Pattern inspection apparatus and pattern inspection method

Abstract

The present invention provides an inspection device that can shorten the time required for calibration processing of the amount of incident light on each imaging sensor. [Solution] The inspection device 100 is characterized by comprising: a light-reducing filter 330 that arbitrarily attenuates the amount of light generated from a light source; a half-wave plate 331 that adjusts the polarization direction of the light; a polarizing beam splitter 332 that splits the light; a first light intensity sensor 130 that measures the amount of first incident light incident on a first imaging sensor; a second light intensity sensor 230 that measures the amount of second incident light incident on a second imaging sensor; an angle calculation unit that calculates the adjustment angle of the half-wave plate so that the ratio of the amount of first incident light to the amount of second incident light becomes a desired ratio; and a transmittance calculation unit that calculates the transmittance of the light-reducing filter so that the amount of first incident light becomes a value within a desired range set for the first light intensity sensor and the amount of second incident light becomes a value within a desired range set for the second light intensity sensor.

Description

[Technical Field]

[0001] One aspect of the present invention relates to a pattern inspection apparatus and a pattern inspection method. For example, it relates to an inspection apparatus for inspecting defects of a pattern formed on a substrate. [Background Art]

[0002] In recent years, along with the higher integration and larger capacity of large-scale integrated circuits (LSIs), the circuit line width required for semiconductor elements has become increasingly narrower. These semiconductor elements are manufactured by exposing and transferring a pattern onto a wafer using a reduction projection exposure apparatus called a so-called stepper with an original pattern (also referred to as a mask or a reticle, hereinafter collectively referred to as a mask) on which a circuit pattern is formed, thereby forming a circuit.

[0003] For the manufacture of LSIs, which requires enormous manufacturing costs, improvement of yield is indispensable. One of the major factors that reduce yield is pattern defects such as shape defects and / or dimensional defects of a mask pattern used when exposing and transferring an ultrafine pattern onto a semiconductor wafer by photolithography technology. In recent years, along with the miniaturization of LSI pattern dimensions formed on semiconductor wafers, the dimensions that must be detected as pattern defects have also become extremely small. Therefore, higher precision is required for pattern inspection apparatuses that inspect defects of transfer masks used in LSI manufacturing.

[0004] As inspection methods, for example, there is "die to die inspection", which compares optical image data obtained by imaging the same pattern at different locations on the same mask, and "die to database inspection", in which drawing data (design data) obtained by converting patterned CAD data into an apparatus input format for a drawing apparatus to input when drawing a pattern on a mask is input to an inspection apparatus, a reference image is generated based on this, and the reference image is compared with an optical image serving as measurement data obtained by imaging the pattern.

[0005] In this context, inspection equipment may perform multiple inspection systems, such as transmission inspection using transmitted light that has passed through the sample, reflection inspection using reflected light from the sample, transmission inspection and transmission inspection using multiple lights with different polarization directions, or reflection inspection and reflection inspection. In such cases, in order to obtain optical images of the desired accuracy for each inspection system, it is necessary to adjust the amount of light incident on each imaging sensor that captures the optical image. Multiple inspection lights for performing such multiple inspection systems are generated by branching the light generated from a single light source. Conventionally, a method has been used in which the setting of optical elements and imaging with these settings have been repeatedly performed while changing the conditions until the desired conditions are met, thereby adjusting the amount of light incident on each imaging sensor. This has resulted in problems such as the time required for light intensity calibration processing becoming long, and the setup time before the inspection process becoming long. This degrades the inspection throughput. In addition, multiple imaging involves repeatedly irradiating the sample with short-wavelength, high-energy laser light, which may damage the pattern formed on the sample. Therefore, there is a need to shorten the processing time for the calibration processing of the amount of light incident on each imaging sensor.

[0006] Here, it is disclosed that the power ratio between the P-polarized component and the S-polarized component changes by adjusting the angle of the λ / 2 wave plate (see, for example, Patent Document 1). [Prior art documents] [Patent Documents]

[0007] [Patent Document 1] Japanese Patent Publication No. 2000-084682 [Overview of the Initiative] [Problems that the invention aims to solve]

[0008] Embodiments of the present invention provide an inspection apparatus and method that can shorten the processing time for calibration of the amount of incident light to each system of imaging sensors. [Means for solving the problem]

[0009] A pattern inspection apparatus according to one aspect of the present invention is: A stage on which a patterned sample can be placed, Light source and A light-reducing filter that arbitrarily attenuates the amount of light emitted from a light source, A half-wave plate that adjusts the polarization direction of light that has passed through the light-reducing filter, A branching element that splits the light that has passed through a half-wave plate, A first imaging sensor captures a first optical image of a sample obtained by irradiating the sample with a first inspection light, which is one of the two lights produced by the branching of the sample. A second imaging sensor captures a second optical image of a sample obtained by irradiating the sample with a second inspection light, which is one of the two light beams produced by the branching process, A first light intensity sensor measures the amount of first incident light incident on the first imaging sensor, A second light intensity sensor measures the amount of second incident light incident on the second imaging sensor, An angle calculation unit calculates the adjustment angle of a half-wave plate such that the ratio of the light intensity of the first incident light incident on the first light intensity sensor to the light intensity of the second incident light incident on the second light intensity sensor becomes a desired ratio. A transmittance calculation unit calculates the transmittance of a light-reducing filter such that the amount of light from a first incident light incident on a first light intensity sensor is within a desired range set for the first light intensity sensor, and the amount of light from a second incident light incident on a second light intensity sensor is within a desired range set for the second light intensity sensor. A comparison unit that compares a first optical image with a first predetermined image, and also compares a second optical image with a second predetermined image, It is characterized by having the following features.

[0010] A pattern inspection method according to one aspect of the present invention is: By using a neutral density filter, the amount of light emitted from the light source can be arbitrarily reduced. Using a half-wave plate, the polarization direction of the light that has passed through the attenuation filter is adjusted. Using a branching element, the light that has passed through the half-wave plate is branched. Using the first light intensity sensor, the amount of first incident light generated by the light source and incident on the first imaging sensor via a light-reducing filter, a half-wave plate, a branching element, and a patterned sample placed on a stage is measured. Using a second light intensity sensor, the amount of second incident light generated by the light source and incident on the second imaging sensor via a light-reducing filter, a half-wave plate, a branching element, and a sample is measured. The adjustment angle of the half-wave plate is calculated so that the ratio of the light intensity of the first and second incident light incident on the first and second light intensity sensors becomes the desired ratio. The transmittance of a light-reducing filter is calculated such that the amount of light from the first incident light incident on the first light intensity sensor is within a desired range set for the first light intensity sensor, and the amount of light from the second incident light incident on the second light intensity sensor is within a desired range set for the second light intensity sensor. Using the first imaging sensor, a first optical image of the sample is captured by irradiating the sample with a first inspection light, which is one of two beams of light produced when light that has passed through a light-reducing filter set to a calculated transmittance and a half-wave plate adjusted to a calculated adjustment angle is split by a branching element. Using a second imaging sensor, a second optical image of the sample is captured by irradiating the sample with a second inspection light, which is one of the two beams of light produced when light that has passed through a light-reducing filter set to a calculated transmittance and a half-wave plate adjusted to a calculated adjustment angle is split by a branching element. The system compares a first optical image with a first predetermined image, and also compares a second optical image with a second predetermined image, and outputs the results. It is characterized by the following: [Effects of the Invention]

