A method for fabricating a buried-channel diamond device

Abstract

The present invention provides a preparation method of a buried-channel diamond device, belonging to the field of ultra-wide bandgap semiconductor devices. It is characterized by including the following steps: 1) Design the device structure and clean the diamond substrate; 2) Prepare a multi-layer graphene structure on the diamond substrate; 3) Epitaxially grow a diamond layer on the graphene layer; 4) Deposit source, drain, and gate electrodes to complete the device preparation. The present invention uses the multi-layer graphene structure as a buried channel and the epitaxial diamond layer as a partial gate oxide, having the advantages of improving the channel mobility, breakdown voltage, and increasing the output power of the diamond device.

Description

Technical Field

[0001] The present invention belongs to the field of ultra-wide bandgap semiconductor devices, and particularly relates to a method for fabricating a buried-channel diamond device. Background Art

[0002] The ultra-wide bandgap semiconductor material diamond has intrinsic properties such as a wide bandgap (5.5 eV), a high breakdown field strength (10 MV / cm), a high carrier mobility (hole: 3800 cm 2 / Vs, electron: 4500 cm 2 / Vs), and ultra-high thermal conductivity (22 W / cmK), and is known as the ultimate semiconductor. It is an ideal material for fabricating next-generation high-temperature, high-frequency, and high-power devices.

[0003] However, for both surface-terminal diamond devices and bulk-doped diamond devices, their channel mobilities are at a relatively low level (in the hundreds), which greatly limits the saturation current and frequency characteristics of the devices, and fails to maximize the advantages of diamond materials. The main reason is that the carriers in surface-terminal devices, such as the conductive channel of hydrogen termination, are easily affected by the scattering on the substrate surface and the interface scattering with the gate oxide layer, while the channel carriers in bulk-doped diamond devices are affected by the scattering of doping atoms, lattice distortion, and deep-level defects. Therefore, to improve the output characteristics of diamond devices, new methods need to be found to overcome the above disadvantages and further improve their channel mobilities.

[0004] Interestingly, the two-dimensional material graphene also has ultra-high conductivity characteristics, especially with great advantages in carrier mobility. The hole mobility of monolayer graphene can reach 200000 cm 2 / Vs, which is more than 40 times that of diamond materials. Utilizing the ultra-high mobility characteristics of graphene to improve the device performance of diamond and fabricating a device similar to a gallium nitride-based high electron mobility transistor (HEMT) will contribute to its rapid development in the field of high-frequency and high-power devices. In addition, graphene and diamond materials can be mutually transformed, which is beneficial to the in-situ growth of the channel layer, reduces the generation of defects, and maximally retains the integrity of the graphene structure. Summary of the Invention

[0005] The purpose of the present invention is to overcome the problem of low channel mobility in existing diamond devices, and to improve the output characteristics of ultra-wide bandgap semiconductor diamond devices by leveraging the high mobility characteristics of graphene materials and their natural advantage of being able to mutually transform with diamond substrates.

[0006] To achieve the above purpose, the present invention provides a method for fabricating a buried-channel diamond device, which is characterized by including the following steps:

[0007] (1) Design the device structure and clean the diamond substrate;

[0008] (2) Prepare a multi-layer graphene structure on a diamond substrate;

[0009] (3) Epitaxially grow a diamond layer on the graphene layer;

[0010] (4) Deposit source, drain, and gate electrodes to complete the device fabrication.

[0011] Optionally, the device structure in step 1 can be one of a transistor, a diode, and a detector; the diamond substrate can be one of doped diamond and surface-terminated diamond.

[0012] Optionally, the method for preparing the multi-layer graphene structure in step 2 can be one of direct high-temperature annealing, catalytic annealing, and chemical vapor deposition growth.

[0013] Optionally, the method for epitaxially growing diamond in step 3 is microwave plasma chemical vapor deposition.

[0014] Optionally, the metal types of the source, drain, and gate electrodes in step 4 are one or a combination of gold, palladium, platinum, titanium gold, and aluminum; the deposition method is one of magnetron sputtering, thermal evaporation, and electron beam evaporation.

