Method for inhibiting anisotropy of epitaxial growth of (001) plane beta-Ga2O3

Abstract

The invention discloses a method for inhibiting anisotropy of epitaxial growth of a (001) plane beta-Ga2O3, which is characterized in that In doping is carried out in the epitaxial growth process of the beta-Ga2O3 before the epitaxial growth of the beta-Ga2O3 is carried out. The (001)-plane beta-Ga2O3 epitaxial layer prepared by the method has high surface flatness performance, and can be directly used for device development.

Description

Technical Field

[0001] The invention relates to a method for suppressing the anisotropy of (001) plane beta-Ga2O3 epitaxial growth, belonging to the technical field of semiconductor materials. Background Art

[0002] β-Ga2O3 single crystal is a new type of ultra-wide bandgap semiconductor material, with a theoretical breakdown field strength of up to 8MV / cm, and a Baliga figure of merit that is more than three thousand times that of Si. Therefore, gallium oxide-based power devices theoretically have higher breakdown voltage and lower on-resistance, and have great application prospects in consumer electronics, electrical appliances, new energy vehicles and other fields. In addition, the absorption cutoff wavelength of β-Ga2O3 single crystal is 257nm, making it a natural semiconductor material for solar-blind ultraviolet detectors.

[0003] Whether preparing power devices or photodetectors, it is usually necessary to perform homoepitaxial growth on a β-Ga2O3 single crystal substrate to obtain an epitaxial layer with controllable resistivity and high crystal quality, and then prepare subsequent devices.

[0004] At present, the most widely used β-Ga2O3 single crystal substrate crystal plane is the (001) plane. Japan's NCT company has achieved the commercialization of 2-4 inch (001) plane β-Ga2O3 single crystal substrates. This is mainly because the (001) plane has lower surface energy and is less difficult to grow. Large-size, high-quality single crystals can be obtained through a variety of growth methods such as the guided mode method and the vertical Bridgman method.

[0005] Since β-Ga2O3 single crystal belongs to the monoclinic system, it has strong anisotropy, and the growth rate in the

[010] direction is more than 2.5 times that of the

[100] surface. Therefore, the morphology of the epitaxial growth of β-Ga2O3 on the (001) surface is in the shape of long strips, with the long side direction being

[010] and the short side direction being

[100] . The height difference between the strips is large, and the surface roughness is as high as tens of nanometers, which cannot directly meet the needs of device use. In order to improve the flatness of the gallium oxide epitaxial layer, a secondary grinding and polishing method is usually used. However, this method will increase the cost, and due to the brittleness of the gallium oxide epitaxial layer, the fragmentation rate will increase, thereby reducing the yield rate. Therefore, obtaining a β-Ga2O3 epitaxial layer with a smooth surface by suppressing the anisotropy in epitaxial growth is a problem that needs to be solved urgently in this field. Summary of the invention

[0006] The purpose of the present invention is to provide a method for suppressing the anisotropy of (001) plane β-Ga2O3 epitaxial growth, which can improve the surface flatness of the β-Ga2O3 epitaxial layer.

[0007] The technical solution adopted by the present invention is:

[0008] A method for suppressing the anisotropy of (001) plane β-Ga2O3 epitaxial growth is disclosed. The epitaxial growth of β-Ga2O3 is carried out on a β-Ga2O3 single crystal substrate, and In doping is performed during the epitaxial growth of the β-Ga2O3.

[0009] Preferably, the process of epitaxial growth is:

[0010] (a) Preparation of β-Ga2O3 nucleation layer: The β-Ga2O3 nucleation layer is grown on the surface of the β-Ga2O3 single crystal substrate by HVPE method, with a growth rate of 0.2 μm / hour to 2 μm / hour. In is doped as a surface catalyst during the growth process, and the In doping amount is 0.05 at% to 0.5 at%;

[0011] (b) Growth of β-Ga2O3 epitaxial layer: stop In doping and continue growing β-Ga2O3 using HVPE method at a growth rate of 1 μm / hour to 10 μm / hour.

[0012] Preferably, the growth conditions in step a are: the Ga source is GaCl generated by the reaction of metallic gallium and Cl2 at 790-810°C, the O source is O2, the flow ratio of O2 and Cl2 is 60-50:1, the O2 flow rate is 100-120sccm, the Cl2 flow rate is 1.6-2.4sccm, the carrier gas is N2, the flow rate is 8-12slm, the growth pressure is 90-110mbar, the growth temperature is 1020-1040°C, and the growth time is 1.7-2.2h.

