A standard sheet and mask

Abstract

The application discloses a standard sheet and a mask, which can be used in the field of optical system performance detection. The standard sheet comprises a scanning electron microscope calibration pattern, which is used for scanning angle correction of a scanning electron microscope. The scanning electron microscope calibration pattern comprises an angle correction pattern, and the scanning electron microscope calibration pattern comprises at least one pattern layer. The angle correction pattern comprises a scanning angle correction pattern, wherein the scanning angle correction pattern comprises a check pattern formed by at least two pattern layers. Thus, a plurality of different patterns used for scanning angle correction of the scanning electron microscope are integrated on the same standard sheet, the function of the standard sheet is more comprehensive, the number of standard sheets required for correcting the scanning electron microscope is greatly reduced, and the cost of correcting the scanning electron microscope is reduced.

Description

Technical Field

[0001] This application relates to the field of optical system performance testing technology, and in particular to a standard sheet and a photomask. Background Technology

[0002] As semiconductor manufacturing processes continue to advance towards greater sophistication and precision, scanning electron microscopes (SEMs) have become core equipment for achieving accurate measurement of critical dimensions in semiconductor production lines.

[0003] To ensure the accuracy of scanning electron microscopes (SEMs), they need to be calibrated regularly using standard slides. Currently, most standard slides can only perform key dimension measurements or single imaging parameter calibrations, and cannot simultaneously perform core calibration functions such as scanning angle correction and offset correction. To meet different calibration needs, multiple sets of different standard slides are usually required, resulting in high costs for SEM calibration.

[0004] Therefore, how to reduce the cost of calibrating scanning electron microscopes and improve calibration accuracy has become a problem that needs to be solved. Summary of the Invention

[0005] To address the aforementioned issues, this application provides a standard sheet and a mask that can reduce the cost of calibrating a scanning electron microscope and improve calibration accuracy and efficiency.

[0006] The embodiments of this application disclose the following technical solutions: In a first aspect, embodiments of this application provide a standard sheet, the standard sheet including a scanning electron microscope calibration pattern, the scanning electron microscope calibration pattern being used to correct the scanning angle of the scanning electron microscope; The scanning electron microscope calibration pattern includes an angle correction pattern, which includes at least one pattern layer. The angle correction pattern includes a scanning angle correction pattern, wherein the scanning angle correction pattern includes a grid pattern formed by at least two pattern layers.

[0007] Optionally, one of the grid patterns consists of four first squares of the same size, with equal spacing between adjacent first squares.

[0008] Optionally, the angle correction pattern further includes a wafer angle correction pattern, which comprises multiple cross-shaped patterns arranged in a preset offset direction by at least one pattern layer.

[0009] Optionally, the interval between adjacent crosses in the length direction is less than or equal to the length of the cross, and the interval between adjacent crosses in the width direction is less than or equal to the width of the cross; the length and width of the cross are the same.

[0010] Optionally, the wafer angle correction pattern further includes at least one set of second squares and at least one set of third squares formed by at least one pattern layer; Two of the second squares in a set of second squares are located diagonally on a first straight line, and two of the third squares in a set of third squares are located diagonally on a second straight line, wherein the first straight line is perpendicular to the second straight line; the size of the third square is smaller than the size of the second square.

[0011] Optionally, the angle correction pattern further includes an imaging center point correction pattern, which includes at least one set of concentric ring patterns formed by at least one pattern layer; A set of concentric rings includes at least two rings of different sizes; among any two rings in the concentric rings, the inner diameter of the ring with the larger inner diameter is greater than the outer diameter of the ring with the smaller inner diameter.

[0012] Optionally, the scanning electron microscope calibration pattern is also used to perform bias correction on the scanning electron microscope, and the scanning electron microscope calibration pattern further includes multiple sets of bias correction patterns; A set of bias correction patterns includes a positioning pattern and a target pattern formed by at least one pattern layer; the positioning pattern is used for field positioning of the scanning electron microscope, and the target pattern is used for bias correction of the scanning electron microscope; In a set of bias correction patterns, the size of the positioning pattern is larger than the size of the target pattern.

[0013] Optionally, the multiple sets of offset correction patterns are respectively applied with at least two target distances; the target distance is the distance between the positioning pattern and the target pattern.

