Method for preparing hexagonal boron nitride heterostructure

Abstract

The disclosure provides a preparation method of a hexagonal boron nitride heterostructure, comprising: S1, performing a temperature rising operation on a dielectric substrate, and introducing ammonia into a deposition chamber; S2, sputtering a boron nitride target by an ion source, and depositing obtained nitrogen and boron atoms on the dielectric substrate to grow; S3, obtaining a hexagonal boron nitride heterostructure by cooling. The preparation method of the disclosure introduces ammonia through an auxiliary gas path to ensure the ideal stoichiometric ratio of the hexagonal boron nitride and realize the growth of the low-temperature hexagonal boron nitride; and direct growth of the hexagonal boron nitride on the dielectric substrate is realized, the transfer process is avoided, and the original properties of the dielectric substrate are changed, for example, the diamond is graphitized, at a higher growth temperature, which has a very important significance for the electronic and optoelectronic applications of the hexagonal boron nitride diamond heterostructure.

Description

TECHNICAL FIELD

[0001] The present disclosure relates to the technical field of semiconductor material preparation, in particular to a preparation method of a hexagonal boron nitride heterostructure. BACKGROUND

[0002] Hexagonal boron nitride and diamond are both ultra-wide bandgap semiconductors, and have a larger bandgap and a higher breakdown field strength than gallium nitride and silicon carbide, and have a more promising application prospect in the field of high-power and high-efficiency power electronic devices. In addition, they also have obvious advantages in short-wavelength optoelectronic devices.

[0003] Hexagonal boron nitride is a layered material, and the boron and nitrogen atoms in the layer form a honeycomb structure through sp 2 hybridization to form a covalent bond, and the layers are affected by van der Waals forces. The boron atoms correspond to the nitrogen atoms in the adjacent atomic layer to form A-A' stacking. Hexagonal boron nitride has similar properties to graphite, which is also a layered material, such as a very high in-plane elastic modulus, high thermal conductivity, chemical stability, etc. However, unlike graphite, the electrons of hexagonal boron nitride are firmly bound around the boron and nitrogen atoms due to the action of the polar covalent bond, so it has good insulation, a high breakdown field strength, and a high bandgap of 5.97 eV. In theory, there are no dangling bonds at the interface of hexagonal boron nitride, and there are also very few charge traps. Because of its stable chemical properties, it has a broad application prospect as a protective layer, gate dielectric layer or substrate material for other two-dimensional and three-dimensional materials.

[0004] Diamond is a three-dimensional material in which carbon atoms are arranged in a diamond structure. The carbon atoms form a tetrahedral structure through sp 3 hybridization, and the valence electrons are bound around the carbon atoms, so it also has good insulation, a bandgap of 5.4 eV, and a high theoretical carrier mobility. Since the doping of diamond is still in the experimental stage, the method of forming a two-dimensional hole gas on the surface of hydrogen-terminated diamond has great value in device applications. Hydrogen termination has poor stability, and the use of hexagonal boron nitride as a protective layer can improve the stability of hydrogen-terminated diamond, improve the lifetime of carriers, and thus improve the performance of the device. In addition, hexagonal boron nitride and diamond also have good development prospects in the field of deep ultraviolet optoelectronic devices.

[0005] Hexagonal boron nitride has a larger band gap than diamond and a larger breakdown electric field. In the preparation of electronic or optoelectronic devices by forming a heterostructure, hexagonal boron nitride is often used as a cover layer of diamond. Therefore, the preparation of high-quality hexagonal boron nitride on a diamond dielectric substrate is the basis and premise of the study of its properties and the application of devices. Hexagonal boron nitride prepared by various transfer methods usually has the problems of impurity introduction, mechanical damage, uncontrollable shape, poor repeatability, and difficulty in large-scale production. Therefore, it is of great significance to grow hexagonal boron nitride directly on a diamond dielectric substrate to prepare a hexagonal boron nitride-diamond heterostructure.

