Overlay error measurement pattern

Abstract

The invention provides an overlay error measurement pattern, which comprises a plurality of measurement areas in array distribution, one measurement area corresponds to one exposure field, n measurement points are reduced in a normal measurement point set in each measurement area according to one of four point reduction modes, n is greater than or equal to 1, and n is greater than or equal to 1 in a predetermined area formed by a plurality of continuous measurement areas, the four point decreasing modes are distributed according to a four-color theorem. According to the overlay error measurement graph, the point reduction mode of each measurement area in the predetermined area is determined by using a four-color principle, so that the measurement points in the predetermined area are distributed uniformly, the distribution uniformity of the measurement points in the whole overlay error measurement graph is further improved, and the precision of an overlay error observation analysis model is improved.

Description

Technical Field

[0001] The present application relates to the field of semiconductor technology, and in particular to an overlay error measurement pattern. Background Art

[0002] Overlay (OVL) refers to the accuracy of the overlapping position between the current layer pattern and the previous layer pattern in the photolithography manufacturing process. After measuring the overlay error, it is necessary to use SSO (Smart Sampling Overlay) to generate the overlay error measurement graph (overlay map) of the entire wafer, and then establish an overlay error observation and analysis model (overlay model) based on the overlay error measurement graph to observe and analyze the overlay error. The overlay error measurement graph has measurement areas that correspond to the exposure areas one by one. In each measurement area, some measurement points of the overlay error will be selected, but not all measurement points. At present, the measurement points selected in each measurement area in the industry are random, resulting in uneven distribution of measurement points in the entire overlay error measurement graph, which leads to inaccurate overlay error observation and analysis model. Summary of the invention

[0003] The purpose of the present application is to provide an overlay error measurement pattern to solve the problem of uneven distribution of measurement points in the existing overlay error measurement pattern.

[0004] In order to achieve the above-mentioned purpose, the present application provides an overlay error measurement graph, including multiple array-distributed measurement areas, one measurement area corresponds to an exposure field, each measurement area reduces n measurement points in a normal measurement point set according to one of four point reduction modes, n is greater than or equal to 1, and within a predetermined area formed by multiple continuous measurement areas, the four point reduction modes are distributed according to the four-color theorem.

[0005] Optionally, the measurement area includes a complete measurement area, a partially complete measurement area and an incomplete measurement area, the complete measurement area is a measurement area that can be fully exposed, the partially complete measurement area is a measurement area with an exposure rate greater than a first predetermined value, the incomplete measurement area is a measurement area with an exposure rate less than or equal to the first predetermined value, and the predetermined area is an area formed by the complete measurement area and the partially complete measurement area.

[0006] Optionally, the first predetermined value is 40% to 60%.

[0007] Optionally, the normal measurement point set includes at least a measurement point located on each vertex of the measurement area.

[0008] Optionally, the four point reduction modes all include at least reducing the measurement points on the vertices of the measurement area, and the four point reduction modes respectively reduce the measurement points on different vertices.

[0009] Optionally, the normal measurement point set includes at least measurement points located on each edge of the measurement area, and the four point reduction modes also include reducing at least one measurement point on at least one edge of the measurement area that does not intersect with the reduced vertex.

[0010] Optionally, the normal measurement point set includes at least measurement points located inside the measurement area, and the four point reduction modes also include reducing at least one measurement point inside the measurement area.

[0011] Optionally, a distance between the reduced measurement points within the measurement area and a diagonal line where the reduced vertices are located is less than a second predetermined value.

[0012] Optionally, the distance between the reduced measurement points and the diagonal line where the reduced vertices are located inside the measurement area is the smallest.

[0013] Optionally, one of the four point reduction modes that can leave the most valid measurement points is selected as the point reduction mode for the incomplete measurement area; if there are at least two point reduction modes that can leave the most valid measurement points, then the smaller one of the average of the total number of valid measurement points in all the measurement areas and the percentage of the total number of measurement points in all the measurement areas is selected as the point reduction mode for the incomplete measurement area; if there are at least two point reduction modes in which the total number of valid measurement points in all the measurement areas and the average of the percentage of the total number of measurement points in all the measurement areas are the same, then the one that complies with the four color theorem is selected as the point reduction mode for the incomplete measurement area.