[0011] According to embodiments of the present invention, the processing time for calibration of the amount of incident light to each system of imaging sensors can be shortened. [Brief explanation of the drawing]

[0012] [Figure 1] It is a configuration diagram showing the configuration of the pattern inspection apparatus according to the first embodiment. [Figure 2] It is a conceptual diagram for explaining an inspection area according to the first embodiment. [Figure 3] It is a diagram for explaining an example of a generation method of two inspection beams according to the first embodiment. [Figure 4] It is a diagram showing an example before and after light amount adjustment according to the first embodiment. [Figure 5] It is a flowchart of a light amount adjustment method in a comparative example of the first embodiment. [Figure 6] It is a block diagram showing an example of the internal configuration of a light amount adjustment circuit according to the first embodiment. [Figure 7] It is a flowchart showing an example of main steps of an inspection method according to the first embodiment. [Figure 8] It is a diagram showing an example of light amounts under initial conditions according to the first embodiment. [Figure 9] It is a diagram showing an example of the relationship between a transmitted light amount ratio and a reflected light amount ratio adjusted by a λ / 2 wavelength plate according to the first embodiment. [Figure 10] It is a diagram for explaining filter processing according to the first embodiment. [Figure 11] It is a diagram showing an example of the internal configuration of a comparison circuit according to the first embodiment. DETAILED DESCRIPTION OF THE INVENTION

[0013] Embodiment 1. FIG. 1 is a configuration diagram showing the configuration of the pattern inspection apparatus according to the first embodiment. In FIG. 1, an inspection apparatus 100 that inspects for pattern defects formed on a substrate 101 (which is an example of a substrate to be inspected) includes an optical image acquisition mechanism 150 and a control circuit 160 (a control unit).

[0014] The optical image acquisition mechanism 150 includes a light source 103 that generates laser light, an ND (neutral density) filter 30, a λ / 2 wave plate 331, a polarizing beam splitter 332 (an example of a branching element), 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, a light intensity sensor 130, a drive mechanism 132, an imaging sensor 105, a sensor circuit 106, a stripe pattern memory 123, a light intensity sensor 230, a drive mechanism 232, an imaging sensor 205, a sensor circuit 206, and a stripe pattern memory 223.

[0015] Figure 1 shows an example of a configuration that allows for two types of inspection: transmission inspection and reflection inspection.

[0016] The transmitted illumination optical system 170 consists of one or more lenses and / or one or more mirrors. In the example in Figure 1, the transmitted illumination optical system 170 has a mirror 172 and a lens 171.

[0017] The reflective illumination optical system 270 consists of one or more lenses and / or one or more mirrors. In the example in Figure 1, the reflective illumination optical system 270 has a mirror 336 and a lens 271.

[0018] A substrate 101 to be inspected, 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. Multiple graphic patterns to be inspected are formed on this photomask. The substrate 101 is placed on the XYθ table 102 with, for example, the pattern-forming surface facing downwards.

[0019] For the imaging sensors 105 and 205, it is preferable to use, for example, a TDI (Time Delay Integral) sensor. A TDI sensor has multiple photosensor elements arranged in two dimensions. When each photosensor element captures an image, a predetermined image storage time (sometimes called a scan time; the same applies hereinafter) is set. In a TDI sensor, the outputs of multiple photosensor elements aligned in the scan direction are integrated and output. Multiple photosensor elements aligned in the scan direction capture the same pixel while shifting time according to the movement of the XYθ table 102.

[0020] In the control system circuit 160, the control computer 110, which controls the entire inspection device 100, is connected via the bus 120 to the magnetic disk drive 109, memory 111, position circuit 107, comparison circuit unit 144 (comparison circuits 108a, 108b), reference image creation circuit 112, table control circuit 114, light intensity adjustment circuit 140, and light intensity sensor control circuit 142. Multiple comparator circuits 108a and 108b are arranged within the comparator circuit unit 144.

[0021] Furthermore, the XYθ table 102 is driven by a drive mechanism 115. The drive mechanism 115 includes, 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, Y-axis motor, and θ-axis motor. The XYθ table 102 is an example of a stage.

[0022] These X-axis motors, Y-axis motors, and θ-axis motors can be, for example, linear motors. The XYθ table 102 is movable in the horizontal and rotational directions by the motors of each of the XYθ axes. The XYθ table 102 is then adjusted under the control of the control computer 110 to the focal position (optical axis direction: Z axis direction) of the pattern-forming surface of the substrate 101 and the imaging sensors 105, 205. The movement position of the substrate 101 placed on the XYθ table 102 is measured by a laser length measuring system (not shown) and supplied to the position circuit 107.

[0023] The drive mechanism 132 drives the light intensity sensor 130, moving it between inside and outside the optical path of the light incident on the image sensor 105. Similarly, the drive mechanism 232 drives the light intensity sensor 230, moving it between inside and outside the optical path of the light incident on the image sensor 205.

[0024] The series of "~circuits," such as the position circuit 107, comparison circuit 108, reference image creation circuit 112, table control circuit 114, light intensity adjustment circuit 140, and light intensity sensor control circuit 142, each have a processing circuit. Such processing circuits include electrical circuits, computers, processors, circuit boards, quantum circuits, or semiconductor devices. Each circuit may use the same processing circuit. For example, the series of "~circuits," such as the position circuit 107, comparison circuit 108, reference image creation circuit 112, table control circuit 114, light intensity adjustment circuit 140, and light intensity sensor control circuit 142, may be configured and executed by the control computer 110. Alternatively, different processing circuits (separate processing circuits) may be used. The input data or calculated results required for the position circuit 107, comparison circuit 108, reference image creation circuit 112, table control circuit 114, light intensity adjustment circuit 140, and light intensity sensor control circuit 142 are stored in a memory (not shown) or memory 111 within each circuit each time. The input data or calculation results required by the control computer 110 are stored in a memory (not shown) or memory 111 within the control computer 110 each time. The program that causes the computer or processor to run can be recorded on a recording medium such as a magnetic disk drive 109.

[0025] In the inspection device 100, a transmission inspection optical system with a high magnification M1 is configured using a light source 103, an ND filter 330, a λ / 2 wave plate 331, a polarizing beam splitter 332, a transmitted illumination optical system 170, an XYθ table 102, an objective lens 104, a beam splitter 176, a mirror 177, an imaging optical system 178, an imaging sensor 105, and a sensor circuit 106. For example, an inspection optical system with a magnification of 200 to 300 times can be configured as the magnification M1.

[0026] Similarly, in the inspection device 100, a reflection inspection optical system with a high magnification M1 is configured using a light source 103, an ND filter 330, a λ / 2 wave plate 331, a polarizing beam splitter 332, a reflection illumination optical system 270, an XYθ table 102, an objective lens 104, a beam splitter 176, a mirror 177, an imaging optical system 278, an imaging sensor 205, and a sensor circuit 206. As the magnification M1, for example, an inspection optical system with a magnification of 200 to 300 times is configured.

[0027] Drawing data (design data) that forms the basis for pattern formation on the substrate 101 under inspection is input from outside the inspection device 100 and stored in the magnetic disk drive 109. Multiple graphic patterns are defined in the drawing data, and each graphic pattern is usually composed of a combination of multiple elemental shapes. However, there may also be graphic patterns composed of a single shape. On the substrate 101 under inspection, corresponding patterns are formed based on each graphic pattern defined in the drawing data.

[0028] Here, Figure 1 shows the components necessary for explaining Embodiment 1. Needless to say, other components that are normally necessary for the inspection device 100 may also be included.

