A diffraction-based waveguide electronic beam exposure method and system that balances high speed with sub-nanometer writing field stitching error

Abstract

This invention belongs to the field of micro-nano technology and electron beam lithography application technology, specifically relating to a diffraction-based waveguide electronic beam exposure method and system that balances high speed with sub-nanometer writing field stitching errors. The method includes: designing a test pattern based on an AR waveguide structure and actual task exposure time; conducting exposure experiments based on the test pattern, testing and recording the stitching error values ​​at the writing field boundaries and four corner positions, and establishing a stitching error database under different writing field correction values; obtaining a coefficient matrix and initial error through polynomial fitting based on the stitching error database under different writing field correction values; and obtaining correction variables for preset design values ​​based on the coefficient matrix and the initial error, and correcting the exposure accordingly. This invention provides an easily implemented electron beam writing field pre-calibration method that can truly meet the dual requirements of high-precision and high-efficiency exposure in industrial production.

Description

Technical Field

[0001] This invention belongs to the field of micro-nano technology and electron beam lithography application technology, specifically relating to a diffraction waveguide electron beam exposure method and system that balances high speed with sub-nanometer writing field splicing error. Background Technology

[0002] Electron beam lithography (EBL) is a primary technology for manufacturing high-precision nano-optical and electronic devices. Currently, the maximum deflection range (i.e., write field size) of electron beam systems from various brands on the market is generally 1 mm (at 100 kV accelerating voltage), with an exposure thickness of 20 mm. Exposure of large-format patterns (20 mm) requires moving the stage. During exposure, the equipment is affected by multiple factors, including ambient magnetic field disturbances, temperature changes, cable noise, beam drift, and stage movement errors, resulting in positioning errors and leading to persistent field stitching problems. Currently, some electron beam lithography systems have a write field stitching acceptance standard of "error less than 25 nm" (based on a 1000 μm write field and a beam current of 8 nA or higher). However, the actual error during pattern exposure is approximately 50 nm or even higher, making it difficult to meet the write field stitching requirements of <10 nm or even <5 nm for precision optical devices such as diffractive waveguides.

[0003] Currently, the main field splicing problem is solved by letting the sample stand for several hours after it is transferred into the system, exposing the overlapping boundaries, or multiple exposures. Other methods include installing an atomic force probe inside the equipment and testing it after each writing field exposure (patent CN212873186 U) to capture the writing field boundary position and calculate the displacement stage offset correction.

[0004] However, samples typically require 4 to 8 hours of resting before exposure can show significant improvement, resulting in low processing efficiency for manufacturing companies. On the other hand, overlapping boundary exposure does not significantly improve grating structure splicing because it merely overlaps the patterns at adjacent boundaries of two write fields, exposing the overlapping pattern with half the original exposure dose, without actually correcting for stage or electron beam deflection errors. Multiple exposure is similar to overlapping exposure, adjusting the overlap area of ​​adjacent write fields to 1 / 2, 1 / 4, or 1 / 9 of the write field. While this method significantly improves splicing errors, the exponentially increased number of stage movements and electron beam settling time leads to a geometric increase in overall exposure time. Compared to the previous two methods, in-situ probe testing increases the additional manufacturing and maintenance costs of the equipment. Its resolution is dependent on the exposed pattern and photoresist properties, and adding probe testing during exposure also reduces exposure speed, severely limiting production efficiency.

[0005] In summary, due to the limitations of write field stitching, existing electron beam exposure technologies cannot simultaneously achieve high precision and high speed. There is an urgent need for an efficient write field stitching correction / revision technology to solve this problem and promote the application of electron beam technology in emerging micro-nano optics research and industrialization. Summary of the Invention

[0006] To address the problems existing in the prior art, this invention provides a diffraction-waveguided electron beam exposure method and system that balances high speed with sub-nanometer writing field stitching errors. It aims to provide an easy-to-implement electron beam writing field pre-calibration method that truly meets the dual requirements of high-precision and high-efficiency exposure in industrial production.

