Growth device capable of accurately controlling PVT crystal growth process

Abstract

The invention relates to a PVT crystal growth process accurate and controllable growth device, and belongs to the technical field of third-generation semiconductor materials. The device comprises a seed crystal support, a growth crucible, an upper weighing device, a lower weighing device, an induction coil and a central control system, the crystal growth amount and the raw material volatilization amount are monitored in real time through the upper weighing device and the lower weighing device, the growth rate and the conversion rate are calculated, the medium-frequency induction power source power and the coil position are dynamically adjusted, and continuous and accurate control over temperature field distribution and the growth rate is achieved. The silicon carbide crystal quality can be remarkably improved, the defect density is reduced, and the industrialization requirement of high-quality crystals is met.

Description

Technical Field

[0001] The present invention relates to a PVT crystal growth device with a precisely controllable growth process, which is used to improve the crystallization quality of silicon carbide (SiC) crystals and belongs to the technical field of third-generation semiconductor materials. Background Art

[0002] With the rapid development of third-generation wide-bandgap semiconductor materials, silicon carbide (SiC) crystals, due to their exceptional physical and chemical properties, have shown great potential in power electronics, radio frequency devices, and high-temperature applications. However, the preparation of SiC crystals still faces many technical challenges, particularly the precise control of the temperature field, fluid field, and raw material evaporation state during physical vapor transport (PVT) growth.

[0003] Although the existing technology has optimized the growth device and process to a certain extent, the real-time controllability of the interface growth state still needs to be further improved to meet the industrialization needs of high-quality, large-size SiC crystals. For example, the patent with publication number CN114836834B adopts a belt-loaded mode or a bubbling mode air intake through a feeding device and combines a mixing device for multi-stage mixing, thereby realizing a continuous supply of raw materials during the growth process of silicon carbide crystals. However, this technical solution mainly focuses on the optimization of the raw material supply method and fails to achieve real-time and precise control of the temperature field distribution and growth rate at the crystal growth interface. In addition, it relies on fixed process parameter settings and lacks an immediate feedback mechanism for dynamic changes during the growth process, which may cause the interface growth state to be unstable, thereby affecting the crystal quality. At the same time, the patent with publication number CN111793825B cooperates with an external heater and an upper heater to repeatedly reverse the axial temperature gradient of the SiC seed crystal growth thermal field, so that the crystal surface undergoes a near-equilibrium state of micro-sublimation and micro-recrystallization, thereby effectively reducing the density of defects such as dislocations. However, the temperature gradient regulation in this technical solution relies on the periodic adjustment of the heater power, which cannot achieve continuous real-time monitoring and regulation of the growth interface state. At the same time, its control accuracy of the temperature field distribution is limited, and the stability of the crystal growth interface may decrease due to fluctuations in process parameters, affecting the quality consistency of the final crystal. The above problems show that the existing PVT method crystal growth device still has shortcomings in terms of real-time monitoring of the growth interface state, continuous and precise regulation of the temperature field distribution, and dynamic feedback mechanism.

[0004] Therefore, there is an urgent need for a device that can monitor the crystal growth quality and material area quality in real time, and dynamically adjust the growth conditions by accurately calculating the raw material evaporation state and crystal growth state, so as to ensure the stability and consistency of the growth interface state throughout the crystal growth process, thereby effectively reducing the defect density and improving the crystal quality. Summary of the Invention

[0005] The present invention addresses the technical issues associated with the inability to precisely control the temperature distribution and growth rate during physical vapor transport (PVT) silicon carbide crystal growth. By providing a precisely controllable PVT crystal growth device, the device achieves continuous and precise control of the crystal growth interface through the design of a split seed crystal holder and growth crucible, signal acquisition from upper and lower weighing devices, data analysis from a central control system, and a dynamic feedback mechanism.

[0006] The present invention provides a PVT crystal growth device with precise and controllable growth process, comprising a seed crystal holder and a growth crucible which are independently arranged, wherein:

[0007] The seed crystal holder is fixedly connected to the upper weighing device via a graphite hanger rod to monitor changes in crystal growth. The growth crucible is fixedly connected to the lower weighing device via a lower crucible support rod to monitor changes in raw material volatilization. Furthermore, both the graphite hanger rod and the lower crucible support rod utilize a non-contact design to avoid interference with thermal conduction or mechanical vibration from the insulation felt. Specifically, the growth crucible and seed crystal holder are separated by a non-contact mechanism to ensure their independence and stability in high-temperature environments.

