A method for checking minute defocus in a lithography process
By setting interlaced test keys on the wafer and monitoring the changes in light and dark states using electron beam scanning, the problem of lithography machines being unable to detect the wafer edge is solved, and accurate out-of-focus monitoring of the lithography process is achieved, and the chip yield is improved.
Patent Information
- Application Number
- CN202111437342.6
- Authority / Receiving Office
- CN · China
- Patent Type
- Patents(China)
- Current Assignee / Owner
- Filing Date
- 2021-11-29
- Publication Date
- 2025-07-18
- Estimated Expiration
- 2041-11-29
AI Technical Summary
The lithography machine cannot effectively monitor the out-of-focus changes in the wafer edge and ultra-far edge, resulting in a decrease in the chip yield in the lithography process.
The test key is set on the wafer, including the first structural test key and the second structural test key interleaved in the X-axis direction, and the light and dark changes are monitored by electron beam scanning in the negative potential mode after metal filling to determine the degree of out-of-focus of the lithography process.
Effectively monitoring the slight loss of focus in the lithography process solves the problem that the lithography machine cannot detect the loss of focus at the wafer edge and improves the chip yield.
Smart Images
Figure CN114156194B_ABST
Abstract
Description
Technical Field
[0001] The present invention relates to the technical field of semiconductor manufacturing, and in particular to a method for inspecting minute defocus in a lithography process. Background Art
[0002] The lithography process is often regarded as the most critical step in integrated circuit manufacturing and requires high performance to achieve a high yield in combination with other processes. Each manufacturing process in the integrated circuit manufacturing process flows in and out of the lithography process. With the development of integrated circuit processes, the critical dimensions are getting smaller and smaller, the requirements for the lithography process are getting higher and higher, and the tests for detection are also getting higher. As a common defect in the lithography process, defocus defects have a very high killing rate on the chip yield. Please refer to Figure 8(a) - 8(b) , Figure 8(a) - 8(b) The electron microscope image of defocus at the far edge of the wafer is shown. As Figure 8(a) - 8(b) can be seen, when the defocus reaches a certain degree, it will cause a short circuit in the metal connection.
[0003] As is well known, there will be obvious morphological changes at the far edge of the wafer, which will affect the detection of the flatness of the wafer by the lithography machine. The flatness detection sensor of the machine tool will avoid the detection blind area at the far edge to prevent the edge interference signal from being collected and fed back to the machine tool. Therefore, from the perspective of the flatness detection result of the product, there is no abnormality, and the lithography machine cannot detect the defocus change at the far edge. In addition, the unit-to-unit comparison method of in-line defect scanning in the optical machine tool array area is also very difficult to capture the defect.
[0004] Finding a method that can effectively solve the problem that the lithography machine tool cannot monitor the defocus at the wafer edge, and can provide a solution for monitoring the defocus at the ultra-far edge of the wafer, and is worthy of promotion in the industry has become one of the technical problems that need to be solved urgently by those skilled in the art.
[0005] Therefore, in view of the problems existing in the prior art, the designer of this case, relying on years of experience in this industry, actively studied and improved, and thus there is a method for inspecting minute defocus in a lithography process of the present invention. Summary of the Invention
[0006] The present invention provides a method for inspecting minute defocus in a lithography process for defects such as that traditional lithography machines cannot detect defocus changes at the far edge in the prior art. In addition, the unit-to-unit comparison method of in-line defect scanning in the optical machine tool array area is also very difficult to capture the defect.
[0007] To achieve the purpose of the present invention, the present invention provides a method for inspecting minute defocus in a lithography process, and the method for inspecting minute defocus in a lithography process includes:
[0008] Execute step S1: Provide a wafer with test keys, where the test keys include a first structure test key and a second structure test key that are longitudinally and alternately arranged at intervals along the X-axis direction. The first unit key of the first structure test key and the second unit key of the second structure test key are linearly arranged along the X-axis direction, and the first unit key of the first structure test key and the second unit key of the second structure test key are both arranged at intervals along the Y-axis direction;
[0009] Execute step S2: After metal filling is completed, detect the wafer with test keys in a negative potential mode;
[0010] Execute step S3: In the negative potential mode, monitor the change in the number of bright or dark states of the first structure test key and the second structure test key by means of electron beam scanning to determine the defocus degree of the lithography process.
