Pattern inspection device and pattern inspection method

Abstract

To accurately correct a height of a stage to reduce the influence of vibration caused by moving of a stage.SOLUTION: A pattern inspection device includes: an optical image acquisition unit having a movable stage on which a substrate to be inspected is placed, virtually dividing the substrate into a plurality of stripes along a predetermined direction, and acquiring an optical image for each stripe; a reference image generation unit for generating a reference image corresponding to the acquired optical image; a comparison unit for comparing the optical image and the reference image with each other; and a stage control unit for controlling the operation of the stage. The stage control unit controls a height of the stage on the basis of the acceleration of the stage in a plane direction.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to a pattern inspection apparatus and a pattern inspection method. [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 an original pattern (also called a mask or reticle, hereinafter collectively referred to as a mask) on a wafer using a reduced projection exposure device known as a stepper.

[0003] Improving yield is essential for the manufacture of LSIs, which incur huge manufacturing costs. One of the 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 mask defects.

[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] The pattern inspection system places the mask to be inspected on a movable stage, irradiates it with laser light, and captures an optical image with a TDI (time delay integration) sensor. By moving the stage, it is possible to capture an optical image of the entire mask surface.

[0006] When an air slider is used for the stage, vibration occurs in the Z direction (height direction) when the stage moves, which can cause blurring in the acquired optical image. Recently, there has been a demand for faster stage movement speeds to improve throughput, and there is a need to quickly and accurately correct the stage height to reduce the effects of Z direction vibration. [Prior art documents] [Patent documents]

[0007] [Patent Document 1] Japanese Patent Application Laid-Open No. 2001-221278 [Patent Document 2] Japanese Patent Application Publication No. 8-293459 Summary of the Invention [Problem to be solved by the invention]

[0008] An object of the present invention is to provide a pattern inspection apparatus and a pattern inspection method that accurately correct the height of a stage so as to reduce the influence of vibrations that accompany stage movement. [Means for solving the problem]

[0009] A pattern inspection device according to one aspect of the present invention has a movable stage on which a substrate to be inspected is placed, and is equipped with an optical image acquisition unit that virtually divides the substrate into a plurality of rectangular stripes along a predetermined direction and acquires an optical image for each stripe, a reference image generation unit that generates a reference image corresponding to the acquired optical image, a comparison unit that compares the optical image with the reference image, and a stage control unit that controls the operation of the stage, and the stage control unit controls the height of the stage based on the acceleration of the stage in a planar direction.

[0010] A pattern inspection method according to one aspect of the present invention comprises the steps of: acquiring optical images for each stripe obtained by virtually dividing the substrate into rectangular stripes along a predetermined direction while moving a stage on which a substrate to be inspected is placed; generating reference images corresponding to the acquired optical images; and comparing the optical images with the reference images, wherein the stage is moved in a planar direction using an air slider, and the height of the stage is controlled based on the acceleration of the stage in the planar direction. [Effects of the Invention]

[0011] According to the present invention, the height of the stage can be accurately corrected so as to reduce the influence of vibrations caused by the movement of the stage. [Brief explanation of the drawings]

[0012] [Figure 1] 1 is a schematic configuration diagram of a pattern inspection apparatus according to an embodiment of the present invention. [Figure 2] FIG. 10 is a conceptual diagram illustrating an inspection area. [Figure 3] FIG. 3A is a plan view of the stage, and FIG. 3B is a side view of the stage. [Figure 4] 10 is a graph showing the relationship between stage acceleration and Z direction deviation. [Figure 5] 10A and 10B are schematic diagrams illustrating deviation in the Z direction due to a force applied to the stage. [Figure 6] 10 is a flowchart illustrating an inspection method. DETAILED DESCRIPTION OF THE INVENTION

[0013] Hereinafter, an embodiment of the present invention will be described with reference to the drawings.

[0014] Fig. 1 shows the configuration of a pattern inspection apparatus according to an embodiment. In Fig. 1, an inspection apparatus 100 for inspecting a substrate to be inspected, for example, a pattern formed on a mask, includes an optical image acquisition mechanism 150 and a control circuit 160.

