Processing method of photoetching master plate for electroforming and micro-fluidic chip

Abstract

The application provides a processing method of a photoetching master plate for electroforming and a micro-fluidic chip. The processing method comprises the following steps: an exposure assembly forming step, placing a mask on the first side of a light-transmitting glass substrate, and spin-coating negative photoresist on the side of the mask away from the glass substrate to form an exposure assembly composed of the glass substrate, the mask and the photoresist; an exposure assembly transferring step, transferring the exposure assembly to the first photoetching card slot of the placing platform of a photoetching machine, and directing the glass substrate of the exposure assembly towards the side of the UV light source of the photoetching machine; and an exposure step, controlling the photoetching machine to turn on the UV light source to perform photoetching, and forming the photoetching master plate for electroforming after the exposure of the exposure assembly. The groove formed on the negative photoresist after the exposure is an inverted trapezoid, that is, the bottom side near the glass substrate is short, and the bottom plate away from the glass substrate is long. In this way, the subsequent injection molding demolding can be facilitated, and the occurrence of the demolding scratch phenomenon can be effectively avoided.

Description

TECHNICAL FIELD

[0001] The application belongs to the field of photoetching, and particularly relates to a processing method of a photoetching master plate for electroforming and a micro-fluidic chip. BACKGROUND

[0002] The UV-LIGA (ultraviolet photoetching, electroforming technology) technology combined with traditional injection molding is a common manufacturing method in the field of micro-fluidic chips. The domestic traditional injection molding industry is limited by the machining precision, and the minimum precision is generally 100 microns, which cannot be used to prepare 10-100 micron structures. Although the foreign precision manufacturing mold has high precision preparation technology, the cost of mold making and mold repairing is extremely high, and the cost of each development, verification and small batch production reaches millions of dollars, which is difficult for small and medium-sized enterprises to bear. Therefore, many domestic scientific research colleges and production and research enterprises use the UV-LIGA technology to prepare injection mold cores, and then embed the mold cores into an injection molding system. In the case that the photoetching-electroforming technology can perfectly guarantee the quality of the microstructure, the development cost is greatly reduced, and the micro-fluidic chip has a wider application prospect in biology and chemistry.

[0003] In order to adapt to the electroforming in the UV-LIGA technology, the photoresist of the photoetching master plate needs to have a certain structural strength and can remain stable in the electroforming liquid at 50 DEG C for 30 days, so the SU-8 / AZ negative photoresist is selected. Due to the negative photoetching characteristics of the optical diffraction phenomenon, the trench is a positive trapezoidal shape after conventional exposure of the silicon wafer, and the mold drawing injury phenomenon occurs in the subsequent injection molding demolding. SUMMARY

[0004] Therefore, the technical problem to be solved by the present application is to provide a processing method of a photoetching master plate for electroforming and a micro-fluidic chip, so as to overcome the defect that the trench is a positive trapezoidal shape after conventional exposure of the silicon wafer due to the optical diffraction phenomenon of the spin-coated negative photoresist of the photoetching master plate for electroforming in the UV-LIGA technology in the prior art, and the mold drawing injury phenomenon occurs in the subsequent injection molding demolding.

[0005] In order to solve the above problems, the present application provides a processing method of a photoetching master plate for electroforming, which comprises the following steps:

[0006] An exposure assembly forming step is provided, in which a mask plate is placed on the first side of a light-transmitting glass substrate, and a negative photoresist is spin-coated on the side of the mask plate away from the glass substrate to form an exposure assembly composed of the glass substrate, the mask plate and the photoresist.

[0007] An exposure assembly transferring step is provided, in which the exposure assembly is transferred and placed in a first photoetching card slot of a placing platform of a photoetching machine, and the glass substrate of the exposure assembly is directed to the side of a UV light source of the photoetching machine.

[0008] An exposure step of controlling the photolithography machine to turn on the UV light source to perform photolithography, and forming a photolithography master plate for electroforming after the exposure assembly is exposed.

[0009] In some embodiments, the method further comprises, after the exposure assembly transferring step and before the exposure step:

[0010] An exposure assembly leveling step of adjusting the glass substrate in the exposure assembly to be parallel to the contact plane of the mechanical pressing component of the photolithography machine.

