Fine structure manufacturing method based on mask protection and non-contact polishing process

Abstract

A fine structure manufacturing method based on mask protection and a non-contact polishing process. The method comprises the following steps: pretreatment; photoresist applying; exposure; development; non-contact polishing; and photoresist removal detection. In a fine structure machining procedure, a region of a substrate (1) that is not covered by a photoresist (2) is polished to realize material removal, and with regard to a region that is protected by the photoresist (2), that is, a mask protected region, material removal is not realized on the substrate (1), and only the photoresist (2) is removed. Since a material removal rate of the photoresist (2) is less than a material removal rate of the substrate (1), a height difference is generated between the mask protected region and the unprotected region, that is, a fine structure that needs to be manufactured is obtained.

Description

A microstructure manufacturing method based on mask protection and non-contact polishing process Technical Field

[0001] The present invention belongs to the field of precision / ultra-precision machining, and in particular relates to a microstructure manufacturing method based on mask protection and non-contact polishing technology. Background Art

[0002] Microstructured surfaces have been widely adopted in defense, optics, microfluidics, and surface engineering due to their unique properties and functions not found in traditional surfaces. In fields like communications and radar, the slow-wave structures of the core components of terahertz radiation source vacuum devices are typical complex thin-walled structures with large aspect ratios, often featuring folded and rectangular microstructures. In the optical field, microstructures such as microlens arrays and Fresnel lens structures play important roles in optical systems, such as imaging, focusing, and illumination. In microfluidics, microstructures are widely used in microfluidic chips or in the molds used to manufacture them. Furthermore, microstructures also play an important role in the preparation of functional surfaces.

[0003] For microstructures, surface accuracy and surface quality are two key factors. Microstructures on core components in fields such as defense, optics, and microfluidics often require submicron surface accuracy and nanometer / subnanometer surface roughness with no surface / subsurface damage. Therefore, achieving high-precision, high-surface-quality manufacturing of microstructures has become a key issue. Currently, commonly used microstructure fabrication methods include etching, electrodeposition, and focused ion beam machining. While these methods can achieve high precision, they are costly, complex, and require long manufacturing cycles. 3D printing and femtosecond laser machining can also be used to fabricate microstructures, but their accuracy and surface quality are poor, failing to meet practical application requirements. Considering factors such as processing efficiency, cost, and accuracy, precision machining techniques such as cutting and grinding are considered a more reasonable and effective method for microstructures measuring tens to hundreds of microns. However, while precision machining techniques can meet submicron precision requirements, they cannot effectively guarantee surface quality, and the resulting microstructures often exhibit surface defects such as ripples, burrs, and tool marks.

[0004] Chinese invention CN201010128839.5 discloses a method for producing ultrafine lines using oxidation and chemical mechanical polishing, belonging to the field of ultra-large-scale integrated circuit manufacturing technology. This method primarily utilizes deposition lithography, chemical mechanical polishing, and dry etching; it essentially still produces microstructures through etching, rather than directly producing them through non-contact polishing.

[0005] Chinese invention CN201310168596.1 discloses a backside polishing process for back-passivated solar cells. The process involves first forming a protective silicon nitride mask of a certain thickness on the front side of the silicon wafer, then using a heated concentrated alkali solution to moderately etch the backside of the wafer to achieve a polishing effect. Essentially, the process uses the mask to protect surfaces that don't need to be etched, and it doesn't involve microstructure processing.

[0006] Chinese invention CN201510977465.7 discloses a method for preparing a mask for soft X-ray exposure, which mainly involves processes such as spin coating, electroplating, ion beam etching, and wet etching, and does not involve the use of non-contact polishing technology to manufacture microstructures.

[0007] Chinese invention CN202110638015.0 discloses a method for producing back-polished monocrystalline silicon cells using a masking process. The main steps are polishing, back masking, front texturing, diffusion PN junction formation, secondary pickling, front silicon nitride coating, screen printing, and sintering. This method essentially involves depositing a silicon nitride protective film via PECVD, followed by single-sided etching, without the need for photolithography or non-contact polishing.

