Pattern inspection device and pattern inspection method

Abstract

PURPOSE: To provide an inspection device that can suppress the accuracy deterioration of an image due to a change in image storage time.CONSTITUTION: A pattern inspection device according to an aspect of the present invention comprises an illumination optical system 170 (171) illuminating an inspection substrate to be tested on which a pattern is formed, an off-set calculation part 64 that calculate an off-set quantity that depends on the image storage time of each photosensor device in a plurality of photosensor devices that are arrayed two-dimensionally, a TDI sensor 105 having a plurality of photosensor devices, imaging the inspection substrate to be tested by receiving the transmitted light or reflected light from the inspection substrate to be tested with the plurality of photosensor devices, correcting the pixel value of the imaged optical image data using the off-set quantity, then outputting the corrected optical image data, and a comparator circuit 108 that compares the optical image constituted with the optical image data outputted from the TDI sensor with a reference image.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to a pattern inspection apparatus and a pattern inspection method, and more particularly to an apparatus and a method for inspecting pattern defects on an exposure mask used in semiconductor manufacturing. [Background technology]

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

[0003] Improving yield is essential for the manufacture of LSIs, which are very costly to manufacture. One of the major factors that reduces yield is pattern defects in the 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 have become increasingly miniaturized, the dimensions that must be detected as pattern defects have also become extremely small. This has led to a need for higher-precision pattern inspection equipment to inspect defects in the transfer masks used in LSI manufacturing.

[0004] Inspection techniques include, for example, "die-to-die inspection," which compares optical image data captured of the same pattern at different locations on the same mask, and "die-to-database inspection," which converts pattern-design CAD data into a device input format for input by a drawing device when drawing the pattern on a mask, inputs the converted 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 from the pattern.

[0005] As patterns become finer, techniques are being adopted to improve transfer resolution by adjusting the transmittance or reflectance of the material of the exposure mask. However, when the transmittance or reflectance of the mask used as the sample decreases, inspection equipment is unable to obtain images with sufficient information. Because there is a limit to how much light can be increased from the light source, increasing the image accumulation time of each photosensor element in the image sensor has been considered as a solution. However, operating the sensor with different image accumulation times changes the sensor temperature, which in turn changes the dark noise level. This results in a problem of reduced image accuracy, which can lead to false defects.

[0006] Although not a pattern inspection device for masks or the like, an image recognition device that recognizes objects such as fingers or barcodes has been disclosed that shortens the accumulation time of the sensor when the ambient temperature is high (see, for example, Patent Document 1). [Prior art documents] [Patent documents]

[0007] [Patent Document 1] JP 2003-032435 JP 2020-42035 JP 2020-42035 JP 2020-42035 JP 2020-42035 Summary of the Invention [Problem to be solved by the invention]

[0008] Therefore, one aspect of the present invention provides an inspection apparatus and method that can suppress deterioration in image accuracy caused by changes in image accumulation time. [Means for solving the problem]

[0009] A pattern inspection apparatus according to one aspect of the present invention comprises: an illumination optical system that illuminates an inspection target substrate on which a pattern is formed; Image accumulation time of each of multiple photosensor elements arranged two-dimensionallyBased on the difference between the dark noise level Dr1 at t1 and the dark noise level Dr2 when the image accumulation time t1 is switched to a different image accumulation time t2 an offset calculation unit that calculates an offset amount; a time delay integration (TDI) sensor having a plurality of photosensor elements, capturing an image of the substrate to be inspected by receiving transmitted light or reflected light from the substrate to be inspected with the plurality of photosensor elements, correcting pixel values ​​of the captured optical image data using an offset amount, and outputting the corrected optical image data; a comparison unit that compares an optical image formed by optical image data output from the TDI sensor with a reference image; The present invention is characterized by the following features.

[0010] In addition, the offset calculation unit Until the dark noise level Dr2 stabilizes Calculate the offset amount according to the imaging timing, It is preferable that the TDI sensor corrects the optical image data at each imaging timing using an offset amount corresponding to the imaging timing.

[0011] Another aspect of the pattern inspection apparatus of the present invention is an illumination optical system that illuminates an inspection target substrate on which a pattern is formed; an offset calculation unit that calculates an offset amount based on a difference between a dark noise level Dr1 of each of a plurality of photosensor elements arranged two-dimensionally at an image accumulation time t1 and a dark noise level Dr2 when the image accumulation time t1 is switched to an image accumulation time t2 different from the image accumulation time t1; a time delay integration (TDI) sensor having a plurality of photosensor elements, capturing an image of the substrate to be inspected by receiving transmitted light or reflected light from the substrate to be inspected with the plurality of photosensor elements, correcting pixel values ​​of the captured optical image data using an offset amount, and outputting the corrected optical image data; a comparison unit that compares an optical image formed by optical image data output from the TDI sensor with a reference image; Equipped with The TDI sensor corrects the optical image data using a certain offset amount after a predetermined period has elapsed since the image accumulation time was switched. It is characterized by:

[0012] Another aspect of the pattern inspection apparatus of the present invention is an illumination optical system that illuminates an inspection target substrate on which a pattern is formed; a temperature change amount calculation unit that calculates a temperature change amount that depends on an image accumulation time of each of the plurality of photosensor elements that are two-dimensionally arranged; a time delay integration (TDI) sensor having a plurality of photosensor elements, which captures an image of the substrate to be inspected by receiving transmitted light or reflected light from the substrate to be inspected with the plurality of photosensor elements while controlling the temperatures of the plurality of photosensor elements using a temperature change amount; a comparison unit that compares the captured optical image with a reference image; The present invention is characterized by the following features.

[0013] The TDI sensor preferably has an air-cooling mechanism, a water-cooling mechanism, or a heat pipe mechanism.

[0014] The temperature sensor further includes an offset calculation unit that calculates an offset amount according to a temperature error when controlling the temperatures of the plurality of photosensor elements, The TDI sensor preferably corrects the optical image data using an offset amount.

[0015] A pattern inspection method according to one aspect of the present invention includes: a step of illuminating an inspection target substrate on which a pattern is formed; calculating an offset amount based on a difference between a dark noise level Dr1 of each of a plurality of photosensor elements arranged two-dimensionally at an image accumulation time t1 and a dark noise level Dr2 when the image accumulation time t1 is switched to an image accumulation time t2 different from the image accumulation time t1; a step of capturing an image of the substrate to be inspected by using a time delay integration (TDI) sensor having a plurality of photosensor elements to receive transmitted light or reflected light from the substrate to be inspected, correcting pixel values ​​of the captured optical image data using the offset amount, and outputting the corrected optical image data; comparing an optical image formed by the optical image data output from the TDI sensor with a reference image; Equipped with 、 calculating the offset amount according to an imaging timing from a point in time when the image accumulation time is switched until the dark noise level Dr2 is stabilized; The TDI sensor corrects the optical image data at each imaging timing using the offset amount corresponding to the imaging timing. It is characterized by:

[0016] A pattern inspection method according to another aspect of the present invention includes: a step of illuminating an inspection target substrate on which a pattern is formed; calculating a temperature change amount depending on an image accumulation time of each of a plurality of photosensor elements arranged two-dimensionally; a step of capturing an image of the substrate to be inspected by using a time delay integration (TDI) sensor having a plurality of photosensor elements and receiving transmitted or reflected light from the substrate to be inspected with the plurality of photosensor elements while controlling the temperatures of the plurality of photosensor elements using the amount of temperature change; comparing the captured optical image with a reference image; The present invention is characterized by the following features. [Effects of the Invention]

[0017] According to one aspect of the present invention, it is possible to suppress deterioration in image accuracy caused by changes in image accumulation time. [Brief explanation of the drawings]

