CN110647014A

CN110647014A - Thin film microstructure processing method based on maskless direct writing lithography

Info

Publication number: CN110647014A
Application number: CN201910906867.6A
Authority: CN
Inventors: 罗先刚; 王炯; 蒲明博; 马晓亮; 李雄; 赵泽宇
Original assignee: Institute of Optics and Electronics of CAS
Current assignee: Institute of Optics and Electronics of CAS
Priority date: 2019-09-24
Filing date: 2019-09-24
Publication date: 2020-01-03
Anticipated expiration: 2039-09-24
Also published as: CN110647014B

Abstract

The invention provides a film microstructure processing method based on maskless direct writing lithography, which comprises the following steps of: step S1, processing a technological tool disc: processing a process tool disc for processing a film microstructure by adopting a material with stable physical and chemical properties through an optical and mechanical processing method; step S2, rigidifying the film: fixing the film on a process tool disc through an adhesive, so that the film generates a rigidization effect under the action of tensile stress in each direction; step S3, maskless direct write lithography: and processing a microstructure pattern on the film through photoetching process flows such as gluing, exposure, development, etching and the like. The processing method can realize non-contact processing of the film, the substrate does not deform in the processing process, the positioning precision of the microstructure can be effectively ensured, and the processing method also has the advantages of large processing caliber and capability of realizing multi-step microstructure processing through alignment.

Description

Thin film microstructure processing method based on maskless direct writing lithography

Technical Field

The invention relates to the technical field of micro-machining, in particular to a thin film microstructure machining method based on maskless direct-writing photoetching.

Background

With the development of aerospace technology, space telescopes have been widely applied to weather observation, resource investigation, mapping, military reconnaissance and the like, and play an important role in the fields of national economy, national defense and military and the like. The imaging resolution of a spatial telescope is directly related to its aperture, generally speaking, the greater the aperture the higher the resolution. However, as the aperture increases, the weight of the telescope also increases, and the aperture of the telescope needs to be strictly limited under the condition that the load of the transmitting device is limited. In view of the above problem, researchers have proposed a research idea of using a thin film material as a material for manufacturing a spatial telescope, and compared with a conventional reflective spatial telescopic imaging system, the diffractive thin film telescopic imaging system has the advantages of light weight, large surface tolerance, expandable space, and the like. Although the thin film mirror has many advantages, since the thin film is a flexible material and is incompatible with the conventional microstructure processing technology, there is a certain difficulty in performing microstructure fabrication on the thin film material, and related research work is less. At present, there are two main processes for processing a film microstructure reported, the first is a contact exposure method, which uses a proximity exposure machine to expose a substrate under the condition that a mask and a film are in close contact, and then transfers the mask pattern to the substrate through processes such as development and etching. The method adopts a contact type exposure mode, the film can deform in the process of being tightly attached to the mask, so that the processing precision is not easy to guarantee, and in addition, the method cannot carry out overlay, so that only two-step microstructures can be processed, but multi-step microstructures cannot be processed. The second method is a tape casting method, which comprises the steps of firstly processing a required microstructure pattern on a hard substrate, then using the microstructure pattern as a master plate, casting a polymer stock solution on the surface, hardening the stock solution to form a film, and then peeling the film from the master plate, thereby forming a film sample with a microstructure. The method can generate a microstructure pattern complementary with the master plate in principle, has multi-step microstructure processing capability, and still has the problems that the peeling process of the film and the master plate is uncontrollable, and the microstructure processing precision cannot be guaranteed.

Disclosure of Invention

In order to solve the technical problems, the invention provides a film microstructure processing method based on maskless direct writing lithography, which realizes non-contact processing of a film through maskless direct writing lithography, can ensure the processing precision of a microstructure, has the alignment capability and can realize multi-step microstructure processing of the film.

The technical scheme adopted by the invention for solving the technical problems is as follows: a thin film microstructure processing method based on maskless direct writing lithography comprises the following steps:

step S1, processing a technological tool disc: processing a process tool disc for processing a film microstructure by adopting a material with stable physical and chemical properties through an optical and mechanical processing method;

step S2, rigidifying the film: fixing the film on a process tool disc through an adhesive, so that the film generates a rigidization effect under the action of tensile stress in each direction;

step S3, maskless direct write lithography: and processing a microstructure pattern on the film through photoetching process flows such as gluing, exposure, development, etching and the like.

In the above technical solution, in the step S1, the shape of the substrate of the process tooling disc is circular, the caliber is 50 mm-800 mm, the thickness is 1 mm-8 mm, and the material is preferably quartz or carbon fiber with low thermal expansion coefficient and stable chemical property.

