Substrate film forming method combining ultrasonic oscillation and blade coating

Abstract

The invention belongs to the field of precision micromachining, and discloses a microstructure substrate film forming method combining ultrasonic oscillation and blade coating, which comprises the following steps: positioning and fixing a microstructure substrate; wettability of the microstructure substrate is improved; and removing the redundant solution on the microstructure substrate, and flattening the liquid film. The method comprises the following steps: immersing a microstructure substrate into a solution in an ultrasonic instrument, driving the solution to generate oscillation through the amplitude and frequency of ultrasonic waves, reducing the contact angle of the solution at the bottom of the microstructure by using the hysteresis effect of the contact angle, and removing an air layer at the bottom of the microstructure by using the cavitation effect of the ultrasonic waves. Therefore, the wettability of the solution to the bottom of the microstructure is enhanced. According to the method, the wettability of the solution to the microstructure substrate is effectively improved, the problems of poor wettability of the solution to the bottom of the microstructure, many repeated operations and long process in an existing single wet coating mode are solved, and the thin film with high coverage rate, ideal film thickness and uniformity is prepared on the microstructure substrate.

Description

Technical Field

[0001] The present invention belongs to the field of precision microfabrication, and particularly relates to a method for forming a film on a microstructured substrate by combining ultrasonic oscillation and blade coating. Background Art

[0002] Preparing microstructures on a substrate is an important technology in the field of micro-nano manufacturing, and is widely used in fields such as semiconductors, optoelectronics, sensors, biosensors, and microelectromechanical systems (MEMS). With the in-depth development of scientific research, many high-performance devices are no longer satisfied with only having a single-layer microstructure. For example, on a silicon-based OLED microdisplay, it is necessary to prepare multi-level microstructures by photolithography on the existing microstructures to achieve a better light-concentrating effect; in the research of hydrophobic materials, preparing smaller secondary microstructures on the primary microstructures can make the microstructures have superhydrophobicity. At the same time, the demand for preparing surface structures by re-coating materials and etching on devices with existing microstructures is also increasing. For example, in a vertical cavity surface emitting laser (VCSEL), coating a new material and etching on a micron-scale circular microstructure can generate a hollow laser beam output; in the transfer of microstructures, it is also necessary to coat a film that is uniform and completely fits into the gaps of the microstructures on the substrate with microstructures to achieve perfect replication of the microstructures.

[0003] However, in the above-mentioned film preparation methods, when directly performing common wet coating methods such as spin coating, blade coating, slot coating, and dip coating on a microstructured substrate, due to the surface tension of the solution, a Cassie-Baxter wetting state will be formed above the microstructures, that is, the liquid droplets are located on the top of the rough surface, and there is an air layer below. Therefore, it is difficult to infiltrate the bottom of the grooves of the microstructures. This insufficient wettability will lead to a non-conformal interaction between the fluid and the substrate, resulting in interface defects. Existing solutions often involve multiple liquid dispensing and spin coating on the substrate surface, and the spin coating speed is often greater than 1000 rpm and the time is greater than 5 min each time. Such a method will cause a large amount of repetitive operations and time waste, and the excessive coating time will cause the film to dry during the spin coating process, resulting in uneven distribution of the film thickness and poor film formation quality, which will further lead to an unsatisfactory microstructural morphology obtained by subsequent etching; while the method of improving the wettability of the solution by chemical modification of the solution or the substrate has poor versatility and will cause serious environmental pollution and toxicology problems; the method of enhancing wettability by pressure often causes damage to the substrate. At the same time, during the spin coating or blade coating process, due to the diversity of the substrate shapes, the existing method of fixing the substrate by vacuum adsorption is prone to problems such as inaccurate substrate positioning, the solution being sucked into the pump tube and causing blockage, and frequent disassembly and cleaning. Therefore, there is an urgent need for a non-destructive film-forming method that can quickly improve the wettability of the solution on a substrate with microstructures, and a substrate fixture that can adapt to this method to solve the problems of transfer and positioning of substrates with various shapes during the film-forming process. Summary of the Invention

[0004] To solve the above problems existing in the prior art, the present invention is designed to provide a film-forming method for a microstructured substrate that combines ultrasonic oscillation and doctor blade coating, which can not only quickly improve the wettability of the solution on the microstructures of the substrate, but also not damage the film.

