A method of fabricating a diamond semiconductor device

Abstract

The present application relates to the technical field of semiconductor devices, and particularly relates to a preparation method of a diamond semiconductor device. After film coating treatment is performed on a (001) crystal face of a diamond seed crystal, first calcination is performed, a high-concentration boron-doped p-type conductive epitaxial layer and a low-concentration boron-doped p-type conductive epitaxial layer are successively grown on the obtained pretreated (001) crystal face of the diamond seed crystal; after a mask is prepared on the surface of the low-concentration boron-doped p-type conductive epitaxial layer, evaporation of a transition metal, second calcination and etching are successively performed on the area without mask shielding, and an inclined-angle mesa of a (110) crystal face is obtained; after an n-type diamond layer is epitaxially grown on the (110) crystal face, the mask and the diamond seed crystal are removed, and an anode and a cathode are respectively prepared on the surfaces of the low-concentration boron-doped p-type conductive epitaxial layer and the high-concentration boron-doped p-type conductive epitaxial layer. The preparation method can avoid etching damage, improve the growth quality of the diamond, and improve the performance of the diamond semiconductor device.

Description

Technical Field

[0001] This invention relates to the field of semiconductor device technology, and in particular to a method for preparing a diamond semiconductor device. Background Technology

[0002] Diamond, the hardest material in nature, has important industrial applications, such as in fine abrasives, high-hardness cutting tools, and drill bits suitable for various applications. Its thermal conductivity is four times that of copper, making it an excellent heat dissipation material for electronic and laser technologies. While third-generation semiconductors are developing rapidly, fourth-generation semiconductor materials such as gallium oxide, aluminum nitride, and diamond are also gaining attention. Among them, diamond, as a novel wideband semiconductor material, exhibits better performance and a wider bandgap than third-generation semiconductor materials SiC and GaN, attracting increasing attention in ultraviolet detection and high-frequency power devices. Research has found that diamond is a material with a bandgap width of E... g Diamond is a wide-bandgap semiconductor with a voltage of 5.5 eV. It has good conductivity and light-emitting properties, so it has broad application prospects in optoelectronic devices. However, the industrial promotion of diamond still faces many challenges.

[0003] On the one hand, the high density of dislocations in current diamond epitaxial materials can lead to reduced carrier lifetime and leakage channels in actual device applications, affecting device performance. Therefore, reducing dislocation propagation is a crucial aspect of single-crystal growth. Shinya Ohmagari et al. (Appl. Phys. Lett. 114, 082104 (2019)) used HFCVD growth technology to dope tungsten, which reduced edge effects during splicing, mitigated the impact of growth dislocations on the uniformity of the spliced ​​pieces, and improved the subsequent crystal growth quality. However, other impurity elements are inevitably introduced during the growth process, affecting the subsequent glass production and use of diamond. Another approach is a lateral epitaxial growth scheme based on mask materials. The presence of the mask can suppress the further extension of dislocation defects beneath it.

[0004] On the other hand, diamond diodes typically require a pn junction to form an efficient junction termination structure. Currently, (100)-plane diamond has become the mainstream diode fabrication material due to its lower defect density, and it is possible to obtain p-type doped materials with controllable concentrations. In the fabrication of (100)-plane n-type doping, nitrogen dopants can only form very deep donor levels (approximately Ec-1.7 eV). Another alternative dopant, phosphorus atoms, form very deep donor levels (approximately Ec-0.57 eV), which results in insufficient activation of the dopant at room temperature. Exposing the (110) plane around the (100) plane through etching is beneficial for improving the n-type doping concentration and doping efficiency. However, due to the characteristics of diamond material such as wide band gap, high atomic density, and high material hardness, traditional plasma etching or laser cutting methods are not easy to control the etching angle and cause a large amount of etching damage. Summary of the Invention

[0005] The purpose of this invention is to provide a method for fabricating diamond semiconductor devices, which can avoid etching damage, improve the growth quality of diamond, and improve the performance of diamond semiconductor devices.

[0006] To achieve the above-mentioned objectives, the present invention provides the following technical solution:

[0007] This invention provides a method for fabricating a diamond semiconductor device, comprising the following steps:

[0008] Provide diamond seed crystals with a (001) crystal facet at the top;

[0009] After coating the (001) crystal plane of the diamond seed crystal, it is first calcined to obtain the pretreated diamond seed crystal.

[0010] A high-concentration boron-doped p-type conductive epitaxial layer and a low-concentration boron-doped p-type conductive epitaxial layer are sequentially grown on the (001) crystal plane of the pretreated diamond seed crystal; the hole concentration of the high-concentration boron-doped p-type conductive epitaxial layer is 1×10⁻⁶. 18 ~10 21 cm -3 The hole concentration of the low-concentration boron-doped p-type conductive epitaxial layer is 1×10⁻⁶. 14 ~10 18 cm -3 Furthermore, the hole concentration of the high-concentration boron-doped p-type conductive epitaxial layer is greater than the hole concentration of the low-concentration boron-doped p-type conductive epitaxial layer.

[0011] After preparing a mask on the surface of the low-concentration boron-doped p-type conductive epitaxial layer, the transition metal is sequentially deposited, the second calcination and etching are performed in the area without mask obstruction to obtain the oblique mesa of the (110) crystal plane.

