Preparation method of PDMS film with micro-pyramid structure and PDMS film

Abstract

The invention provides a preparation method of a PDMS thin film with a micro-pyramid structure and the PDMS thin film, a substrate comprises a substrate body and an oxide layer located on the surface of the substrate body, a chromium metal layer is generated on the surface of the oxide layer through electron beam evaporation deposition, photoresist is spin-coated on the surface of the chromium metal layer, a photoresist layer is formed after drying, and the photoresist layer is formed after drying. A plurality of square hole patterns are generated on the surface of the photoresist layer through photoetching or ultraviolet exposure, an exposed area of the chromium metal layer is removed through wet etching, an exposed area of the oxide layer is removed through ion etching, and an exposed area of the substrate body is etched through wet etching, so that an inverted micro-pyramid structure with an oblique-cone-shaped groove is formed on the substrate body. And spin-coating a substrate with liquid PDMS, curing, and stripping to obtain the PDMS film with the micro-pyramid structure. According to the preparation method, the stability and accuracy of the formed micro-pyramid structure can be improved, the processing steps can be simplified, the production cost is reduced, and large-scale popularization and application of the PDMS thin film are facilitated.

Description

Technical Field

[0001] The invention relates to the technical field of micro-nano processing, and in particular to a method for preparing a PDMS film with a micro-pyramid structure and the PDMS film. Background Art

[0002] With the continuous development of science and technology, piezoresistive force sensors have been applied to health monitoring, wearable electronic devices, electronic skin, human-computer interaction and other fields. In the design of piezoresistive force sensors, pyramid-shaped PDMS, as an innovative active material structure, plays a vital role. Due to its unique geometric shape, the pyramid-shaped PDMS not only significantly increases the contact area with the electrode, thereby improving the detection sensitivity and range of the sensor, but also the stress concentration effect at its tip enables the sensor to produce a significant resistance change response to tiny pressure changes. In addition, the elastic properties of the PDMS material itself ensure that the sensor can quickly return to its original shape when subjected to pressure, reducing the hysteresis of the pressure response. Therefore, the pyramid-shaped PDMS structure plays an indispensable role in improving the performance of piezoresistive force sensors.

[0003] The steps generally adopted in the preparation method of the PDMS film with a micro-pyramid structure under the prior art are: firstly setting a photoresist layer, and depositing a metal layer on the surface after photolithography and development of the photoresist layer are completed. However, the following problems are faced when preparing the PDMS film by adopting the method of first setting the photoresist layer and then depositing the metal layer: during the deposition of the metal layer, since the photoresist layer at the bottom thereof is a non-planar concave-convex structure, the flatness and uniformity of the deposited metal layer are poor, and the deposition process of the metal layer requires a longer time than that of the planar structure; the overall structural stability of the photoresist layer after photolithography is low, and it is easy to fall off or fall off during the processing, resulting in reduced uniformity of the generated micro-pyramid structure; when the photoresist layer is removed, the stability and integrity of the metal layer are affected. The micro-pyramid structure of the PDMS film preparation method under the prior art has low stability and accuracy, and the overall preparation cost is high. Therefore, it is necessary to provide a PDMS film preparation method with low preparation cost, flexible and simple process steps, and the ability to improve the stability and accuracy of the micro-pyramid structure. Summary of the invention

[0004] In view of this, an embodiment of the present invention provides a method for preparing a PDMS film with a micro-pyramid structure to eliminate or improve one or more defects existing in the prior art.

[0005] On the one hand, the present invention provides a method for preparing a PDMS film having a micro-pyramid structure, the method comprising the following steps:

[0006] Step 1, the substrate includes a substrate body and an oxide layer located on the surface of the substrate, a chromium metal layer is formed on the surface of the oxide layer by electron beam evaporation deposition, a photoresist is spin-coated on the surface of the chromium metal layer, and a photoresist layer is formed after drying;

[0007] Step 2: generating a plurality of square hole patterns on the surface of the photoresist layer by photolithography or ultraviolet exposure. After the photoresist layer is developed, the photoresist layer in the area corresponding to the square hole pattern is removed, so that the chromium metal layer in the position corresponding to the removed area of ​​the photoresist layer is exposed;

[0008] Step 3, removing the chromium metal layer exposed in step 2 by wet etching, so that the oxide layer at a position corresponding to the removed area of ​​the chromium metal layer is exposed;

[0009] Step 4: removing the oxide layer exposed in step 3 by ion etching, so that the substrate body at a position corresponding to the removed area of ​​the oxide layer is exposed;

[0010] Step 5: etching the substrate body exposed in step 4 by wet etching to form an inverted micro-pyramid structure with an oblique cone-shaped groove on the substrate body;

[0011] Step 6: Spin-coat liquid PDMS onto the substrate, and peel off the PDMS material from the substrate after curing to obtain a PDMS film with a micro-pyramid structure.

