Dynamic phase change regulation and control heterogeneous substrate and gallium nitride epitaxy manufacturing method

Abstract

The invention belongs to the technical field of wide bandgap semiconductor material preparation, and relates to a dynamic phase change regulation and control heterogeneous substrate and gallium nitride epitaxy manufacturing method. By regulating and controlling lattice matching and stress distribution of the heterogeneous substrate, the quality of the GaN epitaxial layer is improved, the defect density is reduced, and the reliability of the GaN epitaxial layer in high-voltage and high-power application is enhanced.

Description

Technical Field

[0001] This invention belongs to the field of wide bandgap semiconductor material preparation technology, and relates to a method for dynamically phase-change controlled heterostructure and gallium nitride epitaxial fabrication. Background Technology

[0002] Gallium nitride (GaN), a typical wide-bandgap semiconductor material, has become one of the core materials in modern power electronic devices due to its high breakdown electric field, high electron mobility, and excellent thermal conductivity. Compared with traditional silicon, GaN can maintain low-loss switching performance under high voltage and high frequency conditions, and is therefore widely used in 5G base stations, electric vehicle inverters, and high-efficiency fast charging power supplies. However, the quality of the GaN epitaxial layer directly determines the performance of its devices, especially in high-voltage applications, where the crystal quality, defect density, and stress state of the epitaxial layer become key factors limiting its performance.

[0003] Existing GaN epitaxial growth technologies primarily rely on processes such as metal-organic vapor deposition (MOCVD), molecular beam epitaxy (MBE), and hydride vapor phase epitaxy (HVPE). These technologies require the growth of high-quality GaN thin films on substrates. However, due to the significant lattice mismatch and thermal expansion coefficient differences between GaN and commonly used substrates such as silicon, sapphire, or silicon carbide, this heterogeneous growth mode often leads to high-density dislocations and cracks in the epitaxial layer. Especially in thick-layer epitaxy, lattice mismatch stress and thermal stress during cooling further accumulate, ultimately affecting the integrity of the GaN epitaxial layer and the reliability of the device. Furthermore, to alleviate the lattice mismatch problem, traditional techniques typically employ multilayer buffer layer designs, such as AlN or AlGaN buffer layers. While this reduces dislocation density to some extent, its effect remains limited in thick-layer epitaxial fabrication, and the complex buffer layer design also increases manufacturing costs and process difficulty.

[0004] Another key issue is that existing technologies struggle to adjust lattice matching and stress distribution in real time during epitaxial growth, making it difficult to effectively alleviate stress concentration points. Thermal stress release during the cooling stage primarily depends on the substrate's thermal expansion properties; however, traditional substrate materials have relatively fixed coefficients of thermal expansion, making it difficult to dynamically adapt to the needs of GaN epitaxial layers. Consequently, high-stress regions are prone to crack formation or dislocation propagation, not only reducing the quality of the epitaxial layer but also directly impacting the performance of the final device.

[0005] In summary, existing technologies for GaN epitaxial growth mainly face the following problems: First, the stress accumulation problem caused by lattice mismatch and differences in thermal expansion coefficients has not been effectively solved, especially in thick-layer epitaxy, where this problem is more serious; second, the epitaxial growth process lacks a dynamic control mechanism, making it impossible to achieve adaptive optimization of lattice constant and thermal expansion performance during the growth and cooling stages; and third, although complex buffer layer designs can reduce some dislocation density, the process cost is high and the effect is limited. Summary of the Invention

[0006] To address the aforementioned technical problems, this invention provides a method for dynamically phase-change controlled heterostructure substrates and gallium nitride epitaxial fabrication based on the heterostructure substrates. By controlling lattice matching and stress distribution, the quality of GaN epitaxial layers is improved, defect density is reduced, and reliability in high-voltage and high-power applications is enhanced.

[0007] In a first aspect, the present invention provides a dynamically phase-change modulated heterostructure substrate, such as... Figure 1 As shown, the heterogeneous substrate includes a base substrate and a dynamic buffer layer;

[0008] The base substrate is prepared from one of three raw materials: silicon (Si), silicon carbide (SiC), or sapphire (Al2O3). Preferably, the base substrate is prepared by pretreatment of the above-mentioned raw material substrates before sequential cleaning, drying, and deposition of dynamic phase change material. The cleaning and drying are to remove contaminants from the surface of the raw material substrate and reduce roughness. The cleaning is performed using organic solvents such as acetone and isopropanol, followed by rinsing with deionized water. The drying is performed by high-temperature dehydration baking to remove residual moisture and organic matter from the surface. The pretreatment before deposition of dynamic phase change material includes, for example, further plasma cleaning and chemical cleaning of the surface of the raw material substrate to ensure that there are no organic residues and impurities on the surface. The plasma cleaning is, for example, Ar plasma etching, and the chemical cleaning is, for example, soaking in deionized water or organic solvents.

