Imprint template and manufacturing method thereof

Abstract

The invention is suitable for the field of micro lens preparation, and provides an imprint template and a preparation process thereof. The imprint template manufacturing method comprises the following steps: S1, forming a first curved surface on a workpiece through laser direct writing gray photoetching, and measuring surface type data of the first curved surface; s2, baking through a hot reflux oven to obtain a second curved surface, and measuring surface type data of the second curved surface; s3, judging whether the second curved surface conforms to the designed surface type or not; if not, entering S4; if yes, entering S5; s4, calculating an exposure energy value according to the surface type data of the second curved surface and the designed curved surface, and entering S1; and S5, finishing the operation. The imprint template prepared by the imprint template preparation method provided by the invention has good surface precision, surface roughness and strength, and is resistant to acid and alkali to a certain extent.

Description

Technical Field

[0001] The present application relates to the field of microlens preparation, and in particular to a nanoimprint template and a method for preparing the same. Background Art

[0002] With the continuous development of science and technology, devices are developing towards the trend of optical, electrical and mechanical integration. Traditional optical processing methods are difficult to meet technical requirements due to their large size and heavy weight. In recent years, micro-optical components have attracted widespread attention due to their light weight and small size. Microlens arrays are one of the important micro-optical components. Microlens production methods include photolithography hot reflow method, mechanical processing method, spray glue method, laser direct writing method, die preparation technology, etc. The microlenses processed by hot reflow and spray glue methods have low precision and are difficult to meet the requirements. The laser direct writing method has high precision in producing microlenses, but the process is long and difficult to mass produce. The use of die preparation technology to prepare microlenses can achieve mass production, but is relatively limited by the template.

[0003] The compression molding process involves applying pressure to the material through a die template, causing it to plastically deform within the mold cavity, resulting in a product with the same shape as the mold cavity. The embossing template is crucial for producing microlenses using the nanocompression molding process. The condition of the embossing template directly impacts the quality of the microlenses. The hardness and roughness of the template material, as well as the difficulty of template processing, can introduce instability into the subsequent compression molding process.

[0004] Existing imprint template fabrication methods include 1:1 etching of quartz or silicon wafer templates, and metal coating of photoresist templates. The 1:1 etching of quartz is a complex and costly process. Metal coating of photoresist also increases the difficulty and cost. Therefore, improvements are needed to the imprint template fabrication process to balance production and the strength and roughness requirements of the imprint template. Summary of the Invention

[0005] The purpose of this application is to overcome the deficiencies of the above-mentioned prior art and to provide an imprint template and a preparation process thereof, which aims to improve the strength and roughness requirements of the imprint template while taking into account the production cost.

[0006] The present application provides a method for manufacturing an imprint template, comprising:

[0007] S1: forming a first curved surface on a workpiece by laser direct writing grayscale lithography, and measuring surface data of the first curved surface;

[0008] S2: baking in a hot reflow oven to obtain a second curved surface, and measuring surface data of the second curved surface;

[0009] S3: Determine whether the second curved surface is consistent with the designed surface shape; if not, proceed to S4; if consistent, proceed to S5;

[0010] S4: Calculate the exposure energy value according to the surface data of the second curved surface and the designed curved surface, and proceed to S1;

[0011] S5: End the job.

[0012] Optionally, in step S2, the baking temperature is 150-300°C and the baking time is 1-10 minutes.

[0013] Optionally, in step S2, the baking temperature is 200° to 280°C and the baking time is 6 to 10 minutes.

[0014] Optionally, in step S2, the baking temperature and time are fixed.

[0015] Optionally, the step S4 is:

[0016] The second curve and the design curve are divided into several equal parts in the X-axis direction according to the design accuracy, the height value of each equal-division node is obtained, the exposure energy value is calculated according to the height difference, and the process goes to S1: the second curved surface is exposed according to the exposure energy value corresponding to each equal-division node to form the first curved surface.

