KR20230153795A - Universal Patterning method for 2D Van der Waals Materials via Direct Optical Lithography - Google Patents

Abstract

The present invention relates to a universal patterning method on 2D van der Waals materials, comprising:
Preparation steps for growing 2D van der Waals materials on a substrate;
A masking step of laminating a photomask with a specific pattern on the 2D van der Waals material grown on the substrate;
An illumination step of irradiating short-pulse high-output light so that the light source passes through the photomask and directly etches the 2D van der Waals material according to a specific pattern of the photomask; and
Includes a patterning step of removing the photomask,
The short-pulse high-output light is emitted from a mixture of xenon gas and chlorine gas at an output potential of 20 to 25 kV and has a wavelength of 295 to 310 nm.

Description

Universal Patterning method for 2D Van der Waals Materials via Direct Optical Lithography}

The present invention relates to patterning of 2D van der Waals materials.

Patterning is a very important process that determines the performance of electronic or optical devices. Recently, 2D van der Waals materials have been attracting attention, and technology for patterning them is becoming important. However, conventional photolithography methods based on photoresists optimized for existing semiconductors are also used for van der Waals materials, which has a significant adverse effect on the properties of ultra-thin van der Waals materials due to residual polymers and reactive chemical solvents. For example, selective growth technology has limitations such as low resolution or low scalability for various types of materials. This is because the surface treatment for growth is vulnerable to the lithography process and growth conditions are limited depending on the surface treatment. Therefore, there is a need to develop customized patterning technology for van der Waals materials that can optimize the properties of 2D van der Waals materials.

Korean Patent Publication No. 2022-0018884

The purpose of the present invention is to provide a general-purpose patterning method for 2D van der Waals materials rather than the photolithography method, which is a traditional semiconductor patterning method.

Another object of the present invention is to provide patterned 2D van der Waals materials with high resolution and high throughput.

Another object of the present invention is to provide a patterning method for 2D van der Waals materials that does not require photoresist and solvent.

Another object of the present invention is to provide a direct optical lithography patterning method that is universally applicable at multi-scale to various types of 2D van der Waals materials and substrates.

In order to solve the above problem, the general-purpose patterning method on a 2D van der Waals material through direct optical lithography of the present invention includes a preparation step of growing a 2D van der Waals material on a substrate; A masking step of laminating a photomask with a specific pattern on the 2D van der Waals material grown on the substrate; An illumination step of irradiating short-pulse high-output light so that the light source passes through the photomask and directly etches the 2D van der Waals material according to a specific pattern of the photomask; and a patterning step of removing the photomask, wherein the short-pulse high-output light is emitted from a mixture of xenon gas and chlorine gas at an output potential of 20 to 25 kV and has a wavelength of 295 to 310 nm.

Additionally, the present invention provides a 2D van der Waals material selected from single-layer MoS ₂ , double-layer MoS ₂ , graphene, single-layer WSe ₂ , and 2D metal-organic framework (MOF).

The present invention also provides a 2D van der Waals material structure patterned by the above method.

According to the present invention, 2D van der Waals materials such as single-layer MoS ₂ molybdenum disulfide, double-layer MoS ₂ molybdenum disulfide, and graphene can be patterned directly on various types of substrates such as flexible polymers or biocompatible chitosan. .

According to the method of the present invention, general-purpose patterning is possible on 2D van der Waals materials without photoresist and solvent, making the patterning process relatively simple and environmentally friendly.

The 2D van der Waals material structure patterned according to the present invention is capable of high throughput, resolution, and multiscale, has excellent submicro resolution, and has a clean surface.

1 is a flow chart illustrating the method of the present invention.
Figure 2 is a photograph of a structure manufactured according to an embodiment of the present invention.
Figure 3 is a graph showing the relationship between Raman shift and intensity before and after illumination of the structure manufactured according to the method of the present invention.
Figure 4 is a micrograph of a MoS ₂ 2D van der Waals material structure patterned according to an embodiment of the present invention.
Figure 5 (a) is a schematic image and an AFM topography image of a single-layer MoS ₂ van der Waals material in the growth stage, the patterning stage according to the present invention, and the patterning stage using the photoresist method as a comparative example, (b) is their Raman spectra, (c) is their Absorption spectra, and (d) is a graph showing their PL spectra.

