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CN-121992486-A - PVT growth system and technology for preparing 8-inch low-defect silicon carbide single crystal

CN121992486ACN 121992486 ACN121992486 ACN 121992486ACN-121992486-A

Abstract

The invention discloses a PVT growth system and a PVT growth process for preparing 8-inch low-defect silicon carbide single crystals, which relate to the technical field of preparation and growth processes of silicon carbide single crystal materials and comprise the following steps: and constructing a three-dimensional model of the growth device, and carrying out space structure design and parameter setting on the heating unit, the heat insulation assembly and the airflow guiding device to ensure that the thermal field structure is distributed annularly and symmetrically in the radial direction and has uniform temperature gradient areas in the axial direction. According to the invention, through optimizing the thermal field structural design, matching the thermal expansion performance of the graphite component, implementing real-time temperature control and dynamic feedback adjustment, introducing a gas transportation guiding and synchronous cooling strategy, the temperature field uniformity and thermal stress distribution in the crystal growth process are effectively controlled, interface disturbance and crystal warpage are inhibited, the structural integrity and flatness of the silicon carbide single crystal are obviously improved, the product yield is improved, and the processing difficulty and the manufacturing cost are reduced.

Inventors

  • XIE CHUNSONG

Assignees

  • 嘉兴南湖学院
  • 中科超芯(浙江)新材料科技有限公司

Dates

Publication Date
20260508
Application Date
20260228

Claims (10)