[0009] The dynamic buffer layer includes an intermediate buffer layer and a surface buffer layer;

[0010] The intermediate buffer layer is prepared by depositing a dynamic phase change material on the base substrate; the dynamic phase change material deviates from the GaN lattice constant within ±1% to ±3% at the aforementioned high temperature of 800℃~1200℃; preferably, the dynamic phase change material includes perovskite materials such as BaTiO3, SrTiO3, or doped and modified perovskite materials. Based on the high temperature environment of 800℃~1200℃ required for subsequent GaN epitaxial growth, the chemical composition and doping elements are controlled to obtain a perovskite material exhibiting a highly symmetric phase within this temperature range, so that the prepared intermediate buffer layer has an ideal phase transition temperature range and a lattice constant approximately matching that of GaN. Specifically, the phase transition temperature range of the perovskite material is 600℃~1200℃, allowing the material to be in a highly symmetric crystal phase within the epitaxial growth temperature range. The lattice constant of the high-temperature phase is close to that of GaN, which is approximately 3.189Å~3.190Å. The doping modification can be performed using metallic elements such as Sr, Ca, Mg, zirconium (Zr) or rare earth elements such as La, Sm, to partially replace or co-dopate the original perovskite material system, thereby changing the material's lattice constant, phase transition temperature, and coefficient of thermal expansion. The type of dopant element is determined based on the target lattice constant matching degree and thermodynamic stability required for GaN epitaxial growth, with the doping concentration controlled within the range of 0.5 at.% to 10 at.%. It should be noted that at.% in this application represents atomic percentage, and the specific concentration is fine-tuned based on simulation and experimental data. Too low a concentration will not achieve the expected lattice constant adjustment effect, while too high a concentration will lead to a decrease in the chemical stability and mechanical strength of the dynamic phase transition material. Within the high-temperature range of 800℃ to 1200℃, the relative deviation between the lattice constant of the dynamic phase transition material and GaN is preferably maintained within ±1% to reduce lattice mismatch in the epitaxial layer. Upon cooling to room temperature, the material gradually transforms into a low-temperature phase, absorbing thermal stress through volume and lattice distortion caused by the phase transition, thus reducing the risk of warpage and cracking in the GaN epitaxial layer. By adjusting the doping elements and concentration, the center point of the phase transition temperature is controlled within the main epitaxial growth temperature range, such as 900℃ to 1000℃, ensuring a high degree of lattice matching with GaN during the growth temperature range.

[0011] The deposition method of the intermediate buffer layer includes metal-organic chemical vapor deposition (MOCVD), molecular beam epitaxy (MBE), or physical vapor deposition (PVD). Preferably, the deposition temperature range of the intermediate buffer layer is 300℃~600℃; the deposition gas environment of the intermediate buffer layer can be any one or a mixture of two of argon, nitrogen (N2), or oxygen, and is controlled according to the redox state of the desired phase change material; the deposition growth rate of the intermediate buffer layer ranges from 0.1~0.5 μm / h.

[0012] To enhance the bonding strength between the dynamic phase change material and the epitaxial layer, a surface buffer layer is further deposited and grown above the intermediate buffer layer, and interface modification treatment is performed. The surface buffer layer can be made of metal oxides such as TiO2, or metal nitrides such as aluminum nitride (AlN) or aluminum gallium nitride (AlGaN). The material used to prepare the surface buffer layer has a similar lattice constant to the dynamic phase change material and is less prone to chemical decomposition during epitaxy. The coefficient of thermal expansion of the surface buffer layer is 4.2 × 10⁻⁶ within the temperature range of 25℃ to 1200℃. -6 / K~5.6×10 -6 / K, which matches the thermal expansion coefficient of GaN well. The surface buffer layer is deposited and grown using MOCVD technology. As a preferred embodiment, the deposition conditions for the surface buffer layer are specifically set as follows: growth temperature: 800℃~1200℃; V / III ratio range of 1000~3000 based on NH3 / trimethylaluminum (TMA) or trimethylgallium (TMG); growth pressure 200 Torr; growth rate range of 0.2~1 μm / h.

[0013] After the dynamic phase change material and the surface buffer layer are deposited, a high-temperature annealing (RTA) treatment is performed. Preferably, the annealing temperature range of the high-temperature annealing treatment is 600℃~800℃, and the temperature is held for 10 min~30 min to make the lattice fit between the interface layer and the phase change material more stable. Through this annealing step, the uniformity of the distribution of dopants in the phase change material is promoted, and the presence of pores, defects or stress concentration areas is reduced.

[0014] Secondly, the present invention provides a method for gallium nitride epitaxial fabrication based on the above-mentioned heterostructure substrate, such as... Figure 1 As shown, gallium nitride epitaxy, i.e., the epitaxial layer, is fabricated on the heterostructure substrate described in the first aspect; the gallium nitride epitaxial fabrication method includes an initial epitaxial stage, a main epitaxial stage, and a cooling stage.

[0015] The initial epitaxial stage is mainly the low-temperature GaN layer growth stage, with the epitaxial growth temperature set in a relatively low range of 500℃~750℃ to facilitate the formation of a uniform GaN nucleation layer on the surface buffer layer. The V / III ratio is controlled by adjusting the flow ratio of NH3 to TMG sources to reduce nucleation defects and avoid excessive enrichment of nitrogen or gallium sources that could lead to surface roughness. A low growth rate of 0.2~0.5 μm / h is used to ensure a good two-dimensional growth pattern for the initial GaN nucleus layer and to reduce the generation of large particles or island structures. At the initial temperature of 500℃~750℃, combined with the phase transition temperature window of 600℃~1200℃ for the heterostructure substrate, the dynamic phase change material is ensured to remain in a high-temperature or near-high-temperature phase state, making the lattice constant more compatible with GaN. Because the phase change material maintains a high-symmetry phase state, its stress absorption characteristics can play a preliminary buffering role at this stage, reducing large-scale mismatches and interface stress concentrations that occur in the early stages of GaN nucleation. The low-temperature growth process can form a transition region between the buffer layer and the GaN crystal layer, reducing the difference in lattice constant. After the initial nucleation is completed in a low-temperature environment, a GaN thin layer with a dense surface and low defect density can be obtained, laying a good foundation for the subsequent main epitaxial stage.