[0015] The optical image acquisition mechanism 150 includes a light source 103, an illumination optical system 170, a movably arranged stage 102, a magnification optical system 104, a TDI (time delay integration) sensor 105, a sensor circuit 106, a stripe pattern memory 123, a laser measurement system 122, and an autoloader 130. A substrate 101 transferred from the autoloader 130 is placed on the stage 102. The substrate 101 includes, for example, a photomask for exposure that transfers a pattern onto a semiconductor substrate such as a wafer. In addition, this photomask has a plurality of graphic patterns to be inspected formed on it. The substrate 101 is placed on the stage 102 with, for example, the pattern-formed surface facing downward.

[0016] In the control system circuit 160, a control computer 110 that controls the entire inspection device 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 stage control circuit 114, magnetic disk devices 109 and 131, a memory 111, a pattern monitor 118, and a printer 119.

[0017] The sensor circuit 106 is connected to a stripe pattern memory 123. The stripe pattern memory 123 is connected to a comparison circuit 108. The reference image creation circuit 112 is connected to the comparison circuit 108 by a dedicated cable 121.

[0018] 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, and the stage control circuit 114 comprise processing circuits. Processing circuits include electrical circuits, computers, processors, circuit boards, quantum circuits, semiconductor devices, etc.

[0019] For example, a series of "circuits" such as the position circuit 107, comparison circuit 108, reference image creation circuit 112, autoloader control circuit 113, and stage control circuit 114 may be configured and executed by a control computer 110. Input data or calculation results required for the position circuit 107, comparison circuit 108, reference image creation circuit 112, autoloader control circuit 113, and stage control circuit 114 are stored each time in a memory (not shown) within each circuit or in memory 111. A program for executing the processor etc. may be recorded on a recording medium such as a magnetic disk device 109 or a ROM (read only memory).

[0020] In the inspection apparatus 100, a high-magnification inspection optical system is configured by a light source 103, a stage 102, an illumination optical system 170, a magnifying optical system 104, a TDI sensor 105, and a sensor circuit 106. The stage 102 is driven by a table control circuit 114 under the control of a control computer 110. The stage 102 is movable by motors that drive it in the X, Y, and Z directions. The movement position of the substrate 101 placed on the stage 102 is measured by a laser length measurement system 122 and supplied to a position circuit 107.

[0021] The process of transporting the substrate 101 from the autoloader 130 to the stage 102 and the process of transporting the substrate 101 from the stage 102 to the autoloader 130 are controlled by an autoloader control circuit 113 .

[0022] Drawing data (design data) that is the basis for forming a pattern on the substrate 101 to be inspected 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 substrate 101, corresponding patterns are formed based on each graphic pattern defined in the drawing data.

[0023] 2 is a conceptual diagram illustrating an inspection area. 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 multiple rectangular inspection stripes 12 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 12. For each inspection stripe 12, a laser beam (inspection light) is used to capture an image of the graphic pattern arranged within the inspection stripe 12 in the longitudinal direction (X direction) of the stripe area. Note that, to prevent missing images, the multiple inspection stripes 12 are preferably set so that adjacent inspection stripes 12 overlap with each other by a predetermined margin width.

[0024] As the stage 102 moves, the TDI sensor 105 moves continuously in the X direction relative to the stage 102, 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. After capturing an optical image of one inspection stripe 12, the TDI sensor 105 moves in the Y direction to the position of the next inspection stripe 12, 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 outward and return paths.

[0025] 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.

[0026] In actual inspection, the stripe region image of each inspection stripe 12 is divided into images of multiple rectangular frame regions 14, as shown in FIG. 2. Then, inspection is performed on each frame region 14 image. For example, it is divided into images of 512 x 512 pixels. Therefore, a reference image to be compared with the frame image of the frame region 14 is also created for each frame region 14.

[0027] 3A and 3B, an air slider is used for stage 102 that moves substrate 101. For example, stage 102 has a pair of Y-axis guides (guide rails) 23 extending in the Y-axis direction provided on sliding surface 21 of base 20.