The present invention relates to a method for universal patterning on 2D van der Waals materials, using direct optical lithography. 1 is a flowchart illustrating the method of the present invention for general-purpose patterning on 2D van der Waals materials via direct optical lithography. Looking at the present invention with reference to FIG. 1, the present invention includes a preparation step of growing a 2D van der Waals material on a substrate (Prepare); A masking step (Mask) of laminating a photomask with a specific pattern on the 2D van der Waals material grown on the substrate; Illumination step of irradiating short-pulse high-output light, so that the light source passes through the photomask and directly etches the 2D van der Waals material according to the pattern of the photomask; and a patterning step of removing the photomask.

In the present invention, the 2D van der Waals material may be single-layer MoS ₂ , double-layer MoS ₂ , graphene, single-layer WSe ₂ , or 2D metal-organic framework (MOF). 2D van der Waals materials have a layered structure with van der Waals bonds, that is, weak interlayer bonds, and are ultra-thin materials with a thickness of nanometers. Therefore, when using the photoresist method applied to conventional semiconductors for patterning on them, The surface is not smooth, and therefore has problems such as low resolution, narrow scalability, and chemical contamination due to photoresist and solvent. The inventors of the present invention used short-pulse high-output light to achieve optimized patterning on 2D van der Waals materials.

The short-pulse high-output light used in the illumination step of the present invention is emitted from a mixture of xenon gas and chlorine gas at an output potential of 20 to 25 kV and may have a wavelength of 295 to 310 nm. In the present invention, short-pulse high-output light plays an important role in high-resolution patterning on 2D van der Waals materials and preventing side effects, and may specifically be an excimer laser. Figure 4 is a micrograph of a MoS ₂ 2D van der Waals material structure patterned according to an embodiment of the present invention using an excimer laser. Quartz was used as the substrate. Looking at Figure 4, it can be seen that it has high resolution even at the micrometer and nanometer level.

In the present invention, when the 2D van der Waals material is a single-layer MoS ₂ or a double-layer MoS ₂ , the precursor gases are Mo(CO) ₆ and (C ₂ H ₅ ) ₂ S and with the help of a dilution gas the Mo(CO) ₆ flow rate 0.4 to 0.8 sccm, and (C ₂ H ₅ ) ₂ S is injected through a flow controller at a flow rate of 0.2 to 0.4 sccm and reacted at a temperature of 550 to 650 ° C. and a pressure of 2.8 to 3.5 Torr for 12 to 16 hours. Specifically, Mo(CO) ₆ can be injected at a flow rate of 0.6 sccm, and (C ₂ H ₅ ) ₂ S can be injected through a flow controller at a flow rate of 0.4 sccm and reacted at a temperature of 600°C and a pressure of 3.1 Torr for 14 hours. The dilution gas is argon and can be injected at a pressure of 800 Torr.

In the present invention, when the 2D van der Waals material is WSe ₂ , the precursor gases are W(CO) ₆ and (CH ₃ ) ₂ Se and with the help of dilution gas, W(CO) ₆ has a flow rate of 3 to 5 sccm, and (CH ₃ ) ₂ Se is injected through a flow controller at a flow rate of 0.1 to 0.4 sccm and reacted at a temperature of 540 to 660 ℃ and a pressure of 2.8 to 3.5 Torr for 12 to 16 hours. Specifically, W(CO) ₆ can be injected at a flow rate of 4 sccm, and (CH ₃ ) ₂ Se can be injected through a flow controller at a flow rate of 0.2 sccm and reacted at a temperature of 600°C and a pressure of 3.3 Torr for 14 hours. The dilution gas is argon and can be injected at a pressure of 800 Torr.

