Method for preparing sn-doped beta-ga2o3 thin film with improved mobility and carrier concentration

Abstract

The application discloses a preparation method of Sn-doped beta-Ga2O3 film with improved mobility and carrier concentration, and mainly solves the problems of poor crystallization quality of existing beta-Ga2O3 epitaxial film and incapability of simultaneously having high mobility and high carrier concentration. The implementation scheme is as follows: a substrate is selected and cleaned; the cleaned substrate is placed into a reaction cavity of a MOCVD for annealing treatment; N2 is used as a carrier gas of Ga source and Sn source, and N2 and O2 are intermittently input in different stages in a gas path cycle, so as to provide intermittent O atoms, Ga atoms and Sn atoms for the reaction cavity, and Sn-doped beta-Ga2O3 film is formed through the joint action of the three kinds of atoms on the substrate surface after high-temperature annealing, and then cooling is performed to complete the preparation of the beta-Ga2O3 film. The application not only significantly reduces the defect density of the epitaxial film, but also effectively improves the electrical performance of the film, and can be used for manufacturing high-power and high-frequency electronic devices.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of microelectronics, and particularly relates to a growth method of Sn-doped β-Ga2O3 film, which can be used for the preparation of high-frequency and high-voltage devices. BACKGROUND

[0002] Gallium oxide (Ga2O3), especially its most stable β-phase gallium oxide (β-Ga2O3), is considered as one of the core candidates for a new generation of wide-bandgap semiconductor materials due to its super-wide band gap of 4.9 eV, high breakdown field of up to 8 MV / cm, excellent thermal stability, and relatively high dielectric constant. In the field of high-power electronic devices, β-Ga2O3, with its superior material performance, shows higher power density and breakdown resistance than traditional semiconductor materials (such as Si and GaN), and can be widely used in high-voltage switching devices, radio frequency power amplifiers, and inverters and other key equipment. In addition, due to its wide band gap, β-Ga2O3 is highly sensitive to ultraviolet light and has important application potential in the fields of ultraviolet detectors and optical sensors.

[0003] However, due to the low intrinsic conductivity of β-Ga2O3, its further development in electronic devices is limited. By appropriately doping n-type elements (such as Sn, Si, etc.), the carrier concentration can be significantly improved, and the material can be given higher conductivity to meet the performance requirements of high-power, high-frequency and high-temperature devices. In this context, how to efficiently dope to balance the carrier concentration and mobility, and maintain high crystalline quality of the film while improving the conductivity, has become an important research direction in the field of β-Ga2O3 materials. However, existing doping techniques face a series of problems, including poor doping uniformity, many lattice defects, limited carrier mobility, and complex preparation process and low production efficiency, which greatly limit the further application of β-Ga2O3 films.

[0004] In 2020, Akhil Mauze et al. published a paper entitled "Sn doping of (010) β-Ga2O3 films grown by plasma-assisted molecular beam epitaxy" in the journal Applied Physics Letters, 117, 222102, 2020, which proposed to prepare a film by PAMBE method by continuously introducing Sn at high temperature to achieve n-type doping. However, this continuous Sn doping not only causes self-compensation effect at high temperature, resulting in a decrease in carrier concentration, but also causes an undesirable "delay effect", which makes the gradient profile of the doping distribution relatively slow, affecting the uniformity and electrical properties of the film.

[0005] In 2024, Siliang Kuang et al. published a paper titled "Transport and electronic structure properties of MBE grown Sn doped Ga2O3 homo-epitaxial films", which proposed using MBE grown Sn doped β-Ga2O3 thin films to improve the electrical conductivity and carrier concentration of the material, while achieving high quality epitaxy on the film surface through precise control. Although this method has advantages in precise doping and thin film quality control, the use of MBE method for low temperature Sn doping on the one hand introduces band gap defect states, resulting in self-compensation effect, reducing the doping efficiency and mobility; on the other hand, it also causes surface band bending, forming an electron depletion layer, increasing the interface resistance. Therefore, it is urgent to break through the bottleneck of the prior art and improve the electrical properties of β-Ga2O3 thin films to fully release their potential in high power, high frequency electronic devices and optoelectronic applications. SUMMARY

[0006] The purpose of the present application is to overcome the shortcomings of the prior art and provide a Sn doped β-Ga2O3 thin film preparation method with high mobility and high carrier concentration to improve the crystalline quality and electrical properties of epitaxial thin films.

