Focusing depth measuring method

Abstract

The invention belongs to the technical field of semiconductors, and provides a focusing depth measurement method, which comprises the following steps: providing a mask pattern and a test piece to be tested, the mask pattern comprises a plurality of first patterns and second patterns, and the distance between the first pattern and the adjacent second pattern is less than or equal to a first distance; exposing and developing the to-be-tested piece, and transferring the mask pattern to the to-be-tested piece; according to the second pattern, performing first type measurement on the to-be-tested piece to obtain the focusing depth of the second pattern on the to-be-tested piece; performing a second type of measurement on the to-be-tested piece to obtain the focusing depth of the first pattern on the to-be-tested piece; the focusing depths of the dense patterns and the isolated patterns on the to-be-tested piece are accurately measured at the same time within the extremely small measurement range, two adjacent patterns do not need to be measured twice separately, the risk that the dense patterns are distorted is reduced or avoided, and when slice inspection is conducted on the dense patterns subsequently, the accuracy of slice inspection is improved. And the contour structure and the size of the dense pattern can be reflected more accurately.

Description

Technical Field

[0001] The present application relates to the field of semiconductor technology, and in particular to a method for measuring focus depth. Background Art

[0002] The photolithography process is one of the most important manufacturing processes in modern large-scale integrated circuit manufacturing. It can transfer the design pattern of the integrated circuit on the mask pattern to the silicon wafer through the photolithography machine. In the chip manufacturing process, in order to optimize the exposure parameters and ensure the pattern quality on the wafer surface, it is necessary to measure and inspect the depth of field of the pattern after exposure and development on the wafer. Depth of field measurement involves a variety of patterns, such as dense patterns and isolated patterns. After the pattern is exposed and developed, it is measured using a scanning electron microscope (SEM) to obtain the critical dimension CD and depth of field of each pattern, and then determine the depth of field of the overall pattern on the wafer.

[0003] When using SEM for depth of field measurement, SEM is destructive to photoresist. When two graphics are close to each other, the electron beam generated by SEM will inevitably have an adverse effect on the other graphic when measuring one of the graphics, which may cause the contour structure of the other graphic to be distorted. Therefore, it is necessary to separate the two relatively close graphics by a certain distance and measure them separately. In addition, after completing the SEM measurement, in order to further detect the contour of the graphics, slicing is required, and SEM inspection is performed again after slicing, resulting in more serious distortion of the parameters such as the graphic contour, thickness, and key dimensions of the photoresist on the wafer surface.

[0004] Based on this, in order to solve the above problems, the present application provides a focus depth measurement method for realizing focus depth measurement of adjacent graphics, while reducing or avoiding the risk of graphic distortion. Summary of the invention

[0005] In view of the shortcomings of the prior art mentioned above, the purpose of the present application is to provide a focus depth measurement method to solve the problems existing in the prior art such as graphic distortion that is prone to occur during graphic focus depth measurement and inspection. The method can simultaneously determine the focus depths of adjacent isolated graphics and dense graphics, and reduce or avoid the occurrence of graphic distortion during focus depth measurement and inspection.

[0006] To achieve the above objectives and other related objectives, the present application provides a method for measuring focus depth, comprising the following steps:

[0007] Providing a mask pattern and a test piece, wherein the mask pattern includes a plurality of first patterns and a plurality of second patterns;

[0008] exposing and developing the test piece to transfer the mask pattern to the test piece;

[0009] According to the second pattern, performing a first type of measurement on the device to be tested to obtain a focus depth of the second pattern on the device to be tested;

[0010] Performing a second type of measurement on the test piece to obtain a focus depth of a first pattern on the test piece;

[0011] Wherein, on the test piece, the distance between the first pattern and the adjacent second pattern is less than or equal to the first distance.

[0012] Optionally, the first distance is 3 μm to 10 μm.

[0013] Optionally, the mask pattern includes a plurality of first patterns, and on the test piece, a distance between two adjacent first patterns is greater than a second distance.

[0014] Optionally, the second distance is 3 μm to 10 μm.

[0015] Optionally, the mask pattern further includes a plurality of third patterns and a plurality of fourth patterns, and on the test piece, the distance between the first pattern and an adjacent third pattern, the distance between two adjacent third patterns, and the distance between the third pattern and an adjacent fourth pattern are all greater than the second distance.

