A substrate film forming method combining ultrasonic vibration and doctor blade coating

Abstract

The present application belongs to the field of precision microfabrication, and discloses a microstructure substrate film forming method combining ultrasonic oscillation and doctor blade coating, comprising the following steps: positioning and fixing the microstructure substrate; improving the wettability of the microstructure substrate; removing the excess solution on the microstructure substrate and leveling the liquid film. The microstructure substrate is immersed into the solution in the ultrasonic instrument, the solution is oscillated by the amplitude and frequency of the ultrasonic wave, the contact angle of the solution at the bottom of the microstructure is reduced by the hysteresis effect of the contact angle, and the air layer at the bottom of the microstructure is removed by the cavitation effect of the ultrasonic wave, so as to enhance the wettability of the solution to the bottom of the microstructure. 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, multiple repetitive operations and long process in the existing single wet coating method are overcome, and the thin film with high coverage, ideal film thickness and uniformity is prepared on the microstructure substrate.

Description

Technical Field

[0001] This invention belongs to the field of precision micromachining, and specifically relates to a method for forming microstructured substrate films by combining ultrasonic oscillation and doctor blade coating. Background Technology

[0002] Fabricating microstructures on substrates is a crucial technology in micro / nano manufacturing, widely applied in semiconductors, optoelectronics, sensors, biosensors, and microelectromechanical systems (MEMS). With the deepening of scientific research, many high-performance devices are no longer satisfied with single-layer microstructures. For example, in silicon-based OLED microdisplays, multi-level microstructures need to be fabricated on existing microstructures using photolithography to achieve better light-gathering effects. In hydrophobic material research, fabricating even smaller secondary microstructures on primary microstructures can imbue them with superhydrophobicity. Simultaneously, the demand for re-coating and etching surface structures on devices with existing microstructures is also increasing. For instance, coating and etching micron-scale ring microstructures in vertical-cavity surface-emitting lasers (VCSELs) can generate hollow laser beam output. In microstructure transfer, a uniformly coated thin film perfectly fitting the gaps between microstructures is required on a substrate with existing microstructures to achieve perfect replication.

[0003] However, in the aforementioned thin film preparation methods, common wet coating techniques such as spin coating, blade coating, slot coating, and dip coating are used directly on microstructured substrates. Due to the surface tension of the solution, a Cassie-Baxter wetting state is formed above the microstructure, meaning the droplet is located on top of the rough surface with an air layer below. This makes it difficult to wet the bottom of the grooves in the microstructure. This insufficient wettability leads to non-conformal interactions between the fluid and the substrate, resulting in interface defects. Existing solutions often involve multiple applications of liquid and spin coating on the substrate surface, with each spin coating speed often exceeding 1000 rpm and time exceeding 5 minutes. This method results in numerous repetitive operations and wasted time. Furthermore, the excessively long coating time causes the film to dry during spin coating, leading to uneven film thickness distribution, poor film quality, and consequently, unsatisfactory microstructure morphology obtained through subsequent etching. Methods to improve solution wettability through chemical modification of the solution or substrate have poor versatility and can cause serious environmental pollution and toxicological problems. Methods to enhance wettability through pressure often damage the substrate. Meanwhile, in processes such as spin coating or blade coating, due to the diversity of substrate shapes, existing methods for fixing substrates via vacuum adsorption are prone to problems such as inaccurate substrate positioning, solution being sucked into the pump tube causing blockage, and the need for frequent disassembly and cleaning. Therefore, there is an urgent need for a non-destructive film formation method that can rapidly improve the wettability of solutions on substrates with microstructures, as well as a substrate fixture that can be adapted to this method, to solve the problems of transfer and positioning of substrates with various shapes during the film formation process. Summary of the Invention

[0004] To address the aforementioned problems in existing technologies, this invention aims to design a microstructure substrate film-forming method that combines ultrasonic oscillation and doctor blade coating, which can rapidly improve the wettability of the solution on the substrate microstructure without damaging the film.

[0005] To achieve the above objectives, the technical solution of the present invention is as follows: a method for forming a microstructured substrate film by combining ultrasonic oscillation and blade coating, comprising the following steps:

[0006] A. Place the microstructure substrate in the center of the base plate of the multi-functional fixture, and position and fix the microstructure substrate.