[0016] The main epitaxial stage involves rapidly increasing the growth temperature to the main epitaxial range of 800℃ to 1200℃ after the initial epitaxial layer reaches a set thickness of 50~200 nm. During this stage, a stable temperature field must be maintained, with temperature fluctuations controlled within ±5℃ to ensure uniform GaN growth. The growth rate is increased to 0.5~1.0 μm / h, and the V / III ratio is appropriately increased, for example, to 1500~3000, to accelerate the deposition of thick GaN layers and further improve the crystal quality of the material. At high temperatures, dynamic phase change materials possess good elastic adjustment capabilities, effectively absorbing locally generated stress or dislocations during epitaxy and reducing defect diffusion to the epitaxial surface. The final target thickness of the main epitaxial layer is typically in the range of 2~10 μm, and is adjusted within this range according to different device requirements, such as high-voltage GaN HEMTs and IGBTs. At high temperatures, perovskite materials exhibit strong lattice distortion capabilities, rapidly adjusting stress distribution through local distortion or phase transitions when micro-stress occurs. Stress is released at the interface and within the intermediate buffer layer, reducing the likelihood of dislocations extending to the GaN surface, thereby improving the crystal integrity of the epitaxial layer and device performance. High-energy electron diffraction and optical reflection monitoring are used to dynamically observe the epitaxial layer surface growth pattern. When diffraction fringes darken or roughness increases, the temperature, gas flow rate, or V / III ratio is fine-tuned. Periodic inspections using optical microscopy and atomic force microscopy (AFM) reveal significant defects or growth anomalies; in such cases, the holding time is appropriately extended and the growth rate reduced to obtain a smoother epitaxial layer surface.

[0017] The cooling stage, after GaN reaches the target thickness, involves a cooling rate ranging from 1 to 5 °C / s to avoid excessive thermal shock due to a sudden temperature drop. The phase change material transitions from a high-temperature to a low-temperature phase. As the temperature gradually decreases below 600 °C, the dynamic phase change material enters the low-temperature phase, absorbing and dispersing thermal stress through changes in its lattice constant, distortion, or phase domain movement. The difference in thermal expansion coefficients between GaN and the substrate introduces residual stress during cooling; the phase change and lattice slip mechanism of the dynamic phase change material disperses this stress to the substrate interior or interface region. During the phase change process, if microcracks are locally induced, the material can reduce the crack propagation rate through lattice rearrangement and phase deformation nuclei, ensuring the epitaxial layer maintains high integrity at the final room temperature.

[0018] Thirdly, the present invention provides a high-voltage power device, the high-voltage power device comprising an epitaxial layer fabricated using the hetero substrate described in the first aspect or the gallium nitride epitaxial fabrication method described in the second aspect.

[0019] Beneficial effects:

[0020] The first aspect of this invention provides a dynamically phase-change-controlled heterostructure substrate, wherein the intermediate buffer layer can be used for phase change control during subsequent GaN epitaxial growth: that is, it is in a high-symmetry crystal phase in the high-temperature epitaxial state, achieving lattice matching with the GaN layer; during the cooling stage, when the phase change is to a low-temperature phase, it effectively absorbs and disperses thermal stress; it can also be used for stress buffering during subsequent GaN epitaxial growth: that is, it compensates for thermal stress through the dynamic phase change process, reducing warping and cracks in the GaN epitaxial layer when the temperature changes rapidly; the surface buffer layer achieves a closer match with the GaN epitaxial layer in terms of lattice constant and thermal expansion coefficient, playing an epitaxial transition role, retaining the lattice synergy effect of the dynamic phase change material at high temperature, and suppressing lattice defects in the initial growth stage of GaN, thereby reducing dislocation density and lattice mismatch during subsequent growth. The gallium nitride epitaxial fabrication method provided in the second aspect of the present invention further optimizes the epitaxial growth temperature and growth gas, including the V / III ratio and gas flow rate, based on the aforementioned heterostructure substrate, so that the dynamic phase change material can achieve lattice matching with GaN at high temperature and obtain a GaN epitaxial layer with high uniformity and low defect density during the growth process. Attached Figure Description

[0021] Figure 1 This is a schematic diagram of the heterogeneous substrate and epitaxial layer structure described in this invention. Detailed Implementation

[0022] By constructing heterogeneous substrates, key parameters such as temperature, gas, and growth rate are optimized according to different heterogeneous substrates in the three stages of initial epitaxy, main epitaxy, and cooling. The lattice modulation characteristics exhibited by dynamic phase change materials in different temperature ranges are utilized to reduce the defect density and stress concentration of GaN epitaxial layers, laying a good foundation for the fabrication of highly reliable GaN devices, as shown in Examples 1 to 3 below.

[0023] Example 1: The following will take the construction of a dynamically phase-change controlled heterostructure on a sapphire Al2O3 substrate and the subsequent GaN epitaxial growth as an example to illustrate the implementation process of the method of the present invention.

[0024] The embodiments described are only used to illustrate the technical solutions of the present invention and are not intended to limit the present invention.

[0025] Step S1: Fabricate a heterogeneous substrate;

[0026] Step S11: Select a sapphire single crystal substrate with a diameter of 2 inches and a thickness of about 430 μm. The sapphire substrate has a single crystal hexagonal structure with a lattice constant at room temperature and its thermal conductivity meets the initial heat dissipation requirements. Clean the sapphire single crystal substrate in acetone and isopropanol for 5 minutes each, rinse it with deionized water, and then bake it in vacuum at 120°C for 10 minutes to remove residual moisture and organic matter from the surface.

