Diamond diode capable of selectively growing and regulating doping concentration and preparation method thereof

Abstract

The invention discloses a diamond diode capable of selecting growth and regulating doping concentration and a preparation method thereof. The preparation method comprises the following steps: growing a (100) crystal orientation lightly doped diamond layer on a (100) crystal orientation intrinsic diamond substrate; etching the upper surface of the lightly doped diamond layer to form a groove, wherein the depth of the groove is smaller than the thickness of the lightly doped diamond layer; carrying out selective growth in the groove to form a heavily doped diamond layer with (111) crystal orientation; hydrogen terminals on the upper surface of the lightly doped diamond layer and the upper surface of the heavily doped diamond layer are removed; growing an ohmic electrode on the upper surface of the heavily doped diamond layer; and a Schottky electrode grows on the upper surface of the lightly doped diamond layer, and the ohmic electrode and the Schottky electrode are arranged at an interval. According to the invention, the carrier concentration difference between the drift region and the ohmic contact region of the device can be increased to 4-5 orders of magnitude, the reverse breakdown voltage and the breakdown field strength of the Schottky diode are improved, and the leakage current is reduced.

Description

Technical Field

[0001] The invention belongs to the technical field of electronic devices, and in particular relates to a diamond diode capable of selectively growing and regulating doping concentration and a preparation method thereof. Background Art

[0002] Diamond is a new generation of ultra-wide bandgap semiconductor materials with large bandgap width (5.5eV), high breakdown field strength (10MV / cm), high thermal conductivity (22W / (cm·K)), high carrier mobility (electron: 4500cm 2 / (V·s); Hole: 3800cm 2 / (V·s)), high hardness, good chemical stability and other excellent properties, so it is also called the "ultimate semiconductor". Diamond has great application potential in high temperature and high pressure devices, high frequency and high power devices, optical windows, high energy particle detectors, quantum information, biosensors and other fields.

[0003] Diamond power diodes are an important field in diamond devices. Diamond power diodes mainly include Schottky barrier diodes (SBD) and pn junction diodes (PND). SBD has broad application prospects in the high voltage field due to its advantages such as low on-state voltage, low reverse recovery current and high switching frequency.

[0004] The structures of diamond Schottky diodes mainly include lateral diodes, vertical diodes and quasi-vertical diodes. The above three structures require the preparation of n+ layers and n- layers with different doping concentrations. At present, the diamond n-type body doping is mainly achieved by phosphorus doping. The growth of n+ / n- layers with different carrier concentrations is achieved by changing the flow rate of the doping source phosphine during the MPCVD (microwave plasma CVD) growth process to control the concentration of phosphorus doped into the diamond.

[0005] In the in-situ phosphorus-doped CVD epitaxy of diamond, the highest doping concentration in the (100) direction reported so far is only 10 16 cm -3 , it is impossible to obtain diamond with a higher doping concentration. Considering the crystal plane of the diamond substrate, the doping concentration and doping efficiency of n-type diamond grown on the (100) crystal plane are 4 to 5 orders of magnitude lower than those on the (113) and (111) crystal planes. Due to the insufficient concentration difference between the n+ layer and the n- layer, and the low mobility caused by the introduction of lattice defects by phosphorus doping, phosphorus-doped diamond Schottky diode devices cannot be realized at present. Summary of the invention

[0006] In order to solve the above problems existing in the prior art, the present invention provides a diamond diode with selective growth and control of doping concentration and a preparation method thereof. The technical problem to be solved by the present invention is achieved by the following technical solutions:

[0007] One aspect of the present invention provides a method for preparing a diamond diode with selective growth and controlled doping concentration, comprising:

[0008] S1: growing a lightly doped diamond layer with a (100) crystal orientation on an intrinsic diamond substrate with a (100) crystal orientation;

[0009] S2: etching a groove on the upper surface of the lightly doped diamond layer, wherein the depth of the groove is less than the thickness of the lightly doped diamond layer;

[0010] S3: selectively growing in the groove to form a heavily doped diamond layer with a (111) crystal orientation, wherein the doping concentration of the heavily doped diamond layer is 4 to 5 orders of magnitude higher than the doping concentration of the lightly doped diamond layer;

[0011] S4: removing hydrogen terminations on the upper surface of the lightly doped diamond layer and the upper surface of the heavily doped diamond layer;

[0012] S5: growing an ohmic electrode on the upper surface of the heavily doped diamond layer after the hydrogen termination is removed;

[0013] S6: growing a Schottky electrode on the upper surface of the lightly doped diamond layer after the hydrogen terminal is removed, wherein the ohmic electrode is spaced apart from the Schottky electrode.

[0014] In one embodiment of the present invention, the S1 includes:

[0015] An intrinsic diamond substrate having a (100) crystal orientation is selected and cleaned;

[0016] A lightly doped diamond layer with a (100) crystal orientation is grown on the intrinsic diamond substrate using an MPCVD device, wherein the doping element of the lightly doped diamond layer is phosphorus or boron, and the doping concentration of the doping element is as low as 1×10 15 cm -3 .

