A method for epitaxial growth for improving quality of hexagonal boron nitride material

Abstract

The application discloses an epitaxial growth method for improving the quality of hexagonal boron nitride material, and belongs to the technical field of semiconductor epitaxial materials. In the method, a thin amorphous nitride layer is formed on a single crystal substrate through surface nitriding treatment, high-density nucleation sites are provided for subsequent growth of the hexagonal boron nitride material, a source time-transport process is adopted to grow the hexagonal boron nitride material on the surface of the amorphous nitride layer, a surfactant is introduced to improve the surface morphology of the material, and after the growth of the material, a off-site annealing technology is adopted to recrystallize the hexagonal boron nitride material. The method can realize the hexagonal boron nitride material with a smooth surface and high crystal quality, and promote the performance improvement of boron nitride-based deep ultraviolet optoelectronic devices, van der Waals heterojunctions and other novel devices.

Description

Technical Field

[0001] This invention relates to an epitaxial growth method for improving the quality of hexagonal boron nitride materials, belonging to the field of semiconductor epitaxial material technology. Background Technology

[0002] A key bottleneck currently limiting the performance of deep ultraviolet (DUV) optoelectronic devices is the low P-type doping efficiency of conventional V / III nitrides, making the implementation of heavily P-type doping processes for V / III nitrides extremely difficult. Numerous studies have shown that compared to conventional V / III nitride materials such as aluminum nitride and gallium nitride, hexagonal boron nitride (HNB) materials require lower activation energies for magnesium doping, meaning that the process for heavily P-type doped wide-bandgap materials is easier to implement. Therefore, HNB materials are more suitable for developing high-performance DUV optoelectronic devices. Furthermore, HNB has a similar atomic structure to graphene, with a lattice mismatch of only 1.7%, making it an ideal substrate for graphene growth. Reports indicate that graphene grown on HNB substrates has achieved a mobility of 1.4 × 10⁻⁶. 5 cm 2 / (V·s), the highest to date; in addition, hexagonal boron nitride two-dimensional materials have no dangling bonds on their surface and have a flat surface at the atomic level, so they can be used as the dielectric layer of top-gate graphene field-effect transistors, which can significantly reduce the trap and impurity concentration at the graphene-dielectric interface, suppress optical phonon scattering, and thus greatly improve device performance; and the van der Waals heterojunction formed by combining hexagonal boron nitride two-dimensional materials with graphene and other two-dimensional materials has great application potential in room temperature superconductors, energy harvesters, and novel field-effect transistors.

[0003] Hexagonal boron nitride has broad application prospects. Currently, the main technologies for preparing hexagonal boron nitride materials include ion beam sputtering deposition and chemical vapor deposition (CVD) growth on catalytically active metal substrates. Although the materials prepared by these technologies have high quality and process maturity, the material size is small, less than 1cm×1cm. Moreover, during device development, the hexagonal boron nitride material needs to be transferred to a semi-insulating substrate. During the transfer, contamination and wrinkles are easily introduced, which seriously limits the material quality and device performance.

[0004] Recently, research on the fabrication of hexagonal boron nitride (BON) materials based on metal-organic chemical vapor deposition (MOCVD) technology has been reported internationally. This technology enables the direct fabrication of 2-inch wafer-level materials on semi-insulating substrates, effectively overcoming the challenges of ion beam sputtering deposition and metal substrate-based CVD growth techniques. However, semi-insulating substrates generally lack catalytic activity, and the high activation energy required for BON nucleation on semi-insulating substrates leads to difficulties in material nucleation and poor crystal quality. Furthermore, the low surface migration rate of boron atoms during MOCVD epitaxy makes it difficult for BON materials to coalesce into films, resulting in a rough surface. In addition, the severe gas-phase pre-reaction between the metal-organic boron source and ammonia produces particulate matter that adheres to the growth surface, further deteriorating the material surface. By improving epitaxial techniques and controlling the process based on MOCVD, the substrate surface energy can be enhanced, the surface migration rate of boron atoms can be increased, and the gas-phase pre-reaction can be suppressed. This allows for the fabrication of high-quality wafer-level BON materials on semi-insulating substrates, which is of great significance for the development of high-performance boron nitride-based deep ultraviolet optoelectronic devices, van der Waals heterojunctions, and other novel devices. Summary of the Invention