[0027] Step S12: A BaTiO3-based perovskite material with a thickness of approximately 200 nm is deposited on a sapphire substrate using physical vapor deposition (PVD). Approximately 3 at.% Sr is incorporated during deposition to improve its lattice symmetry at high temperatures and its compatibility with epitaxial processes. The deposition temperature is controlled at 500°C, and the vacuum level is approximately 5 × 10⁻⁶. -4 The deposition rate is approximately 0.1 μm / h. The phase transition temperature window of the BaTiO3-based dynamic phase transition material is 600℃~1100℃, and the lattice constant of the material deviates from that of GaN by less than ±2% at high temperature. After deposition, the BaTiO3-based perovskite material is pretreated with Ar plasma micro-etching to enhance the bonding force between the dynamic phase transition material and the subsequently deposited AlN. Through the above operations, 3 at.% Sr doping is introduced into the BaTiO3 matrix lattice. After sintering with a PVD target, the finished film maintains a high symmetry structure in the range of 800℃~1000℃, and the difference between the lattice constant of the material and that of GaN is controlled within ±2%. The molar ratio of titanium source to strontium source set in Example 1 can make the phase transition temperature center point located at approximately 900℃, which matches the commonly used growth temperature range of 800℃~1100℃ for GaN epitaxy. Test results show that the material is in a low-temperature phase at room temperature (25℃~600℃) and a high-temperature phase between 600℃~1100℃, and the phase transition process is stable and reversible.

[0028] Step S13: An approximately 50 nm thick AlN surface layer is grown on the intermediate buffer layer using MOCVD. The growth temperature is set to 1000 °C, the V / III ratio between NH3 and TMA is 2000, the growth pressure is maintained at 200 Torr, and the growth rate is 0.5 μm / h. The coefficient of thermal expansion of the AlN buffer layer is approximately 4.6 × 10⁻⁶. -6 / K, thickness 50nm; after deposition, the AIN surface is pretreated by Ar plasma micro-etching to enhance the bonding force between the AIN surface and the subsequent GaN epitaxial layer;

[0029] Step S14: After deposition, rapid thermal annealing (RTA) is performed at 600℃ for 10 minutes to make the interface structure more compact and the stress distribution more uniform.

[0030] S2, Gallium nitride multi-stage epitaxial growth

[0031] Epitaxy was performed using NH3 as the nitrogen source and TMG as the gallium source in a protective atmosphere of a mixture of hydrogen (H2) and nitrogen (N2). The V / III ratio was adjusted between 2500 and 3000 to ensure a stable two-dimensional growth pattern on the GaN surface. The total gas flow rate was approximately 10 slm, and the reaction chamber pressure was approximately 200 Torr. During growth, the clarity and periodicity of the diffraction pattern on the GaN surface were monitored using Reflected High Energy Electron Diffraction (RHEED). If the diffraction signal weakened or the fringes became blurred, the flow rates of NH3 and TMG or the temperature settings were fine-tuned to maintain a high-quality growth rate.

[0032] S21, the temperature is lowered to 600℃ to grow a low-temperature GaN nucleation layer of about 20nm to further reduce lattice mismatch. At this time, the dynamic phase change material is in a high temperature or near-high temperature phase state, which provides initial buffering for local stress; the growth rate is controlled at 0.3μm / h.

[0033] In step S22, the temperature is rapidly increased to 950℃ for thick-layer GaN growth, with a target thickness of 4 μm. During this process, the V / III ratio is set to 2800, and the growth rate is increased to 0.8 μm / h. The dynamic phase change material (MPC) exhibits elastic regulation capabilities in this temperature range, absorbing localized stresses generated during epitaxy and preventing dislocation propagation along the growth direction. In this step, by heating the MOCVD growth chamber to 950℃ and maintaining it stably, the MPC is kept in a high-temperature phase, ensuring its lattice constant matching with GaN remains within an acceptable range of ±2%.

[0034] S23, after the GaN epitaxial layer reaches the set thickness, it is cooled from 950°C to 600°C at a cooling rate of approximately 3°C / s; then it is slowly cooled to 25°C at a rate of 1°C / s. During this process, the BaTiO3-based material transitions from a high-temperature phase to a low-temperature phase, disperses residual stress through lattice slip, and effectively suppresses crack formation.

[0035] S3, Stress Regulation and Crack Suppression: Online Raman spectroscopy was used to analyze the peak position of the E2 (high) mode. Stress changes were recorded every 50°C during cooling. The results showed that the stress value fluctuated continuously within ±0.1 GPa, with no high stress peak appearing. The coefficient of thermal expansion of the dynamic phase change material gradually decreased in the range of 600°C to room temperature (25°C), and the stress difference with GaN and sapphire was dynamically compensated; at this time, the surface warpage of the GaN epitaxial layer was approximately 2 μm / cm. 2 No obvious cracks were observed. SEM analysis showed that the crack density on the epitaxial layer surface was less than 1 crack / cm² after cooling. 2 The crack length is usually less than 1 μm and is dispersed in local areas, with high overall crystal layer integrity.

[0036] S4, Epitaxial Layer Quality Evaluation and Post-processing: XRD test results show that the FWHM of the GaN (002) surface rocking curve is about 180 arcsec, and the FWHM of the (102) surface is about 230 arcsec, indicating a low dislocation density; AFM detection results show that the scanning area is 5×5μm 2 The RMS value is approximately 0.4 nm, the surface is smooth with no large particles or obvious steps; Raman stress analysis results show that the E2 (high) peak shift is controlled within ±0.1 cm. −1 Within this range, the corresponding residual stress is < ±0.1 GPa; under N2 environment, rapid annealing RTA is performed at 900℃ and held for 10 minutes; the heating rate is 30℃ / s and the cooling rate is 20℃ / s; after annealing, XRD is detected again, showing that the FWHM of the (002) surface is reduced to about 160 arcsec, the AFM morphology is slightly improved, and the RMS value is 0.3 nm.