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

[0018] A groove is formed by etching the upper surface of the lightly doped diamond layer using an inductively coupled oxygen plasma etching process, wherein the groove is located at the center of the upper surface of the lightly doped diamond layer, and the upper surface of the groove is circular or square.

[0019] In one embodiment of the present invention, the depth of the groove is 300-500 nm.

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

[0021] The sample with the groove is placed in an MPCVD device, and selective growth is performed in the groove to form a heavily doped diamond layer with a (111) crystal orientation. The heavily doped diamond layer and the lightly doped diamond layer have the same doping element, and the doping concentration of the doping element in the heavily doped diamond layer is up to 1×10 21 cm -3 .

[0022] In one embodiment of the present invention, the S4 includes:

[0023] The surface of the sample is treated with oxygen using an ICP device to remove hydrogen terminals on the upper surface of the lightly doped diamond layer and the upper surface of the heavily doped diamond layer, wherein the power of the ICP device is 120-150 W, the oxygen flow rate is 80-90 sccm, and the treatment time is 10-15 s.

[0024] In one embodiment of the present invention, the S5 includes:

[0025] On the entire upper surface of the sample from which the hydrogen terminal has been removed, metal Ti with a thickness of 20 to 30 nm and metal Au with a thickness of 90 to 100 nm are deposited from bottom to top by an electron beam evaporation device;

[0026] The photolithography process is performed by coating and photolithography to expose the upper surface of the sample except the ohmic electrode area. After the photolithography is completed, the sample is placed in a potassium iodide solution to etch away the metal Au outside the ohmic electrode area, and then placed in a buffered oxide etching solution to etch away the metal Ti outside the ohmic electrode area.

[0027] The sample is annealed in a nitrogen atmosphere using a rapid thermal annealing device to form a good ohmic contact between the heavily doped diamond layer and the metal Ti, thereby forming an ohmic electrode located on the upper surface of the heavily doped diamond layer.

[0028] In one embodiment of the present invention, the S6 includes:

[0029] Electron beam evaporation equipment is used to deposit metal Al with a thickness of 90 to 100 nm on the entire upper surface of the sample, and a photolithography process is performed through photoresist coating and photolithography to expose the remaining parts except the Schottky electrode area; then the sample is placed in a buffered oxide etching solution to etch away the metal Al outside the Schottky electrode area to form a Schottky electrode on the upper surface of the lightly doped diamond layer.

[0030] Another aspect of the present invention provides a diamond diode with selective growth and controlled doping concentration, which is prepared by the preparation method described in any one of the above embodiments, and the diamond diode comprises an intrinsic diamond substrate with a (100) crystal orientation, a lightly doped diamond layer with a (100) crystal orientation, a heavily doped diamond layer with a (111) crystal orientation, an ohmic electrode and a Schottky electrode, wherein:

[0031] The lightly doped diamond layer is located on the upper surface of the intrinsic diamond substrate, a groove is opened on the upper surface of the lightly doped diamond layer, the heavily doped diamond layer is filled in the groove, and the doping concentration of the heavily doped diamond layer is 3 to 4 orders of magnitude higher than the doping concentration of the lightly doped diamond layer;

[0032] The ohmic electrode is located on the upper surface of the heavily doped diamond layer, the Schottky electrode is located on the upper surface of the lightly doped diamond layer, and the ohmic electrode and the Schottky electrode are arranged at intervals.

[0033] In one embodiment of the present invention, the Schottky electrode is in a ring shape and surrounds the outer side of the ohmic electrode.

[0034] Compared with the prior art, the present invention has the following beneficial effects:

[0035] 1. The present invention provides a method for preparing a diamond diode with selective growth and control of doping concentration. The diamond diode device adopts a Schottky lateral diode structure. Compared with Schottky diodes of other structures, the switching speed of the device can be improved. The specific principle of selective growth and control of doping concentration is to utilize the difference in doping efficiency between (100) and (111) diamonds under the same conditions. First, a lightly doped diamond layer (n-layer) with a lower doping concentration is grown on the (100) diamond. Then, a groove is etched on the (100) lightly doped diamond layer using an ICP process to selectively grow a heavily doped diamond layer (n+ layer) in the (111) crystal direction. This method can increase the carrier concentration difference between the drift region and the ohmic contact region of the device to 4 to 5 orders of magnitude, solve the problem of memory effect of doped diamond in the existing control doping, and realize controllable doping with a large concentration difference, thereby improving the reverse breakdown voltage, breakdown field strength and forward conductivity of the Schottky diode, reducing the leakage current, and effectively improving the performance of the device.

[0036] 2. The present invention uses selective growth to regulate doping to solve the problem of memory effect in phosphorus-doped diamond. When doping other elements, the memory effect problem can also be solved by selective growth to increase the concentration difference between the lightly doped and heavily doped layers. The diamond surface is treated with ICP oxygen plasma to remove the hydrogen terminals on the diamond surface. This method can solve the problem that some 2DHG remains after the hydrogen terminals on the diamond surface are removed by acid washing.