[0006] Since it is difficult to catalyze and nucleate hexagonal boron nitride on a dielectric substrate such as diamond, it is often necessary to grow at an extremely high temperature, which causes the diamond to undergo graphitization. In addition, there is usually a problem of nitrogen loss in hexagonal boron nitride. Ultimately, the substrate surface morphology and original properties are destroyed, and the crystalline quality of hexagonal boron nitride is limited. SUMMARY

[0007] (I) Technical problems to be solved

[0008] To solve the above problems, the present disclosure provides a preparation method of a hexagonal boron nitride heterostructure, which at least partially solves the technical problems of harsh growth conditions and poor product quality of the conventional preparation method.

[0009] (II) Technical solutions

[0010] In one aspect, the present disclosure provides a preparation method of a hexagonal boron nitride heterostructure, comprising: S1, heating a dielectric substrate and introducing ammonia into a deposition chamber; S2, sputtering a boron nitride target by an ion source, and depositing the obtained nitrogen and boron atoms on the dielectric substrate to grow; S3, cooling to obtain a hexagonal boron nitride heterostructure.

[0011] Further, the dielectric substrate comprises one of diamond, sapphire, silicon oxide, and silicon.

[0012] Further, S1 comprises: heating the dielectric substrate to 500-1000℃; and introducing ammonia into the deposition chamber at a flow rate of 5-15sccm.

[0013] Further, S2 comprises: reducing the flow rate of ammonia introduced into the deposition chamber; and introducing argon into the ion source to generate an argon ion beam by ionizing the argon.

[0014] Further, S2 comprises: reducing the flow rate of ammonia introduced into the deposition chamber to 2-8sccm; and introducing argon into the ion source at a flow rate of 2-10sccm.

[0015] Further, S2 comprises: the working voltage of the ion source sputtering is 800V-1500V; the ion beam current density of the argon ion beam is 0.1mA / cm 2 ~0.4mA / cm 2 .

[0016] Further, S2 comprises: the time for depositing nitrogen and boron atoms on the dielectric substrate is 10min-60min.

[0017] Further, the purity of the boron nitride target in S2 is greater than 99.5%.

[0018] Further, S1 further comprises: S01, ultrasonic cleaning the dielectric substrate in acetone, isopropyl alcohol and ethanol in sequence, and drying with nitrogen.

[0019] Further, S1 further comprises: S02, pre-extracting the deposition chamber to a backing vacuum degree, and the backing vacuum degree is 1x10 - 4 Pa or below.

[0020] (III) Beneficial Effects

[0021] The preparation method of the low-temperature direct growth of hexagonal boron nitride heterostructure of the present disclosure can avoid the complex transfer process when preparing the hexagonal boron nitride layer, and the film damage and pollution problems caused by the transfer, which is conducive to realizing controllable large-scale production; and the nitrogen-rich atmosphere is provided by using ammonia gas, and the hexagonal boron nitride is deposited by using argon ion beam sputtering, which can realize the growth of stoichiometric ratio of hexagonal boron nitride at low temperature, effectively improving the crystal quality of the hexagonal boron nitride prepared by the physical vapor deposition method at low temperature; at the same time, since the boron nitride is grown at a lower temperature, the graphitization transformation of the diamond dielectric substrate at high temperature is prevented, which can maximize the original properties of the dielectric substrate, which has important significance for electronic and optoelectronic applications. BRIEF DESCRIPTION OF DRAWINGS

[0022] Figure 1 The flow chart of the preparation method of the hexagonal boron nitride heterostructure in the embodiment of the present disclosure is schematically shown;

[0023] Figure 2 The X-ray photoelectron spectrograms of boron atoms 1s electrons of two samples of the hexagonal boron nitride grown on the diamond dielectric substrate in the embodiment of the present disclosure are schematically shown;

[0024] Figure 3 The Raman spectrograms of two samples of the hexagonal boron nitride grown on the diamond dielectric substrate in the embodiment of the present disclosure are schematically shown;

[0025] Figure 4Absorption spectra of two samples of hexagonal boron nitride grown on a diamond dielectric substrate according to embodiments of the present disclosure are schematically shown. DETAILED DESCRIPTION

[0026] For the purposes of the present disclosure, technical solutions and advantages, the following will be further described in detail in combination with specific embodiments and with reference to the drawings.

