Method and apparatus for measuring alignment error using circular alignment mark

Abstract

The present invention relates to a method and an apparatus for measuring an alignment error and, more specifically, to a method and an apparatus for measuring an alignment error using a circular alignment mark. The present invention provides a method for measuring an alignment error using a circular alignment mark, the method comprising the steps of: a) acquiring an image including a first circular alignment mark and a second circular alignment mark; b) obtaining a first linear alignment mark by changing a geometric property of the first circular alignment mark from a circular shape to a linear shape via coordinate system transformation with respect to a first temporary center, which is a temporary center of the first circular alignment mark; c) obtaining a second linear alignment mark by changing a geometric property of the second circular alignment mark from a circular shape to a linear shape via coordinate system transformation with respect to a second temporary center, which is a temporary center of the second circular alignment mark; d) obtaining a first difference, which is a difference between the first temporary center and a first center that is an actual center of the first circular alignment mark, by using the first linear alignment mark; e) obtaining a second difference, which is a difference between the second temporary center and a second center that is an actual center of the second circular alignment mark, by using the second linear alignment mark; and f) obtaining a difference between the first center and the second center on the basis of the first temporary center, the second temporary center, the first difference, and the second difference.

Description

Method and apparatus for measuring alignment error using circular alignment marks

[0001] The present invention relates to a method and apparatus for measuring alignment error, and more specifically, to a method and apparatus for measuring alignment error using a circular alignment mark.

[0002] Multiple pattern layers are sequentially formed on a semiconductor substrate. Additionally, a circuit of a single layer may be divided into two patterns through double patterning. Only when these pattern layers or multiple patterns of a single layer are accurately formed at predetermined locations can a desired semiconductor device be manufactured.

[0003] Therefore, to verify whether the pattern layers are accurately aligned, overlay marks, which are alignment marks formed simultaneously with the pattern layers, are used.

[0004] The method for measuring an overlay using an overlay mark is as follows. First, a structure that is part of an overlay mark is formed on a pattern layer formed in a previous process, for example, an etching process, simultaneously with the formation of the pattern layer. Then, in a subsequent process, for example, a photolithography process, the remaining structure of the overlay mark is formed on the photoresist.

[0005] Then, through an overlay measuring device (alignment error measuring device), an image of the overlay structure of the pattern layer formed in the previous process (image acquired by passing through the photoresist layer) and an image of the overlay structure of the photoresist layer are acquired. The overlay measuring device measures the offset value between the centers of these images to measure the overlay error (alignment error) value.

[0006] FIG. 1 is a plan view of an example of an overlay mark. The overlay mark (1) illustrated in FIG. 1 has four sets of working zones (4, 5, 6, 7). Each set of working zones (4, 5, 6, 7) has two working zones arranged diagonally opposite each other. Each set of working zones (4, 5, 6, 7) is used to measure the overlay error in the X-axis or Y-axis direction of the pattern layer formed together with the corresponding set of working zones. To prevent interference, the structures (2) formed together with the first pattern layer and the structures (3) formed together with the second pattern layer are arranged so that they do not overlap each other.

[0007] Each working zone includes bars arranged at regular intervals from the center of the overlay mark (1) to the outer edge of the overlay mark (1). Thus, using an overlay measuring device, periodic signals as shown in FIG. 2 can be obtained from each of the two working zones belonging to the set of working zones (4, 5, 6, 7). The graph of FIG. 2 can be obtained, for example, by projecting a selected portion of area (8) in FIG. 1 in the Y-axis direction. That is, a graph as shown in FIG. 2 can be obtained by adding the gray values ​​of pixels with the same X value.

[0008] In the graph of FIG. 2, peaks appear in the areas where the bars are placed. Since the conventional overlay mark (1) has bars placed periodically, the acquired signal also has periodicity. Then, the overlay error is measured through correlation analysis of two periodic signals acquired from two selected areas (8, 8').

[0009] FIG. 3 is a plan view of an example of a circular overlay mark. The circular overlay mark shown in FIG. 3 can be used for purposes such as preventing deformation of the overlay mark during a heat treatment process, measuring alignment errors in various directions, and preventing damage to the overlay mark due to weak step coverage.

