A method for improving the crystalline quality of boron nitride two-dimensional material epitaxial growth

Abstract

This invention discloses an epitaxial growth method for improving the crystallinity quality of boron nitride (BN) two-dimensional materials. Based on epitaxial growth methods such as metal-organic chemical vapor deposition (MOCVD), this method enhances the catalytic activity of the substrate surface by growing an aluminum nitride transition layer on the single-crystal substrate, thereby reducing the activation energy required for subsequent nucleation of BN two-dimensional materials. A silicon nitride isolation layer is introduced to reduce the introduction of impurities from the substrate into the BN two-dimensional material. Furthermore, a zero-transition process is introduced at the aluminum nitride transition layer / BN two-dimensional material interface to reduce disturbances in the interface temperature and flow fields, thus improving the ordered nucleation of the BN two-dimensional material and enhancing its crystallinity quality. This epitaxial growth method can achieve BN two-dimensional materials with smooth surfaces and high crystallinity, promoting the performance improvement of novel devices such as BN-based deep ultraviolet optoelectronic devices and van der Waals heterojunctions.

Description

Technical Field

[0001] This invention belongs to the field of semiconductor epitaxial materials technology, and specifically relates to an epitaxial growth method for improving the crystal quality of boron nitride two-dimensional materials. Background Technology

[0002] A key bottleneck limiting the performance of deep ultraviolet (DUV) optoelectronic devices is the low P-type doping efficiency of conventional V / III nitrides, making it difficult to implement heavily P-type doped epitaxial processes. Research indicates that compared to conventional V / III nitride materials such as aluminum nitride and gallium nitride, boron nitride (BN) materials require lower activation energies for magnesium doping. This means that the processing of heavily P-type doped, wide-bandgap BN materials is easier, making it easier to fabricate high-performance DUV optoelectronic devices based on BN materials. Furthermore, BN 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 BN substrates can achieve a mobility of 1.4 × 10⁻⁶. 5 cm 2 / (V·s), the highest to date; because boron nitride two-dimensional materials have no dangling bonds on their surface and have a flat surface at the atomic level, 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 greatly improve device performance; in addition, van der Waals heterojunctions formed by combining boron nitride two-dimensional materials with graphene and other two-dimensional materials have great application potential in room temperature superconductors, energy harvesters, and novel field-effect transistors.

[0003] Boron nitride (BN) two-dimensional materials have broad application prospects. Current main technologies for preparing BN two-dimensional materials include ion beam sputtering deposition and CVD growth on catalytically active metal substrates. While these technologies produce high-quality materials with mature processes, the material size is small, less than 1 cm × 1 cm. Furthermore, during device fabrication, the BN two-dimensional material needs to be transferred to a semi-insulating substrate, which easily introduces contamination and wrinkles, severely limiting the quality of the two-dimensional material and device performance. Recently, research on the fabrication of BN two-dimensional materials based on MOCVD technology has been reported abroad. 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. However, because semi-insulating substrates generally lack catalytic activity, the activation energy required for nucleation of BN two-dimensional materials on semi-insulating substrates is high, leading to difficulties in nucleation and poor crystal quality. Moreover, the low surface migration rate of boron atoms during MOCVD epitaxy makes it difficult for BN materials to coalesce into films, resulting in a rough surface. Therefore, the development of wafer-level high-crystallinity two-dimensional boron nitride materials on semi-insulating substrates through epitaxial technology improvement and process control based on MOCVD 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.

[0004] The conventional epitaxial growth method for boron nitride two-dimensional materials currently used includes the following steps:

[0005] Step (1): Select a 2-inch silicon carbide single crystal substrate and place it on the base inside the MOCVD equipment;

[0006] Step (2): Set the reaction chamber pressure to 80 torr, introduce H2 at a flow rate of 100 slm, heat the system to 1070℃, bake the substrate for 10 minutes, and remove contaminants from the substrate surface;

[0007] Step (3): Set the reaction chamber pressure to 50 torr and the temperature to 1100℃ in an atmosphere with an H2 flow rate of 120 slm. Introduce 8 slm of NH3 and maintain it for 5 minutes to perform nitriding treatment on the surface of the silicon carbide substrate.

[0008] Step (4): Set the reaction chamber pressure to 30 Torr, H2 flow rate to 80 slm, and temperature to 1050℃. Introduce triethylboron and NH3, and adjust the triethylboron flow rate to make the molar ratio of NH3 to triethylboron reach 2800. Grow a 2nm thick two-dimensional boron nitride material and then turn off triethylboron.