[0014] Optionally, the standard sheet may further include a first stage detection calibration pattern, and / or a first imaging calibration pattern, and / or a first set of engraving measurement patterns, and / or a first key dimension pattern; The first worktable detection calibration pattern is used to calibrate the positioning accuracy of the optical measurement worktable; The first imaging calibration pattern is used to calibrate the imaging lens, camera resolution, and illumination system; The first set of engraving measurement patterns is used to test the measurement function of the engraving equipment. The first critical dimension pattern is used to calibrate the critical dimension measuring equipment.

[0015] Secondly, embodiments of this application provide a photomask for producing a standard sheet as described in any embodiment of the first aspect. The photomask includes at least two independent regions, and different independent regions are used to form different pattern layers in the standard sheet.

[0016] Compared with the prior art, this application has the following beneficial effects: This application provides a standard sheet, which includes a scanning electron microscope (SEM) calibration pattern. The SEM calibration pattern is used to correct the scanning angle of the SEM. The SEM calibration pattern includes an angle correction pattern, which includes at least one pattern layer. The angle correction pattern includes a scanning angle correction pattern, wherein the scanning angle correction pattern includes a grid pattern formed by at least two pattern layers.

[0017] Therefore, on the one hand, by integrating various patterns used for scanning angle correction of scanning electron microscopes onto the same standard sheet, the standard sheet becomes more comprehensive in function, significantly reducing the number of standard sheets required for scanning electron microscope calibration, lowering the cost of calibrating scanning electron microscopes, and reducing the problems of detection accuracy and efficiency caused by replacing different standard sheets; on the other hand, by using a grid pattern formed by at least two pattern layers as the scanning angle correction pattern, high-precision vertical and horizontal narrow channels are constructed, which can more accurately calculate the scanning angle of the scanning electron microscope, thereby significantly improving the accuracy of scanning angle correction of scanning electron microscopes. Attached Figure Description

[0018] To more clearly illustrate the technical solutions in the embodiments of this application or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of this application. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0019] Figure 1 A schematic diagram of a standard sheet structure provided in an embodiment of this application; Figure 2 This is a schematic diagram of a scanning angle correction pattern provided in an embodiment of this application; Figure 3 A schematic diagram of a wafer angle correction pattern provided in an embodiment of this application; Figure 4 This is a schematic diagram of another wafer angle correction pattern provided in an embodiment of this application; Figure 5 A schematic diagram of an imaging center point correction pattern provided in an embodiment of this application; Figure 6 This is a schematic diagram of a bias correction pattern provided in an embodiment of this application; Figure 7 This is a schematic diagram of another bias correction pattern provided in an embodiment of this application; Figure 8 A schematic diagram of a photomask structure provided in an embodiment of this application; Figure 9 This is a schematic diagram of a layout unit provided in an embodiment of this application. Detailed Implementation

[0020] The standard film and photomask provided in this application can be used in the field of optical system performance testing. The above is only an example and does not limit the application field of the standard film and photomask provided in this application.

[0021] The terms "first," "second," "third," and "fourth," etc., used in this application specification, claims, and drawings are used to distinguish different objects, not to limit a specific order.

[0022] In the embodiments of this application, the terms "as an example" or "for example" are used to indicate that they are examples, illustrations, or explanations. Any embodiment or design that is described as "as an example" or "for example" in the embodiments of this application should not be construed as being more preferred or advantageous than other embodiments or design options. Specifically, the use of terms such as "as an example" or "for example" is intended to present the relevant concepts in a specific manner.

[0023] The terminology used in the implementation section of this application is for the purpose of explaining specific embodiments of this application only, and is not intended to limit this application.

[0024] To enable those skilled in the art to better understand the present application, the technical solutions in the embodiments of the present application will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present application, and not all embodiments. Based on the embodiments in the present application, all other embodiments obtained by those of ordinary skill in the art without creative effort are within the scope of protection of the present application.

[0025] See Figure 1 , Figure 1 This is a schematic diagram of a standard sheet structure provided in an embodiment of this application. The standard sheet includes a scanning electron microscope calibration pattern, which is used to correct the scanning angle of the scanning electron microscope.

[0026] The scanning electron microscope calibration pattern includes an angle correction pattern, which includes at least one pattern layer. The angle correction pattern includes a scanning angle correction pattern, wherein the scanning angle correction pattern includes a grid pattern formed by at least two pattern layers.

