A method for preparing a thin film mask plate by using a photolithography method and application thereof

Abstract

The application discloses a method for preparing a thin film mask by using a photoetching method and application thereof, and comprises the following steps: step one, spin-coating a photosensitive polyimide photoresist on the surface of a pretreated substrate, and sequentially performing pre-baking, exposure, baking and developing; step two, heat treatment, so that the polyimide photoresist is solidified into a film; and demolding and peeling to obtain a flexible polyimide thin film mask with a target pattern. The pattern resolution of the flexible thin film mask obtained by the application can reach 3 microns, and the thickness ranges from 5 microns to 30 microns, so that the flexible thin film mask is suitable for micro-nano device processing on any three-dimensional curved surface, flexible and fragile substrate surface in a complex environment.

Description

Technical Field

[0001] This invention relates to the field of microfabrication technology for photosensitive resin materials, specifically to a method for preparing thin film masks using photolithography and its application. Background Technology

[0002] Micro-nano fabrication technology is an important component of advanced manufacturing technology and one of the indicators for measuring the level of a country's high-end manufacturing industry. It is characterized by multidisciplinary integration and extreme manufacturing factors, and plays a key role in promoting scientific and technological progress, industrial development, driving technological progress, and ensuring national defense security.

[0003] Traditional micro-and-nano fabrication technology is based on optical lithography to process materials or raw materials. Today, almost all electronic chips are manufactured using micro-and-nano fabrication techniques, including optical lithography. Optical lithography offers high resolution and relies on photomasks. Specifically, ultraviolet light is passed through a photomask and irradiated onto a substrate spin-coated with photoresist. Certain areas of the photoresist undergo chemical changes according to the mask pattern, forming a latent image of a fine pattern. After development, the mask pattern is transferred to the photoresist. Subsequent processes such as deposition and etching based on the photoresist pattern can then be used to further fabricate the desired micro- and nano-structures or devices.

[0004] Currently, there are two main types of photomasks used in photolithography processes. One type is rigid masks, such as those made of silicon, quartz glass, or stainless steel, which can be reused. However, because they are planar and rigid, and photolithography exposure light sources mostly use ultraviolet mercury lamps, these masks cannot adhere well to curved or flexible substrates, resulting in uneven light intensity distribution on the irradiated surface and affecting the exposure effect. Furthermore, uneven spraying of photoresist on curved or flexible substrates can also negatively impact photolithography. Moreover, using traditional contact exposure methods for brittle substrates can damage them. Therefore, rigid masks are not suitable for patterning non-planar, flexible, or brittle substrates. Consequently, a second type of flexible mask has emerged, such as PDMS (polydimethylsiloxane) masks, SU-8 photoresist masks, or parylene-C (polydichlorotoluene) masks. While this type of mask can effectively solve the problems associated with rigid masks, it also suffers from issues such as complex fabrication process, lack of high resolution, poor adhesion, difficulty in handling, non-reusability, and narrow applicability.

[0005] In summary, the biggest difference between the flexible thin-film mask of this invention and the two types of masks mentioned above is that it avoids the use of traditional photolithography methods on complex planar surfaces, three-dimensional curved surfaces, and flexible and brittle substrates, while still possessing the high precision characteristics of photolithography. The flexible thin-film mask of this invention can be directly attached to the material surface for deposition, etching, etc., to fabricate the required micro / nano structures or devices. On the one hand, this allows for the construction of high-precision micropatterns in scenarios where traditional photolithography is not feasible (non-planar substrates, flexible substrates, and brittle substrates). On the other hand, the fabrication process of this mask is relatively easy and has high resolution. Due to the excellent properties of polyimide material itself, such as good high and low temperature resistance, light transmittance, flexibility, chemical stability, and mechanical properties, this mask has better adhesion, easier alignment, and is more suitable for use in special environments. Summary of the Invention

[0006] This invention aims to provide a flexible, high-precision, high-temperature resistant, chemically stable, and reusable polyimide thin-film mask for application in semiconductor device fabrication. Specifically, it describes a method for fabricating thin-film masks using photolithography and its application. Due to the excellent properties of the mask, it is suitable for constructing different micropatterns on arbitrary surfaces under special environments. It can serve as an extension and supplement to the application range of traditional rigid masks.