[0029] From the light source 103, laser light with a wavelength of approximately 190-200 nm (for example, DUV light) (an example of ultraviolet light) is generated as inspection illumination light. The laser light emitted from the light source 103 is attenuated by the ND filter 330 and its polarization direction is adjusted by the λ / 2 wave plate 331. The ND filter 330 can arbitrarily attenuate the amount of laser light. The laser light 301 with the adjusted polarization direction is then split according to the polarization direction by the polarizing beam splitter 332 to generate two inspection lights, for example, P-wave component light and S-wave component light.

[0030] In transmission inspection, the inspection light for transmission inspection, separated by the polarizing beam splitter 332, is reflected by the mirror 172 and illuminates the substrate 101 by the lens 171. The transmitted light that has passed through the substrate 101 passes through the objective lens 104 and then through the beam splitter 176. It is then reflected, for example, by the mirror 177 and formed as an optical image (transmitted image) by the imaging optical system 178 and incident on the image sensor 105. In this way, the image sensor 105 captures the transmitted image. In Figure 1, the optical paths of the inspection light for transmission inspection and the image are shown by dotted lines.

[0031] The image of the pattern formed on the imaging sensor 105 is photoelectrically converted by each photosensor element of the imaging sensor 105, and the integrated value of the multiple photosensor elements arranged in the scanning direction is output to the sensor circuit 106. Then, the sensor circuit 106 performs A / D (analog-to-digital) conversion.

[0032] In reflection testing, the inspection light for reflection testing, separated by the polarizing beam splitter 332, is reflected by the mirror 336 and guided by the lens 271 to the beam splitter 176. The inspection light for reflection testing is then reflected by the beam splitter 176 and irradiated onto the substrate 101 by the objective lens 104. In other words, the illumination optical system, consisting of the reflection illumination optical system 270, the beam splitter 176, and the objective lens 104, illuminates the substrate 101 on which the pattern is formed. The reflected light reflected from the substrate 101 passes through the objective lens 104 and the beam splitter 174, and is imaged as an optical image (reflected image) by the imaging optical system 278 and incident on the image sensor 205. In this way, the image sensor 205 captures the reflected image.

[0033] The image of the pattern formed on the imaging sensor 205 is photoelectrically converted by each photosensor element of the imaging sensor 205, and the integrated value of multiple photosensor elements arranged in the scanning direction is output to the sensor circuit 206. Then, the sensor circuit 206 performs A / D (analog-to-digital) conversion.

[0034] Furthermore, the transmission test and the reflection test may be performed simultaneously or separately. Alternatively, only one of the tests may be performed.

[0035] Figure 2 is a conceptual diagram illustrating the inspection area in Embodiment 1. As shown in Figure 2, the inspection area 10 (the entire inspection area) of the substrate 101 is virtually divided into multiple strip-shaped inspection stripes 20 with a scan width W of the imaging sensor 105 (205), 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, a laser beam (inspection light) is used to capture an image of the graphic pattern arranged within the inspection stripe 20 in the longitudinal direction (X direction) of the stripe area. In order to prevent image loss, it is preferable that the multiple inspection stripes 20 be set so that adjacent inspection stripes 20 overlap by a predetermined margin width.

[0036] As the XYθ table 102 moves, the imaging sensors 105 and 205 move continuously in the X direction relative to each other, and optical images are acquired. The imaging sensors 105 and 205 continuously capture optical images with a scan width W as shown in Figure 2. In other words, the imaging sensors 105 and 205 capture optical images on the surface of the substrate 101 on which multiple geometric patterns are formed, while moving relative to the integration direction of the imaging sensors 105 and 205. In Embodiment 1, after capturing an optical image of one inspection stripe 20, the system moves in the Y direction to the position of the next inspection stripe 20, and then moves in the reverse direction, similarly capturing optical images with a scan width W continuously. That is, imaging is repeated in the forward (FWD)-back-forward (BWD) direction, moving in opposite directions for the outward and return journeys.

[0037] Furthermore, during the actual inspection, the stripe region image of each inspection stripe 20 is divided into multiple rectangular frame region images 30, as shown in Figure 2. The inspection is then performed on each frame region image 30. For example, it is divided into 1024 x 1024 pixel sizes. Therefore, a reference image to be compared with the frame image 31 of the frame region 30 is similarly created for each frame region 30.

[0038] Here, the imaging direction is not limited to repeated forward (FWD)-backforward (BWD) imaging. Imaging may be performed from one direction. For example, repeated FWD-FWD imaging is also possible, or repeated BWD-BWD imaging.

[0039] Figure 3 is a diagram illustrating two examples of inspection light generation methods in Embodiment 1. In the example in Figure 3, for convenience, light with a polarization direction of 0° is shown as the S wave and light with a polarization direction of 90° is shown as the P wave in a plane perpendicular to the direction of propagation of the laser light incident on the λ / 2 wave plate 331. The laser light emitted from the light source 103 (or the laser light that has passed through an optical element not shown) is generated as linearly polarized laser light. In the example in Figure 3, for example, it is shown when the laser light is generated with a polarization direction of 90° (P wave) in a plane perpendicular to the direction of propagation. This laser light passes through the ND filter 330 and is incident on the λ / 2 wave plate 331. The polarization direction of the laser light is changed by changing the adjustment angle of the λ / 2 wave plate 331. In the example in Figure 3, for example, a polarization direction (a) with a large P wave component is shown, adjusted to an angle greater than 45° in a plane perpendicular to the direction of propagation. Alternatively, for example, a polarization direction (b) with a large S-wave component is shown, adjusted to an angle smaller than 45° in a plane perpendicular to the direction of propagation. When laser light with adjusted polarization direction is incident on the polarization beam splitter 332, the polarization beam splitter 332 transmits one of the P-wave component and the S-wave component and reflects the other. In the example in Figure 3, the case in which the P-wave component is reflected and the S-wave component is transmitted is shown. In polarization direction (a), the reflected P-wave component becomes larger and the S-wave component becomes smaller. In polarization direction (b), the reflected S-wave component becomes larger and the P-wave component becomes smaller.

[0040] Figure 4 shows an example of the light intensity before and after adjustment in Embodiment 1. In the example in Figure 4, a case is shown where two inspection systems are performed: reflection inspection and transmission inspection. The target light intensity of the light incident on the image sensor 105 for transmission inspection and the target light intensity of the light incident on the image sensor 205 for reflection inspection are generally different. In the example in Figure 4, the case is shown where the target light intensity of the image sensor 105 for transmission inspection is greater than the target light intensity of the image sensor 205 for reflection inspection. However, this is not the only case. The magnitude of the target light intensity may be reversed or the same. For example, if the dynamic range of the image sensor output is defined as 256 gradations, it is preferable to set the target light intensity so that the white pattern, which is high-intensity light transmitted through the substrate 101 in transmission inspection, and the black pattern, which is high-intensity light reflected from the substrate 101 in reflection inspection, each have approximately 200 gradations. In addition, a range of approximately 5 gradations each is set as the target light intensity range, with the target light intensity at the top and bottom.

