Mask and forming method thereof

Abstract

The invention provides a mask and a forming method. The forming method comprises the following steps: defining a to-be-improved region in a plurality of regions on the mask; sub-resolution filling patterns are added into the to-be-improved area, the sub-resolution filling patterns are located on the two sides of the initial photoetching OPC pattern to form new mask patterns, and the sub-resolution filling patterns are used for increasing the photoetching pattern density of the to-be-improved area. According to the invention, the to-be-improved region on the mask is firstly defined so as to accurately improve the region needing to increase the photoetching pattern density; and the sub-resolution filling pattern is a virtual pattern and cannot expose the pattern on the chip, so that the uniformity of the pattern density of the photoetching OPC pattern in each region is improved, the process manufacturing on the photomask is optimized, the accuracy of the line width of the photoetching OPC pattern is further improved, and the yield of the photoetching OPC pattern is improved. And the problem that the density of the photoetching OPC pattern in each area on the mask is not uniform is solved.

Description

Technical Field

[0001] The present invention relates to the technical field of integrated circuits, and in particular to a mask and a method for forming the mask. Background Art

[0002] The process of photomask is similar to the current chip production process, and needs to go through processes such as lithography and etching. Therefore, it will face the load effect and affect the distribution of the uniformity of the line size of the photomask. The chip process usually adds a so-called virtual pattern (filled pattern) to improve the distribution density of the photolithography pattern (pattern density distribution) to reduce the impact of the loading effect and improve the uniformity of the line size. However, the virtual patterns in the prior art are all targeted at the chip, and the pattern can be exposed on the chip. And the prior art cannot accurately add virtual patterns to the areas that need to be improved, so the uniformity of the line size needs to be further improved. Summary of the invention

[0003] The object of the present invention is to provide a mask and a method for forming the same, so as to improve the uniformity of line diameter.

[0004] In order to solve the above technical problems, the present invention provides a method for forming a mask, comprising:

[0005] Providing a mask, the mask comprising a plurality of regions, each of the regions being provided with an initial photolithography OPC pattern;

[0006] defining an area to be improved among the plurality of areas on the mask;

[0007] A sub-resolution filling pattern is added to the area to be improved, and the sub-resolution filling pattern is located on both sides of the initial photolithography OPC pattern to form a new mask pattern, wherein the sub-resolution filling pattern is used to increase the photolithography OPC pattern density of the area to be improved.

[0008] Optionally, the method of defining the area to be improved on the mask includes:

[0009] Calculating the pattern density of the initial photolithography OPC pattern in each area on the mask using the pattern density script of the initial photolithography OPC pattern and obtaining an average value of the overall pattern density;

[0010] The pattern density of the initial photolithography OPC pattern in each region is compared with the average value of the overall pattern density, and the region with a density lower than the average value of the overall pattern density is defined as the region to be improved.

[0011] Optionally, the initial photolithography OPC pattern in each region includes a photolithography main pattern and sub-sub-resolution auxiliary strips, wherein the sub-sub-resolution auxiliary strips are located on both sides of the photolithography main pattern, and the sub-sub-resolution auxiliary strips are used to improve the photolithography process window.

[0012] Optionally, before making the mask, the mask pattern is designed first, and the design of the mask pattern includes OPC modeling of the mask pattern; in the OPC modeling, the line width of the sub-resolution fill pattern is one level larger than the line width of the sub-sub-resolution auxiliary strip, and the line spacing of the sub-resolution fill pattern is smaller than the line spacing of the sub-sub-resolution auxiliary strip.

[0013] Optionally, when the main photolithography pattern is a long strip pattern, the sub-resolution filling pattern is parallel to the main photolithography pattern, and if the exposure light source has directionality, the horizontal or vertical pattern of the sub-resolution filling pattern is based on the principle of non-imaging.

[0014] Optionally, when the photolithography main pattern is a hole pattern, the sub-resolution filling pattern is a two-dimensional pattern.

[0015] Optionally, the distance between the sub-resolution filling pattern and the photolithography main pattern is greater than 1 micron.

[0016] Optionally, the distance between the sub-resolution fill pattern and the photolithography main pattern is less than 1 micron, and the sub-resolution fill pattern and the photolithography main pattern need to be simultaneously imported into the OPC model during OPC modeling.

