Diamond field effect transistor with high-temperature stability and preparation method thereof

Abstract

The invention discloses a diamond field effect transistor with high-temperature stability and a preparation method thereof, and the preparation method comprises the steps: cleaning the surface of a diamond substrate, and etching a hydrogen terminal on the clean surface of the diamond substrate; forming source and drain electrodes on the surface of the hydrogen terminal diamond, and performing insulation treatment on a non-channel region on the surface of the hydrogen terminal diamond; forming a boron nitride gate dielectric layer on the channel region on the surface of the hydrogen terminal diamond by adopting magnetron sputtering; and forming a gate electrode on the boron nitride gate dielectric layer. The preparation method is simple and efficient, and the prepared diamond field effect transistor has relatively low off-state leakage current and excellent on-off ratio in a temperature range of 300K to 450K.

Description

Technical Field

[0001] The present invention belongs to the technical field of semiconductor devices, and in particular relates to a diamond field effect transistor with high temperature stability and a preparation method thereof. Background Art

[0002] In recent years, with the rapid development of aerospace, mobile communications, and automobile fields, power semiconductor devices have gradually moved towards extreme applications such as high power, high frequency, high speed, high temperature, and high pressure. Currently, the most mature silicon material has many limitations in its application in high-frequency and high-power devices due to its narrow band gap (1.12eV), small breakdown electric field (0.3MV / cm), and relatively low thermal conductivity (1.5W / cm·K).

[0003] Subsequently, wide bandgap semiconductor materials represented by GaN and SiC showed broad application prospects in high-temperature, high-frequency, and high-power devices due to their excellent properties such as wide band gap and large breakdown electric field. However, due to the low thermal conductivity of GaN (1.3W / cm·K), it has the disadvantage of poor heat dissipation as a high-frequency device, while SiC is mainly concentrated in power device applications.

[0004] Therefore, based on ultra-wide bandgap semiconductor materials (bandgap width E g >3.4eV) device research and industrialization has become an international frontier hotspot. Among the many ultra-wide bandgap semiconductor materials, diamond has wide bandgap (5.47eV), high thermal conductivity (22W / cm·K), high breakdown electric field (10MV / cm), high carrier mobility (electron: 4500cm 2 / V·s; Hole: 3800cm 2 Due to its excellent physical properties such as low dielectric constant (5.7 / V·s) and low dielectric constant, it has extremely important application potential in the field of high-temperature, high-frequency and high-power electronic devices, and is also known as the "ultimate semiconductor material."

[0005] However, the boron and phosphorus dopants commonly used in p-type and n-type diamond bulk doping often have large impurity ionization energies, namely 0.37eV and 0.57eV, respectively, which easily cause incomplete ionization at room temperature, which seriously hinders the application and development of diamond in the field of electronic devices.

[0006] After the diamond is treated with hydrogen plasma, the dangling bonds of the C atoms on the surface will form CH bonds, i.e. hydrogen terminations. When the diamond with hydrogen terminations is exposed to air for a period of time, a layer of two-dimensional hole gas (2DHG) will form on the surface, which also has the characteristics of p-type conductivity. At room temperature, the conductivity of 2DHG is 10 -4 ~10 -5 S level, the carrier concentration is 1012 –10 14 cm -2 , mobility is 50–200 cm 2 V -1 s -1 The discovery of the conductivity of hydrogen-terminated diamond surface provides new ideas for the application of diamond in the field of electronic devices. However, hydrogen-terminated diamond field-effect transistors still face the problem of poor stability and are difficult to withstand working in high-temperature environments, which greatly limits the application of hydrogen-terminated diamond electronic devices in high-temperature environments. Therefore, how to improve the high-temperature stability of hydrogen-terminated diamond transistors and achieve their reliable repeatability is the most important issue that needs to be paid attention to and solved.

[0007] In view of the above-mentioned shortcomings of hydrogen-terminated diamond transistors, the current solution is to deposit a dielectric layer on the surface of diamond to passivate the CH bond surface. Transition metal oxides are commonly used solid-state packaging materials to improve the conductivity stability of the hydrogen-terminated surface. However, this usually results in diamond transistors with higher leakage currents, which reduces the switching ratio of the transistor and is not conducive to the application in high-temperature environments. Summary of the invention

[0008] The invention provides a method for preparing a diamond field effect transistor with high temperature stability. The preparation method is simple and efficient. The prepared diamond field effect transistor has low off-state leakage current and excellent switching ratio within a temperature range of 300K to 450K.

