A diamond diode with selectively controlled doping concentration and its fabrication method

Abstract

This invention discloses a diamond diode with selectively grown and controlled doping concentration and its fabrication method. The fabrication method includes: growing a lightly doped diamond layer with a (100) crystal orientation on an intrinsic diamond substrate with a (100) crystal orientation; etching a groove on the upper surface of the lightly doped diamond layer, the depth of the groove being less than the thickness of the lightly doped diamond layer; selectively growing a heavily doped diamond layer with a (111) crystal orientation in the groove; removing hydrogen terminals from the upper surfaces of the lightly doped diamond layer and the heavily doped diamond layer; growing an ohmic electrode on the upper surface of the heavily doped diamond layer; and growing a Schottky electrode on the upper surface of the lightly doped diamond layer, with the ohmic electrode and the Schottky electrode spaced apart. This invention can increase the carrier concentration difference between the device drift region and the ohmic contact region to 4-5 orders of magnitude, improving the reverse breakdown voltage, breakdown field strength, and forward conductivity of the Schottky diode, while reducing leakage current.

Description

Technical Field

[0001] This invention belongs to the field of electronic device technology, specifically relating to a diamond diode with selectively controlled doping concentration during growth and its preparation method. Background Technology

[0002] Diamond is a new generation of ultrawide bandgap semiconductor material, characterized by a large bandgap (5.5 eV), high breakdown field strength (10 MV / cm), high thermal conductivity (22 W / (cm·K)), and high carrier mobility (electrons: 4500 cm⁻¹). 2 / (V·s); Hole: 3800cm 2 Diamond possesses a series of excellent properties, including high strength (V·s), high hardness, and good chemical stability, thus earning it the title of "ultimate semiconductor." It holds immense application potential in fields such as high-temperature, high-pressure devices, high-frequency, high-power devices, optical windows, high-energy particle detectors, quantum information, and biosensors.

[0003] Diamond power diodes represent an important area of ​​diamond devices. They primarily include two types: Schottky barrier diodes (SBDs) and pn junction diodes (PNDs). SBDs, due to their advantages such as low forward voltage, low reverse recovery current, and high switching frequency, have broad application prospects in high-voltage applications.

[0004] Diamond Schottky diodes mainly include three structures: lateral diodes, vertical diodes, and quasi-vertical diodes. All three structures require the fabrication of n+ and n- layers with different doping concentrations. Currently, diamond n-type bulk doping is primarily achieved through phosphorus doping. The concentration of phosphorus in the diamond is controlled by varying the flow rate of the dopant source phosphine during MPCVD (microwave plasma CVD) growth.

[0005] In in-situ phosphorus-doped CVD epitaxy of diamond, due to the close arrangement of carbon atoms in the (100) crystal orientation, the highest reported doping concentration in the (100) crystal orientation is only 10. 16 cm -3 It is not possible to obtain diamonds with higher doping concentrations. Considering the crystal planes of the diamond substrate, the doping concentration and doping efficiency of n-type diamond growth with the (100) crystal orientation are 4 to 5 orders of magnitude lower than those with the (113) and (111) crystal planes. Due to the insufficient concentration difference between the n+ and n- layers and the low mobility caused by lattice defects introduced by phosphorus doping, it is currently impossible to realize phosphorus-doped diamond Schottky diode devices. Summary of the Invention

[0006] To address the aforementioned problems in the prior art, this invention provides a diamond diode with selectively controlled doping concentration during growth and its fabrication method. The technical problem to be solved by this invention is achieved through the following technical solution:

[0007] One aspect of the present invention provides a method for fabricating a diamond diode with selectively controlled doping concentration during growth, comprising:

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

[0009] S2: A groove is etched on the upper surface of the lightly doped diamond layer, the depth of which is less than the thickness of the lightly doped diamond layer;

[0010] S3: Selective growth is performed 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 that of the lightly doped diamond layer.

[0011] S4: Remove hydrogen terminals from the upper surface of the lightly doped diamond layer and the upper surface of the heavily doped diamond layer;

[0012] S5: An ohmic electrode is grown on the upper surface of the heavily doped diamond layer after hydrogen terminal removal;

[0013] S6: A Schottky electrode is grown on the upper surface of a lightly doped diamond layer after hydrogen terminal removal, wherein the ohmic electrode and the Schottky electrode are spaced apart.