[0010] As illustrated in FIG. 3, the circular overlay mark includes a first circular alignment mark (CM1) and a second circular alignment mark (CM2). FIG. 3 shows the state in which the circular overlay mark is aligned. Thus, the first center (C1), which is the center of the first circular alignment mark (CM1), and the second center (C2), which is the center of the second circular alignment mark (CM2), coincide with each other. When there is an alignment error between the first circular alignment mark (CM1) and the second circular alignment mark (CM2) (an alignment error between the first pattern layer formed together with the first circular alignment mark (CM1) and the second pattern layer formed together with the second circular alignment mark (CM2)), the first center (C1) and the second center (C2) do not coincide, and this difference represents an alignment error between the pattern layers.

[0011] However, there is a problem in that it is difficult to accurately measure alignment errors when using this type of overlay mark. Since the overlay mark is curved, if a signal representing that area is acquired by selecting a rectangular area containing the overlay mark and projecting it along the X or Y axis as in conventional methods, signal loss or distortion may occur due to the mismatch between the projection direction and the extension direction of the overlay mark. Additionally, signal interference caused by adjacent circular alignment marks may occur. In particular, errors caused by these factors can become a significant problem when high precision is required.

[0012] Korean Registered Patent Publication 10-0904732 discloses a measurement method using circular overlay marks, wherein images of a circular mother and a circular son are obtained, contours of the mother and son are obtained from the images, circles that are close to the contours of the mother and son are obtained, the center points of these circles are calculated to extract the center points of the mother and son, and the positional difference and displacement angle between these center points are calculated to measure the degree of alignment.

[0013] However, this method has the problem of very low precision due to errors in the process of obtaining contours and errors in the process of obtaining adjacent circles.

[0014] In addition, Chinese registered patent publication CN 113848687 B discloses a method for measuring alignment error by calculating the area of ​​a region between a first measurement mark and a second measurement mark having a circular outline, and determining the positional deviation between the first measurement mark and the second measurement mark through this.

[0015] However, this method also has the problem of low precision.

[0016] [Prior Art Literature]

[0017] Korean Registered Patent Publication 10-0904732

[0018] Korean Registered Patent Publication 10-0866747

[0019] Korean Published Patent Application 10-2007-0109646

[0020] Chinese Registered Patent Publication CN 113848687 B

[0021] The present invention aims to improve upon the aforementioned problems by providing a new alignment error measurement method applicable to circular alignment marks.

[0022] To achieve the above-mentioned objective, the present invention comprises: a) a step of acquiring an image including a first circular alignment mark and a second circular alignment mark; b) a step of obtaining a first linear alignment mark by changing the geometric properties of the first circular alignment mark from a circle to a straight line through a coordinate system transformation based on a first temporary center, which is the temporary center of the first circular alignment mark; c) a step of obtaining a second linear alignment mark by changing the geometric properties of the second circular alignment mark from a circle to a straight line through a coordinate system transformation based on a second temporary center, which is the temporary center of the second circular alignment mark; d) a step of calculating a first difference, which is the difference between a first center, which is the actual center of the first circular alignment mark, and the first temporary center, using the first linear alignment mark; e) a step of calculating a second difference, which is the difference between a second center, which is the actual center of the second circular alignment mark, and the second temporary center, using the second linear alignment mark; and f) based on the first temporary center, the second temporary center, the first difference, and the second difference, the first center and the second A method for measuring alignment error using circular alignment marks is provided, which includes a step of calculating the difference between centers.

[0023] Additionally, the above step d) comprises: d-1) selecting a first region including a part of the first linear alignment mark and a second region located 180° away from the first region in the first polar coordinate system; d-2) generating a first signal by projecting the first region in an angular direction and generating a second signal by projecting the second region in an angular direction; d-3) obtaining a first direction offset, which is the difference in a first direction between the first temporary center and the first center, which is the actual center of the first circular alignment mark, through correlation analysis of the first signal and the second signal; d-4) selecting a third region including a part of the first linear alignment mark and a fourth region located 180° away from the third region in the first polar coordinate system; d-5) generating a third signal by projecting the third region in an angular direction and generating a fourth signal by projecting the fourth region in an angular direction; and d-6) through correlation analysis of the third signal and the fourth signal, the A method for measuring alignment error using a circular alignment mark is provided, comprising the steps of: calculating a second direction offset which is the difference in a second direction between a first temporary center and a first center which is the actual center of the first circular alignment mark; and d-7) calculating a first difference based on the first direction offset and the second direction offset.

[0024] In addition, the first region and the third region in the first polar coordinate system provide a method for measuring alignment error using circular alignment marks separated by 90°.

