A method for preparing a thick photoresist microstructure

Abstract

The invention discloses a method for preparing a thick photoresist microstructure, comprising: ultrasonic cleaning of a substrate with anhydrous ethanol, rinsing with pure water, and drying with high-purity nitrogen, plating a metal seed layer on the substrate by magnetron sputtering, and pre-treating the surface with hexamethyldisilazane (HDMS); preheating the dry film photoresist after standing at room temperature, and then treating the surface with argon plasma, fixing the substrate on a bottom plate by vacuum adsorption, and pasting the dry film photoresist with a roller, repeating the pasting for multiple times; after pasting, the dry film photoresist is exposed and developed, and then cleaned and post-baked to obtain the photoresist microstructure. The invention adopts multi-layer pasting of dry film photoresist; heat treatment of a single layer of dry film photoresist by a roller can make the film layer adhere flat and release internal stress; before each layer of dry film photoresist is pasted, argon plasma is used to pre-treat the surface of the dry film photoresist to enhance the bonding force between the film layers and further improve the molding quality.

Description

Technical Field

[0001] The invention belongs to the field of photoresists, and in particular relates to a method for preparing a photoresist microstructure with large thickness. Background Art

[0002] As electronic systems develop towards miniaturization, intelligence, and high reliability, components manufactured by traditional mechanical processing and independent assembly methods have gradually exposed many problems such as long production cycle, poor quality consistency, incompatible structure and process, and high cost. Micro-precision processing technology has a very broad application prospect in integrated circuits, smart chips, aerospace, biomedicine, military fields, etc. It has significant advantages in improving the consistency of components and the high integration, large-scale, and low-cost manufacturing of systems. Photolithography is one of the most important steps in micro-processing technology. The dimensional parameters of the photolithographic structure will directly affect the structural dimensional parameters of the final device.

[0003] The thickness of common photoresist films is generally less than 10 microns. The difficulty of preparing thick photoresist structures with a thickness of 100 microns and good verticality and surface roughness increases significantly. Thick photoresist films are usually made using liquid coating processes such as SU8 glue. High-viscosity photoresists are prone to problems such as difficulty in pouring glue, many bubbles, poor leveling, and large contamination during the coating process. In addition, thick SU8 glue films will produce large internal stresses during the thermal baking process. When the thermal expansion coefficient is different from that of the substrate material, the existence of internal stress causes the film to deform and crack, and in severe cases, the film falls off the substrate. Moreover, in subsequent processes, such as long-term electroforming and high electroforming liquid temperatures, SU8 glue is prone to swelling and thermal expansion deformation, which in turn causes the verticality and surface roughness of the side walls of the device to deteriorate. For example, patent CN115016229A discloses a method for preparing a low-temperature cured thick film of photoresist, which adopts a liquid coating process to coat a dry film photoresist, and then continues to perform liquid coating on the dry film photoresist. The preparation process is prone to problems such as difficulty in pouring glue, many bubbles, poor leveling, and large pollution. For example, patent CN108181789A discloses a method for processing a photoresist template for PDMS chip transfer, which adopts traditional SU8 liquid photoresist for multiple coating to increase the thickness of the photoresist, which is prone to swelling and thermal expansion deformation, thereby causing the side wall verticality and surface roughness of the device to deteriorate. Summary of the invention

[0004] An object of the present invention is to solve at least the above problems and / or disadvantages and to provide at least the advantages which will be described hereinafter.

[0005] In order to achieve these purposes and other advantages according to the present invention, a method for preparing a thick photoresist microstructure is provided, comprising the following steps:

[0006] Step 1: ultrasonically clean the substrate with acetone, isopropanol, and anhydrous ethanol in sequence, rinse with pure water, and blow dry with high-purity nitrogen, then plate a metal seed layer on the substrate by magnetron sputtering, and perform surface pretreatment of the metal seed layer with hexamethyldisilazane (HDMS);

[0007] Step 2, leaving the dry film photoresist at room temperature, preheating the dry film photoresist, and then subjecting the surface of the dry film photoresist to argon plasma treatment, and fixing the substrate on the bottom plate by vacuum adsorption, and then pasting the dry film photoresist on the metal seed layer with a roller, and repeating the pasting multiple times;

[0008] Step 3: After lamination is completed, a mask is placed on the dry film photoresist, and then it is exposed and developed. The dry film photoresist of the exposed part is dissolved, and the dry film photoresist of the unexposed part is retained to form the required photoresist microstructure, and then the photoresist microstructure is cleaned and post-baked.