[0008] Chinese invention CN202010289042.7 discloses a single-sided polishing method for solar cells using a mask. The mask essentially involves forming an oxide film through thermal diffusion, using the oxide film as a mask. The oxide film is then removed from one side for etching and polishing. Photolithography and non-contact polishing processes are not involved.

[0009] Chinese invention CN202210720089.3 discloses a P-type IBC solar cell, its preparation method, solar cell assembly, and photovoltaic system. This patent applies to the field of solar cell technology and primarily utilizes deposition, laser ablation, and laser grooving processes, without utilizing photolithography masks or non-contact polishing.

[0010] Chinese invention CN202111601571.7 discloses a method for fabricating a microwave thin film integrated circuit. This method uses vacuum sputtering to form an etch-resistant TiW mask protective layer. A photoresist stripping process is then used to effectively remove the etch-resistant metal mask protective layer from non-patterned areas. The remaining film layers are then removed in a specific order to produce a microwave thin film integrated circuit board. This method essentially involves etching the areas not covered by the mask protective layer, rather than non-contact polishing.

[0011] Chinese invention CN202210928731.7 discloses a method for fabricating micro-nano devices on the surface of a thin-film lithium niobate. This method uses a chromium film as a protective mask, then wet-etches the surface of the thin-film lithium niobate using a microstructure. The microstructure is then post-processed using chemical mechanical polishing, rather than directly polishing the microstructure.

[0012] Chinese invention CN202210942514.3 discloses a method for fabricating a tapered silicon-based solid microneedle array. This method uses magnetron sputtering to create a protective film, which serves as a mask to protect the parts that do not require processing. The microstructure is then fabricated using etching techniques, without involving non-contact polishing.

[0013] Chinese invention CN202011080103.5 discloses a micro-groove jet polishing device and polishing method. This method utilizes various fixing elements to protect the areas that do not require polishing, and then uses a jet polishing method to polish the micro-grooves. This method primarily aims to address the problem of poor surface quality in manufactured micro-grooves.

[0014] Chinese invention CN202010492399.5 discloses a microstructure polishing method based on localized shear thickening. This method places a gap between the microstructured surface of a part and the tool, then adds a non-Newtonian polishing fluid with a shear thickening effect. The microstructured surface is polished through the relative shear motion between the tool and the microstructured surface. This method polishes the existing microstructure on the part surface, rather than directly machining the microstructure on the part surface through polishing.

[0015] In summary, the idea of ​​existing methods is to protect the parts that do not need to be processed by preparing a mask, and then manufacture microstructures through processes such as etching and ion beam. When using the etching method for manufacturing, side etching is prone to occur, and the etching solution is easy to pollute the environment; although ion beam processing can obtain microstructures with higher precision, the equipment required for this technology is expensive and the efficiency is low. In addition, at present, the shear thickening non-contact polishing method is mostly used for polishing microstructures, that is, to further finish the microstructures manufactured by other methods to improve the surface quality, but it has not been used to manufacture microstructures on the surface of parts. Therefore, it is of great significance to study the damage-free and precision manufacturing methods of microstructures.

[0016] Summary of the Invention

[0017] In response to the problems encountered in existing microstructure manufacturing methods, the present invention proposes a microstructure manufacturing method based on mask protection and non-contact polishing process. This method can manufacture microstructures on flat or curved surfaces, and will not cause side etching and polishing liquid contamination problems during the manufacturing process. At the same time, the surface of the manufactured microstructure has no defects such as knife marks and burrs, and the surface quality is good and the surface shape accuracy is high.