[0012] In some embodiments of the present invention, the thickness of the chromium metal layer in step 1 is 8-12 nm, and the vacuum degree during the electron beam evaporation deposition process is 3e10 -4 Pa, and the deposition rate is 0.3 A / s.

[0013] In some embodiments of the present invention, the photoresist in step 2 is dried in a 110° C. environment for 90 seconds to form a photoresist layer with a thickness of 0.8 to 1.2 μm. The photoresist uses AZ5214 positive photoresist, and the spin coating speed of the photoresist is 5000 rpm and the spin coating time is 30 seconds.

[0014] In some embodiments of the present invention, the square hole pattern in step 2 is composed of a plurality of micrometer-scale square grids, and the developer used for developing the photoresist layer is ZX238, and the developing time is 50 seconds.

[0015] In some embodiments of the present invention, the chromium metal layer exposed in step two is removed by wet etching in step three, and the substrate in step two is placed in a chromium etching solution for 15 seconds. After the wet etching of the metal layer in step three is completed, it is immersed in an acetone solution for 10 minutes, and then cleaned with an isopropyl alcohol solution for 10 seconds to remove the remaining photoresist layer.

[0016] In some embodiments of the present invention, in step four, ion etching is performed to remove the oxide layer exposed in step three, and a mixed etching gas containing carbon tetrafluoride and oxygen is introduced during the ion etching process so that the mixed etching gas reacts with the oxide layer exposed in step three. The etching time of the ion etching is 20s, the etching power is 300W, and the ratio of carbon tetrafluoride to oxygen in the introduced mixed etching gas is 4:1.

[0017] In some embodiments of the present invention, the substrate body in step five is a silicon wafer with a surface crystal orientation of (100), which is placed in a silicon etching solution for 10 minutes so that the silicon etching solution is in contact with the substrate body exposed in step four. After the wet etching of the substrate body is completed, it is placed in the chromium etching solution and immersed for 30 seconds to remove the remaining chromium metal layer.

[0018] In some embodiments of the present invention, the chromium corrosion solution is prepared by constant temperature heating at 50° C. in a water bath, and contains 16% by mass of ammonium cerium nitrate, 4% by mass of glacial acetic acid and 80% by mass of deionized water.

[0019] In some embodiments of the present invention, the silicon etching solution contains 20% by mass of potassium hydroxide, 48% by mass of deionized water and 32% by mass of isopropanol. In the process of preparing the silicon etching solution, the potassium hydroxide is firstly completely dissolved in the deionized water, and then the isopropanol is added, and finally heated to 80°C.

[0020] In some embodiments of the present invention, the volume ratio of the liquid PDMS and the curing agent is 10:1, the spin coating speed of the liquid PDMS is 3000 rpm, and the curing of the liquid PDMS and the curing agent is to heat them to 80°C and keep them for 1 hour after vacuum treatment.

[0021] On the other hand, the present invention further provides a PDMS film with a micro-pyramid structure, wherein the PDMS film is a PDMS film with a micro-pyramid structure obtained based on the above-mentioned preparation method.

[0022] According to the method for preparing a PDMS film with a micro-pyramid structure in an embodiment of the present invention, the beneficial effects that can be obtained include at least:

[0023] The method of first depositing chromium metal and then setting a photoresist layer is adopted in the present invention, so that the overall structure of the metal layer can be made flatter and more uniform, which is beneficial to improving the stability of the chromium metal layer structure, so as to improve the accuracy and dimensional stability of the micro-pyramid structure; first depositing chromium metal and then setting a photoresist layer can also have a promoting effect on subsequent process steps; the chromium metal layer can be used as a sacrificial layer, and a set square hole pattern is generated by selective corrosion, which is beneficial to improving the flexibility and controllability of the overall preparation process; the chromium metal layer can be used as a sacrificial layer to remain stable in a high temperature environment, which is beneficial to reducing the influence of steps such as curing and baking in the preparation process on the substrate or material, thereby affecting the accuracy and stability of the micro-pyramid structure; the chromium metal layer can also maintain stable chemical properties, and will not have unnecessary chemical reactions with other materials or solutions in subsequent process steps, which is beneficial to improving the stability and controllability of the preparation process.

[0024] Additional advantages, purposes, and features of the present invention will be described in part in the following description, and will become apparent to those skilled in the art after studying the following, or may be learned from the practice of the present invention. The purposes and other advantages of the present invention may be achieved and obtained by the structures specifically indicated in the specification and the accompanying drawings.

[0025] Those skilled in the art will appreciate that the objectives and advantages that can be achieved with the present invention are not limited to the above specific description, and the above and other objectives that can be achieved by the present invention will be more clearly understood from the following detailed description. BRIEF DESCRIPTION OF THE DRAWINGS

[0026] The drawings described herein are used to provide a further understanding of the present invention, constitute a part of this application, and do not constitute a limitation of the present invention. The components in the drawings are not drawn to scale, but are only for illustrating the principles of the present invention. In order to facilitate the illustration and description of some parts of the present invention, the corresponding parts in the drawings may be enlarged, that is, they may become larger relative to other components in the exemplary device actually manufactured according to the present invention. In the drawings:

[0027] Figure 1 4 is a process flow chart of a method for preparing a PDMS film having a micro-pyramid structure in an embodiment of the present invention.

