JP7703426B2 - Mask inspection apparatus and mask inspection method - Google Patents

Description

The present invention relates to a mask inspection apparatus and a mask inspection method. For example, the present invention relates to an inspection apparatus that inspects a pattern on a mask substrate for defects.

In recent years, as large-scale integrated circuits (LSIs) have become more highly integrated and have larger capacities, the circuit line width required for semiconductor elements has become increasingly narrow. These semiconductor elements are manufactured by forming circuits by exposing and transferring a pattern onto a wafer using a reduced projection exposure device known as a stepper, using an original pattern (also called a mask or reticle, hereafter collectively referred to as a mask) on which a circuit pattern is formed.

And improving yields is essential for the manufacture of LSIs, which incur huge manufacturing costs. One of the major factors that reduce yields is pattern defects, such as shape defects and/or dimensional defects, in the patterns of masks used when exposing and transferring ultra-fine patterns onto semiconductor wafers using photolithography technology. In recent years, as the dimensions of LSI patterns formed on semiconductor wafers become finer, the dimensions that must be detected as pattern defects have become extremely small. For this reason, there is a need for high-precision pattern inspection devices that inspect defects in transfer masks used in LSI manufacturing.

Inspection techniques include, for example, "die-to-die inspection," which compares optical image data captured of the same pattern in different locations on the same mask, and "die-to-database inspection," which converts pattern-designed CAD data into a device input format for input by a drawing device when drawing the pattern on a mask, inputs the drawing data (design data) into an inspection device, generates a reference image based on this, and compares it with an optical image that serves as measurement data captured by capturing the pattern.

Here, the amount of light of the laser light, which is the inspection light for imaging the pattern on the mask, changes over time. Conventionally, the change in the amount of light over time was measured by branching a part of the inspection light in the illumination system, collecting it with a lens, and collecting the entire light beam and measuring the amount of light of the entire light beam with a sensor. A method was considered in which the pixel value of the image was corrected using the change in the amount of light of the entire measured light beam (see, for example, Patent Document 1). However, the amount of light is not unique throughout the entire illumination field, but is distributed. Such changes in the unevenness of the illumination distribution become an error factor in the captured image. With this measurement method, it was difficult to monitor the change in the unevenness of the distribution of the illumination field at the mask conjugate position. Therefore, even if the amount of light by the entire light beam is measured, there was a problem that the change according to the position of the light amount distribution could not be determined. As a method of light amount correction, a method of measuring the amount of light in a part of the image sensor area has been considered, but it is difficult to follow the change in the unevenness of the illumination light distribution, and another method is required.

JP 2006-250944 A

Therefore, an embodiment of the present invention provides an inspection device and method capable of measuring changes in unevenness in the distribution of illumination light.

A mask inspection apparatus according to one aspect of the present invention includes:
a beam splitter for splitting the inspection light;
a time delay integration (TDI) sensor that captures an image of a mask substrate formed with a pattern by irradiating a first branched light of the inspection light onto the mask substrate and outputs image data;
a line sensor that receives a second branched light of the inspection light and measures a time change in light amount distribution in a direction perpendicular to the accumulation direction of the TDI sensor;
a correction unit that corrects image data output from the TDI sensor according to a position of the light quantity distribution using a value of the light quantity distribution that changes over time;
a comparison unit for comparing an inspection image using the corrected image data with a predetermined image;
The present invention is characterized by comprising:

It is also preferable that the correction unit corrects the image data at the target position using the value of the position of the light intensity distribution that corresponds to the target position of the image data when converted into a mask surface value.

It is also preferable that the correction unit corrects the image data of the target pixel using the value of the light intensity distribution measured during the time period when the image of the target pixel on the mask substrate is captured by the TDI sensor.

It is also preferable that the inspection light be illuminated using Kohler illumination.

The correction unit preferably corrects the image data of the target pixel using a moving average value of each value of the light intensity distribution measured during the time period when the image of the target pixel on the mask substrate is captured by the TDI sensor.

A mask inspection method according to one aspect of the present invention includes:
splitting the inspection light;
capturing an image of a mask substrate on which a pattern is formed by irradiating a first branched light of the inspection light onto the mask substrate using a time delay integration (TDI) sensor, and outputting image data;
receiving a second branched light of the inspection light using a line sensor and measuring a time change in light amount distribution in a direction perpendicular to the accumulation direction of the TDI sensor;
correcting image data output from the TDI sensor according to a position of the light quantity distribution using a value of the light quantity distribution that changes over time;
a step of comparing an inspection image using the corrected image data with a predetermined image and outputting the result;
The present invention is characterized by comprising:

According to an embodiment of the present invention, it is possible to measure changes in the unevenness of the illumination light distribution. Therefore, it is possible to correct changes according to the position of the unevenness of the distribution. As a result, it is possible to improve the reproducibility of the device.