[0009] A specific embodiment of the present invention provides a method for preparing a diamond field effect transistor with high temperature stability, comprising:

[0010] (1) cleaning the surface of the diamond substrate and etching a hydrogen terminal on the clean surface of the diamond substrate;

[0011] (2) forming source and drain electrodes on the surface of the hydrogen-terminated diamond and performing insulation treatment on the non-channel region of the surface of the hydrogen-terminated diamond;

[0012] (3) forming a boron nitride gate dielectric layer on the channel region of the hydrogen-terminated diamond surface by magnetron sputtering;

[0013] (4) Forming a gate electrode on the boron nitride gate dielectric layer.

[0014] The present invention forms a device in which a boron nitride dielectric layer is formed on the channel region of the hydrogen-terminated diamond surface. The boron nitride dielectric layer interacts with the conductive medium of the hydrogen terminal to reduce the surface carrier concentration, thereby increasing the barrier height at the interface, thereby reducing the off-state leakage current, so that the prepared field effect transistor has a higher switching ratio. The present invention also utilizes the stability of the boron nitride dielectric layer located in the channel region at high temperatures to protect the hydrogen terminal in the channel region from being oxidized at high temperatures, thereby improving the high-temperature stability.

[0015] The present invention uses magnetron sputtering technology to deposit a boron nitride gate dielectric layer on the surface of hydrogen-terminated metal diamond. Compared with the prior art that forms a boron nitride gate dielectric layer on a two-dimensional material by transfer, the present invention has higher generation efficiency and can better realize industrialization.

[0016] Preferably, the deposition pressure of the magnetron sputtering is 0.5-5 Pa, the power is 80-300 W, the deposition time is 5 s-60 min, and hexagonal boron nitride is used as the target material.

[0017] The present invention controls the process parameters of magnetron sputtering so that the boron nitride dielectric layer has a suitable nitrogen-boron ratio, thereby making the boron nitride dielectric layer have a higher bandgap width. The wide bandgap means that electrons in the material are not easily excited by an external electric field and cross the bandgap, thereby preventing the flow of electrons in the material. In high-voltage and high-frequency applications, regions with different potentials can be effectively isolated to avoid leakage current and current breakdown. At the same time, a boron nitride dielectric layer with high stability at high temperatures can be obtained, so as to realize high-temperature protection of hydrogen terminals.

[0018] Preferably, the atomic ratio of boron to nitrogen in the boron nitride gate dielectric layer is 0.5-5.

[0019] Further preferably, the ratio of boron to nitrogen atoms in the boron nitride gate dielectric layer is 0.5 to 2. In this case, the band gap of boron nitride is closer to the theoretical value (h-BN: 5.9 eV), and the band gap is wider.

[0020] Preferably, the boron nitride gate dielectric layer is single crystal, polycrystalline, amorphous or nano-cluster particles.

[0021] Preferably, the boron nitride gate dielectric layer is amorphous. When the boron nitride gate dielectric layer provided by the present invention is amorphous, the obtained diamond field effect transistor has 10 -12 The off-state leakage current is less than 1A, and the leakage current remains stable at a high temperature of 450K.

[0022] Preferably, the method for cleaning the surface of a diamond substrate comprises:

[0023] (1) Soak the diamond in piranha cleaning solution or nitric acid / sulfuric acid mixed solution to remove impurities on the diamond surface;

[0024] (2) The diamond surface is cleaned by ultrasonic cleaning with deionized water, acetone, and anhydrous ethanol in sequence.

[0025] Preferably, before etching the hydrogen terminal, a diamond epitaxial layer is epitaxially grown on the clean diamond surface. By growing a high-quality diamond epitaxial layer with low defects, scratches and defects on the cleaned diamond surface are covered, so that the formed hydrogen terminal has a relatively flat surface, thereby laying a good foundation for obtaining a diamond field effect transistor with high temperature stability.