[0018] In order to achieve the above object, the technical solution adopted by the present invention is:

[0019] A method for manufacturing a microstructure based on mask protection and non-contact polishing process, comprising the following steps:

[0020] Step 1: Preprocessing

[0021] Pre-treating the substrate surface, wherein the pre-treatment method includes polishing, wiping with acetone or alcohol, ultrasonic cleaning, and nitrogen purging;

[0022] Step 2: Glue

[0023] Evenly apply photoresist on the surface of the substrate, with a thickness of 15-30 μm; the method of applying the photoresist includes spin coating and spray coating;

[0024] Step 3: Exposure

[0025] Designing a corresponding microstructure pattern on a mask plate, and processing the desired microstructure pattern on a photoresist through exposure; the exposure method includes mask alignment exposure, stepper projection exposure, laser direct writing, and electron beam direct writing;

[0026] Step 4: Development

[0027] The photoresist remaining on the substrate surface after the development operation is used as a mask to protect the substrate during the non-contact polishing process; the development method includes immersion development, spray development, and stirring development;

[0028] Step 5: Non-contact polishing

[0029] First, a non-Newtonian fluid polishing liquid with a shear thickening effect is prepared; the non-Newtonian fluid polishing liquid includes a base liquid and abrasive particles; the base liquid is a mixture of a polyhydroxy polymer and deionized water; the abrasive particles include a mixture of one or more of diamond, silicon carbide, aluminum oxide or silicon dioxide.

[0030] Afterwards, the exposed and developed substrate is fixed in a polishing liquid tank, the gap between the polishing tool and the substrate surface is adjusted, and the prepared non-Newtonian fluid polishing liquid is added;

[0031] Adjust the polishing tool speed, and use the rotation of the polishing tool to drive the non-Newtonian fluid to produce shear thickening effect. Several polyhydroxy polymers wrap the abrasive particles to form a "flexible fixed abrasive" on the substrate surface.

[0032] Afterwards, the "flexible fixed abrasive" removes material from the photoresist and substrate surface under the drive of the shear force of the polishing liquid.

[0033] Step 6: Glue removal test

[0034] After polishing, the photoresist on the substrate surface is completely removed; the surface morphology, surface quality, and surface accuracy of the microstructure of the substrate surface after the photoresist removal are tested; the photoresist removal method includes dry photoresist removal or wet photoresist removal.

[0035] Furthermore, in the first step, the substrate includes a flat surface and a curved surface, and there is no microstructure on the surface of the substrate;

[0036] Furthermore, in the fifth step, the gap between the polishing tool and the surface of the substrate is 100-200 μm.

[0037] The beneficial effects of the present invention are:

[0038] 1. The present invention proposes a new process for manufacturing microstructures using mask protection and non-contact polishing. Currently, the shear thickening non-contact polishing process is mostly used to remove surface defects of workpieces, such as burrs and scratches, to improve surface quality and reduce surface roughness, and has not yet been used for the manufacture of microstructures. The new process proposed by the present invention is specifically to pre-treat a flat or curved substrate that does not initially have a microstructure and perform a non-contact polishing process. During the processing, the area of ​​the substrate not covered by the photoresist is polished, resulting in material removal, while the area protected by the photoresist, that is, the mask protection area, does not produce material removal from the substrate, and only the photoresist is removed. Since the material removal rate of the photoresist is lower than the material removal rate of the substrate, a height difference is generated between the mask protection area and the unprotected area, that is, the microstructure to be manufactured.

[0039] 2. The novel process proposed in this invention enables high-quality fabrication of microstructures in a single step. Because the present invention utilizes a shear-thickening, non-contact polishing process to produce microstructures, the polishing tool does not come into direct contact with the substrate surface. Instead, material removal is achieved through the shearing action of the polishing fluid. Consequently, the resulting microstructures are free of surface defects such as knife marks, burrs, and scratches. This eliminates the need for further polishing to remove surface defects, such as knife marks, scratches, and burrs, typically associated with ultra-precision machining of microstructures.

[0040] 2. The microstructures machined by the present invention have high surface precision and no side etching. In traditional etching processes, due to the uncontrollable etching direction, side etching is prone to occur after processing, resulting in poor surface precision of the etched structures. The present invention utilizes a non-contact polishing process with a shearing material removal mechanism, which does not affect the sidewalls of the microstructure, i.e., no side etching occurs. As a result, the machined microstructures have high surface precision.