[0016] Optionally, both the second pattern and the fourth pattern are dense patterns, and according to the second pattern, an optical measurement system is used to perform optical measurement on the device to be tested to obtain the focus depths of the second pattern and the fourth pattern on the device to be tested.

[0017] Optionally, both the first pattern and the third pattern are isolated patterns, and the device to be tested is measured using a scanning electron microscope to obtain the focus depths of the first pattern and the third pattern on the device to be tested.

[0018] Optionally, the second graphic includes a first marking graphic, and the first marking graphic includes a plurality of first lines and a plurality of second lines;

[0019] The first marking pattern has a first direction and a second direction that are perpendicular to each other, and the first lines and the second lines both extend along the first direction and are arranged at intervals along the second direction.

[0020] Optionally, the first marking pattern includes two first lines and a plurality of second lines, the plurality of second lines are evenly spaced between the two first lines, and a width of the first line is greater than a width of the second line.

[0021] Optionally, the second graphic further includes a second marking graphic, and the second marking graphic is rotationally symmetric to the first marking graphic.

[0022] As described above, the focus depth measurement method provided by the present application has at least the following beneficial effects:

[0023] The focus depth measurement method of the present application uses the second graphic as a measurement mark, uses an optical measurement system to measure the second graphic on the surface of the test piece to obtain the focus depth of the second graphic, and uses the SEM to measure the adjacent first graphic to obtain the focus depth of the first graphic, thereby achieving accurate measurement of the focus depths of dense graphics and isolated graphics simultaneously within a very small measurement range, without the need to perform two separate measurements on two relatively adjacent graphics; and through optical measurement, non-destructive measurement of dense graphics is achieved, without the need to subject the dense graphics to the bombardment of a high-energy electron beam at the exact center of the SEM, thereby reducing or avoiding the risk of distortion of the dense graphics, and when the dense graphics are subsequently sliced ​​for inspection, the contour structure and size of the dense graphics can be more accurately reflected. BRIEF DESCRIPTION OF THE DRAWINGS

[0024] In order to more clearly illustrate the technical solutions of the embodiments of the present application, the drawings required for use in the embodiments will be briefly introduced below. It should be understood that the following drawings only show certain embodiments of the present application and therefore should not be regarded as limiting the scope. For ordinary technicians in this field, other related drawings can be obtained based on these drawings without paying creative work.

[0025] Figure 1 Shown is a flow chart of a method for measuring depth of focus provided in an embodiment of the present application.

[0026] Figure 2 Shown is a schematic structural diagram of a first graphic and a second graphic provided as an optional embodiment in the embodiments of the present application.

[0027] Figures 3 to 5 Shown are structural schematic diagrams of the third and fourth figures provided as optional embodiments in the embodiments of the present application.

[0028] Reference numerals:

[0029] 11. First graphic; 12. Second graphic; 121. First marking graphic; 122. Second marking graphic; 1201. Marking sub-graphic; 13. Third graphic; 14. Fourth graphic. DETAILED DESCRIPTION

[0030] In order to make the technical purpose, technical solution and technical effect of the present application clearer, the technical solution in the present application will be clearly and completely described in conjunction with the embodiments below. Obviously, the described embodiments are part of the embodiments of the present application, rather than all the embodiments. The components of the embodiments of the present application described and shown in the drawings here can be arranged and designed in various different configurations.

[0031] Therefore, the following detailed description of the embodiments of the present application is not intended to limit the scope of the present application for protection, but merely represents the selected embodiments of the present application. Based on the embodiments in the present application, all other embodiments obtained by those of ordinary skill in the art without creative work are within the scope of protection of the present application. In addition, the terms "first" and "second" are only used for descriptive purposes and cannot be understood as indicating or implying relative importance.

[0032] In the description of the present application, it should be noted that the description with reference to the terms "one embodiment", "some embodiments", "illustrative embodiments", "example", "specific example" or "some examples" means that the specific features, structures, materials or characteristics described in conjunction with the implementation or example are included in at least one implementation or example of the present application. In this specification, the schematic representation of the above terms does not necessarily refer to the same implementation or example. Moreover, the specific features, structures, materials or characteristics described may be combined in any one or more implementations or examples in a suitable manner.

