Preparation method of Sn-doped beta-Ga2O3 film capable of improving mobility and carrier concentration

Abstract

The invention discloses a preparation method of a Sn-doped beta-Ga2O3 film capable of improving mobility and carrier concentration, and mainly solves the problems that an existing beta-Ga2O3 epitaxial film is poor in crystallization quality and cannot have high mobility and high carrier concentration at the same time. According to the implementation scheme, a substrate is selected and cleaned; putting the cleaned substrate into a reaction cavity of MOCVD (Metal Organic Chemical Vapor Deposition) for annealing treatment; n2 is used as carrier gas of a Ga source and a Sn source, intermittent introduction of N2 and O2 is carried out at different stages in a gas path introduction period, intermittent O atoms, Ga atoms and Sn atoms are provided for a reaction chamber, the Sn-doped beta-Ga2O3 thin film is formed through the combined action of the three atoms on the surface of the substrate subjected to high-temperature annealing, and then the Sn-doped beta-Ga2O3 thin film is cooled to complete preparation of the beta-Ga2O3 thin film. The defect density of the epitaxial film is remarkably reduced, the electrical property of the film is effectively improved, and the epitaxial film can be used for manufacturing high-power and high-frequency electronic devices.

Description

Technical Field

[0001] The invention belongs to the field of microelectronic technology, and in particular relates to a growth method of a Sn-doped beta-Ga2O3 film, which can be used for the preparation of high-frequency, high-voltage and other devices. Background Art

[0002] Gallium oxide (Ga2O3), especially its most stable β-phase gallium oxide (β-Ga2O3), is considered to be one of the core candidates for the new generation of wide bandgap semiconductor materials because of its ultra-wide bandgap of 4.9eV, breakdown electric field up to 8MV / cm, excellent thermal stability and high dielectric constant. In the field of high-power electronic devices, β-Ga2O3, with its superior material properties, exhibits higher power density and breakdown resistance than traditional semiconductor materials (such as Si and GaN), and can be widely used in key equipment such as high-voltage switching devices, RF power amplifiers and inverters. In addition, due to its wide bandgap, β-Ga2O3 is highly sensitive to ultraviolet light and also has important application potential in the field 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 doping with appropriate amounts of n-type elements (such as Sn, Si, etc.), its carrier concentration can be significantly improved, giving the material higher conductivity, thereby meeting the performance requirements of high-power, high-frequency and high-temperature devices. In this context, how to efficiently dope to balance carrier concentration and mobility, and maintain high crystalline quality of the film while improving conductivity has become an important research direction in the field of β-Ga2O3 materials. However, a series of problems faced by existing doping technologies, including poor doping uniformity, many lattice defects, limited carrier mobility, as well as complex preparation processes and inefficient production capacity, have greatly limited the further application of β-Ga2O3 films.

[0004] In 2020, Akhil Mauze et al. proposed to prepare thin films by PAMBE method in the paper “Sn doping of (010) β-Ga2O3 films grown by plasma-assisted molecular beam epitaxy” published in the journal Applied Physics Letters, 117, 222102, 2020. The method achieves n-type doping by continuously introducing Sn at high temperature. However, this continuous Sn doping will not only produce a self-compensation effect under high temperature conditions, resulting in a decrease in carrier concentration, but also 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. proposed the use of Sn-doped β-Ga2O3 films grown by MBE in their paper "Transport and electronic structure properties of MBE grown Sn doped Ga2O3 homo-epitaxial films" to improve the 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 film quality control, this low-temperature Sn doping using the MBE method will, on the one hand, introduce defect states within the band gap, leading to a self-compensation effect, reducing doping efficiency and mobility; on the other hand, it will also cause surface energy band bending, forming an electron depletion layer, and increasing interface resistance. Therefore, there is an urgent need for a method that can break through the bottleneck of existing technologies and improve the electrical properties of β-Ga2O3 films to fully unleash their potential in high-power, high-frequency electronic devices and optoelectronic applications. Summary of the invention

[0006] The purpose of the present invention is to provide a method for preparing a Sn-doped β-Ga2O3 thin film with high mobility and high carrier concentration in order to improve the crystallization quality and electrical properties of the epitaxial thin film in view of the above-mentioned deficiencies in the prior art.