[0017] Optionally, the calculated exposure energy value is: E (i+1) =E i -K*(H BX -H CX ) / H CX *E i , where H Bx and H Cx are the heights of the second curved surface and the designed surface at the same horizontal coordinate x position, E i is the energy value of the i-th exposure, E (i+1) is the energy value of the (i+1)th exposure, K is the energy difference coefficient, K∈(0,2].

[0018] Optional, K∈[0.8, 1.2].

[0019] Optionally, before S1, the method further includes:

[0020] S0: Spin-coating a photoresist on a silicon substrate, wherein the photoresist has a thickness of 8-15 μm, and then pre-baking the substrate at a temperature less than 100° C.

[0021] Optionally, step S1 also includes: measuring the stress of the first curved surface; step S2 also includes: measuring the stress of the second curved surface; after step S5, it also includes inspection: comparing the stress of the second curved surface with the stress of the first curved surface. If the stress of the second curved surface is less than the stress of the first curved surface, it is a defective product.

[0022] Optionally, step S1 also includes: measuring the roughness of the first curved surface; step S2 also includes: measuring the roughness of the second curved surface; after step S5, it also includes inspection: comparing the roughness of the second curved surface with the roughness of the first curved surface. If the roughness of the second curved surface is greater than the roughness of the first curved surface, it is a defective product.

[0023] The present application provides an imprint template for preparing curved microlenses, wherein the imprint template is prepared by any of the above-described imprint template manufacturing methods.

[0024] The imprint template and method provided in this application use laser direct writing grayscale lithography to produce the original imprint template. The surface is then carbonized through high-temperature thermal reflow to improve the strength of the imprint template. Exposure iterative compensation allows the imprint template to approach the designed surface shape, thereby ensuring the template's surface accuracy, surface roughness, and strength, and providing a certain degree of acid and alkali resistance. Through the dual mechanisms of structural closed-loop iterative compensation and material enhancement, the application breaks through the bottlenecks of precision and template durability in traditional laser direct writing and thermal reflow processes, providing a low-cost, high-efficiency solution for the mass production of high-precision micro-nano optical components. BRIEF DESCRIPTION OF THE DRAWINGS

[0025] In order to more clearly illustrate the technical solutions in the embodiments of the present application, the following briefly introduces the drawings required for use in the embodiments. Obviously, the drawings described below are only some embodiments of the present application. For ordinary technicians in this field, other drawings can be obtained based on these drawings without creative work.

[0026] Figure 1 This is a flow chart of a method for manufacturing an imprint template provided in an embodiment of the present application;

[0027] Figure 2 Schematic diagram of the steps of the method for making an imprint template provided in an embodiment of the present application;

[0028] Figure 3 Schematic diagram of the change of the workpiece surface before and after heat reflow in the embodiment of the present application;

[0029] Figure 4 This is a photo of the first curved surface and a roughness curve diagram before thermal reflow in an embodiment of the present application;

[0030] Figure 5 This is a photo of the second curved surface and a roughness curve diagram after thermal reflow in an embodiment of the present application;

[0031] Figure 6 This is a stress distribution diagram before thermal reflow in the embodiment of the present application;

[0032] Figure 7 This is a stress distribution diagram after thermal reflow in the embodiment of the present application. DETAILED DESCRIPTION

[0033] In order to make the purpose, technical solutions and advantages of this application more clear, the following further describes this application in detail with reference to the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are only used to explain this application and are not intended to limit this application.

[0034] The present application provides an imprint template and a method for manufacturing the same. In this embodiment, the imprint template is used to manufacture an imprint template for a curved microlens. In other embodiments, the imprint template can also be used to manufacture other structural parts using a die-stamping process, which is not intended to be the sole limitation.