[0005] This invention proposes an epitaxial growth method to improve the quality of hexagonal boron nitride (BN) materials. A thin amorphous BN layer is formed on a single-crystal substrate using surface nitridation technology to increase the substrate surface energy and provide a high-density nucleation lattice for subsequent BN material growth. Subsequently, a source-based time-division transport process is used to grow the BN material, increasing the surface migration rate of boron atoms and promoting island merging. Simultaneously, a surfactant is introduced to improve the surface morphology of the material. After epitaxy, an off-site annealing technique is used to recrystallize the BN material, further improving its crystal quality.

[0006] To solve its technical problem, the present invention adopts the following technical solution:

[0007] An epitaxial growth method for improving the quality of hexagonal boron nitride materials includes the following steps:

[0008] Step (1): Select a sapphire single crystal substrate and place it on the base inside the equipment for material growth such as MOCVD;

[0009] Step (2): Set the reaction chamber pressure to 50~100 torr, introduce H2, heat the system to 1000~1100℃, bake the substrate in H2 atmosphere for 5~15 minutes to remove surface contaminants;

[0010] Step (3): The reaction chamber is heated to 1100~1300℃ under H2 atmosphere, the pressure is increased to P1, NH3 is introduced, and the NH3 flow rate accounts for 2~20% of the total gas flow in the reaction chamber. The substrate surface is nitrided for 10~30 minutes, and a thin amorphous nitrided layer is formed on the surface of the single crystal substrate.

[0011] Step (4): Keep the reaction chamber temperature constant and reduce the reaction chamber pressure to P2 under an H2 and NH3 atmosphere. After the gas flow stabilizes, continuously introduce an indium source at a flow rate of F, and simultaneously introduce a metal-organic boron source while shutting off NH3, continuously supplying boron for 3-12 seconds; then shut off the boron source while introducing NH3, continuously supplying ammonia for 3-12 seconds; repeat the time-division transport process of the boron source and ammonia source to grow hexagonal boron nitride material with a thickness of 1-100 nm, and then shut off the indium source and boron source. During the growth of hexagonal boron nitride material, adjust the flow rates of the boron source and NH3 to achieve a molar ratio of N for the NH3 source;

[0012] Step (5): After the epitaxial growth of the hexagonal boron nitride material is completed, it is cooled in an atmosphere of H2 and NH3, and then placed on the base inside the radio frequency heating furnace.

[0013] Step (6): Set the pressure of the radio frequency heating furnace to 50~200 torr, introduce N2 or Ar, heat the system to T, recrystallize the hexagonal boron nitride material, and anneal for 15~40 minutes;

[0014] Step (7): Cool in N2 or Ar atmosphere, and finally take out the hexagonal boron nitride material.

[0015] In step (4), the hexagonal boron nitride material is epitaxially grown using a time-sharing source transport process. This means that during the growth of the hexagonal boron nitride material, the boron source and NH3 are supplied and physically isolated in a time-sharing manner. This effectively increases the surface migration rate of boron atoms, promotes island merging and film formation, and improves the crystal quality of the hexagonal boron nitride material. It also reduces the pre-reaction between the boron source and NH3, decreasing the amount of particulate matter generated by the pre-reaction adhering to the growth surface and improving the surface smoothness of the material. Furthermore, the continuous supply of NH3 and boron is maintained for 3-12 seconds. Too short a duration causes unstable airflow, affecting process stability; too long a duration prolongs the interruption of high-temperature epitaxy, easily leading to degradation of the hexagonal boron nitride surface morphology.