[0007] The technical solution to achieve the purpose of the present application is: using metal organic chemical vapor deposition (MOCVD) method, by intermittently introducing Ga, Sn and O elements into the reaction chamber, growing high quality and high electrical performance β-Ga2O3 epitaxial thin film on the substrate surface, the specific steps include as follows:

[0008] (1) Put the substrate into hydrofluoric acid, acetone solution and isopropyl alcohol solution for ultrasonic cleaning;

[0009] (2) Put the cleaned substrate on the graphite base of the MOCVD reaction chamber and perform high temperature annealing treatment at 900-1000℃;

[0010] (3) Grow double pulse Sn doped β-Ga2O3 thin film on the annealed substrate:

[0011] (3a) In the first stage of the gas path, open the N2 valve and close the O2 valve, and introduce the carrier gas N2 into the three ethyl gallium (TEGa) organic source bottle and the four (dimethylamino) tin (TDMASn) organic source bottle at the same time, to bring TEGa molecules and TDMASn molecules into the reaction chamber, providing Ga atoms and Sn atoms intermittently;

[0012] (3b) in the second stage of the gas path input cycle, the N2 valve is closed, the O2 valve is opened, O2 is input into the reaction chamber to intermittently provide O atoms for the reaction chamber, and the Sn doped beta-Ga2O3 film is formed on the substrate surface after high-temperature annealing through the joint action of Ga, Sn and O atoms;

[0013] (3c) the reaction chamber temperature is set to 700-900 DEG C, the gas path input cycle of steps (3a) and (3b) is repeated, until the input time of Ga and Sn gas paths reaches the set time of 60-120 min, and the beta-Ga2O3 film with a thickness of 0.5-1 mu m is formed on the substrate surface after high-temperature annealing;

[0014] (4) after the epitaxial Sn doped beta-Ga2O3 film is cooled to room temperature in an O2 atmosphere, the vacuum valve is closed, high-purity N2 is input until the reaction chamber pressure is equal to the external pressure, and the Sn doped beta-Ga2O3 epitaxial film is prepared.

[0015] Preferably, in step (3a), the carrier gas N2 is input into the triethyl gallium TEGa organic source bottle and the tetra (dimethylamino) tin TDMASn organic source bottle at the same time, the flow rate of the carrier gas N2 input into the TEGa is 20-60 sccm, the flow rate of the carrier gas N2 input into the TDMASn is 2-6 sccm, and the input time is 0.2-0.6 min.

[0016] Preferably, in step (3b), the O2 is input into the reaction chamber at a flow rate of 2000-2200 sccm for 0.1 min.

[0017] Preferably, the above substrate is any one of Ga2O3, GaN, SiC, Al2O3, Si and AlN.

[0018] Compared with the prior art, the present application has the following advantages:

[0019] Firstly, the present application adopts the growth method of intermittent input of Ga and O, which is beneficial to inhibit the formation of defects in the film growth process, and can significantly improve the crystallization quality of the beta-Ga2O3 film growth.

[0020] Secondly, the present application adopts the intermittent doping method of Sn, which is beneficial to the formation of short-range ordered distribution of Sn atoms in the beta-Ga2O3 film, and can significantly improve the electrical properties of the Sn doped beta-Ga2O3 film. BRIEF DESCRIPTION OF DRAWINGS

[0021] Figure 1 The flow chart of the present application is shown in the figure;

[0022] Figure 2Time diagram for the intermittent introduction of TEGa and TDMASn organic source bottles, O2 into the reaction chamber in the present application;

[0023] Figure 3 Schematic diagram of the thin film epitaxially grown on the substrate in the present application. DETAILED DESCRIPTION

[0024] In order to make the present application more clear, the following further describes the embodiments of the present application in combination with the drawings and examples.

