A method for preparing a low resistance ohmic contact on diamond

Abstract

The application relates to a preparation method of a low-resistance ohmic contact on diamond, which comprises the following steps: selecting an undoped diamond as a first substrate layer; depositing a preset film containing silicon on the first substrate layer; first decomposing solid boron nitride at a first preset temperature in a preset system to introduce a boron source; etching the preset film in the preset system at a second preset temperature to diffuse the silicon in the preset film and the boron in the preset system into the first substrate layer, so as to obtain a second substrate layer; standing the second substrate layer in air to obtain a third substrate layer; and depositing a metal layer on the diamond surface terminal in the third substrate layer to complete the preparation of the ohmic resistance. The preset film is used as a silicon source, and the solid boron nitride is used as a boron source; through the diffusion of the silicon and the boron, boron-silicon co-doping in the diamond is realized; then a metal layer is deposited, a good ohmic contact can be directly formed, and the ohmic contact resistance is reduced.

Description

Technical Field

[0001] This invention relates to the field of semiconductor process technology, and specifically to a method for preparing a low-resistivity ohmic contact on diamond. Background Technology

[0002] Ultra-wide bandgap semiconductor diamond possesses numerous advantages, including a large bandgap, high breakdown field strength, high carrier mobility, high thermal conductivity, and radiation resistance. Given the current lack of significant breakthroughs in efficient bulk doping of diamond, hydrogen-terminated diamond field-effect transistors (FETs), which use surface hydrogen-terminated two-dimensional hole gas as the conductive channel, have become the mainstream device choice and hold immense potential in power electronics applications. Currently, hydrogen-terminated diamond FETs (Field Effect Transistors) lag significantly in performance compared to gallium nitride-based HEMTs (High Electron Mobility Transistors), a key factor being the higher ohmic contact resistance. The frequency and output power characteristics of diamond microwave power devices are largely influenced by ohmic contact issues. In high-frequency, small-size devices, the source-drain series resistance, primarily composed of ohmic contact resistance, becomes a major factor limiting frequency characteristics; in power devices, ohmic resistance directly affects the saturation voltage and conduction current, suppressing output power in terms of both voltage and current swing.

[0003] Currently, the ohmic contacts of diamond field-effect transistors are mainly obtained by depositing Au metal in hydrogen-terminated diamond. The ohmic contact resistance is generally about 5 Ω·mm, but it is still an order of magnitude higher than the ohmic contact resistance values ​​(≤0.5 Ω·mm) prepared by other mature semiconductor processes such as Si and GaN.

[0004] When the boron doping concentration exceeds 10 20 cm -3 When diamond is exposed to certain conditions, it becomes a degenerate semiconductor, exhibiting metallic conductivity at room temperature. Ion implantation or in-situ doping in the ohmic contact region can produce boron doping concentrations exceeding 10⁻⁶. 20 cm -3 Boron-doped diamond alloying is one feasible solution to reduce ohmic contact resistance. Currently, boron doping concentrations greater than 1×10⁻⁶ are used in diamond alloys. 22 cm -3 High-temperature annealing of boron-doped diamond to form a TiC alloy achieved a minimum ohmic contact resistance of approximately 1 Ω·mm. However, ion implantation boron doping technology can cause some damage to the diamond lattice, thereby reducing substrate quality and affecting device performance; achieving boron doping concentrations exceeding 10⁻⁶... 20 cm -3The in-situ growth of heavy boron doping requires special diamond doping equipment, which is only possessed by the Kawarada research group at Waseda University.

[0005] Existing methods for fabricating hydrogen-terminated diamond FET devices suffer from problems such as high contact resistance, difficult processing, and high cost, making it difficult to meet the needs of diamond FET device performance improvement and application. Therefore, how to achieve low ohmic contact resistance in diamond devices has become an urgent problem to be solved in diamond FET device research. Summary of the Invention

[0006] To address the aforementioned problems in the prior art, this invention provides a method for fabricating low-resistivity ohmic contacts on diamond. The technical problem to be solved by this invention is achieved through the following technical solution:

[0007] A method for preparing a low-resistivity ohmic contact on diamond, the method comprising:

[0008] Undoped diamond was selected as the first substrate layer;

[0009] A predetermined thin film containing silicon is deposited on the first substrate layer;

[0010] At a first preset temperature, boron in solid boron nitride is diffused in a preset system to introduce a boron source. At a second preset temperature, the preset thin film is etched in the preset system to diffuse silicon in the preset thin film and boron in the preset system into a first substrate layer to obtain a second substrate layer. The second substrate layer includes, from bottom to top, an undoped diamond layer, a silicon-boron co-doped diamond layer, and a diamond surface terminal. The diamond surface terminal is a diamond layer containing carbon-hydrogen bonds and carbon-silicon bonds. A solid boron source dopant is provided in the preset system.

[0011] The second substrate layer is left to stand in air to obtain the third substrate layer;

[0012] A metal layer is deposited on the diamond surface terminal in the third substrate to complete the fabrication of the ohmic resistor.

[0013] In one embodiment of the present invention, before depositing a predetermined thin film containing silicon on the first substrate layer, the method further includes:

[0014] At a third preset temperature, the first substrate layer is treated with a strong acid mixture solution, and then at room temperature, the first substrate layer is cleaned sequentially with acetone, ethanol and deionized water to obtain a clean first substrate layer.

[0015] In one embodiment of the present invention, a predetermined thin film containing silicon is deposited on the first substrate layer, comprising:

[0016] A predetermined thin film is deposited on the first substrate layer using a magnetron sputtering process.

[0017] In one embodiment of the present invention, the preset thin film includes a silicon thin film or a silicon dioxide thin film.

[0018] In one embodiment of the present invention, the thickness of the preset thin film is 200-500 nm.

[0019] In one embodiment of the present invention, at a first preset temperature, boron element in solid boron nitride is diffused into a preset system to introduce a boron source. At a second preset temperature, the preset thin film is etched in the preset system to diffuse silicon in the preset thin film and boron element in the preset system into a first substrate layer, thereby obtaining a second substrate layer, comprising:

[0020] Solid boron nitride is placed into the preset system, and then the solid boron nitride is heated to the first preset temperature. At the first preset temperature, the solid boron nitride in the preset system decomposes, so as to introduce a boron source into the preset system.

[0021] The first substrate layer, on which the preset thin film is deposited, is placed into the preset system in which boron is introduced. Hydrogen is used for ignition, and the preset thin film is etched at a second preset temperature to allow the boron in the preset system and the silicon in the preset thin film to diffuse into the first substrate layer, thereby obtaining the second substrate layer.

[0022] In one embodiment of the present invention, the first preset temperature ranges from 600°C to 700°C.

[0023] In one embodiment of the present invention, the range of the second preset temperature is 900℃-1000℃.

[0024] In one embodiment of the present invention, the second substrate layer is left to stand in air to obtain a third substrate layer, comprising:

[0025] The second substrate layer is left to stand in air for 1-12 hours to obtain the third substrate layer.

[0026] In one embodiment of the present invention, the material of the metal layer includes Au.

[0027] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0028] This invention achieves boron-silicon co-doping in diamond by depositing a pre-defined thin film containing silicon on a first substrate layer, using the pre-defined thin film as a silicon source and boron from solid boron nitride as a boron source, through the diffusion of silicon and boron. A high-concentration doped layer is formed on the diamond surface by silicon-boron co-doping, and then a metal layer is deposited. After annealing, a good ohmic contact can be directly formed, reducing the ohmic contact resistance.

[0029] The present invention will be further described in detail below with reference to the accompanying drawings and embodiments. Attached Figure Description

[0030] Figure 1 This is a schematic flowchart of a method for preparing a low-resistivity ohmic contact on diamond according to an embodiment of the present invention.

[0031] Figures 2a-2c This is a schematic diagram of a method for preparing a low-resistivity ohmic contact on diamond according to an embodiment of the present invention;

[0032] Figure 3 This is a SIMS test result diagram of undoped diamond using the preparation method of the present invention, provided by an embodiment of the present invention. Detailed Implementation

[0033] The present invention will be further described in detail below with reference to specific embodiments, but the implementation of the present invention is not limited thereto.