[0011] Optionally, the test keys are at least arranged at the edge of the wafer.
[0012] Optionally, the test keys are also arranged inside the wafer at the same time.
[0013] Optionally, the first structure test key is a floating structure; the second structure test key is a short-circuit structure.
[0014] Optionally, the first structure test key is characterized as a dark state in the negative potential mode, and the second structure test key is characterized as a bright state in the negative potential mode.
[0015] Optionally, the distance between the first structure test key and the second structure test key that are longitudinally and alternately arranged at intervals is set according to the requirements of the lithography process.
[0016] Optionally, the distance between the first structure test key and the second structure test key that are longitudinally and alternately arranged at intervals gradually decreases from the center to both sides.
[0017] Optionally, when the focusing ability of the lithography process becomes weak, the number of dark states on both sides of each row in the X-axis direction increases, and the number of the second structure test keys remaining bright in the middle decreases. Then, the defocus degree of the lithography process can be monitored according to the number of the second structure test keys remaining bright in the middle.
[0018] In summary, the method for inspecting minute defocus of the lithography process in the present invention determines the defocus degree of the lithography process by monitoring the change in the number of bright or dark states of the first structure test key and the second structure test key by means of electron beam scanning in a negative potential mode through at least arranging test keys with a first test structure and a second test structure at the edge of the wafer. It not only solves the problem that the lithography machine tool cannot monitor the defocus of the wafer edge, but also provides a solution for monitoring the defocus of the ultra-far edge of the wafer, which is worthy of popularization and use in the industry. Brief Description of the Drawings
[0019] Figure 1 The figure shows a flowchart of the method for inspecting minute defocus in a lithography process according to the present invention;
[0020] Figure 2 The figure shows a schematic diagram of a test key of the method for inspecting minute defocus in a lithography process according to the present invention;
[0021] Figure 3 The figure shows a schematic diagram of the structure of the test key of the method for inspecting minute defocus in a lithography process according to the present invention after metal filling;
[0022] Figure 4 The figure shows a light and dark schematic diagram of the test key of the method for inspecting minute defocus in a lithography process according to the present invention under electron beam scanning after metal filling;
[0023] Figure 5 The figure shows a light and dark schematic diagram of the test key of the method for inspecting minute defocus in a lithography process according to the present invention under electron beam scanning after lithography defocus;
[0024] Figure 6 The figure shows a trend chart of defocus monitoring using the method for inspecting minute defocus in a lithography process according to the present invention;
[0025] Figure 7(a) - 7(b) The figure shows a light and dark schematic diagram of defocus monitoring using the method for inspecting minute defocus in a lithography process according to the present invention;
[0026] Figure 8(a) - 8(b) The figure shows an electron microscope image of defocus at the far edge of a wafer. Detailed Description of the Preferred Embodiment
[0027] To describe in detail the technical content, structural features, achieved objectives and effects of the present invention, the following will be described in detail in conjunction with embodiments and with reference to the accompanying drawings.
[0028] Please refer to Figure 1 , Figure 1 The figure shows a flowchart of the method for inspecting minute defocus in a lithography process according to the present invention. The method for inspecting minute defocus in a lithography process includes:
[0029] Performing step S1: providing a wafer with a test key, the test key including a first structural test key and a second structural test key that are longitudinally arranged in an alternating and spaced manner along the X-axis direction, a first unit key of the first structural test key and a second unit key of the second structural test key being linearly arranged along the X-axis direction, and the first unit key of the first structural test key and the second unit key of the second structural test key being spaced along the Y-axis direction;
[0030] Perform step S2: After the metal filling is completed, detect the wafer with the test keys in a negative potential mode;
[0031] Perform step S3: In the negative potential mode, monitor the change in the number of bright or dark states of the first structure test key and the second structure test key by means of electron beam scanning to determine the defocus degree of the lithography process.