[0035] Please refer to Figure 1 and Figure 2 The method for manufacturing an imprint template provided in the embodiment of the present application includes:

[0036] S1: forming a first curved surface on a workpiece by laser direct writing grayscale lithography, and measuring surface data of the first curved surface;

[0037] S2: baking in a hot reflow oven to obtain a second curved surface, and measuring surface data of the second curved surface;

[0038] S3: Determine whether the second curved surface is consistent with the designed surface shape; if not, proceed to S4; if consistent, proceed to S5;

[0039] S4: Calculate the exposure energy value according to the surface data of the second curved surface and the designed curved surface, and proceed to S1;

[0040] S5: End the job.

[0041] In this embodiment, the workpiece is a silicon substrate spin-coated with photoresist.

[0042] The method for producing an imprint template provided in this embodiment uses laser direct writing grayscale lithography to produce the most original imprint template, and then uses a high-temperature thermal reflow method to carbonize the surface to improve the strength of the imprint template. Through exposure iterative compensation, the imprint template is made to approach the designed surface shape, thereby ensuring the template surface accuracy, surface roughness and strength, and is acid and alkali resistant to a certain extent.

[0043] Specifically, laser direct-write grayscale lithography exploits the incomplete development of photoresist under low-dose exposure. By precisely controlling the laser exposure dose at different locations, the depth of the photoresist surface varies, creating a three-dimensional photoresist pattern. Using a mapping table between grayscale values and light intensity, the direct-write machine represents the depth information in the design image as grayscale, and uses laser lithography to precisely reproduce this information on the photoresist.

[0044] Thermal reflow technology softens and melts the photoresist at high temperatures (150-300°C). Surface tension drives the material to flow, tending to minimize surface energy and smoothing sharp edges or discontinuous areas, forming a nearly spherical surface. Thermal reflow baking can improve the surface roughness of the photoresist and enhance the strength of the surface.

[0045] Laser direct-write grayscale lithography eliminates the need for mask production, reducing costs and shortening the manufacturing cycle. However, energy loss occurs when the laser passes through the photoresist, causing the resulting grayscale topography to deviate from the intended design. In this solution, after the initial laser direct-write grayscale lithography, thermal reflow is used to enhance and adjust the process, and iterative compensation is used to achieve the fabrication of high-precision microlens surfaces.

[0046] The iteration method is:

[0047] Record the workpiece's surface data before and after thermal reflow, and compare the surface data after thermal reflow (the second curved surface) with the designed surface data. If there is a deviation, adjust the energy value of the next exposure accordingly. Perform a second laser direct writing grayscale lithography and a second thermal reflow on the workpiece based on the adjusted energy value. After the second thermal reflow is completed, compare the surface data again. If there is still a deviation, adjust the exposure energy value again and perform laser direct writing grayscale lithography and thermal reflow until the surface shape after thermal reflow (the second curved surface) matches the designed surface shape.

[0048] As described above, the method proposed in this application, through the dual mechanisms of structural closed-loop iterative compensation and material enhancement, overcomes the precision and template durability bottlenecks of traditional laser direct writing and thermal reflow processes, providing a low-cost, high-efficiency solution for the mass production of high-precision micro-nano optical components. Its core value lies in transforming the "trial and error" process into quantifiable algorithmic optimization, providing a flexible and efficient technical path for micro-nano optical manufacturing.

[0049] In another embodiment of the present application, in step S2, the baking temperature is 150-300° C. and the duration is 1-10 minutes. In the thermal reflow step, the selection of the temperature and time mainly takes into account the fluidity and strength requirements of the photoresist.

[0050] Preferably, in step S2, the baking temperature is between 200°C and 280°C for 6 to 10 minutes. Selecting a higher baking temperature ensures surface hardening of the photoresist, which is beneficial to the durability of the template. Properly increasing the baking time facilitates the flow of the photoresist and optimizes surface roughness.

[0051] In this embodiment, in the thermal reflow operation of step S2, the baking temperature and time are fixed. In other words, in each iteration, the thermal reflow bakes the workpiece at the same baking temperature and baking time.

