A high-mobility diamond radio frequency field-effect transistor and its fabrication method

Abstract

This invention discloses a high-mobility diamond radio frequency field-effect transistor (RF field-effect transistor) and its fabrication method. The transistor includes a diamond substrate, a hydrogen terminal, a hexagonal boron nitride dielectric layer, a gate metal layer, an ohmic contact metal layer, and a passivation dielectric layer. The transistor fabrication method includes transferring the hexagonal boron nitride dielectric layer onto the hydrogen-terminated diamond substrate; gate fabrication and etching of the hexagonal boron nitride dielectric layer; surface hydrogen plasma treatment; ohmic contact electrode fabrication; passivation dielectric layer deposition; and dielectric via etching. This invention utilizes boron nitride transfer and selective etching techniques under vacuum conditions, which can effectively improve the interface quality between boron nitride and diamond. The fabricated diamond RF field-effect transistor exhibits low interface state density, high carrier mobility, high frequency performance, and high breakdown voltage, and can be applied to the development of high-frequency, high-power diamond RF devices.

Description

Technical Field

[0001] This invention belongs to the field of semiconductor device fabrication technology, specifically relating to a high-mobility diamond radio frequency field-effect transistor and its fabrication method. Background Technology

[0002] High-concentration two-dimensional hole gas channels exist on the surface of hydrogen-terminated diamond. However, due to the channels being on the sample surface and affected by impurity scattering, the hydrogen-terminated channels not only have low mobility but are also unstable, resulting in diamond device performance far below theoretical expectations. Using hexagonal boron nitride as the gate dielectric on hydrogen-terminated diamond can reduce interface density and ionized impurity scattering, thereby improving carrier mobility and device performance. However, the channels under boron nitride exhibit enhancement due to desorption, requiring a gate voltage to open the channels. This necessitates the gate spanning the source and drain electrodes, severely limiting improvements in device frequency and breakdown characteristics. Furthermore, if boron nitride is transferred onto patterned diamond (e.g., with pre-fabricated electrodes, grooves, etc.), the presence of steps prevents the boron nitride from adhering tightly to the diamond substrate, allowing air to enter the gaps between the boron nitride and diamond, leading to decreased gate control capability and increased interface state density. Summary of the Invention

[0003] Technical problem solved: To address the above-mentioned technical problems, the present invention provides a high-mobility diamond radio frequency field-effect transistor and its fabrication method, which can effectively solve the shortcomings of existing diamond field-effect transistor devices, such as high interface state density of transferred boron nitride gate dielectric, low device frequency and low breakdown voltage.

[0004] Technical solution: A high-mobility diamond radio frequency field-effect transistor includes a diamond substrate, a hydrogen terminal, a gate, a source, and a drain. The hydrogen terminal is disposed on the upper surface of the diamond substrate. The gate includes a hexagonal boron nitride dielectric layer and a gate metal layer. The hexagonal boron nitride dielectric layer is disposed on the upper surface of the hydrogen terminal, and the gate metal layer is disposed on the upper surface of the hexagonal boron nitride dielectric layer. The source, gate, and drain are sequentially and spaced apart on the upper surface of the hydrogen terminal. Passivation dielectric layers are provided on the upper surfaces of the hydrogen terminals on both sides of the source, the upper surfaces of the hydrogen terminals on both sides of the drain, the upper surfaces of the source portion, the upper surfaces of the drain portion, and the upper surfaces of the gate portion.

[0005] A method for fabricating a high-mobility diamond radio frequency field-effect transistor includes the following steps:

[0006] S1. Hydrogenation treatment is performed on the surface of the diamond substrate to form hydrogen terminals, resulting in hydrogen-terminated diamond. Then, the hydrogen-terminated diamond is transferred to a vacuum glove box connected to the hydrogenation equipment, and a hexagonal boron nitride dielectric layer is transferred on the surface of the hydrogen-terminated diamond.