[0027] Specifically, the surface of the standard slide is integrated with a scanning electron microscope (SEM) calibration pattern. The SEM calibration pattern is used to correct the scanning angle and offset of the SEM to reduce the deviation of the scanning imaging direction and positioning during SEM operation.

[0028] Scanning electron microscope (SEM) calibration patterns include at least one pattern layer. Different SEM calibration patterns can be designed as single-pattern-layer or multi-pattern-layer structures according to different calibration requirements, so as to achieve high-precision calibration of SEM.

[0029] The calibration patterns for scanning electron microscopes include angle correction patterns.

[0030] The angle correction pattern further includes a scan angle correction pattern, wherein the scan angle correction pattern comprises a grid pattern formed by at least two pattern layers, such as... Figure 2 As shown.

[0031] The scanning angle correction pattern may include one or more grid patterns, such as six grid patterns.

[0032] For example, the grid pattern consists of four identical first squares arranged in a 2×2 array. A predetermined small spacing is reserved between adjacent first squares, and the spacing between adjacent first squares is the same to form vertical and horizontal narrow channels. The vertical and horizontal narrow channels are formed by aligning and stacking at least two pattern layers to provide a high-contrast, accurate scanning reference for SEM.

[0033] Therefore, SEM scans based on horizontal and vertical narrow channels. By utilizing the edge features of the narrow channels, a more accurate SEM scanning angle can be obtained from the imaging pattern. This makes it easier to accurately calculate the deviation angle between the actual scanning direction and the ideal scanning direction, thereby improving the accuracy of SEM scanning angle correction.

[0034] The size of the first square can be designed based on the imaging field of view of the SEM. For example, the side length of the first square can be 200μm±10μm, and correspondingly, the spacing between adjacent first squares can be 0.05μm±0.01μm to form a narrow channel.

[0035] In one embodiment provided in this application, the scanning electron microscope calibration pattern is also used to perform bias correction on the scanning electron microscope, and the scanning electron microscope calibration pattern also includes multiple sets of bias correction patterns.

[0036] Therefore, on the one hand, by integrating the patterns used for scanning angle correction and offset correction of the scanning electron microscope onto the same standard sheet, the standard sheet becomes more comprehensive in function, significantly reducing the number of standard sheets required for scanning electron microscope calibration, lowering the cost of calibrating the scanning electron microscope, and reducing the problems of detection accuracy and efficiency caused by replacing different standard sheets. On the other hand, by using a grid pattern formed by at least two pattern layers as the scanning angle correction pattern, high-precision vertical and horizontal narrow channels are constructed, which can more accurately calculate the scanning angle of the scanning electron microscope. Combined with the measurement results obtained by using the offset correction pattern and other angle correction patterns, the accuracy of the scanning angle correction of the scanning electron microscope can be significantly improved.

[0037] In one embodiment provided in this application, the angle correction pattern further includes a wafer angle correction pattern, which is used to determine the placement angle of the standard wafer itself before correcting the scanning angle of the SEM, so as to provide a reference for subsequent scanning angle correction.

[0038] The wafer angle correction pattern may include multiple cross-shaped patterns arranged in a preset offset direction, formed by at least one pattern layer, such as... Figure 4 As shown, by taking multiple translational photos based on a cross-shaped pattern, the wafer angle can be accurately calculated using a positioning algorithm.

[0039] For example, the cross-shaped pattern is a regular symmetrical structure, and the length and width of the cross can be the same, such as 90μm±10μm.

[0040] The interval between adjacent crosses in the length direction is less than or equal to the length of the cross, and the interval between adjacent crosses in the width direction is less than or equal to the width of the cross.

[0041] High-precision SEMs have a relatively small field of view, requiring multiple stage translations and area-specific image captures during wafer angle calculations. Therefore, the spacing between adjacent crosshairs can be set to be less than or equal to their own size, creating a partially connected or adjacent layout within the SEM field of view. Increasing the density of the crosshairs reduces feature breaks during translational image capture, enabling the positioning algorithm to accurately stitch together and correlate positions using the crosshair features of adjacent fields of view, providing continuous reference data for wafer angle calculations.

[0042] The spacing between adjacent crosses can be designed to match the dimensions of the crosses. For example, if the length and width of the crosses are both 90μm, the spacing between adjacent crosses in the length direction can be 90μm±10μm, and the spacing between adjacent crosses in the width direction can be 10μm±1μm.