[0026] Further preferably, the process parameters of the epitaxial growth are: hydrogen flow rate is 300-600sccm, methane flow rate is 1%-5% of the hydrogen flow rate, pressure is 10-18kPa, power is 3.0-5.0kW, and growth temperature is 800-1200°C.

[0027] Preferably, hydrogen termination is obtained by performing hydrogen plasma etching on the surface of the diamond substrate, wherein the hydrogen gas flow rate of the hydrogen plasma etching is 300-600 sccm, the pressure is 8-15 kPa, the power is 2.0-4.0 kW, the etching temperature is 600-900° C., and the etching time is 5-60 min.

[0028] Preferably, the method for forming a source-drain electrode comprises:

[0029] Metal Au is deposited on the surface of hydrogen-terminated diamond by electron beam or thermal evaporation, and source and drain electrodes are obtained by standard photolithography process.

[0030] Preferably, the method for forming a gate electrode comprises:

[0031] Metal Al is deposited on the boron nitride gate dielectric layer by electron beam or thermal evaporation, and a gate electrode is obtained by a standard photolithography process.

[0032] Preferably, the diamond substrate is single crystal diamond or polycrystalline diamond.

[0033] Preferably, plasma etching (gases such as O2, N2, F2, Ar, etc.) and ultraviolet ozone irradiation are used to perform insulation treatment on the non-channel area of ​​the hydrogen-terminated diamond surface.

[0034] On the other hand, the present invention provides a diamond field effect transistor with high temperature stability, which is prepared by the method for preparing the diamond field effect transistor with high temperature stability.

[0035] Preferably, the gate leakage current of the high temperature stable diamond field effect transistor is less than 10-12 A. When the diamond field effect transistor is placed in a temperature environment of 450K, the device still exhibits stable transistor output characteristics and 10 -12 A leakage current or less.

[0036] Compared with the prior art, the present invention has the following beneficial effects:

[0037] The present invention provides for the first time a method for directly depositing boron nitride on the surface of hydrogen-terminated diamond by magnetron sputtering technology to obtain a hydrogen-terminated diamond field-effect transistor with boron nitride as the gate dielectric layer. The preparation method is simple and efficient, and the leakage current of the prepared diamond field-effect transistor is less than 10 -12 A, the switching ratio is 10 8 And it still has excellent electrical properties at a high temperature of 450K. BRIEF DESCRIPTION OF THE DRAWINGS

[0038] Figure 1 A top view of the structure of a diamond field effect transistor provided by a specific embodiment of the present invention;

[0039] Figure 2 A structural cross-sectional view of a diamond field effect transistor provided in a specific embodiment of the present invention;

[0040] Figure 3 The transfer characteristic curve of the diamond field effect transistor prepared in Example 1 at a temperature of 300-450K;

[0041] Figure 4 The gate leakage current curve of the diamond field effect transistor prepared in Example 1 at a temperature of 300-450K;

[0042] Figure 5 The transfer characteristic curve of the diamond field effect transistor prepared in Comparative Example 1 at a temperature of 300-450K;

[0043] Figure 6 The gate leakage current curve of the diamond field effect transistor prepared in Comparative Example 1 at a temperature of 300-450K;

[0044] Figure 7 This is a morphology diagram of the diamond field effect transistor prepared in Example 3.

[0045] Among them, there are diamond surface hydrogen terminal 1, Al gate electrode 2, source and drain Au electrode 3, and boron nitride gate dielectric layer 4. DETAILED DESCRIPTION

[0046] The present invention will be described in detail below with reference to the accompanying drawings and specific embodiments, but these embodiments do not limit the scope of the present invention in any way.

[0047] In order to solve the problems of large gate leakage current and poor high temperature stability of normally-off diamond transistors in the prior art, a specific embodiment of the present invention provides a diamond field effect transistor using magnetron sputtered BN as a gate dielectric, such as Figure 1 and Figure 2 As shown, the diamond field effect transistor includes a hydrogen terminal 1 on the surface of a diamond substrate, an Al gate electrode 2, a source and drain Au electrode 3, and a boron nitride gate dielectric layer 4. The source and drain Au electrodes 3 are prepared by evaporation on the surface 1 of the diamond hydrogen terminal, the non-channel region is subjected to oxygen plasma insulation treatment, and then the boron nitride dielectric layer 4 and the gate Al electrode 2 are sequentially deposited on the surface of the channel region by magnetron sputtering. The obtained diamond field effect transistor has low leakage current and high temperature stability.