[0007] To achieve the above objectives, the present invention employs the following technical solution:

[0008] A method for preparing a thin film mask using photolithography includes: Step 1: spin-coating a photosensitive polyimide photoresist onto the surface of a pretreated substrate, and sequentially performing pre-baking, exposure, baking, and development; Step 2: heat treatment to cure the polyimide photoresist into a film; demolding and peeling off to obtain a flexible polyimide thin film mask with the target pattern.

[0009] Optionally, the substrate is a quartz sheet or a glass sheet, and the pretreatment includes ultrasonic treatment and surface evaporation of a copper layer; the thickness of the copper layer is 50-100 nm.

[0010] Optionally, the demolding process involves placing the quartz or glass plate carrying the film into a ferric chloride solution with a mass fraction of ≥30% and allowing it to stand for 10–30 minutes for demolding.

[0011] Optionally, the substrate is a SiO2 / Si substrate, and the pretreatment includes surface hydrophilic treatment; the hydrophilic treatment method is O2 Plasma or UV-ozone.

[0012] Optionally, the demolding and peeling process involves placing the SiO2 / Si substrate carrying the thin film into a hydrofluoric acid solution with a mass fraction of ≥20% and allowing it to stand for 10–30 minutes for demolding and peeling.

[0013] Optionally, the intensity of the high-pressure mercury lamp used for exposure is 100–300 mJ / cm²; the baking temperature is 45°C and the time is 60 s; the developing solution used for development is one of acetone, cyclopentanone, and N-methylpyrrolidone, and the developing time is 10–60 s.

[0014] A thin film mask is prepared using any of the methods described in this invention that employ photolithography to prepare a thin film mask.

[0015] Optionally, the thickness of the thin film mask is 5 to 30 μm, and the resolution is 3 μm to 3 mm.

[0016] The thin film mask described in this invention is used in the fabrication of semiconductor devices.

[0017] Optionally, this includes: tightly attaching the electrode pattern portion of a thin film mask to the surface of a low-dimensional semiconductor material, and performing vacuum evaporation to deposit a metal layer; wherein the low-dimensional semiconductor material is a zero-dimensional, one-dimensional, or two-dimensional semiconductor material.

[0018] Compared with the prior art, the beneficial effects of the present invention are:

[0019] (1) The thin film mask of the present invention has excellent properties such as heat resistance, light transmittance, flexibility, chemical stability, mechanical properties and reusability, and is suitable for constructing different micro-patterns on any surface under special environments.

[0020] (2) The flexible thin film mask of the present invention is obtained by using traditional photolithography, and has the characteristics of high precision and high resolution of photolithography. It can be directly attached to two-dimensional planes, three-dimensional non-planar surfaces, flexible substrates and brittle substrates, and can even be used as a protective layer without peeling. It avoids the use of photolithography and can be directly used for coating, etching and other processes based on the mask to fabricate the required micro-nano structures or devices. It avoids the cumbersome exposure and development process steps and reduces costs to a certain extent.

[0021] (3) The flexible thin film mask of the present invention is applied to the preparation of semiconductor devices. For materials that cannot be directly photolithographically transferred, it can reduce the device preparation process steps and reduce costs, and further improve the yield.