[0028] Figure 2 Schematic diagram of the processing flow of the method for preparing a PDMS film with a micro-pyramid structure in an embodiment of the present invention.

[0029] Figure 3 It is a structural schematic diagram of a photoresist layer from a top view in a method for preparing a PDMS film with a micro-pyramid structure in an embodiment of the present invention.

[0030] Figure 4Schematic diagram of the structure of the chromium metal layer from a top view in the method for preparing a PDMS film with a micro-pyramid structure in an embodiment of the present invention.

[0031] Figure 5 It is a schematic diagram of the inverted pyramid structure of a substrate in the method for preparing a PDMS film with a micro-pyramid structure in an embodiment of the present invention. DETAILED DESCRIPTION

[0032] In order to make the purpose, technical solution and advantages of the present invention more clearly understood, the present invention is further described in detail below in conjunction with the embodiments and the accompanying drawings. Here, the illustrative embodiments of the present invention and their descriptions are used to explain the present invention, but are not intended to limit the present invention.

[0033] It should also be noted that, in order to avoid obscuring the present invention due to unnecessary details, only structures and / or processing steps closely related to the solutions according to the present invention are shown in the accompanying drawings, while other details that are not closely related to the present invention are omitted.

[0034] It should be emphasized that the term “include / comprises” when used herein refers to the presence of features, elements, steps or components, but does not exclude the presence or addition of one or more other features, elements, steps or components.

[0035] It should also be noted that, unless otherwise specified, the term “connection” herein may refer not only to a direct connection but also to an indirect connection involving an intermediate.

[0036] Hereinafter, embodiments of the present invention will be described with reference to the accompanying drawings. In the accompanying drawings, the same reference numerals represent the same or similar components, or the same or similar steps.

[0037] The invention aims at the problems that during the preparation process of the PDMS film with a micro-pyramid structure, the deposition surface of the chromium metal layer is uneven, resulting in reduced stability of the chromium metal layer structure, making it difficult to ensure the accuracy and consistency of the micro-pyramid structure; the removal of the photoresist layer will affect the stability of the chromium metal layer structure, resulting in reduced stability of the micro-pyramid structure; the process cycle of removing the chromium metal layer is long, resulting in a high overall production cost; the PDMS film preparation method in the embodiment of the present invention adopts a method different from the prior art of first depositing chromium metal and then setting a photoresist layer, which can make the overall structure of the metal layer more flat and uniform, which is beneficial to improving the stability of the chromium metal layer structure, so as to improve the accuracy and dimensional stability of the micro-pyramid structure; first depositing chromium metal and then setting a photoresist layer can also promote subsequent process steps; the chromium metal layer can be used as a sacrificial layer, and a set square hole pattern is generated by selective corrosion, which is beneficial to improving the flexibility and controllability of the overall preparation process; the use of the chromium metal layer as a sacrificial layer can remain stable in a high temperature environment, which is beneficial to improving the stability and controllability of the preparation process.

[0038] Specifically, the present invention provides a method for preparing a PDMS film having a micro-pyramid structure, such as Figure 1 As shown, the following steps are included: Step 1: The substrate includes a substrate body and an oxide layer located on the surface thereof. The oxide layer can be an oxide film formed by natural reaction with oxygen, or can be a uniform oxide film for protecting the substrate generated by placing the substrate in oxygen for processing and reaction, such as Figure 2 As shown, a chromium metal layer is formed on the surface of the oxide layer by electron beam evaporation deposition. In the preparation method of the PDMS film with a micro-pyramid structure, unlike the preparation steps of first setting a photoresist layer and then setting a metal layer in the prior art, the preparation method of the PDMS film in the embodiment of the invention adopts the preparation steps of first depositing a chromium metal layer and then setting a photoresist layer.

[0039] In the prior art, since the photoresist layer is set first and then the metal layer is deposited, the stability and flatness of the deposited metal layer are poor due to the non-planar structure of the bottom surface of the ion or molecular deposition during the metal layer deposition process. In addition, the high temperature environment during the deposition process is likely to affect the structure of the photoresist layer, thereby affecting the clarity of the photolithographic pattern on the photoresist layer. However, the preparation steps of first depositing the metal layer and then setting the photoresist layer not only prevent the high temperature during the deposition process from affecting the photoresist layer, but also can promote the subsequent photolithography and etching processes.