[0037] Example 2 will use the fabrication of a GaN IGBT high-voltage power device on a silicon (Si) substrate using a dynamically phase-change controlled heterostructure as an example to further illustrate the applicability of the method of the present invention under different substrates and different dynamic phase-change material formulations. Example 2 differs from Example 1 in specific material selection and process parameters, but the overall process and principle are the same, aiming to further demonstrate the feasibility of the present invention on various substrates and material systems.

[0038] This embodiment is for illustrative purposes only and is not intended to limit the scope of the invention.

[0039] Step S1: Fabricate a heterogeneous substrate;

[0040] Step S11: A conductive silicon substrate with a diameter of 4 inches, (111) orientation, and a thickness of 500±10 μm is selected, with a resistivity of 0.02~0.05 Ω·cm to meet the back electrode requirements of high-voltage devices. The substrate is ultrasonically cleaned by immersing it in acetone and isopropanol for 5 minutes, and then rinsed with deionized water; subsequently, it is baked at 120°C for 10 minutes to remove surface moisture and organic impurities. Since silicon substrates are easily oxidized, Ar / H2 plasma treatment is performed for 10 minutes before deposition to remove the surface oxide layer and impurities; Step S12: A Zr-doped perovskite oxide BaTiO3-ZrO2 system with a thickness of 300±10 nm is deposited on the silicon substrate by chemical vapor deposition (CVD). With Zr doping controlled at approximately 5 at.%, the material exhibits lattice stability at high temperatures. Preliminary target synthesis and thermal analysis revealed that the material's lattice constant differs from GaN's by <±1.5% within the 800℃~1100℃ range, with the phase transition temperature concentrated between 650℃ and 1150℃. The deposition temperature was 550℃, the growth rate was 0.15 μm / h, the atmosphere was an Ar / O2 mixture with a volume ratio of Ar to O2 of 4:1, and the system pressure was maintained at 1×10⁻⁶. -3 Torr. In this embodiment, 5 at.% Zr element is selected as the partially substituted ion of BaTiO3 perovskite. Compared with Sr doping in Example 1, it can maintain higher lattice symmetry at high temperature and effectively suppress excessive distortion that may occur during phase transition.

[0041] Step S13: Grow 100nm±5nm Al on the intermediate buffer layer using MOCVD. 0.2 Ga 0.8 An N-layer was applied to further reduce the lattice mismatch with GaN. The growth temperature was set at 1050℃, the V / III ratio was 2500, where III represents the gallium-aluminum (gallium and aluminum ratio 4:1) source gas flow rate, V represents the nitrogen source gas flow rate, the growth pressure was 200 Torr, and the growth rate was set at 0.6 μm / h. Al 0.2 Ga 0.8 The thermal expansion coefficient of the N buffer layer is similar to that of GaN, which is 4~5.5×10⁻⁶. -6 / K can suppress the upward propagation of dislocations during the primary extensional stage;

[0042] Step S14: After the intermediate layer is deposited, it is annealed at 650°C for 15 minutes to make the BaTiO3-ZrO2 layer more tightly bonded to the silicon substrate and AlGaN surface layer, and to make the thermal stress distribution more uniform.

[0043] S2, Multi-stage epitaxial growth process

[0044] NH3 was used as the nitrogen source, TMG as the gallium source, and TMA as the aluminum source. A 3:1 H2 / N2 mixture was used as the carrier gas. The V / III ratio was maintained between 2000 and 2200 during the early growth stages, and increased to 3000 during later thickening to ensure large-area uniformity and low dislocation density. Surface nucleation quality was monitored using reflected high-energy electron diffraction (RHEED) in the early growth stages, and later optical reflection monitoring (optical interferometry) was used for feedback control of the growth rate and film thickness. The system pressure was maintained within the range of 150–250 Torr.

[0045] S21, Initial Epitaxial Stage: At 700℃, a 30nm low-temperature GaN nucleation layer is deposited first, with the growth rate controlled at 0.25μm / h and a V / III ratio of 2000. This thin layer helps reduce the lattice mismatch between AlGaN and GaN and improves the nucleation quality of the epitaxial layer. The dynamic phase change material maintains a high symmetry state at this stage, effectively absorbing stress at the interface and preventing the generation of large-scale dislocations in the early stages of nucleation. This stage ensures the BaTiO3-ZrO2 layer is in a high-temperature phase by rapidly raising the MOCVD growth chamber temperature to 980℃ and maintaining it. Within this temperature range, the lattice difference between the dynamic phase change material and GaN is within ±1.5%, providing good matching for the main GaN epitaxy.

[0046] S22, Main Epitaxial Stage: The temperature is slowly increased to 1050℃, and the growth of the main GaN layer is accelerated, with the growth rate increased to 0.8 μm / h, and the target thickness is 5 μm. The V / III ratio is increased to 2800–3000 to ensure sufficient nitrogen source supply and reduce surface roughness and defects caused by Ga enrichment. At this time, the Zr-doped BaTiO3 remains in a high-temperature phase at 1050℃, exhibiting good elastic distortion capability. Online RHEED or optical reflection monitoring shows that the growth surface maintains a stacked two-dimensional 2D nucleation mode without obvious island morphology.

[0047] S23, Cooling Stage: The temperature was reduced from 1050℃ to 700℃ at a cooling rate of 3℃ / s~4℃ / s; then slowly cooled to room temperature at 1℃ / s; the BaTiO3-ZrO2 material transitioned from a high-temperature phase to a low-temperature phase by absorbing thermal stress through lattice slip and distortion. Tests showed that the substrate warpage was <5μm / cm. 2 Surface crack density is less than 1 / cm 2 .