[0012] After epitaxially growing an n-type diamond layer on the (110) crystal plane, the mask and diamond seed crystal are removed, and positive and negative electrodes are prepared on the surfaces of the low-concentration boron-doped p-type conductive epitaxial layer and the high-concentration boron-doped p-type conductive epitaxial layer, respectively, to obtain the diamond semiconductor device.

[0013] Preferably, before performing the coating process, the diamond seed crystal is further subjected to pretreatment.

[0014] The pretreatment includes polishing, acid immersion, and ultrasonic cleaning of the diamond seed crystal in sequence.

[0015] Preferably, the coating obtained by the coating process is a transition metal film;

[0016] The thickness of the transition metal film is 50–200 nm.

[0017] Preferably, the coating process has a power of 100-500W and a time of 5-30 minutes.

[0018] Preferably, the first calcination is carried out in a protective atmosphere;

[0019] The first calcination temperature is 750–1100℃, and the holding time is 0.5–5h.

[0020] Preferably, after the first calcination is completed, the process further includes cleaning the pretreated diamond seed crystal in an acid solution and then soaking it in aqua regia.

[0021] Preferably, the method for growing the high-concentration boron-doped p-type conductive epitaxial layer is microwave plasma chemical vapor deposition;

[0022] The growth gas for growing the high-concentration boron-doped p-type conductive epitaxial layer is methane, with a volume concentration of 1-5%; the doping gas is trimethylboron, with a molar ratio of B in trimethylboron to C in methane of (100-1000)*10. -6 :1; growth power is 1800~2500W, growth temperature is 800~1000℃, growth pressure is 100~200torr, hydrogen flow rate is 300~1000sccm, and oxygen volume concentration is 0.5~1‰.

[0023] Preferably, the method for growing the low-concentration boron-doped p-type conductive epitaxial layer is microwave plasma chemical vapor deposition;

[0024] The growth gas for growing the low-concentration boron-doped p-type conductive epitaxial layer is methane, with a volume concentration of 1-5%; the doping gas is trimethylboron, with a molar ratio of B in trimethylboron to C in methane of (100-1000)*10.-6 :1; growth power is 1800~2500W, growth temperature is 800~1000℃, growth pressure is 100~200torr, hydrogen flow rate is 300~1000sccm, and oxygen volume concentration is 0.5~1‰.

[0025] Preferably, the material of the mask is Au, Pt, Al, SiO2 or SiN.

[0026] Preferably, a Schottky contact is formed between the surface of the low-concentration boron-doped p-type conductive epitaxial layer and the positive electrode;

[0027] An ohmic contact is formed between the surface of the high-concentration boron-doped p-type conductive epitaxial layer and the negative electrode.

[0028] This invention provides a method for fabricating a diamond semiconductor device, comprising the following steps: providing a diamond seed crystal with a (001) crystal plane as the top surface; performing a coating treatment on the (001) crystal plane of the diamond seed crystal, followed by a first calcination to obtain a pretreated diamond seed crystal; sequentially growing a high-concentration boron-doped p-type conductive epitaxial layer and a low-concentration boron-doped p-type conductive epitaxial layer on the (001) crystal plane of the pretreated diamond seed crystal; wherein the hole concentration of the high-concentration boron-doped p-type conductive epitaxial layer is 1×10⁻⁶. 18 ~10 21 cm -3 The hole concentration of the low-concentration boron-doped p-type conductive epitaxial layer is 1×10⁻⁶. 14 ~10 18 cm -3Furthermore, the hole concentration of the high-concentration boron-doped p-type conductive epitaxial layer is greater than that of the low-concentration boron-doped p-type conductive epitaxial layer. After preparing a mask on the surface of the low-concentration boron-doped p-type conductive epitaxial layer, the transition metal is sequentially deposited, a second calcination and etching are performed in the unmasked area to obtain the beveled mesa of the (110) crystal plane. After epitaxially growing an n-type diamond layer on the (110) crystal plane, the mask and diamond seed crystal are removed, and positive and negative electrodes are prepared on the surfaces of the low-concentration boron-doped p-type conductive epitaxial layer and the high-concentration boron-doped p-type conductive epitaxial layer, respectively, to obtain the diamond semiconductor device. This invention is based on the difference in the dissolution effect of transition metals on different diamond lattice structures and crystal planes, where dissolution preferentially occurs in regions with more dislocations at high temperatures. Due to the low solubility of the (110) plane, the dissolution reaction between the metal and diamond self-stops at the (110) crystal plane, forming inverted pyramid-shaped etch pits. Combined with lateral epitaxy, dislocations in the seed crystal are deflected or annihilated at the pits and no longer continue to inherit upwards, effectively reducing the dislocation density in the upper epitaxial layer. Similarly, with the assistance of a mask, a transition metal layer is formed in a selected region. The high-temperature dissolution effect can form (110) inclined steps around the (100) crystal plane, laying the foundation for realizing a high-concentration n-type doped junction terminal structure. Attached Figure Description

[0029] Figure 1 This is a schematic diagram illustrating the preparation of pretreated diamond seed crystals according to the present invention;

[0030] Figure 2 These are actual images of the object before and after etching as described in Embodiment 1 of the present invention;

[0031] Figure 3 The XRD rocking curves before and after etching as described in Embodiment 1 of the present invention;

[0032] Figure 4 This is a schematic diagram of the structure of the diamond semiconductor device prepared according to the present invention. Detailed Implementation

[0033] This invention provides a method for fabricating a diamond semiconductor device, comprising the following steps:

[0034] Provide diamond seed crystals with a (001) crystal facet at the top;

[0035] After coating the (001) crystal plane of the diamond seed crystal, it is first calcined to obtain the pretreated diamond seed crystal.