[0018] [Figure 1] FIG. 1 is a configuration diagram showing a configuration of a pattern inspection device according to a first embodiment. [Figure 2] FIG. 2 is a conceptual diagram for explaining an inspection area in the first embodiment. [Figure 3] FIG. 4 is a diagram showing an example of a change in dark noise level accompanying switching of image accumulation times of each photosensor element of the TDI sensor in the first embodiment. [Figure 4] 5 is a diagram showing an example of the correlation between the inspection signal and the sensor output in response to changes in the dark noise level in the first embodiment. FIG. [Figure 5] FIG. 3 is a flowchart showing an example of main steps of an image acquisition method according to the first embodiment. [Figure 6] 3 is a block diagram showing an example of the internal configuration of an offset amount calculation circuit according to the first embodiment. FIG. [Figure 7] FIG. 2 is a flowchart showing the main steps of the inspection method according to the first embodiment. [Figure 8] FIG. 3 is a diagram illustrating a filter process according to the first embodiment. [Figure 9] 3 is a diagram showing an example of the internal configuration of each comparison circuit according to the first embodiment; FIG. [Figure 10] FIG. 10 is a configuration diagram showing the configuration of a pattern inspection device according to a second embodiment. [Figure 11] FIG. 10 is a block diagram showing an example of the internal configuration of a temperature adjustment circuit according to a second embodiment. [Figure 12] FIG. 10 is a configuration diagram showing an example of a temperature adjustment mechanism according to the second embodiment. [Figure 13] FIG. 10 is a configuration diagram showing another example of the temperature adjustment mechanism in the second embodiment. [Figure 14] FIG. 10 is a configuration diagram showing another example of the temperature adjustment mechanism in the second embodiment. [Figure 15] FIG. 10 is a configuration diagram showing the configuration of a pattern inspection device according to a third embodiment. DETAILED DESCRIPTION OF THE INVENTION

[0019] Embodiment 1 Fig. 1 is a configuration diagram showing the configuration of a pattern inspection apparatus according to embodiment 1. In Fig. 1, an inspection apparatus 100 that inspects a substrate to be inspected, for example, a pattern formed on a mask, for defects includes an optical image acquisition mechanism 150 and a control circuit 160.

[0020] The optical image acquisition mechanism 150 includes a light source 103, a transmitted illumination optical system 170, a reflected illumination optical system 171, a movably arranged XYθ table 102, a magnifying optical system 104, a beam splitter 174, an imaging optical system 176, a TDI (time delay integration) sensor 105, a stripe pattern memory 123, a laser measurement system 122, and an autoloader 130. When performing a transmitted inspection using transmitted light, the reflected illumination optical system 171 and the beam splitter 174 may be omitted. When performing a reflected inspection using reflected light, the transmitted illumination optical system 170 may be omitted.

[0021] A substrate 101 transferred from an autoloader 130 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. This photomask has a plurality of graphic patterns formed thereon to be inspected. The substrate 101 is placed on the XYθ table 102 with the pattern-formed surface facing downward, for example.

[0022] The TDI sensor 105 has a photosensor array 124, a sensor circuit 125, and an offset circuit 126. The photosensor array 124 has a plurality of photosensor elements arranged two-dimensionally. A predetermined image accumulation time is set for each photosensor element when capturing an image. The TDI sensor 105 integrates and outputs the outputs of the plurality of photosensor elements arranged in the scanning direction. The plurality of photosensor elements arranged in the scanning direction capture the same pixel at different times in accordance with the movement of the XYθ table 102.

[0023] In the control system circuit 160, a control computer 110 that controls the entire inspection apparatus 100 is connected via a bus 120 to a position circuit 107, a comparison circuit 108, a reference image creation circuit 112, an autoloader control circuit 113, a table control circuit 114, an offset amount calculation circuit 136, a magnetic disk drive 109, a memory 111, a magnetic tape drive 115, a flexible disk drive (FD) 116, a CRT 117, a pattern monitor 118, and a printer 119. The TDI sensor 105 is connected to a stripe pattern memory 123, which is connected to a plurality of comparison circuits 108. The XYθ table 102 is driven by an X-axis motor, a Y-axis motor, and a 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 offset amount calculation circuit 136 is connected to an offset circuit 126.

[0024] Note that a series of "circuits" such as the position circuit 107, the comparison circuit 108, the reference image creation circuit 112, the autoloader control circuit 113, the table control circuit 114, and the offset amount calculation circuit 136 include processing circuits. Such processing circuits include electrical circuits, computers, processors, circuit boards, quantum circuits, semiconductor devices, etc. Alternatively, different processing circuits (separate processing circuits) may be used. For example, a series of "circuits" such as the position circuit 107, the comparison circuit 108, the reference image creation circuit 112, the autoloader control circuit 113, the table control circuit 114, and the offset amount calculation circuit 136 may be configured and executed by the control computer 110. Input data or calculated results required for the position circuit 107, the comparison circuit 108, the reference image creation circuit 112, the autoloader control circuit 113, the table control circuit 114, and the offset amount calculation circuit 136 are stored in a memory (not shown) within each circuit or in memory 111. Input data required for the control computer 110 or the results of calculations are stored each time in a memory (not shown) within the control computer 110 or in memory 111. The programs for executing the processors and the like may be recorded on recording media such as the magnetic disk device 109, the magnetic tape device 115, the FD 116, or a ROM (read-only memory).

[0025] In the inspection device 100, a high-magnification transmission inspection optical system is configured by the light source 103, the XYθ table 102, the transmission illumination optical system 170, the magnifying optical system 104, the imaging optical system 176, and the TDI sensor 105. In addition, a high-magnification reflection inspection optical system is configured by the light source 103, the reflective illumination optical system 171, the beam splitter 174, the magnifying optical system 104, the XYθ table 102, the imaging optical system 176, and the TDI sensor 105.

[0026] The XYθ table 102 is driven by a table control circuit 114 under the control of the control computer 110. It can be moved by a drive system such as a three-axis (XY-θ) motor that drives in the X, Y, and θ directions. These X, Y, and θ motors can be, for example, step motors. The XYθ table 102 can be moved horizontally and rotationally by the motors on the X, Y, and θ axes. The movement position of the substrate 101 placed on the XYθ table 102 is measured by a laser measurement system 122 and supplied to the position circuit 107. The transfer of the substrate 101 from the autoloader 130 to the XYθ table 102 and the transfer process of the substrate 101 from the XYθ table 102 to the autoloader 130 are controlled by an autoloader control circuit 113.

[0027] 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 a plurality of graphic patterns, and each graphic pattern is usually composed of a combination of a plurality of element graphics. However, a graphic pattern composed of a single graphic may also be present. On the inspected substrate 101, corresponding patterns are formed based on each graphic pattern defined in the drawing data.

[0028] 1 shows components necessary for explaining the first embodiment. It goes without saying that the inspection device 100 may include other components that are normally required.

[0029] 2 is a conceptual diagram illustrating the inspection area in the first embodiment. As shown in FIG. 2, the inspection area 10 (the entire inspection area) of the substrate 101 is virtually divided, for example, in the Y direction, into a plurality of rectangular inspection stripes 20 each having a scan width W of the TDI sensor 105. 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. Note that, to prevent missing images, the inspection stripes 20 are preferably set so that adjacent inspection stripes 20 overlap with each other by a predetermined margin width.

[0030] The movement of the XYθ table 102 causes the TDI sensor 105 to continuously move relatively in the X direction, thereby acquiring optical images. The TDI sensor 105 continuously captures optical images with a scan width W as shown in FIG. 2. In other words, the TDI sensor 105 captures optical images of the surface of the substrate 101 on which multiple graphic patterns are formed, while moving relatively in the integration direction of the TDI sensor 105. In the first embodiment, after capturing an optical image of one inspection stripe 20, the TDI sensor 105 moves in the Y direction to the position of the next inspection stripe 20, and then moves in the reverse direction while continuously capturing optical images with the scan width W in the same manner. In other words, imaging is repeated in the forward (FWD)-backward (BWD) directions, which are opposite directions on the outgoing and returning passes.