[0005] To achieve the above object, the technical solution of the present invention is as follows: A film-forming method for a microstructured substrate that combines ultrasonic oscillation and doctor blade coating, comprising the following steps:

[0006] A. Place the microstructured substrate at the center of the bottom plate of the multifunctional fixture, and position and fix the microstructured substrate.

[0007] B. Immerse the microstructured substrate into the solution in the ultrasonic instrument by using the multifunctional fixture, and drive the solution to oscillate through the ultrasonic waves generated by the ultrasonic oscillation head to improve the wettability of the microstructured substrate.

[0008] C. Transfer the microstructured substrate to the doctor blade coating platform by using the multifunctional fixture and position it; remove the excess solution on the microstructured substrate by doctor blade coating to flatten the liquid film.

[0009] Further, the surface of the microstructured substrate has micron- or nanoscale microstructures with square wave, trapezoidal, wavy, or triangular cross-sections, and the microstructures are arranged on the surface of the microstructured substrate along a straight line or an arc trajectory; the material of the microstructured substrate is quartz or silicon, the microstructured substrate has a triangular, rectangular, circular, polygonal, or fan-shaped shape, and the thickness is more than 0.5 mm;

[0010] The solution includes photoresist solution, polyurethane solution, perovskite solution, or carbon nanotube solution; the viscosity of the solution is 1-1000 mPa·s;

[0011] The ultrasonic instrument is an ultrasonic cleaner, the microstructured substrate and its multifunctional fixture are completely immersed in the solution, the frequency of the ultrasonic waves is 20-400 kHz, the power is 10-5000 W, and the amplitude is less than the solution atomization amplitude;

[0012] The doctor blade coating method is to perform one or more doctor blade coatings on the ultrasonic wetted microstructured substrate in a certain direction by using a doctor blade or a wire bar, or perform a linear reciprocating doctor blade coating.

[0013] Further, the multifunctional fixture includes a bottom plate, a magnet, a limiting plate, a handle, and a flexible pressing head;

[0014] A through hole is provided at the center of the bottom plate, there are two handles, which are respectively installed on the front and back sides of the bottom plate, a plurality of grooves are distributed on the upper surface of the bottom plate, and the parallelism between the upper and lower surfaces of the bottom plate shall not exceed 0.01 mm, and the roughness shall not exceed Ra1.6.

[0015] The magnet is embedded in the groove on the upper surface of the bottom plate, and the magnet is fixed and sealed by sealant.

[0016] There are two limit plates, which are respectively adsorbed on the left and right sides of the bottom plate.

[0017] The flexible indenter is installed inside the handle and is used to press the micro-structure substrate.

[0018] Furthermore, the limit plate is a rectangular plate, and a fitting curve slot gradually changing from 120° to 30° is cut on the inner side, which is used to limit the micro-structure substrate along the scraping direction. The thickness of the limit plate does not exceed the thickness of the micro-structure substrate, and the plate surface does not exceed the size of the coating area of the scraping machine.

[0019] Furthermore, the lower part of the handle is connected to the side ear of the bottom plate through a pin structure with clearance fit; there is a cross-plate structure inside the handle, and the slot of the flexible indenter is fixedly installed on the cross-plate structure through interference fit; a ring structure is arranged at the top of the handle.

[0020] Furthermore, the material of the flexible indenter is rubber;

[0021] The number, position and size of the protrusions on the flexible indenter are determined according to the size and shape of the flexible indenter substrate. The shapes of the protrusions include cuboids, cylinders or hemispheres, and the protrusions press on the outside of the micro-structures on the micro-structure substrate.

[0022] Furthermore, the using method of the handle is: squeeze the ring structures on both sides of the handle inward, and press the micro-structure substrate on the surface of the bottom plate through the flexible indenter.

