Method for preparing transferable beta-phase gallium oxide film by Van der Waals epitaxy based on L-MBE technology

Abstract

The invention relates to the technical field of semiconductor material preparation, and particularly discloses a Van der Waals epitaxy transferable beta-phase gallium oxide film preparation method based on an L-MBE technology, and the method comprises the steps: transferring hexagonal boron nitride to a c-plane sapphire substrate through a wet method, and carrying out the heat treatment and cleaning processes to obtain a clean substrate; then epitaxially growing a beta-phase gallium oxide thin film on boron nitride by using an L-MBE technology two-step growth method; and finally, depositing a nickel metal stress layer on the surface of the epitaxial film, and stripping and transferring the film by using a heat release adhesive tape. According to the method, through an L-MBE two-step growth method, a high-quality beta-phase gallium oxide epitaxial film is grown on hexagonal boron nitride through Van der Waals epitaxy, and meanwhile, a two-dimensional layer is prevented from being damaged; weak Van der Waals force between the epitaxial layer and boron nitride is utilized to realize complete transfer of the epitaxial film, and the method can be used for constructing heterojunction devices and high-power devices.

Description

Technical Field

[0001] The invention belongs to the technical field of semiconductor material preparation, and in particular relates to a method for producing a transferable beta-phase gallium oxide film by van der Waals epitaxy based on L-MBE technology. Background Art

[0002] Since the 21st century, with the continuous development of semiconductor applications, traditional third-generation wide-bandgap semiconductors such as silicon carbide (SiC) and gallium nitride (GaN) have become increasingly difficult to meet the application requirements of high-power electronic devices and deep-ultraviolet detectors due to their limited bandgap width. To address this problem, scholars have initiated research on ultra-wide-bandgap semiconductors. As an emerging fourth-generation ultra-wide-bandgap oxide semiconductor, β-phase gallium oxide (β-Ga2O3) has an ultra-wide bandgap of 4.9 eV, a theoretical breakdown field strength of 8 MV / cm, a high baliga figure of merit of 3444, and excellent thermal and chemical stability. These characteristics give it enormous development potential and application value in deep-ultraviolet photodetectors, radio frequency electronic transmitters, high-voltage power electronics, quantum communications, and applications in extreme environments.

[0003] Epitaxially growing high-quality gallium oxide (GaO) thin films on lattice-matched substrates is a prerequisite and foundation for fabricating high-performance devices. However, the traditional method of covalent epitaxially growing β-phase GaO on c-plane sapphire or other lattice-matched substrates has certain drawbacks that limit the promotion and application of GaO. On the one hand, due to the certain lattice and thermal mismatch between the GaO epitaxial layer and the substrate, the epitaxial film produces high defect density and large stress accumulation, which reduces the crystal quality of the epitaxial layer. On the other hand, due to the strong covalent bond interaction between the epitaxial layer and the substrate, the epitaxial layer cannot be separated from the substrate, and the GaO epitaxial layer is restricted by the substrate, which prevents the flexible device construction and limits the application of GaO.

[0004] In order to solve the problems brought about by the above-mentioned conventional covalent epitaxy, attempts were made to transfer two-dimensional material layers as substrates during the epitaxial growth of gallium oxide, such as graphene and hexagonal boron nitride (h-BN). By taking advantage of the fact that there are no dangling bonds on the surface of two-dimensional materials and weak van der Waals bonding between layers, the van der Waals epitaxial growth and lift-off transfer of high-quality β-gallium oxide films were achieved.

[0005] Laser molecular beam epitaxy (LMBE) technology is a new type of high-precision film-forming technology that emerged in the 1990s. It is another new technology developed on the basis of molecular beam epitaxy (MBE) and pulsed laser deposition (PLD). It can control epitaxy at the atomic scale and grow high-melting-point, multi-element and complex layered structure thin films, heterojunctions and superlattice materials that are difficult to prepare with other film-making equipment and methods. It is an important platform for exploring and developing new materials and new devices and conducting related basic research.

[0006] This technology is widely used in growing semiconductor superlattice materials, preparing thin films containing complex oxide structures, optical crystals, ferroelectrics, ferromagnets and superconductors, etc.