[0036] A high-concentration boron-doped p-type conductive epitaxial layer and a low-concentration boron-doped p-type conductive epitaxial layer are sequentially grown on the (001) crystal plane of the pretreated diamond seed crystal; the hole concentration of the high-concentration boron-doped p-type conductive epitaxial layer is 1×10⁻⁶.18 ~10 21 cm -3 The hole concentration of the low-concentration boron-doped p-type conductive epitaxial layer is 1×10⁻⁶. 14 ~10 18 cm -3 Furthermore, the hole concentration of the high-concentration boron-doped p-type conductive epitaxial layer is greater than the hole concentration of the low-concentration boron-doped p-type conductive epitaxial layer.

[0037] After preparing a mask on the surface of the low-concentration boron-doped p-type conductive epitaxial layer, the transition metal is sequentially deposited, the second calcination and etching are performed in the area without mask obstruction to obtain the oblique mesa of the (110) crystal plane.

[0038] After epitaxially growing an n-type diamond layer on the (110) crystal plane, the mask and diamond seed crystal are removed, and positive and negative electrodes are prepared on the surfaces of the low-concentration boron-doped p-type conductive epitaxial layer and the high-concentration boron-doped p-type conductive epitaxial layer, respectively, to obtain the diamond semiconductor device.

[0039] In this invention, unless otherwise specified, all raw materials used in the preparation are commercially available products well known to those skilled in the art.

[0040] The present invention provides a diamond seed crystal with a (001) crystal facet on the top surface.

[0041] In this invention, the diamond seed crystal is preferably an HPHT diamond seed crystal or a CVD seed crystal.

[0042] The preparation method of the present invention further includes coating the (001) crystal surface of the diamond seed crystal and then calcining it to obtain the pretreated diamond seed crystal.

[0043] Before performing the coating process, the present invention preferably includes pretreatment of the diamond seed crystal; the pretreatment preferably includes sequentially polishing, acid immersion, and ultrasonic cleaning of the diamond seed crystal. The present invention does not impose any special limitations on the polishing process; any process well-known to those skilled in the art can be used. In an embodiment of the present invention, the polishing method is grinding polishing. In the present invention, the mass concentration of the acid solution used for acid immersion is preferably 10-30%, more preferably 15-25%, and most preferably 18-22%; the acid solution is preferably one or more of hydrochloric acid, sulfuric acid, and nitric acid; more preferably a mixture of nitric acid and sulfuric acid; the mixture of nitric acid and sulfuric acid is preferably obtained by mixing sulfuric acid with a mass concentration of 98% and nitric acid with a mass concentration of 65%; the volume ratio of sulfuric acid to nitric acid is preferably (40-50):(50-60), more preferably 51:49, 45:55, or 49:51. In this invention, the acid immersion temperature is preferably 35–75°C, more preferably 45–65°C, and most preferably 50–55°C; the immersion time is preferably 12–24 h, more preferably 14–22 h, and most preferably 16–20 h. In this invention, the ultrasonic cleaning agent is preferably acetone. This invention does not impose any special limitations on the frequency and time of the ultrasonic cleaning; frequencies and times well-known to those skilled in the art can be used to ensure the removal of metallic or organic impurities from the surface of the polished diamond seed crystal.

[0044] During the coating process, the present invention preferably uses high-temperature resistant tape to cover the bottom and sides of the diamond seed crystal.

[0045] In this invention, the coating treatment method is preferably electron beam evaporation, magnetron sputtering, or atomic layer deposition.

[0046] In this invention, the power of the coating process is preferably 100-500W, more preferably 150-450W, and most preferably 200-400W; the time is preferably 5-30min, more preferably 10-25min, and most preferably 15-20W.

[0047] In this invention, the coating obtained by the coating process is preferably a transition metal film, and the transition metal in the transition metal film is preferably iron, cobalt, or nickel. In this invention, the thickness of the transition metal film is preferably 50–200 nm, more preferably 80–160 nm, and most preferably 100–130 nm.

[0048] In this invention, the purpose of the coating treatment is to treat defects on the surface itself and defects introduced by polishing, which is beneficial to improving the subsequent growth quality.

[0049] In this invention, the first calcination is preferably carried out in a protective atmosphere, preferably a nitrogen atmosphere or an argon atmosphere. In this invention, the protective atmosphere can prevent the coating from oxidizing in air.

[0050] In this invention, the temperature of the first calcination is preferably 750-1100℃, more preferably 800-1000℃, and most preferably 850-950℃; the holding time is preferably 0.5-5h, more preferably 0.8-4h, and most preferably 1-3h.