[0023] Furthermore, when performing ultrasonic oscillation, use a magic tape or a thin line to pass through the ring structure at the top of the handle and apply an inward pulling force;

[0024] After the ultrasonic oscillation is completed, manually lift the handles on both sides, or use a robotic arm to lift the multi-functional fixture, quickly place the multi-functional fixture and the micro-structure substrate on the scraping platform, and at the same time avoid tilting and vibration. After placing in place, pull out the handles on both sides.

[0025] Furthermore, during the scraping process, set the scraping gap in advance to avoid the scraper or wire bar hitting the micro-structure substrate due to too small a gap, or not contacting the solution or removing too little solution due to too large a gap.

[0026] Furthermore, the shape of the groove is circular, rectangular or polygonal.

[0027] Furthermore, the material of the limit plate is iron-cobalt-nickel alloy.

[0028] Compared with the prior art, the beneficial effects of the present invention are:

[0029] 1. The present invention immerses the microstructured substrate into the solution in an ultrasonic instrument, drives the solution to oscillate through the amplitude and frequency of ultrasonic waves, reduces the contact angle of the solution at the bottom of the microstructures by utilizing the hysteresis effect of the contact angle, and simultaneously removes the air layer at the bottom of the microstructures by utilizing the cavitation effect of ultrasonic waves, thereby enhancing the wettability of the solution to the bottom of the microstructures. The present invention effectively improves the wettability of the solution to the microstructured substrate, overcomes the problems of poor wettability of the solution to the bottom of the microstructures, many repetitive operations, and long process in the existing single wet coating method, and prepares a thin film with high coverage, ideal film thickness and uniformity on the microstructured substrate.

[0030] 2. The present invention adjusts the contact angle of the solution through the amplitude and frequency of ultrasonic waves to improve the wettability of the solution. Compared with the method of chemically modifying the solution and the substrate, it can avoid problems such as environmental pollution and toxicology. At the same time, compared with the method of applying pressure to the solution on the substrate surface to improve wettability, it can avoid pressure damage to the integrity of the substrate surface, and it is a more environmentally friendly and convenient method for improving wettability.

[0031] 3. Through the design of the multifunctional fixture for film formation, the present invention solves the problem of transferring from the ultrasonic instrument to the doctor blade coating platform, and at the same time solves the problem of positioning the special-shaped substrate during the doctor blade coating process. The operation is simple, the process is non-hazardous, and the coating accuracy and efficiency are high. Description of the Drawings

[0032] Figure 1 is a schematic diagram of the microstructured substrate;

[0033] Figure 2 is a schematic diagram of the square-wave microstructures;

[0034] Figure 3 is a schematic diagram of the multifunctional fixture fixing the microstructured substrate and performing infiltration in the ultrasonic instrument;

[0035] Figure 4 is a schematic diagram of the bottom plate structure of the multifunctional fixture;

[0036] Figure 5 is a schematic diagram of the handle structure of the multifunctional fixture;

[0037] Figure 6 is a schematic diagram of the flexible indenter structure of the multifunctional fixture;

[0038] Figure 7 is a schematic diagram of doctor blade coating after positioning the microstructured substrate by using the multifunctional fixture;

[0039] Figure 8 is a schematic diagram of the limiting plate positioning the triangular substrate (shaded part);

[0040] Figure 9 It is a schematic diagram of the positioning of the rectangular base (shaded part) by the limit plate;

[0041] Figure 10 It is a schematic diagram of the positioning of the circular base (shaded part) by the limit plate;

[0042] Figure 11 It is a schematic diagram of the positioning of the fan-shaped base with different angles (shaded part) by the limit plate;

[0043] Figure 12 It is a schematic diagram of the positioning of the polygonal base (shaded part, taking hexagon as an example) by the limit plate;

[0044] Figure 13 It is a schematic diagram of the positioning of the randomly shaped base (shaded part) by the limit plate.