[0022] (4) The potential applications of this masking technology involve multiple fields, including MEMS, flexible electronics and biomedicine. Attached Figure Description

[0023] The accompanying drawings are provided to further illustrate the invention and form part of the specification. They are used together with the following detailed description to explain the invention, but do not constitute a limitation thereof. In the drawings:

[0024] Figure 1 This is a cross-sectional schematic diagram of the thin film mask prepared by using glass / quartz as a substrate in this invention;

[0025] Figure 2 This is a cross-sectional schematic diagram of the thin film mask prepared by using SiO2 / Si silicon wafers as the substrate in this invention;

[0026] Figure 3 This is a schematic cross-sectional view of the process for fabricating patterned planar and curved surfaces of the flexible thin film mask according to the present invention.

[0027] Figure 4 An optical microscope image of the surface of the flexible polyimide film mask prepared in Example 1;

[0028] Figure 5 This is a physical image of the flexible polyimide film mask prepared in Example 1;

[0029] Figure 6 An optical micrograph of a field-effect transistor fabricated from the polyimide thin film mask prepared in Example 1;

[0030] Figure 7 This is a schematic diagram of the principle of a field-effect transistor;

[0031] Figure 8 The IV current-voltage test curve of the transistor in Example 1;

[0032] Figure 9 The output characteristic curve of the transistor in Example 2;

[0033] Figure 10 The figure shows the transport characteristic curve of the transistor in Example 3. Detailed Implementation

[0034] The present invention will be further described in detail below with reference to the accompanying drawings and specific embodiments. These embodiments will help those skilled in the art to further understand the present invention, but do not limit the invention in any way. It should be noted that those skilled in the art can make several modifications and improvements without departing from the concept of the present invention. These all fall within the protection scope of the present invention.

[0035] This invention relates to a method for fabricating a flexible, high-temperature resistant thin-film mask and its application in the fabrication of semiconductor devices. This mask possesses the high precision characteristic of traditional photolithography and combines it with self-supporting polymer thin-film fabrication technology. Figure 1 , 2The flexible thin film mask and its application in semiconductor device fabrication steps include: 1) ultrasonic pretreatment of the quartz or glass surface, and blowing away surface dust from the SiO2 / Si substrate using an air gun; 2) evaporating a copper layer on the quartz or glass surface; 3) spin-coating photosensitive polyimide photoresist; 4) pre-baking, exposing, baking, and developing the substrate coated with polyimide photoresist; 5) heat treatment to cure the film; 6) placing the quartz or glass sheet carrying the film in a ferric chloride solution for demolding and peeling, and placing the SiO2 / Si substrate carrying the film in a hydrofluoric acid solution for demolding and peeling, thereby obtaining a flexible polyimide thin film mask with the target pattern; 7) aligning and tightly attaching the electrode pattern portion of the film to the surface of a low-dimensional semiconductor material, and performing vacuum evaporation to deposit a metal layer, thereby forming a semiconductor device. The flexible thin film mask obtained according to the present invention can achieve a pattern resolution of 3 μm and a thickness range of 5 to 30 μm, and is suitable for fabricating micro-nano devices on any three-dimensional curved surface, flexible and brittle substrate surface in complex environments.

[0036] The ultrasonic treatment method is to first use acetone for 3 minutes and then use deionized water for 1 minute.

[0037] A 50-100nm copper layer is deposited on the quartz or glass surface; the hydrophilic treatment method for the SiO2 / Si substrate surface is O2 Plasma or UV-ozone.

[0038] The photosensitive polyimide photoresist is any one of the following: Asahi Kasei Corporation BL-301, JSR ELPAC WPR-5100, SUMIRESIN EXCEL® CRC-8300 series, HD MicroSystems HD-4100 series, Allresist GmbH SX AR-PC 5000 / 82, FUJIFILM LTC9000 series, FB5610, FB6610, and DUR7300.

[0039] The spin coating process parameters are as follows: the first stage rotation speed is 500-1000 rpm, and the duration is 10-30 s; the second stage rotation speed is 2000-4000 rpm, and the duration is 30-60 s; the third stage rotation speed is 1000-2000 rpm, and the duration is 5-30 s. After spin coating, the product is placed on a 100℃ hot plate and heat-treated for 240 s.