1 is a configuration diagram showing a configuration of a pattern inspection device according to a first embodiment; FIG. 2 is a conceptual diagram for explaining an inspection area in the first embodiment. 4A to 4C are diagrams for explaining changes over time in light quantity distribution in the first embodiment. 5A to 5C are diagrams for explaining a method for measuring unevenness in illumination distribution in the first embodiment. 11 is a diagram for explaining light quantity measurement in a comparative example of the first embodiment. FIG. 4A to 4C are diagrams for explaining light quantity measurement in the first embodiment. FIG. 2 is a flowchart showing main steps of the inspection method according to the first embodiment. FIG. 11 is a diagram for explaining a correction method in the first embodiment. 5A to 5C are diagrams for explaining the relationship between magnification and image size at each position in the first embodiment. 10A to 10C are diagrams for explaining the relationship between each position of the light amount distribution and the position of the image of the TDI sensor in the first embodiment. FIG. 2 is a diagram for explaining a filter process in the first embodiment. 4 is a diagram showing an example of an internal configuration of a comparison circuit according to the first embodiment;

Embodiment 1.
Fig. 1 is a configuration diagram showing the configuration of a pattern inspection device in embodiment 1. In Fig. 1, an inspection device 100 that inspects pattern defects formed on a substrate 101 (an example of a substrate to be inspected) includes an optical image acquisition mechanism 150 and a control system circuit 160 (a control unit).

The optical image acquisition mechanism 150 includes a light source 103 that generates laser light, a Kohler illumination optical system 300, a relay lens 31, a beam splitter 32, a transmitted illumination optical system 170, a reflected illumination optical system 270, an XYθ table 102, an objective lens 104, a beam splitter 176, a mirror 177, an imaging optical system 178, an imaging optical system 278, an image sensor 105, a sensor circuit 106, a correction circuit 117, a stripe pattern memory 123, an image sensor 205, a sensor circuit 206, a correction circuit 217, a stripe pattern memory 223, a beam splitter 190, a cylinder lens 192, a line sensor 194, a memory 196, a beam splitter 290, a cylinder lens 292, a line sensor 294, and a memory 296.

The transmitted illumination optical system 170 is composed of one or more lenses and/or one or more mirrors. In the example of FIG. 1, the transmitted illumination optical system 170 has mirror 134, mirror 138, and lens 171.

The reflective illumination optical system 270 is composed of one or more lenses and/or one or more mirrors. In the example of FIG. 1, the reflective illumination optical system 270 has a lens 271.

A substrate 101 transported from an autoloader (not shown) is placed on the XYθ table 102. The substrate 101 includes, for example, a photomask for exposure that transfers a pattern onto a semiconductor substrate such as a wafer. In addition, this photomask has a plurality of geometric patterns formed thereon to be inspected. The substrate 101 is placed on the XYθ table 102 with, for example, the pattern-forming surface facing downwards.

For example, it is preferable to use a TDI (time delay integration) sensor as the imaging sensor 105, 205. A TDI sensor has multiple photosensor elements arranged two-dimensionally. When capturing an image, a predetermined image accumulation time (sometimes called a scan time; the same applies below) is set for each photosensor element. In a TDI sensor, the output of multiple photosensor elements lined up in the scan direction is integrated and output. Multiple photosensor elements lined up in the scan direction capture the same pixel while shifting the time in response to the movement of the XYθ table 102.

The beam splitter 190 is disposed within the transmitted illumination optical system 170. The line sensor 194 is disposed at a position conjugate with the pattern-forming surface of the substrate 101. The beam splitter 290 is disposed within the reflected illumination optical system 270. The line sensor 294 is disposed at a position conjugate with the pattern-forming surface of the substrate 101.

The line sensor 194, 294 has a number of photosensor elements arranged in a direction perpendicular to the scanning direction (e.g., the Y direction). The number of photosensor elements of the line sensor 194, 294 may be the same as or different from the number of photosensor elements arranged in a direction perpendicular to the scanning direction (e.g., the Y direction) of the image sensor 105, 205.

The Kohler illumination optical system 300 includes, for example, a beam expander 302, a rotating phase plate 306, a splitting lens 304, a collimator lens 308, and an illumination slit 310.

In the control system circuit 160, a control computer 110 that controls the entire inspection device 100 is connected to a magnetic disk device 109, a memory 111, a position circuit 107, a comparison circuit 108, a reference image creation circuit 112, and a table control circuit 114 via a bus 120.

The correction circuit 117 is connected to the stripe pattern memory 123, and the correction circuit 217 is connected to the stripe pattern memory 223. The stripe pattern memories 123 and 223 are connected to the comparison circuit 108. It is also preferable that the correction circuit 117 has its function implemented in the sensor circuit 106. Similarly, it is also preferable that the correction circuit 217 has its function implemented in the sensor circuit 206.

The output of line sensor 194 is connected to memory 196, and the output of line sensor 294 is connected to memory 296. Memory 196 is connected to correction circuit 117. Memory 296 is connected to correction circuit 217.

The XYθ table 102 is driven by a driving mechanism 115. The driving mechanism 115 has, for example, an X-axis motor, a Y-axis motor, and a θ-axis motor, and the XYθ table 102 is driven by the X-axis motor, the Y-axis motor, and the θ-axis motor. The XYθ table 102 is an example of a stage. The reference image creation circuit 112 is connected to the comparison circuit 108.

The X-axis motor, Y-axis motor, and θ-axis motor can be, for example, a linear motor. The XYθ table 102 can be moved horizontally and rotationally by the motors of the XYθ axes. The XYθ table 102 is adjusted to the focal position (optical axis direction: Z-axis direction) between the pattern formation surface of the substrate 101 and the image sensors 105, 205 under the control of the control computer 110. The movement position of the substrate 101 placed on the XYθ table 102 is measured by a laser length measurement system (not shown) and supplied to the position circuit 107.