[0014] Optionally, the measurement area has dividing lines that are distributed in a staggered manner horizontally and vertically, and the measurement points are located on four sides, four vertices and the dividing lines of the measurement area.

[0015] In the overlay error measurement graph provided by the present application, a plurality of array-distributed measurement areas are included, one measurement area corresponds to one exposure field, each measurement area reduces n measurement points in a normal measurement point set according to one of four point reduction modes, n is greater than or equal to 1, and in a predetermined area formed by a plurality of continuous measurement areas, the four point reduction modes are distributed according to the four-color theorem. The present application uses the four-color principle to determine the point reduction mode of each measurement area in the predetermined area, so that the measurement points in the predetermined area are distributed more evenly, thereby improving the distribution uniformity of the measurement points in the entire overlay error measurement graph and improving the accuracy of the overlay error observation and analysis model. BRIEF DESCRIPTION OF THE DRAWINGS

[0016] Figure 1 A schematic diagram of the distribution of the measurement area of ​​the overlay error measurement pattern provided in an embodiment of the present application;

[0017] Figure 2 A schematic diagram of the distribution of measurement points in a normal measurement point set within a measurement area provided in an embodiment of the present application;

[0018] Figure 3a A schematic diagram of the distribution of measurement points in the measurement area in the first point reduction mode provided in an embodiment of the present application;

[0019] Figure 3b A schematic diagram of the distribution of measurement points in the measurement area in the second point reduction mode provided in an embodiment of the present application;

[0020] Figure 3c A schematic diagram of the distribution of measurement points in the measurement area in the third point reduction mode provided in an embodiment of the present application;

[0021] Figure 3d A schematic diagram of the distribution of measurement points in the measurement area in the fourth point reduction mode provided in an embodiment of the present application;

[0022] Figure 4 A schematic diagram of the distribution of a point reduction pattern in a predetermined area of ​​an overlay error measurement graph provided in an embodiment of the present application;

[0023] Figure 5 A schematic diagram of the distribution of the point reduction mode in the entire overlay error measurement graph provided by an embodiment of the present application;

[0024] Wherein, the accompanying drawings are marked as follows:

[0025] 101 - complete measurement area; 102 - partially complete measurement area; 103 - incomplete measurement area; A, B, C, D - vertices; L1, L2, L3, L4 - edges. DETAILED DESCRIPTION

[0026] The specific implementation of the present application will be described in more detail below in conjunction with the schematic diagram. Based on the following description, the advantages and features of the present application will become clearer. It should be noted that the drawings are all in a very simplified form and are not in precise proportions, and are only used to conveniently and clearly assist in explaining the purpose of the embodiments of the present application.

[0027] Figure 1 The distribution diagram of the measurement area of ​​the overlay error measurement pattern provided in this embodiment. Figure 1 As shown, the overlay error measurement pattern includes a plurality of array-distributed measurement areas ( Figure 1A rectangular box in the image is a measurement area, and a measurement area corresponds to an exposure field (shot). The exposure field (shot) refers to the area covered by a single imaging of the photolithography machine. In the process of making integrated circuits on a wafer, for the convenience of process production, the wafer will be divided into several exposure fields as the basic unit in production. The exposure fields are distributed in an array on the wafer, so the measurement areas are also distributed in an array.

[0028] Please continue reading Figure 1 The measurement area includes a complete measurement area 101, a partially complete measurement area 102, and an incomplete measurement area 103. The complete measurement area 101 is a measurement area that can be fully exposed, the partially complete measurement area 102 is a measurement area with an exposure rate greater than a first predetermined value, and the incomplete measurement area 103 is a measurement area with an exposure rate less than or equal to the first predetermined value. The complete measurement area 101 is usually located in the center area of ​​the wafer, and the partially complete measurement area 102 and the incomplete measurement area 103 are usually located in the edge area of ​​the wafer.

[0029] Optionally, the first predetermined value may be 40% to 60%, such as 50%, but should not be limited thereto.

