuit 113 via a bus 120 serving as a data transmission path. , Table control circuit 114, magnetic disk device 109 as an example of a storage device, magnetic tape device 115, flexible disk device (FD) 116, CRT 117, pattern monitor 118, printer 119, buffer storage devices 140 and 142, buffer control The circuit 145, the integration circuit 146, the correction circuit 148, the measurement circuit 180, the time difference calculation circuit 182, and the selection circuit 184 are connected.

  The XYθ table 102 is driven by an X-axis motor, a Y-axis motor, and a θ-axis motor. In FIG. 1, constituent parts necessary for explaining the first embodiment are described. It goes without saying that the pattern inspection apparatus 100 may normally include other necessary configurations.

  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, for example, in the Y direction. Then, the operation of the XYθ table 102 is controlled so that each of the divided inspection stripes is continuously scanned, and an optical image is acquired while moving in the X direction. The TDI sensor 105 continuously inputs images having a scan width W as shown in FIG. 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. Although the forward (FWD) -backward (BWD) method is used here, the present invention is not limited to this, and a forward (FWD) -forward (FWD) method may be used.

  FIG. 3 is a graph showing an example of the difference between the TDI sensor output timing and the light amount sensor output timing in the first embodiment. Here, as an example, the light quantity sensor output timing is later than the TDI output timing, but the present invention is not limited to this, and there may be an opposite case.

  As described above, the light amount signal that should originally correspond to the output of the TDI sensor 105 is output from the light amount sensor 144 with a delay from the output of the TDI sensor 105. As a factor of the delay, for example, an analog delay of the light quantity sensor can be considered. The difference between the time required for the laser light generated from the light source 103 to reach the TDI sensor 105 and the time required for the laser light generated from the light source 103 to reach the light quantity sensor 144 is so short as to be substantially negligible. Therefore, as it is, when correcting the light amount fluctuation, the light amount output from the light amount sensor 144 at the output timing of the TDI sensor 105, that is, here, the amount of light measured before the time point when the TDI sensor 105 was imaged is corrected. Will end up. Therefore, the first embodiment is configured to eliminate a shift in the correspondence between the image captured by the TDI sensor 105 and the light amount measured by the light amount sensor 144 caused by the time difference.

  Here, an example is shown in which the TDI sensor 105 that continuously captures the gradation value of one pixel region by a plurality of stages of light receiving elements and integrates each sensor value is used. However, the present invention is not limited to this. Absent. It may be a sensor that captures the gradation value of one pixel region with a single-stage light receiving element. Even in such a case, the same is true in that a deviation occurs between the imaging sensor output timing and the light amount sensor output timing.

  FIG. 4 is a flowchart showing main steps of the pattern inspection pre-processing method and the pattern inspection method in the first embodiment. 4, first, the pattern inspection pre-processing method in the first embodiment performs a series of steps of a measurement condition setting step (S102), a measurement step (S104), and a time difference calculation step (S106). The pattern inspection method according to the first embodiment includes a selection step (S110), a time difference setting step (S112), a light quantity measurement step (S114), an integration step (S116), a TDI imaging step (S118), A series of steps of a gradation correction step (S120) and a comparison step (S122) are performed.

  The time difference due to the difference between the TDI sensor output timing and the light amount sensor output timing varies depending on the moving speed and moving direction of the XYθ table 102.

  FIG. 5 is a conceptual diagram for explaining a change in output timing in the TDI sensor in the first embodiment. In FIG. 5, the TDI sensor 105 includes a photodiode group 10 arranged two-dimensionally, and transfers charges in the right or left direction in synchronization with the XYθ table 102. The charges are integrated (accumulated addition) while being transferred from the left end to the right end or from the right end to the left end, and finally, the charges are read from the right end or the left end. Therefore, the TDI sensor functions as a line sensor that performs exposure only for the time for transferring charges. The hatched portions 20 and 22 are light shielding portions, and in this region, charges are transferred and read out at the moment when they reach the end. Since no light is incident on the light shielding portion, the time required to pass through this region is directly delayed by the time of the TDI sensor. This delay amount ΔT is determined by the charge transfer period t and the number N of pixels of the light shielding portion, and ΔT = Nt. Since the charge transfer period t is proportional to the reciprocal of the X movement speed v in the XYθ table, it is expressed as Δt = α · N / v (α is a proportional coefficient). Therefore, ΔT depends on the number of pixels of the light shielding portion and the x movement speed v of the XYθ table.