[0007] To achieve the above objectives, the present invention provides the following solution: A diffractive waveguide electronic beam exposure method that balances high speed with sub-nanometer writing field stitching error, the method comprising: Based on the AR optical waveguide structure and the actual mission exposure time, a test layout was designed. Exposure experiments were conducted based on the test layout to test and record the splicing error values ​​at the write field boundary and four corner positions, and to establish a splicing error database under different write field correction values. Based on the splicing error database under different write field correction values, the coefficient matrix and initial error are obtained through polynomial fitting; Based on the coefficient matrix and the initial error, correction variables are obtained when the preset design value is obtained, and the exposure is corrected.

[0008] Preferably, the method for conducting exposure experiments based on the test layout, testing and recording the splicing error values ​​at the write field boundaries and four corner positions, and establishing a splicing error database under different write field correction values ​​includes: ; in, Due to splicing error, To correct the variable set, The coefficient matrix, This is the initial error. This is the beam spot drift factor.

[0009] Preferably, the splicing error Decomposed into splicing errors at different locations at the write field boundary: ; in, This is the left vertical error. This is the right vertical error. For top horizontal error, For bottom horizontal error, For top vertical error, For bottom longitudinal error, For left horizontal error, This represents the right horizontal error.

[0010] Preferably, the set of modified variables is: ; in, and These represent scaling correction variables in the X and Y directions, respectively; and These represent the tilt correction variables in the X and Y directions, respectively; and These represent the mirror distortion correction variables in the X and Y directions, respectively.

[0011] Preferably, the method for correcting exposure by obtaining correction variables when setting a preset design value based on the coefficient matrix and the initial error includes: Based on the coefficient matrix and the initial error Obtain splicing error The set of correction variables equal to the preset design value The various values ​​will be obtained The input device system corrects the exposure.

[0012] The present invention also provides a diffraction waveguide electronic beam exposure system that balances high speed with sub-nanometer writing field splicing error. The system is used to implement the aforementioned method and includes: a layout design module, a database module, a fitting module, and a correction module. The layout design module is used to design test layouts based on AR waveguide structures and actual mission exposure times. The database module is used to conduct exposure experiments based on the test layout, test and record the splicing error values ​​at the write field boundary and four corner positions, and establish a splicing error database under different write field correction values. The fitting module is used to obtain the coefficient matrix and initial error by polynomial fitting based on the splicing error database under different write field correction values. The correction module is used to obtain correction variables for the preset design value based on the coefficient matrix and the initial error, and to correct the exposure.

[0013] Preferably, the method for establishing a splicing error database under different write field correction values ​​by performing exposure experiments based on the test layout, testing and recording the splicing error values ​​at the write field boundaries and four corner positions, includes: ; in, Due to splicing error, To correct the variable set, The coefficient matrix, This is the initial error. This is the beam spot drift factor.

[0014] Preferably, the splicing error Decomposed into splicing errors at different locations at the write field boundary: ; in, This is the left vertical error. This is the right vertical error. For top horizontal error, For bottom horizontal error, For top vertical error, For bottom longitudinal error, For left horizontal error, This represents the right horizontal error.

[0015] Preferably, the set of modified variables is: ; in, and These represent scaling correction variables in the X and Y directions, respectively; and These represent the tilt correction variables in the X and Y directions, respectively; and These represent the mirror distortion correction variables in the X and Y directions, respectively.

[0016] Preferably, the correction module obtains the correction variable for the preset design value based on the coefficient matrix and the initial error, and the method for correcting the exposure includes: Based on the coefficient matrix and the initial error Obtain splicing error The set of correction variables equal to the preset design value The various values ​​will be obtained The input device system corrects the exposure.

[0017] Compared with the prior art, the beneficial effects of the present invention are as follows: This invention captures the main field distortion of quantized electron beam exposure through actual exposure, followed by pre-calibration. The advantages of this approach are: 1. No additional calibration is required during the exposure of the process film, nor is it necessary to modify the actual exposure pattern (the pattern used in actual product production) or modify the equipment.

