Exposure focal length determination method
By using the tested wafer into a sample pattern array in the projection optical carvings, screening and analyzing the key size of the sample pattern, the problem of the existing technology mid -distance monitoring requires cyclical shutdown. Monitoring protects the continuous production status of the production line.
Patent Information
- Application Number
- CN202411490325.2
- Authority / Receiving Office
- CN · China
- Patent Type
- Applications(China)
- Current Assignee / Owner
- Filing Date
- 2024-10-24
- Publication Date
- 2025-01-24
AI Technical Summary
When monitoring the focal length of a projection lithography machine, the prior art requires periodic shutdown and startup, resulting in the continuous production status of the production line being destroyed and capacity loss.
By forming a sample pattern array on the test wafer, multiple target sample patterns are screened out, their key dimensions are obtained, the sample focal length is determined, and the exposure focal length of the exposure process is determined based on multiple sample focal lengths to achieve focal length monitoring.
This method allows to regularly test wafers into normal production during the normal operation of the projection optical carvings, realize the monitoring of the exposure focal length, avoid periodic shutdown and startup, protect the continuous production status of the production line, and avoid production capacity loss.
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Figure CN119356037A_ABST
Abstract
Description
Technical Field
[0001] The present invention relates to the technical field of chip manufacturing, and in particular to a method for determining an exposure focal length. Background Art
[0002] As a key equipment in integrated circuit manufacturing, the focal length of the projection lithography machine directly affects the quality and accuracy of the lithography pattern. Therefore, the focal length of the projection lithography machine is monitored.
[0003] The prior art often uses a direct measurement method to monitor the focal length of a projection lithography machine. This method requires the projection lithography machine to be shut down, which can easily cause the projection lithography machine and the machine states of the upstream and downstream production lines to fluctuate. However, focal length monitoring needs to be carried out continuously according to a set cycle. Periodic shutdown and startup will disrupt the continuous production state of the production line, resulting in a loss of production capacity. Summary of the invention
[0004] In view of the above problems, the present application is proposed to provide a method for determining exposure focus that overcomes the above problems or at least partially solves the above problems.
[0005] In a first aspect, a method for determining an exposure focal length is provided, comprising: selecting a plurality of target sample patterns from a sample pattern array on a test wafer, wherein the sample pattern array is obtained by exposing the test wafer using a test mask template using an exposure process;
[0006] Acquire a critical dimension of each target sample pattern among a plurality of target sample patterns, and determine a sample focal length corresponding to each target sample pattern based on the critical dimension of each target sample pattern;
[0007] The exposure focal length of the exposure process is determined according to the sample focal lengths corresponding to the plurality of target sample patterns.
[0008] Optionally, determining a sample focal length corresponding to each target sample pattern based on a critical size of each target sample pattern includes:
[0009] For each target sample pattern among the multiple target sample patterns, the sample focal length corresponding to the target sample pattern is determined according to the following formula:
[0010]
[0011] Among them, F real is the sample focal length corresponding to the target sample pattern, k is the preset correction coefficient, L CD is the expected value of the critical dimension, L is the critical dimension of the target sample pattern, and F design is the expected value of the exposure focal length.
[0012] Optionally, determining the exposure focal length of the exposure process according to the sample focal lengths corresponding to the plurality of target sample patterns includes:
[0013] The exposure focal length of the exposure process is determined according to an average value of the sample focal lengths corresponding to the plurality of target sample patterns.
[0014] Optionally, in the sample pattern array on the test wafer, a plurality of target sample patterns are screened out, including:
[0015] Determining a sampling area on a test wafer;
[0016] A plurality of sample patterns located on a preset sampling path in the sampling area are taken as a plurality of target sample patterns, wherein the preset sampling path crosses the sampling area along N preset directions, where N is a positive integer.
[0017] Optionally, the sampling path includes a first subpath and a second subpath, the first subpath crosses the sampling area along a first preset direction, the second subpath crosses the sampling area along a second preset direction, and the first preset direction and the second preset direction are different.
[0018] Optionally, the sampling area is a circular area, a square area or a ring area.