[0027] It should be noted that in the drawings or the description, similar or identical parts are denoted by the same reference numerals. The implementation not shown or described in the drawings is the form known to those skilled in the art. In addition, although this document can provide examples of parameters including specific values, it should be understood that the parameters do not need to be exactly equal to the corresponding values, but are approximately equal to the corresponding values within an acceptable error tolerance or design constraint.

[0028] Embodiments of the present disclosure provide a preparation method of a hexagonal boron nitride heterostructure, please refer to Figure 1 , comprising: S1, heating the dielectric substrate and introducing ammonia into the deposition chamber; S2, ion source sputtering boron nitride target material, and the obtained nitrogen and boron atoms are deposited on the dielectric substrate to grow; S3, cooling to obtain a hexagonal boron nitride heterostructure.

[0029] The present disclosure uses ion beam sputtering deposition technology to directly grow hexagonal boron nitride diamond heterostructure at low temperature. While sputtering the hexagonal boron nitride target with argon ion beam, ammonia gas is introduced into the auxiliary gas path to obtain boron and nitrogen atoms deposited on the diamond dielectric substrate to grow hexagonal boron nitride. The decomposition of ammonia provides a nitrogen-rich atmosphere, improves the crystalline quality of hexagonal boron nitride, effectively reduces the growth temperature of hexagonal boron nitride, and realizes the direct preparation of hexagonal boron nitride diamond heterostructure at low temperature.

[0030] On the basis of the above-mentioned embodiments, the dielectric substrate comprises one of diamond, sapphire, silicon oxide and silicon.

[0031] The preparation method of the hexagonal boron nitride heterostructure of the present disclosure is suitable for all dielectric substrates. Since the temperature of ion beam sputtering is relatively low, usually at 500-1000℃, boron nitride is grown at a lower temperature, which can maximize the original properties of the dielectric substrate, and has important significance for electronic and optoelectronic applications.

[0032] On the basis of the above-mentioned embodiments, S1 comprises: heating the dielectric substrate to 500-1000℃; the flow rate of ammonia introduced into the deposition chamber is 5-15sccm.

[0033] Heating the dielectric substrate to 500℃~1000℃ facilitates the decomposition of ammonia under lower pressure, providing a nitrogen-rich atmosphere to replenish nitrogen atoms for the boron nitride to be grown. At the same time, the relatively low temperature will not change the original properties of the dielectric substrate.

[0034] The flow rate of ammonia gas within this range is beneficial for maintaining a high vacuum level in the chamber, ensuring the normal operation of the vacuum system, and providing a sufficient nitrogen concentration.

[0035] Based on the above embodiments, S2 includes: reducing the flow rate of ammonia gas introduced into the deposition chamber; introducing argon gas into the ion source, and ionizing the argon gas to generate an argon ion beam.

[0036] Once the deposition chamber is in a nitrogen-rich atmosphere, the ammonia flow rate in the auxiliary gas path is reduced to meet the high vacuum environment required for the ion source to operate, and to prevent excessive scattering of the argon ion beam with the boron and nitrogen atoms that are about to be sputtered.

[0037] Argon gas is continuously introduced, and an argon ion beam is generated by the sputtering ion source to sputter a boron nitride target to obtain nitrogen and boron atoms.

[0038] Based on the above embodiments, S2 includes: reducing the flow rate of ammonia gas introduced into the deposition chamber to 2 sccm to 8 sccm; and reducing the flow rate of argon gas introduced into the ion source to 2 sccm to 10 sccm.

[0039] Ammonia is continuously supplied to replenish the nitrogen atoms that are constantly being consumed, thus providing a nitrogen-rich atmosphere.

[0040] Within this flow rate range, the argon gas is beneficial in two ways: firstly, it allows for the ionization of sufficient argon ions for sputtering boron nitride targets; secondly, it ensures that the argon ions are less affected by backscattering.

[0041] Based on the above embodiments, S2 includes: the operating voltage of the ion source sputtering is 800V to 1500V; the ion beam current density of the argon ion beam is 0.1mA / cm². 2 ~0.4mA / cm 2 .

[0042] Under conditions of 800V to 1500V, ionized argon ions can acquire appropriate kinetic energy, and after sputtering boron nitride target material, generate angular and radial distributions of boron and nitrogen atoms that match the size of the equipment.