[0018] 2. High accuracy after calibration, no need for multiple exposure.

[0019] 3. There is no need to consider the stability issue after the wafer is loaded and left to stand, which greatly improves throughput. Attached Figure Description

[0020] To more clearly illustrate the technical solution of the present invention, the drawings used in the embodiments are briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0021] Figure 1 This is a field splicing test layout diagram for an embodiment of the present invention; Figure 2 This is a schematic diagram of the operation logic for writing field distortion correction in an embodiment of the present invention; Figure 3 This is a schematic diagram of the splicing error test location at the field boundary in an embodiment of the present invention; Figure 4 This is a SEM image showing the calibration code effect at a field size of 1000 μm, according to an embodiment of the present invention. Figure 5 This is an SEM image showing the calibration code effect at a field size of 200 μm, as described in an embodiment of the present invention. Detailed Implementation

[0022] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0023] To make the above-mentioned objects, features and advantages of the present invention more apparent and understandable, the present invention will be further described in detail below with reference to the accompanying drawings and specific embodiments.

[0024] Example 1 This invention provides a diffraction-based waveguide electronic beam exposure method that balances high speed with sub-nanometer writing field stitching error, the method comprising: Based on the AR optical waveguide structure and the actual mission exposure time, a test layout was designed. Exposure experiments were conducted based on the test layout to test and record the splicing error values ​​at the write field boundary and four corner positions, and to establish a splicing error database under different write field correction values. Based on the splicing error database under different write field correction values, the coefficient matrix and initial error are obtained through polynomial fitting; Based on the coefficient matrix and the initial error, correction variables are obtained when the preset design value is obtained, and the exposure is corrected.

[0025] The specific implementation process of this invention is as follows: Furthermore, in this embodiment, the method for conducting exposure experiments based on the test layout, testing and recording the splicing error values ​​at the write field boundaries and four corner positions, and establishing a splicing error database under different write field correction values ​​includes: in, Due to splicing error, To correct the variable set, The coefficient matrix, This is the initial error. This is the beam spot drift factor.

[0026] Furthermore, in this embodiment, the splicing error Decomposed into splicing errors at different locations at the write field boundary: in, This is the left vertical error. This is the right vertical error. For top horizontal error, For bottom horizontal error, For top vertical error, For bottom longitudinal error, For left horizontal error, This represents the right horizontal error.

[0027] Furthermore, in this embodiment, the set of modified variables is: in, and These represent scaling correction variables in the X and Y directions, respectively; and These represent the tilt correction variables in the X and Y directions, respectively; and These represent the mirror distortion correction variables in the X and Y directions, respectively.

[0028] Furthermore, in this embodiment, the method for correcting exposure by obtaining correction variables when setting a preset design value based on the coefficient matrix and the initial error includes: Based on the coefficient matrix and the initial error Obtain splicing error The set of correction variables equal to the preset design value The various values ​​will be obtained The input device system corrects the exposure.

[0029] Example 2 like Figures 1-5 As shown, this embodiment uses the optimization of optical waveguide pattern splicing error, which is commonly used in augmented reality lenses, as an example to illustrate the specific implementation process of the method described in the aforementioned embodiment: The electron beam lithography system uses an EBPG 5200 electron beam exposure machine.

[0030] This embodiment is achieved through the following steps: A 4 mm A 4 mm unit grating array is formed by repeating 210 nm wide lines with a 190 nm spacing (period 400 nm). Figure 1 In the middle, from left to right, there is a display of 25-unit grating array on a 4-inch wafer, a display of the number of main fields in a single unit and the main field division position, and a display of the marking design and wire grating structure at the main field boundary position.

[0031] First, the exposure test pattern design is determined. The test pattern needs to meet two conditions: 1. It should accurately reflect the actual write field stitching of the exposed target structure. This is because the origin mechanism of stitching problems is complex. For example, when the size and exposure time of the test pattern and the target pattern differ significantly, the cumulative beam drift and stage movement error will also be different, leading to inconsistent stitching error results between the test and target exposures, and rendering write field correction ineffective; 2. The exposure test pattern should facilitate the observation and capture of stitching error information, for example, by designing identification marks at the write field stitching positions. By meeting these conditions, the effects of beam drift and other factors during the exposure process that are difficult to characterize through conventional testing are incorporated into the test exposure.