[0037] The present invention will be further described in detail below with reference to the accompanying drawings and embodiments. BRIEF DESCRIPTION OF THE DRAWINGS

[0038] Figure 1 It is a flow chart of a method for preparing a diamond Schottky diode based on selective growth and control of doping concentration provided by an embodiment of the present invention;

[0039] Figure 2a to Figure 2f It is a schematic diagram of a preparation process of a diamond Schottky diode based on selective growth and control of doping concentration provided by an embodiment of the present invention;

[0040] Figure 3a is a top view showing a groove on the upper surface of a lightly doped diamond layer;

[0041] Figure 3b is a top view showing another groove on the upper surface of a lightly doped diamond layer;

[0042] Figure 4 A three-dimensional structural diagram of a diamond diode with selective growth and control of doping concentration provided by an embodiment of the present invention;

[0043] Figure 5 A three-dimensional structural diagram of a diamond diode with selective growth and controlled doping concentration provided by an embodiment of the present invention.

[0044] Description of reference numerals:

[0045] 1-intrinsic diamond substrate; 2-lightly doped diamond layer; 3-heavily doped diamond layer; 4-ohmic electrode; 5-Schottky electrode; 6-groove. DETAILED DESCRIPTION

[0046] In order to further explain the technical means and effects adopted by the present invention to achieve the predetermined purpose of the invention, the following is a detailed description of a diamond diode with selective growth and control of doping concentration and a preparation method thereof proposed in accordance with the present invention, in combination with the accompanying drawings and specific implementation methods.

[0047] 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.

[0048] 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.

[0049] Embodiment 1

[0050] The present invention aims to solve the problem that the carrier concentration difference between the device drift region and the ohmic contact region is not large enough due to the phosphorus doping memory effect in the process of doping control of the traditional device process. In order to realize the application of phosphorus-doped diamond in Schottky diodes, it is necessary to accurately control the concentration of doping elements. The ohmic contact region needs to be doped with high concentration to significantly reduce the surface barrier width, promote carrier tunneling, and make the device have lower contact resistance and nearly linear IV characteristics; while the device drift region needs to be doped with lower concentration to improve the reverse breakdown voltage and forward conductivity of the Schottky diode. The thickness and doping concentration of the n+ layer (heavily doped diamond layer), n- layer (lightly doped diamond layer), and intrinsic layer need to be strictly controlled.

[0051] See also Figure 1 , Figure 1 The present invention provides a flow chart of a method for preparing a diamond Schottky diode based on selective growth and control of doping concentration, the method comprising:

[0052] S1: growing a lightly doped diamond layer 2 with a (100) crystal orientation on an intrinsic diamond substrate 1 with a (100) crystal orientation.

[0053] An intrinsic diamond substrate 1 with a (100) crystal orientation is selected and cleaned. The selected intrinsic diamond substrate is a (100) diamond prepared by the HTHP method (high temperature and high pressure synthesis method), and the quality meets the growth requirements. Specifically, a 5mm×5mm×0.5mm (100) intrinsic diamond substrate is selected. The substrate is subjected to X-ray diffraction (XRD) and atomic force microscopy (AFM) testing before use to ensure that the quality and surface roughness of the substrate meet the requirements of MPCVD growth and subsequent device preparation. Subsequently, acetone, ethanol and water are used for ultrasonic cleaning for 15 minutes respectively before growth to ensure that no impurities are introduced into the intrinsic diamond substrate 1 during the growth process.

[0054] Subsequently, a lightly doped diamond layer 2 with a (100) crystal orientation is grown on the intrinsic diamond substrate 1 using an MPCVD device, wherein the doping element of the lightly doped diamond layer 2 is phosphorus or boron, and the doping concentration of the doping element can be as low as 1×10 15 cm -3 .

[0055] In one embodiment of the present invention, during the growth process, an intrinsic diamond substrate 1 is placed in an MPCVD device, and the cavity pressure is pumped to 0.001 mbar or less; H2 is introduced into the MPCVD device, and the H2 flow rate is 300-400 sccm; when the cavity pressure is increased to 15 mbar, the microwave source is turned on and ignited, so that the cavity pressure is increased to 140-160 mbar, the power is 3000-3600 W, and the surface temperature of the intrinsic diamond substrate 1 is 850-950°C; before growth, the surface of the intrinsic diamond substrate 1 is etched for 10-15 minutes using H plasma, and after the etching is completed, CH4 with a flow rate of 12-18 sccm and PH3 (phosphorus source) or B2H6 with a flow rate of 1.0-1.5 sccm (boron source) are introduced to start growth, and the growth is 30-40 minutes to form a (100) crystal orientation lightly doped diamond layer 2 with a thickness of 500-600 nm, and the doping element is phosphorus or boron, such as Figure 2a The microwave input frequency of the MPCVD equipment used in this embodiment is 2.45 GHz.

[0056] S2: etching the upper surface of the lightly doped diamond layer 2 to form a groove 6 .

[0057] Specifically, an inductively coupled oxygen plasma etching process is used to etch the upper surface of the lightly doped diamond layer 2 to form a groove 6, such as Figure 2b As shown. The ICP power used in etching is 150-200W, the RF power is 40-60W, the oxygen flow rate is 80-100sccm, the etching time is 3-4min, and the ICP oxygen plasma etching rate of diamond is 130-140nm / min. The groove 6 of this embodiment is located at the center of the upper surface of the lightly doped diamond layer 2, and the upper surface of the groove 6 is circular or square, as shown in FIG. Figure 3a and Figure 3b As shown, the depth of the groove 6 is 300-500 nm.