[0007] B. Using a multi-functional clamp, the microstructured substrate is immersed in the solution inside the ultrasonic instrument. The ultrasonic waves generated by the ultrasonic oscillator head cause the solution to oscillate, thereby improving the wettability of the microstructured substrate.

[0008] C. Use a multi-functional fixture to transfer the microstructure substrate to the coating platform and position it; remove excess solution from the microstructure substrate by coating and smooth the liquid film.

[0009] Furthermore, the surface of the microstructure substrate has micron or nanoscale microstructures with square wave, trapezoidal, wavy, or triangular cross-sections, and the microstructures are arranged along straight lines or circular arcs on the surface of the microstructure substrate; the material of the microstructure substrate is quartz or silicon, and the microstructure substrate has triangular, rectangular, circular, polygonal, or fan-shaped shapes, with a thickness of 0.5 mm or more;

[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 microstructure substrate and its multifunctional fixture are completely immersed in the solution. The frequency of the ultrasonic wave is 20-400kHz, the power is 10-5000W, and the amplitude is smaller than the atomization amplitude of the solution.

[0012] The coating method involves using a scraper or wire bar to coat the ultrasonically impregnated microstructure substrate once or multiple times along a certain direction, or performing linear reciprocating coating.

[0013] Furthermore, the multifunctional clamp includes a base plate, a magnet, a limiting plate, a handle, and a flexible pressure head;

[0014] The base plate has a through hole in the center, and there are two handles installed on the front and rear sides of the base plate respectively. Multiple grooves are distributed on the upper surface of the base plate. The parallelism between the upper and lower surfaces of the base plate shall not exceed 0.01 mm, and the roughness shall not exceed Ra1.6.

[0015] The magnet is embedded in a groove on the upper surface of the base plate and is fixed and sealed with sealant.

[0016] There are two limiting plates, which are respectively attached to the left and right sides of the base plate.

[0017] The flexible pressure head is installed on the inside of the handle and is used to press down the microstructure substrate.

[0018] Furthermore, the limiting plate is a rectangular plate with a fitted curve groove cut from 120° to 30° on its inner side, used to limit the microstructure substrate along the coating direction. The thickness of the limiting plate does not exceed the thickness of the microstructure substrate, and the plate surface does not exceed the size of the coating area of ​​the coating machine.

[0019] Furthermore, the lower part of the handle is connected to the side lug of the base plate through a clearance-fitted pin structure; the inner side of the handle has a horizontal plate structure, and the slot of the flexible pressure head is fixedly installed on the horizontal plate structure through an interference fit; a ring structure is provided at the top of the handle.

[0020] Furthermore, the flexible pressure head is made of 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 shape of the protrusions includes cuboids, cylinders, or hemispheres. The protrusions press on the outer side of the microstructure on the microstructure substrate.

[0022] Furthermore, the method of using the handle is as follows: the annular structure of the handles on both sides is pressed inward, and the microstructure substrate is pressed onto the surface of the base plate by the flexible pressure head.

[0023] Furthermore, during ultrasonic oscillation, apply inward tension by threading a Velcro strip or thin thread through the annular structure at the top of the handle;

[0024] After ultrasonic oscillation is completed, manually lift the handles on both sides or use a robotic arm to lift the multi-functional fixture and quickly place the multi-functional fixture and microstructure substrate on the coating platform, while avoiding tilting and vibration. After placing it in place, pull out the handles on both sides.

[0025] Furthermore, during the coating process, the coating gap is set in advance to avoid the gap being too small, causing the scraper or wire bar to hit the microstructure substrate, or the gap being too large, resulting in no contact with the solution or too little solution being removed.

[0026] Furthermore, the groove can be circular, rectangular, or polygonal in shape.

[0027] Furthermore, the limiting plate is made of an iron-cobalt-nickel alloy.

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

[0029] 1. This invention involves immersing a microstructured substrate in a solution within an ultrasonic instrument. The amplitude and frequency of the ultrasound waves cause the solution to oscillate, reducing the contact angle at the bottom of the microstructure by utilizing the hysteresis effect of the contact angle. Simultaneously, the cavitation effect of the ultrasound waves removes the air layer at the bottom of the microstructure, thereby enhancing the wettability of the solution on the microstructure bottom. This invention effectively improves the wettability of the solution on the microstructured substrate, overcoming the problems of poor wettability of the solution on the bottom of the microstructure, numerous repetitive operations, and long processes in existing single wet coating methods. It enables the preparation of thin films with high coverage, ideal film thickness, and uniformity on microstructured substrates.