  1. 1.A PVT growth process for preparing an 8-inch low defect silicon carbide single crystal comprising the steps of: Constructing a three-dimensional model of the growth device, and carrying out space structure design and parameter setting on the heating unit, the heat insulation assembly and the airflow guiding device to ensure that the thermal field structure is distributed annularly and symmetrically in the radial direction and has uniform temperature gradient areas in the axial direction; Based on a thermal field structure, selecting a high-purity graphite material with low thermal expansion coefficient difference, and carrying out correction and matching processing on the size of each structural member by combining an isothermal thermal expansion curve at a target working temperature to ensure that the thermal deformation of each structural member is consistent in a high-temperature environment; The method comprises the steps of respectively installing a sublimation source and a seed crystal in the central area of a thermal field structure, connecting the sublimation source and the seed crystal with independent precise temperature control units, respectively arranging independent thermocouples at a sublimation end and a crystallization end, and collecting the actual temperature of each area in real time; In the crystal growth process, comparing temperature data acquired by a thermocouple with a preset temperature gradient model, and adjusting the power output of a heating unit and the position of a shielding structure in real time through a dynamic feedback control system; Inert gas flow is applied to the inside of the growth cavity, a controlled gas conveying path is formed in the axial direction of the cavity by adjusting the flow speed and the flow direction of the gas, and the conveying track of the sublimated product is accurately guided by using an airflow guiding device; When the silicon carbide single crystal grows to a set thickness, the working temperatures of the sublimation end and the crystallization end are reduced step by step, and synchronous cooling is performed on the basis of keeping a constant differential temperature.
  2. 2. The PVT growth process for preparing an 8-inch low defect silicon carbide single crystal according to claim 1, wherein in the process of constructing a three-dimensional model of a growth apparatus, a finite element thermal field simulation technique is adopted to perform iterative modeling and multi-objective optimization on a heating unit, a heat insulation assembly and an airflow guiding device, and an isotherm model which is symmetrically distributed is constructed according to design constraints that the axial temperature difference fluctuation of a crystal growth region is less than ±3k; through heat flux density analysis, the equivalent thermal resistance ratio of the thermal field model between the heating area and the heat insulation area is ensured to meet the stable temperature difference control range, and the circumferential heat uniformity index is enabled to be more than 90%; meanwhile, a bionic symmetrical disturbance control structure is introduced into the three-dimensional structure model to further reduce edge heat loss, so that an axially gradual-changing and radially symmetrical temperature field structure is formed in the whole thermal field area, and the warping trend of a growth interface caused by heat energy bias current is avoided.
  3. 3. The PVT growth process for preparing an 8-inch low defect silicon carbide single crystal according to claim 1, wherein in the selection of a high purity graphite material and the design of a structural member, the comprehensive evaluation is performed based on the thermal expansion coefficient, the thermal conductivity, the young's modulus and the thermal shock stability of the material, and the materials with graphite brands exhibiting low expansion variability in the working temperature region are selected by constructing a multiparameter thermodynamic stability matrix; in the structural design process, a back calculation matching method is adopted, compensation adjustment factors are calculated according to the thermal expansion predicted value of each key node and the initial size of the assembly, and prestress processing is carried out on the sizes of the supporting frame, the heating cylinder wall and the liner sealing plate component; After processing, a high-temperature simulation prestress loading experiment is adopted, linear matching precision of all structural members in a high-temperature coupling state is verified, and the integral thermal stability of the combined structural members is ensured to be more than 95%.
  4. 4. The PVT process for producing an 8-inch low-defect silicon carbide single crystal according to claim 1, wherein the spatial position between the sublimation source and the seed crystal is precisely aligned so as to ensure that the axial distance is controlled within ±0.5mm; The seed crystal adopts a high-orientation low-dislocation single crystal plate, and a growth starting surface is calibrated by double-sided grinding and laser marking; In the construction of a temperature control system, respectively embedding micro thermocouples in a sublimation source support substrate and a seed crystal carrier, setting the temperature difference stability range of a control loop to be within 3K, and matching with a PID temperature control algorithm with high-frequency response to realize dynamic temperature difference tracking of a sublimation zone and a crystallization zone; and the thermocouple response position is calibrated by a spatial coplanar method, so that the thermal coupling error is controlled to be +/-0.2K, and the symmetry and stability of a thermal field are improved.
  5. 5. The PVT growth process for preparing an 8-inch low defect silicon carbide single crystal according to claim 1, wherein the dynamic feedback control system performs decision regulation by comparing the deviation between the set temperature gradient model and the actual temperature curve in real time and using a mixed algorithm combining a fuzzy control rule base and a neural network prediction algorithm; The shielding structure is driven by an electric linear driving device, and realizes dynamic micro-displacement of +/-1 mm in the longitudinal direction according to an interface speed feedback signal at the crystal growth stage; And automatically acquiring temperature field data every 15 minutes during crystal growth, fitting a temperature distribution trend curve, outputting an interface stability index to a regulation and control module, and eliminating instantaneous deviation caused by external disturbance in an index smooth filtering mode to realize synchronous and stable control of the interface growth speed and morphology.
  6. 6. The PVT growth process for preparing an 8-inch low defect silicon carbide single crystal according to claim 1, wherein for verifying the correlation between the rationality of thermal field structural design and crystal growth stability, thermal field symmetry and gradient control capability are evaluated by constructing a simulation and evaluation model of thermal field design parameters, comprising the steps of: Calculating temperature distribution conditions of a target thermal field structure at different radial positions, and constructing radial temperature uniformity parameters according to the temperature distribution conditions, wherein the calculation expression is as follows: In which, in the process, Is an index of non-uniformity of radial temperature, Is the maximum value of the temperature in all radial measuring points, Is the minimum of the temperatures in all radial stations, Is the arithmetic mean temperature of all radial temperature values, Is a set of temperature values for different "radial positions" in the thermal field; And calculating the standard deviation of the temperature change of the crystal growth area along the axial direction, wherein the standard deviation is used for measuring whether the thermal gradient has local non-uniformity phenomenon or not, and the calculation expression is as follows: In which, in the process, Is the first along the axial direction in the crystal growth cavity The temperature values of the measuring points, Is the average value of all axial temperature measuring points, Is the number of axial measuring points, Is the axial temperature standard deviation; By fusion And (3) with The two indexes are used for constructing a thermal field structure stability factor so as to comprehensively judge the overall stability level of the thermal field structure, and the calculation expression is as follows: In which, in the process, Is a thermal symmetry correction factor which is used to correct the thermal symmetry, Is a thermal field structural stability factor; To be used for Performing design iteration optimization judgment as criterion when When the thermal field structure reaches the standard of low-warpage growth of the crystal, if the condition is not met, the heat source distribution, the heat insulation structure arrangement and the material collocation are required to be planned again so as to improve the symmetry of the thermal field and the thermal gradient control capability.