[0030] Further, each measurement area reduces n measurement points in the normal measurement point set according to one of the four point reduction modes. It should be understood that the overlay error measurement is performed in units of measurement areas. Therefore, the normal measurement point set is all the measurement points in each measurement area that have undergone overlay error measurement. The number of measurement points in the normal measurement point set is usually large and distributed throughout the measurement area. Assume that the number of measurement points in the normal measurement point set is m, m is greater than or equal to 4, n is greater than or equal to 1, and n is less than m.

[0031] Typically, the measurement area is usually a rectangle with 4 vertices and 4 edges. The normal measurement point set of the measurement area at least includes the measurement points located on each vertex of the measurement area. The normal measurement point set may also include the measurement points located on each edge of the measurement area, and each edge may have at least one measurement point. The normal measurement point set may also include the measurement points located inside the measurement area, and the measurement area may have at least one measurement point.

[0032] Figure 2 This is a schematic diagram of the distribution of the measurement points in the normal measurement point set provided in this embodiment within the measurement area. Figure 2As shown, the four vertices of the measurement area are vertex A, vertex B, vertex C and vertex D, the four edges are edge L1, edge L2, edge L3 and edge L4, and there are 12 measurement points in the normal measurement point set, namely measurement points No. 1, No. 2, No. 3, No. 4, No. 5, No. 6, No. 7, No. 8, No. 9, No. 10, No. 11 and No. 12. Among them, 4 measurement points are located on vertex A, vertex B, vertex C and vertex D respectively, measurement point No. 1 is located on vertex A, measurement point No. 3 is located on vertex B, measurement point No. 10 is located on vertex C, and measurement point No. 12 is located on vertex D; 4 measurement points are located on edges L1, edge L2, edge L3 and edge L4 respectively, measurement point No. 2 is located on edge L1, measurement point No. 6 is located on edge L2, measurement point No. 8 is located on edge L3, and measurement point No. 11 is located on edge L4 (in order to avoid ambiguity, measurement points on vertices are not considered to be measurement points on edges); the remaining 4 measurement points (measurement points No. 4, No. 5, No. 7, and No. 9) are located inside the measurement area (in order to avoid ambiguity, measurement points located inside the measurement area are not considered to be located on vertex A, vertex B, vertex C, vertex D, edges L1, edge L2, edge L3, and edge L4).

[0033] It should be noted that the measurement area has dividing lines that are distributed horizontally and vertically. These dividing lines and the four sides of the measurement area (side L1, side L2, side L3 and side L4) correspond to the cutting paths on the wafer. These dividing lines can divide the measurement area into multiple chip areas, and one chip area corresponds to one chip (die) on the wafer. All measurement points are located on the four sides, four vertices and dividing lines of the measurement area, so as to avoid the overlay error measurement affecting the chips on the wafer.

[0034] Understandably, Figure 2 The number and position distribution of the measurement points in the normal measurement point set shown are only examples. In fact, the number and position distribution of the measurement points in the normal measurement point set can be varied, and this embodiment does not show them one by one, but the normal measurement point set must have at least measurement points located on the four vertices of the measurement area.

[0035] Furthermore, each measurement area reduces n (n is greater than or equal to 1) measurement points in the normal measurement point set according to one of the four point reduction modes, that is, each measurement area reduces n measurement points, each measurement area leaves mn measurement points, and each measurement area reduces the measurement points in one of the four point reduction modes.

[0036] Specifically, the four point reduction modes all include at least reducing the measurement points on the vertices of the measurement area, and the four point reduction modes reduce the measurement points on different vertices respectively. For example, the first point reduction mode can reduce the measurement points on the vertex A of the measurement area (i.e., measurement point No. 1), and the remaining 11 measurement points remain, the second point reduction mode can reduce the measurement points on the vertex B of the measurement area (i.e., measurement point No. 3), and the remaining 11 measurement points remain, the third point reduction mode can reduce the measurement points on the vertex C of the measurement area (i.e., measurement point No. 10), and the remaining 11 measurement points remain, and the fourth point reduction mode can reduce the measurement points on the vertex D of the measurement area (i.e., measurement point No. 12), and the remaining 11 measurement points remain.