[0017] Optionally, the method of increasing the pattern density of each region includes: increasing the width of the sub-resolution fill pattern, reducing the spacing between the sub-resolution fill patterns and / or increasing the number of the sub-resolution fill patterns.

[0018] Based on the same inventive concept, the present invention also provides a mask plate, which is made by the mask plate forming method described in any of the above items, and the mask plate includes multiple areas, each of the areas includes an initial photolithography OPC pattern, and some of the areas are areas to be improved, and the areas to be improved include sub-resolution filling patterns, and the sub-resolution filling patterns are located on both sides of the initial photolithography OPC pattern. The sub-resolution filling patterns are used to increase the photolithography OPC pattern density of the areas to be improved.

[0019] In a mask and formation method provided by the present invention, by defining the area to be improved among multiple areas on the mask; adding sub-resolution filling patterns in the area to be improved, the sub-resolution filling patterns are located on both sides of the initial photolithography OPC pattern, and the sub-resolution filling patterns are used to increase the photolithography pattern density of the area to be improved; to form a new mask pattern. The present invention first defines the area to be improved on the mask to accurately improve the area where the photolithography pattern density needs to be increased. And the sub-resolution filling pattern is a virtual pattern, and the pattern cannot be exposed on the chip. It is mainly used to improve the production of the mask and then improve the uniformity of the line width on the chip, that is, to solve the problem of uneven photolithography pattern density in various areas on the mask. BRIEF DESCRIPTION OF THE DRAWINGS

[0020] Those skilled in the art will appreciate that the accompanying drawings are provided for a better understanding of the present invention and do not constitute any limitation on the scope of the present invention.

[0021] Figure 1 The present invention is a flowchart of a method for forming a mask according to an embodiment of the present invention.

[0022] Figure 2 It is a schematic diagram of defining an area to be improved on a mask according to an embodiment of the present invention.

[0023] Figure 3 It is a schematic diagram of a one-dimensional sub-resolution filling pattern of a mask pattern according to an embodiment of the present invention.

[0024] Figure 4 It is a schematic diagram of a one-dimensional sub-resolution filling pattern of another mask pattern according to an embodiment of the present invention.

[0025] Figure 5 is a schematic diagram of a two-dimensional sub-resolution filling pattern according to an embodiment of the present invention.

[0026] Figure 6 is a schematic diagram of a two-dimensional sub-resolution filling pattern according to an embodiment of the present invention.

[0027] Figure 7 It is a schematic diagram of the photolithography pattern density of the active area of ​​the mask according to an embodiment of the present invention.

[0028] Figure 8 It is a schematic diagram of the photolithography pattern density of the polysilicon region of the mask according to an embodiment of the present invention.

[0029] In the attached figure:

[0030] 10-mask; 10a-normal area; 10b-area to be improved; 11-photolithography main pattern; 12-sub-resolution auxiliary strip; 13-sub-resolution filling pattern. DETAILED DESCRIPTION

[0031] In order to make the purpose, advantages and features of the present invention clearer, the present invention is further described in detail below in conjunction with the accompanying drawings and specific embodiments. It should be noted that the drawings are all in a very simplified form and are not drawn to scale, and are only used to conveniently and clearly assist in explaining the purpose of the embodiments of the present invention. In addition, the structure shown in the drawings is often a part of the actual structure. In particular, the emphasis of each drawing is different, and sometimes different scales are used.

[0032] As used in the present invention, the singular forms "one", "an" and "the" include plural objects, the term "or" is usually used to include the meaning of "and / or", the term "several" is usually used to include the meaning of "at least one", and the term "at least two" is usually used to include the meaning of "two or more". In addition, the terms "first", "second" and "third" are only used for descriptive purposes and cannot be understood as indicating or implying relative importance or implicitly indicating the number of indicated technical features. Therefore, the features defined as "first", "second" and "third" can explicitly or implicitly include one or at least two of the features. In addition, as used in the present invention, an element is arranged on another element, which usually only indicates that there is a connection, coupling, matching or transmission relationship between the two elements, and the connection, coupling, matching or transmission between the two elements can be direct or indirect through an intermediate element, and cannot be understood as indicating or implying the spatial position relationship between the two elements, that is, an element can be in any orientation such as inside, outside, above, below or on one side of another element, unless the content clearly indicates otherwise. For those skilled in the art, the specific meanings of the above terms in the present invention can be understood according to specific circumstances.

