A high-thickness, high-quality Ga2O3 thin film material and its preparation method

Abstract

A high-thickness, high-quality Ga2O3 thin film material and a preparation method thereof, belonging to the technical field of semiconductor thin film material preparation. It is composed of a β-Ga2O3 single crystal substrate that has been passivated by NH3 plasma, a low-temperature Ga2O3 buffer layer, a slowly grown Ga2O3 thin layer, a Ga2O3 growth layer, and a rapidly grown high-temperature Ga2O3 thin film layer in sequence, and all growth processes are completed in an MOCVD device. The present invention solves the epitaxy problem of high-thickness, high-quality Ga2O3 thin film materials, overcomes the current problem of poor quality of heterogeneous and homogeneous epitaxial crystals of Ga2O3, and the quality of the obtained Ga2O3 thin film crystal is improved by more than one-third compared to the substrate, and the half-peak width of its double crystal rocking curve is only 68.4 arcsec. The present invention can effectively improve the crystal quality of Ga2O3 thick films, thereby improving the working performance of Ga2O3-based devices.

Description

Technical Field

[0001] The present invention belongs to the technical field of semiconductor thin film material preparation, and in particular relates to a high-thickness, high-quality Ga2O3 thin film material and a preparation method thereof. Background Art

[0002] Gallium oxide (Ga2O3) is an emerging ultra-wide bandgap semiconductor material with a bandgap of about 4.9eV. It is one of the most representative semiconductor materials in the fields of transparent conductivity, optoelectronic devices and gas sensing. The most prominent feature of Ga2O3 is its ultra-wide bandgap. Due to the exponential relationship between the breakdown field strength and the bandgap value, the theoretical breakdown field strength of Ga2O3 is as high as 8MV / cm, which means that in the field of power electronics, especially under high voltage conditions, gallium oxide can at least partially exceed the current Si, SiC and GaN. The wider bandgap also allows Ga2O3-based devices to operate stably at higher temperatures. In addition to its high-voltage and high-temperature resistance, Ga2O3 has a very low theoretical on-resistance. The conduction loss of Ga2O3-based unipolar devices under the same conditions is more than one order of magnitude lower than that of SiC and GaN devices, which can significantly improve the working efficiency of Ga2O3-based devices. Research and preparation of Ga2O3 thin films play an important role in giving full play to the advantages of Ga2O3 materials in the field of high-voltage electronic devices.

[0003] Ga2O3 thin films with high thickness and high crystal quality are the basis for preparing Ga2O3-based power diodes. Since halide vapor phase epitaxy (HVPE) has the unique advantage of fast growth rate, most of the high-thickness Ga2O3 thin films are currently prepared by HVPE process. However, the domestic HVPE process is immature, the equipment penetration rate is low, and the high-thickness Ga2O3 epitaxial wafers used for power devices are basically dependent on imports and the price is extremely high, which seriously hinders the development of Ga2O3-based power devices in my country. Metal organic chemical vapor deposition (MOCVD) equipment has a high penetration rate and mature technology, and is an ideal preparation method for Ga2O3 thin films. However, the growth rate of MOCVD process thin films is slow, and the long growth process puts forward higher requirements for MOCVD equipment. This is also the reason why the preparation of high-thickness and high-quality Ga2O3 thin films has not been achieved, although the MOCVD process is the main means of growing thin films in the current industrialization. Based on the above problems, the present invention proposes a MOCVD preparation method for high-thickness and high-quality Ga2O3 thin film materials. Summary of the invention

[0004] The purpose of the present invention is to provide a high-thickness, high-quality Ga2O3 thin film material and a homoepitaxial preparation method thereof through MOCVD process.

[0005] The present invention uses a β-Ga2O3 single crystal prepared by a guided mode method (EFG) as a substrate, and uses the current mature MOCVD process to first grow a Ga2O3 film at a relatively low temperature on the β-Ga2O3 single crystal substrate to form a low-temperature Ga2O3 buffer layer; then slowly increase the temperature to grow a multi-level Ga2O3 film, and in the process of heating up, the growth of the Ga2O3 film is always maintained and annealed in an O2 atmosphere step by step until the temperature reaches a high temperature, then the temperature is stopped, and a thicker high-temperature Ga2O3 film layer is rapidly grown at this temperature, and finally annealed to reduce defects. Based on the use of a homogeneous substrate to avoid the degradation of crystal quality caused by lattice mismatch and thermal mismatch, the present invention uses a variable temperature epitaxy and a step-by-step O2 atmosphere annealing method to gradually eliminate the influence of defects in the single crystal substrate on the epitaxy of the film, inhibit the generation of defects in the film growth process and relieve stress, thereby proposing a homogeneous epitaxial preparation method for a high-thickness, high-quality Ga2O3 film material.