[0015] Optionally, for the preparation method of the buried-channel diamond device as described above, the specific preparation steps are as follows:

[0016] 1) Design the device structure, clean the diamond substrate with a mixed acid (sulfuric acid and nitric acid) solution, and then ultrasonically rinse it successively with acetone, absolute ethanol, and deionized water, and dry it with nitrogen;

[0017] 2) Place the diamond substrate in a CVD furnace for boron-doped epitaxial growth to form a p+ layer,

[0018] 3) Perform high-temperature annealing on the boron-doped diamond sample to in-situ form a multi-layer graphene structure on the diamond surface with a thickness of 5 - 15 nm;

[0019] 4) Then place the annealed diamond sample in a CVD deposition furnace to epitaxially grow a 5 - 20 nm diamond layer

[0020] 5) Perform oxygen plasma treatment on the diamond sample to form oxygen-terminated isolation,

[0021] 6) Lithograph the source and drain patterns on the sample, form a p++ layer in the source and drain regions through selective re-boron doping, and then perform evaporation and stripping of the source and drain metal electrodes TiPtAu;

[0022] 7) Deposit a layer of gate oxide Al2O3 with a thickness of 5 - 20 nm by atomic layer deposition, and then selectively deposit a gate metal Al electrode by lithography to complete the device fabrication.

[0023] Optionally, for the preparation method of the buried-channel diamond device as described above, the specific preparation steps are as follows:

[0024] 1) Design the device structure, clean the diamond substrate with a mixed acid (sulfuric acid and nitric acid) solution; then ultrasonically rinse it successively with acetone, absolute ethanol, and deionized water, and dry it with nitrogen;

[0025] 2) Place the diamond substrate in a CVD furnace for epitaxial growth, with a thickness of 100 - 200 nm,

[0026] 3) Deposit a catalytic layer on the surface of the epitaxial diamond sample, and form a multi-layer graphene structure in-situ on the diamond surface after rapid annealing, with a thickness of 5 - 20 nm

[0027] 4) Then place the annealed diamond sample in a CVD deposition furnace for epitaxial growth of a 5 - 15 nm diamond layer,

[0028] 5) Perform oxygen plasma treatment on the diamond sample to form oxygen-terminated isolation,

[0029] 6) Lithograph the source-drain pattern on the sample, electron beam evaporate the source-drain metal electrodes TiAu, with a thickness of 10 nm / 100 nm, and lift off;

[0030] 7) Deposit a layer of gate oxide Al2O3 by atomic layer deposition, with a thickness of 5 - 20 nm, and then complete the device preparation by selectively depositing a gate metal Al electrode using a lithography process.

[0031] Compared with the prior art, the present invention has the following remarkable advantages: 1) Reduce the interface state density and solve the problem of low channel mobility of existing diamond devices; 2) The epitaxial diamond layer can be used as part of the gate oxide to improve the breakdown voltage of the device; 3) It is easy to regulate the device performance by changing the number of graphene layers to obtain a high current output power.

[0032] The following further explains the present invention in detail with reference to the accompanying drawings. Description of the Drawings

[0033] Figure 1 is a flowchart for the preparation of a buried-channel diamond device,

[0034] Figure 2 is a schematic diagram of the preparation process of the buried-channel diamond device corresponding to Example 1. Detailed Embodiments

[0035] Example 1

[0036] 1) Design the device structure, clean the diamond substrate (110), as Figure 2As shown in a. Place the single-crystal diamond substrate (110) in a mixed acid solution of sulfuric acid: nitric acid (volume ratio 1:3), heat it at the boiling state for 30 min, and take it out after cooling. Then ultrasonically rinse it with acetone, absolute ethanol, and deionized water in sequence for 15 min, and dry it with nitrogen.

[0037] 2) Place the diamond substrate in a CVD furnace for boron-doped epitaxial growth ( Figure 2 b), to form a p+ layer (120) with a thickness of 100 nm. Among them, the boron doping concentration is 1×10 18 cm -3 , the deposition temperature is 800 °C, the chamber pressure is 10 kPa, the hydrogen flow rate is 85 sccm, the methane flow rate is 5 sccm, and the TMB boron source is 10 sccm.

[0038] 3) Perform high-temperature annealing on the boron-doped diamond sample to in-situ form a multi-layer graphene structure (130) ( Figure 2 c) with a thickness of 10 nm. Among them, the annealing temperature is 1000 °C, the time is 2 min, and the annealing atmosphere is argon: hydrogen (2:1).