[0037] Furthermore, the four point reduction modes can also include reducing at least one measurement point on at least one edge in the measurement area that does not intersect with the reduced vertex. Generally speaking, there are two edges that do not intersect with a vertex, such as the edges L3 and L4 that do not intersect with vertex A, the edges L2 and L4 that do not intersect with vertex B, the edges L1 and L3 that do not intersect with vertex C, and the edges L1 and L2 that do not intersect with vertex D. For example, the first point reduction mode can reduce the measurement point on the vertex A of the measurement area (i.e., measurement point No. 1) and the measurement point on the edge L3 (i.e., measurement point No. 8) or the measurement point on the edge L4 (i.e., measurement point No. 11), and the remaining 10 measurement points remain. The second point reduction mode can reduce the measurement point on the vertex B of the measurement area (i.e., measurement point No. 3) and the measurement point on the edge L2 (i.e., measurement point No. 6) or the measurement point on the edge L4 (i.e., measurement point No. 11), and the remaining 10 measurement points remain. The third point reduction mode can reduce the measurement point on the vertex C of the measurement area (i.e., measurement point No. 10) and the measurement point on the edge L1 (i.e., measurement point No. 2) or the measurement point on the edge L3 (i.e., measurement point No. 8), and the remaining 10 measurement points remain. The fourth point reduction mode can reduce the measurement point on the vertex D of the measurement area (i.e., measurement point No. 12) and the measurement point on the edge L1 (i.e., measurement point No. 2) or the measurement point on the edge L2 (i.e., measurement point No. 6), and the remaining 10 measurement points remain. Alternatively, the first point reduction mode can reduce the measurement point on vertex A of the measurement area (i.e., measurement point No. 1), the measurement point on edge L3 (i.e., measurement point No. 8), and the measurement point on edge L4 (i.e., measurement point No. 11), and the remaining 9 measurement points remain. The second point reduction mode can reduce the measurement point on vertex B of the measurement area (i.e., measurement point No. 3), the measurement point on edge L2 (i.e., measurement point No. 6), and the measurement point on edge L4 (i.e., measurement point No. 11), and the remaining 9 measurement points remain. The three point reduction modes can reduce the measurement points on the vertex C of the measurement area (i.e., measurement point No. 10), the measurement points on the edge L1 (i.e., measurement point No. 2), and the measurement points on the edge L3 (i.e., measurement point No. 8), and the remaining 9 measurement points remain. The fourth point reduction mode can reduce the measurement points on the vertex D of the measurement area (i.e., measurement point No. 12), the measurement points on the edge L1 (i.e., measurement point No. 2), and the measurement points on the edge L2 (i.e., measurement point No. 6), and the remaining 9 measurement points remain.