[0019] Optionally, each target sample pattern includes at least one group of unit patterns; obtaining a critical dimension of each target sample pattern in the plurality of target sample patterns includes:
[0020] For each target sample pattern in the plurality of target sample patterns, a target unit pattern is determined from at least one group of unit patterns in the target sample pattern, and a critical dimension corresponding to the target unit pattern is determined based on a center position of the target unit pattern as the critical dimension of the sample pattern.
[0021] Optionally, the mask pattern of the test mask includes at least one group of marking patterns, the marking pattern includes a plurality of bright field patterns, and the plurality of bright field patterns are periodically arranged along a preset direction.
[0022] Optionally, the multiple bright field patterns are the same, and along a preset direction, the intervals between every two adjacent bright field patterns are equal.
[0023] Optionally, the shape of the bright field pattern includes circle, square, horizontal long strip, and vertical long strip.
[0024] The technical solution provided by this application has at least the following technical effects or advantages:
[0025] The exposure focal length determination method provided by the present application, in the exposure process, uses a test mask template to expose a test wafer to form a sample pattern array on the test wafer, determines the sample focal length corresponding to each target sample pattern by the key dimensions of multiple target sample patterns screened from the sample pattern array, and finally determines the exposure focal length of the exposure process according to the sample focal lengths corresponding to the multiple target sample patterns, so as to realize the focal length monitoring of the exposure process. The exposure focal length determination method provided by the present application can be used in the normal operation of a projection lithography machine, by regularly mixing test wafers into wafers in normal production, and in the exposure process, using a test mask template to expose the test wafer, so as to realize the monitoring of the exposure focal length, without the need for periodic shutdown and startup, so as to avoid the continuous production state of the production line being destroyed and the loss of production capacity.
[0026] The above description is only an overview of the technical solution of the present application. In order to more clearly understand the technical means of the present application, it can be implemented in accordance with the contents of the specification. In order to make the above and other purposes, features and advantages of the present application more obvious and easy to understand, the specific implementation methods of the present application are listed below. BRIEF DESCRIPTION OF THE DRAWINGS
[0027] Various other advantages and benefits will become apparent to those of ordinary skill in the art by reading the detailed description of the preferred embodiments below. The accompanying drawings are only for the purpose of illustrating the preferred embodiments and are not to be considered as limiting the present application. Also, the same reference symbols are used throughout the accompanying drawings to represent the same components. In the accompanying drawings:
[0028] Figure 1 This is a flow chart of a method for determining exposure focal length in an embodiment of the present application;
[0029] Figure 2 This is a schematic diagram of the exposure process in the embodiment of the present application;
[0030] Figure 3 This is a schematic diagram of a horizontally long strip bright field pattern in an embodiment of the present application;
[0031] Figure 4 This is a schematic diagram of a square bright field pattern in an embodiment of the present application;
[0032] Figure 5 This is a schematic diagram of a circular bright field pattern in an embodiment of the present application;
[0033] Figure 6 This is a schematic diagram of a vertically long strip bright field pattern in an embodiment of the present application;
[0034] Figure 7 This is a schematic diagram of a mask pattern in an embodiment of the present application;
[0035] Figure 8A schematic diagram of a sample pattern array on a test wafer in an embodiment of the present application;
[0036] Fig. 9 This is a schematic diagram of the circular sampling area in the embodiment of the present application;
[0037] Fig.10 This is a schematic diagram of the measurement position in the embodiment of the present application;
[0038] Fig.11 This is an example of a statistical process control chart of the focal length of a projection lithography machine in an embodiment of the present application. DETAILED DESCRIPTION
[0039] Exemplary embodiments of the present disclosure will be described in more detail below with reference to the accompanying drawings.
[0040] Various structural schematic diagrams according to embodiments of the present application are shown in the accompanying drawings. These figures are not drawn to scale, and some details are magnified and some details may be omitted for the purpose of clear expression. The shapes of various regions and layers shown in the figures and the relative sizes and positional relationships therebetween are only exemplary, and may deviate in practice due to manufacturing tolerances or technical limitations, and those skilled in the art may further design regions / layers with different shapes, sizes, and relative positions according to actual needs.
[0041] In order to better understand the above-mentioned technical scheme, the above-mentioned technical scheme will be described in detail below in combination with specific implementation methods. It should be understood that the embodiments of the present disclosure and the specific features in the embodiments are detailed descriptions of the technical scheme of the present application, rather than limitations on the technical scheme of the present application. In the absence of conflict, the embodiments of the present application and the technical features in the embodiments can be combined with each other.
