A method for coating photoresist on a large-aperture, anisotropic single-crystal silicon diffraction element

Abstract

The application discloses a large-diameter single-crystal silicon diffraction element photoresist coating method, and solves the problems of small application range, poor coating quality and easy peeling of the photoresist coating method, and specifically comprises the following steps: step 1, surface state screening; step 2, element surface cleaning; step 3, tackifier coating; step 4, photoresist coating; and step 5, quality detection. The tackifier is coated before the photoresist coating, and the main action mechanism of the tackifier is to replace the hydrophilic Si-HO group carried by the oxidation layer on the surface of the single-crystal silicon substrate, so that the single-crystal silicon substrate changes from hydrophilic to hydrophobic, the adhesion between the single-crystal silicon substrate and the photoresist is increased, the phenomenon of peeling is avoided, the firmness of the photoresist layer is improved, and the service life of the photoresist layer is prolonged.

Description

TECHNICAL FIELD

[0001] The present application relates to a photoresist coating method, in particular to a photoresist coating method for large-aperture irregular monocrystalline silicon diffractive element. BACKGROUND

[0002] Monocrystalline silicon diffractive optical element is an important type of element in the field of optics. Compared with traditional catadioptric elements, the optical power of large-aperture monocrystalline silicon diffractive element is entirely introduced by the diffractive structure, rather than relying on the curvature change of the surface. Large-aperture monocrystalline silicon diffractive element has the advantages of small volume, light weight, and low cost, and is widely used in space remote sensing, spectral measurement, optical communication, and other fields.

[0003] Photoresist coating method is one of the core processes in the manufacturing process of optical diffractive elements, including cleaning, photoresist coating, and post-baking of diffractive elements. The photoresist is uniformly coated on the surface of large-aperture diffractive element, which is used for subsequent exposure pattern transfer.

[0004] The existing photoresist coating method usually adopts a rotary coating method. The coating machine rotates at low speed, and the nozzle sprays photoresist on the center of the element surface. When the photoresist usage reaches the preset value, the nozzle stops spraying photoresist, and the coating machine drives the element to perform high-speed circular motion. During the high-speed rotation of the element, the photoresist is coated on the surface of the element by centrifugal force. However, due to the large difference in centrifugal force at different points on the circle, the thickness of the photoresist coating on the surface of the element is different, which seriously affects the coating quality of the photoresist. At the same time, the existing coating method is only suitable for circular, rectangular, and square optical elements. For regular hexagons, the existing coating method is difficult to meet the use requirements.

[0005] In addition, for the single crystal silicon diffraction element, under normal conditions, it does not react with oxygen to produce silicon oxide, but when the single crystal silicon is exposed to a humid, high temperature or strong oxidizing environment for a long time, or is cleaned in a concentrated sulfuric acid and hydrogen peroxide mixture, a native oxide layer with a thickness of about 1-2 nm is formed on the surface, which is also called a silicon oxide passivation layer. The groups on the surface of the silicon oxide exist in two forms, one is a hydrophilic Si-HO group, and the other is a hydrophobic SI-O group. Generally, the surface of the silicon oxide will produce a hydrophobic SI-O group only under high pressure and high temperature conditions, and the conventional silicon oxide surface is generally a hydrophilic Si-HO group. The presence of the hydrophilic Si-HO group will make the adhesion between the photoresist and the element substrate poor, which will further cause the photoresist to be easily delaminated. Controlling the generation of the oxide layer is a solution, but from the actual product development process, this measure is difficult to implement. First, the polishing of the element substrate is a long-term and repeated process, and the polishing is carried out in an aqueous environment, so it is difficult to avoid the generation of the oxide layer, and it is also difficult to meet the requirements of constant temperature and dryness in the storage environment. Second, cleaning the single crystal silicon substrate in a concentrated sulfuric acid and hydrogen peroxide mixture is an effective means to remove surface organic matter. If this cleaning process is not performed, the organic matter on the surface will cause defects in the element surface coating.

[0006] Therefore, there is an urgent need for a single crystal silicon diffraction element photoresist coating method with wide application range, high coating quality and firm glue layer. SUMMARY

[0007] The purpose of the present application is to provide a large-aperture irregular single crystal silicon diffraction element photoresist coating method to solve the technical problems of the existing coating method, such as small application range, poor coating quality and easy delamination of the glue layer.

