N-type doped low-resistance ohmic contact diamond and preparation method thereof

Abstract

The invention discloses an n-type doped low-resistance ohmic contact diamond and a preparation method thereof. The preparation method comprises the following steps: selecting an unintentionally doped diamond as a diamond substrate; injecting P ions on the diamond substrate at a first preset temperature, and forming an injection layer on the upper surface of the diamond substrate; annealing the injection layer at a second preset temperature to redistribute the P element in the injection layer; and depositing a metal layer on the upper surface of the injection layer. According to the method, the n-type doping of the diamond is realized through P ion implantation, the doping concentration is high, relatively high charged carrier concentration and good bulk conductivity can be realized under low activation energy, and the requirement of in-situ growth of the heavily phosphorus-doped diamond on equipment is reduced.

Description

Technical Field

[0001] The invention belongs to the technical field of semiconductor processes, and in particular relates to an n-type doped low-resistance ohmic contact diamond and a preparation method thereof. Background Art

[0002] Ultra-wide bandgap semiconductor diamond has many advantages such as large bandgap width, high breakdown field strength, high carrier mobility, high thermal conductivity, and radiation resistance. At present, there has been no major breakthrough in efficient diamond body doping, and hydrogen-terminated diamond field-effect transistors that use surface hydrogen termination to induce two-dimensional hole gas as a conductive channel have become the current mainstream device choice and have great potential in power electronic device applications.

[0003] There is currently a large performance gap between hydrogen-terminated diamond FET (Field Effect Transistor) devices and gallium nitride-based HEMT (High Electron Mobility Transistor) devices. A key point is that the ohmic contact resistance of hydrogen-terminated diamond FET devices is large. The frequency and output power characteristics of diamond microwave power devices are greatly affected by the ohmic contact problem. In high-frequency small-size devices, the source-drain series resistance with ohmic contact resistance as the main component becomes the main factor restricting the frequency characteristics of the device; in power devices, ohmic contact resistance directly affects the saturation voltage and on-current of the device, and suppresses the output power of the device from both the voltage swing and the current swing.

[0004] At present, the ohmic contact of diamond FET is mainly obtained by depositing Au metal on hydrogen-terminated diamond. The ohmic contact resistance is generally about 5Ω·mm, but it is still an order of magnitude higher than the ohmic contact resistance value (≤0.5Ω·mm) prepared by other mature semiconductor processes such as Si and GaN.

[0005] The ohmic contact of n-type doped hydrogen-terminated diamond FET devices prepared by existing methods has problems such as large contact resistance, high process difficulty, and high cost, which makes it difficult to meet the needs of performance improvement and application of diamond FET devices. Therefore, how to achieve low ohmic contact resistance of n-type doped diamond devices has become an urgent problem to be solved in the research of diamond FET devices. Summary of the invention

[0006] In order to solve the above problems existing in the prior art, the present invention provides an n-type doped low-resistance ohmic contact diamond and a preparation method thereof. The technical problem to be solved by the present invention is achieved by the following technical solutions:

[0007] The present invention provides a method for preparing n-type doped low-resistance ohmic contact diamond, comprising:

[0008] S1: Select unintentionally doped diamond as diamond substrate;

[0009] S2: implanting P ions on the diamond substrate at a first preset temperature to form an implantation layer on the upper surface of the diamond substrate;

[0010] S3: annealing the injection layer at a second preset temperature to redistribute the P element in the injection layer;

[0011] S4: depositing a metal layer on the upper surface of the injection layer.

[0012] In one embodiment of the present invention, the S1 includes:

[0013] S1.1: Select unintentionally doped diamond as the diamond substrate;

[0014] S1.2: Pre-treating the diamond substrate by cutting and grinding, treating the diamond substrate with a strong acid mixed solution at a third preset temperature, and then cleaning the diamond substrate with acetone, ethanol and deionized water in sequence at room temperature to obtain a cleaned diamond substrate.

[0015] In one embodiment of the present invention, the strong acid mixed solution is H 2 SO 4 and HNO 3 of mixed solution.

[0016] In one embodiment of the present invention, the third preset temperature is 200°C to 400°C.

[0017] In one embodiment of the present invention, the S2 includes:

[0018] The cleaned diamond substrate is implanted with P ions using an ion implanter. 3 The molecular gas source is introduced into the ion implanter, and then the gaseous pH in the ion implanter is adjusted at the first preset temperature. 3 Ionization, introduction of phosphorus source, to obtain an injection layer, wherein PH 3 The flow rate is 0.5-1.0 sccm; the first preset temperature ranges from 25° C. to 500° C.; and the ion implantation energy is 1 KeV to 1 MeV.