[0007] For van der Waals epitaxial growth, L-MBE systems offer unique advantages over chemical preparation methods such as CVD. First, the high energy of the sputtered particles in L-MBE systems allows atoms to migrate very quickly on the surface of the two-dimensional material substrate, overcoming migration barriers and avoiding island growth patterns. Second, L-MBE's Rheed system enables in-situ monitoring of the film's crystalline quality, ensuring high-quality epitaxial layers.

[0008] Finally, L-MBE is a physical deposition system. Compared with the chemical deposition system, it can significantly reduce the degree of oxidation of two-dimensional materials during van der Waals epitaxial growth, maintain the integrity of the two-dimensional material layer, and thus achieve high-quality van der Waals epitaxial growth and transfer of thin films.

[0009] In summary, achieving high-quality van der Waals epitaxy of gallium oxide thin films and achieving lossless exfoliation transfer requires both the high energy provided by the L-MBE system to the particles to overcome the migration barrier on the surface of the two-dimensional material during the growth process and the preservation of the integrity of the two-dimensional material and the adoption of appropriate exfoliation methods. This is the basis for the present invention. Summary of the Invention

[0010] The object of the present invention is to provide a method for producing a transferable β-phase gallium oxide thin film by van der Waals epitaxy based on L-MBE technology, so as to solve the problems raised in the above background technology.

[0011] To achieve the above object, the present invention provides the following technical solutions:

[0012] The method for forming a transferable β-phase gallium oxide thin film by van der Waals epitaxy based on L-MBE technology comprises the following steps:

[0013] S1. wet-transferring (5-10 layers) or (more than 10 layers) hexagonal boron nitride onto a dielectric substrate, and pre-treating the transferred hexagonal boron nitride substrate;

[0014] S2. Place the treated hexagonal boron nitride substrate into the L-MBE growth chamber, reduce the background vacuum of the growth chamber to below 5e-5 Pa, and heat the substrate to the buffer layer growth temperature;

[0015] S3. Adjust the power and oxygen flow of the radio frequency oxygen atom source, adjust the oxygen partial pressure to ionize the oxygen molecules, adjust the laser energy and frequency, bombard the gallium oxide target with laser, and grow a gallium oxide buffer layer on the hexagonal boron nitride;

[0016] S4. After the buffer layer growth is completed, the background vacuum is restored, the substrate is heated to 700° C. to 850° C., and the RF oxygen atom source and the laser are adjusted again to grow 3,000 to 30,000 laser pulses;

[0017] S5. Cooling the gallium oxide epitaxial film to obtain a gallium oxide epitaxial film, depositing a nickel metal layer on the gallium oxide epitaxial film, and then using a thermal release tape to peel off and transfer the gallium oxide epitaxial film.

[0018] Preferably, the pretreatment in S1 comprises the following steps:

[0019] In a tube furnace, vacuum annealing is performed to decompose organic matter remaining on the surface of the hexagonal boron nitride, and then ultrasonic cleaning is performed. The vacuum annealing temperature is 200-450°C, and the vacuum annealing time is 1-3 hours. Before starting the ultrasonic cleaning, the hexagonal boron nitride substrate needs to be soaked in acetone for 10-24 hours. The solutions used for the ultrasonic cleaning are acetone, ethanol, and deionized water, in order.

[0020] Preferably, the vacuum annealing temperature is 400° C., the vacuum annealing time is 2 hours, and the hexagonal boron nitride substrate is immersed in acetone for 24 hours.

[0021] Preferably, in said S2, the substrate is heated to a growth temperature of the buffer layer of 250-450° C., and the heating rate is 5-10° C. / min.

[0022] Preferably, the power of the S3 radio frequency oxygen atom source is 200-350W, the oxygen flow rate is 1-3sccm, the oxygen partial pressure is 0.002-0.1Pa, the adjusted laser energy is 220-300mJ, and the frequency is 2-10Hz;

[0023] The gallium oxide target material includes an intrinsic gallium oxide target material and a gallium oxide target material doped with any element type and concentration.

[0024] Preferably, the method of depositing the nickel metal layer in S5 includes thermal evaporation, electroplating and magnetron sputtering.

[0025] Preferably, the thickness of the nickel metal layer deposited in S5 is 100-500 nm.

[0026] Preferably, the nickel metal layer deposited in S5 is removed by using a nickel etching solution after the transfer.

