A method of measuring depth of focus

Abstract

The application belongs to the technical field of semiconductors and provides a focus depth measurement method, including the following steps: providing a mask pattern and a test piece, the mask pattern including a plurality of first patterns and second patterns, the distance between the first pattern and the adjacent second pattern being less than or equal to a first distance; transferring the mask pattern to the test piece by exposing and developing the test piece; performing a first type of measurement on the test piece according to the second pattern to obtain the focus depth of the second pattern on the test piece; performing a second type of measurement on the test piece to obtain the focus depth of the first pattern on the test piece; the focus depth of the dense pattern and the isolated pattern on the test piece is accurately measured in a very small measurement range at the same time, without the need to separately perform two measurements on the two relatively close patterns, and the risk of distortion of the dense pattern is reduced or avoided, and the profile structure and size of the dense pattern can be more accurately reflected when the dense pattern is subsequently checked by slicing.

Description

Technical Field

[0001] This application relates to the field of semiconductor technology, and in particular to a method for measuring focusing depth. Background Technology

[0002] Photolithography is one of the most important manufacturing processes in modern large-scale integrated circuit manufacturing. It transfers the design pattern of an integrated circuit from a photomask onto a silicon wafer using a photolithography machine. During chip manufacturing, to optimize exposure parameters and ensure the quality of the pattern on the wafer surface, depth-of-field measurement and inspection are required after exposure and development. Depth-of-field measurement involves various patterns, such as dense patterns and isolated patterns. After exposure and development, the patterns are measured using a scanning electron microscope (SEM) to obtain the critical dimension (CD) and depth of field of each pattern, thereby determining the overall depth of field of the pattern on the wafer.

[0003] When using SEM for depth measurement, SEM is destructive to photoresist. When two patterns are close together, measuring one pattern will inevitably cause the electron beam generated by the SEM to adversely affect the other pattern, potentially distorting its contour structure. Therefore, it is necessary to separate the two close patterns by a certain distance and measure them separately. Furthermore, after SEM measurement, slicing is required for further contour detection. Performing SEM again after slicing leads to even more severe distortion of parameters such as the pattern contour, thickness, and critical dimensions of the photoresist on the wafer surface.

[0004] In view of this, in order to solve the above problems, this application provides a focusing depth measurement method for realizing focusing 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 described above, the purpose of this application is to provide a focusing depth measurement method to solve the problems of image distortion that easily occurs during image focusing depth measurement and inspection in the prior art. This method can simultaneously determine the focusing depth of adjacent isolated images and dense images, and reduce or avoid image distortion during focusing depth measurement and inspection.

[0006] To achieve the above and other related objectives, this application provides a focusing depth measurement method, comprising the following steps:

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

[0008] The test piece is exposed and developed to transfer the mask pattern onto the test piece;

[0009] Based on the second pattern, a first type of measurement is performed on the test piece to obtain the focusing depth of the second pattern on the test piece;

[0010] A second type of measurement is performed on the test piece to obtain the focusing depth of the 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 3μm to 10μm.

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

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

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

[0016] Optionally, both the second pattern and the fourth pattern are dense patterns. Based on the second pattern, an optical measurement system is used to perform optical measurements on the test piece to obtain the focusing depth of the second and fourth patterns on the test piece.

[0017] Optionally, both the first and third patterns are isolated patterns. The test piece is measured using a scanning electron microscope to obtain the focusing depth of the first and third patterns on the test piece.

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

[0019] The first marker graphic has a first direction and a second direction that are perpendicular to each other. The first line and the second line both extend along the first direction and are spaced apart along the second direction.

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

[0021] Optionally, the second graphic further includes a second marker graphic, which is rotationally symmetrical to the first marker graphic.

[0022] As described above, the focusing depth measurement method provided in this application has at least the following beneficial effects:

[0023] The focusing depth measurement method of this application uses a second pattern as a measurement marker. An optical measurement system is used to measure the second pattern on the surface of the test piece to obtain the focusing depth of the second pattern. Meanwhile, an SEM is used to measure the adjacent first pattern to obtain the focusing depth of the first pattern. This method enables simultaneous and accurate measurement of the focusing depth of dense patterns and isolated patterns within a very small measurement range, without the need to perform two separate measurements on the two relatively close patterns. Furthermore, through optical measurement, non-destructive measurement of dense patterns is achieved, eliminating the need for the dense pattern to be bombarded by a high-energy electron beam at the center of the SEM. This reduces or avoids the risk of distortion of the dense pattern. When performing subsequent slicing inspection of the dense pattern, the method can more accurately reflect the contour structure and size of the dense pattern. Attached Figure Description

[0024] To more clearly illustrate the technical solutions of the embodiments of this application, the accompanying drawings used in the embodiments will be briefly introduced below. It should be understood that the following drawings only show some embodiments of this application and should not be regarded as a limitation of the scope. For those skilled in the art, other related drawings can be obtained based on these drawings without creative effort.