[0042] As a key equipment in integrated circuit manufacturing, the focal length of the projection lithography machine directly affects the quality and accuracy of the lithography pattern. Therefore, monitoring the focal length of the projection lithography machine is an important step to ensure the stability and reliability of the lithography process.
[0043] Focal length refers to the distance between the projection lens and the silicon wafer, which determines the size and clarity of the photolithography pattern projected on the silicon wafer. If the focal length is inaccurate or changes, the photolithography pattern will be distorted, seriously affecting the chip performance and reliability.
[0044] The focal length monitoring of projection lithography machines is an indispensable monitoring step to ensure process stability. Commonly used methods (focal length monitoring) include direct measurement, autofocus, image processing, etc. Taking direct measurement as an example, direct measurement is generally completed through the machine. For example, in the ASML machine, direct measurement is achieved through a function called Focal level. Other methods such as autofocus and image processing will not be described in detail.
[0045] However, in actual production, due to production capacity issues, when the machine is shut down to test the focal level, a large amount of production capacity will be wasted. Since the continuous state of the machine is destroyed, the machine state may shift, resulting in machine loss and production capacity loss.
[0046] In view of this, the present application provides a method for determining exposure focal length, which can effectively monitor the focal length of the machine, maintain the stability of the machine state, and thus improve the product yield. The method is feasible for monitoring the focal length of a projection lithography machine and can well maintain the focal length of the projection lithography machine at an appropriate depth of field.
[0047] Please refer to Figure 1 , Figure 1 This is a flow chart of the exposure focal length determination method in an embodiment of the present application. The exposure focal length determination method provided in an embodiment of the present application includes the following operations S101 to S103.
[0048] S101. Screening out a plurality of target sample patterns from a sample pattern array on a test wafer, wherein the sample pattern array is obtained by exposing the test wafer using a test mask through an exposure process.
[0049] When the focus of the exposure equipment needs to be monitored, the test wafer is inserted into the wafer in the normal production process, and in the exposure process, the test wafer is exposed using a test mask having a specific mask pattern to form a sample pattern array on the test wafer. It can be understood that the sample pattern has a corresponding relationship with the mask pattern.
[0050] The mask pattern of the test mask includes at least one group of marking patterns, and the marking pattern includes a plurality of bright field patterns, and the plurality of bright field patterns are periodically arranged along a preset direction. It can be understood that the bright field pattern is obtained by etching on the mask, and the area where the bright field pattern is not formed can be understood as a dark field pattern.
[0051] Before the exposure process, the test wafer has been coated with photoresist. During the exposure process, Figure 2 As shown, the light emitted by the illumination light source 201 is irradiated on the test mask plate 203 through the convergent lens 202, and diffracted light beams are generated through the test mask plate 203. These diffracted light beams carry the graphic information of the mask pattern on the test mask plate 203. The light beams are focused onto the surface of the test wafer 205 through the projection lens 204, and the image of the mask pattern is formed on the surface of the test wafer 205. The surface of the test wafer 205 is coated with photoresist. After the mask pattern on the test mask plate 203 is projected onto the photoresist, a chemical reaction is stimulated, thereby fixing and preserving the mask pattern. After baking and developing, a photoresist pattern, i.e., a marking pattern, is formed.
[0052] S102 , obtaining a critical size of each target sample pattern among a plurality of target sample patterns, and determining a sample focal length corresponding to each target sample pattern based on the critical size of each target sample pattern.
[0053] It is understood that the critical dimension (CD) refers to a special line graphic dimension that reflects the width of the characteristic lines of the integrated circuit, which is designed to evaluate and control the graphic processing accuracy of the process in the integrated circuit photomask manufacturing and photolithography process.
[0054] For example, CD-SEM is used to measure the critical dimensions of each target sample pattern. CD-SEM is an advanced fully automatic wafer online measurement equipment, which uses electron beam scanning imaging technology to mainly monitor key process parameters during the wafer manufacturing process. It is used for critical dimension measurement of photoresist after development and contact hole diameter / via diameter and gate line width after etching. It is a key equipment for improving chip manufacturing yield and maintaining product quality consistency.
