A method for transferring metal electrodes onto two-dimensional materials

Abstract

The present invention discloses a method for transferring a metal electrode to a two-dimensional material, which comprises: obtaining a structure to be transferred, wherein the structure to be transferred comprises a substrate, a transition layer formed on the substrate, and a metal electrode pattern formed on the transition layer; wet etching the transition layer to remove the transition layer not covered by the metal electrode pattern; using an organic flexible material to integrally bond the metal electrode pattern in the structure to be transferred from the transition layer and adhere it to the two-dimensional material in the target structure; removing the organic flexible material to complete the van der Waals contact between the metal electrode and the two-dimensional material. By introducing a transition layer and combining wet etching and dry transfer, it is easy to realize the overall peeling of the pattern to be transferred, greatly improving the success rate of preparation, and by combining the metal electrode and the two-dimensional material through van der Waals force, the contact performance of the two can be greatly improved.

Description

Technical Field

[0001] The present invention belongs to the technical field of semiconductor structure preparation, and more specifically, relates to a method for transferring a metal electrode onto a two-dimensional material. Background Art

[0002] As the amount of information processing increases day by day, the integration of circuits continues to increase, driving devices towards miniaturization. However, as the size is further reduced, traditional silicon-based devices face physical limitations such as short channel effects. As a new type of material, two-dimensional materials have shown excellent properties in light, electricity, magnetism, and heat, attracting widespread research interest. When the size is reduced to below 10nm, two-dimensional materials can still maintain good gate control capabilities and can effectively alleviate the short channel effect. Therefore, two-dimensional materials are expected to become the next generation of semiconductor materials.

[0003] However, contact resistance is a problem that cannot be ignored in low-dimensional devices. In the traditional device preparation process, metal is directly deposited on the two-dimensional material. Due to the complex interactions at the interface between the metal and the two-dimensional material, such as the chemical bonds formed between the metal and the two-dimensional material, the interfacial strain between the metal and the two-dimensional material, the water and hydrocarbons adsorbed on the surface of the two-dimensional material, the high-energy metal atom bombardment on the surface of the two-dimensional material during the device preparation process, and the photoresist residue during the preparation process, the contact performance between the metal and the two-dimensional material is reduced. Moreover, as the size of the device decreases, the contact resistance between the metal electrode and the two-dimensional material will become more and more obvious, and even dominate the electrical performance of the device. Therefore, it is necessary to propose an effective method to improve the contact problem between metal and two-dimensional materials. Summary of the invention

[0004] In view of the above defects or improvement needs of the prior art, the present invention provides a method for transferring a metal electrode to a two-dimensional material, which aims to solve the technical problem of poor contact performance between the metal electrode and the two-dimensional material.

[0005] To achieve the above object, according to one aspect of the present invention, a method for transferring a metal electrode to a two-dimensional material is provided, comprising:

[0006] Acquire a structure to be transferred, wherein the structure to be transferred includes a substrate, a transition layer formed on the substrate, and a metal electrode pattern formed on the transition layer;

[0007] Wet-etching the transition layer to remove the transition layer not covered by the metal electrode pattern;

[0008] The metal electrode pattern in the structure to be transferred is integrally bonded from the transition layer by an organic flexible material and attached to the two-dimensional material in the target structure;

[0009] The organic flexible material is removed to complete the van der Waals contact between the metal electrode and the two-dimensional material.

[0010] Preferably, the obtaining of the structure to be transferred includes:

[0011] providing a transfer substrate;

[0012] growing a transition layer on the transfer substrate;

[0013] forming a patterned photoresist layer on the transition layer;

[0014] The metal material is evaporated and the photoresist layer is removed to obtain a metal electrode pattern located on the transition layer.

[0015] Preferably, the height of the transition layer ranges from 250 nm to 350 nm.

[0016] Preferably, the metal electrode pattern comprises Cr at the bottom and Au at the top, wherein the height of Cr ranges from 8 nm to 12 nm, and the height of Au ranges from 40 nm to 120 nm.

[0017] Preferably, the transition layer is etched to remove the transition layer not covered by the metal electrode pattern and the transition layer partially covered by the metal electrode pattern.