In the present invention, the substrate that can be supported by the 2D van der Waals material may be flexible polymer, biocompatible chitosan, quartz, and SiO ₂ /Si. When patterning a 2D van der Waals material using a flexible polymer as a substrate, it can be applied to flexible displays, flexible nano semiconductors, etc., and precision and miniaturization are possible. When patterning a 2D van der Waals material using biocompatible chitosan as a substrate, patterning The 2D van der Waals material structure can be used for artificial valves, artificial corneas, etc.

Example

Below, a “patterned 2D van der Waals material structure” was prepared according to the method of the present invention.

MoS ₂ films and WSe ₂ films, which are van der Waals materials, were grown on various substrates. As precursor gases, Mo(CO) ₆ (Sigma-Aldrich 577 766), (C ₂ H ₅ ) ₂ S (Sigma-Aldrich 107 247), W(CO) ₆ (Sigma-Aldrich 472 956), and (CH ₃ ) ₂ Se (Alfa Aesar 593-79-3) was used.

1. Fabrication and growth of 2D van der Waals materials

(1) MoS ₂ Fabrication of 2D van der Waals materials

With Mo(CO) ₆ and (C ₂ H ₅ ) ₂ S as precursor gases, with the help of diluting gas Ar (800 Torr), Mo(CO) ₆ is flowed at a flow rate of 0.6 sccm, and (C ₂ H ₅ ) ₂ S Silver was injected through a flow controller at a flow rate of 0.4 sccm, and in addition to the precursor gas, Ar gas flow rate was 5 sccm and H ₂ gas flow rate was 1000 sccm, and the reaction was performed at a temperature of 600°C and a pressure of 3.1 Torr for 14 hours.

(2) Preparation of WSe2 2D van der Waals material

With W(CO) ₆ and (CH ₃ ) ₂ Se as precursor gases, with the help of diluent gas Ar (800 Torr), W(CO) ₆ was flowed at a flow rate of 4 sccm and (CH ₃ ) ₂ Se was flowed at a flow rate of 0.2 sccm. was injected through a flow controller, and in addition to the precursor gas, Ar gas was introduced at a flow rate of 5 sccm and H ₂ gas flow rate of 1400 sccm, and the reaction was performed at a temperature of 600°C and a pressure of 3.3 Torr for 14 hours.

growth on substrate

The prepared van der Waals materials were deposited on a substrate using polymethyl methacrylate (PMMA) and distilled water (DI). After PMMA-coated MoS ₂ and WSe ₂ were floated on the surface of distilled water, the floated film was spread on the substrate on which MoS ₂ and WSe ₂ were deposited.

The samples were annealed at 180°C for 10 minutes and precipitated in acetone for one day to remove PMMA. Samples were washed with IPA and distilled water, and the remaining solvent was dried with a nitrogen gun.

In order to deposit MoS ₂ and WSe ₂ on the chitosan substrate, both materials were floated on distilled water without PMMA and placed on the chitosan substrate.

(3) Preparation of graphene 2D van der Waals material

Graphene on Cu foil (LG Electronics) was transferred by the following method: PMMA was spin-coated on graphene, and the sample was transferred to 0.5 m (NH ₄ ) ₂ S ₂ O ₈ (Sigma-Aldrich 248) to etch the copper foil. 614) It was precipitated in an aqueous solution at 60°C for 2 hours. PMMA suspended graphene was removed from the copper foil and placed on the solvent surface. The film was transferred to the substrate using a lift-off method.

(4) Preparation of 2D MOF metal-organic composite 2D van der Waals materials

2D MOF was synthesized using a conventional liquid/air interface method. ZnTPyP (Sigma-Aldrich 52 718), a MOF ligand, was dissolved at a concentration of 0.2 mm in a solvent consisting of methanol and dichloromethane at a ratio of 1:3. Then, 20 μL of the resulting ZnTPyP solution was injected into the interface between air and DI-aqueous solution containing 10 m m Cu(NO ₃ ) ₂ (Sigma-Aldrich 223 395) to provide ZnTPyP ligands with Cu ²⁺ ions. Then, the MOF film formed on the surface was transferred to the substrate using a lift-off method.