[0030] 2. This invention improves the wettability of a solution by adjusting the contact angle of the solution through the amplitude and frequency of ultrasound. Compared with methods that chemically modify the solution and substrate, this method avoids environmental pollution and toxicological problems. Furthermore, compared with methods that apply pressure to the solution on the substrate surface to improve wettability, this method avoids pressure damage to the integrity of the substrate surface. It is a greener, more user-friendly, and more convenient method for improving wettability.

[0031] 3. This invention solves the problem of transferring from ultrasonic instruments to a coating platform through the design of a multifunctional fixture for film formation. It also solves the problem of positioning irregularly shaped substrates during the coating process. The operation is simple, the process is safe, and the coating accuracy and efficiency are high. Attached Figure Description

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

[0033] Figure 2 This is a schematic diagram of a square waveform microstructure;

[0034] Figure 3 This is a schematic diagram of the microstructure substrate being impregnated in an ultrasonic instrument after being fixed by a multifunctional clamp;

[0035] Figure 4 This is a schematic diagram of the base plate structure of the multi-functional fixture;

[0036] Figure 5 This is a schematic diagram of the handle structure of a multi-functional clamp;

[0037] Figure 6 This is a schematic diagram of the flexible pressure head structure of a multi-functional clamp;

[0038] Figure 7 This is a schematic diagram of the microstructure substrate being positioned and coated using a multi-functional fixture.

[0039] Figure 8 This is a schematic diagram of how the limiting plate positions the triangular base (shaded area);

[0040] Figure 9 This is a schematic diagram of how the limiting plate positions the rectangular base (shaded area);

[0041] Figure 10 This is a schematic diagram of how the limiting plate positions the circular base (shaded area);

[0042] Figure 11 This is a schematic diagram of how the limiting plate positions the sector base (shaded area) at different angles;

[0043] Figure 12 This is a schematic diagram of how the limiting plate positions the polygonal base (shaded area, hexagonal as an example);

[0044] Figure 13 This is a schematic diagram of how the limiting plate positions the random irregular base (shaded area).

[0045] In the diagram: 1-base plate, 1a-groove, 1b-round hole, 1c-side ear, 2-magnet, 3-limiting plate, 4-handle, 4a-pin structure, 4b-horizontal plate structure, 4c-ring structure, 5-flexible pressure head, 5a-slot, 5b-protrusion, 6-microstructure substrate, 7-ultrasonic instrument, 8-wire bar, 9-scraping platform, 10-ultrasonic oscillating head. Detailed Implementation

[0046] To better understand the above-mentioned objectives, features and advantages of the present invention, the present invention will be further described below in conjunction with the accompanying drawings and specific embodiments.

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

[0048] The microstructure substrate is a square-wave-shaped circular ring microstructure quartz substrate, measuring 60×60mm in size and 0.5mm in thickness. The largest circular ring containing the microstructure has a diameter of 42mm. Figure 1 As shown;

[0049] The width of the square-wave microstructure bosses and grooves is 20–200 μm, and the groove depth is 3–5 μm. Figure 2 As shown.

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

[0051] The handle 4 is connected to the side lug of the base plate 1 via a pin structure, such as Figure 3-5 As shown;

[0052] The flexible pressure head 5 is connected to the protruding structure 4b of the handle 4 via a slot 5a, such as... Figure 3 , 5 As shown in Figure 6;

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

[0054] The microstructure substrate 6 is pressed onto the surface of the base plate 1 by a flexible pressure head 5, and then placed into an ultrasonic instrument 7 containing a photoresist solution, immersing the microstructure substrate 6 in the photoresist solution. Figure 3 As shown;

[0055] The ultrasonic oscillating head 10 is an ultrasonic source, partially immersed in the solution, such as... Figure 3 As shown.