[0009] Preferably, in the step 1, when the metal seed layer is plated on the substrate by magnetron sputtering, the vacuum degree is better than 5×10 -4 Pa, sputtering power 50~250W, growth rate 0.1A / s~20A / s, the metal seed layer material is one of Cr / Au, Ti / Au, Ni / Au, and the thickness of the metal seed layer is 100nm~200nm.

[0010] Preferably, in the step 1, the process of using hexamethyldisilazane (HDMS) to perform surface pretreatment on the metal seed layer is as follows: placing the substrate in a processing chamber, evacuating the chamber, heating to 100-140°C, filling with hexamethyldisilazane, maintaining for 3-7 minutes, cooling to room temperature, filling with nitrogen, evacuating the chamber again, repeating 3 times, and finally taking out the substrate.

[0011] Preferably, in step 2, the standing time at room temperature is more than 2 hours, the preheating temperature is 70° C. to 90° C., and the time is 8 min to 15 min.

[0012] Preferably, in step 2, the argon plasma treatment process is as follows: placing the dry film photoresist in the chamber, evacuating the chamber to a vacuum of 4×10 -4 Below Pa, fill with argon gas at a flow rate of 1~3L / min. After filling for 5 minutes, continue to fill. During this process, run the program with a power of 200~500W and a time of 2~8min to perform surface plasma treatment of the dry film photoresist.

[0013] Preferably, in the step 2, the process of laminating the dry film photoresist is as follows: fix the substrate on the base plate by vacuum adsorption, then place the first layer of dry film photoresist on the substrate, ensure that the substrate is completely covered by the dry film photoresist, adjust the temperature, speed and pressure parameters of the roller, control the roller to roll at a uniform speed from one end to the other end of the dry film photoresist surface, ensure that the dry film photoresist and the substrate are well laminated without bubbles, then place the second layer of dry film photoresist on the first layer of dry film photoresist, adjust the temperature, speed and pressure parameters of the roller, and repeat the laminating multiple times.

[0014] Preferably, in the step 2, the dry film photoresist is a positive photoresist, the thickness of the dry film photoresist is 20-100 μm, and the number of lamination layers is 1-15.

[0015] Preferably, in the step 2, the roller temperature of each layer of lamination is 100° C. to 120° C., the pressure is 0.3 MPa to 0.7 MPa, and the roller speed is 0.4 m / min to 0.6 m / min.

[0016] Preferably, in step 3, a mask is placed on the dry film photoresist within 24 hours after the lamination is completed, and then the dry film photoresist is exposed and developed, and the exposure light intensity is 17 mW / cm 2 ~20mW / cm 2 The exposure time is 25s~30s, the development temperature is 45℃~55℃, and the time is 28min~40min.

[0017] Preferably, in step three, the post-baking temperature is 90° C. to 110° C., and the time is 8 min to 15 min.

[0018] The present invention has at least the following beneficial effects:

[0019] (1) The present invention adopts a solid dry film photoresist multi-layer lamination process to replace the liquid coating process, realizes the preparation and thickness control of a thick photoresist film by multi-layer superposition of dry film photoresist, and adopts multi-layer dry film photoresist overlapping lamination to meet the requirement of a thickness of hundreds of microns;

[0020] (2) The present invention changes the heat treatment method of the dry film photoresist lamination process from the traditional bottom heating plate treatment to roller heat treatment, and only heat treats a single layer of dry film photoresist. On the one hand, the film layer can be attached flat, and the heat treatment releases the internal stress when each layer of dry film photoresist is laminated. On the other hand, it can prevent the multi-layer dry film photoresist from being heated for a long time. On the premise of ensuring the interface quality of the dry film photoresist, the influence of the heat treatment on the photosensitivity and thermal deformation of the dry film photoresist is effectively reduced;

[0021] (3) Before laminating each layer of dry film photoresist, the present invention uses argon plasma to pre-treat the surface of the dry film photoresist to enhance the bonding force between the film layers and further improve the molding quality.

[0022] Other advantages, objectives and features of the present invention will be embodied in part through the following description, and in part will be understood by those skilled in the art through study and practice of the present invention. BRIEF DESCRIPTION OF THE DRAWINGS

[0023] Figure 1 This is a schematic diagram of dry film photoresist coating according to embodiment 1 of the present invention;

[0024] Figure 2 This is a topographical image of the photoresist structure prepared by roller heating in Example 1 of the present invention;

[0025] Figure 3 This is a morphology diagram of the photoresist structure prepared by heating the bottom plate in Comparative Example 1 of the present invention;

[0026] Figure 4 This is a cross-sectional diagram of the temperature distribution of the roller heating in Example 1 of the present invention;

[0027] Figure 5 This is a cross-sectional diagram of the temperature distribution of the bottom plate heated in Comparative Example 1 of the present invention;

[0028] Figure 6 This is a schematic diagram of the conventional liquid SU8 coating process in comparative example 3 of the present invention. DETAILED DESCRIPTION

[0029] The present invention is further described in detail below in conjunction with the accompanying drawings so that those skilled in the art can implement the invention with reference to the description.