[0018] Preferably, the organic flexible material comprises a flexible supporting layer and a flexible adhesive layer located on the flexible supporting layer, and the organic flexible material adheres to the metal electrode pattern through the flexible adhesive layer.

[0019] Preferably, the flexible supporting layer comprises PDMS or PMMA, and the flexible adhesive layer comprises PVA;

[0020] Removing the organic flexible material comprises:

[0021] heating the target structure to tear the flexible support layer off the target structure;

[0022] The target structure to be removed from the flexible support layer is placed in a solution to dissolve and remove the flexible adhesive layer.

[0023] Preferably, after the metal electrode pattern in the structure to be transferred is integrally bonded from the transition layer by the organic flexible material, the metal electrode pattern and the target structure are aligned and bonded by an alignment component on the transfer table.

[0024] Preferably, the transition layer is an oxide layer.

[0025] In general, compared with the prior art, this application has the following advantages:

[0026] (1) The transfer process in the present application includes wet etching and dry transfer. Wet etching is performed before dry transfer. The wet etching process can effectively reduce the adhesion between the metal electrode and the bottom structure. Compared with the dry transfer mentioned in the traditional method, the transfer process of the present application can more easily realize the overall peeling of the pattern to be transferred, greatly improving the success rate of preparation;

[0027] (2) The conventional method of depositing metal electrodes involves the bombardment of the target material by high-energy metal atoms. Under the high-energy action, chemical reactions will occur between the metal atoms and the two-dimensional material to form chemical bonds. The present application uses a transfer method to avoid the formation of chemical bonds or strain between the metal and the two-dimensional material, thereby reducing the contact resistance.

[0028] (3) The present application uses a transfer method to naturally press the metal electrode pattern onto the target site. During this natural bonding process, the adsorbate on the surface of the two-dimensional material can be squeezed out, further improving the performance of the contact interface between the two-dimensional material and the metal;

[0029] (4) In the traditional process, before forming the two-dimensional material, it is necessary to form an alignment mark through a photolithography process to facilitate alignment when forming a patterned metal electrode through an etching process. In the present application, the step of preparing the alignment mark can be omitted, and alignment and bonding can be performed directly through the alignment component, thereby simplifying the process steps. BRIEF DESCRIPTION OF THE DRAWINGS

[0030] Figure 1 is a flow chart of the steps of a method for transferring a metal electrode onto a two-dimensional material in one embodiment of the present application;

[0031] Figure 2 This is a specific experimental flow chart in one embodiment of the present application;

[0032] Figure 3 It is a structural diagram formed by executing relevant steps in an embodiment of the present application;

[0033] Figure 4 It is a physical diagram of the etching process in one embodiment of the present application;

[0034] FIG5( a ) is a diagram showing the effect of PVA adhering to the electrode during the electrode transfer process of Example 1 of the present application;

[0035] FIG5( b ) is a physical picture of the electrode after the transfer is completed in Example 1 of the present application;

[0036] FIG6( a ) is a photo of the electrode of Example 2 of the present application observed under a microscope after the electrode transfer is completed;

[0037] FIG6( b ) is a performance comparison diagram of the device prepared by Example 2 of the present application and a conventional photolithography process. DETAILED DESCRIPTION

[0038] In order to make the purpose, technical solutions and advantages of the present invention more clearly understood, the present invention is further described in detail below in conjunction with the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are only used to explain the present invention and are not intended to limit the present invention. In addition, the technical features involved in the various embodiments of the present invention described below can be combined with each other as long as they do not conflict with each other.

[0039] like Figure 1 The figure is a flow chart of the steps of a method for transferring a metal electrode onto a two-dimensional material in one embodiment of the present application, the method comprising:

[0040] Step S100: obtaining a structure to be transferred, wherein the structure to be transferred includes a substrate, a transition layer formed on the substrate, and a metal electrode pattern formed on the transition layer.

[0041] In one embodiment, the step of obtaining the structure to be transferred includes:

[0042] Step S110: providing a transfer substrate.

[0043] The transfer substrate may be a conventional silicon substrate or other semiconductor substrates.