[0013] Preferably, the growth conditions in step b are: the Ga source is GaCl generated by the reaction of metal gallium and Cl2 at 790-810°C, the O source is O2, the flow ratio of O2 and Cl2 is 10-12:1, the O2 flow rate is 100-120sccm, the Cl2 flow rate is 8-12sccm, the carrier gas is N2, the flow rate is 8-12slm, the growth pressure is 90-110mbar, the growth temperature is 1080-1100°C, and the growth time is 0.5-4h.

[0014] Preferably, before epitaxial growth is performed, a groove-shaped mask is first made on the surface of the β-Ga2O3 single crystal substrate, wherein the long side direction of the groove is in the

[100] direction and the short side direction is in the

[010] direction.

[0015] Preferably, the long side of the groove is equal to the length of the β-Ga2O3 single crystal substrate, the short side is 0.1 μm to 1 μm, the depth is 20 nm to 200 nm, and the spacing between the grooves is 0.5 μm to 5 μm.

[0016] The present invention also discloses another method for suppressing the anisotropy of (001) plane β-Ga2O3 epitaxial growth. A groove-shaped mask is firstly made on the surface of the β-Ga2O3 single crystal substrate, wherein the long side direction of the groove is the

[100] direction and the short side direction is the

[010] direction. Then, the epitaxial growth of β-Ga2O3 is carried out on the surface of the groove-shaped mask.

[0017] Preferably, the long side of the groove is equal to the length of the β-Ga2O3 single crystal substrate, the short side is 0.1 μm to 1 μm, the depth is 20 nm to 200 nm, and the spacing between the grooves is 0.5 μm to 5 μm.

[0018] Beneficial effects of the present invention:

[0019] (1) The present invention adopts In element doping to suppress the anisotropy of epitaxial growth of (001) surface β-Ga2O3. The principle is that β-Ga2O3 has a double chain structure, and the GaO6 octahedral chains are arranged along the

[010] direction. The chains are separated by Ga Ⅰ O4 connection, In ions doped into the β-Ga2O3 lattice tend to replace Ga Ⅱ Ga at the center of O6 octahedron Ⅱ Position, so that the distortion of β-Ga2O3 lattice along

[010] direction is more serious than that along

[100] direction, thereby reducing the growth rate difference between

[010] direction and

[100] direction and obtaining a flat epitaxial layer;

[0020] (2) In is in the same family as Ga, has high solid solubility, and selecting it as a surface catalyst will not affect the electrical properties of the epitaxial layer;

[0021] (3) The present invention also uses a grooved mask to effectively reduce the growth rate in the

[010] direction;

[0022] (4) The combination of In doping and grooves makes the surface roughness of the (001) surface β-Ga2O3 epitaxial layer less than or equal to 1nm, which can be directly used for device development. Even if the epitaxial layer grows to a thickness of 20μm, it still has a high surface flatness;

[0023] (5) The (001) face β-Ga2O3 epitaxial layer prepared by the present invention eliminates the need for secondary processing, thereby saving 20% ​​to 30% of the cost and increasing the yield by more than 30%. BRIEF DESCRIPTION OF THE DRAWINGS

[0024] Figure 1 Schematic diagram of the trench mask structure, where Figure 1 (A) is a schematic diagram of the trench mask from a top-down view along the β-Ga2O3 single crystal substrate. Figure 1 (B) is a schematic diagram of the groove mask at the cross-sectional angle of the β-Ga2O3 single crystal substrate.

[0025] Figure 2 The surface roughness test results of the β-Ga2O3 single crystal epitaxial wafer prepared in Example 1 are as follows: Figure 2 (A) is the finished product photo. Figure 2 (B) is the surface roughness test result.

[0026] Figure 3 This is the test result of the surface roughness of the gallium oxide epitaxial layer prepared in Comparative Example 1.

[0027] Figure 4 This is the test result of the surface roughness of the gallium oxide epitaxial layer prepared in Comparative Example 2.

[0028] Figure 5 The surface roughness test result of the gallium oxide epitaxial layer prepared in Example 3. DETAILED DESCRIPTION

[0029] The present invention is further described below in conjunction with embodiments, but the description of the embodiments does not impose any limitation on the protection scope of the present invention.