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

[0015] An intrinsic diamond substrate with (100) crystal orientation was selected and cleaned.

[0016] A lightly doped diamond layer with a (100) crystal orientation was grown on the intrinsic diamond substrate using an MPCVD apparatus. The doping element of the lightly doped diamond layer was phosphorus or boron, and the doping concentration of the doping element was as low as 1 × 10⁻⁶. 15 cm -3 .

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

[0018] A groove is formed on the upper surface of the lightly doped diamond layer using an inductively coupled oxygen plasma etching process. 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] A sample with grooves is placed in an MPCVD apparatus, where selective growth is performed 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 × 10⁻⁶. 21 cm -3 .

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

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

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

[0025] Metallic Ti with a thickness of 20–30 nm and metallic Au with a thickness of 90–100 nm were deposited from bottom to top on the entire upper surface of the sample after hydrogen removal using an electron beam evaporation apparatus.

[0026] Photolithography is performed by spin coating and photolithography to expose the upper surface of the sample except for the ohmic electrode area. After photolithography, the sample is placed in potassium iodide solution to stand and etch away the metal Au outside the ohmic electrode area. Then it is placed in buffer 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 metallic Ti, thereby forming an ohmic electrode on the upper surface of the heavily doped diamond layer.

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

[0029] Electron beam evaporation equipment is used to deposit a layer of metallic Al with a thickness of 90-100 nm on the entire upper surface of the sample. Photolithography is then performed by spin coating and photolithography to expose the remaining part except for the Schottky electrode region. Subsequently, the sample is placed in a buffer oxide etching solution to etch away the metallic Al outside the Schottky electrode region, forming the Schottky electrode on the upper surface of the lightly doped diamond layer.

[0030] Another aspect of the present invention provides a diamond diode with selectively controlled doping concentration during growth, fabricated using the method described in any one of the above embodiments. 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.

[0031] The lightly doped diamond layer is located on the upper surface of the intrinsic diamond substrate. A groove is formed on the upper surface of the lightly doped diamond layer, and the heavily doped diamond layer fills the groove. The doping concentration of the heavily doped diamond layer is 3 to 4 orders of magnitude higher than that of the lightly doped diamond layer.

[0032] The ohmic electrode is located on the upper surface of the heavily doped diamond layer, and the Schottky electrode is located on the upper surface of the lightly doped diamond layer, with the ohmic electrode and the Schottky electrode spaced apart.

[0033] In one embodiment of the invention, the Schottky electrode is ring-shaped and surrounds the outside of the ohmic electrode.

[0034] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0035] 1. This invention provides a method for fabricating a diamond diode with selectively controlled doping concentration. The diamond diode device adopts a Schottky lateral diode structure, which can improve the switching speed of the device compared with other Schottky diode structures. The specific principle of selectively controlling the 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, by using ICP process to etch grooves on the (100) lightly doped diamond layer, selective growth is performed to grow a heavily doped diamond layer (n+ layer) with the (111) crystal orientation. This method can increase the carrier concentration difference between the device drift region and the ohmic contact region to 4 to 5 orders of magnitude, solving the problem of the doped diamond memory effect in existing controlled doping methods. It realizes controllable doping with a large concentration difference, thereby improving the reverse breakdown voltage, breakdown field strength, and forward conductivity of the Schottky diode, reducing leakage current, and effectively improving the performance of the device.

[0036] 2. This invention utilizes selective growth to control doping and solve the memory effect problem in phosphorus-doped diamond. When doping with other elements, selective growth can also address the memory effect, increasing the concentration difference between lightly and heavily doped layers. ICP oxygen plasma treatment is used to remove hydrogen terminals from the diamond surface. This method solves the problem of residual 2DHG after acid leaching to remove hydrogen terminals from the diamond surface.

