Silicon carbide crystal and growth method thereof
Through the silicon carbide crystal growth method that controls pressure and temperature changes, the problem of high dislocation density in the early stage of silicon carbide crystal growth is solved, and the dislocation density is efficiently reduced, and the crystal quality and application potential are improved.
Patent Information
- Application Number
- CN202411409485.X
- Authority / Receiving Office
- CN · China
- Patent Type
- Applications(China)
- Current Assignee / Owner
- Filing Date
- 2024-10-10
- Publication Date
- 2025-01-10
AI Technical Summary
The prior art is difficult to effectively reduce the penetrating blade dislocation density in the early stages of silicon carbide crystal growth, resulting in low crystal quality, affecting its application in electronic devices and optoelectronic devices.
A silicon carbide crystal growth method is adopted, including the preparation stage, the buffer stage and the growth stage. By controlling the changes in pressure and temperature, gradually reduce the initial growth pressure and temperature of silicon carbide crystals, use inert gas and doped gas to avoid using the position. The lower seed crystals and multi-layer buffer layers are used to simplify the process and improve economic benefits.
In a short time, it effectively reduces the penetrating blade dislocation density of silicon carbide crystals, improves crystal quality, prevents the appearance of multiple types, and enhances its application potential in high-performance products.
Smart Images
Figure CN119287496A_ABST
Abstract
Description
Technical Field
[0001] The present invention belongs to the field of semiconductor technology, and in particular relates to a silicon carbide crystal and a growth method thereof. Background Art
[0002] Silicon carbide (SiC) is an important wide-bandgap semiconductor material with many excellent physical and chemical properties, such as a wider bandgap than silicon, electron mobility much higher than silicon, and thermal conductivity approximately three times that of silicon. These properties make SiC an important alternative to traditional silicon materials in multiple applications and are driving the development and innovation of semiconductor technology. Currently, physical vapor transport (PVT) is a mainstream method for preparing large-diameter, high-quality SiC crystals. During the PVT growth of SiC crystals, some atoms in the crystal lattice deviate from their ideal positions, resulting in dislocations in the SiC crystal. The high dislocation density in SiC crystals can have a serious impact on the electrical, optical, and mechanical properties of SiC. During the PVT process, the temperature, pressure, and atmosphere during growth have a significant impact on the dislocation density of SiC crystals. Because the density of threading edge dislocations (TEDs) in a crystal is typically higher than that of threading screw dislocations (TSDs) and basal plane dislocations (BPDs), the high TED density during PVT is often reduced by controlling the crystal growth rate and annealing the crystal in the later stages of growth. However, slow growth rates result in long growth times, which inevitably affects the yield of SiC crystals. Furthermore, late-stage annealing does not effectively eliminate stress within the crystal and heal dislocations, failing to reduce the overall TED density of the SiC crystal. Therefore, seed crystals with lower TED become an option, as they can reduce the lattice mismatch during the initial growth phase of SiC crystals, thereby reducing the overall TED density. However, consistently growing SiC crystals with low TEDs is not an easy task, and ensuring that the TED density of SiC crystals decreases rather than increases during the initial growth phase is a significant concern.
[0003] In recent years, numerous patents have been published on methods for reducing the dislocation density of silicon carbide crystals. For example, patent CN114277442A establishes a double buffer layer to convert threading dislocations in the crystal first into BPDs and then into TEDs, ultimately reducing the overall threading dislocation density in the crystal. However, this approach results in an increase in the TED dislocation density in the crystal. Furthermore, the three high and low pressure cycles at high temperatures before the double buffer layer is created, as well as the resulting changes in the heating rate within the growth furnace, can easily lead to polymorphic silicon carbide crystals, which directly impacts their quality.
[0004] Therefore, there is an urgent need to provide an economical and efficient way to reduce the TED dislocation density in the early stage of silicon carbide crystal growth to improve the overall quality of silicon carbide crystals. Summary of the Invention
[0005] In response to the shortcomings of the prior art, the present invention aims to provide a silicon carbide crystal and a method for growing the same. The preparation method provided by the present invention does not require the use of seed crystals with low dislocation density, nor does it require modification of the internal structure of the crucible, nor does it require the establishment of multiple buffer layers. It is economical, efficient, and simple to produce, effectively reducing the TED dislocation density in the early stages of silicon carbide crystal growth in a short period of time. This is of great significance for improving the quality of silicon carbide crystals and their application in high-performance products such as electronic and optoelectronic devices.