[0043] Within this range, the ion beam current density of the argon ion beam achieves the technical benefits of obtaining sufficient boron and nitrogen atom yields while preventing excessive backscattering of argon ions from affecting equipment lifespan.

[0044] Based on the above embodiments, S2 includes: the time for nitrogen and boron atoms to be deposited onto the dielectric substrate is 10 min to 60 min.

[0045] The time of growth is within the range, which is conducive to controlling the growth thickness of boron nitride, which can be 5-10 nm, for example.

[0046] On the basis of the above embodiment, the purity of the boron nitride target in S2 is greater than 99.5%.

[0047] The purity of the boron nitride target is greater than 99.5%, which is conducive to ensuring the purity of the prepared boron nitride, thereby maintaining the original performance of the boron nitride.

[0048] On the basis of the above embodiment, S1 further comprises: S01, sequentially placing the medium substrate in acetone, isopropyl alcohol, and ethanol for ultrasonic cleaning, and drying with nitrogen.

[0049] Sequentially placing the medium substrate in acetone, isopropyl alcohol, and ethanol for ultrasonic cleaning is conducive to removing organic contaminants on the surface of the medium substrate without causing residual organic solvents.

[0050] On the basis of the above embodiment, S1 further comprises: S02, pre-evacuating the deposition chamber to a backing vacuum degree, and the backing vacuum degree is 1x10 -4 Pa or below.

[0051] The backing vacuum degree needs to reach 1x10 -4 Pa or below to ensure that there is no interference of oxygen in the deposition chamber, and at the same time to ensure the ultra-high vacuum condition required for the operation of the ion source.

[0052] The disclosure uses a single ion source for sputtering. During the heating stage of the medium substrate and the sputtering stage of the boron nitride target, ammonia gas is introduced through an auxiliary gas path to successfully supplement the nitrogen vacancy defects in the boron nitride, thereby realizing the preparation of high-quality, ideal stoichiometric ratio hexagonal boron nitride.

[0053] The disclosure will be further described through specific embodiments. Taking the method for directly growing a hexagonal boron nitride diamond heterostructure at low temperature as an example, the specific steps of the method are as follows:

[0054] Steps S01-S02, prepare a diamond medium substrate.

[0055] In some embodiments, the steps S01-S02 comprise:

[0056] The diamond medium substrate is sequentially placed in acetone, isopropyl alcohol, and ethanol for ultrasonic cleaning, and then dried with nitrogen and installed in an ion beam sputtering deposition chamber for use. The deposition chamber contains a boron nitride target, an auxiliary gas path, and a sputtering ion source, and the deposition chamber is pre-evacuated to a backing vacuum degree, wherein the backing vacuum degree of the deposition chamber is 1x10 -4 Pa or below;

[0057] Preferably, the diamond medium substrate material is a diamond single crystal.

[0058] Step S1, the auxiliary gas path is used to input ammonia to heat the diamond medium substrate. The growth of hexagonal boron nitride requires the temperature of the diamond medium substrate to be higher than room temperature. In the process of heating the diamond medium substrate, the auxiliary gas path is used to input ammonia into the deposition chamber to provide a nitrogen-rich atmosphere.

[0059] In some embodiments, the step S1 further comprises:

[0060] Sub-step S11, ammonia is input into the deposition chamber through the auxiliary gas path, and the flow rate of the ammonia is between 5sccm and 15sccm, and preferably the flow rate of the ammonia is 10sccm;

[0061] Sub-step S12, the diamond medium substrate is heated to a target temperature, wherein the target temperature is between 500℃ and 1000℃, and preferably in this embodiment, the temperature of the diamond medium substrate is 700℃.

[0062] In this embodiment, in the specific preparation process, based on the above optimal implementation, the flow rate of the ammonia is 10sccm, and the temperature of the diamond medium substrate is 700℃, so as to achieve the temperature conditions for the growth of hexagonal boron nitride on the diamond surface and the nitrogen-rich atmosphere.

[0063] Step S2, the sputtering ion source is used to sputter boron nitride to obtain nitrogen and boron atoms, which are deposited on the diamond medium substrate to grow hexagonal boron nitride.