By the way, the light shielding parts 20 and 22 are provided in order not to use the area because the sensor characteristics are generally poor in the vicinity of the reading part, and a metal diaphragm or the like is used. For this purpose, this diaphragm does not need to be placed with high accuracy with respect to the TDI sensor. Therefore, the width of the light-shielded region is often different between the right side 20 and the left side 22. Accordingly, ΔT varies depending on the direction in which charges are transferred, that is, the direction in which the XYθ table is moved. In summary, the delay amount ΔT depends on both the X movement speed v and the movement direction of the XYθ table.

  Therefore, in the first embodiment, as the pattern inspection preprocessing method, the moving speed and moving direction of the XYθ table 102 are made variable, a plurality of conditions are set by a plurality of combinations, and the TDI sensor output and the light quantity sensor are set for each condition. Find the output time difference. In order to obtain such a time difference, a photomask serving as a sample on which a test pattern is formed under each condition is placed on the XYθ table 102, and the test pattern is imaged. Since the purpose is to check the gradation variation, the test pattern may be a blank mask without a pattern.

  As the measurement condition setting step (S102), the measurement circuit 180 sets a measurement condition consisting of a set of moving speed and moving direction of the XYθ table 102.

  As a measurement step (S104), the measurement circuit 180 places a photomask serving as a sample on which a test pattern is formed on the XYθ table 102, and images the test pattern with the TDI sensor 105. At that time, a part of the laser light from the light source 103 is branched by the half mirror 172 in front of the photomask, and the light amount is measured by the light amount sensor 144. The measurement result of the light quantity sensor 144 is continuously recorded for a predetermined range of time.

  As the time difference calculation step (S106), the time difference calculation circuit 182 corrects the gradation value output from the TDI sensor 105 at a certain time with the light amount output from the light amount sensor 144 at a plurality of times before and after that time. Specifically, first, in order to simulate the integration effect of the light quantity in the TDI sensor 105, the integration circuit 146 integrates (accumulates) a period corresponding to the accumulation time of the TDI sensor 105 with respect to the signal output from the light quantity sensor 144. Add). Then, the gradation value is corrected by multiplying the gradation value output from the TDI sensor 105 by the inverse number of the cumulatively added light quantity. The gradation value output from the TDI sensor 105 is corrected after giving an intentional time difference to the signal integrated by the integration circuit 146 by shifting the timing. At this time, the time difference given intentionally is changed at a plurality of points over a certain range, and a plurality of corrected gradation value fluctuation amounts are calculated.

  FIG. 6 is a graph showing an example of the relationship between the gradation fluctuation amount of the corrected TDI sensor and the time difference intentionally given to the light amount sensor signal in the first embodiment. The white circle plot indicates the corrected gradation variation output from the TDI sensor 105 when the test pattern is imaged under a certain condition (condition 1). When an intentional time difference is given so as to cancel out the time difference between the TDI sensor and the light quantity sensor, the gradation fluctuation amount after correction is minimized, and here, t1 can be regarded as a time difference to be given for correction. it can. Therefore, the time difference calculation circuit 182 calculates the minimum value of the graph for each condition.

  When the time difference to be given under one condition is calculated, the process returns to S102, and at least one of the moving direction and moving speed of the XYθ table 102 is made variable, and the time difference calculating process from the measurement condition setting process (S102). The steps up to (S106) are repeated. As described above, the TDI sensor 105 (imaging sensor) changes at least one of the moving direction and moving speed of the XYθ table 102 (stage) and picks up an optical image of the pattern for each condition. And the light quantity sensor 144 measures the light quantity of a laser beam for every condition on the conditions which the TDI sensor 105 images. Then, the time difference calculation circuit 182 (time difference calculation unit) calculates the time difference for each condition using the captured optical image and the measured light quantity. For example, in the example of FIG. 6, the time difference t1 is the minimum value under the condition 1, and the time difference t2 is the minimum value under the condition 2. The time difference information obtained for each condition is stored in the magnetic disk device 109 in association with the condition. In other words, a plurality of time differences indicating a plurality of time differences between the output timing of the TDI sensor 105 and the output timing of the light quantity sensor 144 obtained by varying at least one of the moving direction and the moving speed of the XYθ table 102. Information is stored in the magnetic disk device 109 (second storage device). As described above, correlation data between the condition and the time difference between the output timings is accumulated. After the pretreatment is completed, a defect inspection of the pattern formed on the photomask 101 that is an actual inspection sample (inspection target) is performed. This pre-processing does not need to be performed for each inspection, but is performed when the apparatus is started up, and time difference information for each condition may be recorded in the magnetic disk device 109.