[0008] In order to achieve the above-mentioned purpose, the present application adopts the following technical solutions:

[0009] A large-aperture irregular single crystal silicon diffraction element photoresist coating method, characterized in that it comprises the following steps:

[0010] Step 1, surface state screening;

[0011] Screening the surface state qualified photoresist coating element; the photoresist coating element is an irregular flat diffraction element with an aperture D≥300mm;

[0012] Step 2, cleaning the surface of the element;

[0013] The screened photoresist coating element is loaded into a cleaning tool for cleaning;

[0014] Step 3, adhesion promoter coating;

[0015] The cleaned element to be coated is loaded into a coating tool, fixed and adsorbed on a coating machine, the coating machine applies an adhesion promoter to the surface of the element to be coated, and then the element to be coated with the coating tool is subjected to first baking;

[0016] Step 4, photoresist coating;

[0017] After the first baking, the element to be coated with the coating tool is fixed and adsorbed on the coating machine again, the coating machine applies photoresist to the surface of the adhesion promoter on the element to be coated, and then the element to be coated with the coating tool is subjected to second baking;

[0018] Step 5, quality detection;

[0019] The photoresist layer quality of the element to be coated after the second baking is detected, if the quality of the glue layer is unqualified, return to step 2, until the quality of the glue layer is qualified, complete the photoresist coating method.

[0020] Further, step 3 is specifically to load the cleaned element to be coated into a coating tool, adsorb the element to be coated on the corresponding position of the coating machine, then fix the coating tool on the coating machine, the nozzle of the coating machine drops the adhesion promoter in the form of a spiral line on the surface of the element to be coated, the coating machine drives the element to be coated with the coating tool to rotate, so that each point on the surface of the element to be coated can be evenly distributed with the adhesion promoter, then the coating tool is disassembled from the coating machine, and the element to be coated with the coating tool is subjected to first baking.

[0021] Further, in step 3, the coating tool includes an aluminum alloy disc and a plurality of buckles;

[0022] The aluminum alloy disc is provided with a mounting groove in the middle, which has a shape matching the outer shape of the element to be coated and is provided with a mounting gap;

[0023] The depth of the mounting groove is less than the thickness of the element to be coated, and the mounting groove is used for mounting the element to be coated; a through hole is arranged in the middle of the bottom of the mounting groove, and the through hole is used for adsorbing the element to be coated by the coating machine;

[0024] The mounting gap has a width of 2mm to 3mm, and the mounting gap is filled by a buffer strip;

[0025] The material of the buffer strip is polytetrafluoroethylene;

[0026] The plurality of buckles are arranged around the edge of the mounting groove, one end of each buckle is connected with the surface of the aluminum alloy disc, and the other end of each buckle is used for clamping the element to be coated; the material of the buckle is polytetrafluoroethylene.

[0027] Further, in step 3, the rotation speed of the coating machine is 1200r / min to 1400r / min, and the rotation time is 0.8min to 1.2min.

[0028] The temperature of the first baking is 90-100℃, and the baking time is 1-3 minutes.

[0029] Further, in step 3, the rotating speed of the glue spreading machine is 1300r / min, and the rotating time is 1 minute.

[0030] The temperature of the first baking is 95℃, and the baking time is 2 minutes.

[0031] Further, in step 3, the rate of the glue dropping head of the glue spreading machine is 2-6ml / s.

[0032] Further, in step 4, after the first baking, the element to be coated is adsorbed again on the corresponding position of the glue spreading machine, and the glue spreading tool is fixed on the glue spreading machine. The glue spreading machine drips the photoresist on the surface of the tackifier of the element to be coated in the form of a spiral line. The glue spreading machine rotates with the element to be coated with the glue spreading tool, so that the photoresist is uniformly distributed on each point of the surface of the element to be coated. Then, the glue spreading tool is detached from the glue spreading machine, and the element to be coated with the glue spreading tool is baked for the second time.

[0033] Further, in step 4, the rotating speed of the glue spreading machine is 1200-1400r / min, and the rotating time is 0.8-1.2 minutes.