  7. 7. The PVT growth process for producing an 8-inch low defect silicon carbide single crystal according to claim 1, wherein in the establishment of the axial gas transport path, the gas flow is guided in a quasi-laminar state by setting the inert gas inlet pressure and outlet back pressure difference to be 0.5kPa to 1.2kPa in combination with the vortex rectifying module; the flow rate control module dynamically adjusts the gas flow rate through the high-precision mass flowmeter, keeps the average axial flow rate within the range of 0.3m/s to 0.8m/s, and ensures that the sublimate is transported along the shortest radial crystallization area above the central axis of the cavity; the air flow guiding device is internally provided with a porous buffer diffusion layer and a conical compression channel, which are used for homogenizing an air pressure field and reducing a flow dead zone, and the thermal barrier reflection coating technology is used for enhancing the local thermal stability of the air flow, reducing the non-uniformity of the desublimation rate caused by flow field disturbance and improving the structural integrity of a crystal growth interface.
  8. 8. The PVT growth process for producing an 8-inch low-defect silicon carbide single crystal according to claim 1, wherein in the temperature control in the crystal cooling stage, the sublimation source and the crystallization end are subjected to a stepwise cooling operation by a two-channel independent temperature control system, respectively, and the entire cooling process is divided into five cooling stages, and the difference in cooling rate in each stage is controlled to be within 2K/min; In the cooling synchronization process, a high heat capacity material is adopted to adjust the delay gradient change of a thermal buffer zone, so as to keep the differential temperature difference stable and prevent thermal shock; the thermal stress distribution of the surface of the crystal is monitored in real time, the thermal stress release time point is accurately judged, and a constant-temperature stay procedure is executed in the final cooling stage to finish the release of residual stress, so that the final yield of the crystal is ensured to be more than 95%.
  9. 9. The PVT growth process for producing an 8-inch low defect silicon carbide single crystal according to claim 1, wherein to realize synchronous cooling and thermal stress cooperative release in a later cooling stage of crystal growth, a time function model of thermal stress response is built, and a mathematical coupling analysis method is introduced to ensure optimal control of the cooling process in terms of structural integrity and thermal balance, comprising the steps of: by setting the initial temperature of the crystallization source and the crystallization end And (3) with Establishing a synchronous cooling function set, respectively defining a sublimation source temperature and a crystallization end temperature, and calculating the following expression: In which, in the process, Is the time of the sublimating source The actual temperature at the moment in time is, Is the crystallization end at the time The actual temperature at the moment in time is, And The initial temperatures of the crystallization source and the crystallization end respectively, And The linear cooling rates of the sublimation end and the crystallization end are respectively; the temperature difference at both ends is defined, and the calculation expression is as follows: In which, in the process, Is the time between the sublimation source and the crystallization end Absolute temperature difference of (2); Establishing transient thermal stress response associated with the temperature difference, and calculating the expression as follows: In which, in the process, Is the crystal at time The moment of time is subjected to an instantaneous thermal stress, Is the Young's modulus of the silicon carbide single crystal material in a cooling temperature region, Is the thermal expansion coefficient of the silicon carbide material; The cumulative thermal stress energy is obtained by integrating the thermal stress response, and the calculation expression is as follows: In which, in the process, Is a crystal slave Time to date Is used for the heat-induced thermal stress, Is a time variable; When (when) When the cooling process is considered to be safe, the crystal is positioned in a thermal stress low risk area; The threshold is a thermal stress failure threshold for the crystalline material.
  10. 10. A PVT growth system for preparing an 8-inch low defect silicon carbide single crystal, for implementing a PVT growth process for preparing an 8-inch low defect silicon carbide single crystal according to any one of claims 1 to 9, comprising a thermal field structure modeling module, a thermal expansion matching and structure regulating module, a precision temperature control and thermal measurement acquisition module, a dynamic feedback control module, a gas transport regulating module, and a synchronous cooling and stress release module; The thermal field structure modeling module is used for constructing a three-dimensional model of the growth device, and carrying out space structure design and parameter setting on the heating unit, the heat insulation assembly and the airflow guiding device so that the thermal field structure is distributed annularly and symmetrically in the radial direction and has uniform temperature gradient areas in the axial direction; The thermal expansion matching and structure regulating module is used for selecting high-purity graphite materials with low thermal expansion coefficient difference based on a thermal field structure, correcting and matching the sizes of the structural members by combining an isothermal thermal expansion curve at a target working temperature, and ensuring that the thermal deformation of the structural members is consistent in a high-temperature environment; the precise temperature control and thermal measurement acquisition module is used for respectively installing a sublimation source and a seed crystal in the central area of the thermal field structure and connecting the sublimation source and the seed crystal with independent precise temperature control units, and simultaneously respectively arranging independent thermocouples at a sublimation end and a crystallization end to acquire the actual temperature of each area in real time; the dynamic feedback control module is used for comparing temperature data acquired by the thermocouple with a preset temperature gradient model in the crystal growth process, and adjusting the power output of the heating unit and the position of the shielding structure in real time through the dynamic feedback control system; the gas transport regulation and control module applies inert gas flow in the growth cavity, forms a controlled gas transport path in the axial direction of the cavity by regulating the flow speed and the flow direction of the gas, and precisely guides the transport track of the sublimated product by using the gas flow guiding device; And the synchronous cooling and stress releasing module is used for synchronously cooling the sublimation end and the crystallization end on the basis of keeping constant differential temperature when the silicon carbide single crystal grows to a set thickness.