[0025] In addition, the first direction and the second direction provide a method for measuring alignment error using a circular alignment mark that is orthogonal to each other.

[0026] Additionally, the above step b) provides a method for measuring alignment error using a circular alignment mark, comprising the step of forming a first linear alignment mark by displaying pixels constituting the first circular alignment mark in a first polar coordinate system based on a first temporary center, which is the temporary center of the first circular alignment mark in the image.

[0027] In addition, a method for measuring alignment error using a circular alignment mark that uses a common center as the first temporary center and the second temporary center is provided.

[0028] In addition, the first temporary center and the second temporary center each provide a method for measuring alignment error using a selected circular alignment mark.

[0029] In addition, the present invention provides an alignment error measuring device comprising an image detector for acquiring an alignment mark image and a controller capable of communicating with the image detector, wherein the controller is configured to perform an alignment error measuring method using the circular alignment mark described above.

[0030] According to the present invention, alignment errors can be measured with high precision using circular alignment marks.

[0031] Figure 1 is a plan view of an example of an overlay mark.

[0032] Figure 2 shows a signal obtained from one working zone of the overlay mark shown in Figure 1.

[0033] Figure 3 is a plan view of an example of a circular overlay mark.

[0034] FIG. 4 is a schematic diagram of an alignment error measuring device according to an embodiment of the present invention.

[0035] FIG. 5 is a flowchart of a method for measuring alignment error using a circular alignment mark according to an embodiment of the present invention.

[0036] Figure 6 is a flowchart of the steps for obtaining the first linear alignment mark.

[0037] Figures 7 and 8 are diagrams illustrating the steps for obtaining the first linear alignment mark.

[0038] Figure 9 is a flowchart of the step of calculating the first difference, which is the difference between the first center and the first temporary center.

[0039] FIGS. 10 to 12 are drawings for explaining the step of finding the first difference.

[0040] Hereinafter, embodiments of the present invention will be described in detail with reference to the attached drawings. However, embodiments of the present invention may be modified in various different forms, and the scope of the present invention should not be interpreted as being limited to the embodiments described below. The embodiments of the present invention are provided to more completely explain the present invention to those with average knowledge in the art. Accordingly, the shapes of elements in the drawings are exaggerated to emphasize clearer explanations, and elements indicated by the same reference numeral in the drawings represent the same elements.

[0041] FIG. 4 is a schematic diagram of an alignment error measuring device according to an embodiment of the present invention. As shown in FIG. 4, the alignment error measuring device (1000) includes an illumination optical system (1010) that illuminates a circular alignment mark on a semiconductor wafer (W), an imaging optical system (1020) that collects reflected light from the circular alignment mark to form an image of the circular alignment mark, an image detector (1030) that acquires the circular alignment mark image formed by the imaging optical system (1020), and a controller (1040).

[0042] The illumination optical system (1010) can be constructed using various optical elements. For example, the illumination optical system (1010) may include a light source (1011), a beam splitter (1013), and an objective lens (1015). Additionally, it may include other optical elements such as lenses or apertures.

[0043] The light source (1011) serves to generate light that illuminates the circular alignment mark. The light source (1011) may include a light source capable of generating light with a wide wavelength band and variable optical filters capable of adjusting the wavelength band of the transmitted light.

[0044] The beam splitter (1013) is positioned between the light source (1011) and the objective lens (1015) and serves to transmit light from the light source (1011) to the objective lens (1015).

[0045] The objective lens (1015) serves to concentrate light onto a measurement position on the surface of the semiconductor wafer (W) and to collect reflected light from the measurement position. The objective lens (1015) is installed in a lens focus actuator (1017). The lens focus actuator (1017) is used to adjust the distance between the objective lens (1015) and the semiconductor wafer (W).

[0046] The imaging optical system (1020) can be constructed using various optical elements. For example, the imaging optical system (1020) may include a tube lens (1021). Additionally, the imaging optical system (1020) may use the objective lens (1015) and beam splitter (1013) of the illumination optical system (1010). Furthermore, it may include additional optical elements such as other lenses or apertures.

[0047] The reflected light collected from the objective lens (1015) passes through the beam splitter (1013) and is then focused to the image detector (1030) by the tube lens (1021).

[0048] The image detector (1030) receives reflected light from the circular alignment mark by illumination and generates an image of the circular alignment mark. The image detector (1030) may be a CCD camera or a CMOS camera.