  After the above-described pretreatment and before the start of inspection, first, the photomask 101 to be inspected with a pattern formed by the autoloader 130 controlled by the autoloader control circuit 113 is rotated horizontally and rotated by motors of XYθ axes. It is loaded on an XYθ table 102 provided so as to be movable in the direction, and is placed on the XYθ table 102. Also, design pattern information (design pattern data) used when forming the pattern of the photomask 101 is input to the pattern inspection apparatus 100 from the outside of the apparatus and stored in the magnetic disk device 109 as an example of a storage device (storage unit). The

  As the selection step (S110), the selection circuit 184 reads a plurality of time difference information stored in the magnetic disk device 109, and selects the TDI according to the conditions at the time of imaging in the current examination from the plurality of time difference information. Time difference information indicating one of a plurality of time differences between the output timing of the sensor 105 (imaging sensor) and the output timing of the light amount sensor 144 is selected. The selection circuit 184 is an example of a selection unit.

  As the time difference setting step (S112), the selection circuit 184 outputs the selected time difference information to the buffer control circuit 145, and the buffer control circuit 145 sets the time difference indicated by the input time difference information and performs buffering based on the time difference. The storage devices 140 and 142 are controlled. Specifically, for example, when the output timing of the light amount sensor 144 is later than the output timing of the TDI sensor 105 by the time difference t1, the information from the TDI sensor 105 is temporarily stored in the storage device 140 for the time difference t1. And then set to output. On the other hand, it sets so that the information input into the memory | storage device 142 which memorize | stores the information from the light quantity sensor 144 temporarily may be output immediately. In other words, the accumulation time is set to zero. Conversely, for example, when the output timing of the TDI sensor 105 is later than the output timing of the light quantity sensor 144 by the time difference t2, the information from the light quantity sensor 144 is temporarily stored in the storage device 142 for the time difference t2, Set to output after that. On the other hand, the information input to the storage device 140 that temporarily stores information from the TDI sensor 105 is set to be output immediately. In other words, the accumulation time is set to zero. As described above, the respective buffer times are set in the storage devices 140 and 142. Imaging at the time of inspection is performed for each inspection stripe. Further, as described above, since the buffer time (time difference information) differs depending on the moving direction of the XYθ table 102, the selection process (S110) and the time difference setting process (S112) described above are performed for each inspection stripe. Then, the inspection is started.

  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. As these X motor, Y motor, and θ motor, for example, a linear motor or a step motor can be used. The movement position of the XYθ table 102 is measured by the laser length measurement system 122 and supplied to the position circuit 107. The photomask 101 on the XYθ table 102 is automatically conveyed from the autoloader 130 driven by the autoloader control circuit 113, and is automatically discharged after the inspection is completed. The magnifying optical system 104 is driven by, for example, a piezoelectric conversion element, and the image is focused on the photodiode array 105.

  Laser light is generated from the light source 103 arranged above the XYθ table 102. The illumination optical system 170 illuminates the photomask 101 on which the pattern is formed with laser light.

  As the light amount measurement step (S114), the light amount sensor 144 measures the light amount of the laser light before the photomask 101 is illuminated. Specifically, a part of the laser light before illuminating the photomask 101 is branched by the half mirror 172 and is incident on the light quantity sensor 144. Then, the light amount sensor 144 measures the amount of incident light. The measured light amount data is output to the integrating circuit 146.

  In the integration step (S116), the integration circuit 146 integrates (accumulates and adds) the amount of light for the accumulation time from the time when the first light receiving element 10 receives light to the time when the last light receiving element 10 receives light in the TDI sensor 105. ) Then, the cumulatively added cumulative light quantity is output to the storage device 142 serving as a buffer. For example, when the output timing of the light amount sensor 144 is later than the output timing of the TDI sensor 105 by the time difference t1, the storage device 142 immediately outputs the input accumulated time data to the correction circuit 180. On the contrary, for example, when the output timing of the TDI sensor 105 is later than the output timing of the light amount sensor 144 by the time difference t2, the storage device 142 accumulates the input accumulated time data for the period of the time difference t2, and then the correction circuit. Output to 180.