[0037] The present invention will be further described in detail below with reference to the accompanying drawings and embodiments. Attached Figure Description

[0038] Figure 1 This is a flowchart of a method for fabricating a diamond Schottky diode based on selective growth to control the doping concentration, provided by an embodiment of the present invention.

[0039] Figures 2a to 2f This is a schematic diagram illustrating the fabrication process of a diamond Schottky diode based on selective growth to control doping concentration, as provided in an embodiment of the present invention.

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

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

[0042] Figure 4 A three-dimensional structural diagram of a diamond diode with selectively controlled doping concentration provided in an embodiment of the present invention;

[0043] Figure 5 This is a three-dimensional structural diagram of a diamond diode with selectively controlled doping concentration provided in an embodiment of the present invention.

[0044] Explanation of reference numerals in the attached figures:

[0045] 1-Intrinsic diamond substrate; 2-Lightly doped diamond layer; 3-Heavily doped diamond layer; 4-Ohmic electrode; 5-Schottky electrode; 6-Groove. Detailed Implementation

[0046] To further illustrate the technical means and effects adopted by the present invention to achieve the intended purpose, the following, in conjunction with the accompanying drawings and specific embodiments, provides a detailed description of a diamond diode with selectively controlled doping concentration and its preparation method based on the present invention.

[0047] The foregoing and other technical contents, features, and effects of the present invention will be clearly presented in the following detailed description of specific embodiments in conjunction with the accompanying drawings. Through the description of the specific embodiments, a more in-depth and concrete understanding can be gained of the technical means and effects adopted by the present invention to achieve its intended purpose. However, the accompanying drawings are for reference and illustration only and are not intended to limit the technical solutions of the present invention.

[0048] It should be noted that, in this document, relational terms such as "first" and "second" are used merely to distinguish one entity or operation from another, and do not necessarily require or imply any such actual relationship or order between these entities or operations. Furthermore, the terms "comprising," "including," or any other variations are intended to cover non-exclusive inclusion, such that an article or apparatus comprising a list of elements includes not only those elements but also other elements not expressly listed. Without further limitations, an element defined by the phrase "comprising one..." does not exclude the presence of other identical elements in the article or apparatus that includes said element.

[0049] Example 1

[0050] The present invention addresses the problem of insufficient carrier concentration difference between the drift region and the ohmic contact region in traditional device manufacturing processes due to the phosphorus doping memory effect. To realize the application of phosphorus-doped diamond in Schottky diodes, precise control of the dopant concentration is required. The ohmic contact region needs high doping concentration to significantly reduce the surface barrier width, promote carrier tunneling, and give the device low contact resistance and near-linear IV characteristics. Conversely, the drift region requires lower doping 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 all need to be strictly controlled.

[0051] Please see Figure 1 , Figure 1 This is a flowchart illustrating a method for fabricating a diamond Schottky diode based on selective growth to control doping concentration, according to an embodiment of the present invention. The method includes:

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

[0053] An intrinsic diamond substrate 1 with a (100) crystal orientation was selected and cleaned. The selected intrinsic diamond substrate was a (100) diamond prepared by the HTHP method (high temperature and high pressure synthesis method), and its quality met the growth requirements. Specifically, a (100) intrinsic diamond substrate with a size of 5 mm × 5 mm × 0.5 mm was selected. Before use, the substrate was subjected to X-ray diffraction (XRD) and atomic force microscopy (AFM) tests to ensure that the quality and surface roughness of the substrate met the requirements of MPCVD growth and subsequent device fabrication. Subsequently, before growth, the substrate was ultrasonically cleaned for 15 min each with acetone, ethanol, and water to ensure that no impurities were 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 an intrinsic diamond substrate 1 using an MPCVD device. 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 1×10⁻⁶. 15 cm -3 .

[0055] In one embodiment of the present invention, during the growth process, the intrinsic diamond substrate 1 is placed in an MPCVD device, and the cavity pressure is evacuated to 0.001 mbar or below; H2 is introduced into the MPCVD device at a flow rate of 300-400 sccm; when the cavity pressure is increased to 15 mbar, the microwave source is turned on to ignite, so that the cavity pressure rises 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 with H plasma for 10-15 min, and after etching, CH4 at a flow rate of 12-18 sccm and PH3 (phosphorus source) or B2H6 (boron source) at a flow rate of 1.0-1.5 sccm are introduced to start growth, which lasts for 30-40 min, forming a lightly doped diamond layer 2 with a (100) crystal orientation and a thickness of 500-600 nm, wherein the doping element is phosphorus or boron, such as Figure 2a As shown. The microwave input frequency of the MPCVD equipment used in this embodiment is 2.45 GHz.