[0049] The controller (1040) is installed to communicate with the image detector (1030) via wired or wireless means. The controller (1040) may include hardware such as a processor, memory, fixed memory (ROM), a storage device such as a hard disk or SSD, and a wired or wireless communication device. Additionally, it includes a program such as firmware or software installed on a storage medium such as memory, fixed memory, or a storage device.

[0050] A computing device such as an MCU (Micro controller unit), a desktop computer, a laptop computer, a smartphone, or a smart pad can be used as the controller (1040).

[0051] The controller (1040) can enable the processor to perform the steps of FIG. 5 below through the instructions of the program. The alignment error measuring device (1000) can measure the alignment error (overlay error) between the first circular alignment mark (CM1) and the second circular alignment mark (CM2) through this.

[0052] FIG. 5 is a flowchart of a method for measuring alignment error using a circular alignment mark according to an embodiment of the present invention.

[0053] First, the step (S1) of acquiring an image containing a first circular alignment mark and a second circular alignment mark is described.

[0054] In this step, an image (see FIG. 3) containing a first circular alignment mark (CM1) and a second circular alignment mark (CM2) formed on different pattern layers on a semiconductor wafer is obtained using an alignment error measuring device (1000). The first circular alignment mark (CM1) and the second circular alignment mark (CM2) can be formed using an exposure device.

[0055] Next, the step (S2) of obtaining the first linear alignment mark is described.

[0056] This step (S2) is a step of changing the geometric properties of the first circular alignment mark (CM1) from circular to straight through coordinate system transformation.

[0057] FIG. 6 is a flowchart of the step of obtaining a first linear alignment mark, and FIG. 7 is a diagram for explaining the step of obtaining a first linear alignment mark.

[0058] As illustrated in FIG. 6, the present step begins with finding a first temporary center, which is the temporary center of a first circular alignment mark in the acquired image (S21).

[0059] This step (S21) may be a step in which the user directly selects a first temporary center (TC1) on an image. That is, an image containing a first circular alignment mark (CM1) is displayed on the screen of a display device, and the user can select the first temporary center (TC1) by clicking a point considered to be the center. At this time, the selection of the first temporary center (TC1) can be aided by enabling visual confirmation through drawing a circle on the acquired image based on the radius entered by the user.

[0060] In addition, this step (S21) may be performed automatically. For example, this step (S21) may be performed by converting the image to grayscale, reducing noise using a method such as Gaussian blur, detecting edges using an edge detection algorithm, and detecting circles using a circle detection algorithm, for example, a Hough transform. In addition, in this step (S21), the center and radius of the detected circle may be used to display a circle on the acquired image to assist the user in visual verification.

[0061] Next, the step (S22) of converting orthogonal coordinate values ​​into polar coordinate values ​​is performed.

[0062] In this step (S22), the orthogonal coordinate values ​​of the pixels constituting the first circular alignment mark (CM1) are converted into polar coordinate values ​​based on the first temporary center (TC1).

[0063] If the orthogonal coordinate value of a pixel constituting the first circular alignment mark (CM1) with respect to the first temporary center (TC1) is (X, Y), then r and θ of the polar coordinate value (r, θ) can be expressed by the following mathematical formula 1.

[0064]

[0065] In this way, the orthogonal coordinate values ​​of the pixels constituting the first circular alignment mark (CM1) are converted into polar coordinate values ​​based on the first temporary center (TC1).

[0066] Next, the step (S23) of displaying the polar coordinate values ​​in the first polar coordinate system is performed.

[0067] When this step is performed, a first linear alignment mark (LM1) can be obtained as shown in FIG. 7. In the ideal case where the first circular alignment mark (CM1) is a perfect circle and the first temporary center (TC1) coincides with the actual center of the first circular alignment mark (CM1), as shown in FIG. 7, the first linear alignment mark (LM1) can form a perfect straight line over the entire range of angle values ​​from 0° to 360°, but if there is an error, it is not in the form of a perfect straight line.

[0068] For example, if the first temporary center (TC1) is offset only in the X-axis direction from the first center (C1), it can take the form of a curved line where the r value is minimized at an angle of 0° and the r value is maximized at 180°, as shown in FIG. 8. If the first temporary center (TC1) is offset only in the Y-axis direction from the first center, the r value will be minimized at 90° and the r value will be maximized at -90°. FIG. 8 is illustrated in an exaggerated manner to aid understanding, and in reality, since the error between the first temporary center (TC1) and the first center (C1) is not very large, it takes the form of a slightly curved line.