[0039] 4) Then place the annealed diamond sample in a CVD deposition furnace for epitaxial growth of a 20-nm diamond layer (111) ( Figure 2 d), the deposition temperature is 750 °C, the time is 15 min, the chamber pressure is 10 kPa, the hydrogen flow rate is 80 sccm, and the methane flow rate is 5 sccm.

[0040] 5) Perform oxygen plasma treatment on the diamond sample to form oxygen-terminated isolation, the plasma power is 100 W, the flow rate is 10 sccm, and the time is 2 min;

[0041] 6) Lithograph the source-drain pattern on the sample, and form a p++ layer (140) in the source-drain region through selective re-boron doping, and then perform evaporation and stripping of the source-drain metal electrode TiPtAu (150) ( Figure 2 e and Figure 2 f). Among them, the boron doping concentration is 1×10 21 cm -3 , the temperature is 800 °C, the chamber pressure is 10 kPa, the hydrogen flow rate is 80 sccm, the methane flow rate is 5 sccm, and the TMB boron source is 15 sccm.

[0042] 7) Deposit a layer of gate oxide Al2O3 (160) by atomic layer deposition with a thickness of 10 nm, and then selectively deposit a gate metal Al (170) electrode by lithography technology ( Figure 2 g) to complete the device preparation.

[0043] Example 2

[0044] 1) Design the device structure and clean the diamond substrate; Place the single-crystal diamond substrate in a mixed acid solution of sulfuric acid: nitric acid (volume ratio 1:3), heat it at the boiling state for 30 min, take it out after cooling. Then ultrasonically rinse it with acetone, absolute ethanol, and deionized water in sequence for 15 min, and dry it with nitrogen.

[0045] 2) Place the diamond substrate in a CVD furnace for epitaxial growth with a thickness of 100 nm. Among them, the deposition temperature is 800 °C, the chamber pressure is 10 kPa, the hydrogen flow rate is 85 sccm, and the methane flow rate is 5 sccm.

[0046] 3) Deposit a catalytic layer on the surface of the epitaxial diamond sample. After rapid annealing, a multi-layer graphene structure is formed in situ on the diamond surface with a thickness of 10 nm. Among them, the catalyst is one of nickel, copper, and cobalt, the annealing temperature is 800 °C, the time is 1 min, and the annealing atmosphere is argon: hydrogen (2:1).

[0047] 4) Then place the annealed diamond sample in a CVD deposition furnace for epitaxial growth of a 10-nm diamond layer. The deposition temperature is 750 °C, the time is 10 min, the chamber pressure is 10 kPa, the hydrogen flow rate is 80 sccm, and the methane flow rate is 5 sccm.

[0048] 5) Perform oxygen plasma treatment on the diamond sample to form oxygen-terminated isolation. The plasma power is 100 W, the flow rate is 10 sccm, and the time is 2 min.

[0049] 6) Lithograph the source-drain pattern on the sample, electron beam evaporate the source-drain metal electrodes TiAu with a thickness of 10 nm / 100 nm, and lift off.

[0050] 7) Deposit a layer of gate oxide Al2O3 by atomic layer deposition with a thickness of 10 nm, and then complete the device preparation by selectively depositing a gate metal Al electrode using a lithography process.

[0051] Example 3

[0052] 1) Design the device structure and clean the diamond substrate; Place the single-crystal diamond substrate in a mixed acid solution of sulfuric acid: nitric acid (volume ratio 1:3), heat it at the boiling state for 30 min, take it out after cooling. Then ultrasonically rinse it with acetone, absolute ethanol, and deionized water in sequence for 15 min, and dry it with nitrogen.

[0053] 2) Place the diamond substrate in a CVD furnace for hydrogen plasma treatment to form hydrogen termination. Among them, the deposition temperature is 700 °C, the chamber pressure is 10 kPa, and the hydrogen flow rate is 100 sccm.

[0054] 3) The hydrogen-terminated diamond sample is subjected to high-temperature annealing to in-situ form a multi-layer graphene structure on the diamond surface with a thickness of 10 nm. The annealing temperature is 1000 °C, the time is 10 min, and the annealing atmosphere is argon:hydrogen (2:1).

[0055] 4) Then, the annealed diamond sample is placed in a CVD deposition furnace to epitaxially grow a 20-nm diamond layer. The deposition temperature is 750 °C, the time is 15 min, the chamber pressure is 10 kPa, the hydrogen flow rate is 80 sccm, and the methane flow rate is 5 sccm.