[0006] In order to achieve the purpose of the invention, the present invention adopts the following technical solutions:
[0007] In a first aspect, the present invention provides a method for growing a silicon carbide crystal, the method comprising the following steps:
[0008] (1) Preparation stage: SiC raw material is placed in the bottom of the crucible, SiC seed crystal is fixed on the crucible cover, the crucible is transferred to the single crystal growth furnace, the single crystal growth furnace is evacuated and filled with inert gas, and the growth chamber is pressurized and heated at the same time, the pressure is raised to a first pressure, and the temperature is raised to a first temperature; then the pressure is reduced and the temperature is raised to a second pressure, and the temperature is raised to a second temperature.
[0009] (2) Buffer stage: After reaching the second temperature, the doping gas is filled in and the pressure is reduced to the third pressure at a constant temperature of time T1.
[0010] (3) Growth stage: After the constant temperature and pressure reduction is completed, the pressure is reduced to the fourth pressure and the temperature is increased to the third temperature; then, the constant temperature and pressure are maintained at the third temperature and the fourth pressure for a time period of T2, and after the end, a silicon carbide crystal with a low TED dislocation density is obtained.
[0011] The preparation method provided by the present invention does not require the use of seed crystals with low dislocations, does not require modification of the structure inside the crucible, and does not require the establishment of a multi-layer buffer layer. It is economical and efficient, and the process is simple. It can effectively reduce the TED dislocation density in the early stage of silicon carbide crystal growth in a short period of time, which is of great significance for improving the quality of silicon carbide crystals and the application of silicon carbide crystals in high-performance products such as electronic devices and optoelectronic devices.
[0012] Preferably, the first pressure in step (1) is 200-500 mbar, for example, 200 mbar, 300 mbar, 400 mbar or 500 mbar.
[0013] Preferably, the first temperature in step (1) is 1600-1800°C, for example, it can be 1600°C, 1650°C, 1700°C, 1750°C or 1800°C.
[0014] Preferably, the second pressure in step (1) is 20-50 mbar, for example, 20 mbar, 30 mbar, 40 mbar or 50 mbar.
[0015] Preferably, the second temperature in step (1) is 2000-2050°C, for example, it can be 2000°C, 2010°C, 2020°C, 2030°C, 2040°C or 2050°C.
[0016] In the present invention, if the temperature during the buffer phase (i.e., the second temperature) is too low, the gas cannot deposit and crystallize stably and orderly at the growth interface. If the temperature during the buffer phase (i.e., the second temperature) is too high, the crystal growth interface will generate significant thermal stress, and during the subsequent filling process of the dopant gas, the concentration of dopant atoms will also increase significantly due to the high gas partial pressure caused by the initial high temperature. Therefore, in order to reduce the thermal stress caused by the initial high temperature and the lattice mismatch at the growth interface caused by the high dopant atom concentration, the temperature during the initial growth phase (i.e., the second temperature) is preferably 2000-2050°C.
[0017] Preferably, the time for the pressure reduction and temperature increase process in step (1) is 1-5 hours, for example, it can be 1 hour, 2 hours, 3 hours, 4 hours or 5 hours.
[0018] Preferably, the inert gas in step (1) includes any one of helium, neon or argon, or a combination of at least two of them.
[0019] Preferably, the third pressure in step (2) is 5-10 mbar, for example, 5 mbar, 6 mbar, 7 mbar, 8 mbar, 9 mbar or 10 mbar.
[0020] Preferably, the value range of T1 in step (2) is 1-5h, for example, it can be 1h, 2h, 3h, 4h or 5h.
[0021] Preferably, the doping gas in step (2) includes at least one of ammonia and nitrogen.
[0022] Preferably, the flow rate of the doping gas in step (2) is 1-7 mlpm, for example, it can be 1 mlpm, 2 mlpm, 3 mlpm, 4 mlpm, 5 mlpm, 6 mlpm or 7 mlpm.
[0023] The present invention slowly reduces the pressure within the furnace during the buffer phase, which helps improve the lattice matching between the gas atoms and the growth surface. Simultaneously, slowly increasing the flow rate of the doping gas helps reduce the stress caused by the gas atoms arranging on the growth surface. As a result, dislocations propagating from the seed crystal during the initial growth of the silicon carbide crystal are effectively suppressed and reduced.