[0055] Exemplarily, for each target sample pattern among the multiple target sample patterns, the sample focal length corresponding to the target sample pattern is determined according to the following formula:
[0056]
[0057] Among them, F real is the sample focal length corresponding to the target sample pattern, k is the preset correction coefficient, which is related to the process and optical correction and can be understood as a constant, L CD is the expected value of the critical dimension, which is the ideal value of the critical dimension of the pattern that the exposure process wants to process on the wafer. L is the critical dimension of the target sample pattern, which can be the actual value of the critical dimension of the sample pattern collected by CD-SEM on the test wafer. design It is the expected value of the exposure focal length, that is, the exposure focal length required for the exposure process to produce a pattern with a desired critical dimension.
[0058] S103 , determining an exposure focal length of an exposure process according to sample focal lengths corresponding to a plurality of target sample patterns.
[0059] Exemplarily, the exposure focal length of the exposure process is determined according to an average value of the sample focal lengths corresponding to a plurality of target sample patterns.
[0060] The exposure focal length determination method provided in the embodiment of the present application can be used in the normal operation of a projection lithography machine. By periodically mixing test wafers into wafers in normal production, the test wafers are exposed using a test mask during the exposure process, thereby monitoring the exposure focal length. There is no need for periodic shutdown and startup, thus avoiding disruption of the continuous production state of the production line and loss of production capacity.
[0061] In some optional embodiments, the plurality of bright field patterns are the same, and along a preset direction, the spacing between each two adjacent bright field patterns is equal. The shapes of the bright field patterns include circular, square, horizontal long strip, and vertical long strip.
[0062] Figure 3 Schematic diagram of a horizontally long strip bright field pattern in an embodiment of the present application, a plurality of horizontally long strip bright field patterns 301 are arranged in sequence at fixed intervals to form a marking pattern, the bright field pattern can be processed on a test mask by an etching process, the area between the horizontally long strip bright field patterns 301 is a dark field pattern, and the width d1 of the bright field pattern is the same as the width d2 of the dark field pattern. It can be understood that the marking pattern composed of the horizontally long strip bright field patterns 301 is transferred to the test wafer by an exposure process to form a sample pattern.
[0063] Figure 4 Schematic diagram of a square bright field pattern in an embodiment of the present application, a plurality of square bright field patterns 401 are arranged in sequence at fixed intervals to form a marking pattern, the square bright field pattern 401 can be processed on a test mask by an etching process, the area between the square bright field patterns 401 is a dark field pattern, and the width d1 of the bright field pattern is the same as the width d2 of the dark field pattern. It can be understood that the marking pattern composed of the square bright field patterns 401 is transferred to the test wafer by an exposure process to form a sample pattern.
[0064] Figure 5 Schematic diagram of circular bright field pattern in the embodiment of the present application, multiple circular bright field patterns 501 are arranged in sequence at fixed intervals to form a marking pattern, the circular bright field pattern 501 can be processed on the test mask by etching process, and the area between the circular bright field patterns 501 is the dark field pattern. It can be understood that the marking pattern composed of square bright field patterns 401 is transferred to the test wafer by exposure process to form a sample pattern.
[0065] Figure 6Schematic diagram of a vertical long strip bright field pattern in an embodiment of the present application, a plurality of vertical long strip bright field patterns 601 are arranged in sequence at fixed intervals to form a marking pattern, the vertical long strip bright field pattern 601 can be processed on a test mask by an etching process, the area between the vertical long strip bright field patterns 601 is a dark field pattern, and the width d1 of the bright field pattern is the same as the width d2 of the dark field pattern. It can be understood that the marking pattern composed of the vertical long strip bright field patterns 601 is transferred to the test wafer by an exposure process to form a sample pattern.
[0066] The above four marking patterns with different bright field pattern shapes can be combined according to needs to form a mask pattern of a test mask. For example, Figure 7 As shown, the mask pattern 701 is composed of a 2×2 array of four marking patterns, and the bright field patterns of the four marking patterns are respectively in the shape of a horizontal long strip, a square, a circle, and a vertical long strip.
[0067] In adopting Figure 7 After the test mask shown in the figure is used to expose the test wafer, the Figure 8 The test wafer 801 shown in FIG. 8 is partially enlarged to show that each sample pattern in the sample pattern array is consistent with Figure 7 The mask pattern 701 shown in FIG.