[0043] The design of matching the spacing between adjacent crosses with their own size ensures that the distance between the feature points of adjacent crosses is within the optimal recognition and calculation range of the positioning algorithm, thereby improving the overall efficiency of the wafer angle calculation and SEM scanning angle correction process while ensuring calculation accuracy.

[0044] In one specific embodiment, the wafer angle correction pattern may further include at least one set of second squares and at least one set of third squares formed by at least one pattern layer.

[0045] The set of second squares comprises two second squares, and the set of third squares comprises two third squares. The two second squares in the set of second squares are located diagonally opposite each other on the first straight line, and the two third squares in the set of third squares are located diagonally opposite each other on the second straight line. The first straight line is perpendicular to the second straight line. The size of the third square is smaller than the size of the second square. (Refer to...) Figure 3 As shown, there is a set of second squares located diagonally on the first straight line, and two sets of third squares located diagonally on the second straight line.

[0046] For example, one third square in one of the two groups has overlapping vertices or intersecting edges with one third square in the other group; at least two second squares in one group have overlapping vertices or intersecting edges.

[0047] A square, being a regular geometric shape, possesses clear edges and vertices that are easily identifiable by SEM imaging, serving as a precise positioning marker in the XY coordinate system. Two squares, each with diagonals aligned on the same straight line, can form a fixed spatial geometric reference relationship. By identifying the relative position and included angle of the edges of two squares, the actual XY position of the wafer on the SEM stage can be accurately determined. This allows for the rapid calculation of angular deviations in the actual wafer placement, improving the accuracy of the positioning reference during subsequent scanning angle correction and providing fundamental angular data for subsequent SEM scanning angle correction.

[0048] In this embodiment, at least two larger second squares and two smaller third squares are designed. The two types of squares work together to ensure that even if the SEM magnification is adjusted, the square features can still be clearly identified. This avoids abnormalities such as blurred pattern imaging or loss of features due to magnification changes, and improves the stability of the angle measurement algorithm and the positioning algorithm at different magnifications.

[0049] By calculating the difference between the wafer angle and the scanning angle, and performing compensation conversion, the specific angle compensation value for SEM scanning angle correction can be obtained, enabling precise correction of the SEM scanning angle.

[0050] In one embodiment provided in this application, the angle correction pattern further includes an imaging center point correction pattern, wherein the imaging center point correction pattern includes at least one set of concentric ring patterns formed by at least one pattern layer.

[0051] Specifically, such as Figure 5 As shown, a set of concentric rings includes at least two rings of different sizes; among any two rings in the concentric rings, the inner diameter of the ring with the larger inner diameter is greater than the outer diameter of the ring with the smaller inner diameter.

[0052] Therefore, different sized rings can be adapted to different SEM field of view ranges. All rings share a common center. When performing center point correction, the circular outline and symmetry features of the rings can be identified through SEM imaging. The geometric center can be fitted using an algorithm and calibrated as the scanning imaging center point. Furthermore, the average value can be obtained by fitting multiple rings to offset the processing error of a single ring and the edge distortion of SEM imaging.

[0053] For example, in a concentric ring pattern, the maximum outer diameter of the ring can be 100μm±10μm, and the minimum inner diameter can be 0.1μm±0.02μm.

[0054] In one embodiment provided in this application, the scanning electron microscope calibration pattern is also used to perform bias correction on the scanning electron microscope, and the scanning electron microscope calibration pattern also includes multiple sets of bias correction patterns.

[0055] A set of offset correction patterns includes a positioning pattern and a target pattern formed by at least one pattern layer, such as Figure 6 As shown. The positioning pattern is used for field-of-view positioning of the scanning electron microscope, and the target pattern is used for offset correction of the scanning electron microscope; in a set of offset correction patterns, the size of the positioning pattern is larger than the size of the target pattern.

[0056] In high-magnification mode, the field of view of SEM is small, making it extremely difficult to directly locate tiny target patterns. With the assistance of a large-sized positioning pattern, based on the known target distance between the target pattern and the positioning pattern, the SEM field of view can be precisely moved to the location of the target pattern in small steps, achieving precise movement of the target pattern towards the center of the field of view.

[0057] In addition, positioning a large-sized positioning pattern first and then moving it to the target pattern can reduce the number of times the target pattern needs to be scanned with a high-magnification electron beam, thus avoiding damage or deformation of the target pattern due to prolonged irradiation.