[0032] After the test layout is designed, an exposure experiment is conducted. During exposure, within the allowable range of the EBL system, a write field correction value with a certain step size should be set. For example, the write field deflection parameter after system self-calibration can be used as the initial value, and the parameter offset can be set with equal step sizes of 2%, 4%, ... up to 10% of the initial value for exposure. After exposure and development, the stitching error values ​​at the write field boundary and four corner positions are observed and recorded using a scanning electron microscope to establish a stitching error database under different write field correction values.

[0033] By using the stitching error value obtained from SEM measurements and the write field correction value set before the experiment, the write field correction coefficient was fitted to obtain a complete mathematical model for write field stitching correction. The final write field correction value was calculated according to the model, and the system was recalibrated.

[0034] Specifically, it includes: S1: Exposure process settings.

[0035] First, based on the product / actual structure, design a test layout that can reflect the actual splicing error. For example... Figure 1The test layout references the AR waveguide structure and uses a grating line array with a line width of 210 nm, a spacing of 190 nm, and a full array length and width of 4 mm. Marks can be set at the corners of the main field to facilitate positioning and observation. The photoresist and exposure process parameters can be changed depending on the photoresist used. In this embodiment, ARP 6200 photoresist is used, the spin coating speed is 4000 rpm, and the pre-baking temperature is 180 ℃ for 60 s to 180 s. The main exposure field is set to 1000 μm in length and width, the subfield (if any) to 4 μm in size, the exposure beam current to 20 nA, the beam spacing to 20 nm, and the exposure dose to 220–280 μC / cm². 2 Exposure is performed in single-pass mode, without setting field overlap.

[0036] S2: Establish a splicing error database.

[0037] The write field splicing error in this embodiment can be expressed as: Among them, splicing error It can be decomposed into splicing error components at different positions on the boundaries of four adjacent write fields (top left, top right, bottom left, bottom right): The definitions of each character are shown in Table 1, and can be directly observed via SEM. Figure 3 Obtained from the corresponding position.

[0038] To correct the variable set: in, and These represent scaling correction variables in the X and Y directions, respectively; and These represent the tilt correction variables in the X and Y directions, respectively; and These represent the mirror distortion correction variables in the X and Y directions, respectively. , , , , and That is, there are 6 correction variables.

[0039] like Figure 2As shown, in this embodiment, 2 to 6 correction variables from the above-mentioned set of correction variables are considered, and these correction variables are added during the automatic exposure program run using the program / code developed in this invention. The correction operation logic is described as follows: The EBL user first needs to determine and confirm whether to perform field correction in the software interface; if correction is required, it will proceed according to... Figure 2 The process outlined in the dashed box on the left involves writing field corrections. First, users input values ​​for various correction variables into the software interface. Then, the program reads a pre-defined template file, generates a writing field correction command, and silently executes the correction. Next, the EBL (Extended Blackout) process exposes the pattern. After exposure, the current writing field correction is canceled, resetting the writing field to its original state. The correction range for the correction variables relative to the system settings is ±10%. 10%. The step size interval ranges from 0.01% to 0.2%. For comparison, Figure 2 The right side shows the default operating logic of the EBL system, that is, the exposure without write field correction.

[0040] Here is the coefficient matrix: coefficient matrix The values ​​in ~ Obtained through curve fitting of experimental data; The intrinsic error matrix (i.e., the initial error): That is when The system intrinsic splicing error E when = 0 (x=0) .

[0041] This is a beam drift factor that depends on the exposure time. This has a near-linear impact on splicing errors when process parameters affecting the cell write field exposure time change (such as beam current, write field size, etc.). In this embodiment, the process parameters are fixed, so its effect is not considered.