[0052] The diameter L1 of the second curved surface after reflow is larger than the diameter L2 of the first curved surface before reflow, and also larger than the designed curved surface diameter L. Therefore, the diameter of the exposed pattern decreases during the reflow process by a factor of l = L1 - L2. The conditions for each subsequent reflow remain unchanged, and the reduction in size of each part of the reflow pattern remains constant, maintaining the reduced size I after reflow. Following this method, the exposure parameters are iterated until the final reflowed microlens diameter L1 is as close to the designed diameter L as possible. This setup facilitates operation and control. In other embodiments, the reflow temperature or time can also be reduced proportionally with the number of iterations, which is not limited here.

[0053] In another embodiment of the present application, step S4 is:

[0054] The second curve and the design curve are divided into several equal parts in the X-axis direction according to the design accuracy, the height value of each equal-division node is obtained, the exposure energy value is calculated according to the height difference, and the process goes to S1: the second curved surface is exposed according to the exposure energy value corresponding to each equal-division node to form the first curved surface.

[0055] In this embodiment, the curved surface is divided into a plurality of equally divided nodes according to the X-axis direction, and the required iterative exposure value is calculated separately for each node to achieve refined adjustment and control.

[0056] Preferably, the design accuracy can be set according to the pixel accuracy size of the exposure graphic file. Figure 3 , in the X-axis direction, divide the first curved surface, the second curved surface, and the target surface from left to right into several equal parts according to the design accuracy of the image file (the design accuracy of the image file is the exposure pattern spacing, which is 50nm, 100nm, 500nm, etc.), obtain the height value of each equal-division node position in the X-axis direction, calculate the exposure energy value based on the height value, and perform iterative compensation.

[0057] Please refer to Figure 3 In another embodiment of the present application, the calculated exposure energy value is: E (i+1) =E i -K*(H BX -H CX ) / H CX *Ei , where H Bx and H Cx are the height values of point B of the second curved surface and point C of the designed surface at the same horizontal coordinate x position, E i is the energy value of the i-th exposure, E (i+1) is the energy value of the (i+1)th exposure, K is the energy difference coefficient, K∈(0,2].

[0058] In this embodiment, the next exposure energy value is adjusted according to the ratio of the height difference between the second curved surface after heat reflow and the designed surface shape to the designed surface shape. Each exposure energy value is reduced appropriately compared to the last time, and the amount of reduction is correlated with the height difference. After many experiments, the energy difference coefficient K is controlled within the range of 0-2, which can quickly and effectively correct the workpiece. Preferably, the energy difference coefficient is 0.8≤K≤1.2. Within this range, the number of exposure iterations can be effectively reduced, and the forming quality of the product can be guaranteed. Those skilled in the art can specifically set the energy difference coefficient to 0.8, 0.85, 0.9, 0.92, 0.94, 0.98, 1.0, 1.2, 1.4, 1.6, 1.8, 1.9, 2.0, etc., which is not limited here.

[0059] In another embodiment of the present application, before S1, the method further includes:

[0060] S0: Spin-coat photoresist on a silicon substrate with a thickness of 8-15 μm, and then pre-bake at a temperature less than 100°C.

[0061] Before laser direct writing grayscale lithography, the photoresist is baked to remove the solvent in the photoresist and enhance the adhesion of the photoresist to the substrate. In addition, during baking, the photoresist molecules undergo thermal motion, eliminating bubbles and gaps, making the glue layer more uniform and dense, and stabilizing the performance of the photoresist.

[0062] In this step, the baking temperature is lower than the reflow temperature. The temperature is controlled within 100 degrees Celsius. Preferably, the temperature is adjusted in stages, for example, preheating for 15 minutes at a temperature between 50-75 degrees Celsius, followed by heating for 20-30 minutes at a temperature between 80-100 degrees Celsius. This arrangement can further improve the molding quality of the photoresist.