[0040] The intensity of the high-pressure mercury lamp used for ultraviolet exposure is 100–300 mJ / cm. 2The baking temperature is 45℃ and the time is 60s; the developer is any one of acetone, cyclopentanone, N-methylpyrrolidone, etc., and the developing time is 10-60s; the cleaning solution is any one of propylene glycol methyl ether acetate, deionized water, etc., and the cleaning time is 5-30s.

[0041] The process parameters for heat treatment to form a film are as follows: under atmospheric conditions, the film is heated from room temperature to 70℃ for 1-2 hours, then heated to 150℃ for 1-2 hours, and then heated to 200℃ for 1-2 hours. The heating rate at each stage is 2-10℃ / min, and finally the film is slowly cooled to room temperature.

[0042] The demolding and peeling process conditions are as follows: Place the quartz or glass substrate carrying the cured film into a ferric chloride solution with a mass fraction ≥30% and let it stand for 10-30 minutes until it self-demolds and peels off. Place the SiO2 / Si substrate carrying the film into a hydrofluoric acid solution with a mass fraction ≥20% and let it stand for 10-30 minutes until it self-demolds and peels off.

[0043] The peeled-off film is immersed in deionized water for cleaning or rinsed with running deionized water. Excess moisture on the surface of the film mask is removed by air drying, blowing, or vacuum drying. A flexible polyimide mask with the target pattern is then obtained.

[0044] Low-dimensional semiconductor materials are zero-dimensional, one-dimensional, and two-dimensional semiconductor materials.

[0045] Example 1:

[0046] A flexible thin-film mask and a semiconductor device are fabricated using the following method:

[0047] (1) The surface of a 5cm×5cm glass substrate was subjected to ultrasonic treatment at 40KHz. First, it was treated with acetone for 3min, and then with deionized water for 1min.

[0048] (2) 100 nm of metallic copper is deposited on the surface of a glass substrate.

[0049] (3) Spin-coat photosensitive polyimide photoresist onto the surface of a copper-plated glass substrate. The first stage has a spin speed of 1000 rpm and a duration of 10 s. The second stage has a spin speed of 3000 rpm and a duration of 40 s. The third stage has a spin speed of 1500 rpm and a duration of 10 s. Immediately after spin coating, place the substrate on a 100℃ hot plate and heat for 240 s.

[0050] (4) Select a photomask with the desired pattern for the glass substrate spin-coated with polyimide photoresist and expose it to ultraviolet light at an intensity of 250 mJ / cm. 2 .

[0051] (5) Develop with 99.5% cyclopentanone for 30 seconds. After development, quickly rinse with propylene glycol methyl ether acetate solution for 2 seconds, then rinse with deionized water for 5 seconds. After drying the surface moisture, observe the electrode pattern under a microscope at different magnifications, as shown in the attached figure. Figure 4 As shown.

[0052] (6) The photolithographic polyimide film attached to the glass substrate is placed in an oven for programmed heat treatment to form a film by thermal imidization. The heat treatment process parameters are: heating rate of 5℃ / min, heating from room temperature to 70℃ and holding for 1h, 150℃ and holding for 1h, 200℃ and holding for 1h, and finally slowly cooling to room temperature.

[0053] (7) Place the cooled glass substrate with the attached polyimide film into a 35% ferric chloride solution to completely immerse the sample. Let it stand for about 10 minutes until the film falls off the substrate automatically. You can use tweezers to gently pick up the edge of the mask film.

[0054] (8) Immerse the film in deionized water and press to clean. Then remove it from the water and use a vacuum drying method to remove excess water from the surface of the mask film to obtain a polyimide flexible film mask, as shown in the attached image. Figure 5 As shown on the left.

[0055] (9) Under a microscope, the electrode pattern of the thin film mask is aligned with the two-dimensional MoS2 material grown on the SiO2 / Si substrate and closely attached to the SiO2 / Si substrate. Vacuum evaporation is then performed to deposit 5nm Cr and 50nm Au.