[0027] Compared with the prior art, the present invention has the following beneficial effects:

[0028] This invention utilizes L-MBE technology to grow and transfer van der Waals epitaxial β-phase gallium oxide thin films onto hexagonal boron nitride substrates. The high-energy laser energy of the L-MBE technique imparts sufficient energy to particles to migrate across the hexagonal boron nitride surface, overcoming the migration barrier on the two-dimensional material surface and ultimately yielding a high-quality gallium oxide epitaxial film. The two-step growth process of the L-MBE technique protects the hexagonal boron nitride layer from damage. The nickel metal layer deposited before stripping acts as both a stress layer to assist in stripping the epitaxial film and a support layer to prevent breakage during stripping. BRIEF DESCRIPTION OF THE DRAWINGS

[0029] Figure 1 Flowchart for the implementation of the present invention;

[0030] Figure 2 X-ray diffraction pattern of epitaxial β-phase gallium oxide thin film on hexagonal boron nitride / sapphire substrate and hexagonal boron nitride / sapphire substrate;

[0031] Figure 3 Actual pictures of the peeled β-phase gallium oxide thin films of Example 1 (left) and Example 2 (right) of the present invention;

[0032] Figure 4 The scanning electron microscope photograph and optical microscope image of the new surface of the β-phase gallium oxide thin film peeled off in Example 1;

[0033] Figure 5 This is a physical picture of β-phase gallium oxide transferred onto a silicon single crystal substrate. DETAILED DESCRIPTION

[0034] The following will clearly and completely describe the technical solutions in the embodiments of the present invention in conjunction with the accompanying drawings. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without making creative efforts are within the scope of protection of the present invention.

[0035] Example 1: Van der Waals epitaxial transferable β-phase gallium oxide thin film on hexagonal boron nitride using L-MBE technology, comprising the following steps:

[0036] Step 1: Cleaning the substrate: Prepare a few-layer hexagonal boron nitride / c-plane sapphire substrate, place it in a tube furnace, and anneal it at 400° C. for 1 hour under vacuum conditions.

[0037] The annealed substrate was then immersed in acetone for 12 hours and then ultrasonically cleaned in acetone solution, anhydrous ethanol, and deionized water for 5 minutes.

[0038] Step 2: The hexagonal boron nitride substrate needs to be fixed on the substrate tray with thermally conductive silver glue, placed on a hot plate and heated to 300 degrees Celsius for 5 minutes to dry the silver glue.

[0039] The hexagonal boron nitride substrate was then placed in the L-MBE growth chamber, the background vacuum was evacuated to 5e-5 Pa, and the substrate was heated to 500°C. Oxygen was introduced through an oxygen atomic source at a flow rate of 1 sccm, an oxygen partial pressure of 0.005 Pa, and an RF power of 200 W to ionize the oxygen. A 248 nm laser was set to 240 mJ of energy and 5 Hz of frequency. The buffer layer was then grown, initially with the RF oxygen baffle disabled, for 1 minute of epitaxial growth. The baffle was then enabled and growth continued for another 2 minutes, resulting in a gallium oxide buffer layer approximately 10 nm thick.

[0040] Step 3: After the buffer layer growth is complete, the substrate is heated to 700°C at a rate of 10°C / min. Oxygen is introduced through an oxygen atomic source at a flow rate of 1 seem, an oxygen partial pressure of 0.01 Pa, and an RF power of 300 W to ionize the oxygen. A 248 nm laser is set to 240 mJ of energy and 5 Hz of frequency. Epitaxial growth is initiated for 60 minutes, resulting in a gallium oxide epitaxial layer approximately 220 nm thick.

[0041] Figure 2 The XRD pattern of the β-phase gallium oxide epitaxial layer grown by this method shows a (-201) preferred orientation, a half-peak width of the (-201) peak of 700 arcsec, and high crystalline quality.

[0042] Step 4: Peel and transfer the gallium oxide epitaxial film: Use a thermal evaporation coating device to A 300nm nickel metal layer was deposited on the gallium oxide epitaxial film at a deposition rate of 100 nm. A thermal release tape was then used to adhere to the surface of the nickel metal layer. The gallium oxide epitaxial film was peeled off from the substrate with uniform force. The peeling photo is shown in FIG. Figure 3 As shown on the left, a 1*1cm gallium oxide epitaxial film is completely peeled off.