[0051] In this invention, during the first calcination process, the transition metal film undergoes a dissolution reaction with the diamond, exposing the dislocation pits in the substrate first, so as to achieve lateral epitaxy, realize the large-angle bending of dislocations, and reduce the genetic effect of dislocations.

[0052] After the first calcination is completed, the process also includes cleaning the pretreated diamond seed crystal in an acid solution and then soaking it in aqua regia.

[0053] In this invention, the mass concentration of the acid solution used for acid immersion is preferably 10-30%, more preferably 15-25%, and most preferably 18-22%. The acid solution is preferably one or more of hydrochloric acid, sulfuric acid, and nitric acid; more preferably a mixture of nitric acid and sulfuric acid. The mixture of nitric acid and sulfuric acid is preferably obtained by mixing sulfuric acid with a mass concentration of 98% and nitric acid with a mass concentration of 65%. The volume ratio of sulfuric acid to nitric acid is preferably (40-50):(50-60), more preferably 51:49, 48:52, or 50:50. In this invention, the cleaning time is preferably 12-24 hours, more preferably 15-21 hours, and most preferably 17-19 hours. In this invention, the cleaning is preferably performed under ultrasonic conditions. This invention does not impose any special limitations on the ultrasonic conditions; conditions well known to those skilled in the art can be used. In this invention, the purpose of the cleaning is to remove undissolved or partially oxidized metals from the surface of the diamond seed crystal, preventing passivation in strong acid.

[0054] In this invention, the soaking time in the aqua regia is preferably 12 to 24 hours, more preferably 16 to 20 hours.

[0055] In this invention, the purpose of soaking in aqua regia is to remove excess metallic nickel and graphite phases from the surface to prevent them from affecting the next step of single crystal growth.

[0056] After obtaining the pretreated diamond seed crystal, the present invention sequentially grows a high-concentration boron-doped p-type conductive epitaxial layer and a low-concentration boron-doped p-type conductive epitaxial layer on the (001) crystal plane of the pretreated diamond seed crystal; the hole concentration of the high-concentration boron-doped p-type conductive epitaxial layer is 1×10⁻⁶. 18~10 21 cm -3 The hole concentration of the low-concentration boron-doped p-type conductive epitaxial layer is 1×10⁻⁶. 14 ~10 18 cm -3 Furthermore, the hole concentration of the high-concentration boron-doped p-type conductive epitaxial layer is greater than the hole concentration of the low-concentration boron-doped p-type conductive epitaxial layer.

[0057] In this invention, the method for growing the high-concentration boron-doped p-type conductive epitaxial layer is preferably microwave plasma chemical vapor deposition (MPCVD); the growth gas for growing the high-concentration boron-doped p-type conductive epitaxial layer is preferably methane, and the volume concentration of the methane is preferably 1-5%, more preferably 2-4%, and most preferably 2.5-3.5%; the doping gas is preferably trimethylboron, and the molar ratio of B in the trimethylboron to C in the methane is preferably (100-1000)*10. -6 :1, more preferably (300~700)*10 -6 :1, the optimal value is (400~600)*10 -6 The growth power is preferably 1800–2500 W, more preferably 2000–2200 W; the growth temperature is preferably 800–1000℃, more preferably 850–950℃, and most preferably 880–920℃; the growth pressure is preferably 100–200 torr, more preferably 120–180 torr, and most preferably 140–160 torr; the hydrogen flow rate is preferably 300–1000 sccm, more preferably 400–800 sccm, and most preferably 500–600 sccm; the oxygen volume concentration is preferably 0.5–1‰. In this invention, the hydrogen and oxygen are used to etch the non-diamond phase and improve the growth quality.

[0058] In this invention, the thickness of the high-concentration boron-doped p-type conductive epitaxial layer is preferably 1.5–4 μm, more preferably 2–3.5 μm, and most preferably 3–3.3 μm; the hole concentration is preferably 1 × 10⁻⁶. 18 ~10 21 cm -3 More preferably, the hole concentration is 1×10 19 ~10 20 cm -3 The preferred boron doping concentration is 10. -6 ~10 -16 cm -3 More preferably 10 -9 ~10 -14 cm -3 .

[0059] In this invention, the method for growing the low-concentration boron-doped p-type conductive epitaxial layer is preferably microwave plasma chemical vapor deposition (MPCVD); the growth gas for growing the low-concentration boron-doped p-type conductive epitaxial layer is preferably methane, and the volume concentration of the methane is preferably 1-5%, more preferably 2-4%, and most preferably 2.5-3.5%; the doping gas is preferably trimethylboron, and the molar ratio of B in the trimethylboron to C in the methane is preferably (100-1000)*10. -6 :1, more preferably (300~700)*10 -6 :1, the optimal value is (400~600)*10 -6 The growth power is preferably 1800–2500 W, more preferably 2000–2200 W; the growth temperature is preferably 800–1000℃, more preferably 850–950℃, and most preferably 880–920℃; the growth pressure is preferably 100–200 torr, more preferably 120–180 torr, and most preferably 140–160 torr; the hydrogen flow rate is preferably 300–1000 sccm, more preferably 400–800 sccm, and most preferably 500–600 sccm; the oxygen volume concentration is preferably 0.5–1‰. In this invention, the hydrogen and oxygen are used to etch the non-diamond phase and improve the growth quality.