[0048] Example 1

[0049] This embodiment provides a method for preparing a diamond field effect transistor with high temperature stability, comprising:

[0050] (1) The single crystal diamond was cleaned with standard piranha liquid for 8 hours to remove organic matter on the surface, and then ultrasonically cleaned with deionized water, acetone, and anhydrous ethanol for 10 minutes respectively, and purged with nitrogen for 15 seconds to obtain a diamond substrate.

[0051] (2) The diamond substrate is treated with hydrogen plasma to obtain a diamond having hydrogen terminals 1 on the surface; the process parameters of the hydrogen plasma treatment are: controlling the hydrogen flow rate to 400 sccm, the pressure to 10 kPa, the microwave power to 3000 W, the temperature to 800° C., and the etching time to 10 min.

[0052] (3) Deposit source and drain Au electrodes, use standard photolithography to obtain a channel region with a width of 50 μm and a length of 12 μm, and then use RIE oxygen plasma etching to insulate the non-channel region.

[0053] (4) A layer of boron nitride nanoparticles is deposited in the channel region by magnetron sputtering. The deposition pressure is 1.0 Pa, the power is 120 W, the deposition time is 3 minutes, the diameter of the deposited nanoparticles is 10-20 nm, the nitrogen:boron ratio of the deposited boron nitride nanoparticles is 1:1, and hexagonal boron nitride is used as the target material.

[0054] (5) Deposit a gate Al electrode 2 and use a standard photolithography process to obtain a gate with a width of 50 μm and a length of 4 μm.

[0055] Example 2

[0056] This embodiment provides a method for preparing a diamond field effect transistor, comprising:

[0057] (1) The single crystal diamond was cleaned with standard piranha liquid for 8 hours to remove organic matter on the surface; deionized water, acetone, and anhydrous ethanol were ultrasonically cleaned for 10 minutes respectively, and nitrogen was purged for 15 seconds to obtain a diamond substrate.

[0058] (2) Epitaxial growth is performed on a diamond substrate to obtain diamond having hydrogen terminals 1 on the surface; the process parameters of the epitaxial growth are: controlling the hydrogen flow rate to 400 sccm, the methane flow rate to 12 sccm, the pressure to 16 kPa, the microwave power to 4200 W, the temperature to 960° C., and the growth time to 2 h.

[0059] (3) Deposit source and drain Au electrodes, use standard photolithography to obtain a channel region with a width of 50 μm and a length of 12 μm, and then use RIE oxygen plasma etching to insulate the non-channel region.

[0060] (4) A layer of boron nitride nanoparticles is deposited in the channel region by magnetron sputtering. The deposition pressure is 1.0 Pa, the power is 150 W, the deposition time is 1 min, the diameter of the deposited BN particles is 5-10 nm, the nitrogen:boron ratio of the deposited boron nitride nanoparticles is 1:2, and hexagonal boron nitride is used as the target material.

[0061] (5) Deposit a gate Al electrode and use standard photolithography to obtain a gate with a width of 50 μm and a length of 2 μm.

[0062] Example 3

[0063] This embodiment provides a method for preparing a diamond field effect transistor, comprising:

[0064] (1) The single crystal diamond was cleaned with standard piranha liquid for 8 hours to remove organic matter on the surface; deionized water, acetone, and anhydrous ethanol were ultrasonically cleaned for 10 minutes respectively, and nitrogen was purged for 15 seconds to obtain a diamond substrate.

[0065] (2) Epitaxial growth is performed on a diamond substrate to obtain diamond having hydrogen terminals 1 on the surface; the process parameters of the epitaxial growth are: controlling the hydrogen flow rate to 400 sccm, the methane flow rate to 12 sccm, the pressure to 16 kPa, the microwave power to 4200 W, the temperature to 960° C., and the growth time to 2 h.