[0056] The base plate 1 and the microstructure substrate 6 are placed above the coating platform 9. The base plate 1 is magnetically attached to the coating platform 9. Figure 7 As shown;

[0057] The two limiting plates 3 are attached to the surface of the base plate 1 by magnets 2 and press against the sides of the microstructure substrate 6 towards the center to position the microstructure substrate 6. Figure 3 As shown;

[0058] The base plate 1 has a circular hole 1b at its center for easy removal of the microstructure substrate 6, such as... Figure 4 As shown;

[0059] The wire rod 8 is positioned above the microstructure substrate 6, with a certain gap between it and the surface of the microstructure substrate 6, such as... Figure 7 As shown;

[0060] The limiting plate 3 is a rectangular plate with a fitted curve groove cut from 120° to 30° on one side. It can limit the position of various planar irregularly shaped microstructure substrates 6 along the coating direction, such as rectangles, triangles, circles, fan shapes at different angles, and polygons, according to the V-shaped iron positioning principle. Different shaped microstructure substrates 6 are indicated by shading, such as... Figures 8-13 As shown;

[0061] The thickness, grooving limit angle, and plate size of the limiting plate 3 can be processed and adjusted according to the coating requirements, but its thickness cannot exceed the thickness of the microstructure substrate 6, and its plate size cannot exceed the area that the scraper can coat.

[0062] The process of this invention is as follows:

[0063] First, the microstructure substrate 6 is cleaned multiple times with anhydrous ethanol and acetone. The microstructure substrate 6 is aligned with the center of the base plate 1. The two annular structures 4c of the handle 4 are lifted with a thin rope and a certain force is applied to the center. The flexible pressure head 5 inserted on the horizontal plate structure 4b of the handle 4 presses against the part of the microstructure substrate 6 that does not have a microstructure, providing the microstructure substrate 6 with a clamping force and a frictional force that hinders the horizontal movement of the microstructure substrate 6.

[0064] The multifunctional fixture and the microstructure substrate 6 were immersed in an ultrasonic instrument 7 containing a photoresist solution. The submersible ultrasonic oscillator 10 was turned on to begin ultrasonic immersion. In this embodiment, the ultrasonic instrument 7 was a Jiekang CE-9600 ultrasonic cleaner, the photoresist solution was RZJ-304-10 positive photoresist, the solvent was PGMEA, and the photoresist raw material was 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 ambient temperature were 20°C, the ultrasonic frequency was 50 kHz, the power was 70 W, and the immersion time was 5 min.

[0065] After the soaking is completed, hold the two annular structures 4c of the handle 4 by hand or operate the robotic arm to remove the microstructure substrate 6 from the solution and place it above the coating platform 9. Then, pull the pin structure 4a of the handle 4 out from the side lug 1c of the base plate 1 to avoid positional interference during the coating process.

[0066] Two limiting plates 3 are attached to the surface of the base plate 1 by magnet 2 and pressed towards the center of the side of the microstructure substrate 6 to position the microstructure substrate 6 and prevent the solution from causing the microstructure substrate 6 to shift position during the coating process, which would affect the coating result.

[0067] After the coating process, the microstructure substrate 6 was placed in a sealed cleanroom environment to allow the solution to dry naturally, forming a photoresist film on the microstructure substrate 6. The microstructure substrate 6 was then removed using the circular hole 1b in the center of the base plate 1 and observed under a VK-X250 confocal microscope (KEYENCE). The film coverage was compared with that obtained by spin coating or scraping alone. The results showed that the film prepared using this invention had a higher coverage of the bottom 6 of the microstructure and a more uniform film thickness distribution. This example verifies that the present invention provides a better coating effect on the microstructure substrate 6 compared to common wet film formation methods.

[0068] As described above, those skilled in the art can make various other corresponding changes and modifications based on the technical solutions and concepts of this invention, and all such changes and modifications should fall within the protection scope of this invention.

