CN113334647A

CN113334647A - Method for copying and forming photoresist master die

Info

Publication number: CN113334647A
Application number: CN202110551179.XA
Authority: CN
Inventors: 王安岩; 陈强; 陈俊杰; 包福兵
Original assignee: China Jiliang University
Current assignee: China Jiliang University
Priority date: 2021-05-20
Filing date: 2021-05-20
Publication date: 2021-09-03

Abstract

The invention discloses a method for copying and forming a photoresist master die. Firstly, obtaining a PDMS female die and a PDMS substrate with a microgroove, and simultaneously placing the PDMS substrate in a plasma cleaning machine for cleaning; secondly, punching a hole on the PDMS substrate by using a puncher, inserting a liquid-transfering gun head, and injecting photoresist into the restricted space until the restricted space of the whole PDMS assembly is completely filled; then, irradiating by using a curing lamp to completely cure the photoresist; and finally, stripping the PDMS female mold, and preparing a copy female mold completely consistent with the original photoresist female mold on the PDMS substrate. The invention can realize low-cost, high-efficiency and high-fidelity copying of the photoresist master mold.

Description

Method for copying and forming photoresist master die

Technical Field

The invention belongs to the technical field of micro-nano manufacturing, and relates to a method for copying and forming a photoresist master die.

Background

Since the concept of micro total analysis systems appeared in the last 90 s, micro total analysis systems represented by microfluidic chips have been rapidly developed, and have achieved remarkable achievements, and have shown good development prospects in the fields of environmental monitoring, food safety, biological medicine and the like.

In order to meet different requirements of different fields, glass, PDMS and thermoplastic materials become the most commonly used materials for manufacturing microfluidic chips, and the physical and chemical properties of the materials can meet the requirements of most fields. The glass microfluidic chip is manufactured by combining an MEMS technology with hydrofluoric acid wet etching, but the method has long manufacturing period and high cost, relates to hazardous chemicals and is difficult to popularize. PDMS and thermoplastic microfluidic chips are widely favored due to relatively low manufacturing cost and difficulty. The manufacture of the microfluidic chip made of thermoplastic material generally includes manufacturing a mold by using MEMS technology, and then manufacturing the chip in batch by using a hot pressing method, an injection molding method and a roller pressing method. However, both hot-pressing and injection molding equipment are very expensive.

The PDMS microfluidic chip is manufactured by adopting a soft lithography technology, is a technology capable of realizing rapid prototype manufacturing of a micro device, and is the most common microfluidic chip manufacturing method in laboratory research and industrial product development. The process comprises the steps of pattern design, mask manufacturing, photoresist master mold manufacturing, PDMS casting, curing and bonding. The manufacturing process of the photoresist master mold is one step with the longest time consumption and the highest cost in the whole process, and comprises the steps of cleaning and drying a silicon wafer, spin coating, pre-baking, exposing, post-baking, developing and mold hardening.

During the PDMS casting process, a heating and cooling process is performed. However, due to the difference between the thermal expansion coefficients of the photoresist and the silicon wafer, the photoresist and the silicon wafer can be layered after multiple cycles, and the photoresist falls off. Secondly, because the adhesive strength between the photoresist and the silicon wafer is poor, the photoresist master mold can be damaged when the PDMS master mold and the photoresist master mold are manually stripped. To avoid these situations, multiple master photoresist molds are manufactured for use, but the manufacturing cost is multiplied accordingly. In addition, the soft lithography technology largely uses manual operation, and has many uncontrollable factors, which can cause the same batch of female dies to have slight structural difference and finally influence the experimental result.

