A method for inhibiting the anisotropy of (001) plane β-ga2o3 epitaxial growth

Abstract

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

Description

TECHNICAL FIELD

[0001] The present application relates to a method for inhibiting the anisotropy of (001) plane beta-Ga2O3 epitaxial growth, and belongs to the technical field of semiconductor materials. BACKGROUND

[0002] Beta-Ga2O3 single crystal is a new type of ultra-wide bandgap semiconductor material, with a theoretical breakdown field strength of 8 MV / cm and a Baliga figure of merit of more than 3,000 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, beta-Ga2O3 single crystal has an absorption cutoff wavelength of 257 nm, making it a natural semiconductor material for solar blind ultraviolet detectors.

[0003] In order to prepare power devices or photodetectors, homoepitaxial growth on a beta-Ga2O3 single crystal substrate is usually required to obtain an epitaxial layer with controllable resistivity and high crystalline quality, and then subsequent device preparation is carried out.

[0004] At present, the most widely used beta-Ga2O3 single crystal substrate crystal plane is the (001) plane, and Japan NCT Company has realized the productization of 2-4 inch (001) plane beta-Ga2O3 single crystal substrates. This is mainly because the (001) plane has a lower surface energy and is easier to grow. Large-size high-quality single crystals can be obtained by various growth methods such as guided mode method and vertical Bridgman method.

[0005] Since beta-Ga2O3 single crystal belongs to monoclinic system and has strong anisotropy, the growth speed of

[010] direction is 2.5 times higher than that of

[100] plane. Therefore, the morphology of (001) plane beta-Ga2O3 epitaxial growth is in the form of long strip splicing, with the long side direction being

[010] and the short side direction being

[100] . The height difference between strips is large, and the surface roughness is as high as tens of nanometers, which cannot directly meet the device use requirements. In order to improve the flatness of gallium oxide epitaxial layer, a secondary grinding and polishing method is usually used. However, this method increases the cost and increases the chip rate due to the brittleness of gallium oxide epitaxial layer, thereby reducing the yield. Therefore, it is an urgent problem in the field to obtain a flat beta-Ga2O3 epitaxial layer by inhibiting the anisotropy during epitaxial growth. SUMMARY

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

[0007] The technical scheme adopted by the present application is:

[0008] A method for inhibiting the anisotropy of (001) plane β-Ga2O3 epitaxial growth, which comprises the following steps: epitaxial growth of β-Ga2O3 on a β-Ga2O3 single crystal substrate, and In doping during the epitaxial growth of β-Ga2O3.

[0009] Preferably, the epitaxial growth process is as follows:

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

[0011] (b) β-Ga2O3 epitaxial layer growth: stop In doping, and continue to grow β-Ga2O3 by HVPE method, the growth rate is 1 μm / hour to 10 μm / hour.

[0012] Preferably, the growth conditions in step a are as follows: the Ga source is GaCl generated by 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 is 100-120 sccm, the Cl2 flow is 1.6-2.4 sccm, the carrier gas is N2, the flow is 8-12 slm, the growth pressure is 90-110 mbar, the growth temperature is 1020-1040°C, and the growth time is 1.7-2.2 h.

[0013] Preferably, the growth conditions in step b are as follows: the Ga source is GaCl generated by reaction of metallic 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 is 100-120 sccm, the Cl2 flow is 8-12 sccm, the carrier gas is N2, the flow is 8-12 slm, the growth pressure is 90-110 mbar, the growth temperature is 1080-1100°C, and the growth time is 0.5-4 h.

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

[100] direction and the short side direction is

[010] direction.

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

[0016] The application also discloses another method for inhibiting the anisotropy of the (001) plane β-Ga2O3 epitaxial growth, which comprises the following steps: firstly, making a trench-shaped mask on the surface of the β-Ga2O3 single crystal substrate, wherein the long side direction of the trench is the

[100] direction and the short side direction is the

[010] direction; and then, performing the epitaxial growth of the β-Ga2O3 on the surface of the trench-shaped mask.