[0008] Furthermore, the device also includes an induction coil, a graphite heating element, and a thermal insulation blanket. The induction coil surrounds the graphite heating element, driving it to generate a high-temperature environment; the thermal insulation blanket wraps the entire device to maintain stable thermal conditions. Specifically, the position of the induction coil is adjustable, with its adjustment range precisely controlled by a servo system to achieve dynamic regulation of the temperature gradient.

[0009] The core innovation of this invention is to achieve dynamic control through weight signal acquisition and conversion rate calculation, which is described in detail as follows:

[0010] S1: The upper weighing device records the weight changes of the seed crystal holder and the crystal on it in real time and calculates the crystal growth rate;

[0011] S2: The lower weighing device records the weight change of the growth crucible and the raw materials in it in real time and calculates the volatilization rate of the raw materials;

[0012] S3: The central control system calculates the crystal growth rate, raw material volatilization rate and conversion rate based on the weight change signals of the upper and lower weighing devices, where the conversion rate is defined as the ratio of the crystal growth weight to the total volatilization amount.

[0013] Furthermore, based on the above data, the central control system performs dynamic control operations:

[0014] S4: When the crystal growth rate is ≥0.5mm / h (setting range: 0.3-0.8mm / h), reduce the output power of the medium frequency induction power supply to slow down the growth rate; when the crystal growth rate is lower than the set value, increase the output power of the medium frequency induction power supply to speed up the growth rate;

[0015] S5: When the conversion rate is less than 60%, the induction coil position is lowered to increase the temperature gradient and improve the conversion rate; when the conversion rate is greater than 95%, the induction coil position is raised to reduce the temperature gradient and reduce the conversion rate;

[0016] S6: During the coil position adjustment process, changes in induction efficiency may cause fluctuations in the crystal growth rate. At this time, the central control system automatically makes compensatory adjustments to the output power of the medium-frequency induction power supply to ensure the stability of the growth interface state.

[0017] In particular, the dynamic control mechanism is implemented through closed-loop feedback, that is, the central control system continuously optimizes the control parameters based on the real-time collected data to ensure continuous and precise control of the temperature field distribution and growth rate at the crystal growth interface.

[0018] Furthermore, the dynamic control mechanism of the present invention can significantly improve the quality of crystals. Through a stable and consistent growth interface state, the internal defect density of the crystal is effectively reduced. The 6-inch silicon carbide crystals prepared using this device have a thickness range of 10mm to 30mm and a diameter range of 150mm to 170mm. After testing, the crystal dislocation density index reaches the following levels: EPD is less than 1000 / cm 2 , TSD is less than 10 / cm 2 , BPD is less than 100 / cm 2 .

[0019] The beneficial effects of the present invention are embodied in the following aspects:

[0020] First, the weight change signals from the upper and lower weighing devices are used to calculate the crystal growth rate and conversion rate in real time, accurately evaluating the operating status of the growth system.

[0021] Second, based on crystal growth rate and conversion rate data, by adjusting the output power of the medium-frequency induction power supply and the position of the induction coil, dynamic feedback and precise control of the temperature field distribution and growth rate are achieved, ensuring the stability and consistency of the growth process.

[0022] Third, the stable and consistent growth interface state effectively reduces the internal defect density of the crystal, improves the crystal quality, and meets the industrialization needs of high-quality silicon carbide crystals.

[0023] In summary, the present invention provides a simple, easy-to-use, and mass-produced PVT crystal growth device through innovative structural design and intelligent dynamic control mechanism, which can significantly improve the quality and production efficiency of silicon carbide crystals and has important application value and market prospects. BRIEF DESCRIPTION OF THE DRAWINGS

[0024] Figure 1 Schematic diagram of a growth device for a precisely controllable PVT crystal growth process according to the present invention;

[0025] Figure 2 The present invention provides a flow chart for the precise and controllable implementation of the growth process.

[0026] In the figure: 1. Induction coil; 2. Insulation felt; 3. Graphite heating element; 4. Growth crucible; 5. Crucible lower support rod; 6. Lower weighing device; 7. Silicon carbide powder; 8. Silicon carbide crystal; 9. Independent seed crystal holder; 10. Graphite suspension rod; 11. Upper weighing device; 12. Ceramic bellows; 13. Laser displacement sensor. DETAILED DESCRIPTION

[0027] The present invention provides a PVT crystal growth process accurately controllable growth device, combined with Figure 1 and Figure 2 Specific embodiments of the present invention are described in detail. Figure 1 Schematic diagram of the PVT crystal growth device of the present invention, Figure 2 The following is a detailed description of the embodiment of the present invention in conjunction with the reference numerals of the various components in the accompanying drawings.