In order to manufacture a photoresist master mold having the same structure, methods of duplicating the photoresist master mold, such as a micro transfer method and a capillary forming method, have also been proposed. The replication of the photoresist master mold can be achieved by filling the prepolymer into the PDMS master mold replicated from the photoresist master mold and curing the prepolymer. Among them, the micro-transfer method is generally to pour a prepolymer onto a PDMS negative mold and then gradually fill the PDMS negative mold under gravity. However, since a small amount of air is trapped in the dead space and cannot be smoothly discharged, the prepolymer is difficult to enter and defects are formed when the prepolymer is finally cured. Although the bubbles can be evacuated by vacuum treatment, PDMS is an elastomeric material and during expansion, the bubbles can compress the PDMS negative features, causing deformation of the features. The capillary method is to gradually fill the PDMS cavity by using capillary force to push the prepolymer forward. However, the dynamic viscosity of the conventional prepolymer is often relatively high, and can reach several tens to several hundreds of mPa · s, and when only the capillary force is used, the prepolymer can only fill a small part of the PDMS negative mold, and the other regions cannot be filled. Therefore, on the basis of capillary molding, researchers add a prepolymer into holes by vacuum processing a PDMS female mold and then attaching the PDMS female mold to a perforated glass, so that the prepolymer fills the PDMS female mold under the combined action of capillary force and internal and external pressure difference. However, the substrate used in the method is made of glass, so that the drilling difficulty is high, a high-power laser cutting machine is needed, and the price is high. Therefore, a new replication method is needed to prepare a defect-free high-precision replicated master mold with low cost and high efficiency, so as to realize batch production of the PDMS microfluidic chip and promote communication and development of the microfluidic technology.

In summary, the problems of the prior art include:

(1) the cost for manufacturing the thermoplastic material micro-fluidic chip is high, and the thermoplastic material micro-fluidic chip needs professional equipment such as an injection molding machine or a hot press and the like, so that the thermoplastic material micro-fluidic chip is not suitable for common laboratories and small entrepreneurship companies.

(2) In the manufacturing process of the PDMS microfluidic chip, the manufactured photoresist master mold is easy to fall off from the silicon wafer due to different thermal expansion coefficients of the photoresist and the silicon wafer.

(3) A large amount of manual operations exist in a soft lithography technology for manufacturing PDMS microfluidic chips, uncontrollable factors are more, and the same batch of female molds have slight structural differences, so that the experimental results are influenced.

(4) The existing photoresist master mould copying method has the problems of incomplete filling of a PDMS master mould or deformation of PDMS micro-features.

(5) The glass substrate punching cost of the existing photoresist master mould copying method is high.

Although the microfluidic technology shows good technical advantages and development prospects, the microfluidic chip is high in manufacturing cost and low in efficiency, cannot meet the requirements of the fields of low cost and disposable detection, such as the fields of environmental monitoring, food safety detection, biomedical testing and the like, and limits popularization and development of the microfluidic technology. Therefore, a low-cost and high-consistency method for batch manufacturing of photoresist master molds is needed, so that users can share the geometry of the master mold, technical communication across disciplines is promoted, and therefore, pioneering enterprises and ordinary laboratories can enjoy the fruits of the development of microfluidic technology.

Disclosure of Invention

Aiming at the problems in the prior art, the invention provides a method for copying and forming a photoresist master die.

The technical scheme adopted for solving the technical problem is as follows:

a method for copying and molding a photoresist master mold comprises the following steps:

firstly, casting a mixture of a PDMS precursor and a curing agent on a photoresist master mold, and curing to obtain a PDMS female mold;

secondly, manufacturing a PDMS substrate with a microgroove, and cleaning the PDMS substrate in a plasma cleaning machine;

thirdly, punching a hole in the PDMS substrate by using a handheld PDMS chip puncher, inserting a pipette gun head, and attaching the PDMS substrate to a PDMS female mold so as to enclose a limiting space for limiting the shape of the photoresist and ensure that the cured shape of the photoresist is consistent with the shape of the photoresist female mold;

and fourthly, putting the bonded PDMS assembly into a vacuum chamber for vacuum degassing treatment. The processed PDMS assembly can continuously absorb air, so that negative pressure is formed in the restricted space, and the photoresist is driven to continuously fill the restricted space in the PDMS assembly;

fifthly, under the action of the internal and external pressure difference, the photoresist continuously enters the restrictive space from the liquid-transferring gun until the restrictive space of the whole PDMS assembly is completely filled;

sixthly, taking down the pipette head, placing the filled PDMS assembly under a curing lamp, and completely curing the photoresist after irradiation;

and seventhly, stripping the PDMS female mold, and preparing a copy female mold completely consistent with the original photoresist female mold on the PDMS substrate.