[0048] S3, Stress Regulation and Crack Suppression: Online Raman spectroscopy was used to monitor the stress distribution of the GaN epitaxial layer during the cooling process. Peak shifts were recorded every 50°C decrease in temperature. The maximum stress was ±0.12 GPa, and no localized abnormal stress peaks were observed. The BaTiO3-ZrO2 phase transition occurred at approximately 700°C, and the resulting lattice slip properties dispersed localized stress into a large-area buffer layer, preventing rapid crack propagation. A 6×10⁻⁶ ohmmeter between the substrate Si and GaN was observed. -6 Despite thermal expansion differences exceeding / K, the surface smoothness and integrity of GaN are significantly improved after cooling under the adjustment of dynamic phase change materials.

[0049] S4, Epitaxial Layer Quality Evaluation and Post-processing: XRD characterization showed that the FWHM of the GaN (002) surface was 190 arcsec, and the FWHM of the (102) surface was 250 arcsec; AFM characterization showed that the 5×5μm 2 The RMS value within the scanned area was 0.5 nm, indicating uniform particle distribution without large-area steps; crack detection showed that the crack density observed by SEM was <1 / cm². 2 The epitaxial layer was characterized by extremely short cracks and no through-cracks. Rapid annealing (RTA) was performed at 900℃ in a nitrogen atmosphere with a holding time of 15 minutes, a heating rate of 25℃ / s, and a cooling rate of 15℃ / s. After annealing, XRD characterization showed that the FWHM of the GaN(002) surface decreased to 170 arcsec, and the RMS value slightly decreased to 0.4 nm. Raman spectroscopy revealed a residual stress of approximately ±0.07 GPa, indicating further improvement in the quality of the epitaxial layer.

[0050] Example 3 will demonstrate the universality and scalability of this invention under various substrates and doping schemes by constructing a dynamically phase-change controlled heterostructure on a silicon carbide (SiC) substrate and performing GaN epitaxial growth to prepare high-power, high-frequency devices such as GaN HEMTs. This example further verifies the universality and scalability of this invention under various substrates and doping schemes. This example differs from the previous two examples in terms of substrate selection, dynamic phase-change material formulation, and epitaxial conditions, and is mainly used to illustrate the applicability of this invention in scenarios with higher thermal conductivity substrates and high-frequency devices. The following are merely illustrative examples and are not intended to limit the invention.

[0051] Step S1: Fabricate a heterogeneous substrate;

[0052] Step S11: A 3-inch diameter 4H-SiC substrate with a resistivity of 0.015~0.03 Ω·cm and a thickness of 350μm is selected. The 4H-SiC substrate has a high thermal conductivity of 3~4.9 W / (cm·K), which can withstand high temperatures and high power densities. Its high thermal conductivity is beneficial for heat dissipation of high-frequency, high-power devices. The SiC substrate is ultrasonically cleaned in acetone and isopropanol for 5 minutes each, rinsed with deionized water, and then vacuum dried at 130℃ for 10 minutes to remove surface organic matter and moisture. Before depositing BCT, the SiC surface is micro-etched using argon plasma for 3 minutes to improve interface roughness and activity.

[0053] Step S12: A 150 nm thick Ca-doped BaTiO3 thin film is deposited on a SiC substrate using molecular beam epitaxy (MBE). 1-X Ca X The TiO3 thin film, abbreviated as BCT film, has x in the range of 0.1 to 0.2; the deposition temperature is set at 550℃, and the MBE vacuum degree is 1×10⁻⁶. -5 Pa, doping rate is precisely controlled by a single Knudsen source, resulting in a deposition rate of 0.15 μm / h. BCT dynamic phase change material: phase change temperature window is 650℃~1200℃, and it exhibits a good, highly symmetric phase structure in the high-temperature range above 800℃;

[0054] Step S13: After completing the BCT thin film deposition, the raw material source in the MBE system is switched to trimethylaluminum (TMA) and ammonia as the reaction source to deposit a 50 nm AlN layer at a growth temperature of 800 °C and a working pressure of 3 × 10⁻⁶. -4 Pa; the AlN layer and subsequent GaN epitaxy have a better match in lattice constant and coefficient of thermal expansion, further reducing lattice mismatch and initial dislocation density. The AlN buffer layer is 50 nm thick and is annealed at 700 °C for 5 minutes after growth to improve density; after AlN deposition, a short 2-minute nitrogen plasma post-treatment is performed to further enhance the bonding force between AlN and BCT layers.

[0055] Compared to the Sr and Zr doping methods described in the previous two examples, this embodiment uses Ca. 2+ Replace Ba 2+Partial doping at specific sites, with a doping concentration of 0.15 ± 0.05, can increase the tetragonal or cubic phase transition temperature of BaTiO3 at high temperatures. Thermal analysis results show that at x = 0.15, the phase transition center temperature is close to 1000℃, matching the main epitaxial temperature range of GaN (900℃ ~ 1100℃). High-temperature X-ray diffraction (XRD) measurements show that the lattice constant of BCT at 900℃ deviates from that of GaN by < ± 1.5%, meeting the approximate matching requirements for dynamic phase transition control. After cooling to room temperature, BCT transforms into a low-temperature phase with moderate lattice shrinkage of 0.05 Å ~ 0.1 Å, effectively absorbing stress between the substrate and GaN.

[0056] S2: Epitaxial growth

[0057] In this embodiment, MOCVD was used for GaN master epitaxy, employing a two-stage heating control: initially maintaining the temperature at 700℃ to facilitate low-temperature GaN nucleation, followed by a rapid increase to 1000℃ for master epitaxy. At 1000℃, the BCT material is in a high-temperature phase, with a lattice constant deviation from GaN of <±1.5%, exhibiting strong stress buffering capacity.