[0016] In step (6), the annealing temperature T ranges from 1450 to 1650°C. If the annealing temperature is too low (T < 1450°C), the recrystallization effect of the hexagonal boron nitride material is not significant; if the annealing temperature is too high (T > 1650°C), the hexagonal boron nitride material will decompose. Therefore, the annealing temperature T ranges from 1450 to 1650°C. Additionally, an inert gas, N2 or Ar, is used in the annealing atmosphere to prevent the hexagonal boron nitride from being decomposed by the etching gas during annealing.

[0017] In step (4), the molar ratio N of NH3 to boron source in the hexagonal boron nitride material ranges from 1500 to 3500. If the molar ratio is low (N < 1500), the initial nucleation lattice density of hexagonal boron nitride is low, and it is impossible to complete the lateral merging between islands. The growth mode is a three-dimensional island mode, the material surface is rough, and the crystal quality is low. If the molar ratio is high (N > 3500), the initial nucleation lattice density of hexagonal boron nitride is basically saturated, and the surface migration rate of boron atoms will decrease. This is also not conducive to the merging between islands to form a film, and at the same time, it aggravates the pre-reaction between NH3 and boron source, which deteriorates the surface morphology. Therefore, the N range is 1500 to 3500.

[0018] The growth pressure P2 of the hexagonal boron nitride material in step (4) ranges from 20 to 80 torr. If the growth pressure is too low (P2 < 20 torr), the gas flow rate in the reaction chamber will be low during epitaxy, resulting in a decrease in process control capability; if the growth pressure is too high (P2 > 80 torr), the surface migration rate of boron atoms will decrease, which is not conducive to inter-island merging and film formation, and will simultaneously aggravate the pre-reaction between NH3 and boron source, deteriorating the surface morphology. Therefore, the P2 range is 20 to 80 torr.

[0019] The hexagonal boron nitride material in step (4) requires an indium source to be introduced during its growth, with a flow rate F ranging from 1*10⁻⁶. -5 ~1*10 -4 The indium source flow rate is mol / min. During boron nitride growth, introducing an appropriate amount of indium source acts as a surfactant, helping to improve the surface morphology of the hexagonal boron nitride material. However, a large indium source flow rate results in a large number of large indium atoms adhering to the growth surface, hindering the orderly bonding of BN bonds and thus affecting the growth of high-quality hexagonal boron nitride. Therefore, the indium source flow rate F is in the range of 1*10 mol / min. -5 ~1*10 -4 A mol / min ratio is more suitable.

[0020] In step (3), the nitriding pressure P1 of the amorphous nitride layer ranges from 150 to 300 torr. The pressure of the surface nitriding process affects the density of the hump protrusions on the surface of the amorphous nitride layer, changing the surface energy of the substrate. To promote island merging during the growth of hexagonal boron nitride, the density of the hump protrusions on the surface of the amorphous nitride layer needs to be sufficiently high; therefore, the nitriding pressure P1 should not be lower than 150 torr. To reduce airflow fluctuations during the transition between the amorphous nitride layer and hexagonal boron nitride processes and ensure a smooth airflow switching, the nitriding pressure P1 should not exceed 300 torr. Therefore, the nitriding pressure P1 ranges from 150 to 300 torr.

[0021] The beneficial effects of this invention are as follows:

[0022] This method can significantly improve the surface flatness and crystal quality of hexagonal boron nitride materials. In addition to sapphire single crystal substrates, this method is also applicable to silicon carbide, gallium nitride, and other semi-insulating substrates suitable for epitaxial growth of group V / III nitrides. Attached Figure Description

[0023] Figure 1 This is a schematic diagram of the hexagonal boron nitride epitaxial structure of the present invention, wherein: 1, a single crystal substrate; 2, an amorphous nitride layer; 3, hexagonal boron nitride material.

[0024] Figure 2 (a) is a surface morphology image of a 20 nm thick hexagonal boron nitride material prepared by conventional processes. Figure 2 (b) is a surface morphology diagram of a 20 nm thick hexagonal boron nitride material prepared using time-division transport of the source and off-site annealing techniques in the embodiments of the present invention.