[0033] In the prior art, due to the complexity and diversity of mask patterns, there are often isolated patterns and dense patterns with relatively close distances in the mask patterns. After exposure and development, some dense patterns on the wafer surface are close to isolated patterns. When measuring the depth of focus of the patterns on the wafer surface, since optical measurement cannot effectively measure the depth of focus of the patterns, a scanning electron microscope (SEM) is currently used to measure the depth of focus. When measuring dense patterns or isolated patterns, since the electron beam energy is high during SEM measurement, it is easy to have an adverse effect on dense patterns with relatively close distances, causing them to be distorted during the depth of focus measurement and inspection process; and if slicing is required to further detect the contour of the pattern after exposure and development on the wafer surface, SEM inspection will be performed again after slicing, which will cause more serious distortion of the pattern.

[0034] Based on the above-mentioned problems in the prior art, the present embodiment provides a focus depth measurement method for measuring the focus depth of an exposure pattern on a test piece, thereby reducing or avoiding the risk of distortion of the pattern on the surface of the test piece when performing focus depth measurement. Optionally, the test piece may be, for example, a wafer or other suitable element, and the exposure pattern is formed by exposing and developing a mask pattern on the wafer.

[0035] Reference Figure 1 The focus depth measurement method provided in this embodiment includes steps S1 to S4, specifically including:

[0036] Step S1: providing a mask pattern and a test piece, wherein the mask pattern includes a plurality of first patterns 11 and a plurality of second patterns 12;

[0037] Step S2: exposing and developing the test object to transfer the mask pattern to the test object;

[0038] Step S3: performing a first type of measurement on the test piece according to the second pattern 12 to obtain a focus depth of the second pattern 12 on the test piece;

[0039] Step S4: performing a second type of measurement on the test piece to obtain a focus depth of the first pattern 11 on the test piece.

[0040] The focus depth measurement method of this embodiment will be described in detail below with reference to the accompanying drawings. It should be noted that the above sequence does not strictly represent the process sequence of the focus depth measurement method protected by this application, and those skilled in the art may change it according to the actual processing steps.

[0041] First, step S1 is performed to provide a mask pattern and a test piece; wherein the mask pattern includes a plurality of first patterns 11 and second patterns 12 .

[0042] Reference Figure 2 The mask pattern has one or more first patterns 11 and one or more second patterns 12. Optionally, for example, the mask pattern includes multiple first patterns 11 and multiple second patterns 12, wherein the multiple first patterns 11 and the first patterns 11 and the second patterns 12 are spaced apart from each other.

[0043] In an alternative embodiment, reference Figures 3 to 5The mask pattern further includes a plurality of third patterns 13 and a fourth pattern 14. Optionally, for example, the mask pattern includes a plurality of third patterns 13 and a plurality of fourth patterns 14, and the plurality of third patterns 13 and the third patterns 13 and the fourth patterns 14 are spaced apart from each other. Optionally, the first pattern 11 and the third pattern 13 are, for example, isolated patterns, the second pattern 12 and the fourth pattern 14 are, for example, dense patterns, and the two adjacent isolated patterns and the adjacent isolated pattern and the dense pattern are spaced apart from each other.

[0044] Among them, the first figure 11 and the second figure 12 can be understood as isolated figures and dense figures that are close to each other, and the dense figure / second figure 12 can be used as a measurement mark to facilitate the subsequent measurement of the depth of focus of the figure. Specifically, the dense figure is, for example, the main figure in the mask figure, and the first figure 11 is, for example, an auxiliary figure and other suitable figures. The third figure 13 and the fourth figure 14 can be understood as isolated figures and dense figures that are far away from the adjacent figures, and will not cause adverse effects on the adjacent figures when measuring the depth of focus of the figure. Furthermore, other types of isolated figures or dense figures can also be set in the mask figure, such as isolated figures and dense figures that are close to each other, and the dense figure cannot be used as a measurement mark.

[0045] In this embodiment, refer to Figure 2 The second graphic 12 includes a first marking graphic 121, and the first marking graphic 121 includes a plurality of first lines and a plurality of second lines; the mask graphic has a longitudinal direction and a transverse direction, and the first lines and the second lines both extend along the longitudinal direction and are arranged at intervals along the transverse direction.