[0056] S2: Grooves 6 are etched on the upper surface of the lightly doped diamond layer 2.

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

[0059] The sample with groove 6 was placed into the MPCVD equipment. The sample obtained by S2 was placed into the MPCVD equipment, and the cavity gas pressure was evacuated to 0.001 mbar or below. H2 was introduced into the MPCVD equipment at a flow rate of 300-400 sccm. When the cavity gas pressure was increased to 15 mbar, the microwave source was turned on to ignite and raise the cavity gas pressure to 140-160 mbar. The power was 3000-3600 W, and the sample surface temperature was 850-950 °C. The upper surface of the lightly doped diamond layer 2 and the inner surface of groove 6 were etched with H plasma for 10 min. After etching, CH4 with a flow rate of 3-4 sccm and PH3 with a flow rate of 1.0-1.5 sccm were introduced to start selective growth. The growth time was 15-20 min to form a (111) crystal orientation heavily doped diamond layer 3, such as Figure 2c and Figure 2d As shown, by controlling the device power, cavity gas pressure, and CH4 concentration, selective growth will only occur in groove 6 and will not occur 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 1×10⁻⁶. 21 cm -3 .

[0060] In this embodiment, during selective growth, the methane concentration is reduced to 0.5% to 1% to ensure that diamond with the (111) crystal orientation is grown only in the groove 6, while no diamond is grown in the unetched areas.

[0061] S4: Remove hydrogen terminals from 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 was 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. This removed hydrogen terminals from the upper surfaces of the lightly doped diamond layer 2 and the heavily doped diamond layer 3, thereby eliminating their influence on the performance of the doped diamond.

[0063] S5: An ohmic electrode 4 is grown on the upper surface of the heavily doped diamond layer 3 after hydrogen terminals have been removed.

[0064] Metallic Ti with a thickness of 20–30 nm and metallic Au with a thickness of 90–100 nm were deposited from bottom to top on the entire upper surface of the sample after hydrogen removal using an electron beam evaporation apparatus.

[0065] Photolithography, including spin coating and photolithography, exposes the surface of the device except for the ohmic electrode region. After photolithography, the sample is placed in a potassium iodide solution to etch away the Au metal outside the ohmic electrode region. Then, the sample is immersed in a buffered oxide etchant (BOE) to etch away the Ti metal outside the ohmic electrode region. Subsequently, rapid thermal annealing (RTP) is used in a nitrogen atmosphere at 750°C for 300 seconds to establish good ohmic contact between the heavily doped diamond layer 3 and the metal, thus forming the ohmic electrode 4 on the upper surface of the heavily doped diamond layer 3. Figure 2e As shown.

[0066] The upper surface of the ohmic electrode 4 in this embodiment can be circular or square, such as... Figure 4 and Figure 5 As shown. 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 in this embodiment uses AZ6112 photoresist and SUSS MA / BA6 photolithography machine.

[0068] S6: A Schottky electrode 5 is grown on the upper surface of a lightly doped diamond layer 2 with hydrogen terminals removed, and an ohmic electrode 4 is spaced apart from the Schottky electrode 5.

[0069] Electron beam evaporation (EBE) was used to deposit a 90–100 nm thick layer of metallic Al on the entire upper surface of the sample. Photolithography, including spin coating and photolithography, exposed the area except for the Schottky electrode region. Then, a wet etching process was used, immersing the sample in a BOE solution for 15 minutes to etch away the metallic Al outside the Schottky electrode region, forming a lightly doped diamond layer 2 on which the Schottky electrode 5 was grown. Figure 2f As shown. The Schottky electrode 5 is a circular or square ring, surrounding the outside of the ohmic electrode 4 and spaced apart from it. In one specific embodiment, when the upper surface of the ohmic electrode 4 is also circular, the Schottky electrode 5 is a circular ring; when the upper surface of the ohmic electrode 4 is also square, the Schottky electrode 5 is a square ring, as shown. Figure 4 and Figure 5 As shown. In this embodiment, the Schottky contact uses an Al metal electrode, which can achieve a barrier height of 1.03V.