[0034] Example 1

[0035] Please see Figure 1 , Figures 2a-2c , Figure 1 This is a schematic flowchart illustrating a method for fabricating a low-resistivity ohmic contact on diamond according to an embodiment of the present invention. Figures 2a-2c This is a schematic diagram illustrating a method for preparing a low-resistivity ohmic contact on diamond according to an embodiment of the present invention. The method includes:

[0036] Step 1, please refer to Figure 2a Undoped diamond was selected as the first substrate layer 1.

[0037] Step 2: At a third preset temperature, the first substrate layer is treated with a strong acid mixture solution. Then, at room temperature, the first substrate layer is cleaned sequentially with acetone, ethanol and deionized water to obtain a clean first substrate layer.

[0038] Specifically, the first substrate layer is first pre-treated by cutting and polishing. Then, the third preset temperature is set to 200℃, and the first substrate layer is treated with a strong acid mixed solution. After that, the first substrate layer is cleaned in sequence with acetone, ethanol and deionized water at room temperature to obtain a clean first substrate layer.

[0039] Optionally, the strong acid mixture solution is H2SO4:HNO3 (3:1).

[0040] Step 3, please refer to Figure 2b A pre-defined thin film 2 containing silicon is deposited on the first substrate layer 1.

[0041] Specifically, a pre-defined thin film 2 is deposited on the first substrate layer 1 using a magnetron sputtering process.

[0042] Optionally, the preset thin film 2 includes a silicon thin film or a silicon dioxide thin film.

[0043] Optionally, the thickness of the preset film is 200-500nm.

[0044] Step 4, please refer to Figure 2c At a first preset temperature, boron in solid boron nitride (BN) is diffused into a preset system to introduce a boron source. At a second preset temperature, a preset thin film 2 is etched in the preset system to diffuse silicon in the preset thin film 2 and boron in the preset system into a first substrate layer 1 to obtain a second substrate layer 3. The second substrate layer 3 includes, from bottom to top, an undoped diamond layer 31 (the undoped diamond layer 31 is the original first substrate layer), a silicon-boron co-doped diamond layer 32, and a diamond surface terminal 33. The diamond surface terminal 33 is a diamond layer including carbon-hydrogen bonds (CH) and carbon-silicon bonds (C-Si). The preset system contains boron elements that have been decomposed and diffused from solid boron nitride.

[0045] In one specific embodiment, step 4 may include:

[0046] Step 4.1: Place solid boron nitride into a preset system, then heat the solid boron nitride to a first preset temperature. At the first preset temperature, the solid boron nitride in the preset system decomposes to introduce a boron source into the preset system.

[0047] Optionally, the default system is an MPCVD (Microwave Plasma Chemical Vapor Deposition) system.

[0048] In this embodiment, solid boron nitride is placed as a solid boron source dopant in a microwave plasma chemical vapor deposition system and etched with hydrogen plasma. The microwave plasma chemical vapor deposition system is heated to a first preset temperature to decompose the solid boron nitride, thereby enriching the boron element in the system environment. Afterwards, the remaining material after decomposition is removed, thus ensuring that a certain amount of boron element exists in the chamber of the MPCVD system to provide a boron source for the boron in the MPCVD system chamber.

[0049] Optionally, the first preset temperature range is 600℃-700℃.

[0050] Step 4.2: Place the first substrate layer 1 of the surface-deposited preset thin film 2 into the preset system that introduces boron elements, use hydrogen to start ignition (that is, add microwave energy to hydrogen under low pressure to form hydrogen plasma), and etch the preset thin film 2 at the second preset temperature so that the boron elements in the preset system and the silicon in the preset thin film 2 diffuse into the first substrate layer 1 to obtain the second substrate layer 3.

[0051] Optionally, the second preset temperature range is 900℃-1000℃.

[0052] For example, the first substrate layer 1 with a pre-deposited thin film 2 on its surface is placed in an MPCVD system, and the vacuum level is evacuated to 10. - 5 Below mbar, hydrogen gas is introduced to initiate ignition and the temperature is raised to 900℃ for surface etching to obtain a second substrate layer 3 with silicon thermal diffusion doping and silicon boron co-doped.