The series of "circuits" such as the position circuit 107, the comparison circuit 108, the reference image creation circuit 112, and the table control circuit 114 have a processing circuit. Such processing circuits include electric circuits, computers, processors, circuit boards, quantum circuits, or semiconductor devices. Alternatively, different processing circuits (separate processing circuits) may be used. For example, the series of "circuits" such as the comparison circuit 108, the reference image creation circuit 112, and the table control circuit 114 may be configured and executed by the control computer 110. Input data or calculated results required for the comparison circuit 108, the reference image creation circuit 112, and the table control circuit 114 are stored in a memory (not shown) in each circuit or in the memory 111. Input data or calculated results required for the control computer 110 are stored in a memory (not shown) in the control computer 110 or in the memory 111. The program for executing the computer or the processor may be recorded on a recording medium such as the magnetic disk device 109.

In the inspection device 100, a transmission inspection optical system with a high magnification M1 is configured by the light source 103, the Kohler illumination optical system 300, the relay lens 31, the beam splitter 32, the transmission illumination optical system 170, the objective lens 104, the beam splitter 176, the mirror 177, the imaging optical system 178, the image sensor 105, the sensor circuit 106, and the correction circuit 117. The inspection optical system has a magnification M1 of, for example, 200 to 300 times.

Similarly, in the inspection device 100, a reflection inspection optical system with a high magnification M1 is configured by the light source 103, the Kohler illumination optical system 300, the relay lens 31, the beam splitter 32, the reflection illumination optical system 270, the beam splitter 176, the objective lens 104, the imaging optical system 278, the image sensor 205, the sensor circuit 206, and the correction circuit 217. The inspection optical system has a magnification M1 of, for example, 200 to 300 times.

Drawing data (design data) that is the basis for forming a pattern on the inspected substrate 101 is input from outside the inspection device 100 and stored in the magnetic disk device 109. The drawing data defines multiple graphic patterns, and each graphic pattern is usually composed of a combination of multiple element graphics. However, a graphic pattern composed of a single graphic may also exist. On the inspected substrate 101, a corresponding pattern is formed based on each of the graphic patterns defined in the drawing data.

Here, FIG. 1 shows the components necessary for explaining the first embodiment. It goes without saying that the inspection device 100 may also include other components that are normally required.

The light source 103 generates, as the inspection illumination light, a laser light (e.g., DUV light) (an example of ultraviolet light) with a wavelength of, for example, about 190 to 200 nm. By making the laser light 301 emitted from the light source 103 incident on the Kohler illumination optical system 300, inspection light that can ideally illuminate a surface uniformly is generated. Specifically, it operates as follows. The laser light 301 emitted from the light source 103 is expanded by the beam expander 302, and spatial coherency is reduced by passing it through the rotating phase plate 306. The light that passes through the rotating phase plate 306 generates a surface light source by the splitting lens 304. After that, the Fourier plane of the surface light source is generated by the collimator lens 308, and the illumination slit 310 is placed at the position of this Fourier plane.

The inspection light that passes through the illumination slit 310 is projected onto the beam splitter 32 by the relay lens 31. The beam splitter 32 splits the inspection light into light for transmitted illumination and light for reflected illumination. If a reflected illumination inspection is not performed, the light that branches to the reflected illumination optical system 270 can be blocked. Conversely, if a transmitted illumination inspection is not performed, the light that branches to the transmitted illumination optical system 170 can be blocked. In FIG. 1, the inspection light and image for transmitted illumination separated by the beam splitter 32 are shown by dotted lines. In FIG. 1, the inspection light and image for reflected illumination separated by the beam splitter 32 are shown by solid lines.

In the transmission inspection, the inspection light for the transmission inspection separated by the beam splitter 32 is reflected by the mirror 134 and enters the beam splitter 190. The inspection light for the transmission inspection is then split into two optical paths by the beam splitter 190. For example, 0.1 to 10% (for example, 1%) of the inspection light for the transmission inspection is separated as light for correction toward the cylindrical lens 192 side. The remaining part of the inspection light becomes the transmitted illumination light. The transmitted illumination light (first light) of the inspection light split by the beam splitter 190 is reflected by the mirror 138 and illuminates the substrate 101 by the lens 171. The transmitted light that has passed through the substrate 101 passes through the beam splitter 176 via the objective lens 104. It is then reflected by the mirror 177 and is imaged by the imaging optical system 178 as an optical image (transmitted image) on the imaging sensor 105 and enters it. In this way, the imaging sensor 105 captures the transmitted image.

The image of the pattern formed on the image sensor 105 is photoelectrically converted by each photosensor element of the image sensor 105, and the integrated value of the multiple photosensor elements arranged in the scanning direction is output to the sensor circuit 106. The sensor circuit 106 then performs A/D (analog-to-digital) conversion.

Or/and in the reflection inspection, the inspection light for the reflection inspection separated by the beam splitter 32 enters the beam splitter 290. Then, the inspection light for the reflection inspection is split into two optical paths by the beam splitter 290. For example, 0.1 to 10% (for example, 1%) of the inspection light for the reflection inspection is split as light for correction to the cylindrical lens 292 side. The remaining part of the inspection light becomes the reflected illumination light. The reflected illumination light (second light) of the inspection light split by the beam splitter 290 is reflected by the beam splitter 176 and irradiated onto the substrate 101 by the objective lens 104. In other words, the illumination optical system composed of the reflection illumination optical system 170, the beam splitter 176, and the objective lens 104 illuminates the inspected substrate 101 on which a pattern is formed. The light reflected from the substrate 101 passes through the objective lens 104 and the beam splitter 174, and is focused as an optical image (reflected image) by the imaging optical system 278 onto the image sensor 205, where it is incident. In this way, the image sensor 205 captures the reflected image.