[0038] Furthermore, the four point reduction modes can also include reducing at least one measurement point inside the measurement area. For example, the first point reduction mode can reduce the measurement point on the vertex A of the measurement area (i.e., measurement point No. 1) and at least one measurement point inside the measurement area (at least one of measurement points No. 4, No. 5, No. 7, and No. 9), and the remaining measurement points are retained; the second point reduction mode can reduce the measurement point on the vertex B of the measurement area (i.e., measurement point No. 3) and at least one measurement point inside the measurement area (at least one of measurement points No. 4, No. 5, No. 7, and No. 9), and the remaining measurement points are retained. The third point reduction mode can reduce the measurement point on the vertex C of the measurement area (i.e., measurement point No. 10) and at least one measurement point inside the measurement area (at least one of measurement points No. 4, No. 5, No. 7, and No. 9), and the remaining measurement points are retained. The fourth point reduction mode can reduce the measurement point on the vertex D of the measurement area (i.e., measurement point No. 12) and at least one measurement point inside the measurement area (at least one of measurement points No. 4, No. 5, No. 7, and No. 9), and the remaining measurement points are retained. Alternatively, the first point reduction mode can reduce the measurement points on the vertex A of the measurement area (i.e., measurement point No. 1), the measurement points on the edge L3 (i.e., measurement point No. 8) and / or the measurement points on the edge L4 (i.e., measurement point No. 11) and at least one measurement point inside the measurement area (at least one of measurement points No. 4, No. 5, No. 7, and No. 9), and the remaining measurement points are retained. The second point reduction mode can reduce the measurement points on the vertex B of the measurement area (i.e., measurement point No. 3), the edge L2 (i.e., measurement point No. 6) and / or the measurement points on the edge L4 (i.e., measurement point No. 11) and at least one measurement point inside the measurement area (at least one of measurement points No. 4, No. 5, No. 7, and No. 9), and the remaining measurement points are retained. Three point reduction modes can reduce the measurement points on the vertex C of the measurement area (i.e., measurement point No. 10), the measurement points on the edge L1 (i.e., measurement point No. 2) and / or the measurement points on the edge L3 (i.e., measurement point No. 8) and at least one measurement point inside the measurement area (at least one of measurement points No. 4, No. 5, No. 7, and No. 9), and the remaining measurement points are retained. The fourth point reduction mode can reduce the measurement points on the vertex D of the measurement area (i.e., measurement point No. 12), the measurement points on the edge L1 (i.e., measurement point No. 2) and / or the measurement points on the edge L2 (i.e., measurement point No. 6) and at least one measurement point inside the measurement area (at least one of measurement points No. 4, No. 5, No. 7, and No. 9), and the remaining measurement points are retained.

[0039] In some embodiments, the distance between the measurement points reduced inside the measurement area and the diagonal line where the reduced vertices are located can be less than a second predetermined value. That is, when selecting the measurement points reduced inside the measurement area, the measurement points with a smaller distance from the diagonal line where the reduced vertices are located can be selected as much as possible, and the measurement points with a larger distance from the diagonal line where the reduced vertices are located can be retained, thereby improving the uniformity of the measurement points left in each measurement area.

[0040] In some embodiments, the distance between the reduced measurement points and the diagonal line where the reduced vertices are located is the smallest within the measurement area. That is, when selecting the reduced measurement points within the measurement area, the measurement points with the smallest distance to the diagonal line where the reduced vertices are located can be selected, thereby improving the uniformity of the measurement points left in each measurement area.

[0041] Next, the four point reduction modes will be described in detail by taking n=3 as an example.

[0042] Figure 3a The distribution diagram of the measuring points in the measuring area under the first point reduction mode provided in this embodiment is as follows: Figure 3a As shown, the first point reduction mode reduces the measurement point on the vertex A of the measurement area (i.e., measurement point No. 1), the measurement point on the edge L4 (i.e., measurement point No. 11) and the measurement point No. 5 inside the measurement area, and the remaining 9 measurement points are retained. Figure 3b The distribution diagram of the measuring points in the measuring area under the second point reduction mode provided in this embodiment is as follows: Figure 3b As shown, the second point reduction mode reduces the measurement point on the vertex B of the measurement area (i.e., measurement point No. 3), the measurement point on the edge L2 (i.e., measurement point No. 6), and the measurement point No. 7 inside the measurement area, and the remaining 9 measurement points are retained. Figure 3c The schematic diagram of the distribution of the measuring points in the measuring area under the third point reduction mode provided in this embodiment is as follows: Figure 3c As shown, the third point reduction mode reduces the measurement point on the vertex C of the measurement area (i.e., measurement point No. 10), the measurement point on the edge L3 (i.e., measurement point No. 8), and the measurement point No. 4 inside the measurement area, and the remaining 9 measurement points are retained. Figure 3d The schematic diagram of the distribution of the measuring points in the measuring area under the fourth point reduction mode provided in this embodiment is as follows: Figure 3d As shown, the fourth point reduction mode reduces the measurement point on the vertex D of the measurement area (ie, measurement point No. 12), the measurement point on the edge L1 (ie, measurement point No. 2), and the measurement point No. 9 inside the measurement area, and the remaining 9 measurement points are retained.

[0043] It should be understood that the above four point reduction modes are only examples, and the four point reduction modes can also be other possible point reduction modes, as long as the four point reduction modes are different, and the measurement points left after the four point reduction modes are combined can cover the entire measurement area as much as possible, and the distribution of the remaining measurement points on the measurement area is relatively uniform.