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

[0008] (1) placing the substrate in hydrofluoric acid, acetone solution, and isopropanol solution in sequence for ultrasonic cleaning;

[0009] (2) placing the cleaned substrate on a graphite susceptor in an MOCVD reaction chamber and performing a high temperature annealing treatment at 900-1000°C;

[0010] (3) Growth of double-pulse Sn-doped β-Ga2O3 thin films on annealed substrates:

[0011] (3a) In the first stage of the gas line introduction cycle, the N2 valve is opened, the O2 valve is closed, and the carrier gas N2 is introduced into the triethylgallium TEGa organic source bottle and the tetramethyl diethyl tin TDMASn organic source bottle at the same time to bring TEGa molecules and TDMASn molecules into the reaction chamber to intermittently provide Ga atoms and Sn atoms thereto;

[0012] (3b) In the second stage of the gas-passing cycle, the N2 valve is closed, the O2 valve is opened, and O2 is passed 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 surface of the substrate after high-temperature annealing to form a Sn-doped β-Ga2O3 film;

[0013] (3c) setting the reaction chamber temperature to 700-900° C., repeating the gas path introduction cycle of steps (3a) and (3b) until the Ga and Sn gas path introduction time reaches the set time of 60-120 min, and forming a β-Ga2O3 film with a thickness of 0.5-1 μm on the surface of the substrate after high temperature annealing;

[0014] (4) After the epitaxial Sn-doped β-Ga2O3 film is cooled 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 world, and then the film is taken out to complete the preparation of the Sn-doped β-Ga2O3 epitaxial film.

[0015] Preferably, in step (3a), carrier gas N2 is simultaneously introduced into triethylgallium TEGa organic source bottle and tetramethyldiethyltin TDMASn organic source bottle, the flow rate of carrier gas N2 into TEGa is 20-60sccm, the flow rate of carrier gas N2 into TDMASn is 2-6sccm, and the introduction time is 0.2-0.6min.

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

[0017] 4. The method according to claim 1, characterized in that the substrate is any one of Ga2O3, GaN, SiC, Al2O3, Si and AlN.

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

[0019] First, the present invention adopts a growth method of intermittently introducing Ga and O, which is beneficial to suppress the formation of defects during the film growth process compared with the prior art, and can significantly improve the crystal quality of the β-Ga2O3 film growth;

[0020] Second, the present invention adopts the intermittent Sn doping method, which is beneficial to the formation of chemical short-range ordered distribution of Sn atoms in the β-Ga2O3 film compared with the existing technology, and can significantly improve the electrical properties of the Sn-doped β-Ga2O3 film. BRIEF DESCRIPTION OF THE DRAWINGS

[0021] Figure 1 It is a flow chart for realizing the present invention;

[0022] Figure 2 It is a time diagram of intermittently passing N2 into TEGa and TDMASn organic source bottles and intermittently passing O2 into the reaction chamber in the present invention;

[0023] Figure 3 It is a schematic diagram of the thin film epitaxially grown on the substrate according to the present invention. DETAILED DESCRIPTION

[0024] In order to make the present invention more clear, the embodiments of the present invention are further described in detail below in conjunction with the accompanying drawings and embodiments.

[0025] Reference Figure 1 , the present invention provides the following three embodiments:

[0026] Example 1: Set the temperature to 700°C, the O2 flow rate to 2000sccm, the carrier gas N2 flow rate to 20sccm for the Ga source, the carrier gas N2 flow rate to 2sccm for the Sn source, and the Ga and Sn source pulse introduction time to 0.2min, and epitaxially grow a double-pulse Sn-doped β-Ga2O3 film on the annealed Ga2O3 substrate.

[0027] Step 1: Clean the Ga2O3 substrate.