[0041] 4. The present invention avoids contamination of the etching solution. The non-Newtonian fluid polishing solution formulated in the present invention does not contain chemical reagents, thus avoiding the disadvantage of traditional etching solutions causing contamination. At the same time, the raw materials of the polishing solution are low-cost and easily available. BRIEF DESCRIPTION OF THE DRAWINGS

[0042] FIG1 is a flow chart of the present invention;

[0043] FIG2 is a schematic diagram of the processing principle of the present invention;

[0044] FIG3 is a schematic diagram of the processing of a planar concentric circle grating structure;

[0045] Figure 4 is a schematic diagram of the microfluidic chip structure processing;

[0046] Figure 5 is a schematic diagram of Fresnel structure processing.

[0047] In the figure: 1 - substrate, 2 - photoresist, 3 - mask, 4 - polishing tool, 5 - polishing liquid tank, 6 - polishing liquid, 7 - polyol polymer, 8 - abrasive, 9 - flexible fixed abrasive. DETAILED DESCRIPTION

[0048] The following provides a clear and complete description of the principles and technical solutions of the present invention in conjunction with the following embodiments and accompanying drawings. The described embodiments are only some embodiments of the present invention, not all embodiments. Based on the following embodiments, other embodiments obtained by ordinary technicians in this field without making any creative efforts are within the scope of protection of the present invention.

[0049] Example 1:

[0050] As shown in Figure 1-3, the steps for manufacturing a planar concentric circular grating structure are as follows:

[0051] Step 1: Surface Pretreatment

[0052] A substrate 1 coated with a nickel-phosphorus alloy coating was selected as the base. To prevent surface impurities from affecting the photoresist 2 coating and to minimize the impact of initial surface quality on the resulting microstructure, the surface of substrate 1 was pretreated. Treatment methods included, but were not limited to, pre-polishing, wiping with acetone or alcohol, ultrasonic cleaning, and nitrogen purging.

[0053] Step 2: Glue

[0054] The photoresist 2 is evenly coated on the surface of the substrate 1. The coating method includes spin coating, spray coating, etc. The thickness of the photoresist 2 is 15 μm.

[0055] Step 3: Exposure

[0056] A concentric grating pattern is designed on the mask plate 3 , and the photoresist 2 is exposed to form the concentric grating pattern on the photoresist 2 .

[0057] Step 4: Development

[0058] The development operation is performed using different developer solutions, and the development methods include immersion, spraying, stirring, etc. After the development operation, the photoresist 2 remaining on the surface of the substrate 1 is used as a mask to serve as a protective film for the substrate during the non-contact polishing process.

[0059] Step 5: Non-contact polishing

[0060] First, a non-Newtonian fluid polishing liquid 6 with a shear thickening effect is prepared. The polishing liquid 6 includes a base liquid and abrasive particles 8. The base liquid is a mixture of a polyhydroxy polymer 7 and deionized water. In this embodiment, the polyhydroxy polymer 7 is starch. In the base liquid, the proportion of the polyhydroxy polymer 7 is 50wt%-55wt%, and the rest is deionized water. The abrasive particles 8 are silicon dioxide with a particle size of 50nm, and the proportion in the polishing liquid 6 is 10wt%-20wt%. In addition, 1wt% H2O2 and 2wt% corrosion inhibitor BTA are added to the polishing liquid, and the pH of the polishing liquid 6 is adjusted to 3 by citric acid. Subsequently, the exposed and developed substrate is fixed in the polishing liquid tank 5, the position of the polishing tool 4 is adjusted so that its end face coincides with the axis of the substrate 1, the gap between the polishing tool 4 and the surface of the substrate 1 is adjusted to 100μm, and the prepared non-Newtonian fluid polishing liquid 6 is added. The polishing tool 4 rotates at a constant speed, driving the non-Newtonian polishing fluid 6 through shear thickening. The polyol polymer 7 grips the abrasive particles 8 and forms a "flexible fixed abrasive 9" on the substrate surface. Simultaneously, the substrate 1 rotates at a constant speed to ensure the polishing track covers the entire surface of the substrate 1. Subsequently, the areas uncovered by the photoresist 2 are polished, resulting in material removal. However, areas protected by the photoresist 2, i.e., the mask-protected areas, experience no material removal. This difference in material removal between the mask-protected and unprotected areas creates a height difference on the surface of the substrate 1, representing the desired concentric grating structure.