[0024] It should be noted that "mlpm" is the unit of gas flow rate, which is milliliters per minute, and the same applies below.
[0025] Preferably, the time for the pressure reduction and temperature increase process in step (3) is 0.5-2 hours, for example, it can be 0.5 hours, 1 hour, 1.5 hours or 2 hours.
[0026] Preferably, the fourth pressure in step (3) is 1-5 mbar, for example, 1 mbar, 2 mbar, 3 mbar, 4 mbar or 5 mbar.
[0027] Preferably, the third temperature in step (3) is 2100-2300°C, for example, it can be 2100°C, 2150°C, 2200°C, 2250°C or 2300°C.
[0028] Preferably, the value range of T2 in step (3) is 100-150h, for example, it can be 100h, 110h, 120h, 130h, 140h or 150h.
[0029] Preferably, the growth method comprises the following steps:
[0030] (1) Preparation stage: SiC raw material is loaded into the bottom of the crucible, SiC seed crystal is fixed on the crucible cover, the crucible is transferred to the single crystal growth furnace, the single crystal growth furnace is evacuated and then filled with inert gas, the inert gas includes any one of helium, neon or argon or a combination of at least two; at the same time, the growth chamber is pressurized and heated, the pressure is raised to a first pressure, the first pressure is 200-500 mbar, and the temperature is raised from room temperature 25°C to a first temperature, the first temperature is 1600-1800°C; after the pressure increase and temperature increase are completed, the pressure is reduced and the temperature is raised, so that the pressure drops from the first pressure to the second pressure within 1-5 hours, the second pressure is 20-50 mbar; at the same time, the temperature is raised from the first temperature to the second temperature, the second temperature is 2000-2050°C.
[0031] (2) Buffering stage: After the pressure reduction and temperature increase, the doping gas is filled in, and the doping gas includes at least one of ammonia and nitrogen, and the flow rate of the doping gas is 1-7 mlpm; at the same time, the constant temperature pressure reduction for a time of T1 is performed at the second temperature, so that the pressure drops from the second pressure to the third pressure, and the third pressure is 5-10 mbar. The value range of T1 is 1-5h.
[0032] (3) Growth stage: After the constant temperature and pressure reduction is completed, the pressure is reduced and the temperature is increased, so that the pressure drops from the third pressure to the fourth pressure within 0.5-2 hours, and the fourth pressure is 1-5 mbar; at the same time, the temperature is increased from the second temperature to the third temperature, and the third temperature is 2100-2300 ° C; after the pressure reduction and temperature increase is completed, the temperature and pressure are kept constant at the third temperature and the fourth pressure for a time of T2, and the value range of T2 is 100-150 hours; after the constant temperature and pressure are completed, a silicon carbide crystal with a low TED dislocation density is obtained.
[0033] In a second aspect, the present invention provides a silicon carbide crystal, which is prepared using the preparation method described in the first aspect.
[0034] The numerical range described in the present invention includes not only the point values listed above, but also any point values between the above numerical ranges that are not listed. Due to space limitations and for the sake of simplicity, the present invention no longer exhaustively lists the specific point values included in the range.
[0035] Compared with the prior art, the present invention has the following beneficial effects:
[0036] The preparation method provided by the present invention does not require the use of seed crystals with low dislocations, does not require modification of the structure inside the crucible, and does not require the establishment of multi-layer buffer layers. It is economical and efficient, and the process is simple. It can effectively reduce the TED dislocation density in the early stage of silicon carbide crystal growth in a short period of time, and can also prevent the occurrence of polymorphism in silicon carbide crystals. This is of great significance for improving the quality of silicon carbide crystals and the application of silicon carbide crystals in high-performance products such as electronic devices and optoelectronic devices. BRIEF DESCRIPTION OF THE DRAWINGS
[0037] Figure 1 This is a schematic diagram of the changes in temperature and pressure with growth time in the silicon carbide crystal growth method provided by the present invention.
[0038] Figure 2 TED dislocation distribution diagram of a wafer having the same origin as the silicon carbide seed crystal used in Example 1 of the present invention.