[0028] A Ga2O3 substrate was selected and placed in hydrofluoric acid, acetone and isopropanol solutions for ultrasonic cleaning for 3 min, 10 min and 20 min respectively, and then dried with nitrogen.

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

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

[0031] 2.2) Raise the temperature to 900°C, open the N2 and O2 control terminals, allow N2 and O2 to flow into the reaction chamber at a flow rate of 500 sccm and 2000 sccm respectively, and maintain the pressure of the reaction chamber at 20 Torr. Under this environment, anneal the substrate for 80 minutes.

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

[0033] The existing method of growing Sn-doped thin films on annealed Ga2O3 substrates is to use N2 as the carrier gas for Ga source and Sn source, and to continuously introduce N2 and O2 into the reaction chamber to grow Sn-doped thin films. The prepared thin films not only have a self-compensation effect, which makes it impossible for the thin films to have both high carrier concentration and high carrier mobility, but also have low crystal quality. To solve this problem, this example adopts a double-pulse Sn doping method, using N2 as the carrier gas for Ga source and Sn source, setting the gas path to different stages during the introduction cycle, and intermittently introducing N2 and O2 at different stages. On the one hand, it is conducive to the formation of chemical short-range ordered distribution of Sn in the thin film, so that the thin film has both high carrier concentration and mobility. On the other hand, it inhibits the formation of defects in the thin film, and the crystal quality of the thin film is improved.

[0034] Reference Figure 2 , the implementation of this step is as follows:

[0035] 3.1) In the first stage of the gas line introduction cycle, the N2 valve is opened, the O2 valve is closed, and the carrier gas N2 is used as the Ga source through a branch line to pass into the triethylgallium TEGa organic source bottle at a flow rate of 20 sccm, and the introduction time is 0.2 min;

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

[0037] 3.3) In the second stage of the gas line introduction cycle, the N2 valve is closed, the O2 valve is opened, and O2 as an O source is introduced into the reaction chamber at a flow rate of 2000 sccm for a time of 0.1 min;

[0038] 3.4) Set the reaction chamber temperature to 700°C, repeat steps 3.1) to 3.3) until the intermittent introduction time of Ga and Sn gas lines reaches the set time of 60 minutes, and form a β-Ga2O3 film with a thickness of 0.50 μm and a half-width of 60 arcsec on the surface of the substrate after high-temperature annealing.

[0039] Step 4: Cooling the β-Ga2O3 film.

[0040] Under O2 atmosphere, the flow rate of O2 was set to 2000 sccm, and the temperature of the reaction chamber was cooled at a rate of 10°C / min until it dropped to 100°C and then began to cool naturally with the furnace;

[0041] 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 that in the outside, then take it out to complete the preparation of β-Ga2O3 thin film. Figure 3 .

[0042] Example 2: Set the temperature to 800°C, the O2 flow rate to 4000sccm, the carrier gas flow rate into the Ga source to 40sccm, the carrier gas flow rate into the Sn source to 4sccm, the Ga and Sn source pulse introduction time to 0.4min, and epitaxially grow a double-pulse Sn-doped β-Ga2O3 film on the annealed SiC substrate.

[0043] Step 1: Clean the SiC substrate.

[0044] A SiC substrate was selected and placed in hydrofluoric acid, acetone and isopropanol solutions for ultrasonic cleaning for 4 min, 20 min and 30 min respectively, and then dried with nitrogen.

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

[0046] First, the cleaned SiC substrate was placed on the graphite tray in the reaction chamber, and the first-stage vacuum pump was turned on to evacuate the reaction chamber. When the pressure in the reaction chamber dropped to 50 Torr, the second-stage vacuum pump was turned on until the pressure in the reaction chamber reached 5×10 - 4 Torr, turn on the graphite tray rotation power supply, and make the graphite tray rotate at a constant speed of 30r / min;

[0047] Next, the temperature was raised to 950°C, and the N2 and O2 control terminals were opened to allow N2 and O2 to flow into the reaction chamber at flow rates of 1000 sccm and 4000 sccm, respectively. The pressure in the reaction chamber was maintained at 30 Torr, and the substrate was annealed in this environment for 90 minutes.