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

[0018] The application has the following advantages:

[0019] (1) The application adopts the In element doping to inhibit the anisotropy of the (001) plane β-Ga2O3 epitaxial growth, and the principle is that the β-Ga2O3 has a double-chain structure, the GaO6 octahedral chain is arranged along the

[010] direction, the chains are connected with each other through Ga Ⅰ O4, and the In ion is more inclined to replace the Ga Ⅱ O6 octahedral center Ga Ⅱ position in the β-Ga2O3 lattice, so that the distortion of the β-Ga2O3 lattice along the

[010] direction is more serious than that along the

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

[010] direction and the

[100] direction, and obtaining a flat epitaxial layer;

[0020] (2) The In element is of the same group as the Ga element, has a high solid solubility, and will not affect the electrical properties of the epitaxial layer when being selected as the surface catalyst;

[0021] (3) The application also adopts the trench-shaped mask to effectively reduce the growth rate of the

[010] direction;

[0022] (4) The In doping cooperates with the trench to make the surface roughness of the (001) plane β-Ga2O3 epitaxial layer less than or equal to 1 nm, so that the epitaxial layer can be directly used for device development, and even if the epitaxial layer is grown to a thickness of 20 μm, the surface flatness is still high;

[0023] (5) The (001) plane β-Ga2O3 epitaxial layer prepared by the application saves the secondary processing process, the cost can be saved by 20-30%, and the yield is increased by more than 30%. BRIEF DESCRIPTION OF DRAWINGS

[0024] Figure 1 Fig. 1 is a schematic diagram of the trench-shaped mask structure, wherein Figure 1 (A) is a schematic diagram of the trench-shaped mask along the overhead angle of the β-Ga2O3 single crystal substrate, Figure 1 (B) is a schematic diagram of the trench-shaped mask along the section angle of the β-Ga2O3 single crystal substrate.

[0025] Figure 2 Surface roughness test results of the β-Ga2O3 single crystal epitaxial wafer prepared in Example 1, wherein Figure 2 (A) is a finished product photo, Figure 2 (B) is a surface roughness test result.

[0026] Figure 3 Surface roughness test results of the gallium oxide epitaxial layer prepared in Comparative Example 1.

[0027] Figure 4 Surface roughness test results of the gallium oxide epitaxial layer prepared in Comparative Example 2.

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

[0029] The present application will be further described by the following examples, but the description of the examples does not impose any limitation on the scope of protection of the present application.

[0030] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this application belongs. The terminology used in the description of the application herein is for the purpose of describing particular embodiments only and is not intended to be limiting of the application. Additionally, although exemplary values of parameters are provided in the description of the application, it is understood that the parameters need not be exactly as stated, but can be approximated within an acceptable error tolerance or design constraint. Directional phrases used herein, such as "upper," "lower," "front," "back," "left," "right," and the like, are made with reference to the orientation of the figures, in which the example embodiments are depicted. Accordingly, directional phrases are used for the purpose of illustration and not to limit the scope of the application.

[0031] The substances or instruments used in the following examples can be obtained from conventional commercial channels, if not otherwise specified.

[0032] Example 1

[0033] A ~10 micron thick homoepitaxy was grown on a 10 mm*10 mm (001) face β-Ga2O3 single crystal substrate using the HVPE method, as shown in Figure 2

[0034] ​a. Masking film production, a masking film 1 is produced on the surface of the (001) plane β-Ga2O3 single crystal substrate, the masking film can be made of common masking film materials, such as SiO2 or Si3N4, the masking film is in a groove shape, the long side direction is