[0040] For example, a chromium metal layer is arranged between a photoresist layer and an oxide layer of a substrate, which can improve the stability of the photoresist layer and enhance its adhesion ability on the surface of the substrate. When a method of first setting a photoresist layer and then depositing a metal layer is adopted, the structure retained by the photoresist layer after photolithography is a mutually separated square array structure, and the photoresist square block structure is only connected to the substrate through the bottom surface, and the stability is poor. During the preparation process, the photoresist square block structure is easy to fall off during the processing, resulting in the inability to generate a corresponding square hole pattern at the corresponding position. In the PDMS film preparation method in the embodiment of the invention, the structure retained by the photoresist layer after photolithography is a grid structure with square holes, and the photoresist layers of the grid structure are interconnected as an integral structure, and the bottom is in contact with the chromium metal. The grid structure has better stability than the separated square array structure, which avoids the photoresist layer structure from falling off during the processing, thereby affecting the accuracy and consistency of the micro-pyramid structure.

[0041] The above-mentioned preparation method of first depositing a chromium metal layer and then setting a photoresist layer makes the overall structure of the metal layer more flat and uniform, which is beneficial to improving the stability of the chromium metal layer structure, so as to enhance the accuracy and dimensional stability of the micro-pyramid structure. First depositing chromium metal and then setting a photoresist layer can also promote subsequent process steps. For example, the chromium metal layer can be used as a sacrificial layer to generate a set square hole pattern through selective corrosion, which is beneficial to improving the flexibility and controllability of the overall preparation process.

[0042] The reason for choosing to deposit a chromium metal layer is that chromium metal has good physical properties. Chromium metal has a high melting point and good thermal stability. Therefore, in the preparation process of the PDMS film, the chromium metal layer can withstand high temperatures without deformation or melting, so as to ensure the integrity of its own structure and pattern, which is conducive to adapting to the steps of curing and baking that require high temperature treatment in the preparation process; and chromium metal also has good chemical stability, and it is not easy to chemically change with other substances. Therefore, in the preparation and subsequent treatment of the PDMS film, the chromium metal layer will not react with other substances or solutions, which can effectively avoid contamination and consumption of the substrate during the preparation process, which is conducive to ensuring the stability and controllability of the preparation process. For example, the chromium metal layer itself has a certain acid resistance. By plating or depositing chromium on the surface of the substrate, the substrate can be made acid-resistant, which can prevent the substrate from being corroded and consumed by other types of acidic liquids such as photoresist or developer during the processing.

[0043] In the preparation process of PDMS film, the methods for removing the sacrificial layer mainly include wet etching and dry etching. Dry etching mainly removes the sacrificial layer through reactive ion etching or ion beam etching. The etching process requires special etching equipment, and the etching process involved is relatively complicated, resulting in an increase in the overall production cost. Using chromium metal as the sacrificial layer can use the corresponding chromium corrosion solution for wet etching, which can remove the sacrificial layer relatively quickly while maintaining a high level of graphic accuracy, which is conducive to simplifying the steps of the sacrificial layer etching process, thereby reducing the overall production cost.

[0044] The chromium metal layer is deposited on the substrate surface by electron beam evaporation deposition technology, and its thickness can be set to 8 to 12 nanometers, for example, 9, 10, 11, and 12 nanometers. The chromium metal layer is deposited on the flat substrate surface, which is conducive to the attachment and deposition of ions during the deposition process. During the deposition process of the chromium metal layer, the chromium metal material is directly heated by an electron beam under vacuum conditions to vaporize the metal chromium and transport it to the substrate, and finally condense on the substrate to form a thin film. During the deposition process, the chromium metal layer is placed in a vacuum degree of 3e10 -4 In the high vacuum environment of Pa, atoms or molecules basically do not interact with other gas molecules during flight, which is conducive to the formation of high-quality chromium metal film, and the energy and focus of the electron beam can be controlled by adjusting the voltage and magnetic field of the electron gun, so the deposition process can be precisely controlled, and the deposition rate of the chromium metal layer can be controlled to be maintained at 0.2-0.4A / s, for example, 0.2A / s, 0.3A / s or 0.4A / s.

[0045] After the deposition of the chromium metal layer is completed, a photoresist is spin-coated on the surface of the chromium metal layer, and the spin-coated photoresist is dried to form a photoresist layer. Specifically, the photoresist is first spin-coated on the top of the chromium metal layer. During the spin-coating process, the rotation speed of the substrate with the chromium metal layer is 5000rpm, and the spin-coating time is 30s, so that the photoresist can be evenly distributed on the top of the chromium metal layer, and the photoresist and the surface of the chromium metal layer can be fully contacted. Then, the substrate is placed on a 110°C hot stage for drying for 90s to obtain a photoresist layer with a thickness of 0.8 to 1.2μm, for example, 0.8μm, 0.9μm, 1.0μm, 1.1μm, 1.2μm. It can be understood that the thickness of the photoresist layer can be adjusted by adjusting the rotation speed and spin-coating time of the substrate during the photoresist spin-coating process. By reducing the rotation speed or increasing the spin-coating time, the remaining photoresist on the substrate is increased to increase the thickness of the photoresist layer. By increasing the rotation speed or reducing the spin-coating time, the remaining photoresist on the substrate is reduced to reduce the thickness of the photoresist layer.