[0058] S3: selective growth is performed in the groove 6 to form a heavily doped diamond layer 3 with a (111) crystal orientation, wherein the doping concentration of the heavily doped diamond layer 3 is 3 to 4 orders of magnitude higher than the doping concentration of the lightly doped diamond layer 2 .

[0059] Place the sample with groove 6 in the MPCVD device, place the sample obtained by S2 in the MPCVD device, and pump the cavity pressure to 0.001 mbar or less; introduce H2 into the MPCVD device, and the H2 flow rate is 300-400 sccm; when the cavity pressure is increased to 15 mbar, turn on the microwave source, start the ignition, so that the cavity pressure is increased to 140-160 mbar, the power is 3000-3600 W, and the sample surface temperature is 850-950°C; use H plasma to etch the upper surface of the lightly doped diamond layer 2 and the inner surface of the groove 6 for 10 minutes, after the etching is completed, introduce CH4 with a flow rate of 3-4 sccm and PH3 with a flow rate of 1.0-1.5 sccm, start selective growth, the growth time is 15-20 minutes, and form a heavily doped diamond layer 3 with a (111) crystal orientation, such as Figure 2c and Figure 2d As shown, by controlling the device power, chamber pressure and CH4 concentration, the selective growth will only grow in the groove 6 and will not grow on other surfaces. In this embodiment, the heavily doped diamond layer 3 and the lightly doped diamond layer 2 have the same doping element, and the doping concentration of the doping element in the heavily doped diamond layer 3 can reach up to 1×10 21 cm -3 .

[0060] In this embodiment, during the selective growth process, the methane concentration is reduced to 0.5% to 1% to ensure that diamonds with a (111) crystal orientation grow only in the grooves 6, while diamonds do not grow in the unetched areas.

[0061] S4: removing hydrogen terminations on the upper surface of the lightly doped diamond layer 2 and the upper surface of the heavily doped diamond layer 3 .

[0062] The sample surface is treated with oxygen using an ICP device with an ICP power of 120-150 W, an oxygen flow rate of 80-100 sccm, and a treatment time of 10-15 s to remove hydrogen terminals on the upper surface of the lightly doped diamond layer 2 and the upper surface of the heavily doped diamond layer 3 to remove the influence on the performance of the doped diamond.

[0063] S5: growing an ohmic electrode 4 on the upper surface of the heavily doped diamond layer 3 from which the hydrogen termination has been removed.

[0064] On the entire upper surface of the sample from which the hydrogen terminal has been removed, metal Ti with a thickness of 20 to 30 nm and metal Au with a thickness of 90 to 100 nm are deposited from bottom to top by an electron beam evaporation device;

[0065] Through photolithography and photolithography, the surface of the device is exposed except for the ohmic electrode area. After the photolithography is completed, the sample is placed in a potassium iodide solution to etch away the metal Au outside the ohmic electrode area. Then the sample is placed in a buffered oxide etchant (BOE) to etch away the metal Ti outside the ohmic electrode area. Subsequently, a rapid thermal annealing device (RTP) is used to anneal in a nitrogen atmosphere at 750°C for 300s to form a good ohmic contact between the heavily doped diamond layer 3 and the metal, thereby forming an ohmic electrode 4 located on the upper surface of the heavily doped diamond layer 3, as shown in FIG. Figure 2e shown.

[0066] The upper surface of the ohmic electrode 4 of this embodiment may be circular or square. Figure 4 and Figure 5 In a specific embodiment, when the upper surface of the heavily doped diamond layer 3 is circular, the upper surface of the ohmic electrode 4 is also circular, and the ohmic electrode 4 is located at the center of the heavily doped diamond layer 3, and the diameter of the ohmic electrode 4 is smaller than the diameter of the heavily doped diamond layer 3; when the upper surface of the heavily doped diamond layer 3 is square, the upper surface of the ohmic electrode 4 is also square, and the ohmic electrode 4 is located at the center of the heavily doped diamond layer 3, and the side length of the ohmic electrode 4 is smaller than the side length of the heavily doped diamond layer 3.

[0067] The photolithography process of this embodiment uses AZ6112 type photoresist and SUSS MA / BA6 type photolithography machine.

[0068] S6: growing a Schottky electrode 5 on the upper surface of the lightly doped diamond layer 2 from which the hydrogen terminal has been removed, and the ohmic electrode 4 and the Schottky electrode 5 are spaced apart.