[0028] The Y stage 22 has a pair of rod portions 22b extending in the X-axis direction and a slider 22a with a U-shaped cross section connected to both ends of the rod portions 22b. The slider 22a connects the ends of the pair of rod portions 22b. The slider 22a is attached to the Y-axis guide 23 so as to face the top surface and both side surfaces of the Y-axis guide 23. By blowing air toward the Y-axis guide 23 from an outlet of the slider 22a (not shown), the slider 22a is slightly lifted from the surface of the Y-axis guide 23, allowing it to move along the Y-axis guide 23.

[0029] An X stage 24 is attached to each of the rod portions 22b of the pair of Y stages 22. The X stage 24 blows air toward the rod portions 22b from a blowing port (not shown) and is slidable along the rod portions 22b (movable in the X-axis direction).

[0030] A Z stage 25 is disposed so as to be supported across the pair of X stages 24. The Z stage 25 moves the placed substrate 101 up and down in the Z direction. An opening 26 is provided in the Z stage 25, the sliding surface 21, and the base 21 to allow the laser light irradiated onto the substrate 101 to pass through. The substrate 101 is placed in the opening of the Z stage 25.

[0031] The X stage 24, Y stage 22, and Z stage 25 are driven by an X motor, a Y motor, and a Z motor, respectively, under the control of a stage control circuit 114.

[0032] When the stage 102 using an air slider moves in a planar direction (X direction and Y direction), vibration occurs in the Z direction (height direction), causing blurring in the optical image captured by the TDI sensor 105. The inventors have found that the vibration is particularly large when the stage 102 starts to move, and that this vibration changes depending on the stage acceleration.

[0033] Figure 4 is a graph showing the relationship between the X-direction acceleration at the start of stage movement in the X direction and the amount of fluctuation in stage height. The horizontal axis of the graph represents the elapsed time from the start of stage movement, the vertical axis on the left represents acceleration, and the vertical axis on the right represents the amount of fluctuation in stage height. As shown in Figure 4, the behavior of the stage acceleration and the change in height fluctuation (vibration) are similar.

[0034] Figure 5 is a schematic diagram showing the relationship between the force F0 applied to the stage and the deviation of the stage in the Z direction. The stage, which is floating due to the air jets, can be modeled as a configuration in which an air spring is attached to the stage.

[0035] The force F0 applied to the stage is expressed by the following equation (1) using the stage weight m and acceleration a. F0=m·a···(1)

[0036] Since the force F0 is also the product of the spring constant of the air spring attached to the stage and its displacement (Z-direction deviation), the acceleration a and the displacement of the spring system are proportional to each other.

[0037] The moment M0 that rotates the stage around the center of gravity is expressed by the following equation (2) using the distance L0 from the center of gravity of the stage to the point of application. M0=F0L0 (2)

[0038] As shown in Figure 5, if we model a configuration in which air springs are attached to both ends of the stage, with the spring constants of the air springs at both ends being k1 and k2, the Z direction deviations that occur at both ends of the stage when force F0 is applied to the stage being d1 and d2, respectively, and the distances from the center of gravity to both ends of the stage being L1 and L2, then force F0 can be expressed by the following equation (3): By substituting F0 from equation (3) into equation (2), moment M0 can be expressed by the following equation (4). F0=(L1 / L0)k1d1+(L2 / L0)k2d2...(3) M0=k1L1d1+k2L2d2 (4)

[0039] The Z-direction deviation d2 is expressed by the following equation (5). Also, the distance from the center of gravity of the stage is L p The Z-direction deviation d at the observation point is p is expressed by the following equation (6). d2=d1·L2 / L1···(5) d p =d1 L p / L1···(6)

[0040] The above equations (1), (4) to (6) are p By solving for, we obtain the following equation (7). d p =a·L p L0m / (L1 2 k1+L2 2 k2) (7)

[0041] From equation (7), L p L0m / (L1 2 k1+L2 2 k2) is the proportionality coefficient, and the Z-direction deviation d p It can be seen that the amount of change in the height direction and the stage acceleration a are proportional to each other. pis a value that depends on the surface conditions of the Y-axis guide 23 and the rod portion 22b, and changes depending on the position on the stage. Therefore, prior to the inspection of the substrate 101, the stage 102 is operated at an acceleration a at each of a plurality of positions (XY coordinates) of the stage 102, and the Z-direction deviation d p is measured, a proportionality coefficient is calculated, and the proportionality coefficient is stored in a storage unit such as the magnetic disk device 109. The storage unit stores proportionality coefficient data (proportionality coefficient map) at multiple positions. By using this proportionality coefficient, the Z-direction deviation d from the stage acceleration a can be calculated. p can be calculated.