[0030] Unless otherwise defined, all technical terms and scientific terms used herein have the same meaning as those generally understood by those skilled in the art of the present invention, and the terms used in the specification of the present invention herein are only for the purpose of describing specific embodiments, and are not intended to limit the present invention. In addition, although demonstrations of parameters containing specific values ​​may be provided herein, it should be understood that the parameters do not need to be exactly equal to the corresponding values, but can be approximated to the corresponding values ​​within an acceptable error tolerance or design constraint. The directional terms mentioned in the embodiments, such as "up", "down", "front", "back", "left", "right", etc., are only directions with reference to the accompanying drawings. Therefore, the directional terms used are used to illustrate rather than to limit the scope of protection of the present invention.

[0031] Unless otherwise specified, the materials and instruments used in the following examples can be obtained from conventional commercial channels.

[0032] Example 1

[0033] The HVPE method was used to grow a ~10 micron thick homoepitaxial on a 10mm*10mm (001) surface β-Ga2O3 single crystal substrate, such as Figure 2 shown.

[0034] a. Mask fabrication: Mask 1 is fabricated on the surface of the (001) plane β-Ga2O3 single crystal substrate. The mask can be made of common mask materials, such as SiO2 or Si3N4. The mask is in a groove shape, with the long side direction being

[100] and the short side direction being

[010] . The short side length is 0.3 microns. The groove 2 has a spacing of 3 microns and a depth equal to the height of the mask layer, which is 70 nm. The bottom of the groove exposes the surface of the β-Ga2O3 single crystal substrate.

[0035] b. Preparation of β-Ga2O3 nucleation layer: HVPE and other methods are used to grow the β-Ga2O3 nucleation layer to completely cover the mask. The Ga source is metal gallium and Cl2 reacting at 800°C to generate GaCl. The O source is O2, the flow ratio of O2 to Cl2 is 60:1, the O2 flow is 120sccm, the Cl2 flow is 2sccm, the carrier gas is N2, the flow is 10slm, the growth pressure is 110mbar, the growth temperature is 1030°C, the growth rate is 1 micron / hour, and the growth time is 2 hours. In doping is performed as a surface catalyst in the process. The In source is metal indium reacting with Cl2 at 650°C to generate InCl, and the doping amount is 0.1at%. This step is grown until the mask is completely covered;

[0036] c. Growth of β-Ga2O3 epitaxial layer, stop In doping, continue growth using the growth method in step b, change the O2 and Cl2 flow ratio to 12:1, O2 flow rate to 120sccm, Cl2 flow rate to 10sccm, carrier gas to N2, flow rate to 10slm, growth pressure to 100mbar, growth temperature to 1100℃, growth rate to 5 microns / hour, growth time to 2 hours. The obtained β-Ga2O3 epitaxial wafer is as follows Figure 2 shown.

[0037] Example 2

[0038] The HVPE method was used to grow a 15 micron thick homoepitaxial on a 10 mm*10 mm (001) surface β-Ga2O3 single crystal substrate.

[0039] a. Mask fabrication: Mask 1 is fabricated on the surface of the (001) plane β-Ga2O3 single crystal substrate. The mask is in the shape of a groove, with the long side direction being

[100] and the short side direction being

[010] . The short side length is 1 micron. The groove 2 has a spacing of 5 microns and a depth equal to the height of the mask layer, which is 200 nm. The bottom of the groove exposes the surface of the β-Ga2O3 single crystal substrate.

[0040] b. Preparation of β-Ga2O3 nucleation layer. HVPE and other methods are used to grow the β-Ga2O3 nucleation layer to completely cover the mask. The Ga source is metal gallium and Cl2 reacting at 810°C to generate GaCl. The O source is O2. The flow ratio of O2 and Cl2 is 50:1. The O2 flow is 120sccm, the Cl2 flow is 2.4sccm, the carrier gas is N2, the flow is 12slm, the growth pressure is 110mbar, the growth temperature is 1040°C, the growth rate is 2 microns / hour, and the growth time is 1.7 hours. In doping is performed as a surface catalyst in this process. The In source is metal indium and Cl2 reacting at 650°C to generate InCl, and the doping amount is 0.5at%;

[0041] c. Growth of β-Ga2O3 epitaxial layer, stop In doping, continue growth using the growth method in step b, change the O2 and Cl2 flow ratio to 10:1, O2 flow is 120sccm, Cl2 flow is 12sccm, carrier gas is N2, flow is 12slm, growth pressure is 110mbar, growth temperature is 1080℃, growth rate is 10 microns / hour, and growth time is 0.5 hours. The surface roughness of the obtained β-Ga2O3 epitaxial layer is below 1nm.