[0009] Step (5): Under the protection of NH3 atmosphere, the epitaxial material is removed when the temperature drops to room temperature. Summary of the Invention

[0010] The purpose of this invention is to provide an epitaxial growth method for improving the crystallinity quality of boron nitride two-dimensional materials. Based on material epitaxial growth methods such as MOCVD, this invention enhances the catalytic activity of the substrate surface and improves the nucleation quality of boron nitride two-dimensional materials through technological improvements and process control, thereby achieving the development of boron nitride two-dimensional materials with smooth surfaces and high crystallinity.

[0011] To achieve the above objectives, the solution of the present invention is:

[0012] An epitaxial growth method for improving the crystallinity of boron nitride two-dimensional materials includes the following steps:

[0013] Step (1): Select a single crystal substrate and place it on the base inside the equipment for material growth such as metal-organic chemical vapor deposition (MOCVD);

[0014] Step (2): Set the reaction chamber pressure to 50-100 torr, introduce hydrogen (H2), heat to 1000-1100℃, bake the substrate for 5-15 minutes, and remove contaminants from the substrate surface;

[0015] Step (3): Set the reaction chamber pressure to 30-150 torr and the temperature to 900-1300℃ in an H2 atmosphere, introduce ammonia (NH3) and maintain it for 1-20 minutes to nitrid the substrate surface;

[0016] Step (4): Keep the pressure and temperature of the reaction chamber constant, turn off NH3 while introducing aluminum source, and continue to supply aluminum for 5-25 seconds; then turn off aluminum source while introducing NH3, and continue to supply ammonia for 5-25 seconds; repeat the pulse process of time-sharing supply of aluminum source and NH3 to grow an aluminum nitride transition layer with a thickness of 10-100 nm, and then turn off aluminum source. During the growth of aluminum nitride transition layer, adjust the flow rates of NH3 and aluminum source to make the molar ratio of NH3 to aluminum source reach N1;

[0017] Step (5): Keep the pressure, temperature and gas flow rate of the reaction chamber constant, introduce silane (SiH4) to grow a 1-3 nm thick silicon nitride isolation layer, and then turn off SiH4;

[0018] Step (6): Keep the pressure, temperature and gas flow rate of the reaction chamber constant, introduce the organometallic boron source, and adjust the boron source flow rate to make the molar ratio of NH3 and boron source reach N2, grow a 1-3 nm thick two-dimensional boron nitride material, and then turn off the boron source.

[0019] Step (7): Under the protection of NH3 atmosphere, the epitaxial material is removed when the temperature drops to room temperature.

[0020] In this invention, the aluminum nitride transition layer in step (4) serves as the transition layer for the nucleation of the boron nitride two-dimensional material in step (6). This significantly enhances the catalytic activity of the single-crystal substrate surface, effectively reducing the activation energy required for the nucleation of the boron nitride two-dimensional material, thereby improving the nucleation quality and material density of the boron nitride two-dimensional material. Simultaneously, the growth of the aluminum nitride transition layer employs a pulsed process with time-sharing supply of aluminum source and NH3, which effectively increases the surface migration rate of aluminum atoms, thereby improving the crystal quality and surface morphology of the aluminum nitride transition layer and providing a high-quality nucleation substrate for the subsequent growth of the boron nitride two-dimensional material. Furthermore, the molar ratio N1 of NH3 and aluminum source in the aluminum nitride transition layer ranges from 200 to 2000. A lower molar ratio (N1 < 200) leads to aluminum-rich cone-shaped protrusions on the aluminum nitride surface due to the aluminum-rich atmosphere, deteriorating the surface morphology of the aluminum nitride transition layer. Conversely, a higher molar ratio (N1 > 2000) leads to a degradation of the surface migration rate of aluminum atoms due to the ammonia-rich atmosphere, inducing an island-like growth mode and causing a degradation in the crystal quality of the aluminum nitride transition layer.