[0019] In one embodiment of the present invention, the depth of the implantation layer is 10 nm to 2000 nm, and the P ion implantation concentration is 1×10 19 ~1×10 21 cm -3 .

[0020] In one embodiment of the present invention, S3 includes:

[0021] The diamond substrate including the implanted layer is placed in an annealing device and N 2 , heating to a second preset temperature for annealing to redistribute the P element in the injection layer, wherein the second preset temperature ranges from 400° C. to 1200° C.

[0022] In one embodiment of the present invention, the material of the metal layer is a stacked metal of Ti, Pt, and Au, and the thicknesses are 20 nm, 20 nm, and 100 nm, respectively.

[0023] In one embodiment of the present invention, the material of the metal layer is a stacked metal of Ti and Au, and the thicknesses are 20 nm and 100 nm respectively.

[0024] Another aspect of the present invention provides an n-type doped low-resistance ohmic contact diamond, which is prepared using the preparation method described in any one of the above embodiments. The n-type doped low-resistance ohmic contact diamond includes a diamond substrate, an injection layer and a metal layer from bottom to top.

[0025] Compared with the prior art, the present invention has the following beneficial effects:

[0026] 1. The present invention provides a method for preparing n-type doped low-resistance ohmic contact diamond, wherein P ions are injected into a diamond substrate to form a high-concentration n-type doping layer on the diamond surface, and then a metal layer is deposited. After annealing, a good ohmic contact can be directly formed, thereby reducing the ohmic contact resistance; a high charged carrier concentration and good bulk conductivity can be achieved at a low activation energy, thereby reducing the requirements for equipment for in-situ growth of heavily phosphorus-doped diamond, and effectively reducing the process difficulty.

[0027] 2. The present invention uses ion implantation to achieve n-type doping of diamond. This method can be applied to large-sized diamond substrates, which is beneficial to further reduce costs. Large-sized diamond substrates are also beneficial to device preparation and can effectively reduce process costs.

[0028] 3. The present invention performs high temperature annealing in a nitrogen atmosphere to redistribute the impurities in the injection layer, thereby making the impurities evenly distributed while also increasing the doping concentration on the diamond surface, reducing the diamond surface work function and the barrier height with Au metal, and further reducing the resistance of the ohmic contact.

[0029] The present invention will be further described in detail below with reference to the accompanying drawings and embodiments. BRIEF DESCRIPTION OF THE DRAWINGS

[0030] Figure 1This is a flow chart of a method for preparing n-type doped low-resistance ohmic contact diamond provided by an embodiment of the present invention;

[0031] Figure 2 It is a schematic diagram of a preparation process of an n-type doped low-resistance ohmic contact diamond provided by an embodiment of the present invention. DETAILED DESCRIPTION

[0032] In order to further explain the technical means and effects adopted by the present invention to achieve the predetermined invention purpose, the following is a detailed description of an n-type doped low-resistance ohmic contact diamond and a preparation method thereof proposed in accordance with the present invention in combination with the accompanying drawings and specific implementation methods.

[0033] The above and other technical contents, features and effects of the present invention are clearly presented in the following detailed description of the specific implementation modes in conjunction with the accompanying drawings. Through the description of the specific implementation modes, the technical means and effects adopted by the present invention to achieve the predetermined purpose can be more deeply and specifically understood. However, the attached drawings are only for reference and explanation purposes and are not used to limit the technical solutions of the present invention.

[0034] It should be noted that, in this article, relational terms such as first and second, etc. are only used to distinguish one entity or operation from another entity or operation, and do not necessarily require or imply any such actual relationship or order between these entities or operations. Moreover, the terms "include", "comprise" or any other variants are intended to cover non-exclusive inclusion, so that an article or device including a series of elements includes not only those elements, but also other elements that are not explicitly listed. In the absence of more restrictions, the elements defined by the statement "including one..." do not exclude the existence of other identical elements in the article or device including the elements.

[0035] The present invention provides a process flow chart of a method for preparing n-type doped low-resistance ohmic contact diamond, see Figure 1 and Figure 2 , the preparation method comprises:

[0036] S1: Select unintentionally doped diamond as the diamond substrate.

[0037] Specifically, step S1 includes:

[0038] S1.1: Select unintentionally doped diamond as diamond substrate 1, such as Figure 2 (a) shown.