Preferably, the thickness of the PDMS master mold in the first step is greater than 1 mm; the PDMS substrate in the second step was larger than 1 mm.

Preferably, the area of the micro-grooves in the second step is larger than the area occupied by the pattern of the photoresist master mold.

Preferably, the vacuum treatment time in the fourth step is more than 30 minutes.

Preferably, the curing lamp in the sixth step is an ultraviolet curing lamp.

The invention has the beneficial effects that: according to the invention, the low-cost, high-efficiency and high-fidelity copying of the photoresist master die can be realized by only one vacuum drying box, a plasma cleaning machine and a UV curing lamp without repeating the photoetching process with complicated steps and high cost, and expensive equipment, and a large number of copied master dies can be used for replacing the photoresist master dies to carry out PDMS casting, so that the photoresist master dies are prevented from falling off from silicon wafers. The precision of the manufactured copy master model is only influenced by the filling result of the photoresist, and the same copy master model can be obtained as long as the photoresist can completely fill the limited space of the PDMS composite body, and is not influenced by other factors. In addition, compared with substrates such as glass and quartz, the PDMS substrate provided by the invention does not need ultrasonic, numerical control or laser drilling, and can be used for drilling through holes at any position by directly using a handheld PDMS chip puncher, so that the cost is lower. The method is used for preparing a large number of photoresist female dies with high consistency, is used for batch production of PDMS microfluidic chips, and is expected to promote the development and popularization of microfluidic technology.

Drawings

FIG. 1 is a flow chart of the method of the present invention;

FIG. 2a, FIG. 2b, FIG. 2c are a master, a negative photoresist replica master made according to the present invention, and a negative PDMS replica, respectively;

FIGS. 3a and 3b are front micrographs of a master mold and a PDMS replica master mold made according to the present invention, respectively;

fig. 4a and 4b are sectional micrographs of the master mold and the PDMS replica cavity mold made according to the present invention, respectively.

Detailed Description

The invention is further described below with reference to the accompanying drawings.

The method for replicating the photoresist master mold comprises the following steps:

firstly, casting a mixture of a PDMS precursor and a curing agent on a photoresist master mold, and curing to obtain a PDMS female mold; and the photoresist filling is carried out in the subsequent steps.

And secondly, manufacturing a PDMS substrate with microgrooves, wherein the areas of the microgrooves are larger than the areas occupied by the photoresist master pattern patterns, and placing the PDMS substrate in a plasma cleaning machine for processing for 60 seconds. Due to the ion cleaning effect, the photoresist can be firmly bonded with the PDMS substrate after being cured, and the untreated PDMS master can be easily separated from the replica master.

And thirdly, punching a hole on the PDMS substrate by using a handheld PDMS chip puncher, inserting the pipette tip, and attaching the PDMS substrate to the PDMS female die. The two are jointed to form a restrictive space for limiting the shape of the photoresist and ensuring that the shape of the cured photoresist is consistent with that of a photoresist master mold; in the laminating process, the natural laminating force among the PDMS is relied on, and no external force is applied, so that the micro-characteristics of the PDMS are not deformed.

And fourthly, putting the bonded PDMS assembly into a vacuum chamber for vacuum degassing treatment. The PDMS assembly after treatment can continuously absorb air, so that negative pressure is formed in the restricted space, and the photoresist is driven to continuously fill the inner space of the PDMS assembly.