[0046] Next, step S2 is performed to expose and develop the test piece to transfer the mask pattern to the test piece.

[0047] In an optional embodiment, step S2 is performed, which specifically includes the following steps: coating a photoresist on the piece to be tested so that the photoresist covers the surface of the piece to be tested; exposing the piece to be tested after the photoresist is coated using a mask pattern; developing the exposed photoresist using a developer; and removing the residual developer on the photoresist after the development process to obtain a piece to be tested having an exposure pattern.

[0048] In an optional embodiment, on the test piece, the distance between the adjacent first graphics 11 and second graphics 12 is less than or equal to the first distance. Optionally, the first distance is 3μm to 10μm, and the first distance can be, for example, 3μm, 5μm, 7μm, 10μm or other suitable values. Preferably, the first distance is 3μm. The first graphics 11 and the second graphics 12 are close to each other. By using the focus depth measurement method of this embodiment, it is possible to simultaneously measure the focus depth of the first graphics 11 and the second graphics 12, and reduce or avoid the risk of distortion of the shape, contour and size of the graphics during the measurement process, thereby improving the accuracy of the focus depth measurement of the exposure graphics on the test piece.

[0049] In an optional embodiment, the mask pattern includes a plurality of first patterns 11, and the shapes and sizes of the plurality of first patterns 11 may be the same or different; the mask pattern may also include a plurality of second patterns 12, and the shapes and sizes of the plurality of second patterns 12 may be the same or different. After the mask pattern is transferred to the test piece, on the test piece, the distance between two adjacent first patterns 11 is greater than the second distance. Optionally, the second distance is 3μm to 10μm. The second distance may be, for example, 3μm, 5μm, 7μm, 10μm or other suitable values. Preferably, the second distance may be 3μm. By controlling the spacing distance between two adjacent first patterns 11 on the test piece to be tested to be larger, it can be ensured that when the focus depth of the pattern on the surface of the test piece is measured, only one first pattern 11 is contained in a window, thereby avoiding adverse effects on adjacent first patterns 11 during focus depth measurement, causing distortion of part of the first patterns 11, and improving the accuracy of focus depth measurement.

[0050] In an optional embodiment, the mask pattern further includes a plurality of third patterns 13 and a fourth pattern 14, wherein, on the test piece, the distance between the first pattern 11 and the adjacent third pattern 13, the distance between two adjacent third patterns 13, and the distance between the third pattern 13 and the fourth pattern 14 are all greater than the second distance. Optionally, the first pattern 11 and the third pattern 13, for example, may be isolated patterns, and the second pattern 12 and the fourth pattern 14, for example, may be dense patterns. By controlling the distances between the first pattern 11 and the third pattern 13, between two adjacent third patterns 13, and between the third pattern 13 and the fourth pattern 14 to be relatively large, it is possible to avoid adverse effects on adjacent patterns when performing focus depth measurement, improve the accuracy of focus depth measurement of the pattern, and reduce or avoid the risk of distortion of the pattern.

[0051] Reference Figure 2The second graphic 12 includes a first marking graphic 121, the first marking graphic 121 includes a plurality of first lines and a plurality of second lines, the first marking graphic 121 has a first direction and a second direction perpendicular to each other, the first lines and the second lines both extend along the first direction and are arranged at intervals along the second direction, optionally, the first marking graphic 121 includes a plurality of first lines and a plurality of second lines, the plurality of first lines and the plurality of second lines are both arranged at intervals along the second direction, and the first lines and the second lines are also arranged at intervals.

[0052] In an optional embodiment, the first marking pattern 121 includes two first lines and a plurality of second lines, and the plurality of second lines are evenly spaced between the two first lines; for example, the first marking pattern 121 includes four second lines, and the first line, the four second lines, and the first line are spaced in sequence. Optionally, the sum of the distance between two adjacent first lines and the width of the first line is twice the critical dimension of the second pattern 12 on the test piece.

[0053] In an optional embodiment, the first mark pattern 121 includes a plurality of periodically arranged mark sub-patterns 1201, the mark sub-patterns 1201 include a first line and a plurality of second lines, and the plurality of second lines are evenly spaced and distributed on one side of the first line, for example, the first mark sub-pattern 1201 includes four periodically arranged mark sub-patterns 1201. Optionally, the period length of the periodically arranged mark sub-patterns 1201 is twice the critical dimension of the first pattern 11 exposed on the test piece.