[0044] Step S120: growing a transition layer on the transfer substrate.

[0045] Specifically, the transition layer may be an oxide layer, and the transition layer grown on the silicon substrate is silicon oxide.

[0046] Step S130: forming a patterned photoresist layer on the transition layer.

[0047] Specifically, a layer of photoresist is spin-coated on the silicon wafer with the silicon transition layer surface, and a pattern on the photoresist is obtained by using a photolithography / electron beam lithography (EBL) process.

[0048] Step S140: evaporating a metal material and removing the photoresist layer to obtain a metal electrode pattern on the transition layer.

[0049] Specifically, metal is evaporated on a silicon substrate using an electron beam evaporation (EBE) process, and finally the silicon wafer is placed in an acetone or dimethylformamide (DMF) solution to remove the photoresist, thereby completing the preparation of the metal electrode pattern.

[0050] In one embodiment, the material of the metal electrode pattern may include Cr at the bottom layer and Au at the top layer. As shown in FIG. 2 , the metal electrode is prepared by step S100. Figure 3 (a) Graph structure in .

[0051] Step S200: wet-etching the transition layer to remove the transition layer not covered by the metal electrode pattern.

[0052] The transition layer is immersed in an etching solution to remove the exposed transition layer. Due to the protection of the metal electrode pattern, the transition layer at the bottom of the metal electrode pattern will not be completely etched away, but a porous loose structure will be formed. The applicant has found through research that, compared with directly forming a metal electrode pattern on a substrate, by adding a transition layer and combining wet etching, the adhesion between the metal electrode pattern and the underlying structure can be reduced, which is conducive to the subsequent peeling of the metal electrode pattern.

[0053] In one embodiment, the etching time may be appropriately increased to remove the transition layer not covered by the metal electrode pattern and the transition layer partially covered by the metal electrode pattern, thereby further reducing the adhesion between the metal electrode pattern and the carrier.

[0054] In one embodiment, in order to improve the success rate of the overall transfer, the height of the transition layer is limited, and the height range of the transition layer is 250nm to 350nm. In one embodiment, the height of the metal electrode pattern is also limited, and the metal electrode pattern includes Cr at the bottom and Au at the top, wherein the height range of Cr is 8nm to 12nm, and the height range of Au is 40nm to 120nm. Within this range, the metal electrode pattern can be peeled off smoothly.

[0055] Specific, combined Figure 2 Taking silicon oxide as the transition layer as an example, the silicon wafer with the prepared metal electrode pattern is placed in a NaOH or KOH solution. Since NaOH (KOH) reacts with silicon oxide, it can etch silicon oxide. After the etching is completed, the silicon wafer is taken out, cleaned with anhydrous ethanol and deionized water, and then placed on a heating table for drying to obtain the following Figure 3 (b) Graph structure in .

[0056] Step S300: The metal electrode pattern in the structure to be transferred is integrally bonded from the transition layer by an organic flexible material and attached to the two-dimensional material in the target structure.

[0057] Selecting an organic flexible material as the transfer medium can avoid damage to the metal electrode pattern during transfer. It is understandable that the organic flexible material can adhere to the metal electrode pattern. In one embodiment, the organic flexible material may include two parts, one part is a thicker flexible support layer, and the other part is a thinner adhesive layer located on the support layer, which is used to contact the metal electrode pattern and adhere it. In one embodiment, the flexible support layer can be made of PDMS (polydimethylsiloxane) or PMMA (polymethyl methacrylate), and the flexible adhesive layer can be made of PVA (polyvinyl alcohol). The specific method can be combined with Figure 2 and Figure 3 Specifically, the metal electrode pattern is bonded as a whole by dry transfer, and the process is as follows Figure 3 As shown in Figure (c) in the figure, and fitted with the two-dimensional material, we can get Figure 3 (d) Graph structure in .

[0058] Step S400: removing the organic flexible material to complete the van der Waals contact between the metal electrode and the two-dimensional material.