  In the TDI imaging step (S118), the TDI sensor 105 receives the laser beam transmitted or reflected by the photomask 101 and captures an optical image of the pattern. In the example of FIG. 1, since it is a transmission type inspection apparatus, the TDI sensor 105 receives the laser light transmitted through the photomask 101 and captures an optical image of the pattern. In the case of a reflective inspection apparatus, the TDI sensor 105 may receive a laser beam reflected from the photomask 101 and capture an optical image of the pattern. Specifically, light that has passed through the photomask 101 due to illumination forms an optical image on the TDI sensor 105 via the magnifying optical system 104 and enters. The pattern image formed on the TDI sensor 105 is photoelectrically converted by the TDI sensor 105, and further A / D (analog-digital) converted by the sensor circuit 106. As described above, the optical image acquisition unit 150 acquires optical image data (stripe data) for each inspection stripe of the sample to be inspected. The captured optical image data is output to the storage device 140 serving as a buffer. For example, when the output timing of the light amount sensor 144 is later than the output timing of the TDI sensor 105 by the time difference t1, the storage device 140 accumulates the input optical image data for the time difference t2, and then outputs it to the correction circuit 180. To do. Conversely, for example, when the output timing of the TDI sensor 105 is later than the output timing of the light amount sensor 144 by the time difference t2, the storage device 140 immediately outputs the input optical image data to the correction circuit 180.

  As described above, the storage devices 140 and 142 are measured by the light amount sensor 144 and the optical image data captured by the TDI sensor 105 during the time difference between the output timing of the TDI sensor 105 and the output timing of the light amount sensor 144. The data with the earlier output timing out of the light quantity (accumulated light quantity) data is temporarily stored and then output. On the other hand, the data with the later output timing is output immediately after input. As described above, the optical image data and the accumulated light amount data can be input to the correction circuit 180 in a state where the output timing is matched.

  Here, the data with the earlier output timing is stored after being stored for the period of time difference, but is not limited thereto. The data with the earlier output timing may be output after being stored for a time t0 further from the time difference period. In such a case, the data with the later output timing may not be output immediately after input, but may be output after time t0 further extended from the time difference period.

  As the gradation correction step (S120), the correction circuit 148 corrects the gradation value of the optical image picked up by the TDI sensor 105 using the light amount value output from the light amount sensor 144 at the time shifted by the time difference. In other words, the correction circuit 148 corrects the gradation value of the optical image captured by the TDI sensor 105 using the light amount value output from the light amount sensor 144 at the time shifted by the selected time difference. The correction circuit 148 is an example of a correction unit. Specifically, the correction circuit 148 corrects the gradation value by, for example, multiplying the gradation value of the optical image output from the TDI sensor 105 by the reciprocal of the cumulatively added light amount.

  The measurement data (optical image data) of each inspection stripe corrected by the correction circuit 148 is sequentially compared with data indicating the position of the photomask 101 on the XYθ table 102 output from the position circuit 107 for each inspection stripe. It is output to 108. The measurement data is, for example, 8-bit unsigned data for each pixel, and the brightness gradation of each pixel is expressed by, for example, 0 to 255. These light source 103, illumination optical system 170, magnifying optical system 104, TDI sensor 105, and sensor circuit 106 constitute a high-magnification inspection optical system.

  The development circuit 111 (an example of a reference image creation unit) reads design pattern data from the magnetic disk device 109 through the control computer 110 for each predetermined region, and the read design pattern data of the photomask 101 is binary or multiple. Conversion (development processing) into design image data (reference image data) which is image data of values. The predetermined region may be an image region (area) corresponding to the optical image to be compared.

  The figure constituting the pattern defined in the design pattern data is a basic figure such as a rectangle or a triangle. The design pattern data includes, for example, coordinates (x, y) at the reference position of the figure, side length, rectangle Stored is graphic data that defines the shape, size, position, etc. of each pattern graphic with information such as a graphic code that is an identifier for distinguishing graphic types such as triangles and triangles.