Fifthly, the photoresist continuously enters a restrictive space from the liquid-transfering gun under the action of the internal and external pressure difference; because air can be continuously absorbed by the PDMS composite body, air bubbles can not be generated in the filling process, so that the air bubbles do not need to be removed by vacuum treatment after the filling is finished, and the micro-feature deformation of PDMS caused by the expansion of the air bubbles is avoided.

And sixthly, taking down the head of the pipette gun, placing the filled PDMS assembly under a UV curing lamp, and irradiating for 30 s. The photoresist is fully cured.

Example, as shown in fig. 1, a PDMS substrate with micro-grooves was first fabricated, and the PDMS substrate was placed in a plasma cleaner for plsma treatment for 60S. And then, casting PDMS on the photoresist master model, curing to obtain a PDMS female mold, manufacturing a through hole on the PDMS substrate, inserting the pipette tip into the through hole, and attaching the PDMS female mold. The two are jointed to form a restrictive space for limiting the shape of the photoresist and ensuring that the shape of the cured photoresist is consistent with that of the photoresist master mould. And then placing the bonded PDMS assembly into a vacuum chamber for vacuum degassing treatment. The PDMS assembly after being processed can continuously absorb air, so that negative pressure is formed in the inner space, and the photoresist is driven to continuously fill the inner space of the PDMS assembly. The photoresist gradually fills the inner space of the whole PDMS assembly under the combined action of capillary force and internal and external pressure difference, and the filling condition can be observed by using a microscope in the filling process. After the internal space is completely filled with the photoresist, the photoresist is cured by adopting the traditional soft lithography process, namely, prebaking, exposing, postbaking and hardening. And finally, stripping the PDMS female die, namely preparing a copy female die which is completely consistent with the original photoresist female die on the PDMS substrate, and then casting the copy female die by using PMDS to obtain a new PDMS copy female die.

The master mold, the photoresist replica master mold made according to the present invention, and the PDMS replica master mold can be seen in fig. 2a, 2b, and 2c, respectively.

FIGS. 3a and 3b are front micrographs of a master mold and a PDMS replica master mold made according to the present invention, respectively; fig. 4a and 4b are sectional micrographs of the master mold and the PDMS replica cavity mold made according to the present invention, respectively. As can be seen from the figure, the negative replica was almost identical to the original negative replica, and the replication effect was good without significant change in height, indicating that the photoresist master mold and the negative replica master mold for casting the PDMS negative were also almost identical.

In summary, in the conventional soft lithography technology, the process of manufacturing the photoresist master mold includes steps of cleaning and drying the silicon wafer, homogenizing the photoresist, pre-baking, exposing, post-baking, developing, and hardening the mold, and takes up to 6 hours, and 20 ml of photoresist (400/400) is used. By using the technical scheme, under the condition that the PDMS female die is prepared, only the steps of preparing a PDMS substrate, punching, vacuum processing, filling photoresist, curing, stripping and the like are needed, the whole process takes about 40min, the photoresist is used for less than 100 microliters (-cutting and drying 2), and the number of the photoresist female dies can be quickly multiplied, so that a considerable number of PDMS female dies can be prepared at the same time.

Claims

1. A method for copying and forming a photoresist master mold is characterized by comprising the following steps:

fourthly, putting the bonded PDMS assembly into a vacuum chamber for vacuum degassing treatment; the processed PDMS assembly can continuously absorb air, so that negative pressure is formed in the restricted space, and the photoresist is driven to continuously fill the restricted space in the PDMS assembly;

2. The method of claim 1, wherein: the thickness of the PDMS female mold in the first step is more than 1 mm; the PDMS substrate in the second step was larger than 1 mm.

3. The method of claim 1, wherein: the area of the micro-groove in the second step is larger than the area occupied by the photoresist master pattern.

4. The method of claim 1, wherein: the vacuum treatment time in the fourth step is more than 30 minutes.

5. The method of claim 1, wherein: and the curing lamp in the sixth step adopts an ultraviolet curing lamp.