[0031] Furthermore, in actual inspection, the stripe region image of each inspection stripe 20 is divided into a plurality of rectangular frame region 30 images, as shown in FIG. 2. Then, inspection is performed for each frame region 30 image. For example, it is divided into a size of 512 × 512 pixels. Therefore, a reference image to be compared with the frame image 31 of the frame region 30 is also created for each frame region 30.

[0032] Here, 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. Alternatively, BWD-BWD may be repeated.

[0033] As described above, with the trend toward finer patterns, techniques for improving transfer resolution by adjusting the transmittance or reflectance of the material of the exposure mask are being adopted. It is desirable to be able to inspect multiple substrates 101 with different transmittances or reflectances using the same inspection system 100. However, in the inspection system 100, if the transmittance or reflectance of the mask that becomes the substrate 101 decreases, the amount of light received by the TDI sensor 105 decreases. As a result, an image with sufficient information cannot be obtained. Because there is a limit to how much light can be increased from the light source 103, this can be addressed by increasing the image accumulation time of each photosensor element of the TDI sensor 105 that captures the image. For example, by doubling the image accumulation time instead of doubling the light amount, an image similar to that obtained when the light amount is doubled can be obtained.

[0034] However, when each photosensor element is operated with a different image accumulation time t, the sensor temperature T changes, and the dark noise level Dr changes. The dark noise level Dr depends on the sensor temperature.

[0035] 3 is a diagram showing an example of changes in dark noise level accompanying switching of the image accumulation time of each photosensor element of the TDI sensor in embodiment 1. When the TDI sensor 105 is driven for a sufficiently long time L with an image accumulation time t1 of the photosensor element from an initial temperature T0 under certain operating conditions, the sensor temperature T becomes T1 based on the operating environment and the power consumption of the photosensor element. The sensor temperature T can be defined by the following equation (1): (1) T=f1(t1,L,T0)=T1

[0036] Moreover, the dark noise level Dr in this state can be defined by the following equation (2). (2) Dr=f2(T1)=Dr1

[0037] For the TDI sensor 105 that has been driven with an image accumulation time t1 of such a photosensor element, the image accumulation time t is switched from t1 to t2. In this case, the sensor temperature T changes based on the operating environment and the power consumption of the photosensor element in accordance with the elapsed time δ from the time of switching. In this case, the sensor temperature T can be defined by the following equation (3): (3) T=f1(t2,δ,T1)=T2

[0038] Moreover, the dark noise level Dr in this state can be defined by the following equation (4). (4) Dr=f2(T2)=Dr2

[0039] Then, when the elapsed time δ reaches a sufficiently long time L, the sensor temperature T2 changes as shown in the following equation (5). (5) T2=f1(t2,L,T1)

[0040] Therefore, as shown in FIG. 3, from the time when the image accumulation time is switched to t2 until the elapsed time δ reaches L (rising period), the dark noise level Dr2 changes according to the elapsed time δ. Specifically, the dark noise level Dr2 rises. The period of the rising period is expected to be several tens of minutes, for example, about 10 to 30 minutes. Then, after the elapsed time δ reaches L (stable period), the dark noise level Dr2 becomes a constant value Dr2(L).

[0041] FIG. 4 is a diagram showing an example of the correlation between the inspection signal and the sensor output accompanying changes in the dark noise level in the first embodiment. In FIG. 4, the vertical axis represents the inspection signal (pixel value). The horizontal axis represents the output (voltage) of the TDI sensor 105. When the inspection light irradiates the inspection sample, the amount of light incident on the TDI sensor 105 (an example of a camera) varies depending on the material of the sample. In the example of FIG. 4, the output (output after integration of each element aligned in the scanning direction) of the photosensor element representing the light-shielding portion (black portion) of sample 1 where a light-shielding film is formed is smaller than the output of the photosensor element representing the light-shielding portion (black portion) of sample 2. Furthermore, the output of the photosensor element representing the transparent portion (white portion) of sample 1, which is a glass substrate without a light-shielding film, is smaller than the output of the photosensor element representing the transparent portion (white portion) of sample 2. Thus, the minimum and maximum values ​​of the output of the photosensor element vary depending on the material of the sample. Meanwhile, in defect inspection, a measurement image of the inspection target is compared with a reference image based on design data or die images captured at different positions on the sample. Therefore, it is necessary to standardize the output of the photosensor element according to a certain standard. Specifically, as shown in Fig. 4, the sensor circuit 125 corrects (calibrates) the output of the photosensor element by linear interpolation so that the inspection signal (pixel value) in the light-shielding portion (black portion) has the same value regardless of the material of the sample. Similarly, the sensor circuit 125 corrects (calibrates) the output of the photosensor element by linear interpolation so that the inspection signal (pixel value) in the light-transmitting portion (white portion) has the same value regardless of the material of the sample. Therefore, the corrected pixel value is output as the inspection signal from the TDI sensor 105.

[0042] In the above example, a case of transmission inspection in which the TDI sensor 105 receives the transmitted light that has passed through the substrate 101 has been described, but the present invention is not limited to this. A reflection inspection may also be performed in which the substrate 101 is irradiated with the inspection light and the TDI sensor 105 receives the light reflected from the substrate 101. In this case, the light-shielding portion of the sample (light-shielding film) becomes a white portion, and the transmission portion (glass substrate) becomes a black portion.

[0043] By this calibration, a correlation, for example, of linear proportion, between the inspection signal and the photosensor element output (after integration) is obtained for each sample, as shown in Figure 4. As shown in Figure 4, the slope and intercept will be different for each sample.

[0044] However, if the dark noise level Dr changes, the photo sensor element output (after integration) of each pixel at the imaging position changes by the amount of change in the dark noise level Dr, ΔDr (=Dr2-Dr1). In the example of Figure 4, it increases. As a result, the inspection signal also changes. In the example of Figure 4, it increases. As a result, an image is generated in which errors have occurred in the pixel values ​​used for inspection. This causes a problem of reduced accuracy in the obtained image. As a result, false defects occur.

[0045] Therefore, in the first embodiment, the amount of change in the inspection signal corresponding to the amount of change ΔDr (=Dr2−Dr1) in the dark noise level Dr is calculated as an offset amount Δt, and the inspection signal is corrected.

[0046] Fig. 5 is a flowchart showing an example of main steps of the image acquisition method according to Embodiment 1. In Fig. 5, the image acquisition method according to Embodiment 1 carries out a series of steps including a correlation acquisition step (S102), a Dr1 calculation step (S104), a parameter recording step (S106), a setting step (S108), a scanning step (S110), a determination step (S112), a δ measurement step (S114), a T2 calculation step (S116), a Dr2 calculation step (S118), a Δt2 calculation step (S120), a determination step (S122), a Δt2 setting step (S124), a scanning step (S126), a recording step (S128), and a recording step (S130).

[0047] In the correlation acquisition step (S102), first, the pattern on the substrate is imaged with the driven TDI sensor 105 for a sufficiently long time L with an image accumulation time t1, and the correlation between the calibrated inspection signal (pixel value) and the photosensor element output is acquired. When switching the image accumulation time for one substrate 101, calibration is performed using that substrate to acquire the correlation. When multiple types of substrates are used, a correlation is acquired for each substrate. This makes it possible to acquire the correlation during the stable period of the image accumulation time t1.

[0048] During calibration, the sensor circuit 125 adjusts the dynamic range of the TDI sensor 105 using a dynamic lens that sets the maximum gradation to a light amount greater than the amount of light incident on the white portion and zero to a light amount less than the amount of light incident on the black portion. For example, assuming a resolution of 256 gradations, the gradation level of the white portion is adjusted to, for example, 200. When multiple types of substrates are used, the sensor circuit 125 adjusts the gradation value levels of the white portion and the black portion so that they are the same for all substrates. This allows correlation data for the dark noise level Dr1 shown in FIG. 4 to be obtained.