[0025] Figure 3 Raman spectra comparison of 20 nm thick hexagonal boron nitride material prepared by conventional processes and by techniques such as time-division transport of the source and off-site annealing in the embodiments of this invention. Detailed Implementation

[0026] The technical solution of the present invention will be described in detail below with reference to the accompanying drawings, but the scope of protection of the present invention is not limited to the embodiments described.

[0027] Example:

[0028] The provided method for improving the quality of hexagonal boron nitride materials in an MOCVD system includes the following steps:

[0029] Step (1): Select a 2-inch sapphire single crystal substrate and place it on the base inside the MOCVD equipment;

[0030] Step (2): Set the reaction chamber pressure to 80 torr, the H2 flow rate to 60 slm, heat the system to 1070℃ and maintain this temperature for 8 minutes to remove contaminants from the substrate surface;

[0031] Step (3): The reaction chamber was heated to 1200℃ and the pressure was increased to 200 torr under an atmosphere of H2 flow rate of 120 slm. Then, 8 slm of NH3 was introduced to nitrid the substrate surface for 15 minutes, forming an aluminum oxynitride layer of about 1 nm thick on the sapphire substrate surface.

[0032] Step (4): Keeping the reaction chamber temperature constant, reduce the reaction chamber pressure to 40 Torr under an atmosphere of 40 slm H2 and 8 slm NH3. After the gas flow stabilizes, continuously introduce a flow rate of 2*10 -5Trimethylindium (TMI) was introduced at a flow rate of mol / min, and triethylboron was introduced while NH3 was shut off for 4 seconds; then, NH3 was introduced while triethylboron was shut off for 8 seconds; this time-division multiplexing process of boron and ammonia sources was repeated to grow a 20 nm thick hexagonal boron nitride material, after which both TMI and triethylboron were shut off. During the growth of the hexagonal boron nitride material, the molar ratio of NH3 to boron source was adjusted to 2880 by adjusting the flow rate of triethylboron.

[0033] Step (5): After the epitaxial growth of the hexagonal boron nitride material is completed, it is cooled in an atmosphere of H2 and NH3, and then placed on the base inside the radio frequency heating furnace.

[0034] Step (6): Set the pressure of the radio frequency heating furnace to 50 torr, introduce argon gas Ar, raise the system temperature to 1600℃, recrystallize the hexagonal boron nitride material, and anneal for 30 minutes.

[0035] Step (7): Cool in an Ar atmosphere and finally remove the hexagonal boron nitride material.

[0036] Figure 1 This is a schematic diagram of the hexagonal boron nitride epitaxial structure provided in the embodiments of the present invention. The method of the present invention uses surface nitriding treatment on a single-crystal substrate 1 to form a thin amorphous nitride layer 2, which can increase the surface energy of the substrate and provide a high-density nucleation lattice for the subsequent growth of hexagonal boron nitride material 3. A source-based time-division transport process is used to grow hexagonal boron nitride material on the surface of the amorphous nitride layer, which can improve the surface migration rate of boron atoms and improve island merging during the growth of hexagonal boron nitride. Simultaneously, a surfactant is introduced to improve the surface morphology of the material. After the material growth is completed, an off-site annealing technique is used to recrystallize the hexagonal boron nitride material, further improving the crystal quality of the material.

[0037] like Figure 2 As shown in (a) and (b), compared with conventional processes, the surface roughness (rms) of the 20nm thick hexagonal boron nitride material prepared by source time-division transport and off-site annealing techniques in the embodiments provided by the present invention is reduced from 5.1nm to 1.8nm under an atomic force microscope with a scanning range of 5μm×5μm, and the density of surface pit defects is reduced, indicating that the surface morphology of the hexagonal boron nitride material is significantly improved.

[0038] like Figure 3 As shown, compared with conventional processes, the 20nm thick hexagonal boron nitride material prepared by surface nitriding, time-division transport of the source, introduction of surfactants, and descaling annealing techniques in the embodiments provided by this invention achieves higher performance in E... 2g The half-height width of Raman Peak in the model is 67 cm -1 Reduced to 44 cm -1This indicates that the crystal quality of hexagonal boron nitride materials has been significantly improved.