[0068] It can be understood that when it is necessary to monitor the exposure focal length of the exposure process when processing a horizontally long strip structure, the actual focal length of the horizontally long strip pattern processed in the exposure process can be determined by collecting the key dimensions of the horizontally long strip pattern area in each sample pattern and then calculating.
[0069] The above embodiment only gives an example of a marking pattern, which almost covers the measurement requirements of the shapes of most patterns in wafer processing, has high data reliability, and reduces the signal-to-noise ratio while improving the reliability of the data.
[0070] In some optional embodiments, a plurality of target sample patterns are screened out from the sample pattern array on the test wafer, including:
[0071] In the first step, the sampling area is determined on the test wafer.
[0072] In the second step, a plurality of sample patterns located on a preset sampling path in the sampling area are used as a plurality of target sample patterns, wherein the preset sampling path crosses the sampling area along N preset directions, where N is a positive integer.
[0073] In some optional embodiments, the sampling path includes a first subpath and a second subpath, the first subpath crosses the sampling area along a first preset direction, and the second subpath crosses the sampling area along a second preset direction, and the first preset direction and the second preset direction are different.
[0074] In some optional embodiments, the sampling area is a circular area, a square area or a ring area.
[0075] Still Figure 8 As shown, the sampling area is circular, and the first subpath 801 (the path where the horizontally arranged five-pointed stars are located) and the second subpath 802 (the path where the vertically arranged five-pointed stars are located) vertically intersect at the circular sampling area 803.
[0076] like Fig. 9 As shown, the sampling area is in the shape of a ring, and the first subpath 901 (the path where the horizontally arranged five-pointed stars are located) and the second subpath 902 (the path where the vertically arranged five-pointed stars are located) intersect vertically at the ring-shaped sampling area 903.
[0077] In some optional embodiments, each target sample pattern includes at least one group of unit patterns; obtaining a critical dimension of each target sample pattern in the plurality of target sample patterns comprises:
[0078] For each target sample pattern in the plurality of target sample patterns, a target unit pattern is determined from at least one group of unit patterns in the target sample pattern, and a critical dimension corresponding to the target unit pattern is determined based on a center position of the target unit pattern as the critical dimension of the sample pattern.
[0079] It is understandable that the specific shape of the unit pattern is affected by the shape of the bright field pattern of the mark pattern of the mask pattern. Figure 7 As shown, the mask pattern 701 is composed of four marking patterns arranged in a 2×2 manner, and the bright field patterns of the four marking patterns are respectively in the shape of a horizontal long strip, a square, a circle, and a vertical long strip. Figure 8 The sample pattern 804 shown is composed of four unit patterns arranged in a 2×2 manner, and the four unit patterns are respectively composed of horizontal long strips, squares, circles, and vertical long strips.
[0080] The focal length determination method provided in the above embodiment can be applied to the focal length monitoring of a projection lithography machine, maintain the stability of the machine state, and thus improve the product yield. The method is feasible for monitoring the focal length of a projection lithography machine, and can well maintain the focal length of the projection lithography machine at an appropriate depth of field. The specific operation is as follows:
[0081] The first step is to design several photolithography patterns. Figures 3 to 6The shape of the marking pattern shown.
[0082] The arrangement of each lithography pattern is taken as a Pattern, and the pitch (the distance between the center lines of two identical patterns) in each Pattern is a specific line width. The graphics designed by the four Patterns can cover the focus monitoring of different line width layers under the same process, and the line width depends on the process capability.
[0083] by Figure 3 Taking the pattern of the horizontal long strip holes shown as an example, the distance between the lateral center lines of two adjacent horizontal long strip holes is a full pitch. If a 0.18um process is used, the pitch is defined as 180nm, and the pitch of a 90nm process is defined as 90nm.
[0084] For another example, Figure 5 The pattern of circular holes shown, the pitch is the distance between the centers of the two nearest circular holes. It is worth noting that the distance between the two closest circular tangents is also equal, and the distance is the diameter.
[0085] The side length of the square hole is equal to the distance between the two nearest square holes, and the side lengths are all the line width of 1 / 2Pitch design. The advantage of this design is that it ensures that the line width of the same measurement is 1 / 2Pitch line width. Secondly, it measures the diversity of graphics, ensures the reliability of the data, and improves the signal-to-noise ratio. In addition, it should be noted that Figures 3 to 6 The dark color represents the clear area, and the light color represents the dark area.