The image of the pattern formed on the image sensor 205 is photoelectrically converted by each photosensor element of the image sensor 205, and the integrated value of the multiple photosensor elements arranged in the scanning direction is output to the sensor circuit 206. The sensor circuit 206 then performs A/D (analog-to-digital) conversion.

Figure 2 is a conceptual diagram for explaining the inspection area in the first embodiment. As shown in Figure 2, the inspection area 10 (whole inspection area) of the substrate 101 is virtually divided into a plurality of rectangular inspection stripes 20 with the scan width W of the TDI sensor 105, for example, in the Y direction. The inspection device 100 then acquires an image (stripe area image) for each inspection stripe 20. For each inspection stripe 20, an image of the figure pattern arranged within the inspection stripe 20 is captured in the longitudinal direction (X direction) of the stripe area using laser light (inspection light). In order to prevent missing images, it is preferable that the inspection stripes 20 are set so that adjacent inspection stripes 20 overlap with a predetermined margin width.

The movement of the XYθ table 102 causes the TDI sensor 105 to move continuously in the X direction relative to the substrate 101, thereby acquiring optical images. The TDI sensor 105 continuously captures optical images of a scan width W as shown in FIG. 2. In other words, the TDI sensor 105 captures optical images of the substrate 101 surface on which multiple graphic patterns are formed, while moving relatively in the integral direction of the TDI sensor 105. In the first embodiment, after capturing an optical image of one inspection stripe 20, the sensor moves in the Y direction to the position of the next inspection stripe 20, and then moves in the reverse direction to capture optical images of the scan width W in the same manner. In other words, imaging is repeated in the forward (FWD)-backward (BWD) directions, which go in opposite directions on the outward and return paths.

Furthermore, for actual inspection, the stripe area image of each inspection stripe 20 is divided into a number of rectangular frame area 30 images, as shown in FIG. 2. Then, inspection is carried out for each frame area 30 image. For example, it is divided into images of 1024 x 1024 pixels. Therefore, a reference image to be compared with the frame image 31 of the frame area 30 is also created for each frame area 30.

The imaging direction is not limited to repeated forward (FWD)-backward (BWD). Imaging may be performed from one direction. For example, FWD-FWD may be repeated. Or BWD-BWD may be repeated.

Figure 3 is a diagram for explaining the change over time in the light amount distribution in the first embodiment. In the example of Figure 3, the image sensor 105 (205) captures the inspection stripe 20 located at Y = Y0 to Y1. As shown in Figure 3, the light amount distribution of the inspection light exists in the direction (Y direction) perpendicular to the scanning direction of the area A arranged in the scanning direction. When the scan proceeds and the area B is scanned, the light amount distribution of the inspection light in the direction (Y direction) perpendicular to the scanning direction of the area B becomes different from the light amount distribution of the inspection light in the direction (Y direction) perpendicular to the scanning direction of the area A. In other words, the light amount distribution of the inspection light changes over time. In this way, the light amount is not unique throughout the entire illumination field, but a distribution occurs. Such a change in the unevenness of the illumination distribution becomes an error factor in the captured image. In the conventional measurement method that measures the light amount by the total light beam, it was difficult to monitor the change in the unevenness of the distribution of the illumination field at the mask conjugate position. Therefore, even if the light amount by the total light beam is measured, there was a problem that the change according to the position of the light amount distribution could not be understood. Although a method of light intensity correction in which the light intensity is measured in a partial area of the image sensor has been considered, it is difficult to follow the changes in the unevenness of the illumination light distribution, and another method is required. Therefore, in the first embodiment, as described in FIG. 1, the change in the unevenness of the illumination distribution is measured by a line sensor 194 (294) placed at a position conjugate with the mask.

Figure 4 is a diagram for explaining a method for measuring unevenness in illumination distribution in embodiment 1. In the example of Figure 4, the illumination optical system after the Kohler illumination optical system 300 is omitted. Although the inspection light is ideally controlled to a uniform light amount within the surface by the Kohler illumination optical system 300, a light amount distribution is generated on the surface of the substrate 101 as shown in Figure 4. Furthermore, the light amount distribution changes over time due to, for example, changes in the beam diameter or optical axis of the laser light emitted from the light source 103. Therefore, in embodiment 1, the light amount distribution in a direction perpendicular to the scanning direction of the image sensor 105 is measured by the line sensor 194.

Figure 5 is a diagram for explaining light quantity measurement in a comparative example of embodiment 1. The comparative example in Figure 5 shows a case where a spherical lens is used as a condenser lens that condenses the illumination light 11. Therefore, the entire luminous flux of the illumination light 11 is condensed to one point, and the condensed light is measured by, for example, one photosensor 300. In such a case, it is difficult to obtain the light quantity distribution from the obtained data.