[0033] Figure 1 FIG. 1 is a flow chart of a method for forming a mask according to an embodiment of the present invention. Figure 1 As shown, this embodiment provides a method for forming a mask, comprising:

[0034] Step S10, providing a mask, wherein the mask includes a plurality of regions, each of which is provided with an initial photolithography OPC pattern;

[0035] Step S20, defining an area to be improved among the plurality of areas on the mask;

[0036] Step S30, adding a sub-resolution fill pattern in the area to be improved, the sub-resolution fill pattern is located on both sides of the initial photolithography OPC pattern to form a new mask pattern, wherein the sub-resolution fill pattern is used to increase the photolithography OPC pattern density of the area to be improved Figure 2 It is a schematic diagram of defining an area to be improved on a mask according to an embodiment of the present invention. Figure 3It is a schematic diagram of a one-dimensional sub-resolution filling pattern of a mask pattern according to an embodiment of the present invention. Figure 4 It is a schematic diagram of a one-dimensional sub-resolution filling pattern of another mask pattern according to an embodiment of the present invention. Figure 5 is a schematic diagram of a two-dimensional sub-resolution filling pattern according to an embodiment of the present invention. Figure 6 is a schematic diagram of a two-dimensional sub-resolution filling pattern according to an embodiment of the present invention.

[0037] Figure 7 It is a schematic diagram of the photolithography pattern density of the active area of ​​the mask according to an embodiment of the present invention. Figure 8 Schematic diagram of the photolithography pattern density of the polysilicon region of the mask of the embodiment of the present invention. In order to make the above-mentioned purpose, features and beneficial effects of the present invention more obvious and easy to understand, the following is a schematic diagram of the photolithography pattern density of the polysilicon region of the mask of the embodiment of the present invention. Figures 2 to 8 The specific embodiments of the present invention are described in detail.

[0038] like Figure 2 As shown, a mask 10 is provided, the mask 10 includes a plurality of regions, each of which is provided with an initial photolithography OPC pattern; the initial photolithography OPC pattern of each region is different, and the pattern density of the initial photolithography OPC pattern is also different. The pattern density uniformity of the photolithography OPC pattern of each region is improved, the process manufacturing on the photomask is optimized, and the line width accuracy of the photolithography OPC pattern is improved.

[0039] Please continue to refer to Figure 2, define the area 10b to be improved among the multiple areas on the mask 10. The method for defining the area 10b to be improved on the mask 10 includes: calculating the pattern density of the initial photolithography OPC pattern in each area on the mask 10 with the pattern density script of the initial photolithography OPC pattern and taking the overall pattern density average of the initial photolithography OPC pattern; comparing the pattern density of the initial photolithography OPC pattern in each area with the overall pattern density average of the initial photolithography OPC pattern, and the area lower than the overall pattern density average of the initial photolithography OPC pattern is the area 10b to be improved. Specifically, the initial photolithography OPC pattern density of each area is calculated with the pattern density script and the overall initial photolithography OPC pattern density average is obtained, and the photolithography OPC pattern density target value of the mask is defined so that the area lower than the overall initial photolithography OPC pattern density target value reaches the photolithography OPC pattern density target value, and the photolithography OPC pattern density target value of the mask is, for example, the average value of the overall pattern density of the initial photolithography OPC pattern in each area. In this embodiment, the mask 10 includes 32 regions, for example, and the average values ​​of the initial photolithography OPC pattern density of the 32 regions are calculated. The regions lower than the average value of the overall initial photolithography OPC pattern density are the regions to be improved 10b, and the regions to be improved 10b are, for example, W1 to W7. The regions higher than the average value of the overall initial photolithography OPC pattern density are normal regions 10a, and the normal regions 10a do not need to be filled with sub-resolution fill patterns.

[0040] like Figure 3 As shown, the initial photolithography OPC pattern in each area includes a photolithography main pattern 11 and a sub-sub-resolution auxiliary strip 12, the sub-sub-resolution auxiliary strips 12 are located on both sides of the photolithography main pattern 11, the sub-sub-resolution auxiliary strips 12 are used to improve the photolithography process window (Process Window), and the pattern cannot be exposed on the chip. A sub-resolution fill pattern 13 is added to the area to be improved 10b, the sub-resolution fill pattern 13 is located on both sides of the initial photolithography OPC pattern, and the sub-resolution fill pattern 13 is located outside the sub-sub-resolution auxiliary strip 12, and the sub-sub-resolution auxiliary strip 12 is located between the photolithography main pattern 11 and the sub-resolution fill pattern 13. The sub-resolution fill pattern 13 is used to increase the photolithography pattern density of the area to be improved 10b, the sub-resolution fill pattern 13 is a virtual pattern, and the pattern cannot be exposed on the chip, that is, the sub-resolution fill pattern 13 cannot be imaged on the chip.