[0021] In this invention, the epitaxial growth pressure, temperature and gas flow rate of the aluminum nitride transition layer in step (4), the silicon nitride isolation layer in step (5) and the boron nitride two-dimensional material in step (6) are all the same. That is, a zero-transition gas flow process is introduced at the interface of the aluminum nitride transition layer / boron nitride two-dimensional material. On the one hand, it reduces the time interruption of high-temperature growth at the interface and suppresses the decomposition of the surface layer of the aluminum nitride transition layer; on the other hand, it suppresses the disturbance of the temperature field and flow field in the early stage of the growth of the boron nitride two-dimensional material, promotes the orderly nucleation of the boron nitride two-dimensional material, and improves the crystal quality of the boron nitride two-dimensional material.

[0022] In this invention, the molar ratio (N2) of NH3 to boron source in the two-dimensional boron nitride material in step (6) ranges from 1000 to 5000. A lower molar ratio (N2 < 1000) results in a low initial nucleation density of boron nitride, making it impossible to achieve lateral merging between islands, leading to a rough material surface and low crystal quality. A higher molar ratio (N2 > 5000) results in a near-saturated initial nucleation density of boron nitride, and a decrease in the surface migration rate of boron atoms, which is also unfavorable for island merging and film formation. Furthermore, it exacerbates the pre-reaction between NH3 and the boron source, worsening the surface morphology. Therefore, the N2 range is 1000–5000.

[0023] In addition to silicon carbide single crystal substrates, this method is also applicable to sapphire, gallium nitride and other semi-insulating substrates suitable for epitaxial growth of group V / III nitrides.

[0024] After adopting the above solution, the beneficial effects of the present invention compared with the prior art are: the surface smoothness and crystal quality of the boron nitride two-dimensional material are significantly improved. Attached Figure Description

[0025] Figure 1(a) and (b) are respectively the surface morphology of a 2nm thick boron nitride two-dimensional material prepared by conventional processes and by the aluminum nitride transition layer, silicon nitride isolation layer and interface airflow zero transition process technology used in the embodiments of the present invention (tested by atomic force microscopy, test range is 1μm×1μm).

[0026] Figure 2 This is a schematic diagram comparing the Raman spectra of a 2nm thick boron nitride two-dimensional material prepared by conventional processes, using an aluminum nitride transition layer, a silicon nitride isolation layer, and an interface airflow zero-transition process technology in this embodiment of the invention.

[0027] Figure 3 This is a flowchart of the present invention. Detailed Implementation

[0028] The technical solution of the present invention will be described in detail below, but the scope of protection of the present invention is not limited to the embodiments described.

[0029] Example:

[0030] Cooperate Figure 3 The epitaxial growth method for improving the crystallinity of two-dimensional boron nitride materials in an MOCVD system, as described in the embodiments of the present invention, includes the following steps:

[0031] Step (1): Select a 2-inch silicon carbide single crystal substrate and place it on the base inside the MOCVD equipment;

[0032] Step (2): Set the reaction chamber pressure to 80 torr, introduce H2 at a flow rate of 100 slm, heat the system to 1070℃, bake the substrate for 10 minutes, and remove contaminants from the substrate surface;

[0033] Step (3): Set the reaction chamber pressure to 50 torr and the temperature to 1100℃ in an atmosphere with an H2 flow rate of 120 slm. Introduce 8 slm of NH3 and maintain it for 5 minutes to perform nitriding treatment on the surface of the silicon carbide substrate.

[0034] Step (4): Keep the H2 flow rate, reaction chamber pressure, and temperature constant, shut off NH3 while introducing trimethylaluminum, and continue supplying aluminum for 12 seconds; then shut off trimethylaluminum while introducing NH3, and continue supplying ammonia for 12 seconds; repeat the pulse process of time-sharing supply of trimethylaluminum and NH3 to grow a 25 nm thick aluminum nitride transition layer, and shut off trimethylaluminum. During the growth of the aluminum nitride transition layer, adjust the flow rates of trimethylaluminum and NH3 to achieve a molar ratio of NH3 to trimethylaluminum of 480;

[0035] Step (5): Keep the pressure, temperature and gas flow rate of the reaction chamber constant, introduce SiH4 with a net flow rate of 1.2 sccm, grow a 1.5 nm thick silicon nitride isolation layer, and turn off SiH4;

[0036] Step (6): Keep the pressure, temperature and gas flow rate of the reaction chamber constant, introduce triethylboron, and adjust the flow rate of triethylboron to make the molar ratio of NH3 to triethylboron reach 2800, grow a 2nm thick two-dimensional boron nitride material, and then turn off triethylboron.