Figure 6 is a diagram for explaining the light quantity measurement in the first embodiment. As shown in Figure 6, in the first embodiment, a cylindrical or semi-cylindrical cylinder lens 192 (292) is used as a focusing lens for focusing the illumination light 11 (second light: light for correction) split by the beam splitter 190 (290) from the inspection light. The cylinder lens 192 (292) is arranged so that the generatrix direction (extension direction) corresponds to the direction perpendicular to the scanning direction of the image sensor 105 (205). The longitudinal direction of the line sensor 194 (294) is also arranged so that it corresponds to the direction perpendicular to the scanning direction. As a result, when the branched illumination light 11 is focused by the cylinder lens 192 (292), the light that spreads in the direction in which the cylinder lens 192 (292) extends in a plane perpendicular to the direction of travel of the illumination light 11 is not focused, and the light that spreads in a direction perpendicular to the direction in which the cylinder lens 192 (292) extends is focused to one point. The light that passes through the cylinder lens 192 (292) is measured by a plurality of photosensor elements arranged in the longitudinal direction of the line sensor 194 (294). Therefore, the light amount distribution in the longitudinal direction of the line sensor 194 (294) that is focused only in the short direction of the line sensor 194 (294) can be measured. The longitudinal direction of the line sensor 194 (294) corresponds to the direction perpendicular to the scanning direction of the image sensor 105 (205). Therefore, it is possible to measure the light amount distribution in a direction perpendicular to the scanning direction of the image sensor 105 (205) that is focused in the scanning direction of the image sensor 105 (205). By monitoring the light amount distribution in this direction, it is possible to measure the change in the light amount distribution over time.

Figure 7 is a flow chart showing the main steps of the inspection method in embodiment 1. In Figure 7, the inspection method in embodiment 1 carries out a series of steps including a calibration step (S102), a correction reference value setting step (S104), a scanning step (S110), a light quantity distribution measurement step (S112), a correction step (S120), a reference image creation step (S130), and a comparison step (S140).

In the calibration step (S102), the image sensor 105 (205) is calibrated. For example, if the sensor has 256 gradations, the sensitivity may be adjusted so that the gradation level when capturing an image of a white pattern is, for example, about 200 gradations. The light quantity distribution of the illumination light at this time is measured by the line sensor 194 (294). The measured light quantity distribution data is stored in the memory 196 (296) and is also output to the correction circuit 117 (207). The light quantity distribution obtained here becomes the reference value at each position.

In the correction reference value setting step (S104), the correction circuit 117 (207) inputs the data of the light quantity distribution measured by the line sensor 194 (294) when calibrated in the calibration step (S102), and sets it as the correction reference value S0.

In the scanning step (S110), the optical image acquisition mechanism 150 uses the calibrated image sensor 105 (205) to capture an image of the substrate 101 on which a pattern is formed by irradiating the substrate 101 with light (first light) split by the beam splitter 190 for use as inspection illumination light from the transmitted inspection light, and outputs the captured optical image data. To this end, the optical image acquisition mechanism 150 first scans the inspection stripe 20 with a laser beam (inspection light) and captures a stripe region image for each inspection stripe 20 with the image sensor 105 (205). Specifically, the operation is as follows. The XYθ table 102 is moved to a position where the target inspection stripe 20 can be imaged. In the transmission inspection, the transmitted light of the substrate 101 is imaged as an optical image on the image sensor 105 and enters it. Or/and in the reflection inspection, the reflected light from the substrate 101 is imaged as an optical image on the image sensor 205 and enters it.

The image of the pattern formed on the image sensor 105 is photoelectrically converted by each photosensor element of the image sensor 105, and is further A/D (analog-to-digital) converted by the sensor circuit 106. At that time, the integrated output of the multiple photosensor elements arranged in the scanning direction is converted by the sensor circuit 106 into a gradation value and output to the correction circuit 117.

Alternatively, the image of the pattern formed on the image sensor 205 is photoelectrically converted by each photosensor element of the image sensor 205, and is further A/D (analog-to-digital) converted by the sensor circuit 206. At that time, the output after integration of the multiple photosensor elements arranged in the scanning direction by the sensor circuit 206 is converted into a gradation value and output to the correction circuit 217.

In the light quantity distribution measurement process (S112), in parallel with the imaging by the image sensor 105, the line sensor 194 receives the light (second light) that is split by the beam splitter 190 for measurement out of the transmitted inspection light, and measures the temporal change in the light quantity distribution in a direction perpendicular to the accumulation direction of the image sensor 105. In other words, the line sensor 194 synchronously measures the illumination light used for imaging by the image sensor 105. The measured light quantity distribution data is stored and accumulated in the memory 196.

Alternatively, in parallel with the imaging by the image sensor 205, the line sensor 294 receives the reflected inspection light split by the beam splitter 290 for measurement (second light) and measures the temporal change in the light intensity distribution in a direction perpendicular to the accumulation direction of the image sensor 205. In other words, the line sensor 294 synchronously measures the illumination light used for imaging by the image sensor 205. The measured light intensity distribution data is stored and accumulated in the memory 296.

In the correction step (S120), the correction circuit 117 (207) (correction unit) uses the time-varying light intensity distribution value to correct the image data output from the image sensor 105 (205) according to the position of the light intensity distribution.

Figure 8 is a diagram for explaining the method of correction in the first embodiment. A plurality of photosensor elements arranged in the scanning direction in the imaging sensor 105 (205) capture the same pixel while shifting the time according to the movement of the XYθ table 102. As shown in Figure 8, the imaging sensor 105 (205) integrates and outputs data of the same pixel captured by a plurality of photosensor elements arranged in the scanning direction while shifting the time. For example, N photosensor elements are arranged in the scanning direction. The image accumulation time (light receiving time, exposure time) per pixel is set for each photosensor element according to the moving speed of the XYθ table 102. Therefore, for the time t calculated by the number of photosensor elements to be accumulated x the image accumulation time, each pixel continues to receive illumination light to acquire an image. In addition, each photosensor element shifts the pixel area on the substrate 101 to be imaged in the scanning direction for each image accumulation time.