[0039] S1.2: Pre-treating the diamond substrate 1 by cutting and grinding, treating the diamond substrate 1 with a strong acid mixed solution at a third preset temperature, and then cleaning the diamond substrate 1 with acetone, ethanol and deionized water in sequence at room temperature to obtain a cleaned diamond substrate 1.

[0040] Optionally, the strong acid mixed solution is a 3:1 volume ratio of H 2 SO 4 and HNO 3 The third preset temperature is 200° C. The thickness of the processed diamond substrate 1 is 500-1000 μm.

[0041] S2: At a first preset temperature, P ions are implanted on the diamond substrate to form an implantation layer 2 on the upper surface of the diamond substrate 1, such as Figure 2 (b) as shown.

[0042] Specifically, an ion implanter is used to implant P ions into the cleaned diamond substrate. 3 The molecular gas source is introduced into the ion implanter, and then the gaseous pH in the ion implanter is adjusted to a predetermined temperature. 3 ionization, introducing a phosphorus source, and obtaining an injection layer 2, optional, PH 3 The gas flow rate is 0.5-1.0 sccm; the first preset temperature ranges from 25° C. to 500° C.; and the ion implantation energy is 1 KeV to 1 MeV.

[0043] In this embodiment, the depth of the implantation layer 2 is 10 nm to 2000 nm, and the P ion implantation concentration is 1×10 19 ~1×10 21 cm -3 This embodiment adopts the method of ultra-high concentration and ultra-thin doping layer, and uses high work function metal as ohmic metal to make carriers tunnel to a certain extent and realize low resistance conductance.

[0044] S3: Annealing the implanted layer at a second preset temperature to redistribute the P element in the implanted layer, such as Figure 2 (c) as shown.

[0045] Specifically, the diamond substrate 1 including the implanted layer 2 is placed in an annealing device, and N 2 , heated to a second preset temperature for annealing, so that the P element in the injection layer is redistributed and the doping distribution is improved. The range of the second preset temperature is The annealing equipment of this embodiment is a rapid thermal processing (RTP) system.

[0046] The present invention performs high temperature annealing in a nitrogen atmosphere to redistribute the impurities of the implanted layer, thereby uniformly distributing the impurities and increasing the doping concentration on the diamond surface, reducing the diamond surface work function and the barrier height with the subsequent metal layer, and further reducing the resistance of the ohmic contact.

[0047] It should be noted that ion implantation is the process of driving doped atoms into the diamond lattice through a high-energy particle beam, which will have an adverse effect on various properties such as crystal quality. The purpose of high-temperature annealing again is to promote the redistribution of doped atoms, repair lattice damage, improve crystal quality, and enhance conductivity.

[0048] S4: Depositing a metal layer 3 on the upper surface of the injection layer 2, such as Figure 2 (d) as shown.

[0049] In one embodiment of the present invention, the material of the metal layer 3 is a stacked metal of Ti, Pt, and Au, and the thicknesses are 20 nm, 20 nm, and 100 nm, respectively. Specifically, the metal layer 3 includes Au, Pt, and Ti, respectively, from bottom to top, that is, the metal Au contacts the upper surface of the injection layer 2.

[0050] In another embodiment of the present invention, the metal layer is made of a stacked metal of Ti and Au, with thicknesses of 20 nm and 100 nm, respectively. Specifically, the metal layer 3 includes Au and Ti, respectively, from bottom to top, that is, the metal Au contacts the upper surface of the injection layer 2 .

[0051] Another aspect of the present invention provides an n-type doped low-resistance ohmic contact diamond, which is prepared using the preparation method described in any one of the above embodiments. The n-type doped low-resistance ohmic contact diamond includes a diamond substrate 1, an injection layer 2 and a metal layer 3 from bottom to top.

[0052] The present invention provides a method for preparing n-type doped low-resistance ohmic contact diamond, wherein P ions are injected into a diamond substrate to form a high-concentration n-type doping layer on the surface of the diamond, and then a metal layer is deposited. After annealing, a good ohmic contact can be directly formed, thereby reducing the ohmic contact resistance; a high charged carrier concentration and good body conductivity can be achieved at a low activation energy, thereby reducing the requirements for equipment for in-situ growth of heavily phosphorus-doped diamond, and effectively reducing the process difficulty.