[0053] Optional, the hydrogen flow rate is 600 sccm.

[0054] In this embodiment, a pre-set thin film is etched using high-temperature hydrogen plasma. During this process, silicon and boron are diffused at high temperature to achieve boron-silicon co-doping of diamond.

[0055] Step 5: Allow the second substrate layer to stand in the air to obtain the third substrate layer.

[0056] Optional, the settling time is 1h-12h.

[0057] Step 6: Deposit a metal layer on the diamond surface terminal in the third substrate layer.

[0058] Optionally, the metal layer may be made of Au and have a thickness of 100 nm.

[0059] This invention effectively reduces the complexity of the manufacturing process. It uses magnetron sputtering to deposit a pre-defined thin film, employing the pre-defined film as a silicon source and solid-state BN as a boron source. Boron-silicon co-doping of diamond is achieved through thermal diffusion, and diamonds with doping levels exceeding 10⁻⁶ can be produced using ordinary MPCVD equipment. 20cm -3 Boron doping concentration (see Figure 3 With high doping concentration, it can achieve high charged carriers and good bulk conductivity even at low activation energy, reducing the equipment requirements for in-situ growth of boron-doped diamond.

[0060] This invention can effectively reduce process costs. It uses magnetron sputtering to deposit a pre-defined thin film, with the film serving as the silicon source and solid boron (BN) as the boron source, which is cheaper than the silanes and boranes used in existing MPCVD growth methods. Furthermore, this invention achieves boron-silicon co-doping of diamond through thermal diffusion, allowing boron atoms to be directly diffused into the diamond structure at high temperatures without requiring new equipment and ensuring compatibility with existing processes. Compared to ion implantation, which introduces new equipment and increases process costs, thermal diffusion, when used with in-situ doping, cannot effectively control the in-situ doping growth of diamond when simultaneously doping with two elements. The thermal diffusion doping method used in this invention is performed at high temperatures. High temperatures increase the kinetic energy of carbon atoms within the diamond, promoting the doping of boron and silicon. Simultaneously, in the initial stages of thermal diffusion doping, a significant concentration gradient is formed between silicon on the diamond surface and boron, which is abundant in the environment, under high-temperature conditions. Diffusion is driven by this concentration gradient, thereby accelerating the diffusion of the dopant into the interior. Therefore, this invention achieves rapid doping. Verification shows that the method of this invention can achieve a thickness exceeding 300 nm and a peak concentration exceeding 10 within 10 minutes. 20 cm -3 Boron-doped diamond grows faster and at a lower cost compared to conventional boron-doped diamond in situ (1 μm / h).

[0061] This invention uses a thermal diffusion method to achieve boron-silicon co-doping of diamond. This method can be applied to large-size diamond substrates, which is beneficial for further cost reduction. In addition, large-size diamond substrates are also beneficial for device fabrication.

[0062] In this invention, boron-silicon co-doping of diamond is achieved by high-temperature annealing in a hydrogen atmosphere during MPCVD. This process not only prepares boron-silicon co-doped diamond but also performs hydrogen passivation on the diamond surface, reducing the work function of the diamond surface and the potential barrier height with Au metal, thereby further reducing the resistance of the ohmic contact.

[0063] In the description of this invention, the terms "first" and "second" are used for descriptive purposes only and should not be construed as indicating or implying relative importance or implicitly specifying the number of indicated technical features. Thus, a feature defined as "first" or "second" may explicitly or implicitly include one or more of that feature. In the description of this invention, "a plurality of" means two or more, unless otherwise explicitly specified.

[0064] In the description of this specification, the references to terms such as "one embodiment," "some embodiments," "example," "specific example," or "some examples," etc., indicate that a specific feature, structure, material, or characteristic described in connection with that embodiment or example is included in at least one embodiment or example of the invention. In this specification, the illustrative expressions of the above terms do not necessarily refer to the same embodiment or example. Furthermore, the specific features, structures, materials, or characteristics described may be combined in any suitable manner in one or more embodiments or examples. In addition, those skilled in the art can combine and integrate the different embodiments or examples described in this specification.