[0054] Further, refer to Figure 2 The first marking pattern 121 may further include a second marking pattern 122, and the second marking pattern 122 is rotationally symmetrical with the first marking pattern 121, for example, the first marking pattern 121 and the second marking pattern 122 are symmetrical when rotated 90° clockwise or counterclockwise. Optionally, the first pattern 11 is a strip-shaped pattern and extends along the first direction, the first pattern 11 is located on one side of the first marking pattern 121 along the second direction, and the second marking pattern 122 is located on one side of the first marking pattern 121 along the first direction, and the distance between the first marking pattern 121 and the first pattern 11 along the first direction, the distance between the second marking pattern 122 and the first pattern 11 along the first direction, and the distance between the second marking pattern 122 and the first pattern 11 along the second direction are all less than or equal to the first distance.

[0055] Next, step S3 is executed to perform a first type of measurement on the test piece according to the second pattern 12 to obtain a focus depth of the second pattern 12 on the test piece.

[0056] In an optional embodiment, the second pattern 12 is a dense pattern. According to the second pattern 12 , an optical measurement system is used to perform optical measurement on the test piece to perform the first type of measurement, thereby obtaining the focus depth of the second pattern 12 on the test piece.

[0057] In an optional embodiment, the mask pattern also includes a fourth pattern 14, and the second pattern 12 and the fourth pattern 14 are both dense patterns. According to the second pattern 12, an optical measurement system is used to perform optical measurement on the test piece to perform a first type of measurement, thereby obtaining the focal depth of the second pattern 12 and the fourth pattern 14 on the test piece.

[0058] In an optional embodiment, before executing step S3, the following steps may be further included: identifying a second pattern 12 from the pattern on the surface of the test piece to perform the first type of measurement. The second pattern 12 may be obtained according to the design structure of the mask pattern, or the second pattern 12 may be obtained from the pattern on the surface of the test piece using an optical measurement system, or the second pattern 12 may be identified from the pattern on the surface of the test piece using other appropriate methods, so as to facilitate the subsequent first type of measurement of the test piece.

[0059] In an alternative embodiment, reference Figure 2 , the second pattern 12 includes a first mark pattern 121 and a second mark pattern 122, the first mark pattern 121 is symmetrical with the second mark by rotation of 90°, the first mark pattern 121 includes at least one mark sub-pattern 1201 and a first line located on one side of the mark sub-pattern 1201, and a plurality of second lines in the mark sub-pattern 1201 are arranged periodically. The number of second lines in the mark sub-pattern 1201 is recorded as n, and the critical dimension actually exposed on the test piece is recorded as L w , the coordinates of the actual alignment position of the second graphic 12 are marked as (x, y), the theoretical imaging position is recorded as (x0, y0), the sum of the distance between the two first lines and the width of the first line is recorded as p, p can also be understood as the period length of the marking sub-graphic 1201, and the period length of the second line in the marking sub-graphic 1201 is recorded as q. The alignment offset Δx and the key dimension exposed on the test piece and the focal length have approximately the same variation relationship. The relationship between the alignment offset Δx and the focal length and the structural dimension parameters p and q of the second graphic 12 can be given by formulas (1) to (4).

[0060] Δx=x-x0=a0+a1Δf+a2(Δf) 2 +R f (1)

[0061]

[0062] Where Δf is the difference between the theoretical value and the actual value of the focal length.w Meet L w1 ≤L w ≤L w2 When , it is considered that the image clarity within the corresponding focal length range meets the design requirements, and the corresponding alignment offset satisfies Δx1≤a0+a1Δf+a2(Δf) 2 ≤Δx2, optionally, L w1 Take the value as 0.9CD, and set L w2 The value is 1.1CD, where CD is the theoretical critical dimension exposed on the test piece. w The values ​​are L w1 and L w2 When , the corresponding Δx1 and Δx2 and formulas (1) to (4) are used to calculate the focus depth corresponding to the pattern through the first mark pattern 121. Similarly, the above method can also be used to calculate the focus depth corresponding to the pattern through the second mark pattern 122.

[0063] Finally, step S4 is executed to perform a second type of measurement on the test piece to obtain the focus depth of the first pattern 11 on the test piece.