[0058] For example, such as Figure 7 As shown, multiple sets of offset correction patterns can be applied to at least two target distances. For example, in one set of offset correction patterns, the target distance between the target pattern and the positioning pattern is 100 μm; in another set of offset correction patterns, the target distance between the target pattern and the positioning pattern is 50 μm.

[0059] The distance between adjacent offset correction patterns can be set based on actual needs. For example, the distance between all adjacent offset correction patterns can be the same, that is, the offset correction patterns of adjacent groups are arranged in an array with equal spacing, so that the SEM can directly perform an automated correction program based on a preset fixed step size, avoiding additional positioning errors introduced by non-equal spacing, and facilitating the reduction of random errors in a single measurement through repeated measurements and data fitting, thereby improving the accuracy of SEM correction.

[0060] As an example, multiple sets of offset correction patterns with different shapes can be designed based on different measurement requirements. In a set of offset correction patterns, the positioning pattern and the target pattern have the same shape.

[0061] During the offset correction process, the shapes of the positioning pattern and the target pattern can be the same or different; the positioning pattern and the target pattern can belong to the same set of offset correction patterns or not.

[0062] In one embodiment provided in this application, the standard sheet may further include any one or more of the following: a first stage detection calibration pattern, a first imaging calibration pattern, a first set of scale measurement patterns, and a first key dimension pattern.

[0063] The first worktable calibration pattern is used to calibrate the positioning accuracy of the optical measurement worktable, and may include multiple square combination patterns, circular patterns, and bar patterns with equal step distances.

[0064] The first imaging calibration pattern is used to calibrate the imaging lens, camera resolution, and illumination system, and may include, but is not limited to, checkerboard patterns, grid stripe patterns with different duty cycles, and other regular patterns with obvious contrast.

[0065] The first set of engraving measurement patterns is used to test the measurement function of the engraving equipment, and can also be used for factory performance testing and acceptance testing of the engraving equipment. It can include multiple identical engraving patterns with different preset spacings and patterns with preset engraving deviations.

[0066] The first critical dimension pattern is used to calibrate critical dimension measuring equipment and may include patterns of multiple known dimensions.

[0067] In addition, other patterns such as advanced packaging markings, manufacturer's trademarks, standard sheet serial numbers, positioning patterns, and production dates can also be set on the standard sheet.

[0068] Therefore, combining the standard sheet used for SEM calibration with other standard sheets into one standard sheet further reduces the types of standard sheets and lowers the complexity and cost of managing standard sheets.

[0069] This application also provides a photomask comprising at least two independent regions, the different independent regions being used to form different pattern layers in the standard sheet.

[0070] As an example, see Figure 8 The figure is a schematic diagram of a mask structure provided in an embodiment of this application. The mask includes at least two independent regions of the same size, and the at least two independent regions are designed in parallel on the mask.

[0071] The standard film includes at least two patterned layers, and each patterned layer requires separate exposure during the fabrication process. In this embodiment, the mask patterns corresponding to different patterned layers are designed in different independent areas on the same mask. During the exposure process, multiple exposures can be performed by moving the mask to directly form multiple patterned layers, thereby saving the production cost of the mask and improving process efficiency and accuracy.

[0072] For example, the photomask has two independent areas of the same size, as shown in the reference. Figure 8 As shown, two independent regions are designed parallel to each other on the mask. Both independent regions 1 and 2 are provided with one or more mask patterns corresponding to the patterns on the standard film. The patterns on the standard film include at least a scanning angle correction pattern formed by the superposition of two pattern layers, and may also include other patterns formed by a single pattern layer or a double pattern layer.

[0073] For a pattern formed by a single pattern layer, part of it can be distributed in independent region 1 and the other part in independent region 2; for a pattern formed by superimposing two pattern layers, one layer can be distributed in independent region 1 and the other layer in independent region 2.

[0074] Therefore, during the exposure process, after one exposure, the mask is moved horizontally by half the distance of the exposure field (shot) and then exposed again, so that a pattern composed of two superimposed pattern layers can be formed on the wafer in one exposure process.

[0075] One of the exposure fields corresponds to, for example: Figure 9 The diagram shows a layout unit of a standard wafer. Multiple layout units can be periodically arranged on the standard wafer along the X and Y directions.

[0076] A standard chip has at least one such Figure 1 The pattern shown can be used directly as a standard wafer, or it can be arranged according to... Figure 1 The pattern shown is used to cut standard wafers to obtain multiple standard wafers.