[0070] Another embodiment of the present invention provides a diamond diode with selectively controlled doping concentration during growth, see below. Figure 2f The diamond diode includes 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. The lightly doped diamond layer 2 is located on the upper surface of the intrinsic diamond substrate 1, and a groove 6 is formed on the upper surface of the lightly doped diamond layer 2. The heavily doped diamond layer 3 fills the groove 6, and the doping concentration of the heavily doped diamond layer 3 is 3 to 4 orders of magnitude higher than that of the lightly doped diamond layer 2. The ohmic electrode 4 is located on the upper surface of the heavily doped diamond layer 3, and the Schottky electrode 5 is located on the upper surface of the lightly doped diamond layer 2, with the ohmic electrode 4 and the Schottky electrode 5 spaced apart. The Schottky electrode 5 is ring-shaped and surrounds the outer side of the ohmic electrode 4.

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

[0072] This embodiment provides a method for fabricating diamond diodes with selectively controlled doping concentration based on the difference in doping efficiency between (100) and (111) diamonds under the same conditions. The technical solution utilizes the fact that the doping efficiency of the (111) crystal orientation of diamond is higher than that of the (100) crystal orientation under the same conditions. First, a lightly doped diamond layer with a low doping concentration is grown in the (100) crystal orientation, with a concentration as low as 1×10⁻⁶. 15 cm -3 Then, by selectively growing grooves on a lightly doped diamond layer with a low doping concentration, a heavily doped diamond layer 3 with a high doping concentration of up to 1×10⁻⁶ is grown on the (111) crystal plane of diamond. 21 cm -3 This method allows for the control of doping concentration, increasing the carrier concentration difference between the device's drift region and ohmic contact region to 4-5 orders of magnitude. This enables tunable doping with a large concentration difference, achieving the device performance of Schottky diodes. Furthermore, the lateral structure of Schottky diodes can improve the switching speed, enhance the reverse breakdown voltage, breakdown field strength, and forward conductivity, and reduce leakage current, thus effectively improving device performance.

[0073] This invention utilizes selective growth to control doping and solve the memory effect problem in phosphorus-doped diamond. When doping with other elements, selective growth can also address the memory effect, increasing the concentration difference between lightly and heavily doped layers. ICP oxygen plasma treatment is used to remove hydrogen terminals from the diamond surface, solving the problem of residual 2DHG after acid leaching to remove hydrogen terminals.

[0074] Example 2

[0075] Based on Example 1, this example provides a specific method for fabricating a diamond diode with selectively controlled doping concentration during growth. This method includes:

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

[0077] An intrinsic diamond substrate with a (100) crystal orientation of 5 mm × 5 mm × 0.5 mm was selected. Before use, the intrinsic diamond substrate was subjected to X-ray diffraction (XRD) and atomic force microscopy (AFM) tests 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 fabrication.

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

[0079] Step 2: Grow 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, phosphorus-doped diamond epitaxial growth was performed on an intrinsic diamond substrate using an MPCVD equipment. The intrinsic diamond substrate was placed in the MPCVD equipment, and the cavity pressure was evacuated to 0.001 mbar or below. H2 was introduced into the MPCVD equipment at a flow rate of 300 sccm. When the cavity pressure was increased to 15 mbar, the microwave source was turned on to ignite the substrate, raising the cavity pressure to 150 mbar with a power of 3200 W. The surface temperature of the intrinsic diamond substrate was 900 °C. Before growth, the surface of the intrinsic diamond substrate was etched with H plasma for 10 min. After etching, CH4 at a flow rate of 18 sccm and PH3 at a flow rate of 1.5 sccm were introduced to start growth. After 30 min, a lightly doped diamond layer with a (100) crystal orientation and a thickness of 600 nm was formed. The doping element was phosphorus with a doping concentration of 10. 16 cm -3 .