[0041] Before making a mask, a mask pattern is designed first, and the mask pattern design includes OPC modeling of the mask pattern; in the OPC modeling, the line width of the sub-resolution fill pattern 13 is one level greater than the line width of the sub-sub-resolution auxiliary strip 12, and the line spacing of the sub-resolution fill pattern 13 is less than the line spacing of the sub-sub-resolution auxiliary strip 12. The actual parameters need to collect information during OPC modeling, with the imaging of the filter resolution fill pattern as the main basis. Specifically, the line width of the sub-sub-resolution auxiliary strip 12 is, for example, 25nm, and the line width of the sub-resolution fill pattern 13 is, for example, 30nm. In other embodiments, the line width W and the spacing S of the sub-resolution fill pattern 13 are variables. If the method for improving the lithography pattern density of the area to be improved 10b includes increasing the width W of the sub-resolution fill pattern 13, reducing the spacing (Space) S of the sub-resolution fill pattern 13 and / or increasing the number of the sub-resolution fill patterns 13, but these sub-resolution fill patterns 13 cannot be imaged on the chip. The segmentation conditions of the above variables can be placed on the early test mask (mask) and the density of the photolithography pattern in the corresponding area can be calculated. When the OPC model is built, the imaging condition can be collected, and the sub-resolution fill pattern 13 with imaging can be filtered out. In addition, the sub-resolution fill pattern 13 cannot affect the result of the OPC (Optical Proximity Correction) of the photolithography pattern. Therefore, the distance d1 between the sub-resolution fill pattern 13 and the photolithography main pattern 11 must be greater than 1um, that is, the distance d1 between the sub-resolution fill pattern 13 and the photolithography main pattern 11 is greater than 1 micron, which does not affect the OPC correction operation. In this embodiment, due to the fact that the area of ​​the sub-resolution fill pattern 13 is much smaller than the area of ​​the sub-resolution fill pattern 13 of the actual product design, adding the sub-resolution fill pattern 13 to the area to be improved 10b can improve the pattern density of the overall open area by about 3%-6%.

[0042] like Figure 4 As shown, if the pattern density of the area to be improved 10b is to be increased by more than 6%, the distance d2 between the sub-resolution fill pattern 13 and the photolithography main pattern 11 can be shortened to less than 1um, that is, the distance d2 between the sub-resolution fill pattern 13 and the photolithography main pattern 11 is less than 1 micron, which affects the accuracy of the OPC correction operation. When the OPC model is built, the effect of the sub-resolution fill pattern 13 needs to be introduced into the OPC model. That is, when the OPC model is built, the sub-resolution fill pattern 13 and the photolithography main pattern 11 are simultaneously introduced into the OPC model.

[0043] like Figures 3 to 6 As shown, the sub-resolution filling pattern 13 is a one-dimensional pattern or a two-dimensional pattern. Figure 3 and Figure 4As shown, when the main photolithography pattern is a long strip pattern, the sub-resolution fill pattern 13 is a one-dimensional pattern. In most cases, the sub-resolution fill pattern 13 is parallel to the main photolithography pattern 11, that is, for a simple design of a one-dimensional pattern, the directionality is determined mainly based on the sub-resolution fill pattern 13 being parallel to the main photolithography pattern 11. If the exposure light source is directional, the horizontal and vertical patterns of the sub-resolution fill pattern are based on the principle of non-imaging, and relevant information needs to be collected for confirmation when the OPC model is built. If the light source is directional, such as dipole Y, in order to increase the pattern density, it can be perpendicular to the main photolithography pattern 11, and the MRC (MASK Rule Check) rule needs to be followed when placing the sub-resolution fill pattern 13. Figure 5 and Figure 6 As shown, when the photolithography main pattern is a hole pattern, when the sub-resolution filling pattern 13 is a two-dimensional pattern, the addition of the two-dimensional sub-resolution filling pattern 13 can refer to the design of mutually perpendicular stripes. A series of sub-resolution filling pattern 13 libraries can be designed and placed on the test mask for evaluation.