[0037] Step (7): Under the protection of NH3 atmosphere, the epitaxial material is removed when the temperature drops to room temperature.

[0038] like Figure 1 As shown in (a) and (b), compared with conventional processes, the surface roughness (rms) of the 1μm×1μm two-dimensional boron nitride material with a thickness of 2nm prepared by introducing an aluminum nitride transition layer, a silicon nitride isolation layer and an interface airflow zero transition process technology in the embodiments of the present invention is reduced from 4.0nm to 0.4nm, indicating that the surface smoothness of the material is significantly improved.

[0039] like Figure 2 As shown, compared with conventional processes, the 2nm thick boron nitride two-dimensional material prepared by introducing an aluminum nitride transition layer, a silicon nitride isolation layer, and an interface airflow zero-transition process in this embodiment of the invention can be used in E... 2g The half-height width of Raman Peak in the model is 92cm -1 Reduced to 54cm -1 This indicates that the crystal quality has been significantly improved.

[0040] In summary, this invention utilizes epitaxial growth methods such as metal-organic chemical vapor deposition (MOCVD) to enhance the catalytic activity of a single-crystal substrate by growing an aluminum nitride transition layer, thereby reducing the activation energy required for subsequent boron nitride (BN) two-dimensional material nucleation. A silicon nitride isolation layer is introduced to reduce impurity introduction from the substrate into the BN two-dimensional material. Furthermore, a zero-transition process is introduced at the aluminum nitride transition layer / BN two-dimensional material interface to reduce disturbances in the interface temperature and flow fields, thus improving the ordered nucleation of the BN two-dimensional material and enhancing its crystallinity. This method can achieve BN two-dimensional materials with smooth surfaces and high crystallinity, promoting the performance improvement of novel devices such as BN-based deep ultraviolet optoelectronic devices and van der Waals heterojunctions.

[0041] 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 crystallinity of boron nitride two-dimensional materials, characterized in that... Includes the following steps: Step 1: Select a single crystal substrate and place it on the base inside the MOCVD equipment; Step 2: Set the reaction chamber pressure to 50~100 torr, introduce H2, heat to 1000~1100℃, bake the substrate for 5~15 minutes, and remove contaminants from the substrate surface; Step 3: Set the reaction chamber pressure to 30~150 torr and the temperature to 900~1300℃ in an H2 atmosphere, introduce NH3 and maintain for 1~20 minutes to perform nitriding treatment on the substrate surface; Step 4: Keep the pressure and temperature of the reaction chamber constant, turn off NH3 while introducing aluminum source, and continue to supply aluminum for 5-25 seconds; then turn off aluminum source while introducing NH3, and continue to supply ammonia for 5-25 seconds; repeat the pulse process of time-sharing supply of aluminum source and NH3 to grow a 10-100 nm thick aluminum nitride transition layer, and turn off aluminum source; during the growth of aluminum nitride transition layer, adjust the flow rate of NH3 and aluminum source to make the molar ratio of NH3 and aluminum source reach N1; Step 5: Keep the pressure, temperature and gas flow rate of the reaction chamber constant, introduce the organometallic boron source, and adjust the boron source flow rate to make the molar ratio of NH3 to boron source reach N2, grow a 1~3nm thick two-dimensional boron nitride material, and then turn off the boron source. Step 6: Under NH3 atmosphere protection, allow the temperature to drop to room temperature, then remove the epitaxial material; Between step 4 and step 5, there is also step a: keeping the pressure, temperature and gas flow rate of the reaction chamber constant, introducing SiH4, growing a 1-3 nm thick silicon nitride isolation layer, and then turning off SiH4. The aluminum nitride transition layer in step 4, the silicon nitride isolation layer in step 5, and the boron nitride two-dimensional material in step 6 all have the same epitaxial growth pressure, temperature, and gas flow rate, which means that a zero-transition gas flow process is introduced at the interface of the aluminum nitride transition layer / boron nitride two-dimensional material. In step 4, the molar ratio N1 of NH3 and aluminum source is in the range of 200~2000; In step 5, the molar ratio of NH3 to the boron source N2 is in the range of 1000~5000.

2. The epitaxial growth method for improving the crystallinity of boron nitride two-dimensional materials as described in claim 1, characterized in that: In step 1, the single crystal substrate is a silicon carbide single crystal substrate or a semi-insulating substrate suitable for epitaxial growth of group V / III nitrides.

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