[0077] Understandably, the photomask can also have more independent areas, such as four or six independent areas, to prepare a pattern formed by stacking more pattern layers.

[0078] It should be noted that the various embodiments in this specification are described in a progressive manner, and the same or similar parts between the various embodiments can be referred to mutually. Each embodiment focuses on describing the differences from other embodiments. In particular, the mask embodiment is basically similar to the standard film embodiment, so the description is relatively simple, and the relevant parts can be referred to the description of the standard film embodiment. The standard film and mask embodiment described above are merely illustrative, and some or all of the modules can be selected to achieve the purpose of this embodiment solution according to actual needs. Those skilled in the art can understand and implement this without creative effort.

[0079] The above description is merely one specific embodiment of this application, but the scope of protection of this application is not limited thereto. Any variations or substitutions that can be easily conceived by those skilled in the art within the technical scope disclosed in this application should be included within the scope of protection of this application. Therefore, the scope of protection of this application should be determined by the scope of the claims.

Claims

1. A standard sheet, characterized in that, The standard sheet includes a scanning electron microscope calibration pattern, which is used to correct the scanning angle of the scanning electron microscope. The scanning electron microscope calibration pattern includes an angle correction pattern, the scanning electron microscope calibration pattern includes at least one pattern layer, and the angle correction pattern includes a scanning angle correction pattern, wherein the scanning angle correction pattern includes a grid pattern formed by at least two pattern layers. A grid pattern consists of four first squares of the same size, with equal spacing between adjacent first squares, forming vertical and horizontal narrow channels; the narrow channels and horizontal narrow channels are formed by aligning and stacking at least two pattern layers.

2. The standard sheet according to claim 1, characterized in that, The angle correction pattern also includes a wafer angle correction pattern, which comprises multiple cross-shaped patterns arranged in a preset offset direction array formed by at least one pattern layer.

3. The standard sheet according to claim 2, characterized in that, The interval between adjacent cross shapes in the length direction is less than or equal to the length of the cross shape, and the interval between adjacent cross shapes in the width direction is less than or equal to the width of the cross shape; the length and width of the cross shape are the same.

4. The standard sheet according to claim 2, characterized in that, The wafer angle correction pattern also includes at least one set of second squares and at least one set of third squares formed by at least one pattern layer; Two of the second squares in a set of second squares are located diagonally opposite each other on a first straight line, and two of the third squares in a set of third squares are located diagonally opposite each other on a second straight line, with the first straight line perpendicular to the second straight line; the size of the third square is smaller than the size of the second square.

5. The standard sheet according to claim 1, characterized in that, The angle correction pattern also includes an imaging center point correction pattern, which includes at least one set of concentric ring patterns formed by at least one pattern layer. A set of concentric rings includes at least two rings of different sizes; among any two rings in the concentric rings, the inner diameter of the ring with the larger inner diameter is greater than the outer diameter of the ring with the smaller inner diameter.

6. The standard sheet according to claim 1, characterized in that, The scanning electron microscope calibration pattern is also used to perform offset correction on the scanning electron microscope, and the scanning electron microscope calibration pattern also includes multiple sets of offset correction patterns; A set of bias correction patterns includes a positioning pattern and a target pattern formed by at least one pattern layer; the positioning pattern is used for field positioning of the scanning electron microscope, and the target pattern is used for bias correction of the scanning electron microscope; In a set of bias correction patterns, the size of the positioning pattern is larger than the size of the target pattern.

7. The standard sheet according to claim 6, characterized in that, The multiple sets of offset correction patterns are respectively applied to at least two target distances; the target distance is the distance between the positioning pattern and the target pattern.

8. The standard sheet according to claim 1, characterized in that, The standard sheet also includes a first worktable detection calibration pattern, and / or a first imaging calibration pattern, and / or a first set of engraving measurement patterns, and / or a first key dimension pattern; The first worktable detection calibration pattern is used to calibrate the positioning accuracy of the optical measurement worktable; The first imaging calibration pattern is used to calibrate the imaging lens, camera resolution, and illumination system; The first set of engraving measurement patterns is used to test the measurement function of the engraving equipment. The first critical dimension pattern is used to calibrate the critical dimension measuring equipment.

9. A photomask, characterized in that, For producing a standard sheet according to any one of claims 1 to 8, the mask includes at least two independent regions, the different independent regions being used to form different pattern layers in the standard sheet.

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