Preparation of chitosan substrate

The chitosan base was prepared by dissolving chitosan powder (Sigma-Aldrich 448 869) in distilled water at 10 wt%. After mixing, acetic acid (Sigma-Aldrich 695 092) was added to the solvent to reach a concentration of 10 wt%. The solvent prepared in this way was poured into a solid plastic dish and dried at 70 °C for one day.

2. Manufacturing of photomask

A sapphire substrate with a thickness of 420 μm was sonicated in acetone, isopropyl alcohol (IPA), and distilled water for 10 minutes each and dried using a nitrogen gun. A photoresist (PR, AZ 5214E, AZ Electronic Materials) pattern was prepared on a sapphire sample cleaned through CP, and about 30 nm of Al was deposited on this sample via sputtering (SRN-110, SORONA). The samples were then developed in KWIK remover for 12 hours and rinsed with distilled water and IPA for 10 minutes each to completely remove the developer. After rinsing, the sample was dried using a nitrogen gun. To fabricate a submicron-scale mask, a PMMA pattern was prepared on the cleaned substrate using an E-Beam Lithography System (JBX-9300FS, JEOL Ltd.), and Al was deposited on the sample through sputtering. Then, lift-off was performed in acetone for 1 hour at room temperature, after which the prepared samples were washed with IPA and DI.

3. Direct Optical Lithography Process

Direct light irradiation for patterning of van der Waals materials was performed using a XeCl excimer laser system (Coherent COMPex Pro 205, wavelength of 308 nm, pulse duration of 25 ns). A laser emitting from a mixture of xenon gas and chlorine gas at an output potential of 22 kV was used to irradiate samples of van der Waals materials and masks. To minimize the gap between the photomask and the van der Waals material, adhesive tape (810R, 3M) was used to bind them together. The beam spot is square with a size of 625 μm ² × 625 μm ² . All laser process parameters, including beam spot size, repetition rate, and stage movement rate, except power density, were kept constant varying between 5.29 and 58.19 MW cm ^-2 depending on the van der Waals material and substrate phase.

Photomask removal

Photomasks used in various examples were removed with running distilled water. After laser irradiation, the photomask was removed from the sample. It was cleaned with distilled water for multiple uses, and after use, the adhesive tape was removed to separate the photomask from the sample and then discarded.

(Comparative example) Conventional photolithography patterning

A photolithographic pattern was patterned on the van der Waals material using a conventional photolithography method, and the van der Waals exposed area was etched in SF ₆ /O ₂ plasma through reactive ion etching. The sample was lifted off in acetone at 70°C for one day and the photoresist pattern was removed. Afterwards, it was washed with IPA and distilled water for 10 minutes, acetone was removed, and the remaining solvent was dried by blowing with a nitrogen gun.

Confirmation example

Figure 2 is a photograph of a structure manufactured according to an embodiment of the present invention. In (a), it can be seen that the single-layer MoS ₂ van der Waals material was patterned according to a specific circular pattern based on polyimide. In (b), it can be seen that the single-layer MoS ₂ van der Waals material was patterned according to a specific circular pattern using chitosan as a base. In (c), it can be seen that the double-layer MoS ₂ van der Waals material was patterned according to a specific circular pattern using quartz as a substrate. In (d), it can be seen that the graphene van der Waals material was patterned according to a specific circular pattern using quartz as a substrate. In (e), it can be seen that the single-layer MoS ₂ van der Waals material was patterned according to a specific circular pattern using quartz as a substrate. In (f), it can be seen that the 2D metal-organic framework (MOF) van der Waals material was patterned according to a specific circular pattern based on SiO ₂ /Si.

FIG. 3 is a graph showing the relationship between Raman shift and intensity before and after illumination of the structures (a) to (f) of FIG. 2 manufactured according to the method of the present invention. In all of the graphs (a) to (f) of Figure 3, it can be seen that the intensity change after illumination is lower than before illumination. Through this, it can be seen that the 2D van der Waals material structure patterned according to the patterning method of the present invention has high resolution.