[0034] The temperature of the second baking is 90-100℃, and the baking time is 1-3 minutes.

[0035] Further, in step 3, the rotating speed of the glue spreading machine is 1300r / min, and the rotating time is 1 minute.

[0036] The temperature of the second baking is 95℃, and the baking time is 2 minutes.

[0037] Further, in step 2, the selected element to be coated is loaded into the cleaning tool, and sequentially passes through the deionized water tank, the isopropyl alcohol tank, the concentrated sulfuric acid + hydrogen peroxide tank, the deionized water tank, and the isopropyl alcohol vapor tank. The cleaning time in each tank is 5 minutes, and the temperature in the isopropyl alcohol vapor tank is 75-85℃.

[0038] Step 5 is specifically that the glue spreading tool is detached from the glue spreading machine, the element with the glue is detached from the glue spreading tool, the glue layer thickness uniformity on the surface of the element with the glue is detected by a glue layer thickness tester, if the glue layer thickness of each point on the surface is inconsistent, the glue layer quality is unqualified, then the glue spreading machine is returned to step 2 and the rotating speed and / or rotating time of the glue spreading machine is adjusted until the glue layer quality is qualified, and the photoresist coating is completed.

[0039] The beneficial effects of the present application are as follows:

[0040] 1、The present application coats the tackifier before the photoresist coating, the main action mechanism of the tackifier is to replace the hydrophilic Si-HO group carried by the surface oxide layer of the single crystal silicon substrate, so that the single crystal silicon substrate changes from hydrophilic to hydrophobic, increases the adhesion with the photoresist, avoids the delamination phenomenon, improves the firmness of the glue layer, and prolongs the service life.

[0041] 2、The present application sets the photoresist coating tool for the single crystal silicon diffraction element, the mounting groove on the photoresist coating tool can be set according to the shape of the element to be coated, whether it is a hexagonal element to be coated or a fan-shaped element to be coated or other special-shaped elements, it can be applied, and the application range of the photoresist coating method is expanded.

[0042] 3、The present application sets the photoresist coating tool for the single crystal silicon diffraction element, the mounting groove on the photoresist coating tool can be set according to the shape of the element to be coated, whether it is a hexagonal element to be coated or a fan-shaped element to be coated or other special-shaped elements, it can be applied, and the application range of the photoresist coating method is expanded.

[0043] 4、The present application sets the photoresist coating tool for the single crystal silicon diffraction element, the depth of the mounting groove is less than the thickness of the element to be coated, which can avoid the accumulation of photoresist on the edge of the element to be coated, and avoid affecting the uniformity of the entire mirror surface glue layer.

[0044] 5、The photoresist coating method provided by the present application can be used to coat the tackifier or the photoresist on the surface of the element to be coated in the form of a spiral line, and then rotate, so as to avoid the difference in centrifugal force of each point on the large-diameter circumference, and to avoid the difference in thickness of the tackifier or the photoresist coating, greatly improving the uniformity of the photoresist coating on the surface of the element to be coated, and improving the quality of the photoresist glue layer. BRIEF DESCRIPTION OF DRAWINGS

[0045] Figure 1 is a flow chart of a large-diameter single crystal silicon diffraction element photoresist coating method embodiment of the present application;

[0046] Figure 2 is a top view of the photoresist coating tool in which the element to be coated is installed.

[0047] REFERENCE NUMERALS:

[0048] 1-element to be coated, 2-photoresist coating tool, 3-mounting gap, 4-suction point, 5-spiral line. DETAILED DESCRIPTION

[0049] The technical solutions of the present application will be described clearly and completely in combination with the drawings and embodiments. Obviously, the described embodiments are only some of the embodiments of the present application, but not all the embodiments. Based on the embodiments of the present application, all the other embodiments obtained by those skilled in the art without creative work fall within the protection scope of the present application.