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

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

[0050] In the first stage of the gas line introduction cycle, the N2 valve was opened and the O2 valve was closed, so that the carrier gas N2 was used as the Ga source and the Sn source and was introduced into the triethylgallium TEGa organic source bottle and the tetramethyl diethyl tin TDMASn organic source bottle at flow rates of 40 sccm and 4 sccm, respectively, for 0.4 min;

[0051] In the second stage of the gas supply cycle, the N2 valve is closed and the O2 valve is opened, so that O2 is introduced into the reaction chamber at a flow rate of 4000 sccm for 0.1 min;

[0052] The reaction chamber temperature was set at 800°C, and the above two stages were repeated until the intermittent introduction time of the Ga and Sn gas paths reached the set time of 90 minutes, and a β-Ga2O3 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 4: Cooling the β-Ga2O3 film.

[0054] In an O2 atmosphere with a flow rate of 3000 sccm, the reaction chamber was cooled at a rate of 20°C / min until it dropped to 130°C and then began to cool naturally with the furnace;

[0055] 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 that in the outside, then take it out to complete the preparation of β-Ga2O3 thin film. Figure 3 .

[0056] Example 3: Setting the temperature to 900°C, the O2 flow rate to 6000sccm, the N2 carrier gas into the Ga source at a flow rate of 60sccm, the N2 carrier gas into the Sn source at a flow rate of 6sccm, and the Ga and Sn source pulse introduction time to 0.6min, epitaxially grow a double-pulse Sn-doped β-Ga2O3 film on the annealed GaN substrate.

[0057] Step A: Cleaning the GaN substrate.

[0058] A GaN substrate was selected and 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: performing high temperature annealing on the cleaned GaN substrate.

[0060] B1) Place the cleaned GaN 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 60 Torr, turn on the secondary vacuum pump until the pressure in the reaction chamber reaches 10 -4 Torr, turn on the graphite tray rotation power supply to make the graphite tray rotate at a constant speed of 40r / min;

[0061] B2) Raise the temperature to 1000°C, open the N2 and O2 control terminals, allow N2 and O2 to flow into the reaction chamber at flow rates of 1500 sccm and 6000 sccm respectively, and maintain the reaction chamber pressure at 40 Torr. Under this environment, anneal the substrate for 100 minutes.

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

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

[0064] C1) In the first stage of the gas line introduction cycle, the N2 valve is opened, the O2 valve is closed, and the carrier gas N2 is used as the Ga source and introduced into the triethylgallium TEGa organic source bottle through a branch at a flow rate of 60 sccm for 0.6 min;

[0065] C2) Under the above conditions of the first stage, carrier gas N2 was simultaneously introduced as a Sn source into the tetramethyl diethyl tin TDMASn organic source bottle through another branch at a flow rate of 6 sccm for 0.6 min;

[0066] C3) In the second stage of the gas supply cycle, the N2 valve is closed and the O2 valve is opened to allow O2 to flow into the reaction chamber at a flow rate of 6000 sccm for 0.1 min;

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

[0068] Step D: Cooling the β-Ga2O3 film.

[0069] Under O2 atmosphere, the O2 flow rate was set to 4000 sccm, and the temperature of the reaction chamber was cooled at a rate of 30°C / min until it dropped to 160°C and then began to cool naturally 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 that in the outside, then take it out to complete the preparation of β-Ga2O3 thin film. Figure 3 .

[0071] The above descriptions are only three preferred embodiments of the present invention, but the protection scope of the present invention is not limited thereto. Any technician familiar with the technical field can easily think of changes or substitutions within the technical scope disclosed by the present invention. For example, in addition to the Ga2O3, SiC and GaN substrates used in this example, Al2O3, AlN and Si substrates can also be used. However, these modifications and changes based on the ideas of the present invention should be covered within the protection scope of the present invention.