[0056] (10) Remove the thin film mask from the SiO2 / Si substrate to obtain the field-effect transistor device. The actual optical micrograph is shown in the attached figure. Figure 6 As shown, Figure 6 The four images show optical micrographs of the same FET device fabricated using a thin-film mask at different magnifications; the principle is as follows. Figure 7 As shown;

[0057] (11) The field-effect transistor was tested using a semiconductor analyzer, and the results are shown in the attached figure. Figure 8 The current-voltage test curves show that the device circuit is conductive and has good ohmic contact.

[0058] Example 2:

[0059] A flexible thin-film mask and a semiconductor device are fabricated using the following method:

[0060] (1) The surface of a 5cm×5cm quartz substrate was subjected to ultrasonic treatment at 40KHz. First, it was treated with acetone for 3min, and then with deionized water for 1min.

[0061] (2) 80 nm of metallic copper is deposited on the surface of a quartz substrate.

[0062] (3) Spin-coat photosensitive polyimide photoresist onto the surface of a quartz substrate. The first stage has a spin speed of 1000 rpm and a duration of 10 s. The second stage has a spin speed of 3600 rpm and a duration of 40 s. The third stage has a spin speed of 1500 rpm and a duration of 10 s. Immediately after spin coating, place the substrate on a 100℃ hot plate and heat for 240 s.

[0063] (4) Select a photomask with the desired pattern for ultraviolet exposure on a quartz substrate spin-coated with polyimide photoresist. The exposure intensity is 200 mJ / cm. 2 .

[0064] (5) Develop with 99.5% cyclopentanone for 22 seconds. After development, rinse with propylene glycol methyl ether acetate solution for 2 seconds, and then rinse with deionized water for 5 seconds.

[0065] (6) The photolithographic polyimide film attached to the quartz substrate is placed in an oven for programmed heat treatment to form a film by thermal imidization. The heat treatment process parameters are: heating rate of 5℃ / min, heating from room temperature to 70℃ and holding for 1h, 150℃ and holding for 1h, 200℃ and holding for 2h, and finally slowly cooling to room temperature.

[0066] (7) Place the cooled quartz substrate with the attached polyimide film into a 30% ferric chloride solution to completely immerse the sample. Let it stand for about 10 minutes until the film falls off the substrate automatically. You can use tweezers to gently pick up the edge of the mask film.

[0067] (8) Use tweezers to pick up the edge of the film and rinse it with running deionized water. Spread the film out and let it air dry to remove excess moisture from the surface of the mask film, obtaining a flexible polyimide film mask, as shown in the attached image. Figure 5 As shown on the right.

[0068] (9) Under a microscope, the electrode pattern of the thin film mask is aligned with the two-dimensional MoS2 material grown on the SiO2 / Si substrate and closely attached to the SiO2 / Si substrate. Vacuum evaporation is then performed to deposit 5nm Cr and 50nm Au.

[0069] (10) Remove the thin film mask from the SiO2 / Si substrate to obtain a field-effect transistor device. The principle is as follows: Figure 7 As shown in the attached figure. The transistor's output characteristic curve was measured using a semiconductor analyzer. Figure 9 As shown.

[0070] Example 3:

[0071] A flexible thin-film mask and a semiconductor device are fabricated using the following method:

[0072] (1) Select an area of ​​approximately ≤9cm² 2 Photosensitive polyimide photoresist was spin-coated onto the surface of a SiO2 / Si substrate. The first stage involved a spin speed of 1000 rpm for 10 seconds, the second stage involved a spin speed of 2000 rpm for 40 seconds, and the third stage involved a spin speed of 1500 rpm for 10 seconds. Immediately after spin-coating, the substrate was placed on a 100°C hot plate and heated for 240 seconds.

[0073] (2) Select a photomask with the desired pattern for ultraviolet exposure on a SiO2 / Si substrate spin-coated with polyimide photoresist. The exposure intensity is 300 mJ / cm. 2 .