[0049] FIG. 6 is a block diagram showing an example of the internal configuration of the offset amount calculation circuit according to the first embodiment. In FIG. 6, the offset amount calculation circuit 136 includes a storage device 59 such as a magnetic disk, a Dr1 calculation unit 50, a recording processing unit 52, a setting unit 54, a determination unit 56, a δ measurement unit 58, a T2 calculation unit 60, a Dr2 calculation unit 62, a Δt2 calculation unit 64, a determination unit 66, and a Δt setting unit 68. The series of units, such as the Dr1 calculation unit 50, the recording processing unit 52, the setting unit 54, the determination unit 56, the δ measurement unit 58, the T2 calculation unit 60, the Dr2 calculation unit 62, the Δt2 calculation unit 64, the determination unit 66, and the Δt setting unit 68, each include a processing circuit. Examples of such a processing circuit include an electric circuit, a computer, a processor, a circuit board, a quantum circuit, or a semiconductor device. Furthermore, each unit may share a common processing circuit (the same processing circuit), or may use different processing circuits (separate processing circuits). The input data or calculated results required for the Dr1 calculation unit 50, the recording processing unit 52, the setting unit 54, the judgment unit 56, the δ measurement unit 58, the T2 calculation unit 60, the Dr2 calculation unit 62, the Δt2 calculation unit 64, the judgment unit 66, and the Δt setting unit 68 are stored each time in a memory (not shown) within the offset amount calculation circuit 136 or in memory 111.

[0050] The correlation data obtained in the correlation obtaining step (S102) is stored in the storage device 59.

[0051] In the Dr1 calculation step (S104), the Dr1 calculation unit 50 calculates the dark noise level Dr1 when the TDI sensor 105 is driven for a sufficiently long time L in terms of the image accumulation time t1. Specifically, first, the sensor temperature T1 in this driving state is found using equation (1), and then the dark noise level Dr1 is calculated using equation (2) using this sensor temperature T1.

[0052] In the parameter recording step (S106), the recording processing unit 52 records the image accumulation time ta=t11, the sensor temperature Ta=T1, and the offset amount Δta=0.

[0053] In the setting step (S108), the setting unit 54 sets the elapsed driving time δ to 0.

[0054] In the scanning step (S110), the optical image acquisition mechanism 150 acquires an optical image of the inspected substrate 101 on which a pattern is formed. To do this, the optical image acquisition mechanism 150 first scans the inspection stripes 20 with laser light (inspection light) and captures an image of the stripe region for each inspection stripe 20 using the TDI sensor 105. 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 pattern formed on the substrate 101 is irradiated via the transmission illumination optical system 170 with laser light (e.g., DUV light) having a wavelength in the ultraviolet range or shorter, which serves as inspection light, from an appropriate light source 103. In other words, the transmission illumination optical system 170 illuminates the inspected substrate on which the pattern is formed. The light transmitted through the substrate 101 passes through the magnifying optical system 104 and is focused as an optical image by the imaging optical system 176 on the TDI sensor 105 (an example of a sensor), where it is incident. Specifically, light transmitted through the substrate 101 passes through the magnifying optical system 104, and is focused as an optical image on the photosensor array 124 by the imaging optical system 176, and is then incident thereon.

[0055] Alternatively, in reflection inspection, a pattern formed on the substrate 101 is irradiated with laser light (e.g., DUV light) having a wavelength in the ultraviolet range or shorter, which serves as inspection light, from an appropriate light source 103 to a beam splitter 174 via a reflection illumination optical system 171. The irradiated laser light is reflected by the beam splitter 174 and is irradiated onto the sample 101 via the magnifying optical system 104. In other words, an illumination optical system consisting of the reflection illumination optical system 171, the beam splitter 174, and the magnifying optical system 104 illuminates the inspected substrate 101 on which the pattern is formed. The light reflected from the sample 101 passes through the magnifying optical system 104 and the beam splitter 174 and is formed as an optical image on a photodiode array 105 (an example of a sensor) by an imaging optical system 176 and then incident thereon. Specifically, the light reflected from the substrate 101 passes through the magnifying optical system 104 and is formed as an optical image on a photosensor array 124 by the imaging optical system 176 and then incident thereon.

[0056] The pattern image formed on the photosensor array 124 is photoelectrically converted by each photosensor element of the photosensor array 124 and then A / D (analog-to-digital) converted by the sensor circuit 125. At this time, the sensor circuit 125 converts the integrated output of the multiple photosensor elements aligned in the scanning direction into an inspection signal (pixel value) according to the correlation described above. The offset circuit 126 then offsets the inspection signal (pixel value) by a set offset amount Δt. The offset amount Δt is set to an initial value of Δt1=0. Therefore, the signal is output to the stripe pattern memory 123 without any offset. The pixel value data of the inspection stripe 20 to be measured is then stored in the stripe pattern memory 123. The measurement data (pixel data) is, for example, 8-bit unsigned data, and represents the brightness gradation (light intensity) of each pixel.

[0057] In the determination step (S112), the determination unit 56 determines whether the image accumulation time t of the photosensor element is the same as the recorded ta. If the image accumulation time t of the photosensor element is the same as the recorded ta, the process returns to the setting step (S108). Then, the steps from the setting step (S108) to the determination step (S112) are repeated until the image accumulation time t of the photosensor element is no longer the same as the recorded ta.

[0058] If the image accumulation time of the photosensor element is not changed when acquiring images of each region within the same substrate, the TDI sensor 105 acquires images of each inspection stripe 20 with the same image accumulation time t1 and an offset of zero. Then, the process proceeds to the comparison process described later.

[0059] The movement speed of the XYθ table 102 (stage) is changed in response to switching of the image accumulation time of the photosensor element. When the image accumulation time of the photosensor element is lengthened, the movement speed of the XYθ table 102 is slowed down accordingly. When the image accumulation time of the photosensor element is shortened, the movement speed of the XYθ table 102 is increased accordingly.

[0060] The image accumulation time of the photosensor element may be changed (switched) when the inspection target (image acquisition target) is replaced with another substrate 101. In other words, the image accumulation time of the photosensor element may be switched for each inspection process. Alternatively, the image accumulation time of the photosensor element may be switched in units of days (hours). Alternatively, the image accumulation time of the photosensor element may be switched between regions, for example, between inspection stripes 20, on the same substrate. Increasing the image accumulation time of the photosensor element requires slowing down the movement speed of the XYθ table 102 (stage). This increases the inspection time per substrate. Therefore, the increase in inspection time can be minimized by inspecting a portion (multiple stripes) of the substrate 101 at high sensitivity (low stage speed: long image accumulation time) and inspecting the rest at the normal stage speed (high stage speed: short image accumulation time).

[0061] If the image accumulation time t of the photosensor element is not the same as ta recorded in the offset amount calculation circuit 136, in other words, if the image accumulation time of the photosensor element is switched from t1 to t2, the process proceeds to the δ measurement step (S114).

[0062] In the δ measurement step (S114), the δ measurement unit 58 measures the elapsed time δ from the point in time when the image accumulation time of the photosensor element is switched from t1 to t2.

[0063] In the T2 calculation step (S116), the T2 calculation unit 60 calculates the sensor temperature T2 according to the elapsed time δ from the point in time when the image accumulation time of the photosensor element is switched from t1 to t2. The sensor temperature at the time of switching can be T1 recorded in Ta. The sensor temperature T2 can be calculated using equation (3).

[0064] In the Dr2 calculation step (S118), the Dr2 calculation unit 62 calculates the dark noise level Dr2 when the sensor temperature T2 changes as the image accumulation time of the photosensor element becomes t2. The dark noise level Dr2 can be calculated using equation (4).

