A method for preparing gallium oxide thin film by plasma thermal oxidation

Abstract

A method for preparing gallium oxide film by plasma thermal oxidation, wherein the gallium nitride film is transferred into a plasma enhanced chemical vapor deposition device and placed in the middle of the heating zone of a tubular furnace, a mechanical pump is started to evacuate the tubular furnace, the pressure in the tubular furnace is maintained at 10-30 Pa, and then the temperature of the tubular furnace is increased to 800-900°C; argon and oxygen are simultaneously input into the tubular furnace, and when the pressure in the tubular furnace is stabilized at 20-100 Pa, a radio frequency power supply is turned on to generate plasma, and the introduction of argon is stopped after the discharge in the tubular furnace is stabilized; after the discharge is stabilized again, the temperature in the tubular furnace is kept unchanged, and thermal oxidation treatment is performed; the radio frequency power supply is turned off, the introduction of oxygen is stopped, and the tubular furnace is naturally cooled to room temperature while the mechanical pump is kept working. The present invention realizes rapid and high-quality preparation of gallium oxide film.

Description

Technical Field

[0001] The invention relates to the technical field of semiconductor materials, and in particular to a method for preparing a gallium oxide film by plasma thermal oxidation. Background Art

[0002] Due to the electrical performance limitations of silicon itself, such as the bandgap width and breakdown field strength, after decades of technological development, silicon-based devices have shown a trend of being unable to fully meet the industry's demand for electronic devices. At present, the third-generation semiconductors, namely wide bandgap semiconductors, such as gallium nitride, silicon carbide, diamond, gallium oxide, etc., have gradually entered the scope of interest of researchers and the industry. Among them, the bandgap width of gallium oxide is 4.9-5.1eV, second only to diamond, and it has extremely high transmittance in the visible light band and light response in the day-blind ultraviolet band. Gallium oxide (Ga2O3) has five main unit cell structures, named α, β, γ, δ, and ε, among which β-Ga2O3 is the most stable and has been studied the most. Gallium oxide in the following text refers to β-Ga2O3. The extremely high breakdown field strength, high carrier mobility, and good thermal stability make gallium oxide have great application potential in the manufacture of high-power, high-voltage devices and ultraviolet band detection, and it is expected to become a semiconductor material with more application prospects after wide bandgap semiconductors such as silicon carbide and gallium nitride.

[0003] At present, the main methods for preparing gallium oxide thin films are mechanical peeling from single crystals, magnetron sputtering, atomic layer deposition, metal organic chemical vapor deposition, pulsed laser deposition, halide vapor phase epitaxy and molecular beam epitaxy. Although the gallium oxide thin films prepared by the above methods have excellent performance, the equipment and raw materials are expensive, and some methods are not suitable for large-scale preparation. The method of thermal oxidation growth of gallium oxide, that is, oxidizing gallium nitride and gallium arsenide thin films at high temperatures, is inexpensive and suitable for large-scale growth, but the prepared film performance has no advantages, low crystallinity, and there are usually residual raw material grains in the film. The required temperature is greater than or equal to 900°C and the required oxidation time is long, and long-term heating consumes a lot of energy. Summary of the invention

[0004] The purpose of the present invention is to solve the above problems in the prior art and provide a method for preparing gallium oxide thin film by plasma thermal oxidation, so as to achieve the growth of gallium oxide thin film material by using a continuous plasma discharge method so as to make gallium nitride thin film in an atmosphere of oxygen and argon.

[0005] In order to achieve the above object, the present invention adopts the following technical scheme:

[0006] A method for preparing a gallium oxide film by plasma thermal oxidation comprises the following steps:

[0007] (1) Using GaN thin films grown on c-plane sapphire substrates;

[0008] (2) cleaning the gallium nitride with an aqueous solution of HCl, and then ultrasonically cleaning with acetone, anhydrous ethanol, and deionized water in sequence;

[0009] (3) transferring the gallium nitride film into a plasma enhanced chemical vapor deposition device and placing it in the middle of the heating zone of the tube furnace, starting a mechanical pump to evacuate the tube furnace, maintaining the pressure in the tube furnace at 10-30 Pa, and then raising the temperature of the tube furnace to 800-900° C.;

[0010] (4) simultaneously inputting argon and oxygen into the tube furnace, when the pressure in the tube furnace is stabilized at 20-100 Pa, turning on the radio frequency power supply to generate plasma, and stopping the introduction of argon after the discharge in the tube furnace is stable; after the discharge is stabilized again, keeping the temperature in the tube furnace unchanged, and performing thermal oxidation treatment;

[0011] (5) Turn off the RF power supply, stop supplying oxygen, keep the mechanical pump running, and allow the tube furnace to cool naturally to room temperature.