[0086] The second step is to design the individual patterns as follows: Figure 7 Arrange in the manner shown to form a DIE.
[0087] The third step is to arrange the DIE Patten designed above periodically on the mask.
[0088] The fourth step is to define the measurement position of the DIE graphics. The measurement position will affect the measurement results. The measurement position is defined as follows: The pattern composed of line and space of the horizontal long strip hole is recorded as the space monitoring pattern, and the third space is measured. The 4×4 circular hole pattern is recorded as the hole monitoring pattern, and the circular hole at the 3*3 position is measured. The 4×4 square hole pattern is recorded as the square hole monitoring pattern, and the square hole position at the 3*3 position is measured. The vertical pattern composed of line and space is recorded as the line monitoring pattern, and the third line is measured. Fig.10 As shown, the triangle arrow in each Patten indicates the measurement position.
[0089] The fifth step is to specify the wafer measurement position. The measurement position will affect the measurement results. The position of the grid represents the wafer shot array. Its die array is 1*1, so one shot contains one DIE. Figure 8 , 9 The measurement position is specified below, such as the DIE where the pentagon icon is located, which is the DIE to be measured.
[0090] In the sixth step, the wafers pre-spin-coated with photoresist are subjected to a photolithography process using the designed mask, and 5 wafers are selected.
[0091] Step 7, measure the corresponding line width according to the measurement positions pre-specified in steps 4 and 5, and collect the line width data.
[0092] For example, in practice, the exposure conditions of a layer projection exposure machine are CD Design: 185nm; Energy: 180mj / cm2; Focus: 0.1; OVL PC is not considered and is entered as 0 by default. Figure 8 In the circular sampling area shown, the actual CD (Critical Dimension) values of the shot units marked with five-pointed stars are shown in Table 1 below:
[0093] 179 182 188 186 185 186 184 183 192 188 185 182 190 184 188
[0094] Table 1
[0095] It can be understood that the measurement of the CD value specifically refers to measuring the CD of at least one pattern in a DIE. For each pattern, its specific CD measurement position refers to the DIE graphic measurement position determined in the fourth step.
[0096] In the eighth step, the auxiliary algorithm normalizes the above data, for example, the operation of S102 in the above embodiment is adopted to normalize CD and Focus, and then obtain the fitting value of Focus, as shown in the following Table 2:
[0097] 0.103 0.102 0.098 0.099 0.100 0.099 0.101 0.101 0.096 0.098 0.100 0.102 0.097 0.101 0.098
[0098] Table 2
[0099] The statistical values are calculated as shown in Table 3 below:
[0100] Minimum Maximum average value Standard Deviation Very bad 0.0962 0.1032 0.0997 0.0018 0.0070
[0101] Table 3
[0102] The ninth step is to create an SPC chart (statistical process control chart) and input the Mean value, that is, the average value, to complete the monitoring of the focal length of the projection lithography machine. Fig.11 As shown, the horizontal axis is the detection cycle in months, the vertical axis is the focal length, UCL (upper spec limit) refers to the upper limit of the specification value, LSL (lower spec limit) refers to the lower limit of the specification value, and the straight line indicated by Target indicates that the expected exposure focal length is 0.1. From January to August, the focal length of the projection lithography machine is detected each time within the preset upper and lower limits of the specification value, proving that although the focal length of the projection lithography machine fluctuates, it can still ensure the normal operation of the projection lithography machine.
[0103] The exposure focal length determination method provided in the embodiment of the present application is designed from aspects such as control pattern design to system monitoring method and data processing to meet the needs of focal length monitoring in the production process of existing projection lithography machines. It aims to solve the focal length monitoring problem of products in actual production and provides a set of effective methods for machine focal length monitoring.
[0104] Based on the demand for focus monitoring during the production of projection lithography machines, four periodically arranged patterns are designed, namely space, hole, line, and square hole. These patterns cover almost all measurement requirements and have high data reliability. While improving data reliability, they also reduce the signal-to-noise ratio and avoid machine trendworse caused by single data.