[0007] S2. A gate region is defined on the upper surface of a hexagonal boron nitride dielectric layer using photoresist;

[0008] S3. Deposit a gate metal layer in the gate region, and then use an organic solution to strip the photoresist to form the gate;

[0009] S4. Using the gate metal layer as a mask, the unmasked hexagonal boron nitride dielectric layer is etched away, and the surface of the hydrogen-terminated diamond is subjected to hydrogen plasma treatment to obtain hydrogen-terminated diamond after hydrogen plasma treatment.

[0010] S5. The source and drain regions are defined on the hydrogen-terminated diamond surface after hydrogen plasma treatment on both sides of the gate using photoresist, and the gate and source / drain regions are hydrogen-terminated channels. Ohmic contact metal layers are deposited in the source / drain regions. The photoresist is stripped using an organic solution to form ohmic electrodes, and annealing is used to form ohmic contacts, thus obtaining the source and drain.

[0011] S6. A passivation dielectric layer is deposited on the hydrogen terminal, the ohmic contact metal layer and the gate metal layer using atomic layer deposition.

[0012] S7. Using photoresist, define the dielectric hole region on the passivation dielectric layer located on the ohmic contact metal layer and the gate metal layer respectively, etch away the passivation dielectric layer in the dielectric hole, and remove the photoresist using an organic solution.

[0013] Preferably, the diamond substrate is a single-crystal diamond substrate or a polycrystalline diamond substrate.

[0014] Preferably, the thickness of the hexagonal boron nitride dielectric layer is 1~100 nm.

[0015] Preferably, the metal of the gate metal layer is one or more of Ti, Al, Au, Pt, Ni, Mo, Cu, Ag, Pd, W, and Fe, and the thickness of the gate metal layer is 10 nm to 1 μm.

[0016] Preferably, the method for etching the hexagonal boron nitride dielectric layer in step S4 is ICP etching or RIE etching, and the etching gas used is one or more mixed gases selected from CF4, SF6, BCl3, Cl2, and Ar.

[0017] Preferably, the metal of the ohmic contact metal layer is one or a combination of Ti, Al, Au, Pt, Ni, Mo, Cu, Ag, Pd, W, and Fe, and the thickness of the ohmic contact metal layer is 10 nm to 1 μm.

[0018] Preferably, in step S5, the annealing atmosphere is nitrogen or argon, and the annealing temperature is from room temperature to 800°C.

[0019] Preferably, the passivation medium layer is one or more combinations of Al2O3, HfO2, ZrO2, Si3N4, SiO2, MoO3, V2O5, and WO3, and the thickness of the passivation medium layer is 10nm~1μm.

[0020] Preferably, the method for etching the passivation dielectric layer in step S7 is wet etching, ICP etching, or RIE etching.

[0021] Beneficial effects: This invention provides a high-mobility diamond radio frequency field-effect transistor and its fabrication method. The method is based on boron nitride transfer and selective etching technology under vacuum environment, which can effectively improve the interface quality between boron nitride and diamond. The fabricated diamond radio frequency field-effect transistor has the characteristics of low interface state density, high carrier mobility, high frequency performance and high breakdown voltage, and can be applied to the development of high-frequency high-power diamond radio frequency devices. Attached Figure Description

[0022] Figure 1 This is a schematic diagram of the structure of a high-mobility diamond radio frequency field-effect transistor according to the present invention;

[0023] Figure 2 This is a flowchart of a method for fabricating a high-mobility diamond radio frequency field-effect transistor according to the present invention;

[0024] The numbers in the diagram are: 1. Diamond substrate, 2. Hexagonal boron nitride dielectric layer, 3. Photoresist, 4. Gate metal layer, 5. Ohmic contact metal layer, 6. Passivation dielectric layer. Detailed Implementation

[0025] The present invention will now be described in detail with reference to the accompanying drawings and specific embodiments:

[0026] Example 1

[0027] like Figure 1 As shown, a high-mobility diamond radio frequency field-effect transistor includes a diamond substrate 1, a hydrogen terminal, a gate, a source, and a drain. The hydrogen terminal is disposed on the upper surface of the diamond substrate 1. The gate includes a hexagonal boron nitride dielectric layer 2 and a gate metal layer 4. The hexagonal boron nitride dielectric layer 2 is disposed on the upper surface of the hydrogen terminal, and the gate metal layer 4 is disposed on the upper surface of the hexagonal boron nitride dielectric layer 2. The source, gate, and drain are sequentially and spaced apart on the upper surface of the hydrogen terminal. A passivation dielectric layer 6 is provided on the upper surfaces of the hydrogen terminals on both sides of the source, the upper surfaces of the hydrogen terminals on both sides of the drain, the upper surface of the source portion, the upper surface of the drain portion, and the upper surface of the gate portion.

[0028] like Figure 2 As shown, a method for fabricating a high-mobility diamond radio frequency field-effect transistor includes the following steps:

[0029] S1. Hydrogenation treatment is performed on the surface of diamond substrate 1 to form hydrogen terminals, and hydrogen-terminated diamond is obtained. Then, the hydrogen-terminated diamond is transferred to a vacuum glove box connected to the hydrogenation equipment. The hydrogen-terminated diamond does not come into contact with air during the transfer to the glove box. A 30nm thick hexagonal boron nitride dielectric layer 2 is transferred on the surface of the hydrogen-terminated diamond.

[0030] S2. A gate region is defined on the upper surface of the hexagonal boron nitride dielectric layer 2 using photoresist 3;

[0031] S3. A 20nm Ti and a 300nm Au gate metal layer 4 are deposited sequentially in the gate region, and then the gate is formed by stripping the photoresist 3 with acetone.

[0032] S4. Using the gate metal layer 4 as a mask, the unmasked hexagonal boron nitride dielectric layer 2 is etched away using ICP etching technology, and the surface of the hydrogen-terminated diamond is treated with hydrogen plasma using MPCVD equipment to obtain hydrogen-terminated diamond after hydrogen plasma treatment.

[0033] S5. Using photoresist 3, the source and drain regions are defined on the hydrogen-terminated diamond surface after hydrogen plasma treatment on both sides of the gate. The gate and the source and drain regions are hydrogen-terminated channels. A 200nm Au ohmic contact metal layer 5 is deposited in the source and drain regions. The photoresist 3 is stripped with acetone to form ohmic electrodes, and annealing is used to form ohmic contacts to obtain the source and drain.

[0034] S6. An Al2O3 passivation dielectric layer 6 with a thickness of 100 nm is deposited on the hydrogen terminal, the ohmic contact metal layer 5 and the gate metal layer 4 using atomic layer deposition (ALD).

[0035] S7. Using photoresist 3, the dielectric hole region is defined on the Al2O3 passivation dielectric layer 6 located on the ohmic contact metal layer 5 and the gate metal layer 4 respectively. The Al2O3 passivation dielectric layer 6 in the dielectric hole is etched away using TMAH solution, and the photoresist 3 is removed using acetone.

[0036] The above description is only a preferred embodiment of the present invention and is 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 within the protection scope of the present invention.