[0050] The large-aperture irregular monocrystalline silicon diffraction element photoresist coating method provided by the embodiment of the present application comprises the following steps: Figure 1 As shown in the figure, the photoresist coating method comprises the following steps:

[0051] Step 1, surface state screening process;

[0052] The surface state qualified photoresist coating element 1 is screened out, which is an irregular flat diffraction element with an aperture D≥300mm, i.e. a large-aperture irregular monocrystalline silicon diffraction element;

[0053] The surface state screening process can check whether there are large particles attached to the surface of the photoresist coating element 1, whether there are scratches, whether there are edge collapses, whether there are contaminations and the like under a strong light lamp, and judge whether the photoresist coating element 1 can enter the next processing process;

[0054] Step 2, element surface cleaning process;

[0055] The screened photoresist coating element 1 is loaded into a cleaning tool, and is sequentially cleaned through a deionized water tank, an isopropyl alcohol tank, a concentrated sulfuric acid + hydrogen peroxide tank, a deionized water tank and an isopropyl alcohol vapor tank, the cleaning time in each tank is 5min, and the temperature in the isopropyl alcohol vapor tank is 75-85℃.

[0056] The cleaning tool is a tool matched with an ultrasonic cleaning device, which is usually suitable for cleaning square or circular wafers, and irregular elements can generally use rectangular tools. For regular hexagonal elements, the bottom edge and left and right vertices of the regular hexagonal element can be fixed on the cleaning tool through buckles, and the buckle position can be located at the midpoint of each side of the hexagonal element.

[0057] The element surface cleaning process aims to remove the water film attached to the element to be coated, improve the adhesion of the photoresist to the surface of the element to be coated, and further remove the small particles and part of the organic matter attached to the element to be coated. In the cleaning process, the cleaning tool is installed on the transmission mechanism, and then passes through the deionized water tank, isopropanol tank, concentrated sulfuric acid + hydrogen peroxide, deionized water tank, isopropanol vapor tank, each tank body has ultrasonic function, the cleaning time of each tank body can be 5 minutes, the temperature of the isopropanol vapor tank is 75-85°C, and in this embodiment, it is about 80°C. The transmission mechanism is a mechanism for driving the cleaning tool to move in each cleaning tank, similar to a gantry crane. After the cleaning time is met, the cleaning tool is lifted and translated to the next cleaning tank, and then the cleaning tool is lowered into the cleaning tank. After the cleaning time is met, the cleaning tool is lifted again, and the process is repeated for each cleaning tank.

[0058] Step 3, adhesion promoter coating process

[0059] After the cleaning is completed, the element to be coated 1 is loaded into the coating tool 2, and the element to be coated 1 is adsorbed on the corresponding position of the coating machine. Then the coating tool 2 is fixed on the coating machine, and the nozzle of the coating machine drips the adhesion promoter in the form of a spiral line 5 on the surface of the element to be coated 1. The coating machine rotates with the coating tool 2, and the rotation speed of the coating machine is in the range of 1200-1400 r / min, and the rotation time is in the range of 0.8-1.2 min. The rate of the adhesion promoter dripping from the nozzle of the coating machine is in the range of 2-6 ml / s. In this embodiment, the rotation speed of the coating machine is 1300 r / min, and the rotation time is 1 min. The rotation of the coating machine with the coating tool 2 enables the adhesion promoter to be evenly distributed on each point on the surface of the element to be coated 1. Then the coating tool 2 is detached from the coating machine, and the element to be coated 1 with the coating tool 2 is subjected to the first baking. The temperature of the first baking is in the range of 90-100°C, and the baking time is in the range of 1-3 min. In this embodiment, the temperature of the first baking is 95°C, and the baking time is 2 min. The purpose of the first baking is to remove the solvent in the adhesion promoter and form a bottom film with strong adhesion to the element to be coated 1 and the photoresist layer.

[0060] In the adhesion promoter coating process and the subsequent photoresist coating process, the element to be coated 1 is fixed in a fixed form by center adsorption on the back of the coating machine. However, for large-diameter flat plate diffraction elements, the center adsorption area accounts for a small proportion, and the adsorption force is insufficient. Therefore, there is a risk of flying pieces during the coating process. Therefore, a special coating tool is designed to solve the above problems.