[0042] Table 1 S3: SEM observation and correction coefficient fitting. Using a scanning electron microscope (ZEISS, Sigma 360), the stitching positions of the four write field boundaries under different correction parameters were observed, and data at various points in the image were measured, such as... Figure 3 .

[0043] After obtaining the splicing error corresponding to each correction parameter, the value of the coefficient matrix C and the initial error c are obtained through polynomial fitting. S4: After obtaining the complete coefficient matrix, substitute it into the aforementioned formula.

[0044] When the components of E are equal to the test layout design values ​​in S1, the values ​​of each variable in the variable set x are corrected, and then the obtained x is input into the device system (electron beam lithography system) to correct the exposure.

[0045] In this embodiment, the variable set x was iterated and optimized three times, and the final exposure result is as follows: Figure 4 , Figure 5 As shown, under the premise of high-speed exposure settings without writing field overlap and single exposure, a stitching error of ≤ 5 nm under a 1000 μm writing field and ≤ 1 nm under a 200 μm writing field is achieved.

[0046] In summary, this invention provides an easily implemented electron beam write field pre-calibration method. First, a test pattern is designed to characterize write field splicing and write field distortion. Then, a set of codes is written to perform pre-calibration of the EBL write field based on actual test feedback, ultimately achieving high-precision write field splicing with an average error ≤ 5 nm under a single exposure of 1000 μm write field and an average error ≤ 1 nm under a 200 μm write field.

[0047] It should be noted that the technology of this invention is actually applicable to all patterns; the embodiment focuses on optical waveguides because the structure and performance of optical waveguides are sensitive to splicing errors. If the splicing error correction of the optical waveguide structure is well done, then similar corrections for other patterns are easier to achieve. For ease of demonstration, the embodiment is selected as follows: Figure 1 The optical waveguide array shown is used as an exposure test pattern, and key design elements are incorporated at the splicing points where the four write fields intersect. Figure 1 The "marker structure" in the rightmost image.

[0048] Example 3 Based on the same inventive concept, the present invention also provides a diffraction waveguide electronic beam exposure system that balances high speed with sub-nanometer writing field splicing error, for implementing the method described in the foregoing embodiments. The system includes: a layout design module, a database module, a fitting module, and a correction module. The layout design module is used to design test layouts based on AR waveguide structures and actual mission exposure times. The database module is used to conduct exposure experiments based on the test layout, test and record the splicing error values ​​at the write field boundary and four corner positions, and establish a splicing error database under different write field correction values. The fitting module is used to obtain the coefficient matrix and initial error by polynomial fitting based on the splicing error database under different write field correction values. The correction module is used to obtain correction variables for the preset design value based on the coefficient matrix and the initial error, and to correct the exposure.

[0049] Furthermore, in this embodiment, the database module performs an exposure experiment based on the test layout, tests and records the splicing error values ​​at the write field boundaries and four corner positions, and establishes a splicing error database under different write field correction values, including: in, Due to splicing error, To correct the variable set, The coefficient matrix, This is the initial error. This is the beam spot drift factor.

[0050] Furthermore, in this embodiment, the splicing error Decomposed into splicing errors at different locations at the write field boundary: in, This is the left vertical error. This is the right vertical error. For top horizontal error, For bottom horizontal error, For top vertical error, For bottom longitudinal error, For left horizontal error, This represents the right horizontal error.

[0051] Furthermore, in this embodiment, the set of modified variables is: in, and These represent scaling correction variables in the X and Y directions, respectively; and These represent the tilt correction variables in the X and Y directions, respectively; and These represent the mirror distortion correction variables in the X and Y directions, respectively.

[0052] Furthermore, in this embodiment, the correction module obtains the correction variable for the preset design value based on the coefficient matrix and the initial error, and the method for correcting the exposure includes: Based on the coefficient matrix and the initial error Obtain splicing error The set of correction variables equal to the preset design value The various values ​​will be obtained The input device system corrects the exposure.