[0081] Step 3: Etch 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 homogenization and photolithography. After photolithography, the part of the upper surface of the lightly doped diamond layer without photoresist protection is etched using an ICP device. The ICP power is 150W, the RF power is 50W, the oxygen flow rate is 90sccm, the etching time is 3min, and the etching rate of ICP oxygen plasma etching is 140nm / min. This etches a groove in the center of the upper surface of the lightly doped diamond layer. The upper surface of the groove can be circular or square, and the depth is less than the thickness of the lightly doped diamond layer. Preferably, the depth of the groove can be 300-500nm.

[0083] Step 4: Selective growth is performed in the groove to form a heavily doped diamond layer with (111) crystal orientation.

[0084] Selective growth was performed in the groove using an MPCVD device. Specifically, the sample obtained in step 3 was placed into the MPCVD device, and the chamber pressure was evacuated to 0.001 mbar or below. H2 was introduced into the MPCVD device at a flow rate of 300 sccm. When the chamber pressure was increased to 15 mbar, the microwave source was turned on to ignite and raise the chamber pressure to 150 mbar. The power was 3200 W, and the sample surface temperature was 900 °C. The upper surface of the lightly doped diamond layer and the inner surface of the groove were etched using H plasma for 10 min. After etching, CH4 at a flow rate of 3 sccm and PH3 at a flow rate of 1.5 sccm were introduced to start selective growth. The growth time was 20 min, forming a (111) crystal orientation heavily doped diamond layer with phosphorus as the doping element and 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 groove and will not grow on other surfaces.

[0085] Step 5: Remove hydrogen terminals from the upper surface of the lightly doped diamond layer and the upper surface of the heavily doped diamond layer.

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

[0087] Step 6: Grow an ohmic electrode on the upper surface of the heavily doped diamond layer with hydrogen terminals removed.

[0088] Metal electrodes were deposited on the entire upper surface of the sample using electron beam evaporation (E-Beam) technology, consisting of a 30 nm thick Ti layer and a 100 nm thick Au layer from bottom to top. Subsequently, photolithography was performed through spin coating and photolithography to expose the surface of the device except for the ohmic electrode area. After photolithography, the sample was placed in a potassium iodide solution and left to stand for 4 seconds to complete the etching of the upper Au layer. Then, the sample was placed in a buffered oxide etchant (BOE) solution for 10 seconds to complete the etching of the lower Ti layer, thereby forming the ohmic electrode located on the upper surface of the heavily doped diamond layer.

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

[0090] Step 7: Grow a Schottky electrode on the upper surface of the lightly doped diamond layer with hydrogen terminals removed.

[0091] An Al layer with a thickness of 100 nm was deposited on the entire upper surface of the sample using an electron beam evaporation (E-Beam) device. Subsequently, a photolithography process was performed through spin coating and photolithography to expose the remaining parts except for the Schottky contacts. Then, a wet etching process was used to immerse the sample in a BOE solution for 15 min to etch away the Al metal outside the Schottky electrode area, forming a lightly doped diamond layer on the upper surface where the Schottky electrode was grown, thus completing the device fabrication.

[0092] Example 3

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

[0094] An intrinsic diamond substrate with a (100) crystal orientation of 5 mm × 5 mm × 0.5 mm was selected. Before use, the intrinsic diamond substrate was subjected to X-ray diffraction (XRD) and atomic force microscopy (AFM) tests 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 fabrication.

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

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

[0097] Boron-doped diamond epitaxial growth was performed on an intrinsic diamond substrate using an MPCVD (Multi-Phase Continuous Catalysis) device. The intrinsic diamond substrate was placed in the MPCVD device, and the cavity pressure was evacuated to 0.001 mbar or below. H2 was introduced into the MPCVD device at a flow rate of 300 sccm. When the cavity pressure was increased to 15 mbar, the microwave source was turned on to ignite the substrate, raising the cavity pressure to 150 mbar with a power of 3200 W. The surface temperature of the intrinsic diamond substrate was 900 °C. Before growth, the surface of the intrinsic diamond substrate was etched with H plasma for 10 min. After etching, CH4 at a flow rate of 18 sccm and B2H6 at a flow rate of 1.5 sccm were introduced. After 30 min of growth, a lightly doped diamond layer with a (100) crystal orientation and a thickness of 600 nm was formed. The doping element was boron (B) with a doping concentration of 10%. 16 cm -3 .