[0046] Step 2: generate a plurality of square hole patterns on the surface of the photoresist layer by photolithography or ultraviolet exposure, such as Figure 3As shown, after the photoresist layer is developed, the photoresist layer in the area corresponding to the square hole pattern is removed, so that the chromium metal layer at the position corresponding to the removed area of ​​the photoresist layer is exposed. After completion, the substrate is placed in a ZX238 developer for development for 50 seconds, and then washed with deionized water for 10 seconds, so that the photoresist layer inside the square grid is completely removed.

[0047] The photolithography process of the above-mentioned photoresist layer includes exposure, development, etching and other processes. The photolithography process is a technology that transfers the square hole pattern on the mask to the substrate through the photoresist under the action of light. Among them, the exposure process can adopt ultraviolet exposure technology. Since the wavelength of ultraviolet light is short, it can reduce the diffraction effect of light, and can achieve higher pattern resolution and clarity in the photolithography process of the substrate. Therefore, the ultraviolet exposure technology can more accurately depict the required square hole pattern, so that the size of the generated square hole pattern is smaller, and the corresponding micro-pyramid structure can be generated; in addition, the ultraviolet light source has a higher energy density, so that the photoresist can be exposed and cured more quickly, which can improve production efficiency and reduce energy consumption in the production process. The stability and reliability of the ultraviolet light source are conducive to improving the stability and reliability of the photolithography process in the preparation process, and can also significantly reduce production costs.

[0048] Positive photoresist can be used as the photoresist. Compared with negative photoresist, positive photoresist has a faster etching rate. Since positive photoresist has higher resolution and higher lateral protection performance, it is easier to achieve high resolution and high precision by controlling the solvent and etching conditions. Positive photoresist has better viscosity and fluidity than negative photoresist, which makes the stability and consistency of the lithography effect achieved in the preparation process better, and the preparation process of positive photoresist is simpler, which is conducive to reducing production costs.

[0049] Among them, the model of positive photoresist that can be used is AZ5214. AZ5214 positive photoresist can be applied to the thickness range of the photoresist layer of 1μm to 150μm, which is conducive to meeting different process requirements and ensuring the stripping effect of the photoresist layer; AZ5214 positive photoresist has high sensitivity and can complete exposure in a short time, which is conducive to improving production efficiency; AZ5214 positive photoresist has high adhesion, which can make the photoresist layer more adherent to the surface of the chromium metal layer, reduce the possibility of falling off, and is conducive to improving the stability of the photoresist layer. AZ5214 positive photoresist has a variety of different viscosity options and can be applied to different process requirements. Including but not limited to this, according to the actual preparation process, photoresists can also use AZ1500, S1800 and BCI-3511 types of photoresists.

[0050] The developer in the development process of the above-mentioned photolithography process can be ZX238 developer, which has high stability and maturity in the photolithography process, is conducive to reducing development abnormalities, improving production efficiency and product quality; in actual applications, ZX238 developer is used in conjunction with positive photoresist to significantly improve the clarity of the photolithography pattern. Including but not limited to this, according to the actual preparation method, the developer can also use other types of developers such as AZ300MIF or AZ400K that have similar effects to ZX238 developer.

[0051] Step 3: Remove the chromium metal layer exposed in step 2 by wet etching, such as Figure 4 As shown, the substrate is placed in a chromium corrosion solution for 15 seconds so that the oxide layer corresponding to the removed area of ​​the chromium metal layer is exposed. The reaction time of the substrate in the chromium corrosion solution is configured so that the chromium metal layer in the area relative to the square pattern just reacts completely. On the one hand, since the lateral structure of the chromium metal layer is an interconnected layered structure, the substrate is placed in the chromium corrosion solution for a long time, which will cause the chromium metal layer structure around the square pattern to be corroded after contacting the chromium corrosion solution, so that the accuracy and uniformity of the square hole pattern generated by the chromium metal layer are reduced; on the other hand, if the substrate is placed in the chromium corrosion solution for too short a time, the chromium metal layer in the area relative to the square grid pattern will not be completely corroded, thereby affecting the accuracy and uniformity of the square hole pattern generated on the chromium metal layer. After the wet etching of the chromium metal layer is completed, it is washed with deionized water for 30 seconds to remove the chromium corrosion solution remaining on the surface of the substrate, which can avoid liquid contamination during the preparation process.

[0052] After the wet etching of the chromium metal layer is completed, the remaining photoresist layer is removed, specifically, the substrate is placed in an acetone solution and soaked for 10 minutes, and then washed with an isopropanol solution for 10 seconds to remove the remaining photoresist layer. In this process, the photoresist layer reacts after contacting the acetone solution, and the photoresist layer is completely removed, so that the chromium metal layer with a square hole structure is completely exposed. In the process of removing the photoresist layer, the chromium metal layer is located on the bottom surface of the photoresist layer, which can provide a certain protection effect for the substrate and prevent the solution from reacting with the substrate unnecessarily.