[0045] In the figure: 1 - bottom plate, 1a - groove, 1b - round hole, 1c - side ear, 2 - magnet, 3 - limit plate, 4 - handle, 4a - pin structure, 4b - cross plate structure, 4c - annular structure, 5 - flexible indenter, 5a - slot, 5b - protrusion, 6 - microstructured substrate, 7 - ultrasonic instrument, 8 - wire rod, 9 - scraping platform, 10 - ultrasonic vibration head. Detailed implementation mode

[0046] In order to more clearly understand the above objects, features and advantages of the present invention, the present invention will be further described below with reference to the accompanying drawings and specific implementation cases.

[0047] The embodiments of the present invention are as follows:

[0048] The microstructured substrate is a square-wave type circular microstructured quartz substrate, with a size of a 60×60 mm square substrate, a thickness of 0.5 mm, and the maximum diameter of the circular ring containing the microstructured part is 42 mm, as Figure 1 shown;

[0049] The width of the square-wave microstructured convex platform and groove is 20 - 200 μm, and the groove depth is 3 - 5 μm, as Figure 2 shown.

[0050] The magnet 2 is inserted into the groove 1a of the bottom plate 1 and sealed and fixed with sealant, as Figure 3 , 4 shown;

[0051] The handle 4 is connected to the side ear of the bottom plate 1 through the pin structure, as Figure 3-5 shown;

[0052] The flexible indenter 5 is connected to the protrusion structure 4b of the handle 4 through the slot 5a, as Figure 3 , 5 , 6 shown;

[0053] The pin structure 4a of the handle 4 and the side ear 1c of the bottom plate 1 are in clearance fit, and the slot 5a of the flexible press head 5 and the cross plate structure 4b on the handle 4 are in interference fit.

[0054] The micro-structure substrate 6 is pressed by the flexible press head 5 on the surface of the bottom plate 1, and then placed in an ultrasonic instrument 7 filled with a photoresist solution, so that the micro-structure substrate 6 is immersed in the photoresist solution, as Figure 3 shown;

[0055] The ultrasonic oscillator head 10 is the ultrasonic source and is partially immersed in the solution, as Figure 3 shown.

[0056] The bottom plate 1 and the micro-structure substrate 6 are placed above the scraping platform 9, and the bottom plate 1 is magnetically adsorbed on the scraping platform 9, as Figure 7 shown;

[0057] The two limiting plates 3 are attached to the surface of the bottom plate 1 by magnets 2 and press the side edges of the micro-structure substrate 6 towards the center to position the micro-structure substrate 6, as Figure 3 shown;

[0058] A circular hole 1b for facilitating the removal of the micro-structure substrate 6 is opened in the center of the bottom plate 1, as Figure 4 shown;

[0059] The wire rod 8 is above the micro-structure substrate 6, and there is a certain scraping gap between the wire rod 8 and the surface of the micro-structure substrate 6, as Figure 7 shown;

[0060] The limiting plate 3 is a rectangular plate, and one side is cut with a fitting curve slot that gradually changes from 120° to 30°. According to the V-shaped iron positioning principle, the limiting plate 3 can limit various planar shaped micro-structure substrates 6 such as rectangles, triangles, circles, sectors with different angles, and polygons along the scraping direction. Among them, different shaped micro-structure substrates 6 are represented by shadows, as Figures 8 to 13 shown;

[0061] The thickness, the limit angle of the slot, and the size of the plate surface of the limiting plate 3 can be processed and adjusted according to the coating requirements, but its thickness cannot exceed the thickness of the micro-structure substrate 6, and the plate surface cannot exceed the area that can be coated by the coater;

[0062] The process of the present invention is as follows:

[0063] First, clean the microstructured substrate 6 multiple times with absolute ethanol and acetone. Align the microstructured substrate 6 with the center of the bottom plate 1. Lift the two annular structures 4c of the handle 4 with a thin string and apply a certain force towards the center, so that the flexible indenter 5 inserted on the crossplate structure 4b of the handle 4 presses on the part of the edge of the microstructured substrate 6 without microstructures, providing a pressing force for the microstructured substrate 6 and a frictional force to prevent the horizontal movement of the microstructured substrate 6.