[0030] Example 1

[0031] A method for preparing a thick photoresist microstructure comprises the following steps:

[0032] Step 1: The substrate is ultrasonically cleaned with anhydrous ethanol, rinsed with pure water, and dried with high-purity nitrogen. Then, a 200nm thick Cr / Au seed layer is plated on the surface of the substrate by magnetron sputtering. The vacuum degree of the magnetron sputtering metal seed layer is better than 5×10 -4 Pa, sputtering power 100W, growth rate 2A / s, then put the substrate into the processing chamber, evacuate, heat to 120°C, fill with hexamethyldisilazane (HDMS), keep for 5 minutes, cool to room temperature, fill with nitrogen, evacuate again, repeat 3 times, and finally take out the substrate;

[0033] Step 2: Place the 54 μm thick dry film photoresist at room temperature for 2.5 h, then preheat the dry film photoresist at 80 °C for 10 min, then place the dry film photoresist in the chamber and evacuate to 4 × 10 -4 Pa, fill with argon gas at a flow rate of 2L / min. After 5 minutes of filling, continue to fill. During this process, run the program at a power of 220W for 4 minutes to perform surface plasma treatment of the dry film photoresist and set aside. Use vacuum adsorption to fix the substrate on the bottom plate, and then follow Figure 1 As shown (it should be noted that Figure 1 In the figure, 1 represents the coating roller, 2 represents the dry film photoresist, 3 represents the metal seed layer, 4 represents the substrate, 5 represents the bottom plate, the curved arrow represents the direction of the roller rotation, and the right arrow represents the direction of the roller forward). Place the first layer of dry film photoresist on the substrate to ensure that the substrate is completely covered by the dry film photoresist. The roller temperature of the first layer of dry film photoresist is 110°C, the pressure is 0.4MPa, and the roller speed is 0.5m / min. Control the roller to roll uniformly from one end of the dry film photoresist surface to the other end to ensure that the dry film photoresist is in contact with the substrate. The coating is intact without bubbles; then the second layer of dry film photoresist is placed on the first layer of dry film photoresist, the roller temperature of the second layer is 110°C, the pressure is 0.5MPa, and the roller speed is 0.5m / min. Repeat the operation to coat a total of six layers of dry film photoresist, the roller temperature of the third, fourth, fifth, and sixth layers is 110°C, the pressure is 0.6MPa, and the roller speed is 0.5m / min. After the coating is completed, the thickness of the six layers of dry film photoresist reaches more than 300μm; the temperature distribution of roller heating-cross-section diagram is shown in Figure 4 As shown;

[0034] Step 3: After lamination, place a mask on the dry film photoresist within 24 hours, and then complete the exposure and development of the dry film photoresist. The exposure intensity is 18mW / cm 2 The exposure time is 28s, the development temperature is 50℃, and the time is 35min. The dry film photoresist of the exposed part is dissolved, and the dry film photoresist of the unexposed part is retained to form the required photoresist microstructure. The photoresist microstructure is then cleaned and post-baked at a temperature of 100℃ for 10min.

[0035] Example 2

[0036] A method for preparing a thick photoresist microstructure comprises the following steps:

[0037] Step 1: The substrate is ultrasonically cleaned with anhydrous ethanol, rinsed with pure water, and dried with high-purity nitrogen. Then, a 200nm thick Cr / Au seed layer is plated on the surface of the substrate by magnetron sputtering. The vacuum degree of the magnetron sputtering metal seed layer is better than 5×10 -4Pa, sputtering power 100W, growth rate 2A / s, then put the substrate into the processing chamber, evacuate, heat to 120°C, fill with hexamethyldisilazane (HDMS), keep for 5 minutes, cool to room temperature, fill with nitrogen, evacuate again, repeat 3 times, and finally take out the substrate;