On the other hand, the line sensor 194 (294) performs multiple measurements during a time t, which is calculated by multiplying the number of photosensor elements in the scanning direction used to capture each pixel by the image accumulation time. For example, 1024 measurements are performed. Then, the light quantity distribution data for each measurement is stored in the memory 196 (296).

The correction circuit 117 (207) corrects the image data of the target pixel using the light intensity distribution value measured during the time period when the image of the target pixel of the substrate 101 is captured by the imaging sensor 105 (205). Specifically, it operates as follows. The correction circuit 117 (207) reads out from the memory 196 (296) multiple pieces of light intensity distribution data measured during the time period when the image of the target pixel of the substrate 101 is captured by the imaging sensor 105 (205). Then, for each position of the light intensity distribution, the correction circuit 117 (207) calculates a moving average value S by adding up the values k at the corresponding positions in the multiple light intensity distributions read out and dividing the total by the number of measurements n.

Next, the correction circuit 117 (207) corrects the image data of the target pixel using the moving average value of each value of the light intensity distribution measured multiple times during the time period when the image of the target pixel was captured. Specifically, the correction circuit 117 (207) performs the correction by multiplying the gradation value d of the target pixel calculated by the sensor circuit 106 (206) by the ratio of the reference value S0 divided by the moving average value S. In other words, the correction is performed by multiplying the ratio of the amount of light during actual capture to the amount of light of the illumination light during calibration.

When a target pixel is shifted in the scanning direction, the time periods in which the image of the target pixel was captured also shift, although there is some overlap. The multiple light intensity distribution data read from memory 196 (296) will also differ by the amount of the time period shift. Therefore, the multiple sets of light intensity distribution data that are the basis for correcting each pixel lined up in the scanning direction will also differ depending on the imaging time period. Therefore, the moving average value S will also be a different value, making it possible to make corrections in accordance with the changes in light intensity distribution over time.

At that time, the correction circuit 117 (207) corrects the image data at the target position using the value of the position of the light intensity distribution that corresponds to the target position of the image data in terms of the mask surface.

Figure 9 is a diagram for explaining the relationship between the magnification and the image size at each position in the first embodiment. In the optical system, the magnification when forming an image may differ. For example, as shown in Figure 9, if the imaging area size of the mask substrate surface (magnification 1) is L1, the magnification on the imaging sensor 105 (205) is M1. In this case, the size of the image of the imaging area of the mask substrate surface imaged by the imaging sensor 105 (205) is L1 multiplied by the magnification M1. On the other hand, on the line sensor 194 (294), the magnification is M2. In this case, the size of the image of the imaging area of the mask substrate surface measured on the line sensor 194 (294) is L1 multiplied by the magnification M2. In this way, the image that was L1 on the mask substrate has a different size on the imaging sensor 105 (205) and the line sensor 194 (294). Therefore, each position of the light quantity distribution measured by the line sensor 194 (294) does not necessarily correspond to a position in a direction perpendicular to the scanning direction of the image captured by the image sensor 105 (205). The corresponding positions differ depending on the difference in magnification. Therefore, a standard is required for the relationship between the positions on the line sensor 194 (294) and the positions on the image sensor 105 (205). Here, the positions on the line sensor 194 (294) are associated with the positions on the image sensor 105 (205) in terms of the mask surface.

Figure 10 is a diagram for explaining the relationship between each position of the light quantity distribution and the position of the image of the TDI sensor in the first embodiment. The example of Figure 10 shows a case where an image of an area from the position Y = Y0 to the position Y1 on the mask substrate is captured. In the example of Figure 10, n3 photosensor elements are arranged in the line sensor 194 (294). On the other hand, m photosensor elements are arranged in the Y direction perpendicular to the scanning direction in the image sensor 105 (205). For example, m is several times larger than n3. However, when viewed in terms of the mask surface, the position Y = Y0 on the mask substrate corresponds to the photosensor of the n1th pixel in the line sensor 194 (294). In this case, it corresponds to the photosensor of the 1st pixel in the image sensor 105 (205). The position Y = Y1 on the mask substrate corresponds to the photosensor of the n2th pixel in the line sensor 194 (294). In this case, it corresponds to the photosensor of the mth pixel in the image sensor 105 (205). In this way, it is sufficient to set in advance which positions on the mask substrate are assigned to which positions on the line sensor 194 (294) and the image sensor 105 (205) in terms of the mask surface. In other words, positions on the line sensor 194 (294) and positions on the image sensor 105 (205) are associated in terms of the mask surface. If there is no data in the light quantity distribution data that corresponds to the target position on the image sensor 105 (205), a value obtained by linear interpolation using data from previous and subsequent positions may be used. The longitudinal size of the line sensor 194 (294) in terms of the mask surface may be equal to or greater than the longitudinal size of the image sensor 105 (205).

As described above, by using the light intensity distribution in the direction perpendicular to the scanning direction, correction can be made according to the difference in the light intensity in the direction perpendicular to the scanning direction. Furthermore, the temporal change in the light intensity in the scanning direction can be averaged by using a moving average value.

The gradation value (image data) of each pixel corrected by the correction circuit 117 (207) is output to the stripe pattern memory 123 (223).