[0065] In the Δt2 calculation step (S120), the Δt2 calculation unit 64 (offset calculation unit) calculates an offset amount that depends on the image accumulation time of the photosensor element. Specifically, the Δt2 calculation unit 64 calculates an offset amount Δt2 corresponding to the amount of change in the dark noise level. In the example of FIG. 4, for example, the amount of change ΔDr in the dark noise level of sample 1 can be obtained as the difference between the dark noise levels Dr1 and Dr2 of sample 1. Then, using, for example, the linear proportional slope k of the correlation of sample 1, the offset amount Δt2 can be defined by equation (6). (6) Δt2=k·ΔDr=k(Dr2-Dr1)

[0066] In the determination step (S122), the determination unit 66 determines whether the recorded Δta is the same value as Δt2. If the recorded Δta is the same value as Δt2, the process proceeds to the recording step (S130). If the recorded Δta is not the same value as Δt2, the process proceeds to the Δt2 setting step (S124). Since Δta=0 is initially recorded, the first determination step (S122) proceeds to the Δt2 setting step (S124).

[0067] In the Δt2 setting step (S124), the Δt setting unit 68 sets the calculated offset amount Δt2 in the offset circuit 126.

[0068] In the scanning step (S126), the optical image acquisition mechanism 150 scans the inspection stripes 20 with laser light (inspection light) and captures an image of the stripe region for each inspection stripe 20 using the TDI sensor 105. Specifically, this operation is the same as the scanning step (S110). Therefore, the transmitted light that has passed through the substrate 101 passes through the magnifying optical system 104 and the imaging optical system 176 to form an optical image on the photosensor array 124 and then enter the optical image. Alternatively, the reflected light that has been reflected from the substrate 101 passes through the magnifying optical system 104 and the imaging optical system 176 to form an optical image on the photosensor array 124 and then enter the optical image.

[0069] The TDI sensor 105 captures an image of the substrate 101 to be inspected by receiving transmitted or reflected light from the substrate 101 using multiple photosensor elements. The TDI sensor 105 then corrects the pixel values ​​of the captured optical image data using an offset amount and outputs the corrected optical image data. Specifically, the sensor operates as follows: The pattern image formed on the photosensor array 124 is photoelectrically converted by each photosensor element of the photosensor array 124 and then A / D (analog-to-digital) converted by the sensor circuit 125. The sensor circuit 125 then converts the integrated output of the multiple photosensor elements aligned in the scanning direction into an inspection signal (pixel value) according to the correlation described above. The offset circuit 126 then offsets the inspection signal (pixel value) by a set offset amount Δt. The offset amount Δt is set to Δt2. Therefore, a correction (offset) is performed in which Δt2 is subtracted from the inspection signal (pixel value) of each pixel. The offset inspection signal (pixel value) of each pixel is then output to the stripe pattern memory 123. Then, data of pixel values ​​of the inspection stripe 20 to be measured is stored in the stripe pattern memory 123. The measurement data (pixel data) is, for example, 8-bit unsigned data, and represents the brightness gradation (light amount) of each pixel.

[0070] As explained in FIG. 3, the dark noise level changes during the rising period. Therefore, during the rising period in FIG. 3, the offset amount calculation circuit 136 (offset calculation unit) calculates the offset amount according to the imaging timing. Then, the TDI sensor 105 corrects the optical image data for each imaging timing using the offset amount according to the imaging timing. Therefore, it operates as follows.

[0071] In the recording step (S128), the recording processing unit 52 records (overwrites) Δta = Δt2. Then, the process returns to the δ measurement step (S114). The steps from the δ measurement step (S114) to the recording step (S128) are repeated until the Δta recorded in the determination step (S122) becomes the same as the latest Δt2 calculated in the Δt2 calculation step (S120). The steps from the δ measurement step (S114) to the recording step (S128) correspond to changes in the dark noise level during the rising phase in FIG. 3. The offset amount is changed each time a new Δt2 is set in the Δt2 setting step (S124). For example, the offset amount is changed for each inspection stripe 20. Alternatively, for example, the offset amount is changed during scanning within the inspection stripe 20.

[0072] Then, when the elapsed time δ reaches time L when the stable period begins, the recorded Δta becomes the same value as the latest Δt2 calculated in the Δt2 calculation step (S120).

[0073] As explained in FIG. 3, the dark noise level remains constant during the stable period. Therefore, the TDI sensor 105 corrects the optical image data using a fixed offset amount after a predetermined period (δ=L) has elapsed since the image accumulation time of the photosensor element was changed from t1 to t2. Specifically, the optical image data is corrected at Δt2(L) during the stable period in FIG. 3. Therefore, the operation is as follows.

[0074] When the Δta recorded in the determination step (S122) becomes the same value as the latest Δt2 calculated in the Δt2 calculation step (S120), the process proceeds to the recording step (S130).

[0075] In the recording step (S130), the recording processing unit 52 records ta=t2 and Ta=T2. Then, the process returns to the setting step (S108). Then, in the determination step (S112), the process repeats the steps from the setting step (S108) to the determination step (S112) until the image accumulation time t of the photosensor element is no longer the same as the recorded ta.

[0076] In the scanning step (S110) at ta=t2, the offset circuit 126 offsets the inspection signal (pixel value) by a set constant offset amount Δt2(L) during the stable period.

[0077] Furthermore, when the image accumulation time of the photosensor element is changed from t2 to t3, t2, T2, Dr2, and Δt2 in the δ measurement step (S114) and subsequent steps are replaced with t3, T3, Dr3, and Δt3.

[0078] By performing the above-described operations, it is possible to acquire image data of each inspection stripe 20 in which the pixel values ​​are offset by an offset amount according to the change in the dark noise level.

[0079] Fig. 7 is a flowchart showing the main steps of the inspection method according to the first embodiment. In Fig. 7, the inspection method according to the first embodiment carries out a series of steps, namely, the scanning steps (S110) and (S126) described above, the reference image creation step (S204), and the comparison step (S106). The contents of the scanning steps (S110) and (S126) are as described above.

[0080] In the reference image creation step (S204), the reference image creation circuit 112 creates a reference image to serve as a reference 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, the operation is as follows: The reference image creation circuit 112 inputs graphic pattern data (design data) for each frame region 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.

[0081] The figures defined in the figure pattern data are, for example, rectangles or 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 between figure types such as rectangles and triangles.

[0082] When the design pattern data that becomes 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 graphic dimensions that indicate the graphic shape of the graphic data are interpreted. Then, it is expanded into binary or multi-valued design pattern image data as a pattern to be arranged in a grid with a predetermined quantized dimension as a unit, and output. In other words, the design data is read, the frame area is virtually divided into grids with a predetermined dimension as a unit, and the occupancy rate of the graphic in the design pattern is calculated for each grid, and n-bit occupancy data (design image data) is output. For example, it is preferable to set one grid as one pixel. Then, 1 / 2 is assigned to one pixel. 8 If a pixel has a resolution of (=1 / 256), a small area of ​​1 / 256 is allocated to the area of ​​the figure placed within the pixel, and the occupancy rate within the pixel is calculated. This is then created as 8-bit occupancy data. The grid (inspection pixel) can be aligned with the pixels of the measurement data.

[0083] Next, the reference image creation circuit 112 performs filtering using a filter function on the design image data of the design pattern, which is image data of the graphic.

[0084] FIG. 8 is a diagram illustrating the filtering process in the first embodiment. The pixel data of the optical image captured from the substrate 101 is filtered according to the resolution characteristics of the optical system used for capturing the image, in other words, is in a continuously changing analog state. Therefore, as shown in FIG. 8, the image intensity (gray value) differs from that of the expanded image (design image), which has a digital value. On the other hand, as described above, the figure pattern data is defined by a figure code, and therefore the image intensity (gray value) of the expanded design image may be a digital value. Therefore, the reference image creation circuit 112 performs image processing (filtering) on ​​the expanded image to create a reference image that approximates the optical image. This allows the design image data, which is image data on the design side with a digital image intensity (gray 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.