[0069] Electron beam evaporation equipment is used to deposit metal Al with a thickness of 90 to 100 nm on the entire upper surface of the sample. The remaining parts except the Schottky electrode area are exposed by photolithography and photolithography. Then, the sample is placed in a BOE solution for 15 minutes using a wet etching process to etch away the metal Al outside the Schottky electrode area, forming a Schottky electrode 5 grown on the upper surface of the lightly doped diamond layer 2. Figure 2f As shown. The Schottky electrode 5 is in the form of a circular ring or a square ring, surrounding the outer side of the ohmic electrode 4, and is spaced apart from the ohmic electrode 4. In a specific embodiment, when the upper surface of the ohmic electrode 4 is also circular, the Schottky electrode 5 is in the form of a circular ring; when the upper surface of the ohmic electrode 4 is also square, the Schottky electrode 5 is in the form of a square ring. Figure 4 and Figure 5 The Schottky contact of this embodiment uses an Al metal electrode, which can achieve a barrier height of 1.03V.

[0070] Another embodiment of the present invention further provides a diamond diode with selective growth and controlled doping concentration, see Figure 2f The diamond diode comprises an intrinsic diamond substrate 1 with a (100) crystal orientation, a lightly doped diamond layer 2 with a (100) crystal orientation, a heavily doped diamond layer 3 with a (111) crystal orientation, an ohmic electrode 4 and a Schottky electrode 5, wherein the lightly doped diamond layer 2 is located on the upper surface of the intrinsic diamond substrate 1, a groove 6 is provided on the upper surface of the lightly doped diamond layer 2, the heavily doped diamond layer 3 is filled in the groove 6, and the doping concentration of the heavily doped diamond layer 3 is 3 to 4 orders of magnitude higher than the doping concentration of the lightly doped diamond layer 2; the ohmic electrode 4 is located on the upper surface of the heavily doped diamond layer 3, the Schottky electrode 5 is located on the upper surface of the lightly doped diamond layer 2, and the ohmic electrode 4 and the Schottky electrode 5 are arranged at intervals. The Schottky electrode 5 is in a ring shape and surrounds the outer side of the ohmic electrode 4.

[0071] The configuration of the lightly doped diamond layer 2 and the heavily doped diamond layer 3 can affect the performance of the device, such as the switching speed and power consumption. Furthermore, by precisely controlling the doping concentration and thickness of the lightly doped diamond layer 2 and the heavily doped diamond layer 3, key parameters of the device, such as the resistivity, carrier mobility and breakdown voltage, can be optimized.

[0072] Based on the difference in doping efficiency between (100) and (111) diamonds under the same conditions, this embodiment provides a method for preparing a diamond diode with selective growth and controlled doping concentration. The technical solution adopted is to use the fact that the doping efficiency of the diamond (111) crystal orientation is higher than that of the diamond (100) crystal orientation under the same conditions, and first grow a lightly doped diamond layer with a low doping concentration on the diamond (100) crystal orientation, with the lowest concentration reaching 1×10 15 cm -3 Then, a groove is etched on the lightly doped diamond layer with a low doping concentration to selectively grow a heavily doped diamond layer 3 with a high doping concentration on the (111) crystal plane of diamond. The high doping concentration can reach up to 1×10 21 cm -3 This method can adjust the doping concentration, increase the carrier concentration difference between the drift region and the ohmic contact region of the device to 4 to 5 orders of magnitude, realize adjustable doping with a large concentration difference, and achieve the device performance of the Schottky diode. In addition, the lateral structure of the Schottky diode can also increase the switching speed of the device, improve the reverse breakdown voltage and breakdown field strength of the Schottky diode, and reduce the leakage current, so that the performance of the device is effectively improved.

[0073] The present invention uses selective growth to regulate doping to solve the problem of memory effect in phosphorus-doped diamond. When doping other elements, the problem of memory effect can also be solved by selective growth to increase the concentration difference between lightly doped and heavily doped layers. The diamond surface is treated with ICP oxygen plasma to remove the hydrogen terminals on the diamond surface. This method can solve the problem that some 2DHG remains after the hydrogen terminals on the diamond surface are removed by acid washing.

[0074] Embodiment 2

[0075] Based on the first embodiment, this embodiment provides a specific method for preparing a diamond diode with selective growth and controlled doping concentration, the preparation method comprising:

[0076] Step 1: Select the substrate and clean it.

[0077] A 5mm×5mm×0.5mm (100) crystal orientation intrinsic diamond substrate was selected. The intrinsic diamond substrate was subjected to X-ray diffraction (XRD) and atomic force microscopy (AFM) testing before use to ensure that the quality and surface roughness of the intrinsic diamond substrate met the requirements of MPCVD (microwave plasma CVD) growth and subsequent device preparation.

[0078] Subsequently, the intrinsic diamond substrate was ultrasonically cleaned for 15 min using acetone, ethanol and water respectively to ensure that no impurities were introduced into the intrinsic diamond substrate during the growth process.

[0079] Step 2: growing a lightly doped diamond layer with a (100) crystal orientation on the surface of an intrinsic diamond substrate with a (100) crystal orientation.