[0039] The hexagonal boron nitride material prepared by surface nitriding, time-division transport of the source, introduction of surfactant, and off-site annealing technology in the embodiments provided by the present invention has significantly improved surface morphology and crystal quality, which is beneficial for realizing high-performance boron nitride-based deep ultraviolet optoelectronic devices, van der Waals heterojunctions and other novel devices.

[0040] The above embodiments are only used to illustrate the technical solutions of the present invention and are not intended to limit it. There are many manufacturing methods that can actually be adopted. All equivalent changes and modifications made in accordance with the claims of the present invention are within the scope of the present invention.

Claims

1. An epitaxial growth method for improving the quality of hexagonal boron nitride materials, characterized in that, Includes the following steps: Step (1): Select a single crystal substrate and place it on the base inside the equipment for growing metal-organic chemical vapor deposition materials; Step (2): Set the reaction chamber pressure to 50-100 torr, introduce H2, heat the system to 1000-1100℃, bake the substrate in H2 atmosphere for 5-15 minutes to remove surface contaminants; Step (3): In the H2 atmosphere, the reaction chamber is heated to 1100-1300℃ and the pressure is increased to P1. NH3 is introduced so that the flow rate of NH3 accounts for 2-20% of the total gas flow in the reaction chamber. The substrate surface is nitrided for 10-30 minutes, and a thin amorphous nitrided layer is formed on the surface of the single crystal substrate. Step (4): Keep the reaction chamber temperature constant and reduce the reaction chamber pressure to P2 under H2 and NH3 atmosphere; after the gas flow stabilizes, continuously introduce an indium source with a flow rate of F, and introduce a metal-organic boron source while turning off NH3, continuously supplying boron for 3 to 12 seconds; then turn off the boron source while introducing NH3, continuously supplying ammonia for 3 to 12 seconds; repeat the time-division transport process of boron source and ammonia source to grow hexagonal boron nitride material with a thickness of 1 to 100 nm, and then turn off the indium source and boron source; during the growth of hexagonal boron nitride material, adjust the flow rates of boron source and NH3 to make the molar ratio of NH3 to boron source reach N; Step (5): After the epitaxial growth of the hexagonal boron nitride material is completed, it is cooled in an atmosphere of H2 and NH3, and then placed on the base inside the radio frequency heating furnace. Step (6): Set the pressure of the radio frequency heating furnace to 50-200 torr, introduce N2 or Ar, heat the system to T, and anneal and recrystallize the hexagonal boron nitride material for 15-40 minutes. Step (7): Cool in N2 or Ar atmosphere, and finally take out the hexagonal boron nitride material.

2. The epitaxial growth method for improving the quality of hexagonal boron nitride materials according to claim 1, characterized in that: The range of P1 in step (3) is 150 to 300 torr.

3. The epitaxial growth method for improving the quality of hexagonal boron nitride materials according to claim 1, characterized in that: The time-division transport process of the boron source and ammonia source in step (4) is as follows: the boron source is continuously introduced while the NH3 is turned off, and then the NH3 is continuously introduced while the boron source is turned off.

4. The epitaxial growth method for improving the quality of hexagonal boron nitride materials according to claim 1, characterized in that: The reaction chamber pressure P2 in step (4) is in the range of 20 to 80 torr.

5. The epitaxial growth method for improving the quality of hexagonal boron nitride materials according to claim 1, characterized in that: The indium source flow rate F in step (4) is in the range of 1*10. -5 ~1*10 -4 mol / min.

6. The epitaxial growth method for improving the quality of hexagonal boron nitride materials according to claim 1, characterized in that: The molar ratio N of NH3 and boron source in step (4) is in the range of 1500 to 3500.

7. The epitaxial growth method for improving the quality of hexagonal boron nitride materials according to claim 1, characterized in that: The annealing temperature T in step (6) is in the range of 1450 to 1650°C.

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