[0044] like Figure 7 As shown, Figure 7 The figure is a distribution diagram of the photolithography OPC pattern density of the active area. The horizontal axis is the pattern density of each area, and the vertical axis is the number of areas with the corresponding pattern density. Before the sub-resolution fill pattern 13 is added to the 50 scanning areas in the active area, the pattern density of each area is distributed between 30 and 41, and the average pattern density is 37.6. The pattern density of each area is quite different and the uniformity is poor. By adding the sub-resolution fill pattern 13 to the mask 10, after adding the sub-resolution fill pattern 13, the pattern density of each area is distributed between 33-41 (areas greater than the average density cannot be improved), and the average pattern density of each area is 38.5. It can be seen that the average pattern density of each area in the active area is improved, and then the uniformity of the pattern density of each area is improved, so as to increase the accuracy of the line width on the chip after the pattern in the mask is transferred to the chip.

[0045] like Figure 8 As shown, Figure 8The figure is a distribution diagram of the photolithography OPC pattern density in the polysilicon area. The horizontal axis is the pattern density of each area, and the vertical axis is the number of areas with the corresponding pattern density. Before the sub-resolution fill pattern 13 was added to the 50 scanning areas in the polysilicon area, the pattern density of each area was distributed between 20 and 30, and the average pattern density was 25.2. The pattern density of each area was quite different and the uniformity was poor. By adding the sub-resolution fill pattern 13 to the mask 10, after adding the sub-resolution fill pattern 13, the pattern density of each area was distributed between 24 and 30 (areas greater than the average density cannot be improved), and the average pattern density of each area was 26.3. It can be seen that the average pattern density of each area in the polysilicon area is improved, and then the uniformity of the pattern density of each area is improved, so as to increase the accuracy of the line width on the chip after the pattern in the mask is transferred to the chip.

[0046] like Figure 2 and Figure 3 As shown, this embodiment also provides a mask, which is made by any of the above mask forming methods, the mask 10 includes multiple areas, each of which includes an initial photolithography OPC pattern, the initial photolithography OPC pattern in each area includes a photolithography main pattern 11 and a sub-sub-resolution auxiliary strip 12, and the normal area 10a and the area to be improved 10b are defined by calculating the photolithography pattern density of each area, and the area to be improved 10b includes a sub-resolution filling pattern 13, the sub-resolution filling pattern 13 is located on both sides of the photolithography main pattern 11, and the sub-resolution filling pattern 13 is used to increase the photolithography pattern density of the area. Sub-sub-resolution auxiliary strips 12 are arranged on both sides of the photolithography main pattern 11 in each area. The sub-resolution filling pattern 13 is located outside the sub-sub-resolution auxiliary strip 12, and the sub-sub-resolution auxiliary strip 12 is located between the photolithography main pattern 11 and the sub-resolution filling pattern 13. The sub-sub-resolution auxiliary strip 12 is used to improve the photolithography process window (Process Window), and the pattern cannot be exposed on the chip. The sub-resolution filling pattern 13 is used to increase the pattern density of the area to be improved 10b. The sub-resolution filling pattern 13 is a virtual pattern and cannot be exposed on the chip, that is, the sub-resolution filling pattern 13 cannot be imaged on the chip. The line width of the sub-resolution filling pattern 13 is one level greater than the line width of the sub-sub-resolution auxiliary strip 12, and the line spacing of the sub-resolution filling pattern 13 is less than the line spacing of the sub-sub-resolution auxiliary strip 12.

[0047] From the above, it can be seen that in a mask and a forming method provided by an embodiment of the present invention, by defining the area to be improved in a plurality of areas on the mask; adding a sub-resolution fill pattern in the area to be improved, the sub-resolution fill pattern is located on both sides of the initial photolithography OPC pattern, and the sub-resolution fill pattern is used to increase the photolithography pattern density in the area to be improved; to form a new mask pattern. When defining the area to be improved, the OPC script is run for the photolithography pattern of each area to add the sub-resolution fill pattern, and the sub-resolution fill pattern that can be imaged must be filtered out, and the parameter definition of the sub-resolution fill image imaging needs to be determined during OPC modeling. The present invention first defines the area to be improved on the mask to accurately improve the area where the photolithography pattern density needs to be increased. And the sub-resolution fill pattern is a virtual pattern, and the pattern cannot be exposed on the chip. It is mainly used to improve the production of the mask and then improve the accuracy of the line width on the chip, that is, to solve the problem of uneven density of the photolithography pattern in each area on the mask.