[0044] Figure 4 Schematic diagram of the distribution of the point reduction pattern of the predetermined area in the overlay error measurement graph provided in this embodiment. Figure 4 As shown, in a predetermined area composed of multiple continuous measurement areas, the four point reduction modes are distributed according to the four-color theorem ( Figure 4One color represents one point reduction mode), and the point reduction mode of each measurement area in the predetermined area is determined by using the four-color principle, so that the measurement points in the predetermined area are distributed more evenly, thereby improving the distribution uniformity of the measurement points in the entire overlay error measurement graph and improving the accuracy of the overlay error observation and analysis model.

[0045] In this embodiment, the predetermined area is an area consisting of all complete measurement areas 101 and all partially complete measurement areas 102, but it should be understood that the predetermined area is not limited to the area consisting of the complete measurement area 101 and the partially complete measurement area 102, and the predetermined area may also be composed of other continuous measurement areas. For example, the predetermined area may also be an area consisting of multiple complete measurement areas 101, or the predetermined area may also be an area consisting of all complete measurement areas 101, all partially complete measurement areas 102 and all incomplete measurement areas 103. Examples will not be given one by one here.

[0046] Figure 5 FIG. 1 is a schematic diagram showing the distribution of the point reduction mode in the entire overlay error measurement graph provided in this embodiment. Figure 5 As shown, the selection of the point reduction mode for the incomplete measurement area 103 can be selected in the following manner:

[0047] First, most of the incomplete measurement area 103 will not be exposed, but a small part will be exposed. If the measurement points left in the incomplete measurement area 103 are located in the non-exposure area of ​​the incomplete measurement area 103, these measurement points are useless and cannot be used for overlay error measurement and analysis, and are invalid measurement points. If the measurement points left in the incomplete measurement area 103 are located in the exposure area of ​​the incomplete measurement area 103, these measurement points can be used for overlay error analysis and are valid measurement points. Therefore, one of the four point reduction modes that can leave the most valid measurement points can be selected as the point reduction mode of the incomplete measurement area 103. In this way, the number of valid measurement points in the incomplete measurement area 103 can be increased to avoid waste of measurement points. For example, for an incomplete measurement area 103, if the first, second, third and fourth point reduction modes leave 4, 5, 2 and 6 valid measurement points respectively, the fourth point reduction mode is selected as the point reduction mode.

[0048] Secondly, if there are at least two point reduction modes that can retain the most valid measurement points, the smaller one of the average of the total number of valid measurement points in all measurement areas and the total number of measurement points in all measurement areas is selected as the point reduction mode for the incomplete measurement area 103. In this way, the incomplete measurement area 103 can be used to increase the measurement points with a smaller proportion, thereby improving the uniformity of the distribution of the measurement points. For example, for an incomplete measurement area 103, if the valid measurement points left by using the first point reduction mode, the second point reduction mode, the third point reduction mode and the fourth point reduction mode are 4, 4, 2 and 1 respectively, then the first point reduction mode and the second point reduction mode can both leave the most valid measurement points. At this time, if the first point reduction mode is used, the average ratio of the total number of valid measurement points in all measurement areas to the total number of measurement points in all measurement areas is 30%; when the second point reduction mode is used, the average ratio of the total number of valid measurement points in all measurement areas to the total number of measurement points in all measurement areas is 10%, then the second point reduction mode is selected as the point reduction mode.