[0066] (3) Deposit source and drain Au electrodes 3, use standard photolithography to obtain a channel region with a width of 50 um and a length of 12 um, and then use RIE oxygen plasma etching to insulate the non-channel region.

[0067] (4) A layer of boron nitride film 4 is deposited in the channel region by magnetron sputtering. The deposition pressure is 1.0 Pa, the power is 150 W, the deposition time is 60 min, the deposited BN thickness is 65 nm, the diameter of the deposited BN particles is 10-20 nm, and the ratio is 1:1.

[0068] (5) Deposit a gate Al electrode 2 and use a standard photolithography process to obtain a gate with a width of 50 μm and a length of 4 μm.

[0069] Comparative Example 1

[0070] This comparative example provides a method for preparing a diamond field effect transistor without a boron nitride dielectric layer, comprising:

[0071] (1) The single crystal diamond was cleaned with standard piranha liquid for 8 hours to remove organic matter on the surface; deionized water, acetone, and anhydrous ethanol were ultrasonically cleaned for 10 minutes respectively, and nitrogen was purged for 15 seconds to obtain a diamond substrate.

[0072] (2) Epitaxial growth is performed on a diamond substrate to obtain diamond having hydrogen terminals 1 on the surface; the process parameters of the epitaxial growth are: controlling the hydrogen flow rate to 400 sccm, the methane flow rate to 12 sccm, the pressure to 16 kPa, the microwave power to 4200 W, the temperature to 960° C., and the growth time to 2 h.

[0073] (3) Deposit source and drain Au electrodes 3, use standard photolithography to obtain a channel region with a width of 50 um and a length of 12 um, and then use RIE oxygen plasma etching to insulate the non-channel region.

[0074] (4) Deposit a gate Al electrode 2 and use a standard photolithography process to obtain a gate with a width of 50 um and a length of 4 um.

[0075] Comparative Example 2

[0076] (1) The single crystal diamond was cleaned with standard piranha liquid for 8 hours to remove organic matter on the surface; deionized water, acetone, and anhydrous ethanol were ultrasonically cleaned for 10 minutes respectively, and nitrogen was purged for 15 seconds to obtain a diamond substrate.

[0077] (2) The diamond substrate is treated with hydrogen plasma to obtain diamond with hydrogen terminals 1 on the surface; the process parameters of the hydrogen plasma treatment are: hydrogen flow rate 400 sccm, pressure 10 kPa, microwave power 3000 W, temperature 800° C., and growth time 10 min.

[0078] (3) Deposit source and drain Au electrodes 3, use standard photolithography to obtain a channel region with a width of 50 um and a length of 12 um, and then use RIE oxygen plasma etching to insulate the non-channel region.

[0079] (4) Deposit the gate Al electrode 2 and use standard photolithography to obtain a gate with a width of 50 μm and a length of 4 μm

[0080] Performance Analysis

[0081] like Figure 3 and Figure 5 As shown in FIG. 1 , for Comparative Example 1, Example 1 respectively measured the transfer characteristic curves of the hydrogen-terminated diamond field effect transistor with boron nitride deposition from 300K to 450K. Compared with the original hydrogen-terminated diamond transistor without boron nitride as the gate dielectric in Comparative Example 1, the hydrogen-terminated diamond transistor after boron nitride deposition obtained in Example 1 can work normally at 450K and still has 10 -12 A below the off-state leakage current and 10 8 The switching ratio is above 425K, while the hydrogen-terminated diamond transistor without boron nitride deposition in Comparative Example 1 is damaged at 425K.

[0082] like Figure 4 and Figure 6 As shown in FIG. 2 , for Comparative Example 2, Example 2 respectively measured the gate leakage current curves of the hydrogen-terminated diamond field effect transistor with boron nitride deposition from 300K to 450K. Compared with the original hydrogen-terminated diamond transistor without boron nitride as the gate dielectric in Comparative Example 2, the hydrogen-terminated diamond transistor after boron nitride deposition obtained in Example 2 still has 10 -12 A below the gate leakage current, while the hydrogen-terminated diamond transistor in Comparative Example 2 without boron nitride deposition had a significant increase in gate leakage current at 425K.