[0012] In step 4, by controlling the thermal oxidation time and gas flux in step (4), the thickness of the gallium oxide film can be obtained as required.

[0013] In the step (4), the thermal oxidation treatment time is 60 to 300 minutes.

[0014] In the step (4), the oxygen flow rate is 20 to 60 sccm, and the argon flow rate is 2 to 10 sccm.

[0015] In the step (4), the discharge current is between 2.0 and 3.5 A.

[0016] In the step (1), the gallium nitride film is prepared by a metal organic chemical vapor deposition method and has a thickness of 700 to 900 nm.

[0017] In the step (2), the volume ratio of the HCl aqueous solution is HCl:H2O=1:1.

[0018] The plasma enhanced chemical vapor deposition device comprises a tube furnace, a heating system, a vacuum system, a gas flow control system and a plasma generating system; one side of the tube furnace is connected to the gas flow control system, and the other side is connected to the vacuum system; the plasma generating system is composed of two metal electrode rods installed at both ends of the tube furnace and a radio frequency power supply; the gas flow control system is used to control the flow rate of gas flowing into the tube furnace; the heating system is arranged on the outer periphery of the tube furnace and is used to heat the tube furnace.

[0019] The tube furnace is made of quartz.

[0020] The vacuum system is composed of a primary mechanical pump, which can evacuate the inside of the tube furnace to a vacuum degree below 20Pa.

[0021] Compared with the prior art, the technical solution of the present invention has the following beneficial effects:

[0022] 1. The present invention uses low-temperature plasma technology to accelerate the growth of gallium oxide. Plasma allows the reaction to proceed quickly, and compared with the traditional thermal oxidation method, the reaction temperature and preparation time can be reduced.

[0023] 2. The gallium oxide film prepared by the present invention has a better crystal quality. The plasma has a higher reactivity, and the prepared gallium oxide film has a lower roughness, a larger grain size and a uniform crystallization.

[0024] 3. The present invention uses a single device, has low equipment cost, is simple to operate, and has better product quality. BRIEF DESCRIPTION OF THE DRAWINGS

[0025] Figure 1 It is a schematic structural diagram of a plasma enhanced chemical vapor deposition device of the present invention;

[0026] Figure 2 This is a scanning electron microscope image of a cross section of a gallium oxide thin film prepared in Example 1;

[0027] Figure 3 This is a scanning electron microscope image of a cross section of a gallium oxide thin film prepared in Comparative Example 1;

[0028] Figure 4 X-ray diffraction patterns of the gallium oxide thin films prepared in Example 1 and Comparative Example 1;

[0029] Figure 5 Atomic force microscope images of gallium oxide films prepared in Example 1 and Comparative Example 1;

[0030] Figure 6 This is a scanning electron microscope image of a cross section of a gallium oxide thin film prepared in Example 2;

[0031] Figure 7 This is a scanning electron microscope image of the cross section of the gallium oxide film prepared in Example 3. DETAILED DESCRIPTION

[0032] In order to make the technical problems, technical solutions and beneficial effects to be solved by the present invention clearer and more understandable, the present invention is further described in detail below in conjunction with the accompanying drawings and embodiments.

[0033] like Figure 1 As shown, the plasma enhanced chemical vapor deposition device of the present invention includes a quartz tube furnace, a heating furnace, a vacuum pump, a gas flow control system and a plasma generation system;

[0034] One side of the tube furnace is provided with an inlet pipe connected to a gas flow control system for controlling the flow of oxygen and argon into the tube furnace, and the other side of the tube furnace is connected to a vacuum pump to discharge the waste gas; the plasma generation system is composed of two metal electrodes installed at both ends of the tube furnace and a radio frequency power supply; the heating furnace is arranged at the periphery of the tube furnace for heating the tube furnace; the gallium nitride-sapphire substrate is placed in a quartz boat, and the quartz boat is placed in the center of the tube furnace. Specifically, the vacuum pump adopts a first-stage mechanical pump, which can evacuate the tube furnace to a vacuum degree below 20Pa.