In the technical scheme, the outer edge of the technological tool disc is provided with a downward step, the height difference of the upper surface and the lower surface of the step is preferably 0.1 mm-1 mm, and the width of the step is preferably 5 mm-20 mm.

In the technical scheme, the small holes are distributed in the aperture of the technological tool disc and processed by adopting a laser ablation method, the aperture of each small hole is preferably 0.1-1 mm, the interval between the small holes is preferably 10-30 mm, and the small holes are used for discharging bubbles generated when the thin film is fixed on the technological tool disc, so that the influence of the bubbles between the thin film and the tool disc on the maskless direct writing photoetching quality is avoided.

In the above technical solution, in the step S2, the film is fixed on the process tooling plate by an adhesive, wherein the adhesive is uniformly coated on the lower surface of the step on the outer edge of the tooling plate, and the coating amount of the adhesive is controlled so that the adhesive cannot overflow the upper surface of the step on the outer edge of the tooling plate under the extrusion of the film in the adhesion process. By adopting the fixing scheme, the flatness of the fixed film can be ensured through the flatness of the process tool disc, and the expansion and contraction deformation of the film in the process engineering can be controlled and adjusted.

In the above technical solution, in the step S3, the maskless direct writing exposure is completed by using a laser direct writing device. The exposure process needs to coat photoresist on the film, then the maskless exposure is carried out on the photoresist according to the designed exposure pattern, a photoresist graph consistent with the designed pattern is formed through development after the exposure is finished, and finally the photoresist graph 1 is etched: 1 are transferred to the film, forming microstructures on the film.

In the above technical solution, in step S3, the maskless direct write lithography needs to be performed 1 or more times according to the number of steps of the microstructure, and the number of steps N and the number of lithography times N satisfy N-2ⁿ. Each maskless direct write lithography requires key process flows including but not limited to glue spreading, exposure, development, etching, and photoresist stripping. In order to improve the processing quality, auxiliary process flows such as substrate cleaning, glue drying and the like can be added. The maskless direct-write lithography of each time adopts the same position reference in the laser direct-write exposure process, the alignment of each exposure pattern is realized in an overlay mode, and the alignment error is preferably less than 0.3 micrometer.

The invention has the beneficial effects that:

the thin film microstructure processing method based on maskless direct writing lithography provided by the invention adopts the specially designed process tool disc, so that the thin film material and the maskless lithography process can be compatible, compared with a proximity thin film exposure method, non-contact exposure can be realized, and the substrate cannot deform in the exposure process, thereby obtaining higher microstructure processing precision. Further, the multi-step microstructure processing of the film can be realized through maskless direct writing overlay, and compared with an indirect processing mode of a tape casting method, the processing method provided by the invention directly processes the film without adding the steps of pattern transfer and stripping, so that the processing error generated by the steps can be avoided.

Drawings

FIG. 1 is a process flow diagram of a thin film microstructure processing method based on maskless direct write lithography according to the present invention;

FIG. 2 is a top view of a process tool tray;

FIG. 3 is a schematic view of a process for rigidizing a thin film;

fig. 4 shows the processing result of a four-step fresnel lens based on a polyimide film substrate, wherein fig. 4(a) is an appearance diagram of a sample, and fig. 4(b) is a fresnel lens microstructure confocal microscope test result.

In the figure, 1 is an exhaust small hole, 2 is a step, 3 is a film stretching metal ring, 4 is a thin film, 5 is an adhesive auxiliary compression ring, and 6 is a process tool disc.

Detailed Description

The invention is described in detail below with reference to the figures and the specific embodiments.

Example 1

The thin film microstructure processing method based on maskless direct writing lithography comprises the following steps:

step S1, processing a technological tool disc: a circular quartz substrate is selected as a processing material of a process tool disc, the diameter of the substrate is 180mm, and the thickness of the substrate is 5.5 mm. Firstly, the substrate is subjected to double-sided polishing, so that the PV value of the substrate surface shape is better than 5 μm. And then, processing a step 2 on the outer edge of the substrate by adopting an optical processing method, wherein the width of the step 2 is 20mm, and the depth is 0.3 mm. Finally, small exhaust holes 1 are machined in the diameter of 150mm of the substrate phi through a laser machining method, the diameter of each small hole is 0.6mm, the distance between the small holes is 20mm, the arrangement mode is triangular arrangement, and a top view of a process tool disc is shown in fig. 2.