Claims

1. A method for fabricating a high-mobility diamond radio frequency field-effect transistor, characterized in that, The transistor includes a diamond substrate (1), a hydrogen terminal, a gate, a source, and a drain. The hydrogen terminal is disposed on the upper surface of the diamond substrate (1). The gate includes a hexagonal boron nitride dielectric layer (2) and a gate metal layer (4). The hexagonal boron nitride dielectric layer (2) is disposed on the upper surface of the hydrogen terminal, and the gate metal layer (4) is disposed on the upper surface of the hexagonal boron nitride dielectric layer (2). The source, gate, and drain are disposed sequentially on the upper surface of the hydrogen terminal. A passivation dielectric layer (6) is provided on the upper surfaces of the hydrogen terminals on both sides of the source, the upper surfaces of the hydrogen terminals on both sides of the drain, the upper surface of the source portion, the upper surface of the drain portion, and the upper surface of the gate portion. The dielectric of the passivation dielectric layer (6) is Al2O3. The preparation method includes the following steps: S1. Hydrogenation treatment is performed on the surface of the diamond substrate (1) to form a hydrogen terminal and obtain a hydrogen-terminated diamond. Then, the hydrogen-terminated diamond is transferred to a vacuum glove box connected to the hydrogenation equipment, and a hexagonal boron nitride dielectric layer (2) is transferred on the surface of the hydrogen-terminated diamond. S2. A gate region is defined on the upper surface of the hexagonal boron nitride dielectric layer (2) using photoresist (3); S3. A gate metal layer (4) is deposited in the gate region, and then the photoresist (3) is stripped using an organic solution to form the gate; S4. Using the gate metal layer (4) as a mask, the unmasked hexagonal boron nitride dielectric layer (2) is etched away, and the surface of the hydrogen-terminated diamond is subjected to hydrogen plasma treatment to obtain hydrogen-terminated diamond after hydrogen plasma treatment. S5. Use photoresist (3) to define the source and drain regions on the hydrogen-terminated diamond surface after hydrogen plasma treatment on both sides of the gate, and the gate and source and drain regions are hydrogen-terminated channels. Deposit ohmic contact metal layer (5) in the source and drain regions, use organic solution to peel off photoresist (3) to form ohmic electrodes, and anneal to form ohmic contacts to obtain source and drain electrodes. S6. A passivation dielectric layer (6) is deposited on the hydrogen terminal, the ohmic contact metal layer (5) and the gate metal layer (4) using atomic layer deposition. S7. Using photoresist (3), a dielectric hole region is defined on the passivation dielectric layer (6) located on the ohmic contact metal layer (5) and the gate metal layer (4), respectively. The passivation dielectric layer (6) in the dielectric hole is etched away, and the photoresist (3) is removed using an organic solution.

2. The method for fabricating a high-mobility diamond radio frequency field-effect transistor according to claim 1, characterized in that: The diamond substrate (1) is a single-crystal diamond substrate or a polycrystalline diamond substrate.

3. The method for fabricating a high-mobility diamond radio frequency field-effect transistor according to claim 1, characterized in that: The thickness of the hexagonal boron nitride dielectric layer (2) is 1~100nm.

4. The method for fabricating a high-mobility diamond radio frequency field-effect transistor according to claim 1, characterized in that: The metal of the gate metal layer (4) is one or more of Ti, Al, Au, Pt, Ni, Mo, Cu, Ag, Pd, W, and Fe, and the thickness of the gate metal layer (4) is 10 nm to 1 μm.

5. The method for fabricating a high-mobility diamond radio frequency field-effect transistor according to claim 1, characterized in that: In step S4, the method for etching the hexagonal boron nitride dielectric layer (2) is ICP etching or RIE etching, and the etching gas used is one or more mixed gases selected from CF4, SF6, BCl3, Cl2, and Ar.

6. The method for fabricating a high-mobility diamond radio frequency field-effect transistor according to claim 1, characterized in that: The metal of the ohmic contact metal layer (5) is one or more of Ti, Al, Au, Pt, Ni, Mo, Cu, Ag, Pd, W, and Fe, and the thickness of the ohmic contact metal layer (5) is 10 nm to 1 μm.

7. The method for fabricating a high-mobility diamond radio frequency field-effect transistor according to claim 1, characterized in that: In step S5, the annealing atmosphere is nitrogen or argon, and the annealing temperature is from room temperature to 800°C.

8. The method for fabricating a high-mobility diamond radio frequency field-effect transistor according to claim 1, characterized in that: The thickness of the passivation medium layer (6) is 10 nm to 1 μm.

9. The method for fabricating a high-mobility diamond radio frequency field-effect transistor according to claim 1, characterized in that: The method for etching the passivation dielectric layer (6) in step S7 is wet etching, ICP etching, or RIE etching.

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