[0041] In the example shown in Figure 4, if the measured light intensity of the image sensor 105 for transmission inspection is higher than the target light intensity range, and the measured light intensity of the image sensor 205 for reflection inspection is also higher than the target light intensity range (upper part of Figure 4), the measured light intensity of both can be adjusted to their respective target light intensity ranges by lowering the transmittance of the ND filter 330. Furthermore, if the measured light intensity of the image sensor 105 for transmission inspection is near the highest value of the target light intensity range, and the measured light intensity of the image sensor 205 for reflection inspection is slightly lower than the target light intensity range (Figure 4, bottom diagram), by adjusting the angle of the λ / 2 wave plate 331 to an angle that increases the ratio of inspection light for reflection inspection (decreases the ratio of inspection light for transmission inspection), the difference in the measured light intensity of the two can be narrowed, and the measured light intensity of both can be adjusted to their respective target light intensity ranges.

[0042] Figure 5 is a flowchart of the light intensity adjustment method in a comparative example of Embodiment 1. In the comparative example, as shown in Figure 5, first, the light intensity of the image sensor 105 for transmission inspection and the light intensity of the image sensor 205 for reflection inspection are measured. Next, it is determined whether both are within the target light intensity range. If either of them is not within the range, it is determined whether the light intensity for transmission inspection is within the target light intensity range. If the light intensity for transmission inspection is not within the target light intensity range, the transmittance of the ND filter 330 is adjusted so that the light intensity for transmission inspection is within the target light intensity range. Then, the light intensity of the image sensor 105 for transmission inspection and the light intensity of the image sensor 205 for reflection inspection are measured. Then, it is determined again whether the light intensity for transmission testing and the light intensity for reflection testing are both within the target light intensity range. If the light intensity for transmission testing is not within the target light intensity range, the transmittance of the ND filter 330 and the measurement of the light intensity of the image sensor 105 for transmission testing and the image sensor 205 for reflection testing are repeated until the light intensity for transmission testing is within the target light intensity range. Next, the adjustment angle of the λ / 2 wave plate 331 is adjusted so that the amount of light for reflection testing is within the target light intensity range. Then, the light intensity of the image sensor 105 for transmission testing and the light intensity of the image sensor 205 for reflection testing are measured. Finally, it is determined again whether both the light intensity for transmission testing and the light intensity for reflection testing are within the target light intensity range. If the light intensity for transmission testing is not within the range, the transmittance of the ND filter 330 is adjusted. If the light intensity for reflection testing is not within the target range, the adjustment angle of the λ / 2 wave plate 331 is adjusted. The light intensity of the image sensor 105 for transmission testing and the image sensor 205 for reflection testing are measured. This process is repeated until both the light intensity for transmission testing and the light intensity for reflection testing are within the target range.

[0043] As described above, the adjustment of the ND filter 330 and the measurement of the light intensity of the image sensor 105 for transmission inspection and the image sensor 205 for reflection inspection are repeated each time, as is the adjustment of the λ / 2 wave plate 331 and the measurement of the light intensity of the image sensor 105 for transmission inspection and the image sensor 205 for reflection inspection. In this way, in the comparative example, the setting of the optical elements and imaging with these settings are repeated while changing the conditions until the desired conditions are met, thereby adjusting the amount of light incident on each image sensor. As a result, in the comparative example, the time required for light intensity calibration processing is long, and the setup time before the inspection process becomes long. This degrades the inspection throughput. Furthermore, during multiple imaging cycles, the substrate 101 is repeatedly irradiated with short-wavelength, high-energy laser light, which may damage the patterns formed on the substrate 101. In light intensity calibration, the calibration patterns formed on the substrate 101 are often irradiated, but since these calibration patterns may be used for calibration in multiple processes, such as semiconductor manufacturing, damaging them would be problematic. To address these issues, it is necessary to reduce the processing time for calibration of the amount of incident light on each imaging sensor and to reduce the number of measurements required.

[0044] Therefore, in Embodiment 1, the transmittance of the ND filter 330 and the adjustment angle of the λ / 2 wave plate 331 are determined by calculation, thereby reducing the number of adjustments required for the transmittance of the ND filter 330 and the adjustment angle of the λ / 2 wave plate 331, as well as the number of measurements of light intensity for transmission and reflection testing. A detailed explanation follows below.

[0045] Figure 6 is a block diagram showing an example of the internal configuration of a light intensity adjustment circuit in Embodiment 1. In Figure 6, the light intensity adjustment circuit 140 includes a storage device 41 such as a magnetic disk drive, an initial value setting unit 40, a light intensity measurement processing unit 42, a determination unit 44, a coefficient calculation unit 45, an angle calculation unit 46, a transmittance calculation unit 48, and a setting unit 49. The series of "~ units" such as the initial value setting unit 40, the light intensity measurement processing unit 42, the determination unit 44, the coefficient calculation unit 45, the angle calculation unit 46, the transmittance calculation unit 48, and the setting unit 49 have processing circuits. Such processing circuits include electrical circuits, computers, processors, circuit boards, quantum circuits, or semiconductor devices. Furthermore, each "~ unit" may use a common processing circuit (the same processing circuit), or it may use different processing circuits (separate processing circuits). The input data or calculated results required for the initial value setting unit 40, light intensity measurement processing unit 42, determination unit 44, coefficient calculation unit 45, angle calculation unit 46, transmittance calculation unit 48, and setting unit 49 are stored in a memory (not shown) or memory 111 within the light intensity adjustment circuit 140 each time.

[0046] Figure 7 is a flowchart showing an example of the main steps of the inspection method in Embodiment 1. In Figure 7, the inspection method in Embodiment 1 performs a series of steps: an initial value setting step (S102), a light intensity measurement step (S104), a determination step (S106), an adjustment angle calculation step (S108), an ND transmittance calculation step (S110), a setting step (S112), a light intensity measurement step (S114), an image acquisition step (S120), a reference image creation step (S122), and a comparison step (S130). In the first embodiment, the light intensity calibration method includes the following steps: initial value setting step (S102), light intensity measurement step (S104), determination step (S106), adjustment angle calculation step (S108), ND transmittance calculation step (S110), setting step (S112), and light intensity measurement step (S114).

[0047] As an initial value setting step (S102), the initial value setting unit 40 sets the initial value NDini of the transmittance ND for the ND filter 330. The initial value setting unit 40 also sets the initial value θini of the adjustment angle θ for the λ / 2 wave plate 331.

[0048] As part of the light intensity measurement process (S104), the light intensity measurement processing unit 42 measures the amount of light incident on the image sensor 105 for transmission inspection and the amount of light incident on the image sensor 205 for reflection inspection, with the initial value NDini of the transmittance ND set for the ND filter 330 and the initial value θini of the adjustment angle θ set for the λ / 2 wave plate 331.

[0049] Here, if there is no light from the light source 103, the measured light intensity will be zero. However, with the adjustment using the λ / 2 wave plate 331, it may not be zero even at the minimum level. This corresponds to what is known as black level distortion. The portion that does not become zero at the minimum level is determined in advance and offset from the results measured by the light intensity sensors 130 and 230 during the light intensity measurement.

[0050] Figure 8 shows an example of the light intensity under initial conditions in Embodiment 1. Specifically, the light intensity measurement process (S104) operates as follows: The light intensity measurement processing unit 42 outputs a command to the light intensity sensor control circuit 142 indicating that light intensity measurement should be performed. Under the control of the light intensity sensor control circuit 142, the drive mechanism 132 moves the light intensity sensor 130 into the optical path. Similarly, under the control of the light intensity sensor control circuit 142, the drive mechanism 232 moves the light intensity sensor 230 into the optical path. Then, with the initial value NDini of the transmittance ND set in the ND filter 330 and the initial value θini of the adjustment angle θ set in the λ / 2 wave plate 331, laser light is generated from the light source 103.