[0011] In some embodiments, the placing platform comprises a second platform and a first platform placed on a second photolithography card slot of the second platform, the first photolithography card slot is configured on the top surface of the first platform, and a plurality of circumferentially spaced soft rubber pads are connected to the bottom surface of the first platform; and / or, in the exposure assembly leveling step, a glass wafer is arranged between the glass substrate and the contact plane.

[0012] In some embodiments, a plurality of circular table slots are configured on the bottom surface of the first platform, and each soft rubber pad is correspondingly embedded in each circular table slot.

[0013] In some embodiments, the photolithography master plate for electroforming is used to manufacture a microfluidic chip, the second platform is a four-inch substrate of the photolithography machine, the first platform is a five-inch substrate, and the length of the microfluidic chip is 80 mm and the width is 40 mm.

[0014] In some embodiments, the mask plate and the glass substrate are integrally configured, and the mask plate and the glass substrate after being integrally configured form a mask plate wafer.

[0015] In some embodiments, in the exposure assembly forming step, before the spin coating of the negative photoresist, the method further comprises:

[0016] The mask plate wafer is sequentially cleaned, plasma treated, and high-temperature heated.

[0017] In some embodiments, the plasma treatment specifically uses high-power vacuum plasma treatment, 200-300w for 15 minutes; or the high-temperature heating treatment specifically is 150-170℃ heating treatment for 30 minutes.

[0018] In some embodiments, the spin coating thickness of the negative photoresist is 50-200μm.

[0019] The application also provides a microfluidic chip manufactured by using the photolithography master plate for electroforming, which is manufactured by using the processing method of the photolithography master plate for electroforming.

[0020] The application provides a processing method of a photoetching master plate for electroforming and a micro-fluidic chip. Different from a traditional front exposure mode, in the application, a mask plate is located on one side of a light-transmitting glass substrate, and a negative photoresist is spin-coated on the side of the mask plate away from the glass substrate. A UV light source is sequentially irradiated on the negative photoresist through the glass substrate and the mask plate from the side of the glass substrate. Due to the diffraction effect of light at the glass substrate, the trench formed on the negative photoresist after exposure is an inverted trapezoid, that is, the bottom side near the glass substrate is short, and the bottom side away from the glass substrate is long. In this way, subsequent injection molding demolding can be facilitated, and the occurrence of a mold pulling injury phenomenon can be effectively avoided. BRIEF DESCRIPTION OF DRAWINGS

[0021] Figure 1 A step schematic diagram of the processing method of the photoetching master plate for electroforming in the embodiment of the application;

[0022] Figure 2 A structure schematic diagram of the exposure assembly in the embodiment of the application;

[0023] Figure 3 A three-dimensional structure schematic diagram of the mask plate original plate formed after the glass substrate and the mask plate are integrally formed in the embodiment of the application;

[0024] Figure 4 A structure schematic diagram of the first platform and the second platform in the embodiment of the application;

[0025] Figure 5 A state schematic diagram of the exposure assembly before being transferred to a photoetching machine for exposure in the embodiment of the application;

[0026] Figure 6 A relative size relationship schematic diagram between a conventional micro-fluidic chip on the market and the electroforming master plate, wherein a refers to an area of the micro-fluidic chip beyond the effective area of the electroforming master plate.

[0027] The reference signs are:

[0028] 11, mask plate; 12, glass substrate; 13, negative photoresist; 21, first platform; 211, first photoetching slot; 212, soft rubber pad; 213, suction hole; 22, second platform; 221, second photoetching slot; 3, glass white sheet. DETAILED DESCRIPTION

[0029] For reference Figures 1 to 6 According to the embodiment of the application, a processing method of a photoetching master plate for electroforming is provided, which comprises the following steps:

[0030] The exposure assembly forming step is to place the mask 11 on the first side of the light-transmissive glass substrate 12, and spin-coat the negative photoresist 13 on the side of the mask 11 away from the glass substrate 12 to form the exposure assembly 1 composed of the glass substrate-mask-photoresist, as shown in Figure 1 ;

[0031] The exposure assembly transferring step is to transfer the exposure assembly 1 to the first photoetching card slot 211 of the placing platform of the photoetching machine, and place the glass substrate of the exposure assembly 1 towards the side of the UV light source (not shown in the figure) of the photoetching machine, that is, the upper area of the exposure assembly 1 in the orientation as shown in the figure, so as to form the back exposure of the exposure assembly; Figure 5

[0032] The exposure step is to control the photoetching machine to turn on the UV light source to perform photoetching, and form the photoetching master plate for electroforming after the exposure of the exposure assembly.