Description

PVT growth system and technology for preparing 8-inch low-defect silicon carbide single crystal Technical Field The invention relates to the technical field of preparation and growth processes of silicon carbide single crystal materials, in particular to a PVT growth system and a PVT growth process for preparing 8-inch low-defect silicon carbide single crystals. Background PVT growth for preparing 8 inch low defect silicon carbide single crystal refers to a process of utilizing physical vapor transport (Physical Vapor Transport, PVT) method to gasify silicon carbide raw material and transport to the surface of seed crystal by sublimation-desublimation under the condition of high temperature and controlled atmosphere, depositing and growing into single crystal silicon carbide (SiC) crystal. The method is particularly suitable for preparing large-size (such as 8 inches) high-quality SiC single crystals, and is characterized in that the temperature field distribution, sublimation rate, atmosphere composition and crystallization interface stability are precisely controlled, so that defects such as dislocation and micropipe in the crystals are reduced, and the structural integrity and electrical performance of the single crystals are improved. The process is a mainstream means for industrially mass-producing large-size SiC single crystals at present, and has key significance for manufacturing high-power, high-frequency and high-temperature electronic devices. The prior art has the defect that in the process of preparing the 8-inch low-defect silicon carbide single crystal by using the PVT method in the prior art, the temperature gradient in the growth cavity locally abnormally induces crystal Warping (Warping). In the high-temperature sublimation and desublimation process, if the temperature field in the cavity is unevenly distributed or the thermodynamic stability is destroyed due to inconsistent thermal expansion of the graphite structural member, the crystal growth interface is deviated, the internal stress is gradually accumulated, and the whole crystal is finally warped. Such deformation would seriously affect subsequent grinding, polishing and planarization of the wafer, reduce product yield, and even result in rejection of the entire wafer, significantly increasing manufacturing costs and extending production cycle. Therefore, controlling the uniformity of the temperature field and the thermal stability of the cavity structure are key to ensuring the stable growth of high-quality silicon carbide single crystals by the PVT method. The above information disclosed in the background section is only for enhancement of understanding of the background of the disclosure and therefore it may include information that does not form the prior art that is already known to a person of ordinary skill in the art. Disclosure of Invention The invention aims to provide a PVT growth system and a PVT growth process for preparing 8-inch low-defect silicon carbide single crystals, which are used for effectively controlling the uniformity of a temperature field and the distribution of thermal stress in the crystal growth process, inhibiting interface disturbance and the warpage of the crystals, remarkably improving the structural integrity and flatness of the silicon carbide single crystals, improving the product yield, reducing the processing difficulty and the manufacturing cost and solving the problems in the background technology by optimizing the structural design of a thermal field, matching the thermal expansion performance of a graphite component, implementing real-time temperature control and dynamic feedback adjustment and introducing a gas transportation guiding and synchronous cooling strategy. In order to achieve the above purpose, the invention provides a PVT growth process for preparing 8 inch low defect silicon carbide single crystal, comprising the following steps: Constructing a three-dimensional model of the growth device, and carrying out space structure design and parameter setting on the heating unit, the heat insulation assembly and the airflow guiding device to ensure that the thermal field structure is distributed annularly and symmetrically in the radial direction and has uniform temperature gradient areas in the axial direction; Based on a thermal field structure, selecting a high-purity graphite material with low thermal expansion coefficient difference, and carrying out correction and matching processing on the size of each structural member by combining an isothermal thermal expansion curve at a target working temperature to ensure that the thermal deformation of each structural member is consistent in a high-temperature environment; The method comprises the steps of respectively installing a sublimation source and a seed crystal in the central area of a thermal field structure, connecting the sublimation source and the seed crystal with independent precise temperature control units, respectively ar