[0060] In this invention, the thickness of the low-concentration boron-doped p-type conductive epitaxial layer is preferably 0.3–2.5 μm, more preferably 0.5–1.8 μm, and most preferably 0.8–1.2 μm; the hole concentration is preferably 1 × 10⁻⁶. 14 ~10 18 cm -3 More preferably, the hole concentration is 1×10 15 ~10 17 cm -3 The preferred boron doping concentration is 10. -12 ~10 -20 cm -3 More preferably 10 -15 ~10 -19 cm -3 .

[0061] In this invention, the sequential arrangement of the high-concentration boron-doped p-type conductive epitaxial layer and the low-concentration boron-doped p-type conductive epitaxial layer serves as the drift layer and substrate of the diode, respectively. After the first calcination and cleaning, re-growth occurs; due to the lateral epitaxy, defects can be masked or offset at large angles, resulting in a diamond layer of higher quality.

[0062] After obtaining the high-concentration boron-doped p-type conductive epitaxial layer and the low-concentration boron-doped p-type conductive epitaxial layer, the present invention prepares a mask on the surface of the low-concentration boron-doped p-type conductive epitaxial layer, and then sequentially performs evaporation of transition metal, second calcination and etching in the area without mask obstruction to obtain the oblique mesa of the (110) crystal plane.

[0063] In this invention, the mask material is preferably Au, Pt, Al, SiO2, or SiN. In this invention, the mask material does not react with the diamond semiconductor material at the interface. The high-concentration boron-doped p-type conductive epitaxial layer serves as a substrate layer in the device, and the low-concentration boron-doped p-type conductive epitaxial layer serves as a buffer layer in the device.

[0064] In this invention, the shape of the mask is preferably square.

[0065] The present invention does not impose any special limitations on the preparation of the mask; any method known to those skilled in the art can be used.

[0066] In this invention, the transition metal is preferably iron, cobalt, or nickel.

[0067] The present invention does not impose any special limitations on the vapor deposition process; any process well known to those skilled in the art can be used.

[0068] In this invention, the thickness of the transition metal is preferably 10-200 nm, more preferably 30-150 nm, and most preferably 80-120 nm.

[0069] In this invention, the function of vapor-depositing the transition metal is to enable the transition metal to undergo a carbonization reaction during the high-temperature etching stage, forming a slanted etched surface with a 110 crystal plane, which is helpful for subsequent slanted doping.

[0070] In this invention, the second calcination is preferably carried out in a protective atmosphere, preferably a nitrogen atmosphere. In this invention, the protective atmosphere can cause the coating to oxidize in air, thereby affecting subsequent growth and doping quality.

[0071] In this invention, the second calcination temperature is preferably 700-1100℃, more preferably 750-1100℃, and most preferably 880-920℃; the holding time is preferably 1-6h, more preferably 2-5h, and most preferably 3-4h.

[0072] In this invention, the purpose of the second calcination is to utilize the dissolution effect of metallic nickel in diamond, so that the etching rate of the (100) facet diamond is faster than that of the (110) facet, thereby forming a beveled structure.

[0073] In this invention, the etching conditions are preferably etched at 900°C for 3 hours in a nitrogen atmosphere.

[0074] In this invention, the etching process exposes the 110 crystal plane in the diamond, which facilitates subsequent n-type doping or ion implantation. 。

[0075] After obtaining the beveled mesa of the (110) crystal plane, the present invention epitaxially grows an n-type diamond layer on the (110) crystal plane, removes the mask and diamond seed crystal, and prepares positive and negative electrodes on the surfaces of the low-concentration boron-doped p-type conductive epitaxial layer and the high-concentration boron-doped p-type conductive epitaxial layer, respectively, to obtain the diamond semiconductor device.

[0076] The present invention does not impose any special limitations on the process of removing the mask; any process known to those skilled in the art can be used.

[0077] In this invention, the n-type doping concentration of the n-type diamond layer is preferably 10. -12 ~10 -25 cm -3 More preferably 10 -14 ~10 -20 cm -3 The optimal value is 10. -16 ~10 -19 cm -3 The thickness of the n-type diamond layer is preferably 20–500 nm, more preferably 50–300 nm, and most preferably 80–150 nm.

[0078] In this invention, the method for epitaxially growing an n-type diamond layer on the (110) crystal plane is preferably microwave plasma chemical vapor deposition (MPCVD).

[0079] In this invention, the preferred conditions for growing the n-type diamond layer are: a growth power of 2100-2200W, a growth pressure of 140 torr, a growth temperature of 880-910℃, a methane volume concentration of 3-3.2%, a hydrogen flow rate of 400-500 sccm, and an oxygen volume concentration of 0.8-1.2‰.

[0080] In this invention, a Schottky contact is preferably used between the surface of the low-concentration boron-doped p-type conductive epitaxial layer and the positive electrode; an ohmic contact is preferably used between the surface of the high-concentration boron-doped p-type conductive epitaxial layer and the negative electrode.

[0081] The present invention does not impose any special limitations on the preparation process of the cathode and anode, and any process known to those skilled in the art can be used.

[0082] In this invention, the structure of the diamond semiconductor device is as follows: Figure 4As shown, it includes a heavily doped p-type diamond substrate, a lightly doped p-type diamond buffer layer, and an n-type doped diamond bevel junction termination.