[0025] Figure 1 The diagram shown is a flowchart illustrating the focusing depth measurement method provided in an embodiment of this application.

[0026] Figure 2 The diagram shows a structural schematic of the first and second graphics provided in an optional embodiment of this application.

[0027] Figures 3 to 5 The diagram shows structural schematics of the third and fourth graphics provided in optional embodiments of this application.

[0028] Illustration of reference numerals in the attached diagram:

[0029] 11. First figure; 12. Second figure; 121. First marker figure; 122. Second marker figure; 1201. Marker sub-figure; 13. Third figure; 14. Fourth figure. Detailed Implementation

[0030] To make the technical objectives, technical solutions, and technical effects of this application clearer, the technical solutions in this application will be clearly and completely described below in conjunction with embodiments. Obviously, the described embodiments are only some embodiments of this application, and not all embodiments. The components of the embodiments of this application described and shown in the accompanying drawings can generally be arranged and designed in various different configurations.

[0031] Therefore, the following detailed description of embodiments of this application is not intended to limit the scope of the claimed application, but merely to illustrate selected embodiments of the application. All other embodiments obtained by those skilled in the art based on the embodiments of this application without inventive effort are within the scope of protection of this application. Furthermore, the terms "first" and "second" are used for descriptive purposes only and should not be construed as indicating or implying relative importance.

[0032] In the description of this application, it should be noted that the terms "one embodiment," "some embodiments," "illustrative embodiment," "example," "specific example," or "some examples," etc., refer to specific features, structures, materials, or characteristics described in connection with an implementation or example, which are included in at least one implementation or example of this application. In this specification, the illustrative expressions of the above terms do not necessarily refer to the same implementation or example. Furthermore, the specific features, structures, materials, or characteristics described may be combined in any suitable manner in one or more implementations or examples.

[0033] In existing technologies, due to the complexity and diversity of mask patterns, there are often isolated and dense patterns that are relatively close together. After exposure and development, the distance between some dense patterns and isolated patterns on the wafer surface becomes even closer. When measuring the depth of focus of the pattern on the wafer surface, optical measurement cannot effectively measure the depth of focus. Currently, scanning electron microscopy (SEM) is used to measure the depth of focus. When measuring dense or isolated patterns, the high electron beam energy during SEM measurement can easily have an adverse effect on dense patterns that are close together, causing distortion during depth of focus measurement and inspection. Furthermore, if slicing is required to further inspect the pattern outline after exposure and development on the wafer surface, SEM inspection will be performed again after slicing, leading to even more severe distortion of the pattern.

[0034] Based on the above-mentioned problems in the prior art, this embodiment provides a focusing depth measurement method for measuring the focusing depth of an exposed pattern on a test piece, thereby reducing or avoiding the risk of distortion of the pattern on the surface of the test piece during focusing depth measurement. Optionally, the test piece can be, for example, a wafer or other suitable component, and the exposed pattern is formed by exposing and developing a mask pattern on the wafer.

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

[0036] Step S1: Provide 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: Expose and develop the test piece to transfer the mask pattern to the test piece;

[0038] Step S3: Based on the second pattern 12, perform a first type of measurement on the test piece to obtain the focusing depth of the second pattern 12 on the test piece;

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

[0040] The focusing 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 order does not strictly represent the process order of the focusing depth measurement method protected by this application, and those skilled in the art can make changes according to the actual processing steps.

[0041] First, step S1 is performed, providing a mask pattern and a test piece; wherein, the mask pattern includes several 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 are spaced apart from each other and the first patterns 11 and the second patterns 12 are spaced apart from each other.

[0043] In an optional embodiment, refer to Figures 3 to 5The mask pattern also includes a plurality of third patterns 13 and fourth patterns 14. Optionally, for example, the mask pattern includes multiple third patterns 13 and multiple fourth patterns 14, and the multiple 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, and the second pattern 12 and the fourth pattern 14 are, for example, dense patterns, with adjacent isolated patterns and adjacent isolated patterns and dense patterns spaced apart.