[0051] As a result, the light intensity Itra of the incident light (first incident light) generated by the light source 103 and incident on the image sensor 105 via the ND filter 330, the λ / 2 wave plate 331, the polarizing beam splitter 332, and the substrate 101 placed on the XYθ table 102 is measured by the light intensity sensor 130. The light intensity sensor 130 receives the transmitted light that passes through the substrate 101 when the substrate 101 is irradiated with the inspection light (first inspection light), which is one of the two lights generated by the splitting of the polarizing beam splitter 332, as the incident light (first incident light) described above. The measured light intensity Itra of the transmitted light is output to the light intensity adjustment circuit 140 and stored in the memory device 41.

[0052] Similarly, the light intensity Iref of the incident light (second incident light) generated by the light source 103 and incident on the image sensor 205 via the ND filter 330, the λ / 2 wave plate 331, the polarizing beam splitter 332, and the substrate 101 placed on the XYθ table 102 is measured by the light intensity sensor 230. The light intensity sensor 230 receives the reflected light from the substrate 101 when the substrate 101 is illuminated with the inspection light (second inspection light), which is one of the two lights produced by the polarizing beam splitter 332, as the incident light (second incident light) described above. The measured light intensity Iref of the reflected light is output to the light intensity adjustment circuit 140 and stored in the memory device 41.

[0053] The example in Figure 8 shows a case where both the measured transmitted light intensity Itra and the reflected light intensity Iref are less than their respective target light intensity ranges.

[0054] In the determination step (S106), the determination unit 44 determines whether the light intensity Itra incident on the image sensor 105 for transmission inspection, measured by the light intensity sensor 130, and the light intensity Iref incident on the image sensor 205 for reflection inspection, measured by the light intensity sensor 230, are both within their respective target light intensity ranges. If both light intensity levels are within the target light intensity range, the light intensity calibration process is considered complete and the process proceeds to the image acquisition step (S120). If both light intensity levels are not within the target light intensity range, the process proceeds to the adjustment angle calculation step (S108).

[0055] As part of the adjustment angle calculation process (S108), the angle calculation unit 46 calculates the adjustment angle θadj of the λ / 2 wave plate 331 (half wave plate) such that the ratio of the light intensity of the transmitted light (first incident light) incident on the light intensity sensor 130 to the light intensity of the reflected light (second incident light) incident on the light intensity sensor 230 is a desired ratio. The adjustment angle θadj is calculated using a trigonometric function (first trigonometric function) that defines the ratio of the light intensity of the transmitted light incident on the light intensity sensor 130 to the light intensity of the light incident on the λ / 2 wave plate 331, which depends on the adjustment angle of the λ / 2 wave plate 331, and a trigonometric function (second trigonometric function) that defines the ratio of the light intensity of the reflected light incident on the light intensity sensor 230 to the light intensity of the light incident on the λ / 2 wave plate 331, which depends on the adjustment angle of the λ / 2 wave plate 331. A detailed explanation follows below.

[0056] Figure 9 shows an example of the relationship between the transmitted light ratio and the reflected light ratio adjusted by the λ / 2 wave plate in Embodiment 1. In Figure 9, the transmitted light ratio F(θ) represents the ratio of the amount of transmitted light (first incident light) incident on the light sensor 130, which depends on the adjustment angle of the λ / 2 wave plate 331, to the amount of light incident on the λ / 2 wave plate 331. The reflected light ratio G(θ) represents the ratio of the amount of reflected light (second incident light) incident on the light sensor 230, which depends on the adjustment angle of the λ / 2 wave plate 331, to the amount of light incident on the λ / 2 wave plate 331. The transmitted light ratio F(θ) is defined by a cosine function (an example of a first trigonometric function) shown in the following equation (1-1) using the coefficient Ktra. The reflected light ratio G(θ) can be defined by a cosine function (an example of a second trigonometric function) shown in the following equation (1-2) using the coefficient Kref.

[0057]

number

[0058] Equations (1-1) and (1-2) can be transformed using the half-angle formulas for trigonometric functions into the cosine function (2-1) (another example of the first trigonometric function) and the sine function (2-2) (another example of the second trigonometric function), respectively.

[0059]

number

[0060] Here, if we redefine 2Ktra as Ktra and 2Kref as Kref, equations (2-1) and (2-2) can be transformed into the cosine function (another example of the first trigonometric function) in equation (3-1) and the sine function (another example of the second trigonometric function) in equation (3-2). Furthermore, the coefficient Ktra is defined by equation (3-3), and the coefficient Kref is defined by equation (3-4).

[0061]

number

[0062] Here, light intensity Tmax represents the light intensity measured by the light intensity sensor 130 when the angle is set so that the transmitted light amount is maximum (100%) on the λ / 2 wave plate 331. Light intensity Tmin represents the light intensity measured by the light intensity sensor 130 when the angle is set so that the transmitted light amount is minimum (0%) on the λ / 2 wave plate 331. Light intensity Rmax represents the light intensity measured by the light intensity sensor 230 when the reflected light amount is set so that the reflected light amount is minimum (0%) on the λ / 2 wave plate 331. Light intensity Rmin represents the light intensity measured by the light intensity sensor 230 when the angle is set so that the reflected light amount is minimum (0%) on the λ / 2 wave plate 331. When there is no light from the light source 103, the measured light intensity will be zero. However, with adjustment using the λ / 2 wave plate 331, it may not be zero even at the minimum level. This corresponds to what is known as black level distortion. The portion that is not zero at the minimum level is offset on the light intensity sensors 130 and 230. Here, the gain components are denoted by the coefficients Ktra and Kref. The light intensity Tmax, Tmin, Rmax, and Rmin are measured in advance as device-specific values.

[0063] Figure 9 shows the cosine function F(θ) defined by equation (3-1), which depends on the adjustment angle θ, and the sine function G(θ) defined by equation (3-2). The information on the cosine function F(θ) defined by equation (3-1), which depends on the adjustment angle θ, and the sine function G(θ) defined by equation (3-2) is stored in the memory device 41 in advance.

[0064] In other words, the trigonometric function used to calculate the transmitted light ratio F(θ) (the first trigonometric function) is defined as a cosine function (the right-hand side of equation (3-1)) using a coefficient Ktra (the first coefficient) calculated using the light intensity measured by the light intensity sensor 130 (the first light intensity sensor) when the angle is set to maximize the transmitted light intensity of the λ / 2 wave plate 331 and the light intensity measured by the light intensity sensor 130 when the angle is set to minimize the transmitted light intensity of the λ / 2 wave plate 331. Furthermore, the trigonometric function used to calculate the reflected light ratio G(θ) (the second trigonometric function) is defined as a sine function (the right-hand side of equation (3-2)) using a coefficient Kref (the second coefficient) calculated using the light intensity measured by the light intensity sensor 230 (the second light intensity sensor) when the angle is set to maximize the reflected light intensity of the λ / 2 wave plate 331 and the light intensity measured by the light intensity sensor 230 when the angle is set to minimize the reflected light intensity of the λ / 2 wave plate 331.