[0080] Specifically, an MPCVD device is used to perform phosphorus-doped diamond epitaxial growth on an intrinsic diamond substrate. The intrinsic diamond substrate is placed in the MPCVD device, and the cavity pressure is pumped to 0.001 mbar or less; H2 is introduced into the MPCVD device, and the H2 flow rate is 300 sccm; when the cavity pressure is increased to 15 mbar, a microwave source is turned on and ignited to raise the cavity pressure to 150 mbar, the power is 3200 W, and the surface temperature of the intrinsic diamond substrate is 900°C; before growth, the surface of the intrinsic diamond substrate is etched with H plasma for 10 minutes, and after etching, CH4 with a flow rate of 18 sccm and PH3 with a flow rate of 1.5 sccm are introduced to start growth, and the growth is 30 minutes to form a (100) crystal orientation lightly doped diamond layer with a thickness of 600 nm, and the doping element is phosphorus, and the doping concentration is 10 16 cm -3 .

[0081] Step 3: Etching grooves on the upper surface of the lightly doped diamond layer.

[0082] Specifically, a photolithography process is performed on the upper surface of the lightly doped diamond layer by photoresist coating and photolithography. After the photolithography is completed, the portion of the upper surface of the lightly doped diamond layer that is not protected by the photoresist is etched using an ICP device. The ICP power is 150 W, the RF power is 50 W, the oxygen flow rate is 90 sccm, the etching time is 3 min, and the etching rate of the ICP oxygen plasma etching is 140 nm / min. A groove is etched in the center of the upper surface of the lightly doped diamond layer. The upper surface of the groove may be circular or square, and the depth is less than the thickness of the lightly doped diamond layer. Preferably, the depth of the groove may be 300 to 500 nm.

[0083] Step 4: Selectively grow in the grooves to form a heavily doped diamond layer with a (111) crystal orientation.

[0084] An MPCVD device is used for selective growth in the groove. Specifically, the sample obtained in step 3 is placed in the MPCVD device, and the cavity pressure is pumped to 0.001 mbar or less; H2 is introduced into the MPCVD device, and the H2 flow rate is 300 sccm; when the cavity pressure is increased to 15 mbar, the microwave source is turned on and ignited to raise the cavity pressure to 150 mbar, the power is 3200 W, and the sample surface temperature is 900°C; the upper surface of the lightly doped diamond layer and the inner surface of the groove are etched with H plasma for 10 minutes. After the etching is completed, CH4 with a flow rate of 3 sccm and PH3 with a flow rate of 1.5 sccm are introduced to start selective growth for 20 minutes to form a heavily doped diamond layer with a (111) crystal orientation, and the doping element is phosphorus with a doping concentration of 10 20 cm -3 By controlling the device power, chamber pressure and CH4 concentration, selective growth will only occur in the grooves and not on other surfaces.

[0085] Step 5: Removing hydrogen terminations on the upper surface of the lightly doped diamond layer and the upper surface of the heavily doped diamond layer.

[0086] The sample surface was treated with oxygen using an ICP device with an ICP power of 150 W, an oxygen flow rate of 90 sccm, and a treatment time of 15 s to remove the hydrogen terminals on the upper surface of the lightly doped diamond layer and the upper surface of the heavily doped diamond layer that affect the performance of phosphorus-doped diamond.

[0087] Step 6: Growing an ohmic electrode on the upper surface of the heavily doped diamond layer from which the hydrogen termination has been removed.

[0088] Metal electrodes are deposited on the upper surface of the entire sample by electron beam evaporation (E-Beam) process, with Ti of 30nm thickness and Au of 100nm thickness from bottom to top. Then, photolithography is performed by photoresist and photolithography to expose the surface of the device except the ohmic electrode area. After the photolithography is completed, the sample is placed in a potassium iodide solution for 4s to complete the corrosion of the upper Au layer, and then the sample is placed in a buffered oxide etchant (BOE) solution for 10s to complete the corrosion of the lower Ti layer, thereby forming an ohmic electrode located on the upper surface of the heavily doped diamond layer.

[0089] Subsequently, a rapid thermal process (RTP) was used in a nitrogen atmosphere to anneal at 750° C. for 300 seconds to form a good ohmic contact between the heavily doped diamond layer and the metal.

[0090] Step 7: Growing a Schottky electrode on the upper surface of the lightly doped diamond layer from which the hydrogen termination has been removed.

[0091] An electron beam evaporation (E-Beam) device was used to deposit 100 nm thick Al on the entire upper surface of the sample. Subsequently, photolithography was performed through photoresist and photolithography to expose the rest of the sample except for the Schottky contact. Then, using a wet etching process, the sample was placed in a BOE solution for 15 minutes to etch away the Al metal outside the Schottky electrode area, forming a Schottky electrode grown on the upper surface of the lightly doped diamond layer to complete the device preparation.

[0092] Embodiment 3

[0093] Step a: Select a substrate and clean it.

[0094] A 5mm×5mm×0.5mm (100) crystal orientation intrinsic diamond substrate was selected. The intrinsic diamond substrate was subjected to X-ray diffraction (XRD) and atomic force microscopy (AFM) testing before use to ensure that the quality and surface roughness of the intrinsic diamond substrate met the requirements of MPCVD (microwave plasma CVD) growth and subsequent device preparation.

[0095] Subsequently, the intrinsic diamond substrate was ultrasonically cleaned for 15 min using acetone, ethanol and water respectively to ensure that no impurities were introduced into the intrinsic diamond substrate during the growth process.