[0056] 5) The diamond sample is subjected to oxygen plasma treatment to form oxygen-terminated isolation. The plasma power is 100 W, the flow rate is 10 sccm, and the time is 2 min.

[0057] 6) The source-drain pattern is lithographed on the sample, and the source-drain metal electrodes Ti / Pt / Au with a thickness of 10 nm / 20 nm / 100 nm are electron beam evaporated and then lifted off.

[0058] 7) A layer of gate oxide Al2O3 with a thickness of 10 nm is deposited by atomic layer deposition, and then the gate metal Al electrode is selectively deposited by a lithography process to complete the device fabrication.

Claims

1. A method for preparing a buried-channel diamond device, characterized in that: The following steps are involved: 1) Design device structure and clean diamond substrate; 2) Preparation of multilayer graphene structures on diamond substrates; 3) epitaxially growing a diamond layer on the graphene layer; 4) Treat the diamond with oxygen plasma to form oxygen terminal isolation; then plate the source, drain, and gate electrodes to complete the device preparation.

2. The method for preparing a buried-channel diamond device according to claim 1, characterized in that: In step 1, the device structure is one of a transistor, a diode, and a detector; and the diamond substrate is one of doped diamond or surface-terminated diamond.

3. The method for preparing a buried-channel diamond device according to claim 1, characterized in that: The method for preparing the multilayer graphene structure in step 2 is one of direct high temperature annealing, catalytic annealing, and chemical vapor deposition growth.

4. The method for preparing a buried-channel diamond device according to claim 1, characterized in that: The method used for epitaxial growth of diamond in step 3 is microwave plasma chemical vapor deposition.

5. The method for preparing a buried-channel diamond device according to claim 1, characterized in that: In step 4, the metal type of the source, drain and gate electrodes is TiAu, Ti / Pt / Au or one or more combinations of gold, palladium, platinum and aluminum; the plating method is one of magnetron sputtering, thermal evaporation and electron beam evaporation.

6. A method for preparing a buried-channel diamond device, characterized in that: The specific preparation steps are as follows: 1) design the device structure, clean the diamond substrate with a mixed acid solution consisting of sulfuric acid and nitric acid, then ultrasonically rinse with acetone, anhydrous ethanol, and deionized water in sequence, and blow dry with nitrogen; 2) Place the diamond substrate in a CVD furnace for boron doping epitaxial growth to form a p+ layer. 3) High temperature annealing of the boron-doped diamond sample to form a multilayer graphene structure in situ on the diamond surface with a thickness of 5-15nm; 4) The annealed diamond is then placed in a CVD deposition furnace to epitaxially grow a 5-20 nm diamond layer. 5) Treat diamond with oxygen plasma to form oxygen terminal isolation. 6) Photolithography of source and drain patterns on diamond, forming a p++ layer in the source and drain regions by selective heavy boron doping, and then evaporation and stripping of the source and drain metal electrodes TiPtAu; 7) A layer of gate oxide Al2O3 is deposited by atomic layer deposition with a thickness of 5-20 nm, and then the gate metal Al electrode is selectively deposited by photolithography to complete the device preparation.

7. A method for preparing a buried-channel diamond device, characterized in that: The specific preparation steps are: 1) Design the device structure, clean the diamond substrate with a mixed acid solution consisting of sulfuric acid and nitric acid; then ultrasonically rinse with acetone, anhydrous ethanol, and deionized water in sequence, and blow dry with nitrogen; 2) Place the diamond substrate in a CVD furnace for epitaxial growth with a thickness of 100-200 nm. 3) A catalytic layer is plated on the surface of epitaxial diamond, and after rapid annealing, a multi-layer graphene structure with a thickness of 5-20 nm is formed in situ on the surface of diamond. 4) The annealed diamond is then placed in a CVD deposition furnace to epitaxially grow a 5-20nm diamond layer. 5) Treat diamond with oxygen plasma to form oxygen terminal isolation. 6) Photolithography of source and drain patterns on diamond, electron beam evaporation of source and drain metal electrodes TiAu with a thickness of 10 nm / 100 nm, and peeling; 7) A layer of gate oxide Al2O3 is deposited by atomic layer deposition with a thickness of 5-20nm, and then the gate metal Al electrode is selectively deposited by photolithography to complete the device preparation.

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