Figure 5 (a) shows a growth step (As-grown) for a single-layer MoS ₂ van der Waals material, a patterning step (DOL) according to the present invention, and a patterning step using a photoresist method as a comparative example ( CP) Schematics image and AFM topography image, (b) is their Raman spectra, (c) is their Absorption spectra, and (d) is a graph showing their PL spectra. As seen in Figure 5, according to the patterning method of the present invention, the surface smoothness is the same as that of the growth stage, whereas when using photoresist, which is a conventional semiconductor patterning method, a rough surface can be expected. Looking specifically at (b) of FIG. 5, it can be seen that there is no significant difference in the intrinsic Raman modes (E2g 1 and A1g) including the 2LA(M) mode with respect to defect density. Looking specifically at (c) of Figure 5, the peak positions of all peaks of MoS ₂ in the photoresist method (CP) slightly shifted to red, which means that the PR residue of CP MoS ₂ has an energy band gap and an energy band gap by Coulomb engineering. This appears to be because it reduces the exciton binding energy. Looking specifically at (d) of Figure 5, it can be seen that the PL intensity is greatly reduced in the photolithography pattern sample compared to other samples.

The above description is an illustrative description of the present invention, and the embodiments published in the specification are not intended to limit the technical idea of the present invention, but are for illustrative purposes, so those skilled in the art Various modifications and variations will be possible without departing from the technical idea of . Therefore, the scope of protection of the present invention should be interpreted based on the matters stated in the claims, and technical matters within the equivalent scope thereof should also be interpreted as being included in the scope of rights of the present invention.

Claims (7)

Preparation steps for growing 2D van der Waals materials on a substrate;
A masking step of laminating a photomask with a specific pattern on the 2D van der Waals material grown on the substrate;
An illumination step of irradiating short-pulse high-output light so that the light source passes through the photomask and directly etches the 2D van der Waals material according to the pattern of the photomask; and
Includes a patterning step of removing the photomask,
Universal patterning on 2D van der Waals materials via direct optical lithography, characterized in that the short-pulse high-power light is emitted from a mixture of xenon gas and chlorine gas at an output potential of 20 to 25 kV and has a wavelength of 295 to 310 nm. method. According to claim 1,
The 2D van der Waals material is characterized in that it is any one selected from single-layer MoS ₂ , double-layer MoS ₂ , graphene, single-layer WSe ₂ and 2D metal-organic framework (MOF). A universal patterning method on 2D van der Waals materials via optical lithography. According to claim 2,
The single-layer MoS ₂ and double-layer MoS ₂ use Mo(CO) ₆ and (C ₂ H ₅ ) ₂ S as precursor gases, and with the help of a dilution gas, Mo(CO) ₆ has a flow rate of 0.4 to 0.8 sccm, (C ₂ H ₅ ) ₂ S is injected through a flow controller at a flow rate of 0.2 to 0.4 sccm and reacted at a temperature of 550 to 650 ° C. and a pressure of 2.8 to 3.5 Torr for 12 to 16 hours. 2D through direct optical lithography Universal patterning method on van der Waals materials According to claim 3,
The WSe ₂ uses W(CO) ₆ and (CH ₃ ) ₂ Se as precursor gases, and with the help of a dilution gas, W(CO) ₆ flows at a flow rate of 4 sccm, and (CH ₃ ) ₂ Se flows at a flow rate of 0.2 sccm. A general-purpose patterning method on a 2D van der Waals material through direct optical lithography, characterized in that it is injected through a controller and reacted at a temperature of 550 to 650 ° C. and a pressure of 3.3 Torr for 12 to 16 hours. According to claim 1,
A method for general-purpose patterning on 2D van der Waals materials through direct optical lithography, wherein the short-pulse high-power light is a XeCl excimer laser. According to claim 1,
A method for universal patterning on 2D van der Waals materials via direct optical lithography, characterized in that the substrate is any one selected from flexible polymers, biocompatible chitosan, quartz and SiO ₂ /Si. A 2D van der Waals material structure patterned according to the method of claim 1.