[0061] Step 6: Glue removal test

[0062] After polishing, the photoresist 2 on the surface of the substrate 1 is removed and the microstructure of the surface of the substrate 1 after the removal of the photoresist is inspected.

[0063] Example 2:

[0064] As shown in Figures 1, 2, and 4, the method for manufacturing a microfluidic chip is different from that of Example 1 in that the substrate 1 is replaced with a microfluidic chip mold substrate; the mask plate 3 is designed with a microfluidic chip structure, and the axial length of the polishing tool 4 is greater than or equal to the width of the substrate 1; the end face of the polishing tool 4 is aligned with the side face of the substrate 1; the polishing tool 4 rotates while performing slow reciprocating motion along the length direction of the substrate 1 to ensure that the entire substrate 1 can be evenly covered.

[0065] Example 3:

[0066] As shown in Figures 1, 2, and 5, the method for manufacturing the Fresnel structure is different from that of Example 1 in that the surface of the substrate 1 is aspherical; the Fresnel structure needs to be manufactured through multiple "coating-exposure-development-non-contact polishing-stripping" processes; the polishing tool 4 is a contoured polishing tool and needs to be replaced according to the structure after each development. Its axial length should be greater than or equal to the length between the two sides of the area not protected by the mask, and the mask plate 3 needs to be designed according to the structure after the previous processing.

[0067] The above-described embodiments merely express the implementation methods of the present invention, but should not be understood as limiting the scope of the patent of the present invention. It should be pointed out that for those skilled in the art, several variations and improvements can be made without departing from the concept of the present invention, and these all fall within the scope of protection of the present invention.

Claims

1. A method for manufacturing a microstructure based on mask protection and non-contact polishing process, characterized in that: The following steps are involved: Step 1: Preprocessing Pre-treating the surface of the substrate, wherein the pre-treatment method includes polishing, wiping with acetone or alcohol, ultrasonic cleaning, and nitrogen purging; Step 2: Glue Evenly coating the photoresist on the surface of the substrate, wherein the thickness of the photoresist is 15-30 μm; the method of coating the photoresist includes spin coating and spray coating; Step 3: Exposure Designing a corresponding fine structure pattern on a mask plate, and processing the desired fine structure pattern on a photoresist through exposure; the exposure method includes mask alignment exposure, step-by-step projection exposure, laser direct writing, and electron beam direct writing; Step 4: Development The developing operation is performed by using different developing solutions. After the developing operation, the photoresist remaining on the surface of the substrate is used as a mask to act as a protective film for the substrate during the non-contact polishing process. The developing method includes immersion developing, spray developing, and stirring developing. Step 5: Non-contact polishing First, a non-Newtonian fluid polishing liquid with a shear thickening effect is prepared; the non-Newtonian fluid polishing liquid comprises a base liquid and abrasive particles; the base liquid is a mixture of a polyhydroxy polymer and deionized water; the abrasive particles comprise a mixture of one or more of diamond, silicon carbide, aluminum oxide or silicon dioxide; Afterwards, the exposed and developed substrate is fixed in a polishing liquid tank, the gap between the polishing tool and the substrate surface is adjusted, and the prepared non-Newtonian fluid polishing liquid is added; Adjust the polishing tool speed, use the polishing tool rotation to drive the non-Newtonian fluid to produce shear thickening effect, and several polyhydroxy polymers will wrap the abrasive particles to form a "flexible fixed abrasive" on the substrate surface; Afterwards, the "flexible fixed abrasive" is driven by the shear force of the polishing liquid to polish the photoresist and the substrate surface. Material removal; Step 6: Glue removal test After polishing, the photoresist on the surface of the substrate is completely removed; the surface morphology, surface quality and surface accuracy of the microstructure of the substrate surface after the removal of the photoresist are tested; the removal method includes dry removal or wet removal.

2. A method for manufacturing a microstructure based on mask protection and non-contact polishing process according to claim 1, characterized in that: In the fifth step, the gap between the polishing tool and the surface of the substrate is 100-200 μm.

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