[0025] Reference Figure 1 The present application gives the following three embodiments:

[0026] Embodiment 1: Set the temperature to 700℃, the O2 flow rate to 2000sccm, the carrier gas N2 flow rate into the Ga source to 20sccm, the carrier gas N2 flow rate into the Sn source to 2sccm, and the Ga and Sn source pulse introduction time to 0.2min, and grow the β-Ga2O3 thin film by double-pulse Sn doping on the annealed Ga2O3 substrate.

[0027] Step 1: Clean the Ga2O3 substrate.

[0028] Select the Ga2O3 substrate, and sequentially place it into the hydrofluoric acid, acetone, and isopropyl alcohol solutions for ultrasonic cleaning for 3min, 10min, and 20min, respectively, and then dry it with nitrogen.

[0029] Step 2: Perform high-temperature annealing treatment on the cleaned Ga2O3 substrate.

[0030] 2.1) Place the cleaned Ga2O3 substrate on the graphite susceptor in the MOCVD reaction chamber, open the primary vacuum pump to vacuumize the reaction chamber, open the secondary vacuum pump when the pressure in the reaction chamber drops to 40Torr, and open the graphite tray rotation power supply when the pressure in the reaction chamber reaches 10 -3 Torr, and make the graphite tray rotate at a speed of 20r / min.

[0031] 2.2) Raise the temperature to 900℃, open the N2 and O2 control ends, make N2 and O2 flow into the reaction chamber at flow rates of 500sccm and 2000sccm respectively, and maintain the pressure in the reaction chamber at 20Torr, and perform substrate annealing for 80min in this environment.

[0032] Step 3: Grow the double-pulse Sn-doped β-Ga2O3 thin film on the annealed Ga2O3 substrate.

[0033] The existing method for growing a Sn-doped thin film on an annealed Ga2O3 substrate is to use N2 as the carrier gas for Ga source and Sn source, continuously introduce N2 and O2 into the reaction chamber for growth of the Sn-doped thin film. The prepared thin film not only has a self-compensation effect, which makes the thin film unable to have high carrier concentration and high carrier mobility, but also has low crystalline quality. To solve this problem, the present example adopts a double-pulse Sn-doping method, uses N2 as the carrier gas for Ga source and Sn source, sets different stages for the gas path in the introduction cycle, and introduces N2 and O2 intermittently in different stages. On the one hand, this is conducive to the formation of a short-range ordered distribution of Sn in the thin film, so that the thin film has high carrier concentration and mobility. On the other hand, this inhibits the formation of defects in the thin film, and the crystalline quality of the thin film is improved.

[0034] Reference Figure 2 The implementation of the present step is as follows:

[0035] 3.1) In the first stage of the gas path introduction cycle, open the N2 valve and close the O2 valve, use the carrier gas N2 as the Ga source to pass through a branch at a flow rate of 20 sccm to introduce the triethyl gallium TEGa organic source bottle, and the introduction time is 0.2 min;

[0036] 3.2) In the first stage of the gas path introduction cycle, keep the N2 valve open and the O2 valve closed, use the carrier gas N2 as the Sn source to pass through another branch at a flow rate of 2 sccm to introduce the tetra (dimethylamino) tin TDMASn organic source bottle, and the introduction time is 0.2 min;

[0037] 3.3) In the second stage of the gas path introduction cycle, close the N2 valve and open the O2 valve, introduce O2 as the O source into the reaction chamber at a flow rate of 2000 sccm, and the introduction time is 0.1 min;

[0038] 3.4) Set the reaction chamber temperature to 700℃, repeat steps 3.1) to 3.3) until the intermittent introduction time of Ga and Sn gas paths reaches the set time of 60 min, and a β-Ga2O3 thin film with a thickness of 0.50μm and a half-width of 60 arcsec is formed on the surface of the high-temperature annealed substrate.