[0065] The adjusted light intensity Tadj of the transmitted light (first incident light) after adjusting the angle θ set on the λ / 2 wave plate 331 from the initial angle θini to the adjustment angle θadj can be calculated by multiplying the initial light intensity Itra by the value obtained by dividing the transmitted light intensity ratio F(θadj) at the adjustment angle θadj by the transmitted light intensity ratio F(θini) at the initial angle θini. Similarly, the adjusted light intensity Radj of the reflected light (second incident light) can be calculated by multiplying the initial light intensity Iref by the value obtained by dividing the reflected light intensity ratio G(θadj) at the adjustment angle θadj by the reflected light intensity ratio G(θini) at the initial angle θini. Here, by adjusting the angle θ set on the λ / 2 wave plate 331 from the initial angle θini to the adjustment angle θadj, the ratio of the light intensity Tadj of the transmitted light (first incident light) after adjustment to the light intensity Radj of the reflected light (second incident light) is made the same as the ratio of the target light intensity Ttar of the transmitted light (first incident light) to the target light intensity Rtar of the reflected light (second incident light). This relationship can be defined by the following equation (4).

[0066]

number

[0067] The ratio of target light intensity Ttar to target light intensity Rtar is defined by equation (5).

[0068]

number

[0069] Using the relationship in equation (5), equation (4) can be transformed into equation (6).

[0070]

number

[0071] Therefore, the unknown adjustment angle θadj can be defined by the following equation (7).

[0072]

number

[0073] First, the coefficient calculation unit 45 calculates the coefficient α using equation (5). Then, the angle calculation unit 46 calculates the adjustment angle θadj using equation (7).

[0074] As an ND transmittance calculation step (S110), the transmittance calculation unit 48 calculates the transmittance NDadj of the ND filter 330 such that the amount of transmitted light incident on the light intensity sensor 130 falls within a preset target light intensity range for transmission (first desired range) for the light intensity sensor 130, and the amount of reflected light incident on the light intensity sensor 230 falls within a preset target light intensity range for reflection (second desired range) for the light intensity sensor 230. The transmittance NDadj is calculated using the calculated adjustment angle θadj. For example, it is preferable to set the target light intensity range to ±10% of the target light intensity. Specifically, the transmittance NDadj of the ND filter 330 is calculated using one of the following: the ratio of one of the light intensity of transmitted light incident on the light intensity sensor 130 and the light intensity of reflected light incident on the light intensity sensor 230, when the λ / 2 wave plate 331 is adjusted by the calculated adjustment angle θadj, to a predetermined target light intensity; or a statistical value obtained using the light intensity of transmitted light and reflected light. A more detailed explanation follows.

[0075] The transmittance NDadj can be calculated, for example, by multiplying the initial transmittance value NDini of the ND filter 330 by the ratio of the target transmitted light amount Ttar to the adjusted transmitted light amount Tadj. That is, the transmittance NDadj can be defined, for example, using the adjusted transmitted light amount Tadj, by the following equation (8). As mentioned above, the transmitted light amount Tadj is the value obtained by multiplying the initial light amount Itra by the value obtained by dividing the transmitted light amount ratio F(θadj) at the adjustment angle θadj (calculated adjustment angle) by the transmitted light amount ratio F(θini) at the initial angle θini.

[0076]

number

[0077] Alternatively, the transmittance NDadj can be calculated, for example, by multiplying the initial transmittance value NDini of the ND filter 330 by the ratio of the target reflected light intensity Rtar to the adjusted reflected light intensity Radj. That is, the transmittance NDadj can be defined, for example, using the adjusted reflected light intensity Radj, by the following equation (9). As mentioned above, the reflected light intensity Radj is obtained by multiplying the initial light intensity Iref by the value obtained by dividing the reflected light intensity ratio G(θadj) at the adjustment angle θadj by the reflected light intensity ratio G(θini) at the initial angle θini.

[0078]

number

[0079] Alternatively, the statistical values ​​of each transmittance NDadj mentioned above, for example, as the average value, may also be used. This can be defined by the following equation (10).

[0080]

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[0081] As a setting step (S112), the setting unit 49 sets the ND filter 330 to the calculated transmittance NDadj. The setting unit 49 also sets the λ / 2 wave plate 331 to the calculated adjustment angle θadj.

[0082] As a light intensity measurement step (S114), the light intensity measurement processing unit 42 measures the amount of light incident on the image sensor 105 for transmission inspection and the image sensor 205 for reflection inspection, with the transmittance NDadj set on the ND filter 330 and the adjustment angle θadj set on the λ / 2 wave plate 331. The method of light intensity measurement is the same as the method described above. Since this measurement is a step to verify the calculated results, it may be omitted.

[0083] As described above, the light intensity calibration process is performed. This ensures that the amount of light incident on the image sensor 105 for transmission inspection and the amount of light incident on the image sensor 205 for reflection inspection both fall within the target light intensity range. After the light intensity calibration process is complete, the light intensity measurement processing unit 42 outputs a command to the light intensity sensor control circuit 142 indicating that the light intensity measurement is complete. Under the control of the light intensity sensor control circuit 142, the drive mechanism 132 moves the light intensity sensor 130 out of the optical path. Similarly, under the control of the light intensity sensor control circuit 142, the drive mechanism 232 moves the light intensity sensor 230 out of the optical path. Next, the inspection process is performed.

[0084] In the image acquisition process (S120), the optical image acquisition mechanism 150 uses an image sensor 105 (205) that has undergone light intensity calibration to capture an image of the substrate 101 and output the captured optical image data. To do this, the optical image acquisition mechanism 150 first scans the inspection stripe 20 with transmitted inspection light and reflected inspection light, respectively, and captures a stripe region image for each inspection stripe 20 using the image sensor 105 (205). Specifically, it operates as follows. Move the XYθ table 102 to a position where the target inspection stripe 20 can be imaged.

[0085] Then, the amount of light generated from the light source 103 is attenuated by an ND filter 330 with a transmittance NDadj set. The polarization direction of the light that has passed through the ND filter 330 is adjusted by a λ / 2 wave plate 331 with an adjustment angle θadj set. The laser light 301 with the adjusted polarization direction is then split by a polarizing beam splitter 332 according to the polarization direction, generating two inspection beams, for example, a P-wave component beam and an S-wave component beam.

[0086] In transmission inspection, the imaging sensor 105 (first imaging sensor) captures an optical image (first optical image) of the substrate 101 by irradiating the substrate 101 with inspection light (first inspection light), which is one of two beams of light produced when light that has passed through an ND filter 330 set to a calculated transmittance NDadj and a λ / 2 wave plate 331 adjusted to a calculated adjustment angle θadj is split by a polarizing beam splitter 332.

[0087] The image of the pattern formed on the imaging sensor 105 is photoelectrically converted by each photosensor element of the imaging sensor 105, and then A / D (analog-to-digital) converted by the sensor circuit 106. The gradation value (image data) of each pixel is output to the stripe pattern memory 123 and temporarily stored. The measurement data (pixel data) of the inspection stripe 20 to be measured, stored in the stripe pattern memory 123, is, for example, 8-bit unsigned data, representing the gradation (light intensity) of the brightness of each pixel. The pixel value data of the inspection stripe 20 is output to the comparison circuit 108.

[0088] In reflection inspection, the imaging sensor 205 (second imaging sensor) captures an optical image (second optical image) of the substrate 101 by irradiating the substrate 101 with the inspection light (second inspection light), which is one of the two beams of light produced when the light that has passed through the ND filter 330 set to the calculated transmittance NDadj and the λ / 2 wave plate 331 adjusted to the calculated adjustment angle θadj is split by the polarizing beam splitter 332.