[0053] The above-mentioned chromium corrosion solution is prepared under constant temperature heating at 50°C in a water bath, and the chromium corrosion solution contains 16% by mass of ammonium cerium nitrate, 4% by mass of glacial acetic acid and 80% by mass of deionized water. Among them, ammonium cerium nitrate is mainly used as a strong oxidant and etchant, which can significantly increase the etching reaction rate, making the surface of the etched substrate smooth and bright, which is beneficial to improving the etching quality and promoting the etching effect; glacial acetic acid is mainly used as a solvent and regulator, which can effectively dissolve trivalent chromium and has a promoting effect on adjusting the pH of the solution. It can be understood that the content of ammonium cerium nitrate and glacial acetic acid in the chromium corrosion solution is determined according to the specific formula and process requirements. During the preparation process, the ratio of ammonium cerium nitrate, glacial acetic acid and deionized water in the chromium corrosion solution can be adjusted according to actual conditions.

[0054] Step 4: Remove the oxide layer exposed in step 3 by ion etching, and place the substrate obtained in the above step into reactive ions for etching so that the substrate body at a position corresponding to the removed area of ​​the oxide layer is exposed. During the etching process, carbon tetrafluoride and oxygen are introduced in a ratio of 4:1, and the ion etching power is 300 W, and the etching time is 20 s. The chromium metal layer has a high hardness, so the chromium metal layer can protect the oxide layer underneath it.

[0055] Optionally, the substrate oxide layer corresponding to the silicon wafer used in the substrate is silicon oxide. In this case, the silicon wafer below the silicon oxide exposes a square grid pattern. The reaction process between the gas and the substrate during the ion etching process is:

[0056] CF 4 +e→CF 3 +F free radical +e

[0057] SiO 2 +4F→SiF 4 +0 2

[0058] Si+4F→SiF 4

[0059] Introducing carbon tetrafluoride gas during the etching process can significantly increase the rate of ion etching. The free radicals generated by the decomposition of carbon tetrafluoride in plasma have strong chemical activity. These free radicals can react rapidly with the surface of the silicon wafer, thereby significantly accelerating the etching speed. The large amount of energy released during the decomposition of carbon tetrafluoride is also conducive to the further progress of the etching reaction. Using carbon tetrafluoride for ion etching makes the ion etching process more precise, which can reduce surface damage and defects, so that the etched substrate surface has better surface quality.

[0060] Furthermore, by adjusting the ratio of carbon tetrafluoride to oxygen, the preferential etching of the silicon oxide layer on the silicon wafer can be achieved. For example, by introducing carbon tetrafluoride and oxygen in a ratio of 4:1, the etching process can be further optimized. Oxygen plays an auxiliary role in etching. It can react with the free radicals generated by the decomposition of carbon tetrafluoride to generate more active substances, thereby enhancing the etching effect. At the same time, the presence of oxygen can also help remove the by-products generated during the etching process, keep the etching environment clean, and help ensure the uniformity and consistency of etching; the combination of carbon tetrafluoride and oxygen also has excellent physical and chemical properties. Carbon tetrafluoride has the characteristics of high cleanliness, no residue, and good volatility, which enables it to quickly complete the decontamination task during the etching process without corroding the surface of the silicon wafer. The addition of oxygen can further enhance the decontamination ability, which is conducive to ensuring the cleanliness of the surface of the silicon wafer after etching.

[0061] During the ion etching process, the etching power will directly affect the etching rate, etching selectivity and surface quality after etching. The etching power determines the energy of ions bombarding the silicon wafer surface, which in turn affects the etching depth and uniformity. For example, the etching power in the ion etching process can be 300W to obtain the best etching effect on the silicon oxide layer on the silicon wafer surface in step four.

[0062] Step 5: Wet-etch the substrate body exposed in step 4 to form an inverted micro-pyramid structure with an oblique cone-shaped groove on the substrate body, and wet-etch to generate an inverted pyramid structure in the area corresponding to the square hole pattern on the substrate surface. The substrate is placed in a silicon etching solution heated to 80° C. for 10 minutes to remove the oxide layer and the substrate body exposed by the chromium metal layer. During the wet etching process, the silicon wafer in the area staggered with the square grid pattern of the chromium metal layer is retained because it is wrapped by the chromium metal layer and the oxide layer and is not in direct contact with the silicon etching solution. Figure 5 As shown, the silicon etching solution contacts and reacts with the silicon wafer in the area corresponding to the square checkered pattern exposed by the chromium metal layer.

[0063] During the reaction of the silicon etching solution, the etching rates of the silicon etching solution for different crystal plane directions of the silicon wafer are very different. For example, the etching rate ratio in the potassium hydroxide solution is (100):(110):(111)=400:200:1. Therefore, for the silicon wafer with a surface having a (100) crystal orientation, the angle between the (111) crystal orientation plane and the (100) crystal orientation plane is 54.74°, and the etching rate in the (111) crystal orientation direction is much lower than that in the (100) crystal orientation direction. After the wet etching is completed, an inverted pyramid structure with oblique cone-shaped grooves is formed on the surface of the silicon wafer.