[100] , the short side direction is

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

[0035] b. β-Ga2O3 nucleation layer preparation, β-Ga2O3 nucleation layer growth is performed by using HVPE and the like, the masking film is completely covered, the Ga source is GaCl generated by the reaction of metallic gallium and Cl2 at 800°C, the O source is O2, the O2 and Cl2 flow ratio is 60:1, the O2 flow is 120 sccm, the Cl2 flow is 2 sccm, the carrier gas is N2, the flow is 10 slm, the growth pressure is 110 mbar, the growth temperature is 1030°C, the growth speed 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 InCl generated by the reaction of metallic indium and Cl2 at 650°C, the doping amount is 0.1 at%, and the step is grown until the masking film is completely covered;

[0036] c. β-Ga2O3 epitaxial layer growth, In doping is stopped, the growth method in step b is used to continue growth, the O2 and Cl2 flow ratio is changed to 12:1, the O2 flow is 120 sccm, the Cl2 flow is 10 sccm, the carrier gas is N2, the flow is 10 slm, the growth pressure is 100 mbar, the growth temperature is 1100°C, the growth speed is 5 microns / hour, and the growth time is 2 hours. The prepared β-Ga2O3 epitaxial wafer is as shown in Figure 2 .

[0037] Example 2

[0038] The HVPE method is used to grow a ~15 micron thick homogeneous epitaxial layer on a 10mm*10mm (001) plane β-Ga2O3 single crystal substrate.

[0039] a. Masking film production, a masking film 1 is produced on the surface of the (001) plane β-Ga2O3 single crystal substrate, the masking film can be made of common masking film materials, such as SiO2 or Si3N4, the masking film is in a groove shape, the long side direction is

[100] , the short side direction is

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

[0040] b. β-Ga2O3 nucleation layer preparation, β-Ga2O3 nucleation layer growth is carried out by HVPE and the like, the mask is completely covered, the Ga source is GaCl generated by reaction of metallic gallium and Cl2 at 810°C, the O source is O2, the O2 and Cl2 flow ratio is 50:1, the O2 flow is 120 sccm, the Cl2 flow is 2.4 sccm, the carrier gas is N2, the flow is 12 slm, the growth pressure is 110 mbar, the growth temperature is 1040°C, the growth speed is 2 microns / hour, and the growth time is 1.7 hours, and In doping is carried out as a surface catalyst in the process, the In source is InCl generated by reaction of metallic indium and Cl2 at 650°C, and the doping amount is 0.5 at%;

[0041] c. β-Ga2O3 epitaxial layer growth, In doping is stopped, and growth is continued by using the growth method in step b, the O2 and Cl2 flow ratio is changed to 10:1, the O2 flow is 120 sccm, the Cl2 flow is 12 sccm, the carrier gas is N2, the flow is 12 slm, the growth pressure is 110 mbar, the growth temperature is 1080°C, the growth speed is 10 microns / hour, and the growth time is 0.5 hours. The prepared β-Ga2O3 epitaxial layer has a surface roughness of less than 1 nm.

[0042] Comparative Example 1

[0043] β-Ga2O3 epitaxial layer growth is directly carried out on a (001) β-Ga2O3 single crystal substrate by HVPE, the Ga source is GaCl generated by reaction of metallic gallium and Cl2 at 800°C, the O source is O2, the O2 and Cl2 flow ratio is changed to 12:1, the O2 flow is 120 sccm, the Cl2 flow is 10 sccm, the carrier gas is N2, the flow is 10 slm, the growth pressure is 100 mbar, the growth temperature is 1100°C, the growth speed is 5 microns / hour, and the growth time is 2 hours.

[0044] Comparative Example 2

[0045] a. Mask preparation, a mask 1 is prepared on the surface of a (001) β-Ga2O3 single crystal substrate, the mask is in a groove shape, the long side direction is

[100] , the short side direction is

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

[0046] b. β-Ga2O3 epitaxial layer growth is carried out by HVPE, the Ga source is GaCl generated by reaction of metallic gallium and Cl2 at 800°C, the O source is O2, the O2 and Cl2 flow ratio is changed to 12:1, the O2 flow is 120 sccm, the Cl2 flow is 10 sccm, the carrier gas is N2, the flow is 10 slm, the growth pressure is 100 mbar, the growth temperature is 1100°C, the growth speed is 5 microns / hour, and the growth time is 2 hours.