[0063] In another embodiment of the present application, step S1 further includes measuring the stress of the first curved surface; step S2 further includes measuring the stress of the second curved surface. After step S5, an inspection step is further included: comparing the stress of the second curved surface with the stress of the first curved surface. If the stress of the second curved surface is less than the stress of the first curved surface, the product is defective; if the stress is greater than or equal to the stress of the first curved surface, the product is qualified.

[0064] By testing the surface stress before and after reflow, changes in the workpiece's properties can be monitored, facilitating subsequent process optimization and improvement. Finally, the workpiece is inspected to ensure the stress on the second curved surface meets design requirements, ensuring sufficient strength for subsequent microlens production and ensuring the template's ability to be laminated multiple times.

[0065] In another embodiment of the present application, step S1 further includes measuring the roughness of the first curved surface; step S2 further includes measuring the roughness of the second curved surface. After step S5, the process further includes comparing the roughness of the second curved surface with the roughness of the first curved surface. If the roughness of the second curved surface is greater than that of the first curved surface, the product is defective; if the roughness is less than or equal to that of the first curved surface, the product is qualified.

[0066] By testing the surface roughness before and after reflow, changes in the workpiece's characteristics can be monitored, facilitating subsequent process optimization and improvement. Finally, the workpiece is inspected to ensure that the roughness of the second curved surface meets design requirements, ensuring sufficient precision in subsequent microlens production and guaranteeing the quality of the finished microlens.

[0067] The following describes a method for preparing an imprint template provided by this application, using experimental equipment and parameters:

[0068] A silicon substrate is selected, for example, a 2-inch silicon substrate with a diameter of 50.8±0.3mm, a thickness of 500±15um, a crystal orientation of P(100), and a resistivity of 1-10Ω·cm.

[0069] The silicon substrate was cleaned by ultrasonic cleaning using acetone, isopropyl alcohol, and deionized water.

[0070] Use a coating machine to evenly coat photoresist (preferably AZ4562) on the silicon substrate at a rotation speed of 1200 r / min and a coating thickness of 11 μm.

[0071] The silicon substrate (workpiece) evenly coated with photoresist was transferred to a hot plate and pre-baked: first baked at 65°C for 15 minutes, and then baked at 95°C for 25 minutes.

[0072] The workpiece was transferred to a lithography machine for laser direct writing grayscale lithography. The exposure design surface was an aspheric lens with a diameter of d = 220 μm and a height of s = 7.5 μm.

[0073] After photolithography, the film was transferred to a beaker and developed for 4 minutes, and residual photoresist was blown off with a dropper every minute.

[0074] The entire workpiece surface was scanned using a laser confocal microscope to obtain the first curved surface. The roughness of the second curved surface was measured using a Park atomic force microscope. The stress of the second curved surface was measured using a thin film stress meter.

[0075] The workpiece was transferred to an oven for high-temperature reflow, with the temperature set to 250°C and the reflow time being 10 minutes.

[0076] The entire workpiece surface is scanned using a laser confocal microscope to obtain the second curved surface.

[0077] The roughness of the second curved surface was measured using a Park atomic force microscope.

[0078] The stress of the second curved surface is measured by a thin film stress meter.

[0079] When the second curved surface does not conform to the designed surface shape, the workpiece is transferred to a photolithography machine and steps are performed until the second curved surface conforms to the designed surface shape.

[0080] Figures 4 and 5 The data of surface roughness before and after the imprint template was heated in an oven at 250℃ for 10 minutes. Figure 4 The left side is a picture of the first curved surface under an atomic force microscope. Figure 4 The right side is the roughness curve distributed along the X-axis; the average roughness Ra is 21.757nm. Figure 5 The left side is a picture of the second curved surface under an atomic force microscope. Figure 5 The right side is a roughness curve distributed along the X-axis; the average roughness Ra is 2.141nm.