[0028] The core structure of the present invention includes a central control system, an independent seed crystal holder 9, a growth crucible 4, a graphite hanger 10, a crucible lower support rod 5, an upper weighing device 11, a lower weighing device 6, an induction coil 1, a graphite heating element 3, an insulation felt 2, and silicon carbide powder 7 and silicon carbide crystals 8. The upper weighing device 11 and the lower weighing device 6 use high-temperature micro-weighing sensors with a measurement accuracy of ≥0.1g and a sampling frequency of ≥1Hz to ensure real-time monitoring of crystal growth / volatilization rate. These components form a complete growth system through a specific design and connection method for achieving high-quality growth of silicon carbide crystals. The independent seed crystal holder 9 is fixedly connected to the upper weighing device 11 through the graphite hanger 10, and the growth crucible 4 is fixedly connected to the lower weighing device 6 through the crucible lower support rod 5. Both the graphite hanger 10 and the crucible lower support rod 5 adopt a non-contact design to avoid heat conduction or mechanical vibration interference with the insulation felt 2. This split design ensures the independence and stability of the seed crystal holder 9 and the growth crucible 4 in a high temperature environment, and provides a basis for real-time monitoring of the crystal growth state. A thermal expansion compensation mechanism is set between the graphite hanger 10 and the weighing device. The thermal expansion compensation mechanism includes a ceramic bellows 12 and a laser displacement sensor 13. The central control system is based on the formula

[0029] The central control system is based on the formula:

[0030] ΔW corrected =ΔW raw -ρ·A·ΔL

[0031] ΔL=α·L0·(T actual -T0)

[0032] Corrected weight data, where ΔW raw is the original reading of the weighing device, ΔW corrected is the corrected effective weight change, ρ is the density of graphite, 1.8 g / cm 3 , A is the cross-sectional area of ​​the graphite hanger 10, 3.14cm 2 , ΔL is the thermal expansion, α is the linear expansion coefficient of graphite, 4.6×10 -6 / ℃, L0 is the initial length of the boom, 800mm, T actual is the real-time temperature of the boom, and T0 is the room temperature, 25°C.

[0033] Working steps: The laser displacement sensor 13 measures the displacement of the graphite boom 10 in real time, transmits the data to the central control system, and simultaneously obtains the boom temperature T actual (accuracy ±5℃),

[0034] The central control system performs compensation calculations every 0.1 seconds:

[0035] Calculate ΔL = α·L0·(T actual -25),

[0036] Calculate the false weight signal ΔW error =ρ·A·ΔL,

[0037] Output correction value ΔW corrected =ΔW raw -ΔW error ,

[0038] Dynamic error suppression effect:

[0039]

[0040]

[0041] During the growth of a 6-inch silicon carbide crystal (20 mm thick):

[0042] Without compensation: Due to the expansion of the boom, the upper weighing device misreads the growth rate as 0.72mm / h (actually 0.38mm / h)

[0043] After enabling compensation: growth rate control error < ±0.05mm / h, crystal EPD reduced to 800 / cm 2 the following.

[0044] S1: At the start of crystal growth, the upper weighing device 11 records the weight change of the seed crystal holder 9 and the crystal 8 thereon. This weight change directly reflects the growth of the crystal 8. By calculating the weight increase per unit time, the crystal growth rate can be calculated. The crystal growth rate is an important indicator for evaluating the growth status of crystals, and its value can reflect the material transfer efficiency at the growth interface.

[0045] S2: Simultaneously, the lower weighing device 6 records the weight change of the growth crucible 4 and the raw material 7 within it. This weight change directly reflects the volatilization amount of the raw material 7. The raw material volatilization rate is calculated by calculating the weight loss per unit time. The raw material volatilization rate is an important indicator for evaluating the evaporation state of the raw material. Its value can reflect the temperature distribution of the material area and the gas phase transmission efficiency.

[0046] S3: The central control system calculates the crystal growth rate, raw material volatilization rate, and conversion rate based on the weight change signals collected by the upper and lower weighing devices 11 and 6. The conversion rate is defined as the ratio of the crystal growth weight to the total volatilization amount: conversion rate = crystal growth weight / total volatilization amount. The conversion rate is a key parameter for evaluating the overall efficiency of the growth system. Its value reflects the rationality of the temperature gradient distribution and the material equilibrium state at the growth interface.

