A process for in-situ large-area preparation of patterned graphene

Abstract

The present invention discloses a process method for in-situ large-area preparation of patterned graphene. First, a metal foil contact layer and a substrate contact layer are respectively prepared on the back of the metal foil and the surface of the substrate. A laminator is used to laminate the contact layers of the metal foil and the substrate under certain temperature and pressure conditions. The substrate of the laminated metal foil is placed in a multi-temperature zone independently controlled thermal CVD system for low-temperature growth of graphene. Patterned lithography is directly performed on the graphene grown in-situ on the single-crystal metal foil laminated on the substrate, and through dry etching and self-aligned wet etching processes in sequence, the fixation of the graphene film layer, the patterning of graphene, and the removal of the metal foil and the contact film layer are achieved in sequence. By removing the photoresist and PMMA on the graphene, patterned graphene is prepared in-situ on the substrate. This method is applicable to the low-temperature and transfer-free preparation of graphene-based materials on large-area substrates, which is conducive to promoting the wide commercial application of graphene.

Description

Technical Field

[0001] The present invention relates to a method for preparing graphene, and in particular to a process method for in-situ large-area preparation of patterned graphene, belonging to the technical field of two-dimensional semiconductor material process preparation. Background Art

[0002] The special structure of two-dimensional semiconductor materials endows them with many unique properties such as adjustable bandgap and nonlinear optics that traditional semiconductor materials do not have, showing great potential application value in the fields of transistors, optoelectronic devices, thermoelectric devices, etc. The preparation of two-dimensional semiconductor materials is the basis for device preparation and application, and has become a current research hotspot.

[0003] Two-dimensional material graphene has many advantages such as high mobility, high specific surface area, high mechanical strength, high physical and chemical stability, and zero bandgap structure, making graphene have great application potential and application value in the fields of optoelectronics, microelectronics, biochemistry, energy, etc. The main methods for preparing graphene include mechanical exfoliation, chemical vapor deposition (CVD), oxidation-reduction, solvent exfoliation, etc. Among them, the CVD method is currently more suitable for preparing large-area high-quality graphene required for device applications.

[0004] Large-area graphene films are mostly obtained by high-temperature catalytic growth on metal foils (such as copper foils) through chemical vapor deposition (CVD). In the actual application process of graphene, since it is impossible to directly grow graphene on the target substrate, or the target substrate is difficult to withstand the high-temperature environment required for growing high-quality graphene, it is often necessary to first transfer the graphene from the metal foil to the target substrate, and then pattern the graphene film through photolithography, and then carry out subsequent preparation processes.

[0005] However, the transfer process will bring the following problems to the preparation and application of graphene:

[0006] 1) In the current graphene preparation and transfer process, the operation of fishing for graphene will inevitably bring problems such as graphene contamination, damage, wrinkles, and dislocation, causing great difficulties to the quality of graphene and the stability of the process.

[0007] 2) Currently, because it is difficult to precisely control the position of graphene after transfer, only the patterned photolithography process can be carried out on the transferred graphene. However, the structure of the transferred graphene is fragile, and the subsequent patterned photolithography process is also likely to cause further damage to the transferred graphene.

[0008] 3) Currently, the graphene transfer process can only be applied to substrates with a wafer size of a few inches. For substrates with a larger area, even up to the meter level, the transfer process is difficult to implement, and there is currently no feasible technical solution for the preparation of high-quality graphene on substrates with an ultra-large area. The technical problem of in-situ preparation of high-quality graphene on an ultra-large area still hinders the further research and application of large-area graphene. Summary of the Invention

[0009] The object of the present invention is to provide a process method for in-situ preparation of high-quality patterned graphene on a large-area substrate, which can realize the transfer-free, large-area, and in-situ low-temperature growth of graphene, laying a foundation for the application of large-area graphene.

[0010] The process method for in-situ large-area preparation of patterned graphene provided by the present invention adopts the following technical solutions:

[0011] The present invention uses a metal foil with good single crystallinity as the catalytic growth substrate for graphene. A substrate contact layer and a metal foil contact layer are respectively prepared on the back of the single-crystal metal foil and the front of the large-area substrate. The single-crystal metal foil and the substrate are pressed together using a press under certain temperature and pressure conditions to form a substrate contact layer-metal foil contact layer. After the pressing is completed, the metal foil is tightly fixed on the surface of the target substrate. From top to bottom, it is: single-crystal metal foil, metal foil contact layer, substrate contact layer, and target substrate. Then, the metal foil on the substrate is placed in a thermal CVD system with independently adjustable multi-temperature zones for low-temperature growth of graphene. The front-end temperature zone in this system is set to a high temperature to assist in the cracking of the carbon source, and the back-end temperature zone is set to a low-temperature zone. The substrate with the metal foil is placed in this temperature zone for graphene growth to ensure that the process of graphene growth on the upper surface of the metal foil is carried out in a low-temperature environment. Next, PMMA is coated as a graphene support layer, and then through photolithography and dry etching, the graphene covered with PMMA is patterned. Under the fixation and protection of the patterned photoresist, the metal foil, substrate contact layer, and metal foil contact layer are removed by self-aligned wet etching drilling, so that the graphene is in-situ located on the substrate. Finally, the photoresist and PMMA on the surface of the patterned graphene are removed in sequence by cleaning, and finally, large-area high-quality patterned graphene is prepared in-situ at low temperature and without transfer on the large-area substrate. From top to bottom, it is: in-situ grown patterned graphene and substrate. The materials and thicknesses of the substrate contact layer and the metal foil contact layer will simultaneously affect the carbon dissolution amount of the metal foil, and further affect the graphene film formation after carbon precipitation on the surface. By adjusting the composition, thickness, and distribution of the contact layer, further control over the number of graphene layers, morphology, and quality of the grown graphene can be achieved.

[0012] Specifically, it includes the following steps:

[0013] Step 1) Prepare a single-crystal metal foil with good single crystallinity and a target substrate;

[0014] Step 2) Prepare a substrate contact layer on the target substrate, and prepare a metal foil contact layer on the back of the metal foil obtained in step 1);

[0015] Step 3) Use a laminator to laminate the metal foil and the substrate under certain temperature and pressure conditions. After lamination, the metal foil contact layer on the back of the metal foil adheres tightly to the surface of the substrate contact layer. From top to bottom, they are: single-crystal metal foil, metal foil contact layer, substrate contact layer, and substrate;

[0016] Step 4) Place the substrate with the metal foil in a thermal CVD system to grow graphene at a low temperature. The graphene grows on the upper surface of the metal foil;

[0017] Step 5) Spin-coat PMMA on the upper surface of the graphene and dry it. Prepare a patterned photoresist mask pattern on the upper surface of the PMMA through photolithography, and then remove the PMMA and graphene in the area not covered by the mask through dry etching to achieve patterning of the graphene structure;

[0018] Step 6) Under the coverage of the patterned photoresist mask in step 5), use an etching solution to self-align and drill-etch to remove the single-crystal metal foil, metal foil contact layer, and substrate contact layer under the graphene, and then rinse the etching solution with deionized water and dry it, so that the patterned graphene falls in place on the substrate under the protection and fixation of the photoresist.

[0019] Step 7) Wash off the photoresist and PMMA on the upper surface of the graphene in sequence. Finally, obtain large-area patterned graphene prepared by low-temperature non-transfer in-situ on a large-area substrate. From top to bottom, they are: in-situ grown and patterned graphene and a large-area target substrate.

[0020] In the above method, the metal foil with good single-crystallinity is a metal foil with a single crystal orientation. The crystal orientation can be any crystal orientation of the metal foil. Taking a copper foil as an example, it mainly includes Cu(111) and Cu(100) crystal orientations. This metal foil can be a commercial single-crystal metal foil or a single-crystal metal foil made by annealing a polycrystalline metal foil by oneself;

[0021] The metal foil with good single-crystallinity has a thickness not exceeding 1 - 10 μm;

[0022] The temperature of the laminator during lamination is 25 - 400 °C;

[0023] The pressure of the laminator during lamination is 100 - 500 Kg / cm 2 ;

[0024] The lamination time of the metal foil and the substrate is within 10 h;

[0025] The thermal CVD system used for the low-temperature growth of graphene is a multi-temperature zone tubular furnace. During growth, the high-temperature zone is set to 800-1100°C, the rear low-temperature zone is set to 25-400°C, and the substrate is placed in the rear temperature zone;

[0026] The present invention uses a contact layer lamination method to directly secure a single-crystal metal foil to a substrate. Leveraging the low-temperature graphene growth advantages of single-crystal metal foil, combined with a multi-temperature-zone CVD low-temperature growth process, this method achieves low-temperature in-situ growth of graphene on the substrate. After photolithography, dry etching is used to pattern, protect, and secure the graphene on the metal foil surface in situ. Self-aligned wet etching then removes the metal foil and contact layer beneath the graphene. Finally, the organic protective film above the graphene is removed, ultimately achieving in-situ large-scale production of patterned graphene. This method effectively avoids subjecting large-area substrates to the typically high temperatures (>500°C) required for graphene growth. It also avoids the potential for graphene damage during transfer and the difficulty associated with large-area substrate transfer operations, contributing to the accelerated commercialization of large-area graphene production.