[0083] The following detailed description of the preparation method of the diamond semiconductor device provided by the present invention, in conjunction with the embodiments, should not be construed as limiting the scope of protection of the present invention.

[0084] Example 1

[0085] After polishing the HPHT diamond seed crystal with the (001) crystal facet, it is first immersed in a 20% dilute acid solution (a 98% sulfuric acid and a 65% nitric acid with a volume ratio of 40:60) for 12 hours, and then ultrasonically cleaned with acetone to remove metal and organic impurities introduced during polishing or handling.

[0086] The bottom and sides of the HPHT diamond seed crystal were covered with high-temperature resistant tape and then placed in a magnetron sputtering device for coating treatment. The coating power was 100W and the time was 5min, resulting in a coating with a thickness of 50nm (the coating material is nickel metal).

[0087] The coated HPHT diamond seed crystal was placed in a tube furnace and calcined at 850°C for 1 hour in a protective atmosphere (specifically nitrogen atmosphere). Figure 1 As shown, the seed crystal was ultrasonically cleaned for 17 hours in a 20% dilute acid solution (a volume ratio of 51:49 of 98% sulfuric acid and 65% nitric acid) to remove undissolved or partially oxidized metals from the surface of the seed crystal and to prevent passivation in strong acid. The seed crystal was then transferred to aqua regia and soaked for 12 hours to obtain the cleaned seed crystal.

[0088] The cleaned seed crystal was transferred to a diamond growth layer with fewer planar defects in MPCVD. The growth power was 2000 W, the temperature was 800 °C, the growth pressure was 160 torr, the hydrogen flow rate was 500 sccm, the methane (growth gas) volume concentration was 3%, the oxygen volume concentration was 0.5‰, and the molar ratio of B in the trimethylboron to C in the methane was 200*10. -6 :1, A high-concentration boron-doped p-type conductive epitaxial layer was obtained (the boron doping concentration was 5*10). -12 cm -3 The thickness is 3μm and the hole concentration is 10. 19 cm -3 Then; change the molar ratio of B in the trimethylboron to C in the methane to 100*10. -6 1. Under otherwise unchanged conditions, a low-concentration boron-doped p-type conductive epitaxial layer was obtained (the boron doping concentration was 1*10⁻⁶). -12 cm-3 The thickness is 0.8 μm, and the hole concentration is 1*10. 16 cm -3 );

[0089] After preparing a mask on the surface of the low-concentration boron-doped p-type conductive epitaxial layer, a transition metal (nickel metal with a thickness of 100 nm) is deposited in the unmasked area, followed by calcination (calcination temperature of 900 °C for 3 h), and etching (etching conditions: calcination in a nitrogen atmosphere at a temperature of 900 °C for 3 h) to form a beveled mesa of the (110) crystal plane. Then, a highly concentrated doped n-type diamond (100 nm thick, n-type doping concentration of 10) is epitaxially grown on this crystal plane. -18 cm -3 After growth at 880℃, 140 torr, 2200W, 3% methane volume concentration, 400 sccm hydrogen flow rate, and 1.0‰ oxygen volume concentration, a terminal extended structure (such as...) is finally formed. Figure 4 As shown), after removing the mask and diamond seed crystal, positive and negative electrodes are prepared on the surfaces of the low-concentration boron-doped p-type conductive epitaxial layer and the high-concentration boron-doped p-type conductive epitaxial layer, respectively. A Schottky contact is formed between the surface of the low-concentration boron-doped p-type conductive epitaxial layer and the positive electrode; an ohmic contact is formed between the surface of the high-concentration boron-doped p-type conductive epitaxial layer and the negative electrode, thus obtaining a diamond semiconductor device.

[0090] Example 2

[0091] After polishing the HPHT diamond seed crystal with the (001) crystal facet, it is first immersed in a 21% dilute acid solution (a 98% sulfuric acid and a 65% nitric acid with a volume ratio of 45:55) for 18 hours, and then ultrasonically cleaned with acetone to remove metal and organic impurities introduced during polishing or handling.

[0092] The bottom and sides of the HPHT diamond seed crystal were covered with high-temperature resistant tape and placed in a magnetron sputtering device for coating treatment. The coating power was 200W and the time was 10min, resulting in a coating with a thickness of 80nm (the material of the coating is iron).

[0093] The coated HPHT diamond seed crystal was placed in a tube furnace and calcined at 900°C for 2 hours in a protective atmosphere (specifically nitrogen atmosphere). Figure 1As shown, the seed crystal was ultrasonically cleaned in a 21% dilute acid solution (a volume ratio of 48:52 of 98% sulfuric acid and 65% nitric acid) to remove undissolved or partially oxidized metals from the surface of the seed crystal and prevent passivation in strong acid. The seed crystal was then transferred to aqua regia and soaked for 18 hours to obtain the cleaned seed crystal.