[0044] In this context, the first graphic 11 and the second graphic 12 can be understood as isolated and densely packed graphics that are relatively close to each other. The dense graphic / second graphic 12 can be used as a measurement marker to facilitate subsequent measurement of the image focus depth. Specifically, the dense graphic is, for example, the main graphic in the mask pattern, and the first graphic 11 is, for example, an auxiliary graphic or other suitable graphics. The third graphic 13 and the fourth graphic 14 can be understood as isolated and densely packed graphics that are relatively far from adjacent graphics, and will not adversely affect adjacent graphics when measuring the image focus depth. Furthermore, other types of isolated or dense graphics can also be set in the mask pattern, such as isolated and densely packed graphics that are relatively close to each other, and these dense graphics cannot be used as measurement markers.

[0045] In this embodiment, refer to Figure 2 The second graphic 12 includes a first marker graphic 121, which includes a plurality of first lines and a plurality of second lines; the mask graphic has a vertical direction and a horizontal direction, and the first lines and the second lines both extend along the vertical direction and are arranged at intervals along the horizontal 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 specifically includes the following steps: coating a photoresist onto the test piece so that the photoresist covers the surface of the test piece; exposing the test piece after coating with photoresist using a mask pattern; developing the exposed photoresist using a developer; and removing the residual developer from the photoresist after the development process to obtain a test piece with an exposure pattern.

[0048] In an optional embodiment, on the test piece, the distance between adjacent first patterns 11 and second patterns 12 is less than or equal to a first distance. Optionally, the first distance is 3μm to 10μm, and for example, it can be 3μm, 5μm, 7μm, 10μm, or other suitable values. Preferably, the first distance is 3μm. Since the first patterns 11 and second patterns 12 are relatively close, the focusing depth measurement method of this embodiment can simultaneously measure the focusing depth of the first patterns 11 and second patterns 12, reducing or avoiding the risk of distortion in the shape and size of the patterns during the measurement process, and improving the accuracy of focusing depth measurement of the exposed patterns on the test piece.

[0049] In an optional embodiment, the mask pattern includes multiple first patterns 11, which may have the same shape and size or may not have different shapes and sizes. The mask pattern may also include multiple second patterns 12, which may have the same shape and size or may have different shapes and sizes. After the mask pattern is transferred to the test piece, the distance between two adjacent first patterns 11 on the test piece is greater than a second distance. Optionally, the second distance is 3μm to 10μm, and the second distance may be 3μm, 5μm, 7μm, 10μm or other suitable values. Preferably, the second distance may be 3μm. By controlling the interval between two adjacent first patterns 11 on the test piece to be larger, it can be ensured that when the focus depth measurement is performed on the pattern on the surface of the test piece, only one first pattern 11 is contained in a window. This avoids adverse effects on adjacent first patterns 11 during focus depth measurement, preventing distortion of some first patterns 11 and improving the accuracy of focus depth measurement.

[0050] In an optional embodiment, the mask pattern further includes several third patterns 13 and fourth patterns 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 can be isolated patterns, and the second pattern 12 and the fourth pattern 14 can be dense patterns. By controlling the distance 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, adverse effects on adjacent patterns are avoided when performing depth-of-focus measurements, thereby improving the accuracy of depth-of-focus measurements and reducing or avoiding the risk of pattern distortion.

[0051] Reference Figure 2The second graphic 12 includes a first marking graphic 121, which 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 that are perpendicular to each other. The first lines and the second lines extend along the first direction and are spaced apart 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 spaced apart along the second direction, and the first lines and the second lines are also spaced apart.

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

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

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

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

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

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

[0058] In an optional embodiment, before performing step S3, the following step may be included: identifying the second pattern 12 from the pattern on the surface of the test piece for performing a first type of measurement. The second pattern 12 can be obtained based on the design structure of the mask pattern, or it can be obtained from the pattern on the surface of the test piece using an optical measurement system, or other suitable methods can be used to identify the second pattern 12 from the pattern on the surface of the test piece, so as to facilitate subsequent first type of measurement of the test piece.

[0059] In an optional embodiment, refer to Figure 2 The second pattern 12 includes a first marker pattern 121 and a second marker pattern 122. The first marker pattern 121 is rotated 90° symmetrically to the second marker pattern. The first marker pattern 121 includes at least one marker sub-pattern 1201 and a first line located on one side of the marker sub-pattern 1201. A plurality of second lines in the marker sub-pattern 1201 are arranged periodically. The number of second lines in the marker sub-pattern 1201 is denoted as n, and the critical dimension actually exposed on the test piece is denoted as L. w The coordinates of the actual alignment position of the second pattern 12 are marked as (x, y), the theoretical imaging position is marked as (x0, y0), the sum of the distance between the two first lines and the width of the first lines is marked as p, and p can also be understood as the period length of the marker sub-pattern 1201. The period length of the second line in the marker sub-pattern 1201 is marked as q. The alignment offset Δx and the key dimension exposed on the test piece have approximately the same change relationship with the focal length. The relationship between the alignment offset Δx and the focal length, as well as the structural dimension parameters p and q of the second pattern 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 and actual focal length. When Lw Satisfy L w1 ≤L w ≤L w2 At that time, it is assumed that the image sharpness 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 can be w1 The value is 0.9CD, and L is... w2 The value is 1.1CD, where CD is the theoretical critical dimension exposed on the test piece. When L w The values ​​are respectively L w1 and L w2 At that time, using the corresponding Δx1 and Δx2 and formulas (1) to (4), the focus depth corresponding to the first marked graphic 121 can be calculated. Similarly, the focus depth corresponding to the second marked graphic 122 can also be calculated using the above method.