[0047] S4: Based on the above data, the central control system performs dynamic control operations. When the crystal growth rate is higher than the set value, the central control system reduces the output power of the medium-frequency induction power supply to slow the growth rate; when the crystal growth rate is lower than the set value, the central control system increases the output power of the medium-frequency induction power supply to accelerate the growth rate. The medium-frequency induction power supply drives the graphite heating element 3 through the induction coil 1 to generate a high-temperature environment. Adjustment of its output power directly affects the heating efficiency of the graphite heating element 3, thereby changing the temperature field distribution at the growth interface.

[0048] S5: When the conversion rate is less than 60%, the central control system lowers the position of the induction coil 1 to increase the temperature gradient. For every 10 mm the coil position is lowered, the axial temperature gradient increases by 8°C / cm. When the conversion rate is greater than 95%, the central control system raises the position of the induction coil 1 to reduce the temperature gradient and lower the conversion rate.

[0049] The position of induction coil 1 is precisely controlled by a servo system. The vertical displacement range of the induction coil is ±50 mm, with a response time of ≤10 seconds. Changes in the temperature gradient directly affect the gas-phase transmission efficiency between the feed zone and the growth interface, thereby altering the evaporation state of feedstock 7 and the growth conditions of crystal 8.

[0050] S6: During the coil position adjustment process, the change in induction efficiency may cause fluctuations in the crystal growth rate. At this time, the central control system automatically performs compensatory adjustments to the output power of the medium-frequency induction power supply to ensure the stability of the growth interface state. This closed-loop feedback mechanism realizes continuous and precise control of the crystal growth interface state by collecting data in real time and dynamically adjusting parameters. The compensation algorithm is: ΔP = k·Δh (k = 0.8kW / mm, Δh is the coil displacement); when the position of the induction coil 1 is adjusted, its coupling efficiency with the graphite heating element 3 changes, resulting in temperature field disturbances. The compensation algorithm ΔP = 0.8kW / mm·Δh maintains the surface temperature fluctuation of the heating element ≤±2°C through reverse power regulation (measured data are shown in the table below)

[0051] Displacement Δh (mm) Temperature fluctuation without compensation (℃) Temperature fluctuation after compensation (℃) -20 +15 ±1.5 +30 -22 ±1.8

[0052] The present invention significantly improves crystal quality through the above-mentioned structural design and dynamic control mechanism. The 6-inch silicon carbide crystals prepared using this device have a thickness range of 10mm to 30mm and a diameter range of 150mm to 170mm. After testing, the crystal dislocation density index reaches the following levels: EPD is less than 1000 / cm 2 , TSD is less than 10 / cm 2 , BPD is less than 100 / cm 2 (Compared with comparative example CN111793825B (EPD≥3000 / cm 2) by 67%, as tested using ASTM F47-06. These excellent performance indicators are attributed to the stable and consistent growth interface state, which effectively reduces the internal defect density of the crystal. This invention has broad applicability in practical applications, such as power electronics, radio frequency devices, and high-temperature applications, and can meet the industrial demand for high-quality silicon carbide crystals.

[0053] The operating principle and process of the present invention are as follows: First, silicon carbide powder 7 is loaded into the growth crucible 4, and the silicon carbide crystal 8 on the seed crystal holder 9 is placed above the growth crucible 4. After starting the device, the induction coil 1 drives the graphite heating element 3 through the medium frequency induction power supply to generate a high-temperature environment, so that the silicon carbide powder 7 sublimates under high temperature conditions. The sublimated gas phase material is transmitted toward the seed crystal holder 9 under the action of the temperature gradient, and recrystallizes on the surface of the seed crystal holder 9 to form silicon carbide crystal 8. During this process, the upper weighing device 11 and the lower weighing device 6 respectively record the weight changes of the seed crystal holder 9 and the growth crucible 4. The central control system calculates the crystal growth rate, raw material volatilization rate and conversion rate based on these data, and performs dynamic control operations based on these parameters. By adjusting the output power of the medium frequency induction power supply and the position of the induction coil 1, continuous and precise control of the temperature field distribution and growth rate is achieved, thereby ensuring the stability and consistency of the growth interface state throughout the crystal growth process.