[0085] FIG. 9 is a diagram showing an example of the internal configuration of each comparison circuit in the first embodiment. In FIG. 9, comparison circuit 108 includes storage devices 70, 72, and 76, such as a magnetic disk device, a frame image creation unit 74, an alignment unit 78, and a comparison processing unit 79. A series of "units" such as frame image creation unit 74, alignment unit 78, and comparison processing unit 79 each have a processing circuit. Such processing circuits include an electric circuit, a computer, a processor, a circuit board, a quantum circuit, or a semiconductor device. Each "unit" may share a common processing circuit (the same processing circuit), or may use different processing circuits (separate processing circuits). Input data or calculation results required for frame image creation unit 74, alignment unit 78, and comparison processing unit 79 are stored in a memory (not shown) in comparison circuit 108 or memory 111 each time.

[0086] 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.

[0087] In the comparison step (S106), the comparison circuit 108 (an example of a comparison unit) compares the optical image formed from the optical image data output from the TDI sensor 105 with the reference image. Specifically, the operation is as follows.

[0088] 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, the size is divided into 512 x 512 pixels. Data for each frame region 30 is stored in the storage device 76.

[0089] 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, 76, and aligns the frame image 31 with the corresponding reference image using a predetermined algorithm. For example, alignment is performed using the least squares method.

[0090] Then, the comparison processing unit 79 (another example of a comparison unit) compares the frame image 31 with the reference image corresponding to that frame image 31. For example, a comparison is made pixel by pixel. Here, the two are compared pixel by pixel according to predetermined judgment conditions to determine the presence or absence of a defect, such as a shape defect. The judgment conditions may, for example, be to compare the two pixel by pixel according to a predetermined algorithm to determine the presence or absence of a defect. For example, a difference value between the pixel values ​​of the two images is calculated pixel by pixel, and if the difference value is greater than a threshold value Th, it is determined to be a defect. The comparison results may then be output to, for example, the magnetic disk device 109, magnetic tape device 115, flexible disk device (FD) 116, CRT 117, pattern monitor 118, or printer 119.

[0091] Although the above example describes the case of die-to-database inspection, die-to-die inspection may also be used. In this case, for frame regions 30 among the plurality of frame regions 30 for which die-to-die inspection is performed, the comparison circuit 108 uses the frame image (optical image) of die 2 acquired for one of the frame regions as a reference (reference image). First, for each frame region 30 for which die-to-die inspection is performed, the alignment unit 78 reads the frame image 31 of die 1 and the frame image of die 2 corresponding to the frame region 30 for which die-to-die inspection is performed from the storage device 76, 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 pixel by pixel for each frame region 30 for which die-to-die inspection is performed.

[0092] As described above, according to the first embodiment, by performing an offset in accordance with a change in the dark noise level caused by a change in the image accumulation time of the photosensor element, it is possible to suppress deterioration in image accuracy caused by a change in the image accumulation time of the photosensor element.

[0093] Embodiment 2 In the first embodiment, correction is performed in accordance with changes in the dark noise level caused by changes in the image accumulation time of the photosensor element, but the method of suppressing image degradation is not limited to this. In the second embodiment, changes in the dark noise level itself are suppressed when the image accumulation time of the photosensor element is switched. The contents other than those specifically explained below are the same as those of the first embodiment.

[0094] Fig. 10 is a configuration diagram showing the configuration of a pattern inspection device according to embodiment 2. Fig. 10 is the same as Fig. 1 except that the configuration of the TDI sensor 105 is different and a temperature adjustment circuit 134 and a coolant supply device 131 are provided instead of the offset amount calculation circuit 136.

[0095] FIG. 11 is a block diagram showing an example of the internal configuration of a temperature adjustment circuit according to the second embodiment. In FIG. 11, a series of "units" such as T2 calculation unit 51, temperature change amount ΔT calculation unit 53, refrigerant temperature adjustment unit 55, and refrigerant flow rate adjustment unit 57 are arranged in temperature adjustment circuit 134. These units include a processing circuit. Examples of such processing circuits include an electric circuit, a computer, a processor, a circuit board, a quantum circuit, or a semiconductor device. Each of the "units" may share 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 T2 calculation unit 51, temperature change amount ΔT calculation unit 53, refrigerant temperature adjustment unit 55, and refrigerant flow rate adjustment unit 57 are stored in a memory (not shown) in temperature adjustment circuit 134 or memory 111.

[0096] The TDI sensor 105 includes a photosensor array 124, a temperature adjustment mechanism 127, and a sensor circuit 125. In the second embodiment, the temperature adjustment mechanism 127 keeps the sensor temperature of the photosensor array 124 constant, thereby suppressing changes in the dark noise level.

[0097] FIG. 12 is a structural diagram illustrating an example of a temperature adjustment mechanism according to the second embodiment. In FIG. 12, the temperature adjustment mechanism 127 includes, for example, an air-cooling mechanism. Specifically, the temperature adjustment mechanism 127 includes an air intake 40, an exhaust 41, and a heat sink 42. A plurality of fins 44 are disposed within the heat sink 42. The photosensor array 124 has a light-receiving surface that converts an inspection image into an electrical signal. The photosensor array 124 is disposed in contact with the heat sink 42, which has good thermal conductivity. Specifically, the bottom surface of the photosensor array 124 is disposed in contact with the heat sink 42. Cooling air, an example of a refrigerant, is supplied to the temperature adjustment mechanism 127 from a refrigerant supply device 131. The cooling air, an example of a refrigerant, is drawn in through the air intake 40, passes through the heat sink 42, and is exhausted through the exhaust 41. The cooling air cools the photosensor array 124 via the fins 44 within the heat sink 42, and the heated refrigerant is then exhausted through the exhaust 41. By arranging a plurality of fins 44, a large surface area can be brought into contact with the cooling air, and by arranging a plurality of fins 44, the heat exchange efficiency can be improved.

[0098] The T2 calculation unit 51 calculates the sensor temperature T2 in the stable period when the elapsed time δ from the time point when the image accumulation time of the photosensor element is switched from t1 to t2 reaches a predetermined period L. T1 may be used as the sensor temperature at the time of switching.

[0099] The temperature change amount calculation unit 53 calculates a temperature change amount ΔT that depends on the image accumulation time of each of the multiple photosensor elements that are two-dimensionally arranged. Specifically, the temperature change amount calculation unit 53 calculates the temperature change amount ΔT (=T2-T1) when the elapsed time δ from the time when the image accumulation time of the photosensor element is switched from t1 to t2 reaches a predetermined period L.

[0100] Refrigerant temperature adjustment unit 55 adjusts the temperature of the refrigerant using the temperature change amount ΔT. In the example of Fig. 12, the temperature of the cooling air is adjusted. Specifically, the target value of the refrigerant temperature is output to refrigerant supply device 131 so that the temperature change amount ΔT occurring over a predetermined period L of elapsed time δ becomes zero.

[0101] The refrigerant flow rate adjusting unit 57 adjusts the refrigerant flow rate using the temperature change amount ΔT. In the example of FIG. 12, the flow rate of cooling air is adjusted. Specifically, the set value of the refrigerant flow rate is output to the refrigerant supply device 131 so that the temperature change amount ΔT occurring over a predetermined period L when the elapsed time δ is zero. The relationship between the temperature change amount ΔT occurring over a predetermined period L when the elapsed time δ is δ, the target temperature value, and the set value of the flow rate can be measured in advance through experiments or simulations. Specifically, to obtain the amount of heat Q that generates the temperature change amount ΔT over the predetermined period L, heat is generated at a rate of q (=Q / L) per unit time. Therefore, the relationship between the target temperature value and the set value of the flow rate at which the amount of heat q per unit time can be exchanged can be found. The previously measured relationship between the temperature change amount ΔT, the target temperature value, and the set value of the flow rate is stored in advance in the storage device 59 as refrigerant correlation data.