[0027] The beneficial effects of the present invention are:

[0028] (1) The present invention proposes to realize low-temperature in-situ transfer-free preparation of patterned graphene on a large-area substrate by laminating a contact layer, growing graphene in a low-temperature zone by CVD on a single-crystal metal foil, and drilling a metal foil based on the patterned graphene fixed with a self-aligned photolithography mask. This method can free the large-area substrate from the high-temperature environment required for conventional graphene growth, and prevent the graphene from damage caused by transfer and the limitation of substrate area.

[0029] (2) The present invention proposes that by controlling the material composition, thickness and morphology of the contact layer, the number, distribution and morphology of the grown high-quality graphene can be achieved;

[0030] (3) The present invention ensures that the target substrate is not subjected to high-temperature (greater than 400°C) treatment during the growth of graphene, thus achieving the matching of the graphene growth temperature with the temperature tolerance of large-area substrates such as glass substrates;

[0031] (4) The present invention ensures the in-situ growth of graphene, avoids the use of a large-area substrate to fish out the graphene in the transfer technology method, and avoids the contamination of the graphene caused by the transfer, thereby achieving the compatibility of the in-situ growth of graphene with the preparation process of large-area substrates such as glass substrates;

[0032] (5) Through the wet etching with photoresist mask self-alignment, on the one hand, it plays a role in covering and protecting graphene during the soaking and flushing processes of substrate cleaning and wet etching of metal foil. At the same time, with the help of photoresist, graphene is fixed to prevent dislocation during the corrosion process of graphene, realizing the compatibility of in-situ fixation and protection of patterned graphene with the preparation processes such as lithography and wet etching on large-area substrates such as glass substrates.

[0033] (6) The present invention uses a multi-temperature zone thermal CVD system. By separating the high-temperature zone for maintaining the effective cracking of carbon source methane from the low-temperature zone for graphene growth, it ensures the low-temperature growth of high-quality graphene. Brief Description of the Drawings

[0034] Figure 1 To prepare a substrate contact layer and a metal foil contact layer on the front side of the substrate and the back side of the metal foil;

[0035] Figure 2 To press the substrate contact layer and the metal foil contact layer using a press under certain temperature and pressure conditions, and fix the metal foil on the substrate through the contact surface pressing;

[0036] Figure 3 To coat a PMMA protective layer after graphene growth on the surface of the metal foil;

[0037] Figure 4 To perform photolithographic development on the graphene coated with PMMA;

[0038] Figure 5 To perform patterning on the graphene coated with PMMA through dry etching;

[0039] Figure 6 To show the structure after wet self-alignment etching of the metal foil and the contact layer under the patterned graphene;

[0040] Figure 7 To show the schematic diagram of the patterned graphene structure prepared by low-temperature in-situ non-transfer on a large-area substrate after removing the photoresist and PMMA. Detailed Description of the Embodiment

[0041] The following is a detailed description of the present invention in conjunction with the drawings and embodiments.

[0042] The process method for directly growing patterned graphene on an integrated circuit chip provided by the present invention adopts the following technical solutions:

[0043] The present invention uses a metal foil with good single crystallinity as the substrate for low-temperature catalytic growth of graphene. First, as Figure 1 shown, a substrate contact layer and a metal foil contact layer are respectively prepared on the front side of the substrate and the back side of the single-crystal metal foil, and then as Figure 2As shown, two substrate contact layers and a metal foil contact layer are pressed face to face using a laminator under certain temperature and pressure conditions. After pressing, the metal foil will be fixed on the substrate surface. The substrate coated with single-crystal metal foil is placed in the low-temperature zone of a multi-temperature zone CVD system to grow graphene. The front-end temperature zone in this system is set to a high temperature to assist in the cracking of carbon sources (such as methane), and the back-end temperature zone is set to a low-temperature zone. The sample is placed in the low-temperature zone for graphene growth, ensuring that the substrate can withstand the graphene growth temperature. After growth, PMMA is coated as a graphene support layer, as Figure 3 shown. Next, a photolithography process is performed on the sample to form a patterned photoresist mask on the PMMA, as Figure 4 shown. Next, the graphene covered with PMMA is patterned by dry etching. The PMMA and graphene in the areas not covered by the photoresist are etched away, exposing the single-crystal metal foil, as Figure 5 shown. Next, with the patterned photoresist remaining, the exposed single-crystal metal foil is subjected to self-aligned wet etching using an etching solution. The single-crystal metal foil, the substrate contact layer, and the metal foil contact layer are etched away using the dry etching window and the drill etching, as Figure 6 shown. During this process, the photoresist fixes and protects the graphene coated with PMMA. After etching is completed, the etching solution is washed away with pure water. Finally, the photoresist and PMMA are removed in sequence, and high-quality patterned graphene grown in situ at low temperature without transfer is finally obtained on a large-area substrate. The materials and thicknesses of the substrate contact layer and the metal foil contact layer will simultaneously affect the carbon dissolution amount of the metal foil, and further affect the graphene film formation after carbon precipitation on the surface. By adjusting the composition, thickness, and distribution of the contact layer, further control over the number of graphene layers, morphology, and quality of the grown graphene can be achieved.