[0053] The embodiments described above are merely preferred embodiments of the present invention and are not intended to limit the scope of the present invention. Various modifications and improvements made by those skilled in the art to the technical solutions of the present invention without departing from the spirit of the present invention should fall within the protection scope defined by the claims of the present invention.

Claims

1. A diffractive waveguide electronic beam exposure method that balances high speed with sub-nanometer writing field stitching error, characterized in that, The method includes: Based on the AR optical waveguide structure and the actual mission exposure time, a test layout was designed. Exposure experiments were conducted based on the test layout to test and record the splicing error values ​​at the write field boundary and four corner positions, and to establish a splicing error database under different write field correction values. Based on the splicing error database under different write field correction values, the coefficient matrix and initial error are obtained through polynomial fitting; Based on the coefficient matrix and the initial error, correction variables are obtained when the preset design value is obtained, and the exposure is corrected.

2. The method according to claim 1, characterized in that, The method for conducting exposure experiments based on the test layout, testing and recording the splicing error values ​​at the write field boundaries and four corner positions, and establishing a splicing error database under different write field correction values ​​includes: ； in, Due to splicing error, To correct the variable set, The coefficient matrix, This is the initial error. This is the beam spot drift factor.

3. The method according to claim 2, characterized in that, splicing error Decomposed into splicing errors at different locations at the write field boundary: ； in, This is the left vertical error. This is the right vertical error. For top horizontal error, For bottom horizontal error, For top vertical error, For bottom longitudinal error, For left horizontal error, This represents the right horizontal error.

4. The method according to claim 3, characterized in that, The set of corrected variables is as follows: ； in, and These represent scaling correction variables in the X and Y directions, respectively; and These represent the tilt correction variables in the X and Y directions, respectively; and These represent the mirror distortion correction variables in the X and Y directions, respectively.

5. The method according to claim 4, characterized in that, Based on the coefficient matrix and the initial error, the correction variables for obtaining the preset design value are obtained, and the method for correcting the exposure includes: Based on the coefficient matrix and the initial error Obtain splicing error The set of correction variables equal to the preset design value The various values ​​will be obtained The input device system corrects the exposure.

6. A diffractive waveguide electronic beam exposure system that balances high speed with sub-nanometer writing field stitching error, said system being used to implement the method described in any one of claims 1-5, characterized in that, The system includes: a layout design module, a database module, a fitting module, and a correction module; The layout design module is used to design test layouts based on AR waveguide structures and actual mission exposure times. The database module is used to conduct exposure experiments based on the test layout, test and record the splicing error values ​​at the write field boundary and four corner positions, and establish a splicing error database under different write field correction values. The fitting module is used to obtain the coefficient matrix and initial error by polynomial fitting based on the splicing error database under different write field correction values. The correction module is used to obtain correction variables for the preset design value based on the coefficient matrix and the initial error, and to correct the exposure.

7. The system according to claim 6, characterized in that, The database module performs exposure experiments based on the test layout, tests and records the splicing error values ​​at the write field boundaries and four corner positions, and establishes a splicing error database under different write field correction values. The method includes: ； in, Due to splicing error, To correct the variable set, The coefficient matrix, This is the initial error. This is the beam spot drift factor.

8. The system according to claim 7, characterized in that, splicing error Decomposed into splicing errors at different locations at the write field boundary: ； in, This is the left vertical error. This is the right vertical error. For top horizontal error, For bottom horizontal error, For top vertical error, For bottom longitudinal error, For left horizontal error, This represents the right horizontal error.

9. The system according to claim 8, characterized in that, The set of corrected variables is as follows: ； in, and These represent scaling correction variables in the X and Y directions, respectively; and These represent the tilt correction variables in the X and Y directions, respectively; and These represent the mirror distortion correction variables in the X and Y directions, respectively.

10. The system according to claim 9, characterized in that, The correction module obtains correction variables for the preset design value based on the coefficient matrix and the initial error, and the method for correcting exposure includes: Based on the coefficient matrix and the initial error Obtain splicing error The set of correction variables equal to the preset design value The various values ​​will be obtained The input device system corrects the exposure.

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