[0102] In the air-cooling mechanism, the relationship between the temperature change amount ΔT occurring in a predetermined period L, the target temperature value, and the set value of the flow rate may be measured in advance by experiment or simulation using cooling air.

[0103] In the refrigerant supply device 131, a temperature adjustment function adjusts the temperature of the refrigerant so that it approaches a target value. Then, the refrigerant supply device 131 supplies the temperature-adjusted refrigerant at a set flow rate to the temperature adjustment mechanism 127. The refrigerant exhausted from the temperature adjustment mechanism 127 is recovered by the refrigerant supply device 131 and reused.

[0104] As a result, it is possible to suppress temperature changes in the photosensor array 124 when switching the image accumulation time of the photosensor elements. By suppressing temperature changes, it is possible to suppress changes in the dark noise level itself. In other words, it is possible to keep the temperature of the photosensor array constant and prevent changes in the dark noise level.

[0105] Therefore, in the scanning process, the TDI sensor 105 receives transmitted or reflected light from the inspected substrate 101 using the multiple photosensor elements while controlling the temperatures of the multiple photosensor elements using the temperature change amount ΔT. In this way, an image of the inspected substrate 101 is captured. Since changes in the dark noise level can be suppressed, gradation errors can be prevented.

[0106] FIG. 13 is a structural diagram showing another example of the temperature adjustment mechanism according to the second embodiment. In FIG. 13, the temperature adjustment mechanism 127 includes, for example, a water-cooling mechanism. Specifically, the temperature adjustment mechanism 127 includes a water inlet 80, a water outlet 81, and a heat sink 82. A cooling pipe 84 is disposed within the heat sink 82. The photosensor array 124 is disposed so as to be in contact with the heat sink 82, which has good thermal conductivity. Specifically, the bottom surface of the photosensor array 124 is disposed so as to be in contact with the heat sink 82. Cooling water, which is an example of a refrigerant, is supplied to the temperature adjustment mechanism 127 from a refrigerant supply device 131. The cooling water, which is an example of a refrigerant, is absorbed through the water inlet 80 and then drained through the heat sink 82 via the water outlet 81. The cooling water cools the photosensor array 124 through the cooling pipe 84 within the heat sink 82, and the heated refrigerant is then drained through the water outlet 81. The cooling pipe 84 is disposed in a serpentine manner within the heat sink 82. The serpentine shape allows for heat conduction over a large surface area, improving heat exchange efficiency.

[0107] In the water-cooling mechanism, the relationship between the temperature change amount ΔT occurring in a predetermined period L, the target temperature value, and the set value of the flow rate may be measured in advance by experiment or simulation using cooling water.

[0108] In the refrigerant supply device 131, a temperature adjustment function adjusts the temperature of the cooling water to approach a target value. Then, the refrigerant supply device 131 supplies the temperature-adjusted cooling water at a set flow rate to the temperature adjustment mechanism 127. The cooling water drained from the temperature adjustment mechanism 127 is collected in the refrigerant supply device 131 and reused.

[0109] FIG. 14 is a structural diagram showing another example of the temperature adjustment mechanism according to the second embodiment. In FIG. 14, the temperature adjustment mechanism 127 includes, for example, a heat pipe mechanism. Specifically, the temperature adjustment mechanism 127 includes a heat sink 92, one or more heat pipes 94, and a heat sink 96. One end of the one or more heat pipes 94 is disposed within the heat sink 92. The other end of the one or more heat pipes 94 is disposed within the heat sink 96. The photosensor array 124 is disposed so as to be in contact with the heat sink 92, which has good thermal conductivity. Specifically, the bottom surface of the photosensor array 124 is disposed in contact with the heat sink 92. A refrigerant is supplied to the temperature adjustment mechanism 127 from a refrigerant supply device 131. Heat exchange occurs between the photosensor array 124 and one end of the heat pipe 94 within the heat sink 92. Heat exchange occurs between the other end of the one or more heat pipes 94 and the refrigerant within the heat sink 96. The coolant may be either cooled air or cooled water.

[0110] In a heat pipe mechanism, the relationship between the temperature change amount ΔT occurring in a predetermined period L, the target temperature value, and the set flow rate value may be measured in advance by experiment or simulation using the refrigerant to be used.

[0111] As a result, in the scanning step (S110), changes in the dark noise level can be suppressed, and tone errors can be prevented. The contents of each step after the reference image creation step (S204) are the same as those in the first embodiment.

[0112] As described above, according to the second embodiment, by suppressing the change in the dark noise level caused by the change in the image accumulation time of the photosensor element, it is possible to suppress the deterioration of image accuracy caused by the change in the image accumulation time of the photosensor element.

[0113] Embodiment 3 In the second embodiment, a case where a change in the dark noise level is suppressed by suppressing the temperature change itself has been described. In the third embodiment, a configuration is described in which measures are taken to deal with the case where an error in suppressing such a temperature change occurs. The contents other than those specifically described below are the same as those of the first and second embodiments.

[0114] Fig. 15 is a configuration diagram showing the configuration of a pattern inspection device according to embodiment 3. Fig. 15 is the same as Fig. 1 except that the configuration of the TDI sensor 105 is different and a temperature adjustment circuit 134 and a coolant supply device 131 are further provided. In embodiment 3, an inspection device 100 is provided that combines embodiments 1 and 2.

[0115] As in the second embodiment, the temperature change of the photosensor array 124 when switching the image accumulation time of the photosensor elements is suppressed by the temperature adjustment mechanism 127. Here, a change in the dark noise level may occur due to an error after the temperature control by the temperature adjustment mechanism 127.

[0116] The TDI sensor 105 includes a photosensor array 124, a temperature adjustment mechanism 127, a sensor circuit 125, an offset circuit 126, and a temperature sensor 128. In the third embodiment, as in the second embodiment, the temperature adjustment mechanism 127 keeps the sensor temperature of the photosensor array 124 constant, thereby suppressing changes in the dark noise level.

[0117] In the offset amount calculation circuit 136, the Dr2 calculation unit 62 calculates the dark noise level Dr2 when the sensor temperature T2 changes due to the image accumulation time t2 of the photosensor element. The dark noise level Dr2 can be calculated using equation (4). The sensor temperature T2 used here is the value measured by the temperature sensor 128. This makes it possible to calculate the dark noise level Dr2 based on the error temperature after temperature control by the temperature adjustment mechanism 127.

[0118] In the above example, the error temperature after temperature control is determined using the measured value of the temperature sensor 128. However, the error temperature may also be calculated. For example, the ambient temperature where the photosensor array 124 is placed, the constant temperature system capacity (amount of heat exhausted per unit time), the power consumption of the photosensor array 124 (per accumulation time), the heat transfer coefficient of the photosensor array 124, the surface area of ​​the photosensor array 124, and the heat capacity of the photosensor array 124 are used. These values ​​can be calculated in advance once the embodiment of the TDI sensor 105 is determined. Once the initial state (accumulation time t1, sensor temperature T1) is determined, the temperature of the photosensor array 124 after the image accumulation time changes from t1 to t2, t3, etc. can be calculated from the above parameters.

[0119] The Δt2 calculation unit 64 (offset calculation unit) calculates an offset amount corresponding to a temperature error when controlling the temperatures of multiple photosensor elements. Specifically, the Δt2 calculation unit 64 calculates an offset amount Δt2 corresponding to a change in dark noise level. In the example of FIG. 4, for example, the change in dark noise level ΔDr for sample 1 can be calculated as the difference between the dark noise levels Dr1 and Dr2 for sample 1. Then, using the slope k of the linear proportionality of the correlation for sample 1, for example, the offset amount Δt2 can be defined by equation (6). (6) Δt2=k·ΔDr=k(Dr2-Dr1)

[0120] The TDI sensor 105 corrects the optical image data using the offset amount corresponding to the temperature error. Specifically, the operation is as follows.