[0054] Example 1: To verify the rationality of the conversion rate threshold (60% / 95%), a comparative experiment was conducted under the same temperature field conditions (2100°C, 50mbar), as shown in the following table:

[0055]

[0056] Test standard: ASTM F47-06; Number of experimental repetitions: n = 5;

[0057] As shown in the table above, a conversion rate range of 60%-95% can maintain the optimal material balance and significantly reduce the defect density.

[0058] In summary, the present invention provides a simple, easy-to-use, and mass-produced PVT crystal growth device through innovative structural design and intelligent dynamic control mechanism, which can significantly improve the quality and production efficiency of silicon carbide crystals and has important application value and market prospects.

Claims

1. A PVT crystal growth device with precise and controllable growth process, characterized in that The invention comprises a central control system, an independently arranged seed crystal holder (9) and a growth crucible (4), wherein the seed crystal holder (9) is connected to an upper weighing device (11) via a graphite suspension rod (10) for monitoring changes in crystal growth, and the growth crucible (4) is connected to a lower weighing device (6) via a crucible lower support rod (5) for monitoring changes in raw material volatilization. The device further comprises an induction coil (1), a graphite heating element (3) and a thermal insulation felt (2), wherein the induction coil (1) is arranged around the graphite heating element (3), and the thermal insulation felt (2) wraps the entire device; a thermal expansion compensation mechanism is arranged between the graphite suspension rod (10) and the weighing device, and the thermal expansion compensation mechanism comprises a ceramic bellows (12) and a laser displacement sensor (13), wherein the ceramic bellows (12) is wrapped around the connection end between the graphite suspension rod (10) and the upper weighing device (11), and the laser displacement sensor (13) is vertically aligned with the graphite suspension rod (10); the central control system is based on the formula: ΔW corrected =ΔW raw -ρ·A·ΔL ΔL=α·L0·(T actual -T0) Corrected weight data, where ΔW raw is the original reading of the weighing device, ΔW corrected is the corrected effective weight change, ρ is the graphite density, A is the cross-sectional area of ​​the graphite hanger (10), ΔL is the thermal expansion, α is the graphite linear expansion coefficient, L0 is the initial length of the hanger, T actual is the real-time temperature of the boom, and T0 is the room temperature.

2. A PVT crystal growth device with precise controllable growth process as claimed in claim 1, characterized in that The graphite suspension rod (10) and the crucible lower support rod (5) adopt a non-contact design.

3. A PVT crystal growth device with precise controllable growth process as claimed in claim 2, characterized in that The growth crucible (4) and the seed crystal holder (9) are arranged in a non-contact separation manner.

4. A PVT crystal growth device with precise controllable growth process as claimed in claim 1, characterized in that The position of the induction coil (1) is controlled by a servo system and is adjustable.

5. A PVT crystal growth device with precise controllable growth process as claimed in claim 4, characterized in that The vertical displacement range of the induction coil (1) is: ±50 mm, and the response time is ≤10 s.

6. A PVT crystal growth device with precise controllable growth process as claimed in claim 1, characterized in that The central control system calculates the crystal growth rate, the raw material volatilization rate and the conversion rate according to the weight change signals collected by the upper weighing device (11) and the lower weighing device (6).

7. A PVT crystal growth device with precise controllable growth process as claimed in claim 6, characterized in that When the crystal growth rate is ≥0.5mm / h, the set value range is: 0.3-0.8mm / h. When the real-time rate is ≥ the set value, the power is reduced, and when it is lower than the set value, the power is increased; the power adjustment response time is ≤5s.

8. A PVT crystal growth device with precise controllable growth process as claimed in claim 6, characterized in that When the conversion rate is less than 60%, the central control system lowers the position of the induction coil (1) to increase the temperature gradient. When the conversion rate is greater than 95%, the central control system raises the position of the induction coil (1) to reduce the temperature gradient. The selection of the conversion rate thresholds of 60% and 95% is based on the experimental data of the lattice defect rate: when the conversion rate is less than 60%, EPD>2500cm -2 , TSD>50cm when >95% -2 .

9. A PVT crystal growth device with precise controllable growth process as claimed in claim 8, characterized in that During the coil position adjustment process, the central control system automatically performs compensatory adjustment of the output power of the medium-frequency induction power supply. The compensation algorithm is: ΔP = k·Δh, where k = 0.8kW / mm and Δh is the coil displacement.

10. A PVT crystal growth device with precise controllable growth process according to claim 1, characterized in that The silicon carbide crystals prepared by the device have a thickness ranging from 10 mm to 30 mm and a diameter ranging from 150 mm to 170 mm.

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