[0042] Comparative Example 1

[0043] The HVPE method is used to directly grow a β-Ga2O3 epitaxial layer on a (001) surface β-Ga2O3 single crystal substrate. The Ga source is metal gallium and Cl2 reacting at 800°C to generate GaCl. The O source is O2, and the flow ratio of O2 and Cl2 is changed to 12:1. The O2 flow rate is 120sccm, the Cl2 flow rate is 10sccm, the carrier gas is N2, the flow rate is 10slm, the growth pressure is 100mbar, the growth temperature is 1100°C, the growth rate is 5 microns / hour, and the growth time is 2 hours.

[0044] Comparative Example 2

[0045] a. Mask fabrication: Mask 1 is fabricated on the surface of a (001)-plane β-Ga2O3 single crystal substrate. The mask is in a groove shape, with the long side direction being

[100] and the short side direction being

[010] . The short side length is 0.3 microns, the groove 2 spacing is 3 microns, and the depth is 70 nm.

[0046] b. HVPE method was used to grow β-Ga2O3 epitaxial layer. The Ga source was metal gallium and Cl2 reacting at 800℃ to generate GaCl. The O source was O2. The flow ratio of O2 and Cl2 was changed to 12:1. The O2 flow rate was 120sccm, the Cl2 flow rate was 10sccm, the carrier gas was N2, the flow rate was 10slm, the growth pressure was 100mbar, the growth temperature was 1100℃, the growth rate was 5μm / hour, and the growth time was 2 hours.

[0047] Example 3

[0048] a. Preparation of β-Ga2O3 nucleation layer: HVPE method is used to grow β-Ga2O3 nucleation layer on the surface of (001) surface β-Ga2O3 single crystal substrate, and the mask is completely covered. The Ga source is metal gallium and Cl2 reacting at 800℃ to generate GaCl, the O source is O2, the flow ratio of O2 and Cl2 is 60:1, the O2 flow is 120sccm, the Cl2 flow is 2sccm, the carrier gas is N2, the flow is 10slm, the growth pressure is 100mbar, the growth temperature is 1030℃, the growth rate is 1 micron / hour, and the growth time is 2 hours. In doping is performed as a surface catalyst in this process. The In source is metal indium reacting with Cl2 at 650℃ to generate InCl, and the doping amount is 0.1at%;

[0049] b. Growth of β-Ga2O3 epitaxial layer, stop In doping, continue growth using the growth method in step b, change the O2 and Cl2 flow ratio to 12:1, the O2 flow is 120sccm, the Cl2 flow is 10sccm, the carrier gas is N2, the flow is 10slm, the growth pressure is 100mbar, the growth temperature is 1100℃, the growth rate is 5μm / hour, and the growth time is 2 hours.

[0050] The surface roughness of the epitaxial layers grown in Comparative Examples 1-2 and Example 3 were tested using an atomic force microscope. The results are as follows: Figure 3-5 As shown. It can be seen that the preparation of grooves on the substrate surface and the In doping method can significantly reduce the surface roughness of the β-Ga2O3 epitaxial layer. The combination of the two methods can achieve a better effect in reducing the surface roughness of the β-Ga2O3 epitaxial layer.

[0051] Example 4

[0052] The HVPE method was used to grow a 15 micron thick homoepitaxial on a 10 mm*10 mm (001) surface β-Ga2O3 single crystal substrate.

[0053] a. Mask fabrication: Mask 1 is fabricated on the surface of the (001) plane β-Ga2O3 single crystal substrate. The mask is in the shape of a groove, with the long side direction being

[100] and the short side direction being

[010] . The short side length is 0.1 micron. The groove 2 has a spacing of 0.5 micron and a depth equal to the height of the mask layer, which is 20 nm. The bottom of the groove exposes the surface of the β-Ga2O3 single crystal substrate.