[0121] In the scanning steps (S110) (S126), the TDI sensor 105 captures an image of the substrate 101 to be inspected by receiving transmitted or reflected light from the substrate 101 with multiple photosensor elements. The TDI sensor 105 then corrects pixel values ​​of the captured optical image data using an offset amount and outputs the corrected optical image data. Specifically, the operation is as follows: The pattern image formed on the photosensor array 124 is photoelectrically converted by each photosensor element of the photosensor array 124 and then A / D converted by the sensor circuit 125. At this time, the sensor circuit 125 converts the integrated output of the multiple photosensor elements aligned in the scanning direction into an inspection signal (pixel value) according to the correlation described above. The offset circuit 126 then offsets the inspection signal (pixel value) by a set offset amount Δt. The offset amount Δt is set to Δt2. Therefore, a correction (offset) is performed in which Δt2 is subtracted from the inspection signal (pixel value) of each pixel. Then, the offset inspection signal (pixel value) of each pixel is output to the stripe pattern memory 123. Then, pixel value data of the inspection stripe 20 to be measured is stored in the stripe pattern memory 123. The measurement data (pixel data) is, for example, 8-bit unsigned data, and represents the brightness gradation (light amount) of each pixel.

[0122] Since the change in the dark noise level can be suppressed and the change in the dark noise level caused by the temperature control error can be offset, the occurrence of gradation errors can be prevented. The contents of each step after the reference image creation step (S204) are the same as those in the first embodiment.

[0123] As described above, according to the third embodiment, even if a control error occurs due to the temperature adjustment mechanism 127, the control error can be corrected by using an offset. Therefore, it is possible to suppress deterioration in image accuracy caused by changes in the image accumulation time of the photosensor element.

[0124] In the above-described embodiments, each circuit, such as the position circuit 107, the comparison circuit 108, the reference image creation circuit 112, the autoloader control circuit 113, the table control circuit 114, the temperature adjustment circuit 134, and the offset calculation circuit 136, has a processing circuit. Such processing circuits include an electric circuit, a computer, a processor, a circuit board, a quantum circuit, or a semiconductor device. Each "unit" may share a common processing circuit (the same processing circuit). For example, each process may be executed by the control computer 110. Alternatively, different processing circuits (separate processing circuits) may be used. Input data required for each circuit or the results of calculations are stored in a memory (not shown) within the corresponding circuit or in memory 111. A program for executing the computer or processor may be stored in the storage device 109.

[0125] The above describes the embodiments with reference to specific examples. However, the present invention is not limited to these specific examples. For example, in the embodiments, a case where a transmitted illumination optical system and a reflected illumination optical system are combined and an image is captured using a common TDI sensor 105 has been described, but the present invention is not limited to this. It is also preferable to separately arrange a TDI sensor that captures images when a transmitted illumination optical system and a TDI sensor that captures images when a reflected illumination optical system are performed.

[0126] Furthermore, while the above example shows the case where an image is captured using a TDI sensor, the present invention is not limited to this. Any camera using a photosensor will suffice. In cameras using photosensors, changes in dark noise level can occur with changes in image accumulation time, and can be corrected in the same manner as in the above-described embodiments.

[0127] Furthermore, although descriptions of the device configuration, control method, and other parts 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.

[0128] In addition, all pattern inspection devices and pattern inspection methods that include the elements of the present invention and that can be appropriately modified by those skilled in the art are included within the scope of the present invention. [Explanation of symbols]

[0129] 20 Inspection Stripes 30 Frame Area 31 frame images 50 Dr1 calculation part 51 T2 calculation unit 52 Recording processing section 53 Temperature change calculation unit 54 Settings 55 Refrigerant temperature adjustment section 56 Judgment section 57 Refrigerant flow rate adjustment section 58 δ measurement section 59 Storage device 60 T2 calculation unit 62 Dr2 calculation section 64 Δt2 calculation section 66 Judgment section 68 Δt setting section 70,71,72,76 Storage device 74 Frame image generation unit 78 Alignment section 79 Comparison processing section 100 Inspection equipment 101 Substrate 102 XYθ table 103 Light source 104 Magnifying Optical System 105 TDI sensor 109 Magnetic disk unit 107 Position circuit 108 Comparison circuit 110 Control computer 111 memory 112 Reference image creation circuit 113 Autoloader control circuit 114 Table control circuit 115 Magnetic Tape Unit 116FD 117 CRT 118 Pattern Monitor 119 Printer 120 Bus 122 Laser length measurement system 123 Stripe Pattern Memory 124 photosensor array 125 Sensor Circuit 126 Offset Circuit 127 Temperature adjustment mechanism 128 Temperature Sensor 130 Autoloader 131 Refrigerant supply device 134 Temperature adjustment circuit 136 Offset calculation circuit 150 Optical image acquisition mechanism 160 Control Circuits 170 Transmitted illumination optical system 171 Reflected illumination optical system 174 Beam Splitter 176 Imaging Optical System

Claims

1. an illumination optical system that illuminates an inspection target substrate on which a pattern is formed; an offset calculation unit that calculates an offset amount based on a difference between a dark noise level Dr1 of each of the photosensor elements at an image accumulation time t1 and a dark noise level Dr2 when the image accumulation time t1 is switched to an image accumulation time t2 different from the image accumulation time t1; a time delay and integration (TDI) sensor having the plurality of photosensor elements, capturing an image of the substrate to be inspected by receiving transmitted light or reflected light from the substrate to be inspected with the plurality of photosensor elements, correcting pixel values ​​of the captured optical image data using the offset amount, and outputting the corrected optical image data; a comparison unit that compares an optical image formed by the optical image data output from the TDI sensor with a reference image; Equipped with the offset calculation unit calculates the offset amount according to an imaging timing from a point in time when the image accumulation time is switched until the dark noise level Dr2 is stabilized, The pattern inspection device is characterized in that the TDI sensor corrects optical image data for each imaging timing using the offset amount corresponding to the imaging timing.

2. an illumination optical system that illuminates an inspection target substrate on which a pattern is formed; an offset calculation unit that calculates an offset amount based on a difference between a dark noise level Dr1 of each of the photosensor elements at an image accumulation time t1 and a dark noise level Dr2 when the image accumulation time t1 is switched to an image accumulation time t2 different from the image accumulation time t1; a time delay and integration (TDI) sensor having the plurality of photosensor elements, capturing an image of the substrate to be inspected by receiving transmitted light or reflected light from the substrate to be inspected with the plurality of photosensor elements, correcting pixel values ​​of the captured optical image data using the offset amount, and outputting the corrected optical image data; a comparison unit that compares an optical image formed by the optical image data output from the TDI sensor with a reference image; Equipped with The pattern inspection apparatus is characterized in that the TDI sensor corrects the optical image data using a fixed offset amount after a predetermined period has elapsed since the image accumulation time was switched.

3. a step of illuminating an inspection target substrate on which a pattern is formed; calculating an offset amount based on a difference between a dark noise level Dr1 of each of the photosensor elements at an image accumulation time t1 and a dark noise level Dr2 when the image accumulation time t1 is switched to an image accumulation time t2 different from the image accumulation time t1; a step of capturing an image of the substrate to be inspected by using a time delay and integration (TDI) sensor having the plurality of photosensor elements to receive transmitted light or reflected light from the substrate to be inspected, correcting pixel values ​​of the captured optical image data using the offset amount, and outputting the corrected optical image data; comparing an optical image formed by the optical image data output from the TDI sensor with a reference image; Equipped with The offset amount is calculated according to an imaging timing from the time when the image accumulation time is switched until the dark noise level Dr2 is stabilized, The pattern inspection method is characterized in that the TDI sensor corrects optical image data at each imaging timing using the offset amount corresponding to the imaging timing.

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