When such graphic data is input to the expansion circuit 111, it expands to data for each graphic, and interprets graphic codes, graphic dimensions, etc., indicating the graphic shape of the graphic data. Then, binary or multivalued image data is developed as a pattern arranged in a grid having a grid with a predetermined quantization size as a unit. The developed image data (developed image data) is stored in a pattern memory (not shown) in the circuit or in the magnetic disk device 109. In other words, the design pattern data is read and the occupancy rate of the figure in the design pattern is calculated for each cell formed by virtually dividing the inspection area as a cell with a predetermined dimension as a unit, and n-bit occupancy data Is output to a pattern memory (not shown) or a magnetic disk device 109. For example, it is preferable to set one square as one pixel. If a resolution of 1/2 ⁸ (= 1/256) is given to one pixel, 1/256 small areas are allocated by the figure area arranged in the pixel, and the occupation ratio in the pixel is set. Calculate. The developed image data is stored in the pattern memory or the magnetic disk device 109 as area-unit image data defined by 8-bit occupancy data for each pixel.

  The reference circuit 112 performs data processing (image processing) on the developed image data, and performs appropriate filter processing. The optical image data (measurement data) is in a state in which the filter is acted on due to the resolution characteristics of the magnifying optical system 104, the aperture effect of the TDI sensor 105, or the like, in other words, in an analog state that continuously changes. For this reason, the developed image data, which is the image data on the design side of which the image intensity (shading value) is a digital value, can also be matched to the measurement data by performing a filtering process according to a predetermined model. For example, filter processing such as resizing processing for performing enlargement or reduction processing, corner rounding processing, or blurring processing is performed. In this way, a reference image to be compared with the optical image is created. The predetermined region may be an image region (area) corresponding to the optical image to be compared. The created reference image data is output to the comparison circuit 108.

  As a comparison step (S122), the comparison circuit 108 inputs a reference image to be compared and compares the optical image with the corrected gradation value with the reference image in units of pixels. Specifically, it operates as follows. In the comparison circuit 108 (comparison unit), the optical image data for each stripe is read out, and the optical image data is cut out so that the optical image data becomes an image having the same size as the reference data. Then, the comparison circuit 108 compares the corresponding optical image data with the reference data for each pixel under a predetermined determination condition. Such an inspection technique is a die-to-database inspection. Then, the comparison result is output. The comparison result may be output from the magnetic disk device 109, the magnetic tape device 115, the flexible disk device (FD) 116, the CRT 117, the pattern monitor 118, or the printer 119.

  Alternatively, the die-to-die inspection may be performed using the photomask 101 in which a plurality of pattern regions (inspected regions) drawn with the same design pattern are formed. In such a case, for example, the whole of the two pattern regions is virtually divided into a plurality of inspection stripes shown in FIG. Then, the optical image acquisition unit 150 acquires optical image data (measurement data) for each inspection stripe. Therefore, the measurement data of one inspection stripe includes both images of the two pattern areas. Then, the die-to-die inspection may be performed using one image of the two regions as an inspection target image and the other as a reference image.

  As described above, according to the first embodiment, the gradation value of the captured optical image is output from the light amount sensor 144 at a time when the time difference between the output timing of the TDI sensor 105 and the output timing of the light amount sensor 144 is shifted. It can be corrected with the light intensity value. Therefore, the difference between the output timing of the light quantity sensor output and the output timing of the TDI sensor output can be eliminated. Therefore, more accurate inspection can be performed.

  FIG. 7 is a diagram for explaining another optical image acquisition method. In the configuration of FIG. 1 and the like, the TDI sensor 105 that simultaneously enters the number of pixels of the scan width W is used. However, the present invention is not limited to this, and as shown in FIG. 7, the XYθ table 102 is moved at a constant speed in the X direction. Each time a movement with a constant pitch is detected by the laser interferometer, the laser beam is scanned in the Y direction by a laser scanning optical device (not shown) in the Y direction, and transmitted light or reflected light is detected to a predetermined size. A method of acquiring a two-dimensional image for each area may be used.

  In the above description, what is described as “to part”, “to circuit”, or “to process” can be configured by a computer-operable program. 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 the magnetic disk device 109, the magnetic tape device 115, the FD 116, or a ROM (Read Only Memory). For example, position circuit 107, comparison circuit 108, expansion circuit 111, reference circuit 112, autoloader control circuit 113, table control circuit 114, buffer control circuit 145, integration circuit 146, correction circuit 148, measurement circuit 180, time difference calculation circuit 182, The selection circuit 184 and the like may be configured by an electric circuit, or may be realized as software that can be processed by the control computer 110. 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 the embodiment, a transmissive optical system using transmitted light is used, but a configuration in which reflected light or transmitted light and reflected light are used simultaneously may be employed.