Then, pixel value data of the inspection stripe 20 to be measured is stored in the stripe pattern memory 123 (223). The measurement data (pixel data) is, for example, 8-bit unsigned data, and represents the brightness gradation (amount of light) of each pixel. The pixel value data of the inspection stripe 20 is output to the comparison circuit 108.

In the reference image creation step (S130), the reference image creation circuit 112 uses the graphic pattern data (design data) to create a reference image that serves as a reference. The creation of the reference image is performed for each inspection stripe 20 in parallel with the scanning operation of that inspection stripe 20. Specifically, it operates as follows. The reference image creation circuit 112 inputs graphic pattern data (design data) for each frame area 30 of the target inspection stripe 20, and converts each graphic pattern defined in the graphic pattern data into binary or multi-value image data.

The figures defined in the figure pattern data are, for example, rectangles and triangles as basic figures, and the figure data stored defines the shape, size, position, etc. of each pattern figure using information such as the coordinates (x, y) at the reference position of the figure, the length of the sides, and a figure code that serves as an identifier to distinguish the type of figure, such as a rectangle or triangle.

When the design pattern data that becomes such figure data is input to the reference image creation circuit 112, it is expanded to data for each figure, and the figure code and figure dimensions indicating the figure shape of the figure data are interpreted. Then, it is expanded into binary or multi-value design pattern image data as a pattern arranged in a grid with a predetermined quantization dimension as a unit, and output. In other words, the design data is read, and the occupancy rate of the figure in the design pattern is calculated for each grid formed by virtually dividing the frame area into grids with a predetermined dimension as a unit, and n-bit occupancy data (design image data) is output. For example, it is preferable to set one grid as one pixel. Then, if one pixel has a resolution of 1/2 ⁸ (=1/256), a small area of 1/256 is assigned to the area of the figure arranged in the pixel, and the occupancy rate in the pixel is calculated. Then, it is created as 8-bit occupancy data. Such grids (inspection pixels) can be aligned with the pixels of the measurement data.

Next, the reference image creation circuit 112 applies filtering to the design image data of the design pattern, which is image data of the figure, using a filter function.

Figure 11 is a diagram for explaining the filter processing in the first embodiment. The pixel data of the optical image captured from the substrate 101 is in a state where a filter has been applied due to the resolution characteristics of the optical system used for capturing the image, in other words, in an analog state that changes continuously, so that, for example, as shown in Figure 11, the image intensity (gray value) is different from the developed image (design image) in which the image intensity (gray value) is a digital value. On the other hand, as described above, the figure pattern data is defined by the figure code, etc., so that the image intensity (gray value) may be a digital value in the developed design image. Therefore, the reference image creation circuit 112 creates a reference image that is close to the optical image by performing image processing (filter processing) on the developed image. This allows the design image data, which is the image data on the design side with the image intensity (gray value) being a digital value, to be matched to the image generation characteristics of the measurement data (optical image). The created reference image is output to the comparison circuit 108.

Figure 12 is a diagram showing an example of the internal configuration of the comparison circuit in the first embodiment. In Figure 12, the comparison circuit 108 includes storage devices 70, 72, 76 such as magnetic disk devices, a frame image creation unit 74, a positioning unit 78, and a comparison processing unit 79. A series of "~ units" such as the frame image creation unit 74, the positioning unit 78, and the comparison processing unit 79 have processing circuits. Such processing circuits include electric circuits, computers, processors, circuit boards, quantum circuits, or semiconductor devices. In addition, each "~ unit" may use a common processing circuit (the same processing circuit). Alternatively, different processing circuits (separate processing circuits) may be used. Input data or calculation results required for the frame image creation unit 74, the positioning unit 78, and the comparison processing unit 79 are stored in a memory (not shown) in the comparison circuit 108 or memory 111 each time.

The stripe data (stripe area image) input to the comparison circuit 108 is stored in the storage device 70. The reference image data input to the comparison circuit 108 is stored in the storage device 72.

In the comparison step (S140), the comparison circuit 108 (an example of a comparison unit) compares the inspection image using the corrected image data with a specified image. Specifically, it operates as follows.

In the comparison circuit 108, the frame image creation unit 74 first generates a plurality of frame images 31 by dividing the stripe region image (optical image) at a predetermined width. Specifically, as shown in FIG. 2, the stripe region image is divided into a plurality of rectangular frame region 30 frame images. For example, it is divided into a size of 512 x 512 pixels. The data of each frame region 30 is stored in the storage device 76.

Next, the alignment unit 78 reads out the corresponding frame image 31 and the corresponding reference image for each frame region 30 from the storage devices 72 and 76, and aligns the frame image 31 with the corresponding reference image using a predetermined algorithm. For example, the alignment is performed using the least squares method.

Then, the comparison processing unit 79 (another example of a comparison unit) compares the frame image 31 with the reference image corresponding to the frame image 31. For example, it compares them pixel by pixel. Here, the two are compared pixel by pixel according to a predetermined judgment condition to judge the presence or absence of a defect, such as a shape defect. The judgment condition may be, for example, to compare the two pixel by pixel according to a predetermined algorithm to judge the presence or absence of a defect. For example, the difference value between the pixel values of the two images is calculated for each pixel, and if the difference value is greater than a threshold value Th, it is judged to be a defect. The comparison result may then be output, for example, to the magnetic disk device 109 or a pattern monitor (not shown), or output from a printer (not shown).