[0098] Step c: Etch grooves 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 homogenization and photolithography. After photolithography, the part of the upper surface of the lightly doped diamond layer without photoresist protection is etched using an ICP device. The ICP power is 150W, the RF power is 50W, the oxygen flow rate is 90sccm, the etching time is 3min, and the etching rate of the ICP oxygen plasma etching is 140nm / min, so that a groove is etched on the upper surface of the lightly doped diamond layer. The upper surface of the groove can be circular or square, and the depth is less than the thickness of the lightly doped diamond layer. Preferably, the depth of the groove can be 300-500nm.

[0100] Step d: Selective growth is performed in the groove to form a heavily doped diamond layer with (111) crystal orientation.

[0101] Selective growth was performed in the groove using an MPCVD device. Specifically, the sample obtained in step 3 was placed into the MPCVD device, and the chamber pressure was evacuated to 0.001 mbar or below. H2 was introduced into the MPCVD device at a flow rate of 300 sccm. When the chamber pressure was increased to 15 mbar, the microwave source was turned on to ignite and raise the chamber pressure to 150 mbar. The power was 3200 W, and the sample surface temperature was 900 °C. The upper surface of the lightly doped diamond layer and the inner surface of the groove were etched using H plasma for 10 min. After etching, CH4 at a flow rate of 3 sccm and B2H6 at a flow rate of 1.5 sccm were introduced to start growth. Selective growth began, and the growth time was 20 min, forming a (111) crystal orientation heavily doped diamond layer with boron (B) as the doping element and a doping concentration of 10. 21 cm -3By controlling the device power, chamber pressure, and CH4 concentration, selective growth will only occur in the groove and will not grow on other surfaces.

[0102] Step e: Remove hydrogen terminals from the upper surface of the lightly doped diamond layer and the upper surface of the heavily doped diamond layer.

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

[0104] Step f: An ohmic electrode is grown on the upper surface of the heavily doped diamond layer with hydrogen terminals removed.

[0105] Ti / Au metal electrodes were deposited on the entire upper surface of the sample using an electron beam evaporation process, with a Ti layer of 30 nm thickness and an Au layer of 100 nm thickness from bottom to top. Subsequently, a photolithography process was performed through spin coating and photolithography to expose the surface of the device except for the ohmic electrode area. After photolithography, the sample was placed in a potassium iodide solution and left to stand for 4 seconds to complete the etching of the upper Au layer. Then, the sample was placed in a buffer oxide etching solution for 10 seconds to complete the etching of the lower Ti layer, thereby forming the ohmic electrode located on the upper surface of the heavily doped diamond layer.

[0106] Subsequently, a rapid thermal annealing device was used to anneal at 750°C for 300 seconds under a nitrogen atmosphere, so that a good ohmic contact was formed between the heavily doped diamond layer and the metal.

[0107] Step g: A Schottky electrode is grown on the upper surface of a lightly doped diamond layer with hydrogen terminals removed.

[0108] An Al layer with a thickness of 100 nm was deposited on the entire upper surface of the sample using an electron beam evaporation device. Subsequently, a photolithography process was performed through spin coating and photolithography to expose the remaining parts except for the Schottky contacts. Then, a wet etching process was used to immerse the sample in a BOE solution for 15 min to etch away the Al metal outside the Schottky electrode area, forming a lightly doped diamond layer on the upper surface where the Schottky electrode was grown, thus completing the device fabrication.

[0109] The above description, in conjunction with specific preferred embodiments, provides a further detailed explanation of the present invention. It should not be construed that the specific implementation of the present invention is limited to these descriptions. For those skilled in the art, various simple deductions or substitutions can be made without departing from the concept of the present invention, and all such modifications and substitutions should be considered within the scope of protection of the present invention.