[0043] Figure 4 The scanning electron microscope image (left) and optical microscope image (right) of the new surface after peeling show that the new surface is smooth, without cracks or large particles, which is conducive to further transfer or direct construction of devices. Figure 4The right image shows the new surface after peeling. The thermal release tape, with the gallium oxide side attached, is tightly adhered to the target substrate (such as a single-crystal silicon substrate). The heating table is heated to 130°C, and the silicon substrate and tape are placed on the heating table. The tape is heated until it foams and loses its stickiness, automatically detaching from the gallium oxide surface, completing the transfer of the gallium oxide epitaxial film to the silicon single-crystal substrate. The nickel metal layer can be etched using a nickel etchant. Figure 5 Shown is a photo of β-phase gallium oxide transferred to a silicon single crystal substrate.

[0044] Example 2: Compared with Example 1, this example does not grow the buffer layer of gallium oxide at low temperature, but directly grows gallium oxide epitaxially at 700° C. in one step. The specific steps are as follows:

[0045] Step 1: Substrate Cleaning: Prepare a few-layer hexagonal boron nitride / c-plane sapphire substrate and anneal it in a tube furnace at 400°C under vacuum for 1 hour. Then, soak the annealed substrate in acetone for 12 hours. Then, ultrasonically clean the substrate in acetone, anhydrous ethanol, and deionized water for 5 minutes each.

[0046] Step 2: The hexagonal boron nitride substrate needs to be fixed to the substrate tray with thermally conductive silver glue. Place it on a hot plate and heat it to 300 degrees Celsius for 5 minutes to dry the silver glue. Then, transfer the hexagonal boron nitride substrate to the L-MBE growth chamber, evacuate the background vacuum to 5e-5 Pa, and heat the substrate to 700°C at a heating rate of 10°C / min. Oxygen is introduced through an oxygen atom source at a flow rate of 1 sccm, an oxygen partial pressure of 0.005 Pa, and an RF power of 200 W to ionize the oxygen. Set the 248nm laser energy to 240 mJ and a frequency of 5 Hz. Oxygen is introduced through an oxygen atom source at a flow rate of 1 sccm, an oxygen partial pressure of 0.01 Pa, and an RF power of 300 W to ionize the oxygen. Set the 248nm laser energy to 240 mJ and a frequency of 5 Hz. Start epitaxial growth for 60 minutes, ultimately obtaining a gallium oxide epitaxial layer with a thickness of approximately 220 nm.

[0047] Step 3: Peel and transfer the gallium oxide epitaxial film: Use a thermal evaporation coating apparatus to deposit a 300nm Ni metal layer on the gallium oxide epitaxial film at a deposition rate of 1.5A / s. Then use a thermal release tape to adhere to the surface of the Ni metal layer. Apply even force to peel the gallium oxide epitaxial film from the substrate. The peeling photo is shown in the figure below. Figure 3 As shown on the right, the lack of a low-temperature buffer layer to protect the hexagonal boron nitride results in a loss of integrity in the exfoliated gallium oxide. A thermal release tape with the gallium oxide layer adhered tightly to the target substrate (such as a single-crystal silicon substrate). The heating plate is heated to 130°C, and the silicon substrate and tape are placed on the heating plate. The tape is heated until it foams and loses its stickiness, allowing the tape to automatically detach from the gallium oxide surface, completing the transfer of the gallium oxide epitaxial film to the single-crystal silicon substrate. The nickel metal layer can be etched using a nickel etchant.

[0048] In summary, this method provides a method for the van der Waals epitaxial growth and transfer of β-phase gallium oxide thin films onto hexagonal boron nitride substrates using L-MBE. The high-energy laser energy of L-MBE imparts sufficient energy to particles to migrate across the hexagonal boron nitride surface, overcoming the migration barrier on the surface of the two-dimensional material layer and ultimately yielding high-quality epitaxial gallium oxide films. The two-step L-MBE growth method preserves the hexagonal boron nitride layer intact. Combined with a nickel-assisted exfoliation method, it enables non-destructive exfoliation of large-scale gallium oxide films.