[0058] NH3 was used as the nitrogen source, TMG as the gallium source, and a mixture of hydrogen (H2) and nitrogen (N2) as the carrier gas at a flow ratio of 2:1, with a total flow rate of approximately 10 slm. The initial V / III ratio during the nucleation period (early epitaxial stage) was set at 1500, increasing to 2500 during the main epitaxial stage. The reaction chamber pressure was set to 200 Torr. RHEED was used to monitor changes in the surface two-dimensional growth pattern during early nucleation. An optical reflectance spectrometer was used to measure the GaN thickness and growth rate online, and the NH3 or TMG flow rates were fine-tuned based on the feedback data to maintain growth uniformity.

[0059] S21, Initial epitaxial stage: The MOCVD furnace temperature is adjusted to 700℃, and a 30nm low-temperature GaN layer is first grown on the AIN surface, with a growth rate of 0.2μm / h. At this time, the BCT layer temperature is 700℃, which is still in the upper part of the phase transition region, and the lattice adaptation ability is better, which can reduce the stress difference of the GaN substrate.

[0060] S22, main epitaxial stage: The temperature is rapidly increased from 700℃ to 1000℃ and maintained at this temperature for 5μm thick GaN epitaxial growth; the V / III ratio is increased from 2000 to 2800, and the growth rate is increased to 0.7μm / h; BCT has a stable high-symmetry phase in this high-temperature range, and effectively absorbs the dislocation driving stress generated during the growth process through spontaneous distortion, reducing defect penetration.

[0061] S23, Cooling stage: Cooling to 600℃ at a rate of 4℃ / s, and then cooling to room temperature at a rate of 1℃ / s; the BCT phase transition gradually transitions from cubic / tetragonal phase to low-temperature phase, accompanied by lattice slip and micro-deformation to effectively disperse and release residual stress between the substrate and GaN layer.

[0062] S3, Stress Regulation and Crack Suppression: The peak shift of the E2 (high) mode was monitored using an online Raman spectrometer, and the residual stress value was recorded every 50℃ decrease. The results showed that the stress remained within the range of ±0.1~0.15 GPa, with no obvious high stress concentration. The thermal expansion coefficients of SiC and GaN are similar, with SiC having a coefficient of 4.7 × 10⁻⁶. -6 / K, GaN is 5.59×10 -6 / K, but micro-warping is still prone to occur in large-area substrate scenarios; BCT further relieves stress through phase transformation shrinkage during the cooling stage, so that the final warping is controlled at <3μm / cm. 2 Surface crack density is less than 1 / cm 2 SEM examination of the cooled epitaxial surface revealed a very small number of microcracks (less than 1 μm in length); AFM morphology showed an RMS of 0.4 nm, indicating good surface smoothness and low defect distribution.

[0063] S4, Epitaxial Layer Quality Evaluation and Post-processing: XRD characterization showed that the FWHM of the GaN (002) surface rocking curve was 180 arcsec, and the FWHM of the (102) surface was 240 arcsec. The dislocation density was estimated to be within 10 5 ~10 6 cm -2 Range; E2 (high) peak shift corresponds to residual stress < ±0.1 GPa; AFM scan 5 × 5 μm 2 The RMS value was 0.4 nm. Rapid thermal annealing (RTA) was performed at 850℃~900℃ in a N2 atmosphere for 10 minutes, with a heating / cooling rate of 20℃ / s. After annealing, XRD analysis showed that the FWHM value decreased by about 10%~20%, and Raman results showed that the residual stress was closer to zero and the dislocation density continued to decrease.

[0064] Comparative Example 1: Conventional GaN epitaxial growth method (without dynamic phase transition to control heterogeneous substrate)

[0065] The following describes a traditional and common GaN epitaxial growth process using MOCVD growth of GaN on a sapphire Al2O3 substrate as an example. This comparative example is intended to be used in contrast to the "dynamic phase transition controlled heterogeneous substrate" scheme described in this invention, and is not limited to this specific implementation.

[0066] Step S1: Select a 2-inch diameter (0001) oriented sapphire substrate with a thickness of 430±10 μm. First, ultrasonically clean it in acetone solution for 5 minutes, then ultrasonically clean it in isopropanol IPA solution for 5 minutes. Rinse the surface with deionized water and dry it. Place the cleaned substrate on a 120℃ hot stage or in an oven to dry for 10 minutes to remove moisture and organic residues. In the MOCVD reaction chamber, heat the substrate to 1050℃ and hold for 10 minutes to further remove trace contaminants and surface-adsorbed moisture. During this process, hydrogen (H2) or nitrogen (N2) is introduced for surface passivation or cleaning.

[0067] Step S2, Epitaxial Growth: The substrate temperature is lowered to 550℃, and nitrogen source NH3 and gallium source are introduced to grow a GaN nucleation layer with a thickness of 25nm±5nm at a lower temperature; the molar flow ratio of NH3 to TMG, i.e., the V / III ratio, is set to 1000, and the growth rate is 0.3μm / h; Step S3, After the nucleation layer is completed, the temperature is rapidly raised to 1100℃ to grow the main GaN layer; at this time, the V / III ratio can be appropriately increased to 3000 and the growth rate can be increased to 1.0μm / h; during the growth process, H2 / N2 mixed gas is used as the carrier gas, and the pressure is generally controlled at 200±50Torr. By optimizing the gas flow rate and ratio, a smooth, low-defect GaN epitaxial layer is obtained, and the main GaN layer grows to a thickness of 5μm;

[0068] Step S4: After the epitaxial layer reaches the target thickness, stop the supply of metal sources such as TMG and continue to purge with hydrogen, nitrogen or NH3; slowly cool the reaction chamber to room temperature, for example at a rate of 3℃ / s and avoid sudden cooling to reduce the thermal stress between the substrate and the GaN layer; after cooling is completed, remove the substrate to obtain a GaN / sapphire epitaxial wafer with the main epitaxy completed.