[0033] In the technical scheme, different from the traditional front exposure mode, in the present application, the mask 11 is placed on the side of the light-transmissive glass substrate 12, and the negative photoresist 13 is spin-coated on the side of the mask 11 away from the glass substrate 12, the UV light source irradiates and exposes the negative photoresist 13 from the side of the glass substrate 12, through the glass substrate 12 and the mask 11 in sequence, due to the diffraction effect of the light at the glass substrate 12, the trench formed at the negative photoresist 13 after exposure will be an inverted trapezoid (with reference to the orientation of the negative photoresist 13, the mask 11 and the glass substrate 12 placed from top to bottom), that is, the bottom side near the glass substrate 12 is shorter and the bottom side away from the glass substrate 12 is longer, so that the subsequent injection molding can be smoothly demolded, and the occurrence of the demolding damage phenomenon can be effectively avoided.

[0034] It should be noted that in the process of combining the UV-LIGA technology with the traditional injection molding technology, the electroforming link needs to keep the 50℃ environment for tens of days, therefore, the photoresist needs to have strong anti-swelling and anti-wrinkling performance, and the physical structure must be firm, the aforementioned negative photoresist generally adopts SU-8 / AZ negative photoresist, the light-transmissive part of the negative photoresist after development will be reserved, and the non-light-transmissive part will be removed, the trench position after the front exposure in the prior art forms a positive trapezoid, which affects the injection molding demolding and causes the injection molding demolding defect, while the back exposure technology is adopted in the present application, that is, the negative photoresist is not placed on the front during photoetching, but the photoresist faces downward and receives exposure at the back, the trench position of the negative photoresist after exposure is an inverted trapezoid, which can ensure the smooth injection molding demolding.

[0035] ​In the application scenario of manufacturing a microfluidic chip, after the negative photoresist (i.e., the negative photoresist 13 described above) is spin-coated on the mask original plate (i.e., the assembly formed by the glass substrate 12 and the mask 11), the photoresist thickness is concentrated in the range of 50-200 μm, i.e., the spin-coating thickness of the negative photoresist 13 in the present application is 50-200 μm. The photoresist is both solid and relatively thick, and the conventional method of removing the photoresist edge bump by using a photoresist remover is completely unsuitable. Due to the randomness of spin-coating, the thickness of the photoresist surface itself is controllable, but the height difference of the edge bump at different positions can reach 10 μm at most. Placing the photoresist plate in the photoetching machine will cause a slight tilt, which will affect the photoetching quality. Based on this phenomenon, after the exposure assembly transfer step and before the exposure step, the exposure assembly leveling step is further included, which adjusts the glass substrate 12 in the exposure assembly to a state parallel to the contact plane of the mechanical pressing component (not shown in the figure) possessed by the photoetching machine. That is, the leveling is performed before the exposure of the exposure assembly, so that the glass substrate 12 is parallel to the contact plane, specifically in a horizontal state, which can improve the photoetching quality. In a specific embodiment, as shown in Figure 4 The placing platform includes a second platform 22 and a first platform 21 placed on the second photoetching slot 221 of the second platform 22. The first photoetching slot 211 is formed on the top surface of the first platform 21, and a plurality of soft rubber pads 212 are connected to the bottom surface of the first platform 21. In a specific leveling process, the exposure assembly is placed in the first photoetching slot 211 to make it stable and reliable in position. Then, the mechanical pressing component possessed by the photoetching machine is controlled to slowly descend. Since the contact plane has a horizontal contact plane, it will apply force to the top plane of the exposure assembly 1. The plurality of soft rubber pads will compensate for the height fluctuation of the photoresist edge, disperse the pressure, and achieve the purpose of automatic leveling, i.e., adapt to the height difference of the negative photoresist thick edge, further increasing the photoetching precision and stability. The plurality of soft rubber pads 212 can be spaced apart by at least three or four in the circumferential direction. In a specific embodiment, a plurality of circular groove are formed on the bottom surface of the first platform 21, and each soft rubber pad 212 is correspondingly embedded in each circular groove. Embedding the soft rubber pads 212 in this way instead of bonding them can avoid the adverse effects of the thickness difference of the adhesive layer on leveling. Continuing to refer to Figure 4 As shown in FIG. 8, the bottom surface of the first platform 21 is formed as a disc structure that can be accommodated in the second photoetching slot 221. The soft rubber pads 212 are connected to the bottom surface of the disc structure. The disc structure is further formed with a suction hole 213 that communicates with the first photoetching slot 211. The suction hole 213 communicates with the vacuum suction structure possessed by the second photoetching slot 221, so that the exposure assembly 1 in the first photoetching slot 211 can be reliably positioned by a vacuum pump.