[0049] It will be appreciated that in the development of any actual embodiment, as in any engineering or design project, numerous implementation-specific decisions may be made. Such a development effort may be complex and time-consuming, but will, for those of ordinary skill having the benefit of this disclosure, be a routine undertaking of design, fabrication, and production without undue experimentation.

[0050] It should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention and are not intended to limit the present invention. Although the present invention has been described in detail with reference to the preferred embodiments, those skilled in the art should understand that the technical solutions of the present invention may be modified or replaced by equivalents without departing from the spirit and scope of the technical solutions of the present invention, which should all be included in the scope of the claims of the present invention.

Claims

1. A method for producing a transferable β-phase gallium oxide thin film using van der Waals epitaxy based on L-MBE technology, characterized in that: The following steps are involved: S1. wet-transferring (5-10 layers) or (more than 10 layers) hexagonal boron nitride onto a dielectric substrate, and pre-treating the transferred hexagonal boron nitride substrate; S2. Place the treated hexagonal boron nitride substrate into the L-MBE growth chamber, reduce the background vacuum of the growth chamber to below 5e-5 Pa, and heat the substrate to the buffer layer growth temperature; S3. Adjust the power and oxygen flow of the radio frequency oxygen atom source, adjust the oxygen partial pressure to ionize the oxygen molecules, adjust the laser energy and frequency, bombard the gallium oxide target with laser, and grow a gallium oxide buffer layer on the hexagonal boron nitride; S4. After the buffer layer growth is completed, the background vacuum is restored, the substrate is heated to 700° C. to 850° C., and the RF oxygen atom source and the laser are adjusted again to grow 3,000 to 30,000 laser pulses; S5. Cooling the gallium oxide epitaxial film to obtain a gallium oxide epitaxial film, depositing a nickel metal layer on the gallium oxide epitaxial film, and then using a thermal release tape to peel off and transfer the gallium oxide epitaxial film.

2. The method for forming a transferable β-phase gallium oxide thin film by van der Waals epitaxy based on L-MBE technology according to claim 1, characterized in that: The pre-processing in S1 comprises the following steps: In a tube furnace, vacuum annealing is performed to decompose organic matter remaining on the surface of the hexagonal boron nitride, and then ultrasonic cleaning is performed. The vacuum annealing temperature is 200-450°C, and the vacuum annealing time is 1-3 hours. Before starting the ultrasonic cleaning, the hexagonal boron nitride substrate needs to be soaked in acetone for 10-24 hours. The solutions used for the ultrasonic cleaning are acetone, ethanol, and deionized water, in order.

3. The method for forming a transferable β-phase gallium oxide thin film by van der Waals epitaxy based on L-MBE technology according to claim 2, characterized in that: The vacuum annealing temperature is 400° C., the vacuum annealing time is 2 hours, and the hexagonal boron nitride substrate is immersed in acetone for 24 hours.

4. The method for producing a transferable β-phase gallium oxide thin film by van der Waals epitaxy based on L-MBE technology according to claim 1, characterized in that: In the step S2 , the substrate is heated to a growth temperature of the buffer layer of 250-450° C. at a heating rate of 5-10° C. / min.

5. The method for forming a transferable β-phase gallium oxide thin film by van der Waals epitaxy based on L-MBE technology according to claim 1, characterized in that: The power of the S3 radio frequency oxygen atom source is 200-350W, the oxygen flow rate is 1-3sccm, the oxygen partial pressure is 0.002-0.1Pa, the adjusted laser energy is 220-300mJ, and the frequency is 2-10Hz; The gallium oxide target material includes an intrinsic gallium oxide target material and a gallium oxide target material doped with any element type and concentration.

6. The method for forming a transferable β-phase gallium oxide thin film by van der Waals epitaxy based on L-MBE technology according to claim 1, characterized in that: The method for depositing the nickel metal layer in S5 includes thermal evaporation, electroplating and magnetron sputtering.

7. The method for forming a transferable β-phase gallium oxide thin film by van der Waals epitaxy based on L-MBE technology according to claim 1, characterized in that: The thickness of the nickel metal layer deposited in S5 is 100-500 nm.

8. The method for forming a transferable β-phase gallium oxide thin film by van der Waals epitaxy based on L-MBE technology according to claim 7, characterized in that: The nickel metal layer deposited in S5 is removed by using a nickel etching solution after the transfer.

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