[0049] It should be noted that the average of the total number of valid measurement points in all measurement areas and the total number of measurement points in all measurement areas can be calculated. For example, when selecting a point reduction mode for an incomplete measurement area 103, the valid measurement points obtained by each point reduction mode can be determined first, and then the percentage of the total number of corresponding measurement points in all measurement areas to the total number of measurement points in all measurement areas can be calculated, and finally the average value is taken. For example, if the valid measurement points left by a certain point reduction mode are measurement points 1 and 2, the total number of measurement points 1 and 2 in all measurement areas is 10 and 15 respectively, and the total number of measurement points in all measurement areas is 100, then the total number of measurement points 1 and 2 accounts for 10% and 15% of the total number of measurement points, respectively, and the average value is 12.5%; the valid measurement points left by another point reduction mode are measurement points 1, 3 and 4, and the total number of measurement points 1, 3 and 4 in all measurement areas is 30, 20 and 35 respectively. And 5, the total number of measurement points in all measurement areas is 100, then the total number of measurement points No. 1, No. 3 and No. 4 accounts for 30%, 20% and 5% of the total number of all measurement points respectively, and the average value is 18.3%, which indicates that measurement points No. 1 and No. 2 account for a small proportion of the measurement points in all measurement areas. The point reduction mode corresponding to 12.5% ​​can be selected as the point reduction mode of the incomplete measurement area 103, so as to add more measurement points No. 1 and No. 2, increase the proportion of measurement points No. 1 and No. 2 in all measurement points, and then improve the distribution uniformity of the measurement points.

[0050] Furthermore, if there are at least two point reduction modes with the same average percentage of effective measurement points to the total of corresponding measurement points in all measurement areas, the one that complies with the four-color theorem is selected as the point reduction mode for the incomplete measurement area, thereby increasing the uniformity of the distribution of measurement points. For example, for an incomplete measurement area 103, if the valid measurement points left by using the first point reduction mode, the second point reduction mode, the third point reduction mode and the fourth point reduction mode are 4, 4, 2 and 1 respectively, then the first point reduction mode and the second point reduction mode can both leave the most valid measurement points. At this time, if the first point reduction mode is used, the average percentage of valid measurement points to the total sum of corresponding measurement points in all measurement areas is 30%, and when the second point reduction mode is used, the average percentage of valid measurement points to the total sum of corresponding measurement points in all measurement areas is also 30%. However, the first point reduction mode does not comply with the four-color theorem, and the second point reduction mode complies with the four-color theorem. In this case, the second point reduction mode is selected as its point reduction mode. If both the first point reduction mode and the second point reduction mode do not comply with the four-color theorem, a point reduction mode can be randomly selected as its point reduction mode.

[0051] It should be noted that, by selecting the point reduction mode for the incomplete measurement area 103 through the above-mentioned strategy, the number of effective measurement points in the incomplete measurement area 103 can be increased, thereby avoiding the insufficient number of effective measurement points in the edge measurement area, which in turn leads to the problem of insufficient observation and analysis capabilities of the overlay error observation and analysis model for the edge, and reduces the imbalance in the number of measurement points at the edge and center of the wafer, thereby improving the distribution uniformity of the measurement points in the overlay error measurement graph, and thereby improving the accuracy of the overlay error observation and analysis model.

[0052] In summary, the overlay error measurement graph provided in the embodiment of the present application includes a plurality of array-distributed measurement areas, one of which corresponds to one exposure field, and each of which reduces n measurement points in a normal measurement point set according to one of the four point reduction modes, where n is greater than or equal to 1, and in a predetermined area formed by a plurality of continuous measurement areas, the four point reduction modes are distributed according to the four-color theorem. The present application uses the four-color principle to determine the point reduction mode of each of the measurement areas in the predetermined area, so that the distribution of the measurement points in the predetermined area is relatively uniform, thereby improving the distribution uniformity of the measurement points in the entire overlay error measurement graph and improving the accuracy of the overlay error observation and analysis model.

[0053] It should be noted that the various embodiments in this specification are described in a progressive manner, and each embodiment focuses on the differences from other embodiments, and the same or similar parts between the various embodiments can be referred to each other. For the system disclosed in the embodiment, since it corresponds to the method disclosed in the embodiment, the description is relatively simple, and the relevant parts can be referred to the method part description.

[0054] It should also be noted that, although the present application has been disclosed as above with preferred embodiments, the above embodiments are not intended to limit the present application. For any technician familiar with the art, without departing from the scope of the technical solution of the present application, the technical content disclosed above can be used to make many possible changes and modifications to the technical solution of the present application, or modified into equivalent embodiments of equivalent changes. Therefore, any simple modification, equivalent change and modification made to the above embodiments based on the technical essence of the present application without departing from the content of the technical solution of the present application still falls within the scope of protection of the technical solution of the present application.