[0059] See also Figure 3 , accurately align on the two-dimensional material transfer platform, make the metal electrode pattern fit with the target two-dimensional material, then heat the transfer platform to 50°C to make the PVA fit closely with the substrate; finally, Figure 3 As shown in Figure (e), the PDMS is slowly lifted, and the silicon wafer bonded with PVA is placed in deionized water to dissolve and remove the PVA. The silicon wafer is taken out and dried to complete the electrode transfer, and the result is as shown in FIG. Figure 3 (f) Graph structure in .

[0060] For ease of understanding, two specific embodiments are used for illustration below.

[0061] Embodiment 1

[0062] (1) Preparation of metal electrodes: a layer of photoresist is spin-coated on a silicon wafer with a silicon oxide layer, and an electrode pattern on the photoresist is obtained by photolithography / electron beam lithography (EBL) process. Then, 10 nm / 50 nm Cr / Au metal electrodes are evaporated on the silicon substrate by electron beam evaporation (EBE) process. Finally, the silicon wafer is placed in a dimethylformamide (DMF) solution to remove the photoresist, thereby completing the preparation of the metal electrode pattern.

[0063] (2) Etching of silicon oxide layer on the surface of silicon wafer: Place the silicon wafer with metal electrode pattern prepared in a 40% by mass NaOH solution. Since NaOH reacts with silicon oxide, it can etch silicon oxide. Figure 4 As shown; 48 hours later, the silicon wafer was taken out, cleaned with anhydrous ethanol and deionized water, and blown dry with a laboratory ear-cleaning bulb;

[0064] (3) Metal electrode transfer: Since the metal electrode has a strong adhesion to silicon oxide, the silicon oxide at the bottom of the metal electrode will not be completely etched. After partially etching the silicon oxide, the metal electrode will adhere to the silicon wafer with a smaller adhesion force. Then, a small piece of PVA is glued to one side of the PDMS, and the entire electrode pattern is glued to the PVA on the two-dimensional material transfer platform, obtaining the result shown in Figure 5(a). After that, the electrode pattern is precisely aligned on the two-dimensional material transfer platform to fit the target two-dimensional material WSe2, and the transfer platform is heated to 50°C to make the PVA fit tightly to the silicon wafer. Finally, the PDMS is slowly lifted, and the silicon wafer bonded with PVA is placed in deionized water to dissolve and remove the PVA. The silicon wafer is taken out and dried to complete the electrode transfer, obtaining the result shown in Figure 5(b).

[0065] Embodiment 2

[0066] (1) Preparation of metal electrodes: a layer of photoresist is spin-coated on a silicon wafer with a silicon oxide layer, and an electrode pattern on the photoresist is obtained by photolithography / electron beam lithography (EBL) process. Then, 10 nm / 50 nm Cr / Au metal electrodes are evaporated on the silicon substrate by electron beam evaporation (EBE) process. Finally, the silicon wafer is placed in an acetone solution to remove the photoresist, and the preparation of the metal electrode pattern is completed.

[0067] (2) Etching of the oxide layer on the surface of the silicon wafer: The silicon wafer with the metal electrode pattern prepared is placed in a 30% by mass KOH solution. Since KOH reacts with silicon oxide, it can etch silicon oxide. After 72 hours, the silicon wafer is taken out, cleaned with anhydrous ethanol and deionized water, and blown dry with a laboratory ear bulb.

[0068] (3) Metal electrode transfer: Since the metal electrode has a strong adhesion to silicon oxide, the silicon oxide at the bottom of the metal electrode will not be completely etched. After partially etching the silicon oxide, the metal electrode will adhere to the silicon wafer with a smaller adhesion force. Then, a small piece of PVA is glued to one side of the PDMS, and the entire electrode pattern is glued to the PVA on the two-dimensional material transfer platform. After that, the electrode pattern is precisely aligned on the two-dimensional material transfer platform to fit the target two-dimensional material ReS2, and the transfer platform is heated to 50°C to make the PVA fit tightly to the silicon wafer. Finally, the PDMS is slowly lifted, and the silicon wafer bonded with PVA is placed in deionized water to dissolve and remove the PVA. The silicon wafer is taken out and dried to complete the electrode transfer, and the result shown in Figure 6(a) is obtained.