[0038] Step 2: Place the 54 μm thick dry film photoresist at room temperature for 2.5 h, then preheat the dry film photoresist at 80 °C for 10 min, then place the dry film photoresist in the chamber and evacuate to 4 × 10 -4 Pa, fill with argon gas at a flow rate of 2L / min, and continue to fill for 5 minutes. During this process, run the program with a power of 220W and a time of 4 minutes to perform surface plasma treatment of the dry film photoresist for standby use; use vacuum adsorption to fix the substrate on the base plate, and then place the first layer of dry film photoresist on the substrate to ensure that the substrate is completely covered by the dry film photoresist. The roller temperature of the first layer of dry film photoresist is 120°C, the pressure is 0.4MPa, and the roller speed is 0.6m / min. Control the roller from the surface of the dry film photoresist to Rolling at a uniform speed from one end to the other end ensures that the dry film photoresist and the substrate are well coated without bubbles; then placing the second layer of dry film photoresist on the first layer of dry film photoresist, the roller temperature of the second layer is 120°C, the pressure is 0.5MPa, and the roller speed is 0.6m / min. Repeat the operation to coat a total of six layers of dry film photoresist, and the roller temperature of the third, fourth, fifth, and sixth layers is 120°C, the pressure is 0.6MPa, and the roller speed is 0.6m / min. After the coating is completed, the thickness of the six layers of dry film photoresist reaches more than 300μm;

[0039] Step 3: After lamination, place a mask on the dry film photoresist within 24 hours, and then complete the exposure and development of the dry film photoresist. The exposure intensity is 18mW / cm 2 The exposure time is 28s, the development temperature is 50℃, and the time is 35min. The dry film photoresist of the exposed part is dissolved, and the dry film photoresist of the unexposed part is retained to form the required photoresist microstructure. The photoresist microstructure is then cleaned and post-baked at a temperature of 100℃ for 10min.

[0040] Comparative Example 1

[0041] The difference between this comparative example and Example 1 is that in step 2, after the dry film photoresist is treated with argon plasma, the substrate is fixed on the bottom plate by vacuum adsorption, and then the dry film photoresist is attached to the metal seed layer by a roller. The heating method is to heat the bottom plate without heating the roller. The temperature distribution of the roller heating is shown in the cross-sectional diagram. Figure 5As shown, the bottom plate heating temperature is 180°C, the roller pressure of the first layer of dry film photoresist is 0.4MPa, the roller speed is 0.5m / min, the roller pressure of the second layer is 0.5MPa, the roller speed is 0.5m / min, the roller pressure of the third, fourth, fifth and sixth layers is 0.6MPa, the roller speed is 0.5m / min, after the coating is completed, the thickness of the six layers of dry film photoresist reaches more than 300μm. The remaining steps are consistent with Example 1.

[0042] Comparative Example 2

[0043] The difference between this comparative example and Example 1 is that after the dry film photoresist is preheated in step 2, the dry film photoresist is not subjected to argon plasma treatment, and then the dry film photoresist is directly heated and laminated by a roller. The remaining steps are consistent with Example 1.

[0044] Comparative Example 3

[0045] This comparative example adopts the traditional liquid SU8 coating. The specific process is as follows: the ceramic substrate is vacuum adsorbed on the coating machine, the speed is set to 1100rpm, the acceleration is 800rpm, and the time is 15s. Then the SU8 glue is manually poured on the substrate. After the spin coating is completed, the sample is placed on a hot plate for heat baking. The processing process is as follows Figure 6 As shown, (it should be noted that Figure 6 A represents SU8 photoresist, a represents the deformed SU8 photoresist after heat treatment, B represents the ceramic substrate, and the lower arrow represents the heat treatment process).

[0046] from Figure 2 It can be seen that Example 1 of the present invention adopts Figure 4 The roller heating shown in the figure can produce a thick photoresist with a smooth microstructure, and the argon plasma treatment can form a nano-forest structure on the surface of the photoresist, which can increase the adhesion between the photoresist and the metal seed layer. Figure 5 The bottom plate is heated as shown, and the resulting photoresist is as Figure 3 As shown, the photoresist microstructure is irregular. At the same time, due to the use of base plate heating, the earlier the dry film photoresist is applied, the longer the heat treatment will be, which will lead to a decrease in the resolution and photosensitivity of the dry film photoresist.

[0047] Compared with the thick photoresist microstructures of Examples 1 and 2 of the present invention, the photoresist structure of Comparative Example 2 is not treated with argon plasma, and no nano-forest structure is formed on the surface of the photoresist. Figure 6It can be seen that in Example 3, the traditional liquid glue is used to prepare thick glue, which will cause glue accumulation to form at the edge of the sample. The thickness of the edge glue and the center glue are quite different, forming a concave glue surface. The thicker the glue, the more obvious the concave surface is, and the greater the thickness difference is. The thick SU8 glue film prepared by traditional liquid glue will also produce large internal stress during the heat baking process, causing the glue film to deform and crack, and in severe cases, cause the glue film to fall off the substrate.