[0064] The silicon etching solution contains 20% potassium hydroxide by mass, 48% deionized water by mass and 32% isopropanol by mass. In the process of preparing the silicon etching solution, the potassium hydroxide is first completely dissolved in the deionized water, and then the isopropanol is added, and finally heated to 80°C. Potassium hydroxide is mainly used as an etchant. Potassium hydroxide has strong alkalinity and can react with oxides or impurities on the surface of the silicon wafer to generate salt and water, which is conducive to the rapid removal of organic matter, metal ions, oxides and other impurities on the surface of the silicon wafer; potassium hydroxide as an etchant can react with silicon to form a number of the above-mentioned inverted pyramid structures. The substrate is placed in the silicon etching solution for 30 seconds to remove the remaining chromium metal layer on the surface of the substrate, and a silicon wafer with an outer silicon oxide layer and an inverted pyramid structure is obtained as a silicon mold used in the preparation of PDMS film.

[0065] During the preparation of PDMS film, chromium metal can be used as a sacrificial layer, and a set square hole pattern is generated through selective corrosion, making the preparation method of PDMS film flexible and controllable. The chromium metal layer has good physical and chemical properties and is relatively easy to remove. The chromium metal layer structure can be quickly and completely removed using a specific corrosion solution, so that metallic chromium can be effectively used as a sacrificial layer material in the preparation process, assisting in the preparation of micro-pyramid structures.

[0066] Step 6: Evenly mix the liquid PDMS and the curing agent in a volume ratio of 10:1, and spin-coat it on the silicon mold obtained in the above step at 3000rpm. After vacuum treatment, place it in an environment of 80℃ and heat it for 1h to solidify the PDMS. Finally, peel off the PDMS from the silicon mold to obtain a PDMS film with an inverted pyramid structure. Among them, the curing agent used in the preparation process can be an organic peroxide or hydrogen silicone oil. The type of curing agent used can be selected according to the actual type of PDMS film. For example, the organic peroxide type curing agent can effectively promote the cross-linking reaction of dimethylsiloxane, so it is suitable for preparing PDMS film after mixing with liquid PDMS of polydimethylsiloxane type; hydrogen silicone oil type curing agent can react with vinyl siloxane under specific conditions to achieve film curing, so it is suitable for preparing PDMS film after mixing with liquid PDMS of vinyl siloxane type.

[0067] Furthermore, the mixing ratio of liquid PDMS to curing agent of 10:1 is a common standard for preparing PDMS film, which can ensure that PDMS has good performance and stability after curing. It is understandable that the mixing ratio of liquid PDMS to curing agent can also be adjusted to 10:2 or 10:3, etc., depending on the specific PDMS type and curing agent type, as well as the specific requirements of the prepared PDMS film.

[0068] According to the method for preparing a PDMS film having a micro-pyramid structure and the PDMS film in the embodiment of the present invention, the beneficial effects that can be achieved include at least:

[0069] (1) In the preparation method of the PDMS film with a micro-pyramid structure, a preparation method of first depositing a chromium metal layer and then setting a photoresist layer is adopted, so that the structure of the photoresist layer after photolithography is more stable, and the structure of the photoresist layer can be prevented from falling off during the preparation process, which is conducive to ensuring the accuracy and consistency of the micro-pyramid structure;

[0070] (2) In the method for preparing a PDMS film with a micro-pyramid structure, a preparation method of first depositing a chromium metal layer and then setting a photoresist layer is adopted, so that the deposited chromium metal layer has good flatness and uniformity, which is beneficial to improving the stability of the chromium metal layer structure. In the subsequent step of removing the photoresist layer, the chromium metal layer is completely located under the photoresist layer, and the stability of its structure will not be affected.

[0071] (3) In the method for preparing a PDMS film with a micro-pyramid structure, a chromium metal layer is used as a sacrificial layer in the preparation process. The stable physical and chemical properties of the chromium metal layer can provide good protection for the substrate during the preparation process, which is beneficial to reducing the influence of adverse factors on the accuracy and stability of the micro-pyramid structure.

[0072] (4) In the method for preparing a PDMS film with a micro-pyramid structure, a chromium metal layer is used as a sacrificial layer in the preparation process. The chromium metal reacts fully to a specific chromium corrosion solution and the reaction conditions are simple, so that the sacrificial layer can be quickly and conveniently removed during the preparation process, which is conducive to simplifying the processing technology and reducing production costs.

[0073] It should be clear that the present invention is not limited to the specific configuration and processing described above and shown in the figures. For the sake of simplicity, a detailed description of the known method is omitted here. In the above embodiments, several specific steps are described and shown as examples. However, the method process of the present invention is not limited to the specific steps described and shown, and those skilled in the art can make various changes, modifications and additions, or change the order between the steps after understanding the spirit of the present invention.

[0074] In the present invention, features described and / or illustrated for one embodiment may be used in the same or similar manner in one or more other embodiments, and / or combined with features of other embodiments or replace features of other embodiments.