Claims

1. A method of forming a film on a microstructured substrate by combining ultrasonic oscillation and doctor blading, characterized by: It comprises the following steps: A. Place the microstructure substrate (6) in the center of the bottom plate (1) of the multifunctional clamp and position and fix the microstructure substrate (6); B. Use the multifunctional clamp to immerse the microstructure substrate (6) in the solution in the ultrasonic instrument (7), and use the ultrasonic waves generated by the ultrasonic vibration head (10) to drive the solution to vibrate, thereby improving the wettability of the microstructure substrate (6); C. Use the multifunctional clamp to transfer the microstructure substrate (6) to the scraping platform (9) and position it; remove the excess solution on the microstructure substrate (6) by scraping method and level the liquid film. The multifunctional clamp comprises a bottom plate (1), a magnet (2), a limiting plate (3), a handle (4) and a flexible pressing head (5); The center of the bottom plate (1) is provided with a circular hole (1b), the handle (4) has two parts, which are respectively installed on the front and rear sides of the bottom plate (1), and a plurality of grooves (1a) are distributed on the upper surface of the bottom plate (1), the parallelism of the upper and lower surfaces of the bottom plate (1) should not exceed 0.01 mm, and the roughness should 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 sealing glue; The limiting plate (3) has two parts, which are respectively adsorbed on the left and right sides of the bottom plate (1); The flexible pressing head (5) is installed on the inner side of the handle (4) and is used to press the microstructure substrate (6); The limiting plate (3) is a rectangular plate, which is cut with a fitting curve slot gradually changing from 120° to 30° on the inner side, which is used to limit the microstructure substrate (6) in the scraping direction; the thickness of the limiting plate (3) should not exceed the thickness of the microstructure substrate (6), and the plate surface should not exceed the size of the coating area of the scraping machine.

2. The method according to claim 1, wherein the method is characterized by: The surface of the microstructure substrate (6) has microstructures of square wave type, trapezoidal, wavy and triangular cross section at micron or nanometer level, and the microstructures are arranged along a straight line or a circular arc track on the surface of the microstructure substrate (6); the material of the microstructure substrate (6) is quartz or silicon, and the microstructure substrate (6) has a circular, polygonal or sector shape with a thickness of more than 0.5mm; The solution comprises photoresist solution, polyurethane solution, perovskite solution or carbon nanotube solution; the viscosity of the solution is 1~1000 mPa·s; The ultrasonic instrument (7) is an ultrasonic cleaning instrument, the microstructure substrate (6) and its multifunctional clamp are completely immersed in the solution, the frequency of the ultrasonic wave is 20~400 kHz, the power is 10~5000 W, and the amplitude is less than the atomization amplitude of the solution; The scraping method is to use a scraper or a wire bar (8) to scrape the microstructure substrate (6) after ultrasonic immersion in a certain direction for one or more times, or to perform linear reciprocating scraping.

3. The method according to claim 1, wherein the method is characterized by: The lower part of the handle (4) is connected with the side ear (1c) of the bottom plate (1) through a clearance fit column pin structure (4a); the inner side of the handle (4) has a horizontal plate structure (4b), the insertion slot (5a) of the flexible pressing head (5) is fixedly installed on the horizontal plate structure (4b) through interference fit; the top of the handle (4) is provided with an annular structure (4c).

4. The method according to claim 1, wherein the method is characterized by: The material of the flexible pressing head (5) is rubber. The number, position and size of the protrusions (5b) on the flexible pressure head (5) are determined according to the size and shape of the substrate of the flexible pressure head (5), the shape of the protrusions (5b) includes cuboid, cylinder or hemisphere, and the protrusions (5b) are pressed on the outer side of the microstructure on the microstructure substrate (6).

5. The method according to claim 1, wherein the method is characterized by: The use method of the handle (4) is to press the annular structure (4c) of the two handles (4) inward, and press the microstructure substrate (6) on the surface of the bottom plate (1) through the flexible pressure head (5).

6. The method according to claim 1, wherein the method is characterized by: When the ultrasonic oscillation is performed, a magic tape or a thin wire is used to apply a pulling force inward through the annular structure (4c) at the top of the handle (4); After the ultrasonic oscillation is completed, the two handles (4) are manually lifted, or the multifunctional clamp is lifted by using a mechanical arm, and the multifunctional clamp and the microstructure substrate (6) are quickly placed on the scraping platform (9), while avoiding tilting and vibration, and after being placed in place, the two handles (4) are pulled out.

7. The method according to claim 1, wherein the method is characterized by: During the scraping process, the scraping gap is set in advance to avoid that the scraping knife or the wire rod (8) hits the microstructure substrate (6) due to too small gap, or that the solution is not contacted or the amount of removed solution is too small due to too large gap.

8. The method according to claim 1, wherein the method is characterized by: The shape of the groove (1a) is circular or polygonal; the material of the limiting plate (3) is iron-cobalt-nickel alloy.

Images