  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 or pattern inspection methods that include the 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.

  Further, the defect inspection method for blanks or the defect inspection method for blanks of a light exposure mask or EUV exposure mask for semiconductor manufacturing is also included in the scope of the present invention because the effect of light quantity correction can be expected.

DESCRIPTION OF SYMBOLS 10 Light receiving element 20, 22 Light-shielding part 100 Pattern inspection apparatus 101 Photomask 102 XY (theta) table 103 Light source 104 Magnifying optical system 105 TDI sensor 106 Sensor circuit 107 Position circuit 108 Comparison circuit 109 Magnetic disk apparatus 110 Control computer 112 Design image creation circuit 115 Magnetic Tape device 120 Bus 140, 142 Storage device 144 Light amount sensor 145 Buffer control circuit 146 Integration circuit 148 Correction circuit 150 Optical image acquisition unit 160 Control circuit 170 Illumination optical system 172 Half mirror 180 Measurement circuit 182 Time difference calculation circuit 184 Selection circuit

Claims (3)

A light source for generating laser light;
An illumination optical system that illuminates the laser beam onto the inspection sample on which a pattern is formed;
A light amount sensor that is provided between the light source and the sample to be inspected and measures a light amount of the laser beam by branching a part of the light;
An imaging sensor that receives a laser beam transmitted or reflected by the sample to be inspected and captures an optical image of the pattern;
When the output timing of the imaging sensor is earlier than the output timing of the light quantity sensor, the output data of the imaging sensor is temporarily stored for a time difference period between the output timing of the imaging sensor and the output timing of the light quantity sensor. A first storage device;
When the output timing of the light sensor is earlier than the output timing of the imaging sensor, the output data of the light sensor is temporarily stored for the time difference between the output timing of the imaging sensor and the output timing of the light sensor. A second storage device;
A correction unit that corrects the gradation value of the optical image captured by the imaging sensor using the light amount value output from the light amount sensor at the time when the time difference is shifted;
A comparison unit that inputs a reference image to be compared and compares the optical image with the corrected gradation value and the reference image in units of pixels;
A movable stage for placing the sample to be inspected;
A plurality of pieces of time difference information indicating a plurality of time differences between the output timing of the imaging sensor and the output timing of the light quantity sensor, which are obtained by changing at least one of the moving direction and moving speed of the stage, are stored. A third storage device;
A selection unit that selects one of the plurality of time differences according to a condition at the time of imaging;
Equipped with a,
The correction unit corrects a gradation value of an optical image captured by the imaging sensor using a light amount value output from the light amount sensor at a time shifted by a selected time difference. . The imaging sensor makes at least one condition of the moving direction and moving speed of the stage variable, and takes an optical image of the pattern for each condition,
The light amount sensor measures the light amount of the laser light for each condition under the condition that the imaging sensor images.
By using the amount of light measured captured optical image, pattern inspection apparatus according to claim 1, further comprising a time difference calculating section for calculating the time difference for each condition. Generating laser light from a light source;
Illuminating the laser beam onto the inspection sample on which a pattern is formed;
Measuring a light amount of the laser light before the sample to be inspected is illuminated using a light amount sensor;
A step of receiving an optical image of the pattern by receiving a laser beam transmitted or reflected by the inspection sample using an imaging sensor;
The output timing of the time difference between the output timing of the imaging sensor and the output timing of the light quantity sensor is early among the optical image data taken by the imaging sensor and the light quantity data measured by the light quantity sensor. Temporarily storing the other data in a storage device;
Correcting using the light amount value output from the light amount sensor at the time when the gradation value of the captured optical image is shifted by the time difference;
A step of inputting a reference image to be compared and comparing the optical image with the corrected gradation value and the reference image in units of pixels;
A plurality of output timings of the imaging sensor and output timing of the light quantity sensor, obtained by varying at least one of a moving direction and a moving speed of a movable stage on which the sample to be inspected is placed Reading a plurality of time difference information from a storage device that stores a plurality of time difference information indicating a time difference, and selecting one of the plurality of time differences according to a condition at the time of imaging;
Equipped with a,
A pattern inspection method , wherein a gradation value of an optical image picked up by the image sensor is corrected using a light amount value output from the light amount sensor at a time shifted by a selected time difference .

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