[0064] In some embodiments, the step S2 further comprises:

[0065] Sub-step S21, the flow rate of the ammonia in the auxiliary gas path is reduced to ensure the normal operation of the sputtering ion source;

[0066] Sub-step S22, the temperature of the diamond medium substrate is ensured to be stable, argon is input into the deposition chamber, and argon ions are generated by the sputtering ion source to sputter the boron nitride target to obtain nitrogen and boron atoms. In this step:

[0067] The temperature of the diamond medium substrate is between 500℃ and 1000℃, and preferably the temperature of the medium substrate is 700℃. The flow rate of the ammonia is between 2sccm and 8sccm, and preferably the flow rate of the ammonia is 5sccm. The flow rate of the argon is between 2sccm and 10sccm, and preferably the flow rate of the argon is 5sccm. The working voltage of the sputtering ion source is between 800V and 1500V, and preferably the working voltage is 1000V. The ion beam current density of the argon ion beam is between 0.1mA / cm 2 and 0.4mA / cm 2 , and preferably the ion beam current density is 0.2mA / cm 2The growth time of the hexagonal boron nitride is between 10 min and 60 min, and the preferred growth time is 40 min.

[0068] In the embodiment, in the specific preparation process, based on the above optimal embodiment, the flow rate of ammonia is 5 sccm, the flow rate of argon is 5 sccm, the medium substrate temperature is 700 DEG C, the working voltage of the sputtering ion source is 1000 V, the ion beam current density of the argon ion beam is 0.2 mA / cm 2 , and the growth time is 40 min, so as to realize the low-temperature direct growth of the hexagonal boron nitride diamond heterostructure, ensure the original physical properties of the diamond medium substrate, prevent the graphitization transformation of the diamond medium substrate, and improve the crystallization quality of the hexagonal boron nitride film.

[0069] Step S3: cooling to obtain the hexagonal boron nitride diamond heterojunction material.

[0070] Based on the above embodiment, another aspect of the present disclosure provides a hexagonal boron nitride diamond heterostructure, which is directly grown at low temperature by the above method, and the specific growth method is embodied in the above embodiment, which is not repeated here.

[0071] The method for directly growing the hexagonal boron nitride diamond heterostructure at low temperature provided by the present disclosure and the embodiments thereof has the advantages that Figure 2 That is, the X-ray photoelectron spectrograms of boron atoms 1s electrons of two samples of hexagonal boron nitride grown on a diamond medium substrate according to the embodiments of the present disclosure, wherein Figure 2 (a) the flow rate of ammonia in the auxiliary gas path during the sample preparation process is 0, Figure 2 (b) the flow rate of ammonia in the auxiliary gas path during the sample preparation process is set according to the parameters in the technical solution of the present disclosure; and Figure 2 (a) and Figure 2 In (a) and (b), a peak can be observed at 190 eV, which corresponds to a boron-nitrogen bond, and in (a), another peak exists at 188 eV, which corresponds to a boron-boron bond. Figure 2 In (a), the flow rate of ammonia in the auxiliary gas path is 0, which cannot guarantee the ideal stoichiometric ratio of the hexagonal boron nitride, and the boron nitride has a boron-rich phenomenon. Figure 2 In (b), no characteristic peak of the boron-boron bond is observed, which proves that the hexagonal boron nitride maintains the ideal stoichiometric ratio. Figure 3 That is, the Raman spectrograms of two samples of hexagonal boron nitride grown on a diamond medium substrate according to the embodiments of the present disclosure, and a peak can be observed at 1370 cm -1A Raman shift peak corresponding to a hexagonal boron nitride Raman characteristic peak is observed, and the lower curve in the figure corresponds to a sample in which the ammonia flow in the auxiliary gas path during growth is 0, and the Raman characteristic peak half-width is relatively large and the signal-to-noise ratio is relatively low. In comparison, the upper curve corresponds to a sample prepared under conditions according to the parameters in the technical solution of the present disclosure, and the Raman characteristic peak half-width is relatively small and the signal-to-noise ratio is relatively high. Figure 4 That is, the absorption spectrum diagrams of two hexagonal boron nitride samples grown on a diamond medium substrate according to the embodiments of the present disclosure, in which Figure 4 (a) the ammonia flow in the auxiliary gas path during sample preparation is 0, Figure 4 (b) the ammonia flow in the auxiliary gas path during sample preparation is set according to the parameters in the technical solution of the present disclosure; in Figure 4 (a) and Figure 4 Both (a) and (b) can observe a peak at 200 nm, corresponding to the characteristic optical absorption peak of the band gap width of hexagonal boron nitride, and Figure 4 (a) has obvious tailing on the long-wavelength side of the absorption peak, because the ammonia flow in the auxiliary gas path during the preparation of the sample is 0, resulting in poor crystalline quality of the hexagonal boron nitride. In comparison, Figure 4 (b) corresponds to the sample prepared under conditions according to the parameters in the technical solution of the present disclosure, and the obtained absorption peak is relatively sharp, indicating that the crystalline quality of the hexagonal boron nitride is relatively high.