Claims

1. A method for preparing Sn-doped β-Ga2O3 thin film with improved mobility and carrier concentration, characterized in that: The following steps are involved: (1) placing the substrate in hydrofluoric acid, acetone solution, and isopropanol solution in sequence for ultrasonic cleaning; (2) placing the cleaned substrate on a graphite susceptor in an MOCVD reaction chamber and performing a high temperature annealing treatment at 900-1000°C; (3) Growth of double-pulse Sn-doped β-Ga2O3 thin films on annealed substrates: (3a) In the first stage of the gas line introduction cycle, the N2 valve is opened, the O2 valve is closed, and the carrier gas N2 is introduced into the triethylgallium TEGa organic source bottle and the tetramethyl diethyl tin TDMASn organic source bottle as the Ga source and the Sn source, respectively, to bring the TEGa molecules and the TDMASn molecules into the reaction chamber to intermittently provide Ga atoms and Sn atoms thereto; (3b) In the second stage of the gas-passing cycle, the N2 valve is closed, the O2 valve is opened, and O2 is passed 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 surface of the substrate after high-temperature annealing to form a Sn-doped β-Ga2O3 film; (3c) setting the reaction chamber temperature to 700-900° C., repeating the gas path introduction cycle of steps (3a) and (3b) until the Ga and Sn gas path introduction time reaches the set time of 60-120 min, and forming a β-Ga2O3 film on the surface of the substrate after high temperature annealing; (4) After the epitaxial Sn-doped β-Ga2O3 film is cooled 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 world, and then the film is taken out to complete the preparation of the β-Ga2O3 film.

2. The method according to claim 1, characterized in that In step (3a), carrier gas N2 is simultaneously introduced into triethylgallium TEGa organic source bottle and tetramethyldiethyltin TDMASn organic source bottle, the flow rate of carrier gas N2 into TEGa is 20-60sccm, the flow rate of carrier gas N2 into TDMASn is 2-6sccm, and the introduction time is 0.2-0.6min.

3. The method according to claim 1, characterized in that In step (3b), O2 is introduced into the reaction chamber at a flow rate of 2000-6000 sccm for a time of 0.1 min.

4. The method according to claim 1, characterized in that The thickness of the β-Ga2O3 film in step (3c) is 0.50-1.00 μm, and the half-width is 60-100 arcsec.

5. The method according to claim 1, characterized in that The substrate is any one of Ga2O3, GaN, SiC, Al2O3, Si and AlN.

6. The method according to claim 1, characterized in that In step (1), hydrofluoric acid, acetone solution and isopropanol solution are used for ultrasonic cleaning, and the process conditions are as follows: Ultrasonic cleaning in hydrofluoric acid for 3-5 minutes; Ultrasonic cleaning in acetone solution for 20-40 minutes; Ultrasonic cleaning was performed in isopropanol solution for 30-50 min.

7. The method according to claim 1, characterized in that In step (2), the cleaned substrate is subjected to a high temperature annealing treatment at 900° C. to 1000° C., and the implementation steps include the following: 2.1) Place the cleaned 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 40-60 Torr, turn on the secondary vacuum pump until the pressure in the reaction chamber drops to 10 -3 ~10 - 4 Torr, turn on the graphite tray rotation power supply, and make the graphite tray rotate at a constant speed of 20-40r / min; 2.2) Raise the temperature to 900-1000°C, open the N2 and O2 control terminals, allow N2 to flow into the reaction chamber at a flow rate of 500-1500sccm, and allow O2 to flow into the reaction chamber at a flow rate of 2000-6000sccm, maintain the reaction chamber pressure at 20-60Torr, and anneal the substrate for 80-100 minutes.

8. The method according to 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 2000-4000sccm; The cooling rate during the reaction chamber cooling process is 10-30℃ / min; After the temperature drops to 100-160℃, turn off O2 and start cooling naturally to room temperature with the furnace.

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