[0054] b. Preparation of β-Ga2O3 nucleation layer: HVPE and other methods are used to grow the β-Ga2O3 nucleation layer, and the mask is completely covered. The Ga source is metal gallium and Cl2 reacting at 790°C to generate GaCl, the O source is O2, the flow ratio of O2 and Cl2 is 55:1, the O2 flow is 100sccm, the Cl2 flow is 1.6sccm, the carrier gas is N2, the flow is 8slm, the growth pressure is 90mbar, the growth temperature is 1020°C, the growth rate is 0.2 microns / hour, and the growth time is 2.2 hours. In doping is performed as a surface catalyst in this process. The In source is metal indium and Cl2 reacting at 650°C to generate InCl, and the doping amount is 0.05at%;

[0055] c. Growth of β-Ga2O3 epitaxial layer, stop In doping, continue growth using the growth method in step b, change the O2 and Cl2 flow ratio to 11:1, O2 flow is 100sccm, Cl2 flow is 8sccm, carrier gas is N2, flow is 8slm, growth pressure is 90mbar, growth temperature is 1100℃, growth rate is 1 micron / hour, and growth time is 4 hours. The surface roughness of the obtained β-Ga2O3 epitaxial layer is below 1nm.

Claims

1. A method for suppressing the anisotropy of (001)-plane β-Ga2O3 epitaxial growth, characterized in that: Epitaxial growth of β-Ga2O3 is performed on a β-Ga2O3 single crystal substrate, and In doping is performed during the epitaxial growth of the β-Ga2O3.

2. The method for suppressing the anisotropy of epitaxial growth of (001)-plane β-Ga2O3 according to claim 1, characterized in that The process of epitaxial growth is: (a) Preparation of β-Ga2O3 nucleation layer: The β-Ga2O3 nucleation layer is grown on the surface of the β-Ga2O3 single crystal substrate by HVPE method, with a growth rate of 0.2 μm / hour to 2 μm / hour. In is doped as a surface catalyst during the growth process, and the In doping amount is 0.05 at% to 0.5 at%; (b) Growth of β-Ga2O3 epitaxial layer: stop In doping and continue growing β-Ga2O3 using HVPE method at a growth rate of 1 μm / hour to 10 μm / hour.

3. The method for suppressing anisotropy of epitaxial growth of (001)-plane β-Ga2O3 according to claim 2, characterized in that: The growth conditions in step a are as follows: the Ga source is GaCl generated by the reaction of metal gallium and Cl2 at 790-810°C, the O source is O2, the flow ratio of O2 to Cl2 is 60-50:1, the O2 flow rate is 100-120sccm, the Cl2 flow rate is 1.6-2.4sccm, the carrier gas is N2, the flow rate is 8-12slm, the growth pressure is 90-110mbar, the growth temperature is 1020-1040°C, and the growth time is 1.7-2.2h.

4. The method for suppressing anisotropy of (001)-plane β-Ga2O3 epitaxial growth according to claim 3, characterized in that: The growth conditions in step b are: the Ga source is GaCl generated by the reaction of metal gallium and Cl2 at 790-810°C, the O source is O2, the flow ratio of O2 and Cl2 is 10-12:1, the O2 flow rate is 100-120sccm, the Cl2 flow rate is 8-12sccm, the carrier gas is N2, the flow rate is 8-12slm, the growth pressure is 90-110mbar, the growth temperature is 1080-1100°C, and the growth time is 0.5-4h.

5. The method for suppressing the anisotropy of epitaxial growth of (001)-plane β-Ga2O3 according to any one of claims 1 to 4, characterized in that: Before epitaxial growth, a groove mask is first made on the surface of the β-Ga2O3 single crystal substrate, wherein the long side direction of the groove is the [100] direction and the short side direction is the [010] direction.

6. The method for suppressing anisotropy of (001)-plane β-Ga2O3 epitaxial growth according to claim 5, characterized in that: The long side of the groove is equal to the length of the β-Ga2O3 single crystal substrate, the short side is 0.1μm to 1μm, the depth is 20nm to 200nm, and the spacing between the grooves is 0.5μm to 5μm.

7. A method for suppressing the anisotropy of (001)-plane β-Ga2O3 epitaxial growth, characterized in that: First, a groove mask is made on the surface of a β-Ga2O3 single crystal substrate, wherein the long side direction of the groove is in the [100] direction and the short side direction is in the [010] direction, and then epitaxial growth of β-Ga2O3 is performed on the surface of the groove mask.

8. The method for suppressing anisotropy of (001)-plane β-Ga2O3 epitaxial growth according to claim 7, characterized in that: The long side of the groove is equal to the length of the β-Ga2O3 single crystal substrate, the short side is 0.1μm to 1μm, the depth is 20nm to 200nm, and the spacing between the grooves is 0.5μm to 5μm.

Images