[0064] Immerse the multifunctional fixture and the microstructured substrate 6 in an ultrasonic instrument 7 filled with a photoresist solution. Turn on the immersion ultrasonic oscillator head 10 and start ultrasonic infiltration. In the embodiment, the selected ultrasonic instrument 7 is a Jiekang CE-9600 ultrasonic cleaner, the photoresist solution is RZJ-304-10 positive photoresist, the solvent is PGMEA, and the original photoresist is diluted at a ratio of 1:4 to obtain the solution used in the experimental case, with a viscosity of 1.6 mPa·s. The solution and environmental temperature is 20 °C, the ultrasonic frequency is 50 kHz, the power is 70 W, and the infiltration time is 5 min.

[0065] After the infiltration is completed, hold or operate the robotic arm to pull the two annular structures 4c of the handle 4, take out the microstructured substrate 6 from the solution, place it above the scraping platform 9, and pull out the pin structure 4a of the handle 4 from the side ear 1c of the bottom plate 1 to avoid position interference during the scraping process.

[0066] Attach the two limit plates 3 to the surface of the bottom plate 1 by relying on the magnet 2 and press tightly against the side of the microstructured substrate 6 towards the center to position the microstructured substrate 6 and prevent the solution from driving the microstructured substrate 6 to shift in position during the scraping process, which may affect the coating result.

[0067] After the scraping is completed, place the microstructured substrate 6 in a closed clean room environment and wait for the solution to dry naturally, forming a photoresist film on the microstructured substrate 6. Use the circular hole 1b in the center of the bottom plate 1 to remove the microstructured substrate 6, place it under a VK-X250 confocal microscope (KEYENCE) to observe the film coverage, and compare it with the film coverage effect obtained only by spin coating or scraping. The results show that the film prepared by the present invention has a higher coverage rate of the bottom of the microstructures 6 and a more uniform film thickness distribution. This example verifies that the present invention has a better coating effect on the microstructured substrate 6 compared to common wet film formation methods.

[0068] As described above, for those of ordinary skill in the art, various corresponding changes and deformations can be made according to the technical solutions and technical concepts of the present invention, and all such changes and deformations should fall within the protection scope of the present invention.

Claims

1. A method for forming a film on a microstructured substrate by combining ultrasonic oscillation and blade coating, characterized in that: It includes the following steps: A. Place the microstructured substrate (6) at the center of the bottom plate (1) of the multi-functional fixture, and position and fix the microstructured substrate (6); B. Immerse the microstructured substrate (6) into the solution in the ultrasonic instrument (7) by using the multi-functional fixture. The ultrasonic waves generated by the ultrasonic vibration head (10) drive the solution to oscillate, and the wettability of the microstructured substrate (6) is improved; C. Transfer the microstructured substrate (6) to the doctor blade coating platform (9) by using the multi-functional fixture and position it; remove the excess solution on the microstructured substrate (6) by the doctor blade coating method to level the liquid film.

2. The method for forming a film on a microstructured substrate by combining ultrasonic oscillation and blade coating according to claim 1, wherein: The surface of the microstructured substrate (6) has micron- or nanoscale microstructures with square wave, trapezoidal, wavy, or triangular cross-sections, and the microstructures are arranged along a straight line or circular arc trajectory on the surface of the microstructured substrate (6); the material of the microstructured substrate (6) is quartz or silicon, the microstructured substrate (6) has a triangular, rectangular, circular, polygonal, or fan-shaped shape, and the thickness is more than 0.5 mm; The solution includes a photoresist solution, a polyurethane solution, a perovskite solution, or a carbon nanotube solution; the viscosity of the solution is 1 to 1000 mPa·s; The ultrasonic instrument (7) is an ultrasonic cleaner, the microstructured substrate (6) and its multi-functional fixture are completely immersed in the solution, the frequency of the ultrasonic waves is 20 to 400 kHz, the power is 10 to 5000 W, and the amplitude is less than the solution atomization amplitude; The doctor blade coating method is to use a doctor blade or a wire bar (8) to perform one or more doctor blade coatings on the ultrasonically wetted microstructured substrate (6) in a certain direction, or perform a linear reciprocating doctor blade coating.