[0035] A method for preparing a gallium oxide film by plasma thermal oxidation comprises the following steps:

[0036] (1) Using a gallium nitride film grown on a c-plane sapphire substrate; the gallium nitride film is prepared by a metal organic chemical vapor deposition method and has a thickness of 700 to 900 nm;

[0037] (2) cleaning the gallium nitride with an aqueous HCl solution, and then ultrasonically cleaning with acetone, anhydrous ethanol, and deionized water in sequence; the volume ratio of the aqueous HCl solution is HCl:H2O=1:1;

[0038] (3) transferring the gallium nitride film into a plasma enhanced chemical vapor deposition device and placing it in the middle of the heating zone of a tube furnace, starting a mechanical pump to evacuate the tube furnace, maintaining the pressure in the tube furnace at 10 to 30 Pa, and then raising the temperature of the tube furnace to 800 to 900° C.; the heating rate of the tube furnace can be 10 to 20° C. / min;

[0039] (4) simultaneously inputting argon and oxygen into the tube furnace, when the pressure in the tube furnace is stabilized at 20-100 Pa, turning on the radio frequency power supply to generate plasma, and stopping the introduction of argon after the discharge in the tube furnace is stable; after the discharge is stabilized again, keeping the temperature in the tube furnace unchanged, and performing thermal oxidation treatment;

[0040] (5) Turn off the RF power supply, stop introducing oxygen, keep the mechanical pump running, and allow the tubular furnace to cool naturally to room temperature; specifically, the pressure in the tubular furnace can be maintained at 10 to 30 Pa.

[0041] In the step (4), the thermal oxidation time and gas flux are controlled to obtain the thickness of the gallium oxide film as required; the thermal oxidation treatment time is 60 to 300 minutes; the oxygen flow rate is 20 to 60 sccm, and the argon flow rate is 2 to 10 sccm; the discharge current is 2.0 to 3.5A.

[0042] Experimental Example 1

[0043] A method for preparing a gallium oxide film by plasma thermal oxidation comprises the following steps:

[0044] (1) A GaN film grown on a c-plane sapphire substrate; the GaN film was prepared by metal organic chemical vapor deposition, with a thickness of 900 nm and a size of 10 mm × 10 mm;

[0045] (2) cleaning the gallium nitride with an aqueous HCl solution, and then ultrasonically cleaning with acetone, anhydrous ethanol, and deionized water in sequence; the volume ratio of the aqueous HCl solution is HCl:H2O=1:1;

[0046] (3) Transfer the GaN film to the middle position of the heating zone of the tube furnace, start the vacuum pump to evacuate the tube furnace, maintain the pressure in the tube furnace at 20 Pa, and then increase the temperature of the tube furnace to 900 °C;

[0047] (4) simultaneously inputting 5 sccm argon and 20 sccm oxygen into the tube furnace. When the pressure in the tube furnace is stable, turning on the radio frequency power supply to generate plasma, and stopping the introduction of argon after the discharge in the tube furnace is stable; after the discharge is stable again, adjusting the power to 3.0 A, keeping the temperature in the tube furnace unchanged, and performing thermal oxidation treatment for 60 min;

[0048] (5) Turn off the RF power supply, stop supplying oxygen, keep the vacuum pump running, and allow the tube furnace to cool naturally to room temperature.

[0049] Figure 2 This is a scanning electron microscope image of a cross section of the gallium oxide film prepared in Example 1, wherein the thickness of the gallium oxide layer is about 180 nm.

[0050] Comparative Example 1

[0051] A method for preparing a gallium oxide film by thermal oxidation comprises the following steps:

[0052] (1) A GaN film grown on a c-plane sapphire substrate; the GaN film was prepared by metal organic chemical vapor deposition, with a thickness of 900 nm and a size of 10 mm × 10 mm;

[0053] (2) cleaning the gallium nitride with an aqueous HCl solution, and then ultrasonically cleaning with acetone, anhydrous ethanol, and deionized water in sequence; the volume ratio of the aqueous HCl solution is HCl:H2O=1:1;

[0054] (3) Transfer the GaN film to the middle position of the heating zone of the tube furnace, start the vacuum pump to evacuate the tube furnace, maintain the pressure in the tube furnace at 20 Pa, and then increase the temperature of the tube furnace to 900 °C;

[0055] (4) introducing 20 sccm of oxygen into the tube furnace for 60 min of thermal oxidation treatment;

[0056] (5) Turn off the power, stop supplying oxygen, keep the vacuum pump running, and allow the tube furnace to cool naturally to room temperature.