[0048] 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. The same or similar parts between the various embodiments can be referenced to each other. In addition, the different parts between the various embodiments can also be used in combination with each other, and the present invention is not limited to this.

[0049] In addition, it should be recognized that although the present invention has been disclosed as a preferred embodiment, the above embodiment is not intended to limit the present invention. For any technician familiar with the art, without departing from the scope of the technical solution of the present invention, the technical content disclosed above can be used to make many possible changes and modifications to the technical solution of the present invention, or modified into equivalent embodiments of equivalent changes. Therefore, any simple modification, equivalent change and modification made to the above embodiment according to the technical essence of the present invention without departing from the content of the technical solution of the present invention still belongs to the scope of protection of the technical solution of the present invention.

Claims

1. A method for forming a mask, characterized in that: include: Providing a mask, the mask comprising a plurality of regions, each of the regions being provided with an initial photolithography OPC pattern; defining an area to be improved among the plurality of areas on the mask; A sub-resolution filling pattern is added to the area to be improved, and the sub-resolution filling pattern is located on both sides of the initial photolithography OPC pattern to form a new mask pattern, wherein the sub-resolution filling pattern is used to increase the photolithography OPC pattern density of the area to be improved.

2. The method for forming a mask according to claim 1, characterized in that: The method of defining the area to be improved on the mask includes: Calculating the pattern density of the initial photolithography OPC pattern in each area on the mask using the pattern density script of the initial photolithography OPC pattern and obtaining an average value of the overall pattern density; The pattern density of the initial photolithography OPC pattern in each region is compared with the average value of the overall pattern density, and the region with a density lower than the average value of the overall pattern density is defined as the region to be improved.

3. The method for forming a mask according to claim 1, characterized in that: The initial photolithography OPC pattern in each area includes a photolithography main pattern and sub-sub-resolution auxiliary strips, wherein the sub-sub-resolution auxiliary strips are located at both sides of the photolithography main pattern and are used to improve the photolithography process window.

4. The method for forming a mask according to claim 3, characterized in that: Before making a mask, the mask pattern is designed first, and the design of the mask pattern includes OPC modeling of the mask pattern; In OPC modeling, the line width of the sub-resolution fill pattern is one level larger than the line width of the sub-sub-resolution auxiliary strip, and the line spacing of the sub-resolution fill pattern is smaller than the line spacing of the sub-sub-resolution auxiliary strip.

5. The method for forming a mask according to claim 4, characterized in that: When the main photolithography pattern is a long strip pattern, the sub-resolution fill pattern is a one-dimensional pattern. The sub-resolution fill pattern is parallel to the main photolithography pattern. If the exposure light source is directional, the horizontal or vertical pattern of the sub-resolution fill pattern is based on the principle of non-imaging.

6. The method for forming a mask according to claim 4, characterized in that: When the photolithography main pattern is a hole pattern, the sub-resolution filling pattern is a two-dimensional pattern.

7. The method for forming a mask according to claim 4, characterized in that: The distance between the sub-resolution filling pattern and the photolithography main pattern is greater than 1 micron.

8. The method for forming a mask according to claim 4, characterized in that: The distance between the sub-resolution filling pattern and the photolithography main pattern is less than 1 micron, and the sub-resolution filling pattern and the photolithography main pattern need to be simultaneously introduced into the OPC model during OPC modeling.

9. The method for forming a mask according to claim 1, wherein: The method of increasing the pattern density of each region includes: increasing the width of the sub-resolution fill pattern, reducing the spacing of the sub-resolution fill pattern and / or increasing the number of the sub-resolution fill pattern.

10. A mask, characterized in that: The mask is manufactured by the method for forming a mask according to any one of claims 1 to 9, wherein the mask comprises a plurality of areas, each of the areas comprises an initial OPC lithography pattern, and some of the areas are areas to be improved, wherein the areas to be improved comprise sub-resolution filling patterns, the sub-resolution filling patterns are located on both sides of the initial lithography OPC pattern, and the sub-resolution filling patterns are used to increase the lithography OPC pattern density of the areas to be improved.

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