[0053] The present invention uses an ion implantation method to achieve n-type doping of diamond. This method can be applied to large-sized diamond substrates, which is beneficial to further reduce costs. Large-sized diamond substrates are also beneficial to device preparation, which can effectively reduce process costs. The present invention performs high-temperature annealing in a nitrogen atmosphere to redistribute impurities in the implanted layer, thereby uniformly distributing impurities while also increasing the doping concentration on the diamond surface, reducing the diamond surface work function and the barrier height with Au metal, and further reducing the resistance of the ohmic contact.

[0054] In the several embodiments provided by the present invention, it should be understood that the apparatus and method disclosed by the present invention can be implemented in other ways. For example, the apparatus embodiments described above are only illustrative, for example, the division of the modules is only a logical function division, and there may be other division methods in actual implementation, for example, multiple modules or components can be combined or integrated into another system, or some features can be ignored or not executed.

[0055] In addition, each functional module in each embodiment of the present invention may be integrated into one processing module, or each module may exist physically separately, or two or more modules may be integrated into one module. The above-mentioned integrated module may be implemented in the form of hardware or in the form of hardware plus software functional modules.

[0056] The above contents are further detailed descriptions of the present invention in combination with specific preferred embodiments, and it cannot be determined that the specific implementation of the present invention is limited to these descriptions. For ordinary technicians in the technical field to which the present invention belongs, several simple deductions or substitutions can be made without departing from the concept of the present invention, which should be regarded as falling within the protection scope of the present invention.

Claims

1. A method for preparing n-type doped low-resistance ohmic contact diamond, characterized in that: include: S1: Select unintentionally doped diamond as diamond substrate; S2: implanting P ions on the diamond substrate at a first preset temperature to form an implantation layer on the upper surface of the diamond substrate; S3: annealing the injection layer at a second preset temperature to redistribute the P element in the injection layer; S4: depositing a metal layer on the upper surface of the injection layer.

2. The method for preparing n-type doped low-resistance ohmic contact diamond according to claim 1, characterized in that: The S1 includes: S1.1: Select unintentionally doped diamond as the diamond substrate; S1.2: Pre-treating the diamond substrate by cutting and grinding, treating the diamond substrate with a strong acid mixed solution at a third preset temperature, and then cleaning the diamond substrate with acetone, ethanol and deionized water in sequence at room temperature to obtain a cleaned diamond substrate.

3. The method for preparing n-type doped low-resistance ohmic contact diamond according to claim 2, characterized in that: The strong acid mixed solution is a mixed solution of H2SO4 and HNO3 in a volume ratio of 3:

1.

4. The method for preparing n-type doped low-resistance ohmic contact diamond according to claim 2, characterized in that: The third preset temperature is 200°C to 400°C.

5. The method for preparing n-type doped low-resistance ohmic contact diamond according to claim 2, characterized in that: The S2 includes: An ion implanter is used to implant P ions on the cleaned diamond substrate, and a PH3 molecular gas source is introduced into the ion implanter. Then, the gaseous PH3 in the ion implanter is ionized at the first preset temperature, and a phosphorus source is introduced to obtain an implantation layer, wherein the flow rate of PH3 is 0.5 to 1.0 sccm; the range of the first preset temperature is 25°C to 500°C; and the ion implantation energy is 1KeV to 1MeV.

6. The method for preparing n-type doped low-resistance ohmic contact diamond according to claim 2, characterized in that: The depth of the injection layer is 10nm to 2000nm, and the P ion injection concentration is 1×10 19 ~1×10 21 cm -3 .

7. The method for preparing n-type doped low-resistance ohmic contact diamond according to claim 2, characterized in that: The S3 includes: The diamond substrate including the implanted layer is placed in an annealing device, N2 is introduced, and the substrate is heated to a second preset temperature for annealing to redistribute the P element in the implanted layer. The second preset temperature ranges from 400°C to 1200°C.

8. The method for preparing n-type doped low-resistance ohmic contact diamond according to claim 2, characterized in that: The material of the metal layer is a stacked metal of Ti, Pt and Au, and the thicknesses are 20nm, 20nm and 100nm respectively.

9. The method for preparing n-type doped low-resistance ohmic contact diamond according to claim 2, characterized in that: The material of the metal layer is a stacked metal of Ti and Au, and the thicknesses are 20nm and 100nm respectively.

10. An n-type doped low-resistance ohmic contact diamond, characterized in that: Prepared by the preparation method described in any one of claims 1 to 9, the n-type doped low-resistance ohmic contact diamond comprises a diamond substrate, an injection layer and a metal layer in sequence from bottom to top.

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