[0069] Next, the step (S3) of obtaining the second linear alignment mark is described.

[0070] This step (S3) is a step of changing the geometric properties of the second circular alignment mark (CM2) from a circle to a straight line in the second polar coordinate system through coordinate system transformation.

[0071] This step (S3) can be performed in the same manner as the step (S2) of obtaining the first linear alignment mark.

[0072] In this step (S3), the second temporary center (TC2) can be selected separately from the first temporary center (TC1).

[0073] Additionally, a single temporary center may be selected as the common temporary center of the first circular alignment mark (CM1) and the second circular alignment mark (CM2). For example, the first temporary center (TC1) may be selected as the second temporary center (TC2).

[0074] Additionally, a point between the approximate center of the first circular alignment mark (CM1) and the approximate center of the second circular alignment mark (CM2) may be selected and used as a common temporary center of the first circular alignment mark (CM1) and the second circular alignment mark (CM2).

[0075] If the alignment error between the first circular alignment mark (CM1) and the second circular alignment mark (CM2) is large, it is preferable to select the first temporary center (TC1) and the second temporary center (TC2) respectively, and if the alignment error is small, a common temporary center can be used as the first temporary center (TC1) and the second temporary center (TC2).

[0076] The remaining steps proceed in the same manner as the step (S2) of obtaining the first linear alignment mark, so a detailed explanation is omitted.

[0077] Next, the step (S4) of calculating the first difference, which is the difference between the first center and the first temporary center, is explained.

[0078] In this step (S4), the first difference is calculated using the first linear alignment mark (LM1), which is the difference between the first center (C1), the actual center of the first circular alignment mark (CM1), and the first temporary center (TC1).

[0079] FIG. 9 is a flowchart of the step of calculating the first difference, which is the difference between the first center and the first temporary center, and FIGS. 10 to 12 are drawings for explaining the step of calculating the first difference.

[0080] As illustrated in FIG. 9, this step (S4) begins with a step (S41) of selecting a first region and a second region 180° away from the first region.

[0081] As illustrated in FIG. 10, the first region (R1) is a rectangular region containing a part of the first linear alignment mark (LM1) in the first polar coordinate system. The second region (R2) is a region 180° away from the first region (R1). The second region (R2) is a region obtained by moving the first region (R1) 180° in the angular direction.

[0082] In FIG. 10, the first region (R1) is shown as being between -45° and 45° and the second region (R2) as being between 135° and 225°, but the width of the first region (R1) and the width of the second region (R2) may be less than 90° or greater than 90°. For example, the first region (R1) may be between -30° and 30° and the second region (R2) may be between 150° and 210°. Also, the center of the first region (R1) does not have to be 0°. Also, the angular widths of the first region (R1) and the second region (R2) do not necessarily have to coincide.

[0083] Next, the step (S42) of generating the first signal and the second signal is described.

[0084] In this step (S42), as illustrated in FIG. 11, the first region (R1) is projected in an angular direction to generate a first signal (S1) representing the first region (R1). For example, the first signal (S1) can be generated by setting the sum or average of the gray values ​​of pixels that have the same r value and different θ values ​​as the first signal value of the corresponding r value.

[0085] Then, in the same way, the second region (R2) is projected in an angle direction to generate the second signal (S2).

[0086] Next, the step (S43) of obtaining the first direction offset through correlation analysis of the first signal and the second signal is explained.

[0087] The first direction offset refers to the difference in the first direction between the first temporary center (TC1) and the first center (C1), which is the actual center of the first circular alignment mark (CM1). The first direction may be the direction of the central axis crossing the area corresponding to the first region (R1) and the second region (R2) when reduced to an orthogonal coordinate system.

[0088] As illustrated in FIG. 10, if a first region (R1) and a second region (R2) are selected, the region corresponding to the first region (R1) in the orthogonal coordinate system becomes a quarter circle spanning the first and fourth quadrants, and the region corresponding to the second region (R2) becomes a quarter circle spanning the first and fourth quadrants. Therefore, the first direction becomes the X-axis direction. If the first region (R1) and the second region (R2) are selected differently, the first direction may change. That is, the first direction may be the diagonal direction or the Y-axis direction.