[0074] (4) Develop with 99.5% cyclopentanone for 40 seconds. After development, quickly rinse with propylene glycol methyl ether acetate solution for 2 seconds, and then rinse with deionized water for 5 seconds.

[0075] (5) The photolithographic polyimide film attached to the SiO2 / Si substrate is placed in an oven for programmed heat treatment to form a film by thermal imidization. The heat treatment process parameters are: heating rate of 5℃ / min, heating from room temperature to 70℃ and holding for 1h, 150℃ and holding for 2h, 200℃ and holding for 2h, and finally slowly cooling to room temperature.

[0076] (6) Transfer the cooled SiO2 / Si substrate with attached polyimide film to a 20% hydrofluoric acid solution, so that the solution completely submerges the sample. Let it stand for about 15 minutes until the film automatically detaches from the substrate. You can use tweezers to gently pick up the edge of the mask film.

[0077] (7) Use tweezers to pick up the edge of the film and rinse it with running deionized water. Use a blower to remove excess moisture from the surface of the mask film.

[0078] (9) Under a microscope, the electrode pattern of the thin film mask is aligned with the two-dimensional MoS2 material grown on the SiO2 / Si substrate and closely attached to the SiO2 / Si substrate. Vacuum evaporation is then performed to deposit 5nm Cr and 50nm Au.

[0079] (10) Remove the thin film mask from the SiO2 / Si substrate to obtain a field-effect transistor device. The principle is as follows: Figure 7 As shown in the attached figure. The semiconductor analyzer was used to test its transport characteristic curves. Figure 10 As shown, based on this, a series of data such as the carrier mobility and on / off ratio of the MoS2 material can be calculated.

[0080] The above description is only a preferred embodiment of the present invention. It should be noted that for those skilled in the art, several improvements and modifications can be made without departing from the principle of the present invention, and these improvements and modifications should also be considered within the scope of protection of the present invention.

Claims

1. A method for preparing a thin film mask using photolithography, characterized in that, include: Step 1: Spin-coat photosensitive polyimide photoresist onto the pretreated substrate surface, and sequentially perform pre-baking, exposure, baking, and development; the high-pressure mercury lamp intensity for exposure is 100-300 mJ / cm2; the baking temperature is 45℃ and the time is 60s; the developing solution used for development is one of acetone, cyclopentanone, and N-methylpyrrolidone, and the development time is 10-60s; Step 2: Heat treatment to cure the polyimide photoresist into a film; demolding and peeling off yields a flexible polyimide thin film mask with the target pattern; The substrate is a quartz sheet or a glass sheet, and the pretreatment includes ultrasonic treatment and surface evaporation of a copper layer; the thickness of the copper layer is 50-100 nm; the demolding and peeling is to place the quartz sheet or glass sheet carrying the film into a ferric chloride solution with a mass fraction of ≥30% and let it stand for 10-30 minutes for demolding and peeling. Alternatively, the substrate is a SiO2 / Si substrate, and the pretreatment includes surface hydrophilic treatment; the hydrophilic treatment method is O2Plasma or UV-ozone; the demolding and peeling is to place the SiO2 / Si substrate carrying the film into a hydrofluoric acid solution with a mass fraction of ≥20% and let it stand for 10 to 30 minutes for demolding and peeling.

2. A thin film mask, characterized in that, The thin film mask is prepared by the method described in claim 1, which uses photolithography to prepare a thin film mask. The thickness of the thin film mask is 5-30 μm, and the resolution is 3 μm-3 mm.

3. The application of the thin film mask of claim 2 in the fabrication of semiconductor devices, comprising: The electrode pattern portion of a thin film mask is tightly attached to the surface of a low-dimensional semiconductor material, and a metal layer is deposited by vacuum evaporation. The low-dimensional semiconductor material mentioned is a zero-dimensional, one-dimensional, or two-dimensional semiconductor material.

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