[0006] The high-thickness, high-quality Ga2O3 thin film material described in the present invention is composed of a β-Ga2O3 single crystal substrate 1, a low-temperature Ga2O3 buffer layer 2 grown on the β-Ga2O3 single crystal substrate 1, a Ga2O3 thin layer 3 slowly grown on the low-temperature Ga2O3 buffer layer 2, a Ga2O3 growth layer 4 grown on the Ga2O3 thin layer 3, and a high-temperature Ga2O3 thin film layer 5 rapidly grown on the Ga2O3 growth layer 4 (such as Figure 1 shown).

[0007] The homoepitaxial preparation method of a high-thickness, high-quality Ga2O3 thin film material described in the present invention comprises the following steps:

[0008] A. Substrate 1 is a β-Ga2O3 single crystal substrate obtained by EFG method (Aida, H.; Nishiguchi, K.; Takeda, H.; Aota, N.; Sunakawa, K.; Yaguchi, Y.; Growth of β-Ga2O3 single crystals by the edge-defined, film fed growth method. Jpn. J. Appl. Phys. 2008, 47, 8506), with a thickness of 600-700 μm; the β-Ga2O3 single crystal substrate 1 is ultrasonically cleaned with acetone, ethanol, and deionized water for 5-10 minutes in sequence, blown dry with high-purity nitrogen gas, and then subjected to NH3 plasma passivation treatment; the radio frequency power of NH3 plasma passivation treatment is 200-300 W, the treatment temperature is 350-400° C., and the treatment time is 4-5 minutes;

[0009] B. Using trimethylgallium and high-purity oxygen as reaction sources, using high-purity argon as carrier gas for trimethylgallium, with a high-purity argon flow rate of 10-20 sccm, and a high-purity oxygen flow rate of 400-500 sccm; using MOCVD equipment to grow a low-temperature Ga2O3 buffer layer 2 with a thickness of 40-80 nm on a β-Ga2O3 single crystal substrate 1 for 5-8 minutes under the conditions of a substrate temperature of 450-500°C and a reaction chamber pressure of 20-30 mbar; after the growth is completed, the O2 atmosphere in the chamber is maintained at a substrate temperature of 450-500°C for 5-10 minutes, thereby improving the film quality;

[0010] C. Using trimethylgallium and high-purity oxygen as reaction sources, high-purity argon as carrier gas for trimethylgallium, the high-purity argon flow rate is 5-10sccm, and the high-purity oxygen flow rate is 200-250sccm; under the conditions of substrate temperature of 600-650°C and reaction chamber pressure of 10-15mbar, MOCVD equipment is used to grow on the low-temperature Ga2O3 buffer layer 2 for 3-5min to grow a Ga2O3 thin layer 3 with a thickness of 40-50nm; after the growth is completed, the O2 atmosphere in the reaction chamber is maintained, and the substrate temperature is maintained at 600-650°C for 5-10min, thereby optimizing the surface nucleation state, and forming a two-level composite buffer layer with the buffer layer 2, providing a good surface and nucleation site for subsequent layered films;

[0011] D. Using trimethylgallium and high-purity oxygen as reaction sources, using high-purity argon as carrier gas for trimethylgallium, with a high-purity argon flow rate of 10-20 sccm, and a high-purity oxygen flow rate of 400-500 sccm; using MOCVD equipment to grow a Ga2O3 thin layer 3 for 90-100 minutes at a growth temperature of 750°C-800°C and a reaction chamber pressure of 20-30 mbar, growing a Ga2O3 growth layer 4 with a thickness of 2-2.5 μm; maintaining an O2 atmosphere in the reaction chamber after the growth is completed, and then maintaining the substrate temperature at 750°C-800°C for 20-25 minutes, thereby relieving stress and reducing defects;

[0012] E. Using trimethylgallium and high-purity oxygen as reaction sources, using high-purity argon as the carrier gas of trimethylgallium, the high-purity argon flow rate is 30-40sccm, and the high-purity oxygen flow rate is 600-800sccm; under the conditions of substrate temperature of 850-900°C and reaction chamber pressure of 20-30mbar, using MOCVD equipment to grow on Ga2O3 growth layer 4 for 60-80min, growing a high-temperature Ga2O3 thin film layer 5 with a thickness of 2-3μm; after the growth is completed, the substrate is heated to 900-950°C, annealed in O2 atmosphere in the reaction chamber for 0.8-1.2 hours, and finally cooled to room temperature, thereby obtaining the high-thickness, high-quality Ga2O3 thin film material described in the present invention.