[0032] Please refer to Figure 2 、 Figure 3 、 Figure 4 and, in combination with reference to Figure 1 , Figure 2 The figure shows a schematic diagram of the test key for the method of the present invention to check the minute defocus of the lithography process. Figure 3 The figure shows a schematic diagram of the structure of the test key for the method of the present invention to check the minute defocus of the lithography process after metal filling. Figure 4 The figure shows a bright and dark schematic diagram of the test key for the method of the present invention to check the minute defocus of the lithography process under electron beam scanning after metal filling. In the present invention, without limitation, the first structure test key 11 is a floating structure; the second structure test key 12 is a short-circuit structure. The first structure test key 11 and the second structure test key 12 can be realized by means of traditional metal filling processes and the like, which will not be elaborated here.
[0033] More specifically, the first structure test key 11 is characterized as a dark state in the negative potential mode, and the second structure test key 12 is characterized as a bright state in the negative potential mode. The test key 1 includes a first structure test key 11 and a second structure test key 12 that are longitudinally arranged in an alternating and spaced manner along the X-axis direction. The first unit key 111 of the first structure test key 11 and the second unit key 121 of the second structure test key 12 are linearly arranged along the X-axis direction, and the first unit key 111 of the first structure test key 11 and the second unit key 121 of the second structure test key 12 are both spaced along the Y-axis direction. The spacing distance between the first structure test key 11 and the second structure test key 12 that are longitudinally arranged in an alternating and spaced manner is set according to the requirements of the lithography process. The test key 1 is at least arranged at the edge of the wafer, and can also be arranged inside the wafer at the same time.
[0034] As a specific implementation manner, for example, the spacing distances between the first structure test key 11 and the second structure test key 12 along the X-axis direction are X1, X2,..., X n ; the first unit key 111 of the first structure test key 11 and the second unit key 121 of the second structure test key 12 are both spaced along the Y-axis direction, and the spacing distances are both Y1, Y2,..., Y n .
[0035] Please refer to Figure 5, and refer to Figures 2 - 4 , Figure 5 The figure shows a schematic diagram of the light and dark of the test key of the method for checking the slight defocus of the lithography process using the present invention under the electron beam scanning after the lithography is defocused. As a person skilled in the art, it is easy to know that when a slight defocus occurs in the lithography process, it will inevitably cause the pattern to deform, and then cause leakage between the first structure test key 11 and the second structure test key 12, which is characterized by the light and dark changes of the first structure test key 11 and the second structure test key 12, so that the degree of defocus of the lithography process can be further determined.
[0036] In order to more intuitively disclose the technical solution of the present invention and highlight the beneficial effects of the present invention, the specific steps and working principles of the method for checking slight defocus of the photolithography process are now described in combination with a specific implementation method. In the specific implementation method, the number and spacing of the first structure test key and the second structure test key are only for example and should not be regarded as limiting the technical solution of the present invention.
[0037] Implementation Method 1
[0038] See also Figure 6 , and refer to Figures 1 - 5 , Figure 6 The figure shows the trend of defocus monitoring using the method of the present invention for checking micro defocus in the photolithography process. In the first embodiment, the current exposure capability of the machine is obtained according to the number of rows in the X-axis direction that become dark. Define V = a / n, where a is the number of rows that become dark. Obviously, according to the above definition of V, V1, V2, ..., V n , and then the arithmetic mean of V is used as the defocus change characterizing the wafer edge. More specifically, when n=25 and a approaches 5, the wafer with test key 1 is tested, and the trend is as follows: Figure 6 When the machine's focusing ability weakens, for example, when a approaches 7, the trend graph jumps significantly, which can reflect the change in the machine's ability.