[0089] The first direction offset can be calculated, for example, in the following way. If the first temporary center (TC1) and the first center (C1) are perfectly aligned, the peak positions of the first signal and the second signal will be the same. However, if the first temporary center (TC1) and the first center (C1) differ in the first direction (X-axis direction), the first linear alignment mark (LM1) will be skewed in opposite directions on the first region (R1) and the second region (R2). That is, as shown in FIG. 8, if the first temporary center (TC1) is skewed to the right (X-axis direction), the first linear alignment mark (LM1) is skewed downward within the first region (R1), and the first linear alignment mark (LM1) is skewed upward within the second region (R2). If the first linear alignment mark (LM1) is located at the center within the first region (R1), it is skewed further upward within the second region (R2). Accordingly, as shown in FIG. 12, a first direction offset (ΔX, where the first direction is the X-axis direction) can be obtained based on the difference in peak positions between the first signal (S1) and the second signal (S2). That is, half of the difference in peak positions can be the first direction offset (ΔX).

[0090] Next, the step (S44) of selecting a third region and a fourth region located 180° away from the third region is described.

[0091] As illustrated in FIG. 10, the third region (R3), like the first region (R1), is a rectangular region that includes a portion of the first linear alignment mark (LM1) in the first polar coordinate system. The fourth region (R4) is a region 180° away from the third region (R3). The fourth region (R4) is a region obtained by moving the third region (R3) 180° in the angular direction.

[0092] The third region (R3) may be a region 90° away from the first region (R1).

[0093] In FIG. 10, the third region (R3) is shown as being between 45° and 135° and the fourth region (R4) as being between 225° and 315°, but the width of the third region (R3) may be less than 90° or greater than 90°. For example, the third region (R3) may be between 60° and 120° and the fourth region (R4) may be between 240° and 300°.

[0094] Next, the step (S45) of generating the third and fourth signals is described.

[0095] In this step (S45), a third signal representing the third region (R3) and a fourth signal representing the fourth region (R4) can be obtained in the same way as in the step (S42) of generating the first signal (S1) and the second signal (S2).

[0096] Next, the step (S46) of obtaining the second direction offset through correlation analysis of the third signal and the fourth signal is explained.

[0097] The second direction offset refers to the difference in the second direction between the first temporary center (TC1) and the first center (C1), which is the actual center of the first circular alignment mark (CM1). The second direction may be the direction of the central axis crossing the area corresponding to the third region (R3) and the fourth region (R4) when reduced to an orthogonal coordinate system. As illustrated in FIG. 10, if the third region (R3) and the fourth region (R4) are selected, the area corresponding to the third region (R3) in the orthogonal coordinate system becomes a quarter circle spanning the first and second quadrants, and the area corresponding to the fourth region (R4) becomes a quarter circle spanning the third and fourth quadrants. Therefore, the second direction becomes the Y-axis direction. If the third region (R3) and the fourth region (R4) are selected differently, the second direction may be different. That is, the second direction may be the diagonal direction or the X-axis direction. It is desirable that the first direction and the second direction are orthogonal.

[0098] The second direction offset can be obtained by using the difference in peak positions between the third signal and the fourth signal, just like the first direction offset.

[0099] Next, the step (S47) of calculating the first difference based on the first direction offset and the second direction offset is described.

[0100] Since the difference in the first direction between the first temporary center (TC1) and the first center (C1) is the first direction offset and the difference in the second direction is the second direction offset, the first difference, which is the difference between the actual position of the first center (C1) and the first temporary center (TC1) and the first center (C1), can be easily determined.

[0101] Next, the step (S5) of calculating the second difference, which is the difference between the second center and the second temporary center, is described.

[0102] This step proceeds in the same manner as the step (S4) of calculating the first difference, which is the difference between the first center and the first temporary center, except that the second linear alignment mark (LM2) is used instead of the first linear alignment mark (LM1).

[0103] The angular range of the regions including the second linear alignment mark (LM2) may be selected to be the same range as in step S4, but may also be a different range.

[0104] Finally, the step (S6) of calculating the difference between the first center and the second center is explained.

[0105] In this step (S6), the difference between the first center (C1) and the second center (C2) is calculated based on the position of the first temporary center (TC1), the position of the second temporary center (TC2), the first difference, and the second difference. The difference between the first center (C1) and the second center (C2) represents the alignment error between the first circular alignment mark (CM1) and the second circular alignment mark (CM2).