[0039] Step 4: cooling treatment of the β-Ga2O3 thin film.

[0040] Under the O2 atmosphere, the flow rate of O2 is 2000 sccm, the temperature of the reaction chamber is reduced at a rate of 10℃ / min, and then the furnace is naturally cooled after being reduced to 100℃;

[0041] After cooling to room temperature, the vacuum valve is closed, high-purity N2 is introduced again until the pressure in the reaction chamber is equal to the outside, and then it is taken out, and the preparation of the β-Ga2O3 thin film is completed, as shown inFigure 3 .

[0042] Example 2: The temperature is set to 800℃, the O2 flow rate is 4000sccm, the carrier gas flow rate into the Ga source is 40sccm, the carrier gas N2 flow rate into the Sn source is 4sccm, and the Ga and Sn source pulse time is 0.4min. The β-Ga2O3 film is grown by epitaxy on the annealed SiC substrate.

[0043] Step 1: Clean the SiC substrate.

[0044] Select the SiC substrate, and sequentially place it in a hydrofluoric acid, acetone, and isopropanol solution for ultrasonic cleaning for 4min, 20min, and 30min, respectively, and then dry it with nitrogen.

[0045] Step 2: Perform high-temperature annealing treatment on the cleaned SiC substrate.

[0046] First, place the cleaned SiC substrate on the graphite tray in the reaction chamber, turn on the primary vacuum pump to evacuate the reaction chamber, and when the pressure in the reaction chamber drops to 50Torr, turn on the secondary vacuum pump until the pressure in the reaction chamber reaches 5x10 - 4 Torr, turn on the graphite tray rotation power supply, and rotate the graphite tray at a speed of 30r / min;

[0047] Next, increase the temperature to 950℃, open the N2 and O2 control ports, and allow N2 and O2 to flow into the reaction chamber at flow rates of 1000sccm and 4000sccm, respectively, and maintain the pressure in the reaction chamber at 30Torr. Anneal the substrate for 90min in this environment.

[0048] Step 3: Grow a double-pulse Sn-doped β-Ga2O3 film on the annealed SiC substrate.

[0049] Referring to Figure 2 , the implementation of this step is as follows:

[0050] In the first stage of the gas path input cycle, open the N2 valve and close the O2 valve, allowing the carrier gas N2 to flow into the TEGa and TDMASn organic source bottles at flow rates of 40sccm and 4sccm, respectively, for a period of 0.4min;

[0051] In the second stage of the gas path input cycle, close the N2 valve and open the O2 valve, allowing O2 to flow into the reaction chamber at a flow rate of 4000sccm for a period of 0.1min;

[0052] The temperature of the reaction chamber was set to 800℃, and the above two stages were repeated until the intermittent time of Ga and Sn gas passage reached the set time of 90 min. The β-Ga2O3 thin film with a thickness of 0.75 μm and a half-width of 80 arcsec was formed on the surface of the substrate after high-temperature annealing.

[0053] Step four: cooling treatment was performed on the β-Ga2O3 thin film.

[0054] The reaction chamber was cooled at a rate of 20℃ / min under an O2 atmosphere with a flow rate of 3000 sccm until it was cooled to 130℃, and then the furnace was naturally cooled;

[0055] After cooling to room temperature, the vacuum valve was closed, and high-purity N2 was introduced until the pressure in the reaction chamber was equal to that outside, and then the β-Ga2O3 thin film was taken out, and the preparation was completed. Figure 3 .

[0056] Example 3: The temperature was set to 900℃, the O2 flow rate was 6000 sccm, the carrier gas N2 flow rate into the Ga source was 60 sccm, the carrier gas N2 flow rate into the Sn source was 6 sccm, and the Ga and Sn source pulse passage time was 0.6 min. The β-Ga2O3 thin film was epitaxially grown on the GaN substrate after annealing by double-pulse Sn doping.