[0047] Example 3

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

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

[0050] The epitaxial layers grown in Comparative Example 1-2 and Example 3 are all tested for surface roughness using atomic force microscopy, and the results are shown in Figures 3-5 It can be seen that both the way of preparing trenches on the substrate surface and In doping can significantly reduce the surface roughness of the β-Ga2O3 epitaxial layer, and the effect of using the two methods together is better.

[0051] Example 4

[0052] Using HVPE method to grow ~ 15 micron thick homoepitaxial on 10mm*10mm (001) β-Ga2O3 single crystal substrate.

[0053] a, mask making, making mask 1 on the surface of (001) β-Ga2O3 single crystal substrate, the mask is in the form of a trench, the long side direction is

[100] , the short side direction is

[010] , the short side length is 0.1 micron, the trench 2 pitch is 0.5 micron, the depth is equal to the height of the mask layer, which is 20nm, and the trench bottom exposes the surface of the β-Ga2O3 single crystal substrate;

[0054] b. Preparation of β-Ga2O3nucleation layer, growth of β-Ga2O3nucleation layer by HVPE, etc. The mask is completely covered. Ga source is metallic gallium and Cl2reacting at 790°C to form GaCl. O source is O2. The flow ratio of O2and Cl2is 55:1. The flow of O2is 100 sccm. The flow of Cl2is 1.6 sccm. The carrier gas is N2. The flow is 8 slm. The growth pressure is 90 mbar. The growth temperature is 1020°C. The growth rate is 0.2 microns / hour. The growth time is 2.2 hours. In doping is performed as a surface catalyst during the process. In source is metallic indium and Cl2reacting at 650°C to form InCl. The doping amount is 0.05 at%;

[0055] c. Growth of β-Ga2O3epitaxial layer. In doping is stopped. The growth method in step b is continued. The flow ratio of O2and Cl2is changed to 11:1. The flow of O2is 100 sccm. The flow of Cl2is 8 sccm. The carrier gas is N2. The flow is 8 slm. The growth pressure is 90 mbar. The growth temperature is 1100°C. The growth rate is 1 micron / hour. The growth time is 4 hours. The surface roughness of the prepared β-Ga2O3epitaxial layer is below 1 nm.

Claims

1. A method of suppressing the anisotropy of the epitaxial growth of a (001) plane β-Ga2O3, characterized by: The epitaxial growth of β-Ga2O3 is carried out on a β-Ga2O3 single crystal substrate, and In doping is carried out during the epitaxial growth of β-Ga2O3. Before the epitaxial growth, a trench-shaped mask is first made on the surface of the β-Ga2O3 single crystal substrate, wherein the long side direction of the trench is [100] direction, the short side direction is [010] direction, the long side of the trench is equal in length to the β-Ga2O3 single crystal substrate, the short side length is 0.1-1 μm, the depth is 20-200 nm, and the distance between the trenches is 0.5-5 μm. The epitaxial growth of β-Ga2O3 includes two processes of nucleation layer preparation and epitaxial layer growth. The nucleation layer preparation is to grow a β-Ga2O3 nucleation layer on the surface of the β-Ga2O3 single crystal substrate by using the HVPE method, the growth rate is 0.2-2 μm / h, In doping is carried out as a surface catalyst during the growth process, and the In doping amount is 0.05-0.5 at %.

2. The method of suppressing the anisotropy of the (001) -plane β-Ga2O3 epitaxial growth according to claim 1, characterized by The epitaxial layer growth of β-Ga2O3: stop In doping, continue to grow β-Ga2O3 by using the HVPE method, the growth rate is 1-10 μm / h.

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

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

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