[0013] Effects and benefits of the present invention:

[0014] The present invention solves the problem of epitaxy of high-thickness and high-quality Ga2O3 thin film materials, and overcomes the problem that the current Ga2O3 heteroepitaxial and homoepitaxial crystals have poor quality and affect the performance of Ga2O3-based power devices; the present invention proposes a new specific method for obtaining high-thickness and high-quality Ga2O3 thick films by homoepitaxiality, which can effectively improve the crystal quality of the Ga2O3 thick film, and thus improve the working performance of Ga2O3-based devices. BRIEF DESCRIPTION OF THE DRAWINGS

[0015] Figure 1 : Schematic diagram of the structure of the high-thickness, high-quality Ga2O3 film prepared in Example 1;

[0016] Among them, the names of the various parts are: β-Ga2O3 single crystal substrate 1, low-temperature Ga2O3 buffer layer 2, Ga2O3 thin layer 3, Ga2O3 growth layer 4, high-temperature Ga2O3 thin film layer 5; the shadow in the single crystal substrate 1 is the substrate part that has been treated with NH3 plasma.

[0017] Figure 2 : XRD double crystal rocking curves of the high-thickness, high-quality Ga2O3 film (curve 1) and substrate (curve 2) prepared in Example 1 (tested using an Ultima IV X-ray diffractometer);

[0018] from Figure 2 It can be found that the quality of the Ga2O3 thin film crystal obtained by the method of the present invention is improved by more than one third compared with the substrate, and the half-peak width of the double crystal rocking curve is only 68.4 arcsec. This result proves that the present invention is effective in improving the quality of Ga2O3 thin film crystal. DETAILED DESCRIPTION

[0019] Embodiment 1:

[0020] A high-thickness, high-quality Ga2O3 homoepitaxial thin film material, the structural schematic diagram of which is shown in Figure 1 As shown, it is composed in sequence of a β-Ga2O3 single crystal substrate 1, a low-temperature Ga2O3 buffer layer 2 grown on the β-Ga2O3 single crystal substrate 1, a Ga2O3 thin layer 3 slowly grown on the low-temperature Ga2O3 buffer layer 2, a Ga2O3 growth layer 4 grown on the Ga2O3 thin layer 3, and a high-temperature Ga2O3 thin film layer 5 rapidly grown on the Ga2O3 growth layer 4.

[0021] A homoepitaxial preparation method of a high-thickness, high-quality Ga2O3 thin film material is provided by using MOCVD equipment, and the steps are as follows:

[0022] (1) The substrate 1 used for epitaxy is a high-quality β-Ga2O3 single crystal prepared by the EFG method, with a thickness of 650 μm. The β-Ga2O3 substrate 1 is ultrasonically cleaned with acetone, ethanol, and deionized water for 8 minutes in sequence, blown dry with high-purity nitrogen, and placed in the reaction chamber of the MOCVD equipment after NH3 plasma passivation treatment; the RF power of the NH3 plasma passivation treatment is 250 W, the temperature is 380°C, and the treatment time is 4 minutes.

[0023] (2) Growth of low-temperature Ga2O3 buffer layer 2: trimethylgallium and high-purity oxygen are used as reaction sources, high-purity argon is used as the carrier gas of trimethylgallium, the high-purity argon flow rate is 10sccm, the high-purity oxygen flow rate is 400sccm, the substrate temperature is 500℃, the growth pressure is 20mbar, the growth time is 8min, and the film thickness is 80nm; after the growth is completed, the O2 atmosphere in the reaction chamber is maintained at a substrate temperature of 500℃ for 5min to improve the film quality.

[0024] (3) During the growth of Ga2O3 thin layer 3, the substrate temperature was increased from 500°C to 650°C within 2 minutes, during which the film growth was maintained, and high-purity argon was used as the carrier gas for trimethylgallium. The high-purity argon flow rate was 5 sccm, the high-purity oxygen flow rate was 200 sccm, the growth pressure was 10 mbar, the growth time was 3 minutes, and the film thickness was 50 nm. After the growth was completed, the O2 atmosphere in the reaction chamber was maintained at a substrate temperature of 650°C for 5 minutes to achieve low-speed growth to achieve uniform atomic migration, so as to provide uniform nucleation sites for subsequent multi-level films.

[0025] (4) During the growth of the Ga2O3 growth layer 4, the growth temperature was increased from 650°C to 800°C within 5 minutes, high-purity argon was used as the carrier gas for trimethylgallium, the high-purity argon flow rate was 10 sccm, the high-purity oxygen flow rate was 400 sccm, the growth pressure was 20 mbar, the growth time was 90 minutes, and the film thickness was 2.5 μm; after the growth was completed, the O2 atmosphere in the reaction chamber was maintained at a substrate temperature of 800°C for 20 minutes to relieve stress and reduce defects;

[0026] (5) During the growth of the high-temperature Ga2O3 thin film layer 5, the growth temperature was increased from 800°C to 900°C within 3 minutes, high-purity argon was used as the carrier gas of trimethylgallium, the high-purity argon flow rate was 40 sccm, and the high-purity oxygen flow rate was 800 sccm; the growth pressure was 20 mbar, the growth time was 60 minutes, and the film thickness was 2.5 μm; after the growth was completed, the O2 atmosphere in the reaction chamber was maintained, and high-temperature annealing at 900°C was performed in the reaction chamber for 60 minutes. Finally, the temperature was lowered and samples were taken to obtain the high-thickness, high-quality Ga2O3 thin film material of the present invention.