[0036] In another preferred embodiment, the design of the dimensions of the first platform 21 and the second platform 22 can further expand the application scenarios of smaller lithography machines. Specifically, for subsequent use, most dPCR microfluidic chips (hereinafter referred to as chips) are in the range of 77-80mm in length. After electroforming, the mold core needs to be extended by at least 2mm on each side to match the injection mold cavity, so the length direction needs to be at least 81-84mm. However, if the current four-inch lithography system (lithography machine) is used, the maximum range is limited to 100mm due to the lithography range of the lithography machine and the size of the silicon wafer. After removing the width of the conductive ring and the width of the edge narrowing during electroforming, 100mm-8mm-6mm leaves only an effective mold core range of 86mm, which has reached the limit in terms of length. If the chip width is wider than 40mm ( Figure 6 As shown, if the surface area is too large, it directly exceeds the effective flatness range of the die core after electroforming and cannot be used. Of course, a six-inch lithography machine can perfectly solve this problem, but the price of a six-inch lithography machine is in the millions (usually 2-4 million yuan), which is obviously too high. Based on the aforementioned problems, in this invention, the photolithography motherboard for electroforming is used to fabricate microfluidic chips. The microfluidic chip is 80mm long and 40mm wide. The second platform 22 is a four-inch substrate for the lithography machine, and the first platform 21 is a five-inch substrate. That is, the first platform 21 of this invention is designed to be five inches while being leveled, so that a five-inch substrate can be placed. After expansion, the effective diameter increases to 125-14=111mm, which not only greatly increases the effective area of ​​photolithography and electroforming, but also greatly reduces the technical threshold of UV-LIGA, making it very suitable for industrial mass production.

[0037] In the exposure assembly leveling step, a glass white sheet 3 is placed between the glass substrate 12 and the contact plane. The glass white sheet 3 is a glass plate without a mask. It is used to replace the original mask in the traditional front exposure process. Although most ordinary lithography machines have a maskless lithography mode, negative resist thick resist exposure requires contact exposure. At this time, the stability of the lithography system can be increased by contacting the glass white sheet 3 with the mother plate to be lithographic.

[0038] The traditional back explosion technology needs to transfer the mask to the bottom of the glass substrate, which needs a complex photolithography process, and the transferred pattern is generally a chromium metal layer. In order to process the glass substrate, the chromium layer and the photoresist of the sacrificial layer, a chromium etching solution and a chromium pickling solution need to be configured, and a large amount of chemicals such as fuming nitric acid, sulfuric acid, cerium ammonium nitrate, perchloric acid and potassium dichromate need to be used. The technology is complex and dangerous, and the quality of the transferred mask pattern is not very reliable. Because of the complexity of the technology, the process and many interference factors, the probability of pattern falling off and appearing pinholes is not low, and the yield is only 30-50%. The material cost of simply transferring a mask pattern is more than 2000 yuan. Based on the shortcomings of the foregoing traditional technology, in a preferred embodiment, the mask 11 is integrated with the glass substrate 12 to form a shape, and the mask 11 is integrated with the glass substrate 12 to form a mask original piece. The mask original piece can be purchased, that is, the present application creates a technology route of directly using a mask finished product for photolithography. Because of the difference in preparation principle, the directly purchased mask does not have the phenomenon of chromium layer falling off and appearing pinholes, completely bypassing the complex chemical treatment process, and directly processing the mask, for example, customizing a 1.5mm thick mask, and then cutting the mask to form a five-inch mask original piece (as shown). Figure 3

[0039] In the exposure component forming step, before spin-coating the negative photoresist 13, the mask original piece is sequentially cleaned, plasma treated and high-temperature heated. Through cleaning and modification treatment of the mask original piece, the original piece and the negative resist are provided with bonding force, and the original bottom glue (no bottom glue needs to be spin-coated on the glass substrate in the process of the present application) is removed to produce adverse effects on the subsequent electroforming link. The plasma treatment is specifically: using high-power vacuum plasma treatment, 200-300w for 15 minutes; or the high-temperature heating treatment is specifically 150-170℃ heating treatment for 30min, to ensure the reliable combination of the original piece and the negative resist.