[0044] Example 1: A large-area high-temperature glass is used as the substrate, a single-crystal copper foil is used as the metal foil, a tin thin film is used as the substrate contact layer, a nickel thin film is used as the metal foil contact layer, and methane is used as the carbon source gas. It specifically includes the following steps:

[0045] Step 1) Prepare a glass substrate and a single-crystal copper foil. A 500-nanometer-thick tin thin film as the substrate contact layer and a 1-micrometer-thick nickel thin film as the metal foil contact layer are respectively sputtered on the area of the glass substrate where graphene needs to be prepared on the front side and the back side of the single-crystal copper foil;

[0046] Step 2) Use a laminator to press the substrate contact layer and the metal foil contact layer face to face, so that the single-crystal copper foil and the glass substrate are fixed in the target position through the contact layer;

[0047] Step 3) Place the pressed sample in the low-temperature zone of a thermal CVD system to grow graphene;

[0048] Step 4) Spin-coat 400 nm PMMA on the upper surface of the graphene and dry it at 150 °C for 10 min in air to form a support layer. Then, perform photolithography on the PMMA to form a patterned photoresist mask. Next, pattern the graphene covered with PMMA by RIE oxygen plasma dry etching. The RIE pressure is 10 mTorr, the power is 100 W, and the time is 10 min;

[0049] Step 5) Etch the metal foil contact layer, the substrate contact layer, and the single-crystal copper foil in sequence using a commercial metal etching liquid. Then, wash the etching liquid with pure water and dry it at 150 °C in air for 10 min;

[0050] Step 6) Remove the PMMA and photoresist covering the graphene with acetone and isopropyl alcohol. Finally, a patterned graphene film is prepared in-situ without transfer at low temperature on a large-area high-temperature glass.

[0051] In the above method, the copper foil is selected from commercial single-crystal Cu(111) foil or Cu(100) copper foil, and the thickness is less than 10 μm;

[0052] The temperature of the laminator during the lamination process is 160 - 400 °C;

[0053] The pressure of the laminator during the lamination process is 100 - 500 Kg / cm 2 ;

[0054] The time for laminating the copper foil and the target integrated circuit chip is 1 h;

[0055] The thermal CVD system used for low-temperature growth of graphene is a multi-temperature zone tube furnace. During growth, the temperature of the high-temperature zone is set to 700 - 1100 °C, and the temperature of the low-temperature zone is set to room temperature - 400 °C. During the graphene growth process, the sample is placed in the low-temperature zone;

[0056] The present invention adopts a contact layer lamination method to directly fix a single-crystal metal foil on a substrate. Utilizing the advantage of low-temperature growth of graphene on the single-crystal metal foil and cooperating with the multi-temperature zone CVD low-temperature growth process, the low-temperature in-situ growth of graphene on the substrate is realized. After photolithography, dry etching is used to pattern, protect, and in-situ fix the graphene on the metal foil surface. Then, self-aligned wet etching is used to remove the metal foil and the contact layer under the graphene. Finally, the organic protective film layer above the graphene is removed, and the in-situ large-area preparation of patterned graphene is ultimately realized. This method effectively avoids the high-temperature environment above 500 °C usually required for graphene growth on a large-area substrate, and at the same time avoids the drawbacks of graphene breakage caused by graphene transfer and the difficulty of transferring a large-area substrate, which is beneficial to accelerating the commercial application of industrial large-area graphene.