[0064] In an optional embodiment, the first pattern 11 is an isolated pattern, and the scanning electron microscope is used to measure the test piece to perform the second type of measurement, thereby obtaining the focus depth of the first pattern 11 on the test piece.

[0065] In an optional embodiment, the mask pattern also includes a third pattern 13, and the first pattern 11 and the third pattern 13 are both isolated patterns. The scanning electron microscope is used to measure the test piece to perform the second type of measurement, thereby obtaining the focal depth of the first pattern 11 on the test piece.

[0066] As described above, the focus depth measurement method of this embodiment uses the second figure 12 as a measurement mark, uses an optical measurement system to measure the dense graphics on the surface of the test piece, and uses SEM to measure the adjacent isolated graphics, thereby achieving accurate measurement of the focus depth of the dense graphics and the focus depth of the isolated graphics in a very small measurement range, without the need to perform two separate measurements on the two graphics that are close to each other; and through optical measurement, non-destructive measurement of the dense graphics is achieved, without the need to subject the dense graphics to the bombardment of a high-energy electron beam at the exact center of the SEM, thereby reducing or avoiding the risk of distortion of the dense graphics, and when the dense graphics are subsequently sliced ​​for inspection, the contour structure and size of the dense graphics can be more accurately reflected.

[0067] The above embodiments are merely illustrative of the principles and effects of the present application and are not intended to limit the present application. Anyone familiar with the technology may modify, change or combine the above embodiments without violating the spirit and scope of the present application. Therefore, all equivalent modifications or changes made by a person of ordinary skill in the art without departing from the spirit and technical ideas disclosed in the present application shall still be covered by the claims of the present application.

Claims

1. A method for measuring focal depth, characterized in that: The following steps are involved: Providing a mask pattern and a test piece, wherein the mask pattern includes a plurality of first patterns and a plurality of second patterns; exposing and developing the test piece to transfer the mask pattern to the test piece; According to the second pattern, performing a first type of measurement on the device to be tested to obtain a focus depth of the second pattern on the device to be tested; Performing a second type of measurement on the test piece to obtain a focus depth of a first pattern on the test piece; Wherein, on the test piece, the distance between the first pattern and the adjacent second pattern is less than or equal to the first distance.

2. The method for measuring the depth of focus according to claim 1, characterized in that: The first distance is 3 μm to 10 μm.

3. The method for measuring focal depth according to claim 1, characterized in that: The mask pattern includes a plurality of first patterns. On the test piece, a distance between two adjacent first patterns is greater than a second distance.

4. The method for measuring the depth of focus according to claim 3, characterized in that: The second distance is 3 μm to 10 μm.

5. The method for measuring focus depth according to claim 1, characterized in that: The mask pattern also includes a plurality of third patterns and a plurality of fourth patterns. On the test piece, the distance between the first pattern and an adjacent third pattern, the distance between two adjacent third patterns, and the distance between the third pattern and an adjacent fourth pattern are all greater than the second distance.

6. The method for measuring the depth of focus according to claim 5, characterized in that: The second pattern and the fourth pattern are both dense patterns. According to the second pattern, an optical measurement system is used to perform optical measurement on the device to be tested to obtain the focus depths of the second pattern and the fourth pattern on the device to be tested.

7. The method for measuring focal depth according to claim 5, characterized in that: The first pattern and the third pattern are both isolated patterns. The device to be tested is measured using a scanning electron microscope to obtain the focus depths of the first pattern and the third pattern on the device to be tested.

8. The method for measuring focal depth according to claim 1, characterized in that: The second graphic includes a first marking graphic, and the first marking graphic includes a plurality of first lines and a plurality of second lines; The first marking pattern has a first direction and a second direction that are perpendicular to each other, and the first lines and the second lines both extend along the first direction and are arranged at intervals along the second direction.

9. The method for measuring the depth of focus according to claim 8, characterized in that: The first marking pattern includes two first lines and a plurality of second lines, the plurality of second lines are evenly spaced between the two first lines, and the width of the first line is greater than the width of the second line.

10. The method for measuring focal depth according to claim 8, characterized in that: The second graphic further includes a second marking graphic, and the second marking graphic is rotationally symmetric to the first marking graphic.

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