[0042] 6 is a flowchart showing the main steps of the inspection method of this embodiment. This inspection method involves a series of steps: a Z correction step (S100), a scanning step (S102), a frame image creation step (S104), a reference image creation step (S110), a positioning step (S140), and a comparison step (S142).

[0043] When inspection of substrate 101 begins, stage control circuit 114 starts moving stage 102. Stage control circuit 114 controls the X motor so that the acceleration changes as shown in FIG. 4. In the Z correction step (S100), stage control circuit 114 retrieves coefficient data from magnetic disk device 109 and calculates the Z direction deviation using the current X direction acceleration a and the coefficient data corresponding to the current position of substrate 101. Stage control circuit 114 controls the Z motor and adjusts the stage height so as to correct this Z direction deviation.

[0044] In the scanning step (S102), the optical image acquisition mechanism 150 acquires optical images of multiple frame regions 14 of the substrate 101 on which a pattern is formed. To do this, the optical image acquisition mechanism 150 first scans the inspection stripes 12 with laser light (inspection light) and captures a stripe region image for each inspection stripe 12 using the TDI sensor 105. Specifically, the operation is as follows: The stage 102 is moved to a position where the target inspection stripe 12 can be imaged. Laser light (e.g., DUV light) with a wavelength in the ultraviolet range or shorter, which serves as inspection light, is irradiated onto the pattern formed on the substrate 101 from an appropriate light source 103 via the illumination optical system 170. The light transmitted through the substrate 101 passes through the magnifying optical system 104 and is focused as an optical image on the TDI sensor 105 (an example of a sensor).

[0045] The pattern image formed on the TDI sensor 105 is photoelectrically converted by each photodiode of the TDI sensor 105 and then A / D (analog-to-digital) converted by the sensor circuit 106. Then, pixel data of the inspection stripe 12 to be measured is stored in the stripe pattern memory 123. When capturing such pixel data (stripe area image), the dynamic range of the TDI sensor 105 uses a dynamic range whose maximum gradation is, for example, when the amount of illumination light incident is 60%. The measurement data (pixel data) is, for example, 8-bit unsigned data, and represents the brightness gradation (light amount) of each pixel. The stripe area image (stripe data) is then sent to the comparison circuit 108 together with data indicating the position of the substrate 101 on the stage output from the position circuit 107.

[0046] In the frame image creation step (S104), the comparison circuit 108 reads stripe data from the stripe pattern memory 123 for each inspection stripe 12 and creates a frame image for each frame region 14 shown in FIG. 2 for the region it is responsible for. For example, a frame image of 512 × 512 pixels is created. The multiple frame images are created so that adjacent frame images overlap with a predetermined margin width. This process acquires multiple frame images (optical images) corresponding to the multiple frame regions. The multiple frame images are stored in a storage unit such as a magnetic disk device 131. As a result of the above, one image (measured image) data to be compared for inspection is generated.

[0047] In the reference image creation step (S110), the reference image creation circuit 112 (reference image creation unit) creates multiple reference images corresponding to the stripe images (optical images) of the multiple inspection stripes 12. For example, a reference image is created for each frame area so as to correspond to the frame image as a reference image for each inspection stripe 12. However, this is not a limitation. A reference image may also be created for each inspection stripe 12. Specifically, the operation is as follows: The reference image creation circuit 112 first reads drawing data (design pattern data) from the magnetic disk device 109 through the control computer 110, and converts each figure pattern defined in the read design pattern data into binary or multi-value image data.

[0048] The figures defined in the design pattern data are based on basic figures such as rectangles and triangles, 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 different types of figures such as rectangles and triangles.

[0049] When the design pattern data that will become 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 placed 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.