Claims

1. A process for in-situ large-area preparation of patterned graphene, characterized in that: It includes the following steps: Step 1) Prepare a single-crystal metal foil and a target substrate; Step 2) Prepare a substrate contact layer on the target substrate, and prepare a metal foil contact layer on the back of the single-crystal metal foil in Step 1); Step 3) Use a press to press the metal foil contact layer and the substrate contact layer under certain temperature and pressure conditions. After the pressing is completed, the metal foil contact layer adheres to the surface of the substrate contact layer. From top to bottom, they are: single-crystal metal foil, metal foil contact layer, substrate contact layer, and target substrate; Step 4) Place the target substrate with the metal foil contact layer in Step 3) in a thermal CVD system for low-temperature growth of graphene, and the graphene grows on the upper surface of the single-crystal metal foil; Step 5) Spin-coat PMMA on the upper surface of the graphene and dry it. Prepare a patterned photoresist mask pattern on the upper surface of the PMMA through lithography. Remove the PMMA and graphene in the area not covered by the mask through dry etching to achieve graphene patterning; Step 6) Under the coverage of the patterned photoresist mask pattern in Step 5), use an etching solution to self-align and drill and etch to remove the single-crystal metal foil, metal foil contact layer, and substrate contact layer under the graphene. Then rinse the etching solution with deionized water and dry it, so that the patterned graphene falls in place on the target substrate under the protection and fixation of the photoresist; Step 7) Wash off the photoresist and PMMA on the upper surface of the graphene in sequence. Finally, obtain large-area patterned graphene prepared by low-temperature non-transfer in-situ on a large-area target substrate. From top to bottom, they are: in-situ grown and patterned graphene and a large-area target substrate.

2. The process method for in-situ large-area preparation of patterned graphene according to claim 1, wherein: The single-crystal metal foil has a single crystal orientation, and the crystal orientation is any crystal orientation of the metal single crystal. The single-crystal metal foil is a metal foil with a thickness not exceeding 10 μm.

3. A process for in-situ large-area preparation of patterned graphene according to claim 1, characterized in that: The metal foil contact layer is an amorphous metal thin film prepared by sputtering or electron beam evaporation. The materials include amorphous copper thin film, nickel thin film, copper-nickel alloy thin film, or tin thin film; the metal foil contact layer is a single-layer or multi-layer structure, and the thickness of each layer does not exceed 1 micron.

4. A process for in-situ large-area preparation of patterned graphene according to claim 1, characterized in that: The substrate contact layer is an amorphous metal thin film prepared by sputtering or electron beam evaporation. The materials include amorphous copper thin film, nickel thin film, copper-nickel alloy thin film, or tin thin film; the substrate contact layer is a single-layer or multi-layer, and the thickness of each layer does not exceed 1 micron.

5. A process for in-situ large-area preparation of patterned graphene according to claim 1, characterized in that: There is at least one of the metal foil contact layer and the substrate contact layer, that is, there is at least a metal foil contact layer or a substrate contact layer between the target substrate and the single-crystal metal foil before pressing.

6. A process for in-situ large-area preparation of patterned graphene according to claim 1, characterized in that: The temperature of the press during pressing is 25 - 400 °C; The pressure of the laminating machine during lamination is 100 - 500 Kg / cm 2 .

7. A process for in-situ large-area preparation of patterned graphene according to claim 1, characterized in that: The pressing time for the single-crystal metal foil and the target substrate is within 10 h.

8. A process for in-situ large-area preparation of patterned graphene according to claim 1, characterized in that: The CVD system used for low-temperature growth of graphene is a multi-temperature zone tube furnace. During growth, the temperature of the front high-temperature zone is set to 700 - 1100 °C, and the temperature of the rear low-temperature zone is set to 25 - 400 °C. The substrate is placed in the rear low-temperature zone.

9. A process for in-situ large-area preparation of patterned graphene according to claim 1, characterized in that: Directly perform patterned lithography on the graphene grown in-situ on the single-crystal metal foil pressed on the target substrate, prepare a photoresist mask plate on its surface, and use the etching plasma gas generated by RIE, ICP, and glue applicator equipment to etch and pattern the graphene; the etching gas includes oxygen and argon, and the etching time is within 1 h.

10. The process method for in-situ large-area preparation of patterned graphene according to claim 1, characterized in that: After dry etching the patterned graphene, the single-crystalline metal foil and the contact layer between the graphene and the substrate are removed by self-aligned wet drilling under the coverage of the photoresist mask, so that the patterned graphene falls in place on the target substrate under the fixation and protection of the photoresist. Different etching solutions are used to etch the different materials of the metal foil and the contact layer step by step.

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