3. The method for forming a film on a microstructured substrate by combining ultrasonic oscillation and blade coating according to claim 1, characterized in that: The multi-functional fixture includes a bottom plate (1), a magnet (2), a limit plate (3), a handle (4), and a flexible pressing head (5); A circular hole (1b) is provided at the center of the bottom plate (1), there are two handles (4) which are respectively installed on the front and rear sides of the bottom plate (1), a plurality of grooves (1a) are distributed on the upper surface of the bottom plate (1), and the parallelism between the upper and lower surfaces of the bottom plate (1) shall not exceed 0.01 mm, and the roughness shall not exceed Ra1.6; The magnet (2) is embedded in the groove (1a) on the upper surface of the bottom plate (1), and the magnet (2) is fixed and sealed by using a sealant; There are two limit plates (3) which are respectively adsorbed on the left and right sides of the bottom plate (1); The flexible pressing head (5) is installed inside the handle (4) and is used to press the microstructured substrate (6).

4. The method for forming a film on a microstructured substrate by combining ultrasonic oscillation and blade coating according to claim 3, wherein: The limit plate (3) is a rectangular plate, and a fitting curve slot gradually changing from 120° to 30° is cut on the inner side, which is used to limit the microstructured substrate (6) along the doctor blade coating direction; the thickness of the limit plate (3) does not exceed the thickness of the microstructured substrate (6), and the plate surface does not exceed the size of the coating area of the doctor blade coater.

5. The method for forming a microstructured substrate film by combining ultrasonic oscillation and blade coating according to claim 3, wherein: The lower part of the handle (4) is connected to the side ear (1c) of the bottom plate (1) through a pin structure (4a) with clearance fit; a horizontal plate structure (4b) is provided inside the handle (4), and the slot (5a) of the flexible pressing head (5) is fixedly installed on the horizontal plate structure (4b) by interference fit; a ring structure (4c) is provided at the top of the handle (4).

6. The method for forming a film on a microstructured substrate by combining ultrasonic oscillation and blade coating according to claim 3, characterized in that: The material of the flexible pressing head (5) is rubber; The number, position and size of the protrusions (5b) on the flexible indenter (5) are determined according to the size and shape of the substrate of the flexible indenter (5). The shape of the protrusions (5b) includes a cuboid, a cylinder or a hemisphere. The protrusions (5b) press on the outside of the microstructures on the microstructured substrate (6).

7. The method for forming a film on a microstructured substrate by combining ultrasonic oscillation and blade coating according to claim 3, characterized in that: The usage method of the handle (4) is as follows: squeeze the annular structures (4c) on both sides of the handle (4) inward, and press the microstructured substrate (6) on the surface of the bottom plate (1) through the flexible indenter (5).

8. The method for forming a film on a microstructured substrate by combining ultrasonic oscillation and blade coating according to claim 3, characterized in that: When performing ultrasonic oscillation, use a magic tape or a thin wire to pass through the annular structure (4c) at the top of the handle (4) and apply an inward pulling force; After the ultrasonic oscillation is completed, manually lift the handles (4) on both sides, or use a robotic arm to lift the multifunctional fixture, quickly place the multifunctional fixture and the microstructured substrate (6) on the doctor blade platform (9), while avoiding tilting and vibration. After placing it in place, pull out the handles (4) on both sides.

9. The method for forming a film on a microstructured substrate by combining ultrasonic oscillation and blade coating according to claim 3, wherein: During the doctor blade coating process, set the doctor blade coating gap in advance to avoid the doctor blade or wire bar (8) hitting the microstructured substrate (6) due to too small a gap, or the solution not being contacted or the amount of solution removed being too small due to too large a gap.

10. The method for forming a film on a microstructured substrate by combining ultrasonic oscillation and blade coating according to claim 1, characterized in that: The shape of the groove (1a) is circular, rectangular or polygonal; the material of the limiting plate (3) is a FeCoNi alloy.

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