[0072] In summary, the method for low-temperature direct growth of a hexagonal boron nitride-diamond heterostructure according to the present disclosure not only can simply and efficiently realize the direct growth of hexagonal boron nitride on a diamond medium substrate, avoid the complex transfer process, and the problems of mechanical damage and impurity introduction caused by transfer, but also can provide a nitrogen-rich atmosphere by introducing ammonia through an auxiliary gas path, ensure the ideal stoichiometric ratio of hexagonal boron nitride, and realize the growth of high-quality hexagonal boron nitride at a relatively low temperature, avoid the graphitization transformation of the diamond medium substrate under high-temperature conditions, and have very important significance for the electronic and optoelectronic applications of the hexagonal boron nitride-diamond heterostructure.

[0073] The above-described specific embodiments further illustrate the purpose, technical solution, and beneficial effects of the present disclosure, and it should be understood that the above-described specific embodiments are merely specific embodiments of the present disclosure and are not intended to limit the present disclosure. Any modifications, equivalent replacements, improvements, etc. made within the spirit and principles of the present disclosure shall be included in the protection scope of the present disclosure.

Claims

1. A method for preparing a hexagonal boron nitride heterostructure, characterized in that, include: S1, the dielectric substrate is heated to 500℃~1000℃ and ammonia gas is introduced into the deposition chamber; S2, ion source sputters boron nitride target material, and the obtained nitrogen and boron atoms are deposited onto the dielectric substrate for growth; S2 includes: Reduce the flow rate of ammonia gas introduced into the deposition chamber; Argon gas is introduced into an ion source, and the ion source ionizes the argon gas to generate an argon ion beam. The operating voltage of the ion source sputtering is 800V~1500V; The ion beam current density of the argon ion beam is 0.1 mA / cm². 2 ~0.4mA / cm 2 ; S3, cooling yields a hexagonal boron nitride heterostructure.

2. The method for preparing a hexagonal boron nitride heterostructure according to claim 1, characterized in that, The dielectric substrate includes one of diamond, sapphire, silicon oxide, and silicon.

3. The method for preparing the hexagonal boron nitride heterostructure according to claim 1, characterized in that, S1 includes: The flow rate of ammonia gas introduced into the deposition chamber is 5 sccm to 15 sccm.

4. The method for preparing a hexagonal boron nitride heterostructure according to claim 1, characterized in that, S2 includes: Reduce the flow rate of ammonia gas introduced into the deposition chamber by 2 sccm to 8 sccm; The flow rate of argon gas introduced into the ion source is 2 sccm to 10 sccm.

5. The method for preparing a hexagonal boron nitride heterostructure according to claim 1, characterized in that, S2 includes: The time for nitrogen and boron atoms to be deposited onto the dielectric substrate is 10 min to 60 min.

6. The method for preparing a hexagonal boron nitride heterostructure according to claim 1, characterized in that, The purity of the boron nitride target in S2 is greater than 99.5%.

7. The method for preparing a hexagonal boron nitride heterostructure according to claim 1, characterized in that, S1 further includes: S01, the dielectric substrate is ultrasonically cleaned in acetone, isopropanol and ethanol in sequence, and then dried with nitrogen gas.

8. The method for preparing a hexagonal boron nitride heterostructure according to claim 7, characterized in that, S1 further includes: S02, pre-evacuate the deposition chamber to a back-bottom vacuum level of 1×10⁻⁶. -4 Below Pa.

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