[0069] (4) Device electrical performance measurement: The device electrical performance was measured using a Keithley 4200 semiconductor analyzer and compared with the device electrical performance obtained using a conventional photolithography process. The comparison results are shown in FIG6( b ). Experimental verification shows that by using this scheme to achieve contact between the metal electrode and the two-dimensional material, the I / V performance of the resulting semiconductor device is better.

[0070] In summary, the transfer process in the present application includes wet etching and dry transfer. Wet etching is performed before dry transfer. The wet etching process can effectively reduce the adhesion between the metal electrode and the bottom structure. Compared with the dry transfer mentioned in the traditional method, the transfer process of the present application can more easily achieve the overall peeling of the pattern to be transferred, which greatly improves the success rate of preparation. At the same time, the present application can avoid the formation of chemical bonds or strain between metals and two-dimensional materials through the transfer method, thereby reducing contact resistance. Moreover, the transfer method of the present application will naturally press the metal electrode pattern onto the target site. In this natural bonding process, the adsorbate on the surface of the two-dimensional material can be squeezed out, further improving the performance of the contact interface between the two-dimensional material and the metal. Furthermore, in the present application, the step of preparing the alignment mark can be omitted, and the alignment and bonding can be performed directly through the alignment assembly, and the process steps are simplified.

[0071] It will be easily understood by those skilled in the art that the above are only preferred embodiments of the present invention and are not intended to limit the present invention. Any modifications, equivalent substitutions and improvements made within the spirit and principles of the present invention should be included in the protection scope of the present invention.

Claims

1. A method for transferring a metal electrode to a two-dimensional material, characterized in that: include: Obtaining a structure to be transferred, the structure to be transferred comprising a substrate, a transition layer formed on the substrate, and a metal electrode pattern formed on the transition layer, the substrate being a silicon substrate, the transition layer being silicon oxide, the transition layer having a height ranging from 250 nm to 350 nm, the metal electrode pattern comprising Cr at the bottom and Au at the top, wherein the height of Cr is in the range of 8 nm to 12 nm, and the height of Au is in the range of 40 nm to 120 nm; Wet-etching the transition layer to remove the transition layer not covered by the metal electrode pattern, wherein the solution used for the wet etching is a NaOH solution or a KOH solution, and the adhesion between the metal electrode pattern and the transition layer after the wet etching is reduced; The metal electrode pattern in the structure to be transferred is integrally bonded from the transition layer to the two-dimensional material in the target structure by an organic flexible material, wherein the organic flexible material comprises a flexible support layer and a flexible adhesive layer located on the flexible support layer, and the organic flexible material bonds the metal electrode pattern through the flexible adhesive layer, wherein the flexible support layer comprises PDMS or PMMA, and the flexible adhesive layer comprises PVA; The organic flexible material is removed to complete the van der Waals contact between the metal electrode and the two-dimensional material.

2. The method for transferring a metal electrode onto a two-dimensional material according to claim 1, characterized in that: The step of obtaining the structure to be transferred includes: providing a transfer substrate; growing a transition layer on the transfer substrate; forming a patterned photoresist layer on the transition layer; The metal material is evaporated and the photoresist layer is removed to obtain a metal electrode pattern located on the transition layer.

3. The method for transferring a metal electrode onto a two-dimensional material according to claim 1, characterized in that: The transition layer is etched to remove the transition layer not covered by the metal electrode pattern and the transition layer partially covered by the metal electrode pattern.

4. The method for transferring a metal electrode onto a two-dimensional material according to claim 1, wherein: The flexible support layer comprises PDMS or PMMA, and the flexible adhesive layer comprises PVA; Removing the organic flexible material comprises: heating the target structure to tear the flexible support layer off the target structure; The target structure to be removed from the flexible support layer is placed in a solution to dissolve and remove the flexible adhesive layer.

5. The method for transferring a metal electrode onto a two-dimensional material according to claim 1, characterized in that: After the metal electrode pattern in the structure to be transferred is integrally bonded from the transition layer by the organic flexible material, the metal electrode pattern and the target structure are aligned and bonded by the alignment component on the transfer table.

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