[0061] As Figure 2As shown, the outer envelope size of the gluing tool 2 is slightly larger than the size of the element to be glued 1, the gluing tool 2 includes an aluminum alloy disc and a plurality of buckles; the middle of the aluminum alloy disc is provided with a mounting groove which is matched with the shape of the element to be glued 1 and is provided with a mounting gap 3; the depth of the mounting groove is less than the thickness of the element to be glued 1, which is used to mount the element to be glued 1; the middle of the groove bottom of the mounting groove is provided with a through hole for adsorbing the adsorption point 4 on the back of the element to be glued 1 to the corresponding position of the glue machine; the glue machine adsorbs the back of the element to be glued 1 by vacuumizing; the width of the mounting gap 3 is 2mm-3mm, and the mounting gap 3 is filled with a buffer strip; the material of the buffer strip is polytetrafluoroethylene, which plays a buffering role to avoid damage to the element during high-speed gluing caused by rigid contact between the tool and the element; a plurality of buckles are arranged around the edge of the mounting groove, one end of each buckle is connected with the surface of the aluminum alloy disc, and the other end is used to clamp the element to be glued 1; the material of the buckle can be polytetrafluoroethylene, which can avoid scratching the surface of the element to be glued 1.

[0062] Step 4, photoresist coating process;

[0063] After the first baking, the element to be glued 1 is adsorbed again at the corresponding position of the glue machine, and the gluing tool 2 is fixed on the glue machine. The nozzle of the glue machine drips photoresist in the form of a spiral line 5 on the tackifier surface of the element to be glued 1. The glue machine rotates with the gluing tool 2. The rotation speed of the glue machine is in the range of 1200r / min-1400r / min, and the rotation time is in the range of 0.8min-1.2min. In this embodiment, the rotation speed of the glue machine is 1300r / min, and the rotation time is 1min. The rotation of the glue machine makes the photoresist evenly distributed on each point of the surface of the element to be glued 1. Then the gluing tool 2 is detached from the glue machine, and the element to be glued 1 with the gluing tool 2 is subjected to the second baking. The temperature of the second baking is in the range of 90℃-100℃, and the baking time is in the range of 1min-3min. In this embodiment, the temperature of the second baking is 95℃, and the baking time is 2min. The purpose of the second baking is to remove the excess solvent in the glue layer, so that the glue layer adheres more firmly to the primary mirror substrate.

[0064] Step 5, quality detection process;

[0065] The gluing tool 2 is detached from the glue machine, and the glued element is detached from the gluing tool 2. The glue layer thickness uniformity on the surface of the glued element is detected by a glue layer thickness tester. If the glue layer thickness at each point on the surface is not consistent, the glue layer quality is unqualified, then return to step 2 and adjust the rotation speed and / or rotation time of the glue machine until the glue layer quality is qualified, and the photoresist coating method is completed.

[0066] The large-diameter special-shaped monocrystalline silicon diffraction element photoresist coating method provided by the embodiment can meet the photoresist coating processing requirements of special-shaped monocrystalline silicon diffraction elements such as regular hexagons and sectors, and can solve the problem of photoresist uniformity of large-diameter special-shaped flat plate monocrystalline silicon diffraction elements.

[0067] The above merely provides a specific implementation of the present application, but the protection scope of the present application is not limited thereto, and any change or replacement within the technical scope disclosed by the present application should be covered within the protection scope of the present application. Therefore, the protection scope of the present application should be subject to the protection scope of the claims.