[0089] The image of the pattern formed on the imaging sensor 205 is photoelectrically converted by each photosensor element of the imaging sensor 205, and then A / D (analog-to-digital) converted by the sensor circuit 206. The gradation value (image data) of each pixel is output to the stripe pattern memory 223 and temporarily stored. The measurement data (pixel data) of the inspection stripe 20 to be measured, stored in the stripe pattern memory 223, is, for example, 8-bit unsigned data, representing the gradation (light intensity) of the brightness of each pixel. The pixel value data of the inspection stripe 20 is output to the comparison circuit 108.

[0090] As part of the reference image creation process (S122), the reference image creation circuit 112 creates a reference image using graphic pattern data (design data). The creation of the reference image is performed for each inspection stripe 20 in parallel with the scanning operation of the inspection stripe 20. Specifically, it operates as follows: The reference image creation circuit 112 receives 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-level image data.

[0091] The shapes defined in the shape pattern data are based on basic shapes such as rectangles and triangles. The data stores shape data that defines the shape, size, position, etc., of each pattern shape, including information such as the coordinates (x, y) at the reference position of the shape, the length of the sides, and a shape code that serves as an identifier to distinguish between different shape types such as rectangles and triangles.

[0092] When the design pattern data, which will become such graphic data, is input to the reference image creation circuit 112, it is expanded into data for each graphic, and the graphic code and dimensions indicating the shape of the graphic data are interpreted. Then, it is expanded into binary or multi-level design pattern image data as a pattern to be placed in a grid of predetermined quantization dimensions and output. In other words, the design data is read, the frame area is virtually divided into a grid of predetermined dimensions, the occupancy rate of the graphic in the design pattern is calculated for each resulting grid, and n-bit occupancy rate data (design image data) is output. For example, it is preferable to set one grid as one pixel. Then, 1 / 2 8 If we want a resolution of (=1 / 256), we allocate a small area of ​​1 / 256 the size of the area of ​​the shape placed within the pixel and calculate the occupancy rate within the pixel. This is then created as 8-bit occupancy rate data. The grid (inspection pixels) used for this should match the pixels of the measurement data.

[0093] Next, the reference image creation circuit 112 applies a filter function to the design image data of the design pattern, which is the image data of the shape.

[0094] Figure 10 is a diagram illustrating the filtering process in Embodiment 1. The pixel data of the optical image captured from the substrate 101 is in a state where a filter is applied by the resolution characteristics of the optical system used for imaging, in other words, it is in a continuously changing analog state. For example, as shown in Figure 10, the image intensity (grayscale value) differs from that of the unfolded image (design image), which has digital values. On the other hand, in graphic pattern data, as described above, it is defined by graphic codes, etc., so in the unfolded design image, the image intensity (grayscale value) may be a digital value. Therefore, the reference image creation circuit 112 applies image processing (filtering) to the unfolded image to create a reference image that is closer to the optical image. This makes it possible to match the design image data, which is design-side image data with digital image intensity (grayscale value), to the image generation characteristics of the measurement data (optical image). The created reference image is output to the comparison circuit 108.

[0095] Here, we create reference images for transmission inspection and reference images for reflection inspection. For example, the black and white colors of the pattern are inverted in the reference images for transmission and reflection inspection.

[0096] As a comparison step (S130), the comparison circuit unit 144 compares the optical image for transmission inspection (first optical image) with the reference image for transmission inspection (first predetermined image), and also compares the optical image for reflection inspection (second optical image) with the reference image for reflection inspection (second predetermined image).

[0097] Figure 11 shows an example of the internal configuration of a comparison circuit in Embodiment 1. In Figure 11, each comparison circuit 108 contains a storage device 70, 72, 76 such as a magnetic disk drive, a frame image creation unit 74, a alignment unit 78, and a comparison processing unit 79. The series of "~ units," such as the frame image creation unit 74, the alignment unit 78, and the comparison processing unit 79, each have a processing circuit. Such processing circuits include electrical circuits, computers, processors, circuit boards, quantum circuits, or semiconductor devices. Furthermore, each "~ unit" may use a common processing circuit (the same processing circuit), or it may use different processing circuits (separate processing circuits). The input data or calculated results required by the frame image creation unit 74, the alignment unit 78, and the comparison processing unit 79 are stored in a memory or memory 111 (not shown) within the comparison circuit 108 each time.

[0098] Of the multiple comparison circuits 108a and 108b with the same configuration, comparison circuit 108a performs transmission testing and comparison circuit 108b performs reflection testing. Alternatively, for example, a single comparison circuit 108 may perform both transmission testing and reflection testing.

[0099] The stripe data (striped region image) input to the comparison circuit 108a (108b) is stored in the storage device 70. The reference image data input to the comparison circuit 108 is stored in the storage device 72.

[0100] In the comparison circuit 108, the frame image creation unit 74 first generates multiple frame images 31 in which the striped region image (optical image) is divided by a predetermined width. Specifically, as shown in Figure 2, the striped region image is divided into frame images of multiple rectangular frame regions 30. For example, it is divided into 1024 × 1024 pixel sizes. The data of each frame region 30 is stored in the storage device 76.

[0101] Next, the alignment unit 78 reads the corresponding frame image 31 and the corresponding reference image from the storage devices 72 and 76 for each frame region 30, and aligns the frame image 31 and the corresponding reference image using a predetermined algorithm. For example, the least squares method is used for alignment.

[0102] The comparison processing unit 79 (another example of a comparison unit) then compares the frame image 31 with the reference image corresponding to the frame image 31. For example, it compares each pixel. Here, the two are compared pixel by pixel according to predetermined judgment conditions to determine the presence or absence of defects, such as shape defects. As for the judgment conditions, for example, the two are compared pixel by pixel according to a predetermined algorithm to determine the presence or absence of defects. For example, the difference value of the pixel values ​​of both images is calculated for each pixel, and if the difference value is greater than a threshold Th, it is determined to be a defect. The comparison result can then be output to, for example, a magnetic disk drive 109, or a pattern monitor (not shown), or output from a printer (not shown).

[0103] The above example describes the case of die-database inspection, but die-die inspection is also acceptable. 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 that are subjected to die-die inspection as a reference (reference image). First, the alignment unit 78 reads the corresponding frame image 31 of die 1 and the frame image of die 2 from the storage device 76 for each frame area 30 that is subjected to die-die inspection, and aligns the frame image 31 of die 1 and the frame image of die 2 using a predetermined algorithm. For example, the least squares method is used for alignment. Then, the comparison processing unit 79 (comparison unit) compares the corresponding frame image 31 of die 1 and the frame image of die 2 pixel by pixel for each frame area 30 that is subjected to die-die inspection.

[0104] As described above, according to Embodiment 1, the number of light intensity measurements and the number of adjustments required for the ND filter 330 and the λ / 2 wave plate 331 can be significantly reduced. Therefore, the processing time for calibration of the amount of incident light to each system of imaging sensors, such as transmission inspection and reflection inspection, can be shortened.

[0105] The embodiments have been described above with reference to specific examples. However, the present invention is not limited to these specific examples.

[0106] Furthermore, while descriptions of the device configuration, control methods, and other parts not directly necessary for explaining the present invention have been omitted, it goes without saying that the necessary device configuration and control methods can be appropriately selected and used. For example, although the control unit configuration for controlling the inspection device 100 has been omitted, it goes without saying that the necessary control unit configuration can be appropriately selected and used.