[0106] By using the first temporary center (TC1) and the first difference, the location of the first center (C1) can be determined, and by using the second temporary center (TC2) and the second difference, the location of the second center (C2) can be determined, and the difference between the first center (C1) and the second center (C2) can also be determined.

[0107] The embodiments described above are merely illustrative of preferred embodiments of the present invention, and the scope of the present invention is not limited to the described embodiments. Various changes, modifications, or substitutions may be made by those skilled in the art within the technical spirit and scope of the claims of the present invention, and such embodiments should be understood to fall within the scope of the present invention.

[0108] [Explanation of the symbol]

[0109] CM1: 1st circular alignment mark

[0110] CM2: Second circular alignment mark

[0111] TC1: 1st Provisional Center

[0112] TC2: 2nd Provisional Center

[0113] LM1: First linear alignment mark

[0114] LM2: Second linear alignment mark

[0115] C1: 1st center

[0116] C2: Second center

[0117] R1: Zone 1

[0118] R2: Area 2

[0119] R3: The Third Zone

[0120] R4: The Fourth Zone

[0121] 1000: Alignment error measuring device

[0122] 1010: Illumination optical system

[0123] 1020: Imaging optical system

[0124] 1030: Image detector

[0125] 1040: Controller

Claims

1. a) A step of acquiring an image including a first circular alignment mark and a second circular alignment mark, and b) a step of obtaining a first linear alignment mark by changing the geometric properties of the first circular alignment mark from a circle to a straight line through a coordinate system transformation based on the first temporary center, which is the temporary center of the first circular alignment mark, and c) a step of obtaining a second linear alignment mark by changing the geometric properties of the second circular alignment mark from a circle to a straight line through a coordinate system transformation based on the second temporary center, which is the temporary center of the second circular alignment mark, and d) a step of calculating a first difference, which is the difference between the first center, which is the actual center of the first circular alignment mark, and the first temporary center, using the first linear alignment mark, and e) a step of calculating a second difference, which is the difference between the second center, which is the actual center of the second circular alignment mark, and the second temporary center, using the second linear alignment mark, and f) A method for measuring alignment error using a circular alignment mark, comprising the step of calculating the difference between the first center and the second center based on the first temporary center, the second temporary center, the first difference, and the second difference.

2. In Paragraph 1, Step d) above is, d-1) a step of selecting a first region including a part of the first linear alignment mark in the first polar coordinate system and a second region 180° away from the first region, and d-2) a step of generating a first signal by projecting the first region in an angular direction and generating a second signal by projecting the second region in an angular direction, and d-3) A step of obtaining a first direction offset, which is the difference in the first direction between the first temporary center and the first center, which is the actual center of the first circular alignment mark, through correlation analysis of the first signal and the second signal, and d-4) a step of selecting a third region including a part of the first linear alignment mark in the first polar coordinate system and a fourth region 180° away from the third region, and d-5) a step of generating a third signal by projecting the third region in an angular direction and generating a fourth signal by projecting the fourth region in an angular direction, and d-6) A step of obtaining a second direction offset, which is the difference in the second direction between the first temporary center and the first center, which is the actual center of the first circular alignment mark, through correlation analysis of the third signal and the fourth signal, and d-7) A method for measuring alignment error using a circular alignment mark, comprising the step of calculating a first difference based on the first direction offset and the second direction offset.

3. In Paragraph 2, A method for measuring alignment error using circular alignment marks separated by 90° between the first region and the third region in the first polar coordinate system.

4. In Paragraph 2, A method for measuring alignment error using circular alignment marks that are orthogonal to the first direction and the second direction.

5. In Paragraph 1, The above step b) is, A method for measuring alignment error using a circular alignment mark, comprising the step of forming a first linear alignment mark by displaying pixels constituting the first circular alignment mark in a first polar coordinate system based on a first temporary center, which is the temporary center of the first circular alignment mark in the above image.

6. In Paragraph 1, A method for measuring alignment error using a circular alignment mark that uses a common center as the first temporary center and the second temporary center.

7. In Paragraph 1, The above first temporary center and the above second temporary center are each selected methods for measuring alignment errors using circular alignment marks.

8. An image detector that acquires an alignment mark image, and An alignment error measuring device comprising a controller capable of communicating with the above-mentioned image detector, The above controller is, An alignment error measuring device configured to perform the alignment error measuring method using the circular alignment mark of claim 1.

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