[0063] Finally, step S4 is performed to conduct 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. A scanning electron microscope is used to measure the test piece to perform a second type of measurement, thereby obtaining the focusing depth of the first pattern 11 on the test piece.

[0065] In an optional embodiment, the mask pattern further includes a third pattern 13. Both the first pattern 11 and the third pattern 13 are isolated patterns. The test piece is measured using a scanning electron microscope to perform a second type of measurement, thereby obtaining the focusing depth of the first pattern 11 on the test piece.

[0066] As described above, the focusing depth measurement method of this embodiment uses the second pattern 12 as a measurement mark, uses an optical measurement system to measure the dense pattern on the surface of the test piece, and uses SEM to measure the adjacent isolated pattern. This achieves simultaneous and accurate measurement of the focusing depth of the dense pattern and the focusing depth of the isolated pattern within a very small measurement range, without having to perform two separate measurements on the two closely spaced patterns. Furthermore, through optical measurement, non-destructive measurement of the dense pattern is achieved, without having the dense pattern bombarded by a high-energy electron beam at the center of the SEM, reducing or avoiding the risk of distortion of the dense pattern. When the dense pattern is subsequently sliced ​​for inspection, the contour structure and size of the dense pattern can be more accurately reflected.

[0067] The above embodiments are merely illustrative of the principles and effects of this application and are not intended to limit this application. Any person skilled in the art can modify, alter, or combine the above embodiments without departing from the spirit and scope of this application. Therefore, all equivalent modifications or alterations made by those skilled in the art without departing from the spirit and technical concept disclosed in this application should still be covered by the claims of this application.

Claims

1. A method for measuring focusing depth, characterized in that, Includes the following steps: A mask pattern and a test piece are provided, wherein the mask pattern includes a plurality of first patterns and a plurality of second patterns; The test piece is exposed and developed to transfer the mask pattern onto the test piece; Based on the second pattern, a first type of measurement is performed on the test piece to obtain the focusing depth of the second pattern on the test piece; A second type of measurement is performed on the test piece to obtain the focusing depth of the 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 a first distance, the first distance being 3μm~10μm; The first type of measurement is to perform optical measurement on the test piece using an optical measurement system, and the second type of measurement is to measure the test piece using a scanning electron microscope; The mask pattern includes multiple first patterns, and the distance between two adjacent first patterns on the test piece is greater than a second distance, which is 3μm~10μm.

2. The focusing depth measurement method according to claim 1, characterized in that, The mask pattern also includes several third patterns and several fourth patterns. On the test piece, the distance between the first pattern and the adjacent third pattern, the distance between two adjacent third patterns, and the distance between the third pattern and the adjacent fourth pattern are all greater than the second distance.

3. The focusing depth measurement method according to claim 2, characterized in that, Both the second and fourth patterns are dense patterns. Based on the second pattern, an optical measurement system is used to perform optical measurements on the test piece to obtain the focusing depth of the second and fourth patterns on the test piece.

4. The focusing depth measurement method according to claim 2, characterized in that, Both the first and third patterns are isolated patterns. The test piece is measured using a scanning electron microscope to obtain the focusing depth of the first and third patterns on the test piece.

5. The focusing depth measurement method according to claim 1, characterized in that, The second graphic includes a first marker graphic, which includes a plurality of first lines and a plurality of second lines; The first marker graphic has a first direction and a second direction that are perpendicular to each other. The first line and the second line both extend along the first direction and are spaced apart along the second direction.

6. The focusing depth measurement method according to claim 5, characterized in that, The first marker graphic includes two first lines and several second lines, the several second lines being evenly spaced between the two first lines, and the width of the first lines being greater than the width of the second lines.

7. The focusing depth measurement method according to claim 5, characterized in that, The second graphic also includes a second marker graphic, which is rotationally symmetrical to the first marker graphic.

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