[0048] Although the embodiments of the present invention have been disclosed as above, they are not limited to the applications listed in the specification and the implementation modes, and they can be fully applied to various fields suitable for the present invention. For those familiar with the art, additional modifications can be easily implemented. Therefore, without departing from the general concept defined by the claims and the scope of equivalents, the present invention is not limited to the specific details and the illustrations shown and described herein.

Claims

1. A method for preparing a thick photoresist microstructure, characterized in that: The following steps are involved: Step 1: ultrasonically clean the substrate with acetone, isopropanol, and anhydrous ethanol in sequence, rinse with pure water, and blow dry with high-purity nitrogen, then plate a metal seed layer on the substrate by magnetron sputtering, and perform surface pretreatment of the metal seed layer with hexamethyldisilazane; Step 2, leaving the dry film photoresist at room temperature, preheating the dry film photoresist, and then subjecting the surface of the dry film photoresist to argon plasma treatment, and fixing the substrate on the bottom plate by vacuum adsorption, and then pasting the dry film photoresist on the metal seed layer with a roller, and repeating the pasting multiple times; Step 3: After lamination, a mask is placed on the dry film photoresist, and then it is exposed and developed. The dry film photoresist of the exposed part is dissolved, and the dry film photoresist of the unexposed part is retained to form the desired photoresist microstructure, and then the photoresist microstructure is cleaned and post-baked; In the step 2, the process of laminating the dry film photoresist is as follows: the substrate is fixed on the bottom plate by vacuum adsorption, and then the first layer of dry film photoresist is placed on the substrate to ensure that the substrate is completely covered by the dry film photoresist, the temperature, speed and pressure parameters of the roller are adjusted to reach the set values, and the roller is controlled to roll uniformly from one end to the other end of the dry film photoresist surface to ensure that the dry film photoresist and the substrate are well laminating without bubbles, and then the second layer of dry film photoresist is placed on the first layer of dry film photoresist, and the temperature, speed and pressure parameters of the roller are adjusted to reach the set values, and the laminating is repeated for multiple times; the roller temperature of each layer is 100° C.~120° C., the pressure is 0.3MPa~0.7MPa, and the roller speed is 0.4m / min~0.6m / min.

2. The method for preparing a thick photoresist microstructure according to claim 1, characterized in that: In the step 1, when the metal seed layer is deposited on the substrate by magnetron sputtering, the vacuum degree is better than 5×10 -4 Pa, sputtering power 50~250W, growth rate 0.1A / s~20A / s, the metal seed layer material is one of Cr / Au, Ti / Au, Ni / Au, and the thickness of the metal seed layer is 100nm~200nm.

3. The method for preparing a thick photoresist microstructure according to claim 1, characterized in that: In the step 1, the process of using hexamethyldisilazane to pretreat the surface of the metal seed layer is as follows: placing the substrate in a processing chamber, evacuating the chamber, heating to 100-140° C., filling with hexamethyldisilazane, maintaining for 3-7 minutes, cooling to room temperature, filling with nitrogen, evacuating the chamber again, repeating 3 times, and finally taking out the substrate.

4. The method for preparing a thick photoresist microstructure according to claim 1, characterized in that: In the step 2, the standing time at room temperature is more than 2 hours, the preheating temperature is 70° C. to 90° C., and the time is 8 min to 15 min.

5. The method for preparing a thick photoresist microstructure according to claim 1, characterized in that: In step 2, the argon plasma treatment process is as follows: put the dry film photoresist into the cavity and evacuate to 4×10 -4 Below Pa, fill with argon gas at a flow rate of 1~3L / min. After filling for 5 minutes, continue to fill. During this process, run the program with a power of 200~500W and a time of 2~8min to perform surface plasma treatment of the dry film photoresist.

6. The method for preparing a thick photoresist microstructure according to claim 1, characterized in that: In the step 2, the dry film photoresist is a positive photoresist, the thickness of the dry film photoresist is 20-100 μm, and the number of lamination layers is 1-15.

7. The method for preparing a thick photoresist microstructure according to claim 1, characterized in that: In step 3, a mask is placed on the dry film photoresist within 24 hours after the lamination is completed, and then the dry film photoresist is exposed and developed. The exposure light intensity is 17 mW / cm 2 ~20mW / cm 2 The exposure time is 25s~30s, the development temperature is 45℃~55℃, and the time is 28min~40min.

8. The method for preparing a thick photoresist microstructure according to claim 1, characterized in that: In the step 3, the post-baking temperature is 90° C. to 110° C., and the time is 8 min to 15 min.

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