[0039] Implementation Method 2
[0040] See also Figure 7(a) - 7(b) , Figure 7(a) - 7(b)The figure shows a light and dark schematic diagram of defocus monitoring using the method for inspecting minute defocus in a lithography process according to the present invention. The test key 1 includes a first structural test key 11 and a second structural test key 12 that are longitudinally arranged in a staggered and spaced manner along the X-axis direction. The first unit key 111 of the first structural test key 11 and the second unit key 121 of the second structural test key 12 are linearly arranged along the X-axis direction, and the first unit key 111 of the first structural test key 11 and the second unit key 121 of the second structural test key 12 are both arranged at intervals along the Y-axis direction. The spacing distance between the first structural test key 11 and the second structural test key 12 that are longitudinally arranged in a staggered and spaced manner is set according to the requirements of the lithography process. Without limitation, for example, along the X-axis direction, the spacing distance between the first structural test key 11 and the second structural test key 12 that are longitudinally arranged in a staggered and spaced manner gradually decreases from the center to both sides.
[0041] As is readily understood by those skilled in the art, when the second structural test key 12 remains in the bright state, the change in defocus of the lithography process can be monitored according to the number of dark states on both sides in the X-axis direction. According to the number of dark states on both sides of each row in the X-axis direction and the number of bright states of the second structural test key 12 in the middle remaining in the bright state, when the focusing ability of the lithography process becomes weaker, the number of dark states on both sides of each row in the X-axis direction increases. Correspondingly, the number of bright states of the second structural test key 12 in the middle remaining in the bright state decreases. Thus, the degree of defocus of the lithography process can be monitored according to the number of bright states of the second structural test key 12 in the middle remaining in the bright state.
[0042] In summary, the method for inspecting minute defocus in a lithography process according to the present invention determines the degree of defocus of the lithography process by at least arranging a test key having a first test structure and a second test structure at the edge of the wafer and monitoring the change in the number of bright or dark states of the first structural test key and the second structural test key by means of electron beam scanning in a negative potential mode. It not only solves the problem that the lithography machine tool cannot monitor the defocus at the edge of the wafer, but also provides a solution for monitoring the defocus at the ultra-far edge of the wafer, and is worthy of popularization and use in the industry.
[0043] Those skilled in the art should understand that various modifications and variations can be made to the present invention without departing from the spirit or scope of the present invention. Therefore, if any modification or variation falls within the protection scope of the appended claims and their equivalents, the present invention is considered to cover these modifications and variations.
Claims
1. A method for inspecting minute defocus in a lithography process, characterized in that, The method for inspecting minute defocus of a lithography process includes: Performing step S1: providing a wafer with test keys, where the test keys include a first structure test key and a second structure test key that are longitudinally arranged in an interleaved and spaced manner along the X-axis direction. The first unit key of the first structure test key and the second unit key of the second structure test key are linearly arranged along the X-axis direction, and the first unit key of the first structure test key and the second unit key of the second structure test key are both spaced along the Y-axis direction; Performing step S2: after metal filling is completed, detecting the wafer with test keys in a negative potential mode; Performing step S3: in the negative potential mode, monitoring the change in the number of bright or dark states of the first structure test key and the second structure test key by means of electron beam scanning to determine the defocus degree of the lithography process; wherein, the test keys are at least arranged at the edge of the wafer. The first structure test key is characterized as a dark state in the negative potential mode, and the second structure test key is characterized as a bright state in the negative potential mode.
2. The method for inspecting minute defocus in a lithography process according to claim 1, wherein The test keys are simultaneously arranged inside the wafer.
3. The method for inspecting a minute defocus of a lithography process according to claim 1, wherein The first structure test key is a floating structure; the second structure test key is a short-circuited structure.
4. The method for inspecting minute defocus in a lithography process according to claim 1, wherein The spacing distance between the first structure test key and the second structure test key that are longitudinally arranged in an interleaved and spaced manner is set according to the requirements of the lithography process.
5. The method for inspecting minute defocus in a lithography process as claimed in claim 4, wherein, The spacing distance from the center to both sides of the first structure test key and the second structure test key that are longitudinally arranged in an interleaved and spaced manner gradually decreases.
6. The method for inspecting minute defocus in a lithography process as claimed in claim 5, wherein, When the focusing ability of the lithography process becomes weaker, the number of dark states on both sides of each row in the X-axis direction increases, and the number of bright states of the second structure test key in the middle decreases. Then, the defocus degree of the lithography process can be monitored according to the number of bright states of the second structure test key in the middle.
Citation Information
Patent Citations
Photolithography defocusing detection method
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