[0075] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. For those skilled in the art, the embodiments of the present invention may have various modifications and variations. Any modification, equivalent replacement, improvement, etc. made within the spirit and principle of the present invention shall be included in the protection scope of the present invention.

Claims

1. A method for preparing a PDMS film having a micro-pyramid structure, characterized in that: The following steps are involved: Step 1, the substrate includes a substrate body and an oxide layer located on the surface of the substrate, a chromium metal layer is formed on the surface of the oxide layer by electron beam evaporation deposition, a photoresist is spin-coated on the surface of the chromium metal layer, and a photoresist layer is formed after drying; Step 2: generating a plurality of square hole patterns on the surface of the photoresist layer by photolithography or ultraviolet exposure. After the photoresist layer is developed, the photoresist layer in the area corresponding to the square hole pattern is removed, so that the chromium metal layer in the position corresponding to the removed area of ​​the photoresist layer is exposed; Step 3, removing the chromium metal layer exposed in step 2 by wet etching, so that the oxide layer at a position corresponding to the removed area of ​​the chromium metal layer is exposed; Step 4: removing the oxide layer exposed in step 3 by ion etching, so that the substrate body at a position corresponding to the removed area of ​​the oxide layer is exposed; Step 5: etching the substrate body exposed in step 4 by wet etching to form an inverted micro-pyramid structure with an oblique cone-shaped groove on the substrate body; Step 6: Spin-coat liquid PDMS onto the substrate, and peel off the PDMS material from the substrate after curing to obtain a PDMS film with a micro-pyramid structure.

2. The method for preparing a PDMS film with a micro-pyramid structure according to claim 1, wherein: The thickness of the chromium metal layer in step 1 is 8-12 nm, and the vacuum degree during the electron beam evaporation deposition process is 3e10 -4 Pa, and the deposition rate is 0.3 A / s.

3. The method for preparing a PDMS film with a micro-pyramid structure according to claim 1, wherein: The photoresist in step 2 is dried in an environment of 110° C. for 90 seconds to form the photoresist layer with a thickness of 0.8 to 1.2 μm; The photoresist adopts AZ5214 positive photoresist, and the spin coating speed of the photoresist is 5000 rpm and the spin coating time is 30 s.

4. The method for preparing a PDMS film having a micro-pyramid structure according to claim 1, wherein: The square hole pattern in step 2 is composed of a plurality of micrometer-scale square grids; The developer used for developing the photoresist layer is ZX238, and the developing time is 50s.

5. The method for preparing a PDMS film with a micro-pyramid structure according to claim 4, wherein: In step 3, the chromium metal layer exposed in step 2 is removed by wet etching, which is to place the substrate in step 2 in a chromium etching solution for 15 seconds; After the wet etching of the metal layer in step 3 is completed, it is immersed in an acetone solution for 10 minutes and then cleaned with an isopropanol solution for 10 seconds to remove the remaining photoresist layer.

6. The method for preparing a PDMS film having a micro-pyramid structure according to claim 5, wherein: In step 4, the oxide layer exposed in step 3 is removed by ion etching, wherein a mixed etching gas containing carbon tetrafluoride and oxygen is introduced during the ion etching process so that the mixed etching gas reacts with the oxide layer exposed in step 3; The etching time of ion etching is 20s, and the etching power is 300W; The ratio of carbon tetrafluoride to oxygen in the mixed etching gas introduced is 4:

1.

7. The method for preparing a PDMS film having a micro-pyramid structure according to claim 6, wherein: In step 5, the substrate body is a silicon wafer with a surface crystal orientation of (100), which is placed in a silicon etching solution for 10 minutes so that the silicon etching solution contacts and reacts with the substrate body exposed in step 4; After the wet etching of the substrate is completed, the substrate is immersed in the chromium etching solution for 30 seconds to remove the remaining chromium metal layer.

8. The method for preparing a PDMS film having a micro-pyramid structure according to claim 7, wherein: The chromium corrosion solution is prepared by heating a water bath at a constant temperature of 50° C., and contains 16% by mass of ammonium cerium nitrate, 4% by mass of glacial acetic acid and 80% by mass of deionized water; The silicon etching solution contains 20% by mass of potassium hydroxide, 48% by mass of deionized water and 32% by mass of isopropanol. In the process of preparing the silicon etching solution, the potassium hydroxide is firstly completely dissolved in the deionized water, and then the isopropanol is added, and finally heated to 80°C.

9. The method for preparing a PDMS film having a micro-pyramid structure according to claim 1, wherein: The volume ratio of the liquid PDMS to the curing agent is 10:1; The spin coating speed of the liquid PDMS is 3000 rpm; The curing of the liquid PDMS and the curing agent is performed by vacuum treatment and then heating to 80° C. and maintaining the temperature for 1 hour.

10. A PDMS film having a micro-pyramid structure, characterized in that: The PDMS film is a PDMS film having a micro-pyramid structure obtained by the preparation method according to any one of claims 1 to 9.

Images