[0096] Step b: growing a lightly doped diamond layer with a (100) crystal orientation on the surface of an intrinsic diamond substrate with a (100) crystal orientation.

[0097] The MPCVD equipment was used to carry out the epitaxial growth of boron-doped diamond on the intrinsic diamond substrate. The intrinsic diamond substrate was placed in the MPCVD equipment, and the cavity pressure was pumped to 0.001 mbar or less. H2 was introduced into the MPCVD equipment with a flow rate of 300 sccm. When the cavity pressure was increased to 15 mbar, the microwave source was turned on and ignited to raise the cavity pressure to 150 mbar with a power of 3200 W. The surface temperature of the intrinsic diamond substrate was 900°C. Before the growth, the surface of the intrinsic diamond substrate was etched with H plasma for 10 min. After the etching was completed, CH4 with a flow rate of 18 sccm and B2H6 with a flow rate of 1.5 sccm were introduced. After the growth for 30 min, a lightly doped diamond layer with a (100) crystal orientation of 600 nm in thickness was formed. The doping element was boron (B) with a doping concentration of 10 16 cm -3 .

[0098] Step c: etching a groove on the upper surface of the lightly doped diamond layer.

[0099] Specifically, a photolithography process is performed on the upper surface of the lightly doped diamond layer by photoresist coating and photolithography. After the photolithography is completed, the portion of the upper surface of the lightly doped diamond layer that is not protected by the photoresist is etched using an ICP device. The ICP power is 150 W, the RF power is 50 W, the oxygen flow rate is 90 sccm, the etching time is 3 min, and the etching rate of the ICP oxygen plasma etching is 140 nm / min. A groove is etched on the upper surface of the lightly doped diamond layer. The upper surface of the groove may be circular or square, and the depth is less than the thickness of the lightly doped diamond layer. Preferably, the depth of the groove may be 300 to 500 nm.

[0100] Step d: selectively growing in the grooves to form a heavily doped diamond layer with a (111) crystal orientation.

[0101] An MPCVD device is used for selective growth in the groove. Specifically, the sample obtained in step 3 is placed in the MPCVD device, and the cavity pressure is pumped to 0.001 mbar or less; H2 is introduced into the MPCVD device, and the H2 flow rate is 300 sccm; when the cavity pressure is increased to 15 mbar, the microwave source is turned on and ignited to raise the cavity pressure to 150 mbar, the power is 3200 W, the sample surface temperature is 900°C, and the upper surface of the lightly doped diamond layer and the inner surface of the groove are etched with H plasma for 10 minutes. After the etching is completed, CH4 with a flow rate of 3 sccm and B2H6 with a flow rate of 1.5 sccm are introduced to start growth, and selective growth is started for 20 minutes to form a heavily doped diamond layer with a (111) crystal orientation, and the doping element is boron (B) with a doping concentration of 10 21 cm -3By controlling the device power, chamber pressure and CH4 concentration, selective growth will only occur in the grooves and not on other surfaces.

[0102] Step e: removing hydrogen terminations on the upper surface of the lightly doped diamond layer and the upper surface of the heavily doped diamond layer.

[0103] The sample surface was treated with oxygen using an ICP device with an ICP power of 150 W, an oxygen flow rate of 90 sccm, and a treatment time of 15 s to remove the hydrogen terminals on the upper surface of the lightly doped diamond layer and the upper surface of the heavily doped diamond layer that affect the performance of phosphorus-doped diamond.

[0104] Step f: growing an ohmic electrode on the upper surface of the heavily doped diamond layer from which the hydrogen termination has been removed.

[0105] Ti / Au metal electrodes are deposited on the upper surface of the entire sample by electron beam evaporation process, with Ti of 30nm thickness and Au of 100nm thickness from bottom to top. Subsequently, photolithography process is performed by photoresist and photolithography to expose the surface of the device except the ohmic electrode area. After the photolithography is completed, the sample is placed in potassium iodide solution for 4s to complete the corrosion of the upper Au layer, and then the sample is placed in a buffered oxide etching solution for 10s to complete the corrosion of the lower Ti layer, thereby forming an ohmic electrode located on the upper surface of the heavily doped diamond layer.

[0106] Subsequently, rapid thermal annealing equipment was used in a nitrogen atmosphere at 750° C. for 300 seconds to form a good ohmic contact between the heavily doped diamond layer and the metal.

[0107] Step g: growing a Schottky electrode on the upper surface of the lightly doped diamond layer from which the hydrogen termination has been removed.

[0108] An electron beam evaporation device is used to deposit Al with a thickness of 100 nm on the entire upper surface of the sample. Subsequently, photolithography is performed through photoresist and photolithography to expose the rest of the sample except for the Schottky contact. Then, using a wet etching process, the sample is placed in a BOE solution for 15 minutes to etch away the Al metal outside the Schottky electrode area, forming a Schottky electrode grown on the upper surface of the lightly doped diamond layer to complete the device preparation.