[0040] The present application also provides a microfluidic chip made of the electroforming photolithography master plate processed by the processing method of the electroforming photolithography master plate.

[0041] Those skilled in the art can easily understand that the above-mentioned advantageous modes can be freely combined and superimposed without conflict.

[0042] The above is only a preferred embodiment of the present application, and should not be used to limit the present application. Any modification, equivalent replacement and improvement made within the spirit and principles of the present application should be included in the protection scope of the present application. The above is only a preferred embodiment of the present application, and should not be used to limit the present application. Any modification, equivalent replacement and improvement made within the spirit and principles of the present application should be included in the protection scope of the present application.​

Claims

1. A method for processing a photolithography master plate for electroforming, characterized in that, Includes the following steps: In the exposure assembly formation step, a mask (11) is placed on the first side of a transparent glass substrate (12), and a negative photoresist (13) is spin-coated on the side of the mask (11) away from the glass substrate (12) to form an exposure assembly (1) consisting of a glass substrate, a mask, and photoresist. The spin-coating thickness of the negative photoresist (13) is 50-200 μm. In the exposure component transfer step, the exposure component (1) is transferred to the first lithography slot (211) of the placement platform of the lithography machine, and the glass substrate of the exposure component (1) is oriented toward the UV light source of the lithography machine. In the exposure step, the lithography machine is controlled to turn on the UV light source for photolithography, so that the groove formed at the negative photoresist (13) after exposure is an inverted trapezoid by utilizing the diffraction effect of light at the glass substrate (12). After exposure, the exposure assembly forms a photolithography master plate for electroforming. The procedure includes the following steps after the exposure component transfer step and before the exposure step: In the exposure assembly leveling step, the glass substrate (12) in the exposure assembly is adjusted to be parallel to the contact plane of the mechanical pressing component of the lithography machine; the placement platform includes a second platform (22) and a first platform (21) placed on the second lithography slot (221) of the second platform (22). The first lithography slot (211) is constructed on the top surface of the first platform (21), and a plurality of circumferentially spaced soft rubber pads (212) are connected to the bottom surface of the first platform (21).

2. The processing method for the photolithography master plate for electroforming according to claim 1, characterized in that, In the exposure assembly leveling step, a glass blank (3) is placed between the glass substrate (12) and the contact plane.

3. The processing method for the photolithography master plate for electroforming according to claim 2, characterized in that, The bottom surface of the first platform (21) is constructed with multiple frustum grooves, and each soft rubber pad (212) is correspondingly embedded in each frustum groove.

4. The method for processing a photolithography master plate for electroforming according to claim 2, characterized in that, The photolithography mother plate for electroforming is used to fabricate microfluidic chips. The second platform (22) is a four-inch substrate of the photolithography machine, and the first platform (21) is a five-inch substrate. The microfluidic chip has a length of 80 mm and a width of 40 mm.

5. The method for processing a photolithography master plate for electroforming according to claim 1, characterized in that, The photomask and the glass substrate are integrally formed, and the integrally formed photomask and the glass substrate form the original photomask.

6. The method for processing a photolithography master plate for electroforming according to claim 5, characterized in that, In the exposure component formation step, before spin coating the negative photoresist (13), the process further includes cleaning, plasma treatment, and high-temperature heating treatment of the original photomask in sequence.

7. The method for processing a photolithography master plate for electroforming according to claim 6, characterized in that, The plasma treatment specifically refers to: using high-power vacuum plasma treatment at 200-300W for 15 minutes; or, the high-temperature heating treatment specifically refers to heating at 150-170℃ for 30 minutes.

8. A microfluidic chip, fabricated using a photolithography master substrate for electroforming, characterized in that, The photolithography master plate for electroforming is formed by the processing method for photolithography master plates for electroforming as described in any one of claims 1 to 7.

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