[0057] Step A: cleaning the GaN substrate.

[0058] The GaN substrate was selected and sequentially placed in hydrofluoric acid, acetone, and isopropanol solutions for ultrasonic cleaning for 5 min, 30 min, and 40 min, respectively, and then dried with nitrogen.

[0059] Step B: high-temperature annealing treatment was performed on the cleaned GaN substrate.

[0060] B1) The cleaned GaN substrate was placed on a graphite tray in the reaction chamber, and a primary vacuum pump was turned on to evacuate the reaction chamber. When the pressure in the reaction chamber dropped to 60 Torr, a secondary vacuum pump was turned on, and the pressure in the reaction chamber was maintained at 10 Torr. The graphite tray rotation power was turned on, and the graphite tray rotated at a speed of 40 r / min. -4

[0061] B2) The temperature was raised to 1000℃, and the N2 and O2 control ends were turned on. N2 and O2 were introduced into the reaction chamber at flow rates of 1500 sccm and 6000 sccm, respectively, and the pressure in the reaction chamber was maintained at 40 Torr. The substrate was annealed for 100 min in this environment.

[0062] Step C: growing a double-pulse Sn-doped β-Ga2O3 thin film on the annealed GaN substrate. ​

[0063] Referring to Figure 2 , the implementation of this step is as follows:

[0064] C1) In the first stage of the gas path introduction cycle, open the N2 valve and close the O2 valve, introduce carrier gas N2 as Ga source through one branch at a flow rate of 60 sccm into the triethyl gallium TEGa organic source bottle, and the introduction time is 0.6 min;

[0065] C2) Under the above conditions in the first stage, at the same time, introduce carrier gas N2 as Sn source through another branch at a flow rate of 6 sccm into the tetra (dimethylamino) tin TDMASn organic source bottle, and the introduction time is 0.6 min;

[0066] C3) In the second stage of the gas path introduction cycle, close the N2 valve and open the O2 valve, and introduce O2 into the reaction chamber at a flow rate of 6000 sccm for 0.1 min;

[0067] C4) Set the reaction chamber temperature to 900℃, repeat steps C1) to C3) until the intermittent introduction time of Ga and Sn gas paths reaches the set time of 120 min, and the β-Ga2O3 thin film with a thickness of 1.00 μm and a half-height width of 100 arcsec is formed on the substrate surface after high-temperature annealing.

[0068] Step D: cooling treatment of the β-Ga2O3 thin film.

[0069] Under O2 atmosphere, set the flow rate of O2 to 4000 sccm, and cool the temperature of the reaction chamber at a rate of 30℃ / min, until it is reduced to 160℃, and then start natural cooling with the furnace;

[0070] After cooling to room temperature, close the vacuum valve, and then introduce high-purity N2 until the pressure in the reaction chamber is equal to the outside, and then take out, to complete the preparation of the β-Ga2O3 thin film, as Figure 3 .

[0071] The above description is only three preferred embodiments of the present application, but the protection scope of the present application is not limited thereto, any person skilled in the art can easily think of changes or replacements within the technical range disclosed by the present application, for example, the substrate can be Al2O3, AlN and Si in addition to the Ga2O3, SiC and GaN substrates used in the present example, but these modifications and changes based on the idea of the present application should be covered within the protection scope of the present application.