[0081] By reading Figure 4 and Figure 5 From the roughness data, we can see that after thermal reflow, the average surface roughness Ra of the curved surface is reduced from about 21.757nm to about 2.141nm. This shows that thermal reflow can quickly and effectively reduce surface roughness.

[0082] Figures 6 and 7 These are the stress data of the surface before and after the imprinted template was refluxed in an oven at 250°C for 10 minutes. Figure 6 The right side is a picture of the first curved surface under the thin film stress meter. Figure 6 The left side is the stress diagram of the first surface along the X-axis; based on the stress data, the average stress value is 3.715 MPa. Figure 7 The right side is a picture of the second curved surface under the thin film stress meter. Figure 7 The left side is the stress diagram distributed along the X-axis; based on the stress data, the average stress value is 9.225 MPa.

[0083] Comparing the stress data above shows that after thermal reflow, the photoresist surface stress increases from approximately 3.715 MPa to approximately 9.225 MPa. This demonstrates that thermal reflow enhances the strength of the photoresist surface, allowing it to withstand more molding cycles.

[0084] The above description is only a preferred embodiment of the present application and is not intended to limit the present application. Any modifications, equivalent replacements or improvements made within the spirit and principles of the present application should be included in the scope of protection of the present application.

Claims

1. A method for making an imprint template, characterized in that: include: S1: forming a first curved surface on a workpiece by laser direct writing grayscale lithography, and measuring surface data of the first curved surface; S2: baking in a hot reflow oven to obtain a second curved surface, and measuring surface data of the second curved surface; S3: Determine whether the second curved surface is consistent with the designed surface shape; if not, proceed to S4; if consistent, proceed to S5; S4: Calculate the exposure energy value according to the surface data of the second curved surface and the designed curved surface, and proceed to S1; S5: End the job.

2. The method for making an imprint template according to claim 1, wherein: In step S2, the baking temperature and time are fixed.

3. The method for making an imprint template according to claim 1, wherein: In step S2, the baking temperature is 150-300°C and the baking time is 1-10 minutes.

4. The method for making an imprint template according to claim 1, wherein: In step S2, the baking temperature is 200° to 280°C and the baking time is 6 to 10 minutes.

5. The method for making an imprint template according to claim 1, wherein: Before the S1, it also includes: S0: Spin-coating a photoresist on a silicon substrate, wherein the photoresist has a thickness of 8-15 μm, and then pre-baking the substrate at a temperature less than 100° C.

6. The method for making an imprint template according to claim 1, wherein: The step S1 further includes: measuring the stress of the first curved surface; the step S2 further includes: measuring the stress of the second curved surface and measuring the roughness of the second curved surface; after step S5, it also includes an inspection: comparing the stress of the second curved surface with the stress of the first curved surface, and comparing the roughness of the second curved surface with the roughness of the first curved surface. If the stress of the second curved surface is less than the stress of the first curved surface, or the roughness of the second curved surface is greater than the roughness of the first curved surface, it is a defective product.

7. The method for making an imprint template according to any one of claims 1 to 6, wherein: The step S4 is: The second curve and the design curve are divided into several equal parts in the X-axis direction according to the design accuracy, the height value of each equal-division node is obtained, the exposure energy value is calculated according to the height difference, and the process goes to S1: the second curved surface is exposed according to the exposure energy value corresponding to each equal-division node to form the first curved surface.

8. The method for making an imprint template according to claim 7, wherein: The calculated exposure energy value is: E (i+1) =E i -K*(H BX -H CX ) / H CX *E i , where H Bx and H Cx are the heights of the second curved surface and the designed surface at the same horizontal coordinate x position, E i is the energy value of the i-th exposure, E (i+1) is the energy value of the (i+1)th exposure, K is the energy difference coefficient, K∈(0,2].

9. The method for making an imprint template according to claim 8, wherein: K∈[0.8，1.2]。 10. An imprint template for preparing curved microlenses, characterized in that: The imprint template is prepared by the imprint template manufacturing method according to any one of claims 1 to 9.

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