[0105] Secondly, define the measurement graphics and related measurement rules. By designing the graphics and measurement positions, multiple measurement methods can be adopted, or different patterns can be measured to monitor the focal length. The designed pattern can be measured at different periods according to actual needs. This not only enriches the data, but also allows the designed method to be used for monitoring the focal length of different technical nodes, while improving the robustness of the focal length test method.
[0106] Finally, the focal length monitoring is completed through normalization processing in data processing. The invention provides a systematic method for monitoring the focal length of a projection lithography machine that can be used for mass production. The method is feasible in mass production verification, covers a wide range of technical nodes, and achieves good benefits.
[0107] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present application, rather than to limit it. Although the present application has been described in detail with reference to the aforementioned embodiments, those skilled in the art should understand that they can still modify the technical solutions described in the aforementioned embodiments, or replace some or all of the technical features therein with equivalents. However, these modifications or replacements do not cause the essence of the corresponding technical solutions to deviate from the scope of the technical solutions of the embodiments of the present application.
[0108] In the description provided herein, a large number of specific details are described. However, it is understood that the embodiments of the present application can be practiced without these specific details. In some instances, well-known methods, structures and techniques are not shown in detail so as not to obscure the understanding of this description.
Claims
1. A method for determining exposure focal length, characterized in that: include: Screening out a plurality of target sample patterns from a sample pattern array on a test wafer, wherein the sample pattern array is obtained by exposing the test wafer using a test mask using an exposure process; Acquire a critical dimension of each target sample pattern among the plurality of target sample patterns, and determine a sample focal length corresponding to each target sample pattern based on the critical dimension of each target sample pattern; The exposure focal length of the exposure process is determined according to the sample focal lengths corresponding to the multiple target sample patterns.
2. The exposure focal length determination method according to claim 1, wherein: The determining, based on the critical size of each target sample pattern, the sample focal length corresponding to each target sample pattern comprises: For each target sample pattern in the plurality of target sample patterns, a sample focal length corresponding to the target sample pattern is determined according to the following formula: Among them, F real is the sample focal length corresponding to the target sample pattern, k is the preset correction coefficient, L CD is the expected value of the critical dimension, L is the critical dimension of the target sample pattern, and F design is the expected value of the exposure focal length.
3. The exposure focal length determination method according to claim 1 or 2, characterized in that: The step of determining the exposure focal length of the exposure process according to the sample focal lengths corresponding to the plurality of target sample patterns comprises: The exposure focal length of the exposure process is determined according to an average value of the sample focal lengths corresponding to the plurality of target sample patterns.
4. The exposure focal length determination method according to claim 1, wherein: The method of screening out a plurality of target sample patterns from the sample pattern array on the test wafer comprises: determining a sampling area on the test wafer; A plurality of sample patterns located on a preset sampling path in the sampling area are used as the plurality of target sample patterns, wherein the preset sampling path crosses the sampling area along N preset directions, where N is a positive integer.
5. The exposure focal length determination method according to claim 4, characterized in that: The sampling path includes a first sub-path and a second sub-path, the first sub-path traverses the sampling area along a first preset direction, and the second sub-path traverses the sampling area along a second preset direction, and the first preset direction and the second preset direction are different.
6. The exposure focal length determination method according to claim 4, characterized in that: The sampling area is a circular area, a square area or a ring area.
7. The exposure focal length determination method according to claim 1, wherein: Each target sample pattern includes at least one group of unit patterns; The obtaining of the critical dimension of each target sample pattern in the plurality of target sample patterns comprises: For each target sample pattern in the multiple target sample patterns, a target unit pattern is determined from at least one group of unit patterns in the target sample pattern, and based on the center position of the target unit pattern, a critical dimension corresponding to the target unit pattern is determined as the critical dimension of the sample pattern.
8. The exposure focal length determination method according to claim 1, wherein: The mask pattern of the test mask includes at least one group of marking patterns, and the marking pattern includes a plurality of bright field patterns, and the plurality of bright field patterns are periodically arranged along a preset direction.
9. The exposure focal length determination method according to claim 8, wherein: The plurality of bright field patterns are identical, and along the preset direction, the intervals between any two adjacent bright field patterns are equal.
10. The exposure focal length determination method according to claim 8, wherein: The shape of the bright field pattern includes circle, square, horizontal long strip, and vertical long strip.