Claims

1. A method for photoresist coating of a large-aperture irregularly shaped single-crystal silicon diffraction element, characterized in that, Includes the following steps: Step 1: Surface condition screening; Select the elements to be coated with adhesive that have qualified surface conditions; the elements to be coated with adhesive are irregularly shaped flat diffraction elements with an aperture D≥300mm; Step 2: Clean the component surface; The selected components to be coated with adhesive are placed into a cleaning fixture for cleaning. Step 3: Apply tackifier; After cleaning, the components to be coated are placed into the coating fixture, which is then attached to the corresponding position on the coating machine. The coating fixture is then fixed onto the coating machine. The nozzle of the coating machine drips the tackifier onto the surface of the components in a spiral pattern. The coating machine rotates the components with the coating fixture attached, ensuring that the tackifier is evenly distributed on all points of the surface of the components. Then, the coating fixture is removed from the coating machine, and the components with the coating fixture attached are baked for the first time. The adhesive application fixture includes an aluminum alloy disc and multiple clips. The aluminum alloy disc has a mounting groove in its center, the shape of which matches the shape of the component to be coated and includes an installation gap. The depth of the mounting groove is less than the thickness of the component to be coated, and it is used to mount the component. A through hole is provided in the center of the bottom of the mounting groove for the adhesive applicator to adsorb the component. The installation gap is 2mm to 3mm wide and is filled by a buffer strip. The buffer strip is made of polytetrafluoroethylene (PTFE). The multiple clips are arranged around the edge of the mounting groove, one end of each clip is connected to the surface of the aluminum alloy disc, and the other end is used to hold the component to be coated. The clips are also made of PTFE. Step 4: Photoresist coating; After the first baking, the component to be coated with adhesive, with the adhesive coating fixture, is fixed again and adsorbed onto the adhesive coating machine. The adhesive coating machine applies photoresist to the surface of the adhesive agent on the component to be coated, and then the component to be coated with adhesive, with the adhesive coating fixture, is baked a second time. Step 5: Quality Inspection; After the second baking, the photoresist coating quality of the coated components is inspected. If the quality of the coating is unqualified, return to step 2 until the coating quality is qualified, thus completing the photoresist coating method.

2. The photoresist coating method for large-aperture irregularly shaped single-crystal silicon diffraction elements according to claim 1, characterized in that: In step 3, the rotation speed of the glue applicator is 1200 r / min to 1400 r / min, and the rotation time is 0.8 min to 1.2 min; The temperature of the first baking is 90℃~100℃, and the baking time is 1min~3min.

3. The photoresist coating method for large-aperture irregularly shaped single-crystal silicon diffraction elements according to claim 2, characterized in that: In step 3, the glue applicator rotates at a speed of 1300 r / min for 1 minute. The first baking temperature was 95℃, and the baking time was 2 minutes.

4. The photoresist coating method for large-aperture irregularly shaped single-crystal silicon diffraction elements according to claim 2, characterized in that: In step 3, the rate at which the adhesive applicator drips the tackifier is 2 ml / s to 6 ml / s.

5. The photoresist coating method for large-aperture irregularly shaped single-crystal silicon diffraction elements according to any one of claims 1-4, characterized in that: Step 4 specifically involves the following steps: After the first baking, the component to be coated is re-adsorbed onto the corresponding position on the coating machine, and the coating fixture is then fixed onto the coating machine. The coating machine's nozzle drips photoresist in a spiral pattern onto the adhesion promoter surface of the component to be coated. The coating machine rotates the component to be coated with the coating fixture, ensuring that the photoresist is evenly distributed on all points of the component's surface. Then, the coating fixture is removed from the coating machine, and the component to be coated with the coating fixture is baked a second time.

6. The photoresist coating method for large-aperture irregularly shaped single-crystal silicon diffraction elements according to claim 5, characterized in that: In step 4, the rotation speed of the glue applicator is 1200 r / min to 1400 r / min, and the rotation time is 0.8 min to 1.2 min; The second baking temperature is 90℃~100℃, and the baking time is 1min~3min.

7. The photoresist coating method for large-aperture irregularly shaped single-crystal silicon diffraction elements according to claim 6, characterized in that: In step 3, the glue applicator rotates at a speed of 1300 r / min for 1 minute. The second baking temperature was 95°C, and the baking time was 2 minutes.

8. The photoresist coating method for large-aperture irregularly shaped single-crystal silicon diffraction elements according to claim 7, characterized in that: Step 2 specifically involves loading the selected components to be coated into a cleaning fixture and sequentially cleaning them through a deionized water tank, an isopropanol tank, a concentrated sulfuric acid + hydrogen peroxide tank, a deionized water tank, and an isopropanol vapor tank. The cleaning time in each tank is 5 minutes, and the temperature in the isopropanol vapor tank is 75℃~85℃. Step 5 specifically involves removing the coating fixture from the coating machine, removing the coated components from the coating fixture, and using a coating thickness tester to check the uniformity of the coating thickness on the surface of the coated components. If the coating thickness is inconsistent at different points on the surface, the coating quality is unqualified. In this case, return to step 2 and adjust the rotation speed and / or rotation time of the coating machine until the coating quality is qualified, thus completing the photoresist coating.

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