Claims

1. A homoepitaxial preparation method of a high-thickness, high-quality Ga2O3 thin film material, the steps of which are as follows: A. The β-Ga2O3 single crystal substrate (1) is ultrasonically cleaned with acetone, ethanol, and deionized water for 5 to 10 minutes in sequence, blown dry with high-purity nitrogen, and then subjected to NH3 plasma passivation treatment; B. Using trimethylgallium and high-purity oxygen as reaction sources, growing a low-temperature Ga2O3 buffer layer (2) with a thickness of 40 to 80 nm on a β-Ga2O3 single crystal substrate (1) using an MOCVD device at a substrate temperature of 450 to 500° C. and a reaction chamber pressure of 20 to 30 mbar for 5 to 8 minutes; after the growth is completed, an O2 atmosphere is maintained in the chamber at a substrate temperature of 450 to 500° C. for 5 to 10 minutes; C. Using trimethylgallium and high-purity oxygen as reaction sources, growing a Ga2O3 thin layer (3) with a thickness of 40 to 50 nm on the low-temperature Ga2O3 buffer layer (2) using an MOCVD device under the conditions of a substrate temperature of 600 to 650° C. and a reaction chamber pressure of 10 to 15 mbar for 3 to 5 minutes; after the growth is completed, an O2 atmosphere is maintained in the reaction chamber, and the substrate temperature is maintained at 600 to 650° C. for 5 to 10 minutes; D. Using trimethylgallium and high-purity oxygen as reaction sources, growing a Ga2O3 thin layer (3) for 90 to 100 minutes using a MOCVD device at a growth temperature of 750° C. to 800° C. and a reaction chamber pressure of 20 to 30 mbar, thereby growing a Ga2O3 growth layer (4) with a thickness of 2 to 2.5 μm; maintaining an O2 atmosphere in the reaction chamber after the growth is completed, and then maintaining the substrate temperature at 750° C. to 800° C. for 20 to 25 minutes; E. Using trimethylgallium and high-purity oxygen as reaction sources, under the conditions of substrate temperature of 850-900° C. and reaction chamber pressure of 20-30 mbar, MOCVD equipment is used to grow a high-temperature Ga2O3 thin film layer (5) with a thickness of 2-3 μm on the Ga2O3 growth layer (4) for 60-80 minutes; after the growth is completed, the substrate is heated to 900-950° C., annealed in an O2 atmosphere in the reaction chamber for 0.8-1.2 hours, and finally cooled to room temperature, thereby obtaining a high-thickness, high-quality Ga2O3 thin film material.

2. The homoepitaxial preparation method of a high-thickness, high-quality Ga2O3 thin film material according to claim 1, characterized in that: In step A, the radio frequency power of the NH3 plasma passivation treatment is 200-300W, the treatment temperature is 350-400°C, and the treatment time is 4-5 minutes.

3. The homoepitaxial preparation method of a high-thickness, high-quality Ga2O3 thin film material according to claim 1, characterized in that: In step B, high-purity argon is used as the carrier gas of trimethylgallium, the flow rate of the high-purity argon is 10-20 sccm, and the flow rate of the high-purity oxygen is 400-500 sccm.

4. The homoepitaxial preparation method of a high-thickness, high-quality Ga2O3 thin film material according to claim 1, characterized in that: In step C, high-purity argon is used as the carrier gas of trimethylgallium, the flow rate of the high-purity argon is 5-10 sccm, and the flow rate of the high-purity oxygen is 200-250 sccm.

5. The homoepitaxial preparation method of a high-thickness, high-quality Ga2O3 thin film material according to claim 1, characterized in that: In step D, high-purity argon is used as the carrier gas of trimethylgallium, the flow rate of the high-purity argon is 10-20 sccm, and the flow rate of the high-purity oxygen is 400-500 sccm.

6. The homoepitaxial preparation method of a high-thickness, high-quality Ga2O3 thin film material according to claim 1, characterized in that: In step E, high-purity argon is used as a carrier gas for trimethylgallium, the flow rate of the high-purity argon is 30-40 sccm, and the flow rate of the high-purity oxygen is 600-800 sccm.

7. A high-thickness, high-quality Ga2O3 thin film material, characterized by: The method is prepared by any one of claims 1 to 6.

Images