In the above example, the case of die-database inspection has been described, but die-die inspection may also be performed. In such a case, the comparison circuit 108 uses the frame image (optical image) of die 2 acquired for one of the frame areas 30 for which die-die inspection is performed as a reference (reference image). First, the alignment unit 78 reads out the frame image 31 of die 1 and the frame image of die 2 from the storage device 76 for each frame area 30 for which die-die inspection is performed, and aligns the frame image 31 of die 1 with the frame image of die 2 using a predetermined algorithm. For example, the alignment is performed using the least squares method. Then, the comparison processing unit 79 (comparison unit) compares the frame image 31 of die 1 with the frame image of die 2 for each frame area 30 for which die-die inspection is performed, pixel by pixel.

As described above, according to the first embodiment, it is possible to measure changes in the uneven distribution of illumination light. Therefore, it is possible to correct changes according to the position of the uneven distribution. As a result, it is possible to improve the reproducibility of the device. Furthermore, with Kohler illumination, ideally, the illumination is uniform within the plane. Therefore, even if uneven distribution occurs, the difference in unevenness is small. In the first embodiment, for example, Kohler illumination light is created by the Kohler illumination optical system 300. In the first embodiment, it is possible to correct changes according to the position of the uneven distribution even for minute uneven distribution caused by this Kohler illumination.

In the above description, the term "circuit" has a processing circuit. Such processing circuits include, for example, an electric circuit, a computer, a processor, a circuit board, a quantum circuit, or a semiconductor device. Each "circuit" may use a common processing circuit (the same processing circuit), or may use different processing circuits (separate processing circuits). In addition, when a program is used, the program is recorded on a recording medium such as a magnetic disk device, a magnetic tape device, a FD, or a ROM (read-only memory).

The above describes the embodiments with reference to specific examples. However, the present invention is not limited to these specific examples.

In addition, although the description of the device configuration, control method, and other parts that are not directly necessary for the explanation of the present invention have been omitted, the required device configuration and control method can be appropriately selected and used. For example, although the description of the control unit configuration that controls the inspection device 100 has been omitted, it goes without saying that the required control unit configuration can be appropriately selected and used.

All other pattern inspection devices and pattern inspection methods that incorporate the elements of the present invention and that can be modified by those skilled in the art are included within the scope of the present invention.

10 Inspection area 11 Illumination light 20 Inspection stripe 30 Frame area 31 Projection lens 32 Beam splitter 70, 72, 76 Storage device 74 Frame image creation unit 78 Alignment unit 79 Comparison processing unit 100 Inspection device 101 Mask substrate 102 XYθ table 103 Light source 104 Magnification optical system 105, 205 Image sensor 106, 206 Sensor circuit 107 Position circuit 108 Comparison circuit 109 Magnetic disk device 110 Control computer 111 Memory 112 Reference image creation circuit 114 Table control circuit 115 Drive mechanism 117, 217 Correction circuit 120 Bus 123, 223 Stripe pattern memory 134 Mirror 138 Mirror 150 Optical image acquisition mechanism 160 Control system circuit 176 Beam splitter 171, 271 Lens 170 Transmitted illumination optical system 177 Mirrors 178, 278 Imaging optical system 190, 290 Beam splitter 192 Cylinder lens 194, 294 Line sensor 196, 296 Memory 270 Reflection illumination optical system 300 Kohler illumination optical system 302 Beam expander 304 Split lens 306 Rotating phase plate 308 Collimator lens 310 Illumination slit

Claims (6)

a beam splitter for splitting the inspection light;
a time delay integration (TDI) sensor that captures an image of a mask substrate on which a pattern is formed by irradiating a first light beam branched from the inspection light beam onto the mask substrate and outputs image data;
a line sensor that receives a second branched light of the inspection light and measures a time change in a light amount distribution in a direction perpendicular to an accumulation direction of the TDI sensor;
a correction unit that corrects image data output from the TDI sensor according to a position of the light quantity distribution by using the value of the light quantity distribution that changes over time;
a comparison unit for comparing an inspection image using the corrected image data with a predetermined image;
A mask inspection apparatus comprising: The mask inspection device according to claim 1, characterized in that the correction unit corrects the image data at the target position using the value of the position of the light quantity distribution that corresponds to the target position of the image data in terms of the mask surface. The mask inspection device according to claim 1 or 2, characterized in that the correction unit corrects the image data of the target pixel using the value of the light quantity distribution measured during the time period when the image of the target pixel on the mask substrate is captured by the TDI sensor. A mask inspection apparatus according to any one of claims 1 to 3, characterized in that the inspection light is illuminated using Kohler illumination. A mask inspection device according to any one of claims 1 to 4, characterized in that the correction unit corrects the image data of the target pixel using a moving average value of each value of the light quantity distribution measured during the time period when the image of the target pixel on the mask substrate is captured by the TDI sensor. splitting the inspection light;
capturing an image of a mask substrate on which a pattern is formed by irradiating a first branched light of the inspection light onto the mask substrate using a time delay integration (TDI) sensor, and outputting image data;
receiving a second branched light of the inspection light using a line sensor and measuring a time change in a light amount distribution in a direction perpendicular to an accumulation direction of the TDI sensor;
correcting image data output from the TDI sensor according to a position of the light quantity distribution using a value of the light quantity distribution that changes over time;
a step of comparing an inspection image using the corrected image data with a predetermined image and outputting the result;
A mask inspection method comprising:

Images