[0094] The cleaned seed crystal was transferred to a diamond growth layer with fewer planar defects in MPCVD. The growth power was 2300 W, the temperature was 850 °C, the growth pressure was 180 torr, the hydrogen flow rate was 400 sccm, the methane (growth gas) volume concentration was 4%, the oxygen volume concentration was 0.6‰, and the molar ratio of B in the trimethylboron to C in the methane was 400*10. -6 :1, A high-concentration boron-doped p-type conductive epitaxial layer was obtained (the boron doping concentration was 5*10). -11 cm -3 The thickness is 1.2 μm, and the hole concentration is 3*10. -19 cm -3 After that, the molar ratio of B in the trimethylboron to C in the methane was changed to 300*10. -6 1. Under otherwise unchanged conditions, a low-concentration boron-doped p-type conductive epitaxial layer was obtained (the boron doping concentration was 1*10⁻⁶). -11 cm -3 The thickness is 3.2 μm, and the hole concentration is 3*10. -16 cm -3 );

[0095] After preparing a mask on the surface of the low-concentration boron-doped p-type conductive epitaxial layer, a transition metal (iron with a thickness of 110 nm) is deposited in the unmasked area, followed by calcination (at a temperature of 910 °C for 3.5 h) and etching (calcination is carried out in a nitrogen atmosphere at a temperature of 900 °C for 3 h) to form a beveled mesa of the (110) crystal plane. Then, a highly concentrated doped n-type diamond (120 nm thick, n-type doping concentration of 5*10⁻⁶) is epitaxially grown on this crystal plane. -18 cm -3 After growth at 910℃, 155 torr, 200W, 3.2% methane volume concentration, 450 sccm hydrogen flow rate, and 0.8‰ oxygen volume concentration, a terminal extended structure (such as...) is finally formed. Figure 4As shown), after removing the mask and diamond seed crystal, positive and negative electrodes are prepared on the surfaces of the low-concentration boron-doped p-type conductive epitaxial layer and the high-concentration boron-doped p-type conductive epitaxial layer, respectively. A Schottky contact is formed between the surface of the low-concentration boron-doped p-type conductive epitaxial layer and the positive electrode; an ohmic contact is formed between the surface of the high-concentration boron-doped p-type conductive epitaxial layer and the negative electrode, thus obtaining a diamond semiconductor device.

[0096] Example 3

[0097] After polishing the CVD diamond seed crystal with the (001) crystal facet, it is first immersed in a 22% dilute acid solution (a 98% sulfuric acid and a 65% nitric acid with a volume ratio of 49:51) for 24 hours, and then ultrasonically cleaned with acetone to remove metal and organic impurities introduced during polishing or handling.

[0098] The bottom and sides of the HPHT diamond seed crystal were covered with high-temperature resistant tape and then placed in a magnetron sputtering device for coating treatment. The coating power was 500W and the time was 30min, resulting in a coating with a thickness of 200nm (the material of the coating was cobalt).

[0099] The coated HPHT diamond seed crystal was placed in a tube furnace and calcined at 950°C for 3 hours in a protective atmosphere (specifically nitrogen atmosphere). Figure 1 As shown, the seed crystal was ultrasonically cleaned for 19 hours in a 22% (volume ratio of 98% sulfuric acid and 65% nitric acid) solution to remove undissolved or partially oxidized metals from the surface of the seed crystal and to prevent passivation in strong acid. The seed crystal was then transferred to aqua regia and soaked for 24 hours to obtain the cleaned seed crystal.

[0100] The cleaned seed crystal was transferred to a diamond growth layer with fewer planar defects in MPCVD. The growth power was 2200W, the temperature was 915℃, the growth pressure was 160 torr, the hydrogen flow rate was 600 sccm, the methane (growth gas) volume concentration was 3.5%, the oxygen volume concentration was 1‰, and the trimethylboron (doping gas) concentration was 5*10. -10 cm -3 The molar ratio of B in the trimethylboron to C in the methane is 600*10. -6 :1, A high-concentration boron-doped p-type conductive epitaxial layer was obtained (the boron doping concentration was 5*10). -10 cm -3 The thickness is 3.3 μm, and the hole concentration is 5*10. -19 cm -3 After that, the concentration of trimethylboron (doped gas) was changed to 1*10. -10 cm-3 The molar ratio of B in the trimethylboron to C in the methane is 500*10. -6 1. Under otherwise unchanged conditions, a low-concentration boron-doped p-type conductive epitaxial layer was obtained (the boron doping concentration was 1*10⁻⁶). -10 cm -3 The thickness is 1.2 μm, and the hole concentration is 5*10⁻⁶. -16 cm -3 );

[0101] After preparing a mask on the surface of the low-concentration boron-doped p-type conductive epitaxial layer, a transition metal (cobalt, 120 nm thick) is deposited in the unmasked area, followed by calcination (at 920°C for 4 hours in a nitrogen atmosphere), and etching (calcination is performed in a nitrogen atmosphere at 900°C for 3 hours) to form a beveled mesa of the (110) crystal plane. Then, a highly concentrated doped n-type diamond (130 nm thick, n-type doping concentration 1*10) is epitaxially grown on this crystal plane. -17 cm -3 After growth at 920℃, 160 torr, 2000 W, 3.1% methane volume concentration, 500 sccm hydrogen flow rate, and 1.2‰ oxygen volume concentration, a terminal extended structure (such as...) is finally formed. Figure 4 As shown), after removing the mask and diamond seed crystal, positive and negative electrodes are prepared on the surfaces of the low-concentration boron-doped p-type conductive epitaxial layer and the high-concentration boron-doped p-type conductive epitaxial layer, respectively. A Schottky contact is formed between the surface of the low-concentration boron-doped p-type conductive epitaxial layer and the positive electrode; an ohmic contact is formed between the surface of the high-concentration boron-doped p-type conductive epitaxial layer and the negative electrode, thus obtaining a diamond semiconductor device.