[0050] Next, the reference image creation circuit 112 applies a filter function to the design pattern image data, which is image data of the figure, to create a reference image that is closer to the optical image. This allows the design image data, which is image data on the design side with image intensity (gray value) as a digital value, to be matched with the image generation characteristics of the measurement data (optical image). In this way, the optical image (stripe data) of the target inspection stripe 12 is acquired, and a reference image is created.

[0051] In the alignment step (S140), the comparison circuit aligns the frame image (optical image) to be compared with the reference image using a predetermined algorithm, for example, the least squares method.

[0052] In the comparison step (S142), the comparison circuit 108 compares the frame image with the reference image for each frame area (inspection unit area). For example, the frame image and the reference image are compared pixel by pixel to inspect for pattern defects. The comparison circuit 108 compares the two for each 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 such that the two are compared pixel by pixel according to a predetermined algorithm to determine the presence or absence of a defect. For example, a difference value is calculated for each pixel by subtracting the pixel value of the frame image from the pixel value of the reference image, and if the difference value is greater than a predetermined threshold, it is determined to be a defect. The comparison result is then output.

[0053] The comparison results may be stored in the magnetic disk device 109 or may be output using the pattern monitor 118 or printer 119 .

[0054] As described above, according to this embodiment, the Z-direction deviation due to stage vibration is calculated based on the acceleration of the stage 102, and the Z-stage is controlled to correct this. Since the height of the substrate 101 can be maintained at a desired position, blurring of the acquired optical image can be suppressed, and inspection accuracy can be improved.

[0055] In the above embodiment, an example of performing die-to-database inspection processing in which optical image data is compared with reference image data created from design pattern data has been described. However, die-to-die inspection processing in which optical image data is compared using optical images previously acquired from substrates on which the same pattern is formed may also be performed.

[0056] The present invention is not limited to the above-described embodiments, and the components can be modified and embodied in practice without departing from the spirit of the invention. Furthermore, various inventions can be created by appropriately combining multiple components disclosed in the above-described embodiments. For example, some components may be omitted from all the components shown in the embodiments. Furthermore, components from different embodiments may be appropriately combined. [Explanation of symbols]

[0057] 10 Inspection Area 12 Inspection Stripes 14 Frame Area 100 Inspection equipment 101 Substrate 102 Stages 103 Light source 105 TDI sensor 114 Stage control circuit 150 Optical image acquisition mechanism 160 Control Circuits 170 Illumination optical system

Claims

1. an optical image acquisition unit having a movable stage on which a substrate to be inspected is placed, the optical image acquisition unit virtually dividing the substrate into a plurality of rectangular stripes along a predetermined direction, and acquiring an optical image for each of the stripes; a reference image generating unit that generates a reference image corresponding to the acquired optical image; a comparison unit that compares the optical image with the reference image; a stage control unit that controls the operation of the stage; a storage unit that stores proportionality coefficient data that indicates the relationship between the acceleration due to the movement of the stage in the planar direction and the amount of positional fluctuation of the stage in the height direction at each of a plurality of positions of the stage in the planar direction; Equipped with The stage has a planar movement mechanism configured with an air slider, The stage control unit extracts the proportional coefficient data corresponding to the planar position of the stage while the optical image acquisition unit is acquiring the optical image for each stripe, calculates the amount of positional fluctuation in the height direction of the stage using the extracted proportional coefficient data and the acceleration of the stage, and controls the height of the stage based on the calculated amount of fluctuation.

2. a step of acquiring an optical image for each stripe obtained by virtually dividing the substrate into strips along a predetermined direction while moving a stage on which the substrate to be inspected is placed; generating a reference image corresponding to the acquired optical image; comparing the optical image with the reference image; Equipped with The stage moves in a planar direction using an air slider, A pattern inspection method, in which, while acquiring an optical image for each stripe, proportionality coefficient data corresponding to a position in a planar direction of the stage is extracted from a memory unit that stores proportionality coefficient data indicating the relationship between the acceleration of the stage and the amount of positional fluctuation in the height direction of the stage at each of a plurality of planar direction positions of the stage, the proportionality coefficient data corresponding to the position in a planar direction of the stage is calculated using the extracted proportionality coefficient data and the acceleration of the stage, and the height of the stage is controlled based on the calculated amount of fluctuation.

Images