[0057] Figure 3 This is a scanning electron microscope image of a cross section of a gallium oxide thin film prepared in Comparative Example 1, wherein the thickness of the gallium oxide layer is about 80 nm.

[0058] By comparison Figure 2 and Figure 3 , it can be proved that the use of plasma enhanced thermal oxidation can accelerate the oxidation rate of gallium oxide films.

[0059] Figure 4 X-ray diffraction patterns of the gallium oxide films prepared in Example 1 and Comparative Example 1, in which the crystal plane orientations corresponding to gallium oxide are marked, wherein a is the sample of Example 1 subjected to plasma enhanced thermal oxidation for 60 min, and b is the sample of Comparative Example 1 subjected to ordinary thermal oxidation for 60 min. The characteristic crystal peaks of plasma enhanced thermal oxidation are more obvious.

[0060] Figure 5 These are atomic force microscopy images of gallium oxide films prepared in Example 1 and Comparative Example 1, wherein a is the sample of Example 1 subjected to plasma enhanced thermal oxidation for 60 min, and b is the sample of Comparative Example 1 subjected to ordinary thermal oxidation for 60 min. Ra represents the average roughness, and the surface roughness of the surface subjected to plasma enhanced thermal oxidation is lower and the quality is better.

[0061] Example 2

[0062] A method for preparing a gallium oxide film by plasma thermal oxidation comprises the following steps:

[0063] (1) A GaN film grown on a c-plane sapphire substrate; the GaN film was prepared by metal organic chemical vapor deposition, with a thickness of 900 nm and a size of 5 mm × 5 mm;

[0064] (2) cleaning the gallium nitride with an aqueous HCl solution, and then ultrasonically cleaning with acetone, anhydrous ethanol, and deionized water in sequence; the volume ratio of the aqueous HCl solution is HCl:H2O=1:1;

[0065] (3) Transfer the GaN film to the middle position of the heating zone of the tube furnace, start the vacuum pump to evacuate the tube furnace, maintain the pressure in the tube furnace at 20 Pa, and then increase the temperature of the tube furnace to 900 °C;

[0066] (4) 10 sccm argon and 60 sccm oxygen were simultaneously introduced into the tube furnace. When the pressure in the tube furnace was stable, the RF power supply was turned on to generate plasma. After the discharge in the tube furnace was stable, the introduction of argon was stopped. After the discharge was stable again, the power was adjusted to 3.2 A, the temperature in the tube furnace was kept constant, and thermal oxidation treatment was performed for 60 minutes.

[0067] (5) Turn off the RF power supply, stop supplying oxygen, keep the vacuum pump running, and allow the tube furnace to cool naturally to room temperature.

[0068] Figure 6 This is a scanning electron microscope image of a cross section of the gallium oxide film prepared in Example 2, wherein the thickness of the gallium oxide layer is about 270 nm.

[0069] By comparison Figure 2 and Figure 6 It can be proved that the thickness of gallium oxide film can be changed by adjusting the gas flow rate.

[0070] Example 3

[0071] A method for preparing a gallium oxide film by plasma thermal oxidation comprises the following steps:

[0072] (1) A GaN film grown on a c-plane sapphire substrate; the GaN film was prepared by metal organic chemical vapor deposition, with a thickness of 900 nm and a size of 5 mm × 5 mm;

[0073] (2) cleaning the gallium nitride with an aqueous HCl solution, and then ultrasonically cleaning with acetone, anhydrous ethanol, and deionized water in sequence; the volume ratio of the aqueous HCl solution is HCl:H2O=1:1;

[0074] (3) Transfer the GaN film to the middle position of the heating zone of the tube furnace, start the vacuum pump to evacuate the tube furnace, maintain the pressure in the tube furnace at 20 Pa, and then increase the temperature of the tube furnace to 900 °C;

[0075] (4) 10 sccm argon and 60 sccm oxygen were simultaneously introduced into the tube furnace. When the pressure in the tube furnace was stable, the RF power supply was turned on to generate plasma. After the discharge in the tube furnace was stable, the introduction of argon was stopped. After the discharge was stable again, the power was adjusted to 3.2 A, the temperature in the tube furnace was kept constant, and thermal oxidation treatment was performed for 180 min.

[0076] (5) Turn off the RF power supply, stop supplying oxygen, keep the vacuum pump running, and allow the tube furnace to cool naturally to room temperature.