[0083] With respect to Comparative Example 1, Example 3 measured the transfer characteristics of the hydrogen-terminated diamond field effect transistor after boron nitride deposition. Since the carrier concentration in the channel region was too low, the transistor characteristics could not be measured at this time.

[0084] like Figure 7 As shown, Example 3 provides a TEM interface after boron nitride is deposited on the diamond surface, wherein the lower layer is a diamond single crystal structure (Diamond) and the upper layer is an amorphous structure (BN) of deposited boron nitride.

[0085] The above embodiments are preferred embodiments of the present invention, but the embodiments of the present invention are not limited to the above embodiments. Any other changes, modifications, substitutions, combinations, and simplifications that do not deviate from the spirit and principle of the present invention should be equivalent replacement methods. Some non-essential improvements and adjustments made by technicians in this field based on the above content of the present invention belong to the protection scope of the present invention. The specific equipment parameters, time, etc. in the following examples are only examples within a suitable range, that is, those skilled in the art can make a selection within a suitable range through the description of this article, and are not limited to the specific values ​​​​exemplified below. Therefore, all equivalents or modifications that are completed without departing from the spirit disclosed by the present invention fall within the scope of protection of the present invention.

[0086] All documents mentioned in the present invention are cited as references in this application, just as each document is cited as reference individually. In addition, it should be understood that after reading the above teachings of the present invention, those skilled in the art can make various changes or modifications to the present invention, and these equivalent forms also fall within the scope defined by the claims attached to this application.

Claims

1. A method for preparing a diamond field effect transistor with high temperature stability, characterized in that: include: (1) cleaning the surface of the diamond substrate and etching a hydrogen terminal on the clean surface of the diamond substrate; (2) forming source and drain electrodes on the surface of the hydrogen-terminated diamond and performing insulation treatment on the non-channel region of the surface of the hydrogen-terminated diamond; (3) forming a boron nitride gate dielectric layer on the channel region of the hydrogen-terminated diamond surface by magnetron sputtering; (4) Forming a gate electrode on the boron nitride gate dielectric layer.

2. The method for preparing a diamond field effect transistor with high temperature stability according to claim 1, wherein: The magnetron sputtering has a deposition pressure of 0.5-5 Pa, a power of 80-300 W, a deposition time of 5 s-60 min, and hexagonal boron nitride as a target material.

3. The method for preparing a diamond field effect transistor with high temperature stability according to claim 1, wherein: The ratio of boron to nitrogen atoms in the boron nitride gate dielectric layer is 0.5-5.

4. The method for preparing a diamond field effect transistor with high temperature stability according to claim 3, wherein: The ratio of boron to nitrogen atoms in the boron nitride gate dielectric layer is 0.5-2.

5. The method for preparing a diamond field effect transistor with high temperature stability according to claim 1, wherein: The boron nitride gate dielectric layer is single crystal, polycrystalline, amorphous or nano-cluster particles.

6. The method for preparing a diamond field effect transistor with high temperature stability according to claim 5, wherein: The boron nitride gate dielectric layer is amorphous.

7. The method for preparing a diamond field effect transistor with high temperature stability according to claim 1, wherein: The method for cleaning the surface of a diamond substrate comprises: (1) Soak the diamond in piranha cleaning solution or nitric acid / sulfuric acid mixed solution to remove impurities on the diamond surface; (2) The diamond surface is cleaned by ultrasonic cleaning with deionized water, acetone, and anhydrous ethanol in sequence.

8. The method for preparing a diamond field effect transistor with high temperature stability according to claim 1, wherein: Before etching the hydrogen termination, a diamond epitaxial layer is epitaxially grown on the clean diamond surface.

9. The method for preparing a diamond field effect transistor with high temperature stability according to claim 1, wherein: Hydrogen termination is obtained by performing hydrogen plasma etching on the surface of the diamond substrate. The hydrogen plasma etching has a hydrogen flow rate of 300-600sccm, a pressure of 8-15kPa, a power of 2.0-4.0kW, an etching temperature of 600-900°C, and an etching time of 5-60min.

10. A diamond field effect transistor with high temperature stability, characterized in that: The diamond field effect transistor is prepared by the method for preparing a diamond field effect transistor with high temperature stability according to any one of claims 1 to 9.

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