Claims

1. A method for preparing Sn-doped β-Ga2O3 thin films with improved mobility and carrier concentration, characterized in that, Includes the following steps: (1) The substrate was placed in hydrofluoric acid, acetone solution and isopropanol solution in sequence for ultrasonic cleaning; (2) Place the cleaned substrate on the graphite base of the MOCVD reaction chamber and perform high-temperature annealing at 900-1000℃. (3) Growth of double-pulse Sn-doped β-Ga2O3 thin films on annealed substrates: (3a) In the first stage of the gas flow cycle, the N2 valve is opened and the O2 valve is closed. The carrier gas N2 is introduced into the triethylgallium (TEGa) organic source bottle and the tetra(dimethylamino)tin (TDMASn) organic source bottle as Ga source and Sn source respectively, so as to carry TEGa molecules and TDMASn molecules into the reaction chamber and intermittently provide Ga atoms and Sn atoms for them. The carrier gas N2 is introduced into the triethylgallium (TEGa) organic source bottle and the tetra(dimethylamino)tin (TDMASn) organic source bottle at the same time. The flow rate of the carrier gas N2 into TEGa is 20-60 sccm, and the flow rate into TDMASn is 2-6 sccm. The introduction time is 0.2-0.6 min for both. (3b) In the second stage of the gas passage cycle, the N2 valve is closed and the O2 valve is opened. O2 is introduced into the reaction chamber to intermittently provide O atoms to the reaction chamber, and the three atoms of Ga, Sn and O work together on the substrate surface after high-temperature annealing to form a Sn-doped β-Ga2O3 film; the flow rate of O2 introduced into the reaction chamber is 2000-6000 sccm and the introduction time is 0.1 min. (3c) Set the reaction chamber temperature to 700-900℃, repeat the gas passage cycle of steps (3a) and (3b) until the passage time of Ga and Sn gas passages reaches the set time of 60-120min, and form a β-Ga2O3 film on the substrate surface after high temperature annealing. (4) After cooling the epitaxial Sn-doped β-Ga2O3 film to room temperature in an O2 atmosphere, the vacuum valve is closed, and high-purity N2 is introduced until the pressure in the reaction chamber is equal to that in the outside environment. The film is then removed to complete the preparation of the β-Ga2O3 film.

2. The method as described in claim 1, characterized in that, In step (3c), the thickness of the β-Ga2O3 film is 0.50-1.00 μm and the full width at half maximum (FWHM) is 60-100 arcsec.

3. The method as described in claim 1, characterized in that, The substrate is any one of Ga2O3, GaN, SiC, Al2O3, Si, and AlN.

4. The method as described in claim 1, characterized in that, In step (1), ultrasonic cleaning is performed using hydrofluoric acid, acetone solution, and isopropanol solution, under the following process conditions: Ultrasonic cleaning in hydrofluoric acid for 3-5 minutes; Sonicate in acetone solution for 20-40 minutes; Ultrasonic cleaning in isopropanol solution for 30-50 minutes.

5. The method as described in claim 1, characterized in that, In step (2), the cleaned substrate is subjected to a high-temperature annealing treatment at 900℃-1000℃. The steps include the following: 2.1) Place the cleaned substrate onto the graphite tray inside the reaction chamber. Turn on the primary vacuum pump to evacuate the reaction chamber. When the pressure in the reaction chamber drops to 40-60 Torr, turn on the secondary vacuum pump until the pressure in the reaction chamber drops to 10 Torr. -3 ~10 -4 When torturing, turn on the power supply for the graphite tray rotation, so that the graphite tray rotates at a constant speed of 20-40 r / min. 2.2) Raise the temperature to 900-1000℃, turn on the N2 and O2 control terminals, and let N2 flow into the reaction chamber at a flow rate of 500-1500 sccm, while letting O2 flow into the reaction chamber at a flow rate of 2000-6000 sccm. Maintain the reaction chamber pressure at 20-60 Torr and perform substrate annealing for 80-100 min.

6. The method as described in claim 1, characterized in that, In step (4), the epitaxial film is cooled in an O2 atmosphere, and the parameters are set as follows: The flow rate of O2 is 2000-4000 sccm; The cooling rate during the reaction chamber cooling process is 10-30℃ / min; After the temperature drops to 100-160℃, turn off the O2 and allow the furnace to cool naturally to room temperature.

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