[0102] Test case

[0103] Figure 2 These are actual images of the object before and after etching as described in Embodiment 1 of the present invention; by Figure 2 It can be seen that the etching process does not hinder the secondary growth of the seed crystal, and a relatively obvious step flow growth state can still be grown, indicating that the growth state is excellent.

[0104] Figure 3 The XRD rocking curves before and after etching as described in Embodiment 1 of the present invention are obtained from... Figure 3 It can be seen that after the second growth, the full width at half maximum (FWHM) of the XRD decreased from 160 to 99, indicating that the dislocation density was significantly reduced and the crystal quality was improved.

[0105] The above description is only a preferred embodiment of the present invention. It should be noted that for those skilled in the art, several improvements and modifications can be made without departing from the principle of the present invention, and these improvements and modifications should also be considered within the scope of protection of the present invention.

Claims

1. A method for fabricating a diamond semiconductor device, characterized in that, Includes the following steps: Provide diamond seed crystals with a (001) crystal facet at the top; After coating the (001) crystal plane of the diamond seed crystal, it is first calcined to obtain the pretreated diamond seed crystal. A high-concentration boron-doped p-type conductive epitaxial layer and a low-concentration boron-doped p-type conductive epitaxial layer are sequentially grown on the (001) crystal plane of the pretreated diamond seed crystal; the hole concentration of the high-concentration boron-doped p-type conductive epitaxial layer is 1×10⁻⁶. 18 ~10 21 cm -3 The hole concentration of the low-concentration boron-doped p-type conductive epitaxial layer is 1×10⁻⁶. 14 ~10 18 cm -3 Furthermore, the hole concentration of the high-concentration boron-doped p-type conductive epitaxial layer is greater than the hole concentration of the low-concentration boron-doped p-type conductive epitaxial layer. After preparing a mask on the surface of the low-concentration boron-doped p-type conductive epitaxial layer, the transition metal is sequentially deposited, the second calcination and etching are performed in the area without mask obstruction to obtain the oblique mesa of the (110) crystal plane. After epitaxially growing an n-type diamond layer on the (110) crystal plane, the mask and diamond seed crystal are removed, and positive and negative electrodes are prepared on the surfaces of the low-concentration boron-doped p-type conductive epitaxial layer and the high-concentration boron-doped p-type conductive epitaxial layer, respectively, to obtain the diamond semiconductor device.

2. The preparation method according to claim 1, characterized in that, Before performing the coating process, the diamond seed crystal is also pretreated. The pretreatment includes polishing, acid immersion, and ultrasonic cleaning of the diamond seed crystal in sequence.

3. The preparation method according to claim 1, characterized in that, The coating obtained by the coating process is a transition metal film; The thickness of the transition metal film is 50–200 nm.

4. The preparation method according to claim 1 or 3, characterized in that, The coating process has a power of 100-500W and a time of 5-30 minutes.

5. The preparation method according to claim 1, characterized in that, The first calcination is carried out in a protective atmosphere; The first calcination temperature is 750–1100℃, and the holding time is 0.5–5h.

6. The preparation method according to claim 1, characterized in that, After the first calcination is completed, the process also includes cleaning the pretreated diamond seed crystal in an acid solution and then soaking it in aqua regia.

7. The preparation method according to claim 1, characterized in that, The method for growing the high-concentration boron-doped p-type conductive epitaxial layer is microwave plasma chemical vapor deposition; The growth gas for growing the high-concentration boron-doped p-type conductive epitaxial layer is methane, with a volume concentration of 1-5%; the doping gas is trimethylboron, with a molar ratio of B in trimethylboron to C in methane of (100-1000)*10. -6 :1; growth power is 1800~2500W, growth temperature is 800~1000℃, growth pressure is 100~200torr, hydrogen flow rate is 300~1000sccm, and oxygen volume concentration is 0.5~1‰.

8. The preparation method according to claim 1, characterized in that, The method for growing the low-concentration boron-doped p-type conductive epitaxial layer is microwave plasma chemical vapor deposition; The growth gas for growing the low-concentration boron-doped p-type conductive epitaxial layer is methane, with a volume concentration of 1-5%; the doping gas is trimethylboron, with a molar ratio of B in trimethylboron to C in methane of (100-1000)*10. -6 :1; growth power is 1800~2500W, growth temperature is 800~1000℃, growth pressure is 100~200torr, hydrogen flow rate is 300~1000sccm, and oxygen volume concentration is 0.5~1‰.

9. The preparation method according to claim 1, characterized in that, The mask is made of Au, Pt, Al, SiO2, or SiN.

10. The preparation method according to claim 1, characterized in that, Schottky contact between the surface of the low-concentration boron-doped p-type conductive epitaxial layer and the positive electrode; An ohmic contact is formed between the surface of the high-concentration boron-doped p-type conductive epitaxial layer and the negative electrode.

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