[0065] Although the invention has been described herein in conjunction with various embodiments, those skilled in the art will understand and implement other variations of the disclosed embodiments by reviewing the accompanying drawings, disclosure, and appended claims in carrying out the claimed invention. In the claims, the word "comprising" does not exclude other components or steps, and "a" or "an" does not exclude a plurality. A single processor or other unit can implement several functions listed in the claims. While different dependent claims may recite certain measures, this does not mean that these measures cannot be combined to produce good results.

[0066] The above description, in conjunction with specific preferred embodiments, provides a further detailed explanation of the present invention. It should not be construed that the specific implementation of the present invention is limited to these descriptions. For those skilled in the art, any modifications made without departing from the inventive concept should be considered within the scope of protection of the present invention.

Claims

1. A method for preparing a low-resistivity ohmic contact on diamond, characterized in that, The preparation method includes: Undoped diamond was selected as the first substrate layer; A predetermined thin film containing silicon is deposited on the first substrate layer; At a first preset temperature, boron in solid boron nitride is diffused in a preset system to introduce a boron source. At a second preset temperature, the preset thin film is etched in the preset system to diffuse silicon in the preset thin film and boron in the preset system into a first substrate layer to obtain a second substrate layer. The second substrate layer includes, from bottom to top, an undoped diamond layer, a silicon-boron co-doped diamond layer, and a diamond surface terminal. The diamond surface terminal is a diamond layer containing carbon-hydrogen bonds and carbon-silicon bonds. A solid boron source dopant is provided in the preset system. The second substrate layer is left to stand in air to obtain the third substrate layer; A metal layer is deposited on the diamond surface terminal in the third substrate to complete the fabrication of the ohmic contact.

2. The method for preparing a low-resistivity ohmic contact on diamond according to claim 1, characterized in that, Before depositing a predetermined thin film containing silicon on the first substrate, the process further includes: At a third preset temperature, the first substrate layer is treated with a strong acid mixture solution, and then at room temperature, the first substrate layer is cleaned sequentially with acetone, ethanol and deionized water to obtain a clean first substrate layer.

3. The method for preparing a low-resistivity ohmic contact on diamond according to claim 1, characterized in that, A predetermined thin film containing silicon is deposited on the first substrate layer, comprising: A predetermined thin film is deposited on the first substrate layer using a magnetron sputtering process.

4. The method for preparing a low-resistivity ohmic contact on diamond according to claim 1 or 3, characterized in that, The preset thin film includes a silicon thin film or a silicon dioxide thin film.

5. The method for preparing a low-resistivity ohmic contact on diamond according to claim 1 or 3, characterized in that, The thickness of the preset thin film is 200-500 nm.

6. The method for preparing a low-resistivity ohmic contact on diamond according to claim 1, characterized in that, At a first preset temperature, boron is diffused from solid boron nitride in a preset system to introduce a boron source. At a second preset temperature, the preset thin film is etched in the preset system to diffuse silicon from the preset thin film and boron from the preset system into a first substrate layer, resulting in a second substrate layer comprising: Solid boron nitride is placed into the preset system, and then the solid boron nitride is heated to the first preset temperature. At the first preset temperature, the solid boron nitride in the preset system decomposes, so as to introduce a boron source into the preset system. The first substrate layer, on which the preset thin film is deposited, is placed into the preset system in which boron is introduced. Hydrogen is used for ignition, and the preset thin film is etched at a second preset temperature to allow the boron in the preset system and the silicon in the preset thin film to diffuse into the first substrate layer, thereby obtaining the second substrate layer.

7. The method for preparing a low-resistivity ohmic contact on diamond according to claim 1 or 6, characterized in that, The first preset temperature range is 600℃-700℃.

8. The method for preparing a low-resistivity ohmic contact on diamond according to claim 1 or 6, characterized in that, The second preset temperature range is 900℃-1000℃.

9. The method for preparing a low-resistivity ohmic contact on diamond according to claim 1, characterized in that, The second substrate layer is left to stand in air to obtain a third substrate layer, comprising: The second substrate layer is left to stand in air for 1-12 hours to obtain the third substrate layer.

10. The method for preparing a low-resistivity ohmic contact on diamond according to claim 1, characterized in that, The material of the metal layer includes Au.

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