[0107] Furthermore, all pattern inspection devices and pattern inspection methods that incorporate elements of the present invention and can be appropriately modified by those skilled in the art are included within the scope of the present invention. [Explanation of Symbols]

[0108] 10 Examination Areas 20 inspection stripes 30 frame area 31 frame images 40 Initial value setting section 41 Storage device 42 Light intensity measurement processing unit 44 Judgment section 45 Coefficient Calculation Unit 46 Angle Calculation Unit 48 Transmittance calculation section 49. Settings section 70,72,76 storage device 74 Frame Image Creation Section 78 Alignment section 79 Comparison Processing Unit 100 Inspection device 101 circuit board 102 XYθ Table 103 Light source 104 Objective lens 105,205 imaging sensors 106,206 Sensor Circuits 107 Position circuit 108 Comparison circuit 109 Magnetic disk drive 110 Control Computer 111 memory 112 Reference Image Creation Circuit 114 Table Control Circuit 120 bus 123,223 Stripe Pattern Memory 130,230 light intensity sensor 132,232 Drive mechanism 140 Light intensity adjustment circuit 142 Light intensity sensor control circuit 144 Test Circuit Unit 150 Optical image acquisition mechanism 160 Control System Circuits 170 Transmitted illumination optical system 171 Lens 172 Miller 176 Beam Splitter 177 Miller 178,278 Imaging optical system 270 Reflected illumination optical system 271 Lens 272 Miller 330 ND filter 331 λ / 2 wave plate 332 Polarizing Beam Splitter

Claims

1. A stage on which a patterned sample can be placed, Light source and A light-reducing filter that arbitrarily attenuates the amount of light emitted from the aforementioned light source, A half-wave plate that adjusts the polarization direction of light that has passed through the light-reducing filter, A branching element that branches the light that has passed through the half-wave plate, A first imaging sensor captures a first optical image of the sample obtained by irradiating the sample with a first inspection light, which is one of the two lights produced by the branching of the sample. A second imaging sensor captures a second optical image of the sample obtained by irradiating the sample with a second inspection light, which is one of the two lights produced by the branching, A first light intensity sensor that measures the amount of first incident light incident on the first imaging sensor, A second light intensity sensor that measures the amount of second incident light incident on the second imaging sensor, An angle calculation unit that calculates the adjustment angle of the half-wave plate such that the ratio of the light intensity of the first incident light incident on the first light intensity sensor to the light intensity of the second incident light incident on the second light intensity sensor is a desired ratio, A transmittance calculation unit calculates the transmittance of the light-reducing filter such that the amount of light from the first incident light incident on the first light intensity sensor is within a desired range set for the first light intensity sensor, and the amount of light from the second incident light incident on the second light intensity sensor is within a desired range set for the second light intensity sensor. A comparison unit that compares the first optical image with a first predetermined image, and also compares the second optical image with a second predetermined image, A pattern inspection apparatus characterized by being equipped with the following features.

2. The first optical image is captured using a first inspection light, which is one of two beams of light produced when light passing through the attenuation filter set to the calculated transmittance and the half-wave plate adjusted to the calculated adjustment angle is split. The second optical image is captured using a second inspection light, which is one of the two beams of light produced when light passing through the attenuation filter set to the calculated transmittance and the half-wave plate adjusted to the calculated adjustment angle is split. The pattern inspection apparatus according to claim 1, characterized in that

3. The first light intensity sensor receives transmitted light that has passed through the sample when the sample is irradiated with the first inspection light. The second light intensity sensor receives reflected light from the sample when the sample is irradiated with the second inspection light. The pattern inspection apparatus according to claim 1, characterized in that

4. The pattern inspection apparatus according to claim 1, characterized in that the transmittance is calculated using the calculated adjustment angle.

5. The adjustment angle is calculated using a first trigonometric function that defines the ratio of the amount of light of the first incident light incident on the first light intensity sensor, which depends on the adjustment angle of the half-wave plate, to the amount of light of the light incident on the half-wave plate, and a second trigonometric function that defines the ratio of the amount of light of the second incident light incident on the second light intensity sensor, which depends on the adjustment angle of the half-wave plate, to the amount of light of the light incident on the half-wave plate. The pattern inspection apparatus according to claim 1, characterized in that the transmittance is calculated using one of the following: the ratio of one of the light intensity of the first incident light incident on the first light intensity sensor and the light intensity of the second incident light incident on the second light intensity sensor when the half-wave plate is adjusted at the calculated adjustment angle, to a predetermined target light intensity; and a statistical value obtained using the light intensity of the first incident light and the light intensity of the second incident light.

6. The pattern inspection apparatus according to claim 5, characterized in that the average value is used as the aforementioned statistical value.

7. The pattern inspection apparatus according to claim 5, characterized in that the first trigonometric function is defined by a cosine function using a first coefficient calculated using the amount of light measured by the first light intensity sensor when the angle is set so that the amount of transmitted light transmitted by the half-wave plate is maximized and the amount of light measured by the first light intensity sensor when the angle is set so that the amount of transmitted light transmitted by the half-wave plate is minimized.

8. The pattern inspection apparatus according to claim 5, characterized in that the second trigonometric function is defined by a sine function using a second coefficient calculated using the amount of light measured by the second light intensity sensor when the amount of reflected light from the half-wave plate is set to the maximum and the amount of light measured by the second light intensity sensor when the angle is set so that the amount of reflected light from the half-wave plate is set to the minimum.

9. The aforementioned transmittance is calculated by multiplying the initial value of the transmittance of the light-reducing filter by the ratio of the target amount of transmitted light to the amount of transmitted light after adjustment. The pattern inspection apparatus according to claim 4, characterized in that the amount of transmitted light after adjustment is the value obtained by multiplying the initial amount of transmitted light by the value obtained by dividing the ratio of transmitted light at the calculated adjustment angle by the ratio of transmitted light at the initial angle.

10. By using a neutral density filter, the amount of light emitted from the light source can be arbitrarily reduced. Using a half-wave plate, the polarization direction of the light that has passed through the attenuation filter is adjusted. Using a branching element, the light that has passed through the half-wave plate is branched, Using the first light intensity sensor, the amount of first incident light generated by the light source and incident on the first imaging sensor via the attenuation filter, the half-wave plate, the branching element, and the patterned sample placed on the stage is measured. Using a second light intensity sensor, the amount of second incident light generated by the light source and incident on the second imaging sensor via the attenuation filter, the half-wave plate, the branching element, and the sample is measured. The adjustment angle of the half-wave plate is calculated so that the ratio of the light intensity of the first and second incident light incident on the first and second light intensity sensors becomes a desired ratio. The transmittance of the light-reducing filter is calculated such that the amount of light from the first incident light incident on the first light intensity sensor is within a desired range set for the first light intensity sensor, and the amount of light from the second incident light incident on the second light intensity sensor is within a desired range set for the second light intensity sensor. Using the first imaging sensor, the sample is irradiated with a first inspection light, which is one of two beams of light produced when the light passing through the attenuation filter set to the calculated transmittance and the half-wave plate adjusted to the calculated adjustment angle is split by the branching element, thereby capturing a first optical image of the sample. Using the second imaging sensor, the sample is irradiated with a second inspection light, which is one of the two beams of light produced when the light that has passed through the attenuation filter set to the calculated transmittance and the half-wave plate adjusted to the calculated adjustment angle is split by the branching element, thereby capturing a second optical image of the sample. The first optical image is compared with a first predetermined image, and the second optical image is compared with a second predetermined image, and the results are output. A pattern inspection method characterized by the following features.

Images