[0069] Step S5: Observe the surface morphology of the epitaxial layer using an optical microscope or atomic force microscope (AFM). The RMS value is between 0.5 nm and 1.0 nm (5 × 5 μm). 2 (Scan). X-ray diffraction (XRD) was used to measure the double rocking curves of the (002) and (102) planes. The FWHM dislocation density was found to be between 10200 arcsec and 400 arcsec. 6 ~10 7 cm -2 The magnitude of the stress was measured using Raman spectroscopy to detect the E2 (high) mode of the GaN epitaxial layer. The residual stress was inferred by the peak position shift. If the stress was large, appropriate defect repair could be carried out in the subsequent annealing step.

[0070] Step S6: To enhance p-type activation or repair some lattice defects, perform rapid annealing (RTA) in a N2 or H2 atmosphere at a temperature of 700℃~900℃ for 5~10 minutes. For the n-type layer, a short-time annealing at 600℃~700℃ can be performed to further reduce stress or improve surface condition.

[0071] The performance of the epitaxial layers prepared in Examples 1-3 and Comparative Example 1 was compared, and the overall results are shown in Table 1 below. It can be seen that the dislocation density and crack density of the epitaxial layers prepared in Examples 1-3 of this application are significantly better than those in Comparative Example 1.

[0072] Table 1: Comparison of Epitaxial Layer Quality and Stress Indicators

[0073]

Claims

1. A dynamically phase transition regulated hetero-substrate, characterized in that, The hetero-substrate comprises a base substrate and a dynamic buffer layer, the base substrate is made of one of the three raw materials substrates of silicon Si, silicon carbide SiC or sapphire Al2O3; the dynamic buffer layer comprises an intermediate buffer layer and a surface buffer layer; the intermediate buffer layer is prepared by depositing a dynamic phase change material on the base substrate, the dynamic phase change material refers to a material with a lattice constant deviation of ±1% to ±3% from GaN at a high temperature of 800-1200℃; a surface buffer layer is further deposited on the intermediate buffer layer, the preparation material of the surface buffer layer is similar to the lattice constant of the dynamic phase change material, and is not prone to chemical decomposition in the epitaxial process; the thermal expansion coefficient of the surface buffer layer is 4.2×10 -6 / K to 5.6×10 -6 / K in the temperature range of 25-1200℃; after the deposition of the dynamic phase change material and the surface buffer layer is completed, a high-temperature annealing treatment is performed.

2. The dynamically phase-transition regulated hetero-substrate of claim 1, wherein, The dynamic phase change material comprises a perovskite material or a perovskite material of a doping modification system.

3. The dynamically phase-transition-regulated heterogeneous substrate of claim 2, wherein, In the perovskite material of the doping modification system, the doping modification is partial substitution or co-doping of the original perovskite material system by a metal element such as Sr, Ca, Mg, zirconium Zr or a rare earth element such as La, Sm.

4. The dynamically phase-transition regulated hetero-substrate of claim 1, wherein, The preparation raw material of the surface buffer layer is TiO2, aluminum nitride AIN or aluminum gallium nitride AIGaN.

5. The dynamically phase-transition regulated hetero-substrate of claim 1, wherein, The deposition mode of the intermediate buffer layer comprises metal organic chemical vapor deposition MOCVD, molecular beam epitaxy MBE or physical vapor deposition PVD.

6. The dynamically phase-transition-regulated heterogeneous substrate of claim 5, wherein, The deposition temperature range of the intermediate buffer layer is 300-600 DEG C; the deposition gas environment of the intermediate buffer layer is selected from any one or a mixture of two of argon, nitrogen or oxygen; and the deposition growth rate range of the intermediate buffer layer is 0.1-0.5 μm / h.

7. The dynamically phase-transition regulated hetero-substrate of claim 1, wherein, The deposition growth of the surface buffer layer adopts the MOCVD process.

8. The dynamically phase-transition-regulated heterogeneous substrate of claim 7, wherein, The deposition conditions of the surface buffer layer are specifically set as follows: growth temperature: 800-1200 DEG C; V / III ratio range based on NH3 / trimethylaluminum (TMA) or trimethylgallium (TMG) is 1000-3000; growth pressure: 200 Torr; and growth rate range is 0.2-1.0 μm / h.

9. A gallium nitride epitaxial fabrication method based on the hetero-substrate of claim 1, the gallium nitride epitaxial fabrication method comprising an initial epitaxial stage, a main epitaxial stage and a cooling stage; The initial epitaxial stage is a low-temperature GaN layer growth stage, the epitaxial growth temperature is set at 500-750 DEG C, and the growth rate is 0.2-0.5 μm / h; The main epitaxial stage is that after the initial epitaxial layer reaches a set thickness of 50-200 nm, the growth temperature is rapidly increased to the main epitaxial interval of 800-1200 DEG C, the temperature fluctuation is controlled within ±5 DEG C, the growth rate is increased to 0.5-1.0 μm / h, the V / III ratio is appropriately increased, for example, 1500-3000, and the final thickness of the main epitaxial layer is in the range of 2-10 μm; The cooling stage is that after the GaN reaches the target thickness, the cooling rate is 1-5 DEG C / s, and the temperature is gradually reduced to below 600 DEG C.

10. A high-voltage power device, comprising an epitaxial layer fabricated by the hetero-substrate of any one of claims 1-8 or the gallium nitride epitaxial fabrication method of claim 9.

Images