Claims

1. A method for fabricating a diamond diode with selectively controlled doping concentration during growth, characterized in that, include: S1: A lightly doped diamond layer with a (100) crystal orientation is grown on an intrinsic diamond substrate with a (100) crystal orientation, wherein the doping element of the lightly doped diamond layer is phosphorus or boron. S2: A groove is etched on the upper surface of the lightly doped diamond layer, the depth of which is less than the thickness of the lightly doped diamond layer; S3: Selective growth is performed in the groove to form a (111) crystal orientation heavily doped diamond layer, wherein the doping concentration of the heavily doped diamond layer is 4 to 5 orders of magnitude higher than that of the lightly doped diamond layer, and the heavily doped diamond layer and the lightly doped diamond layer have the same doping elements. S4: Remove hydrogen terminals from the upper surface of the lightly doped diamond layer and the upper surface of the heavily doped diamond layer; S5: An ohmic electrode is grown on the upper surface of the heavily doped diamond layer after hydrogen terminal removal; S6: A Schottky electrode is grown on the upper surface of a lightly doped diamond layer after hydrogen terminal removal, wherein the ohmic electrode and the Schottky electrode are spaced apart.

2. The method for fabricating a diamond diode with selectively controlled doping concentration according to claim 1, characterized in that, S1 includes: An intrinsic diamond substrate with (100) crystal orientation was selected and cleaned. A lightly doped diamond layer with a (100) crystal orientation was grown on the intrinsic diamond substrate using an MPCVD apparatus, wherein the doping concentration of the doping element was as low as 1 × 10⁻⁶. 15 cm -3 .

3. The method for fabricating a diamond diode with selectively controlled doping concentration according to claim 1, characterized in that, S2 includes: A groove is formed on the upper surface of the lightly doped diamond layer using an inductively coupled oxygen plasma etching process. 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 fabricating a diamond diode with selectively controlled doping concentration according to claim 3, characterized in that, The depth of the groove is 300~500nm.

5. The method for fabricating a diamond diode with selectively controlled doping concentration according to claim 1, characterized in that, S3 includes: A sample with grooves is placed in an MPCVD apparatus, where selective growth is performed to form a heavily doped diamond layer with a (111) crystal orientation. The doping concentration of the dopant element in the heavily doped diamond layer is up to 1 × 10⁻⁶. 21 cm -3 .

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

7. The method for fabricating a diamond diode with selectively controlled doping concentration according to claim 4, characterized in that, S5 includes: Metallic Ti with a thickness of 20-30 nm and metallic Au with a thickness of 90-100 nm were deposited from bottom to top on the entire upper surface of the sample after hydrogen removal using an electron beam evaporation device. Photolithography is performed by spin coating and photolithography to expose the upper surface of the sample except for the ohmic electrode area. After photolithography, the sample is placed in potassium iodide solution to stand and etch away the metal Au outside the ohmic electrode area. Then it is placed in buffer 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 metallic Ti, thereby forming an ohmic electrode on the upper surface of the heavily doped diamond layer.

8. The method for fabricating a diamond diode with selectively controlled doping concentration according to claim 4, characterized in that, S6 includes: Electron beam evaporation equipment is used to deposit a layer of metallic Al with a thickness of 90-100 nm on the entire upper surface of the sample. Photolithography is then performed by spin coating and photolithography to expose the remaining part except for the Schottky electrode region. Subsequently, the sample is placed in a buffer oxide etching solution to etch away the metallic Al outside the Schottky electrode region, forming the Schottky electrode on the upper surface of the lightly doped diamond layer.

9. A diamond diode with selectively controlled doping concentration during growth, characterized in that, The diamond diode is prepared using 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 formed on the upper surface of the lightly doped diamond layer, and the heavily doped diamond layer fills the groove. The doping concentration of the heavily doped diamond layer is 4 to 5 orders of magnitude higher than that of the lightly doped diamond layer. The ohmic electrode is located on the upper surface of the heavily doped diamond layer, and the Schottky electrode is located on the upper surface of the lightly doped diamond layer, with the ohmic electrode and the Schottky electrode spaced apart.

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

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