Step S2, rigidifying the film: this example uses a polyimide film substrate with a thickness of 20 μm. Firstly, a film 4 is fixed by using a film stretching metal ring 3, wherein the film stretching metal ring 3 consists of an outer ring and an inner ring, the inner diameter of the outer ring is 230mm positive tolerance, the outer diameter of the inner ring is 230mm negative tolerance, and fastening screws are arranged at corresponding positions of the outer ring and the inner ring. The specific film stretching process comprises the following steps: the film 4 is laid on the inner ring, the outer ring is tightly pressed, the fastening screw is screwed, and the film 4 is in a tight state under the tensile stress in each direction, as shown in fig. 3a, the effect after film stretching is achieved. The film 4 in the stretched state is then transferred to a process tool plate, as shown in fig. 3 b: ultraviolet curing glue is uniformly coated on the steps 2 on the outer edge of the process tool disc 6, the tightened film is placed on the process tool disc 6, the adhesive auxiliary pressing ring 5 is placed above the film and used for improving the bonding effect of the film and the process tool disc 6, and the ultraviolet curing glue can be cured after 1 hour under the irradiation of an ultraviolet light source below the ultraviolet curing glue. After the uv glue is cured, the annular block 5 is removed and the excess film is cut off along the outer edge of the process tool disk 6, as shown in fig. 3c for the final film stiffening effect.

Step S3, maskless direct write lithography: in this embodiment, a four-step fresnel lens is adopted as a processing pattern, wherein the effective clear aperture is 80mm, and the characteristic line width is 2.6 μm. Four-step microstructures require 2 maskless direct write lithography passes, where the two passes are performed in an overlay manner. Each lithography comprises: substrate cleaning, glue coating, glue drying, exposure, development, etching, glue removal and other process flows. The substrate is cleaned by treating the surface of the substrate with acetone, alcohol and the like, so as to achieve the purposes of removing organic matters, impurities and the like on the surface of the substrate; after cleaning, uniformly coating photoresist on the surface of a substrate in a rotary coating manner, determining the type of the photoresist and the thickness of a film layer according to the required etching depth, wherein AZ1500 photoresist is selected, and the coating thickness is 500 nm; after the glue spreading is finished, putting the substrate into an oven, and drying for 10min at the temperature of 100 ℃ so as to improve the adhesive force and the stability of the photoresist layer on the substrate; after the substrate is cooled, the substrate is placed into laser direct writing equipment for exposure, an exposure graph needs to be firstly led into the equipment before exposure, and after necessary format conversion is carried out, the equipment exposes the photoresist in the area corresponding to the substrate according to a design graph; after exposure is finished, developing the photoresist, removing the photoresist in an exposure area, and leaving the photoresist in an unexposed area to form a photoresist pattern consistent with a design pattern; and finally, transferring the photoresist pattern to the substrate by adopting reactive ion etching to remove the material in a specific area of the substrate, wherein the first etching depth and the second etching depth are respectively 210nm and 420nm according to the design parameters of the four-step Fresnel lens, and after the etching is finished, removing the residual photoresist, thus finishing the complete process flow. Fig. 4 shows the actual processing result of example 1, wherein fig. 4(a) is an appearance diagram of a sample, and fig. 4(b) is a fresnel lens microstructure confocal microscope test result.

The embodiments of the present invention have been described above with reference to the accompanying drawings, but the present invention is not limited to the above-described specific embodiments, which are merely illustrative and not restrictive. The invention has not been described in detail and is part of the common general knowledge of a person skilled in the art.

Claims

1. A thin film microstructure processing method based on maskless direct writing lithography is characterized by comprising the following steps:

2. The method of claim 1, wherein in step S1, the process tool disc is circular, with an aperture of 50mm to 800mm and a thickness of 1mm to 8 mm.

3. The method of claim 2, wherein the process tool disk is made of quartz or carbon fiber.

4. The method of claim 2, wherein the outer edge of the tooling plate has a downward step, the height difference between the upper and lower surfaces of the step is 0.1 mm-1 mm, and the width of the step is 5 mm-20 mm.

5. The method for processing the film microstructure according to claim 2, wherein the small holes are distributed in the aperture of the process tool disc, the aperture of the small holes is 0.1 mm-1 mm, and the distance between the small holes is 10 mm-30 mm.

6. The method of claim 1, wherein in step S2, the adhesive is coated on the step of the outer edge of the process tool disc.

7. The method of claim 1, wherein the maskless direct writing lithography process of step S3 is performed by a laser direct writing device.

8. The method as claimed in claim 1, wherein the microstructure pattern is a 2-step or multi-step microstructure in step S3.

9. The method of claim 1, wherein the microstructural features have a line width of 0.5-500 μm and an etching depth of 10 nm-50 μm.