[0109] 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 a diamond diode with selective growth and controlled doping concentration, characterized in that: include: S1: growing a lightly doped diamond layer with a (100) crystal orientation on an intrinsic diamond substrate with a (100) crystal orientation; S2: etching a groove on the upper surface of the lightly doped diamond layer, wherein the depth of the groove is less than the thickness of the lightly doped diamond layer; S3: selectively growing in the groove to form a heavily doped diamond layer with a (111) crystal orientation, wherein the doping concentration of the heavily doped diamond layer is 4 to 5 orders of magnitude higher than the doping concentration of the lightly doped diamond layer; S4: removing hydrogen terminations on the upper surface of the lightly doped diamond layer and the upper surface of the heavily doped diamond layer; S5: growing an ohmic electrode on the upper surface of the heavily doped diamond layer after the hydrogen termination is removed; S6: growing a Schottky electrode on the upper surface of the lightly doped diamond layer after the hydrogen terminal is removed, wherein the ohmic electrode is spaced apart from the Schottky electrode.

2. The method for preparing a diamond diode with selective growth and controlled doping concentration according to claim 1, characterized in that: The S1 includes: An intrinsic diamond substrate having a (100) crystal orientation is selected and cleaned; A lightly doped diamond layer with a (100) crystal orientation is grown on the intrinsic diamond substrate using an MPCVD device, wherein the doping element of the lightly doped diamond layer is phosphorus or boron, and the doping concentration of the doping element is as low as 1×10 15 cm -3 .

3. The method for preparing a diamond diode with selective growth and controlled doping concentration according to claim 1, characterized in that: The S2 includes: A groove is formed by etching the upper surface of the lightly doped diamond layer using an inductively coupled oxygen plasma etching process, wherein the groove is located at the center of the upper surface of the lightly doped diamond layer, and the upper surface of the groove is circular or square.

4. The method for preparing a diamond diode with selective growth and controlled doping concentration according to claim 3, characterized in that: The depth of the groove is 300-500 nm.

5. The method for preparing a diamond diode with selective growth and controlled doping concentration according to claim 1, characterized in that: The S3 includes: The sample with the groove is placed in an MPCVD device, and selective growth is performed in the groove to form a heavily doped diamond layer with a (111) crystal orientation. The heavily doped diamond layer has the same doping element as the lightly doped diamond layer, and the doping concentration of the doping element in the heavily doped diamond layer is up to 1×10 21 cm -3 .

6. The method for preparing a diamond diode with selective growth and controlled doping concentration according to claim 1, characterized in that: The S4 includes: The surface of the sample is treated with oxygen using an ICP device to remove hydrogen terminals on the upper surface of the lightly doped diamond layer and the upper surface of the heavily doped diamond layer, wherein the power of the ICP device is 120-150 W, the oxygen flow rate is 80-100 sccm, and the treatment time is 10-15 s.

7. The method for preparing a diamond diode with selective growth and controlled doping concentration according to claim 4, characterized in that: The S5 includes: On the entire upper surface of the sample from which the hydrogen terminal has been removed, metal Ti with a thickness of 20 to 30 nm and metal Au with a thickness of 90 to 100 nm are deposited from bottom to top by an electron beam evaporation device; The photolithography process is performed by coating and photolithography to expose the upper surface of the sample except the ohmic electrode area. After the photolithography is completed, the sample is placed in a potassium iodide solution to etch away the metal Au outside the ohmic electrode area, and then placed in a buffered oxide etching solution to etch away the metal Ti outside the ohmic electrode area. The sample is annealed in a nitrogen atmosphere using a rapid thermal annealing device to form a good ohmic contact between the heavily doped diamond layer and the metal Ti, thereby forming an ohmic electrode located on the upper surface of the heavily doped diamond layer.

8. The method for preparing a diamond diode with selective growth and controlled doping concentration according to claim 4, characterized in that: The S6 includes: Electron beam evaporation equipment is used to deposit metal Al with a thickness of 90 to 100 nm on the entire upper surface of the sample, and a photolithography process is performed through photoresist coating and photolithography to expose the remaining parts except the Schottky electrode area; then the sample is placed in a buffered oxide etching solution to etch away the metal Al outside the Schottky electrode area to form a Schottky electrode on the upper surface of the lightly doped diamond layer.

9. A diamond diode with selective growth and controlled doping concentration, characterized in that: The diamond diode is prepared by the preparation method according to any one of claims 1 to 8, comprising an intrinsic diamond substrate with a (100) crystal orientation, a lightly doped diamond layer with a (100) crystal orientation, a heavily doped diamond layer with a (111) crystal orientation, an ohmic electrode and a Schottky electrode, wherein: The lightly doped diamond layer is located on the upper surface of the intrinsic diamond substrate, a groove is opened on the upper surface of the lightly doped diamond layer, the heavily doped diamond layer is filled in the groove, and the doping concentration of the heavily doped diamond layer is 4 to 5 orders of magnitude higher than the doping concentration of the lightly doped diamond layer; The ohmic electrode is located on the upper surface of the heavily doped diamond layer, the Schottky electrode is located on the upper surface of the lightly doped diamond layer, and the ohmic electrode and the Schottky electrode are arranged at intervals.

10. The selectively grown diamond diode with controlled doping concentration according to claim 9, characterized in that: The Schottky electrode is ring-shaped and surrounds the outer side of the ohmic electrode.

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