[0055] It should also be understood that, unless otherwise specified or indicated, the terms "first", "second", "third", etc. in the specification are merely used to distinguish between the various components, elements, steps, etc. in the specification, and are not used to indicate the logical relationship or sequential relationship between the various components, elements, steps, etc.

[0056] It should also be recognized that the terms described herein are only used to describe specific embodiments and are not used to limit the scope of the present application. It should be noted that the singular forms "one" and "a kind" used herein and in the appended claims include plural references unless the context clearly indicates the opposite meaning. For example, a reference to "a step" or "a device" means a reference to one or more steps or devices, and may include secondary steps and secondary devices. All conjunctions used should be understood in the broadest sense. And, the word "or" should be understood to have a definition of logical "or", rather than a definition of logical "exclusive or", unless the context clearly indicates the opposite meaning. In addition, the implementation of the method and / or device in the embodiment of the present application may include performing the selected task manually, automatically, or in combination.

Claims

1. An overlay error measurement pattern, characterized in that: It includes a plurality of array-distributed measurement areas, one measurement area corresponds to an exposure field, each measurement area reduces n measurement points in a normal measurement point set according to one of four point reduction modes, n is greater than or equal to 1, and within a predetermined area formed by a plurality of continuous measurement areas, the four point reduction modes are distributed according to the four-color theorem.

2. The overlay error measurement pattern according to claim 1, wherein: The measurement area includes a complete measurement area, a partially complete measurement area and an incomplete measurement area. The complete measurement area is a measurement area that can be fully exposed, the partially complete measurement area is a measurement area with an exposure rate greater than a first predetermined value, and the incomplete measurement area is a measurement area with an exposure rate less than or equal to the first predetermined value. The predetermined area is an area formed by the complete measurement area and the partially complete measurement area.

3. The overlay error measurement pattern as claimed in claim 2, wherein: The first predetermined value is 40% to 60%.

4. The overlay error measurement pattern according to claim 1, wherein: The normal measurement point set at least includes a measurement point located on each vertex of the measurement area.

5. The overlay error measurement pattern according to claim 4, wherein: The four point reduction modes all include at least reducing the measurement points on the vertices of the measurement area, and the four point reduction modes respectively reduce the measurement points on different vertices.

6. The overlay error measurement pattern according to claim 5, wherein: The normal measurement point set includes at least measurement points located on each edge of the measurement area, and the four point reduction modes also include reducing at least one measurement point on at least one edge of the measurement area that does not intersect with the reduced vertex.

7. The overlay error measurement pattern according to claim 5 or 6, characterized in that: The normal measurement point set at least includes measurement points located inside the measurement area, and the four point reduction modes all include reducing at least one measurement point inside the measurement area.

8. The overlay error measurement pattern according to claim 7, wherein: The distance between the reduced measurement points within the measurement area and the diagonal line where the reduced vertices are located is less than a second predetermined value.

9. The overlay error measurement pattern according to claim 7, wherein: The distance between the reduced measurement points and the diagonal line where the reduced vertices are located inside the measurement area is the smallest.

10. The overlay error measurement pattern according to claim 2, wherein: Selecting one of the four point reduction modes that can leave the most valid measurement points as the point reduction mode for the incomplete measurement area; if there are at least two point reduction modes that can leave the most valid measurement points, selecting the smaller one of the average of the total number of valid measurement points in all the measurement areas and the total number of measurement points in all the measurement areas as the point reduction mode for the incomplete measurement area; If there are at least two point reduction modes in which the total number of valid measurement points in all the measurement areas is the same as the average ratio of the total number of measurement points in all the measurement areas, the one that complies with the four-color theorem is selected as the point reduction mode for the incomplete measurement area.

11. The overlay error measurement pattern according to claim 1, wherein: The measuring area has dividing lines that are distributed in a staggered manner horizontally and vertically, and the measuring points are located on the four sides, four vertices and the dividing lines of the measuring area.

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