[0077] Figure 7 This is a scanning electron microscope image of a cross section of the gallium oxide film prepared in Example 3, wherein the thickness of the gallium oxide layer is about 650 nm.

[0078] By comparison Figure 6 and Figure 7 It can be proved that the thickness of gallium oxide film can be changed by adjusting the thermal oxidation time.

[0079] In the plasma-enhanced oxidation reaction of the present invention, the collision of a large number of electrons causes the oxygen molecules to dissociate, excite or ionize, so that the oxygen plasma contains a large number of oxygen atoms, positively charged oxygen ions, electrons and neutral oxygen molecules, etc. These particles can promote the oxidation reaction of the reactants, reduce the temperature required for the reaction to a certain extent, and accelerate the oxidation reaction. The present invention combines the radio frequency oxygen plasma enhanced reaction with the thermal oxidation to prepare gallium oxide, and takes the advantages of both, so as to achieve the rapid preparation of high-quality crystalline gallium oxide film using equipment with low cost and simple operation. The present invention can achieve rapid and high-quality preparation of gallium oxide film by adjusting the growth temperature, oxygen flow rate and discharge power.

Claims

1. A method for preparing a gallium oxide thin film by plasma thermal oxidation, characterized in that The following steps are involved: (1) Using GaN thin films grown on c-plane sapphire substrates; (2) Clean the gallium nitride with an aqueous solution of HCl, and then ultrasonically clean it with acetone, anhydrous ethanol, and deionized water in sequence; (3) Transfer the GaN film to the plasma enhanced chemical vapor deposition device and place it in the middle of the heating zone of the tube furnace. Start the mechanical pump to evacuate the tube furnace and maintain the pressure in the tube furnace at 10-30 Pa. Then, raise the temperature of the tube furnace to 800-900 °C. (4) Argon and oxygen are introduced into the tube furnace at the same time. When the pressure in the tube furnace is stable at 20-100 Pa, the RF power supply is turned on to generate plasma. After the discharge in the tube furnace is stable, the introduction of argon is stopped. After the discharge is stable again, the temperature in the tube furnace is kept unchanged and thermal oxidation treatment is carried out. (5) Turn off the RF power supply, stop supplying oxygen, keep the mechanical pump running, and allow the tube furnace to cool naturally to room temperature; The plasma enhanced chemical vapor deposition device comprises a tube furnace, a heating system, a vacuum system, a gas flow control system and a plasma generating system; one side of the tube furnace is connected to the gas flow control system, and the other side is connected to the vacuum system; the plasma generating system is composed of two metal electrode rods installed at both ends of the tube furnace and a radio frequency power supply; the gas flow control system is used to control the flow rate of gas flowing into the tube furnace; the heating system is arranged on the outer periphery of the tube furnace and is used to heat the tube furnace.

2. The method for preparing gallium oxide thin film by plasma thermal oxidation according to claim 1, characterized in that: By controlling the thermal oxidation time and gas flux in step (4), the thickness of the gallium oxide film can be obtained as required.

3. The method for preparing gallium oxide thin film by plasma thermal oxidation according to claim 1, characterized in that: In the step (4), the thermal oxidation treatment time is 60 to 300 minutes.

4. The method for preparing a gallium oxide thin film by plasma thermal oxidation according to claim 1, characterized in that: In the step (4), the oxygen flow rate is 20-60 sccm, and the argon flow rate is 2-10 sccm.

5. The method for preparing a gallium oxide thin film by plasma thermal oxidation according to claim 1, characterized in that: In the step (4), the discharge current is between 2.0 and 3.5 A.

6. The method for preparing a gallium oxide thin film by plasma thermal oxidation according to claim 1, characterized in that: In the step (1), the gallium nitride film is prepared by a metal organic chemical vapor deposition method and has a thickness of 700-900 nm.

7. The method for preparing gallium oxide thin film by plasma thermal oxidation according to claim 1, characterized in that: In the step (2), the volume ratio of the HCl aqueous solution is HCl:H2O=1:

1.

8. The method for preparing gallium oxide thin film by plasma thermal oxidation according to claim 1, characterized in that: The tube furnace is made of quartz.

9. The method for preparing a gallium oxide thin film by plasma thermal oxidation according to claim 1, characterized in that: The vacuum system is composed of a primary mechanical pump, which can evacuate the tube furnace to a vacuum degree below 20 Pa.

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