[0039] Figure 3 This is a TED dislocation distribution diagram of the third substrate among the substrates obtained after processing the silicon carbide crystal prepared in Example 1 of the present invention. DETAILED DESCRIPTION
[0040] The technical solution of the present invention is further described below by way of specific embodiments. It should be understood by those skilled in the art that the embodiments are merely to help understand the present invention and should not be regarded as specific limitations of the present invention.
[0041] Example 1
[0042] This embodiment provides a method for growing a silicon carbide crystal, the method comprising the following steps:
[0043] (1) Preparation stage: SiC raw material is placed in the bottom of the crucible, SiC seed crystal is fixed on the crucible cover, the crucible is transferred to the single crystal growth furnace, the single crystal growth furnace is evacuated and filled with helium. At the same time, the growth chamber is pressurized and heated, the pressure is raised to a first pressure of 500 mbar, and the temperature is raised from room temperature 25°C to a first temperature of 1600°C. After the pressure and temperature are raised, the following steps are performed: Figure 1 The growth process shown in the figure is to first reduce the pressure and increase the temperature, so that the pressure is reduced from the first pressure to the second pressure of 20mbar within 3 hours. At the same time, the temperature is increased from the first temperature to the second temperature of 2000℃. The TED dislocation density of the silicon carbide seed crystal is about 1100cm -2 .
[0044] (2) Buffering stage: After the decompression and temperature increase, ammonia gas is added at a flow rate of 2 ml / min. Simultaneously, a constant temperature decompression is performed at the second temperature for a time period T1, so that the pressure drops from the second pressure to the third pressure, the third pressure being 10 mbar, and T1 being 3 hours.
[0045] (3) Growth stage: After the constant temperature and pressure reduction is completed, the pressure is reduced and the temperature is increased, so that the pressure drops from the third pressure to the fourth pressure within 0.5 hours, and the fourth pressure is 5 mbar. At the same time, the temperature is increased from the second temperature to the third temperature, and the third temperature is 2180°C. After the pressure reduction and temperature increase is completed, the temperature and pressure are kept constant at the third temperature and the fourth pressure for a time period of T2, and T2 is 100 hours. After the constant temperature and pressure are completed, a silicon carbide crystal with a low TED dislocation density is obtained.
[0046] Figure 2 The TED dislocation distribution diagram of the wafer with the same origin as the silicon carbide seed crystal used in this embodiment is shown. It can be inferred from the figure that the TED dislocation density of the seed crystal is about 1100 cm -2 .
[0047] Figure 3 The TED dislocation distribution diagram of the third substrate obtained after processing the silicon carbide crystal prepared in this embodiment is shown. As can be seen from the figure, the growth method reduces the TED dislocation density of the crystal in the early stage of silicon carbide crystal growth.
[0048] Example 2
[0049] This embodiment provides a method for growing a silicon carbide crystal, the method comprising the following steps:
[0050] (1) Preparation stage: The silicon carbide raw material is loaded into the bottom of the crucible, the silicon carbide seed crystal is fixed on the crucible cover, the crucible is transferred to the single crystal growth furnace, and the single crystal growth furnace is evacuated and filled with neon gas. At the same time, the growth chamber is pressurized and heated, the pressure is raised to a first pressure, the first pressure is 300mbar, and the temperature is raised from room temperature 25°C to a first temperature, the first temperature is 1700°C. After the pressure increase and temperature increase are completed, the pressure is reduced and the temperature is raised, so that the pressure drops from the first pressure to the second pressure within 4 hours, the second pressure is 30mbar. At the same time, the temperature is raised from the first temperature to the second temperature, the second temperature is 2010°C. Among them, the TED dislocation density of the silicon carbide seed crystal is about 2300cm -2 .
[0051] (2) Buffering stage: After the decompression and temperature increase, nitrogen gas is introduced at a flow rate of 4 mlpm. Simultaneously, constant temperature decompression is performed at the second temperature for a time period T1, so that the pressure drops from the second pressure to the third pressure, the third pressure being 8 mbar, and T1 being 4 hours.
[0052] (3) Growth stage: After the constant temperature and pressure reduction is completed, the pressure is reduced and the temperature is increased, so that the pressure drops from the third pressure to the fourth pressure within 1 hour, and the fourth pressure is 4 mbar. At the same time, the temperature is increased from the second temperature to the third temperature, and the third temperature is 2200°C. After the pressure reduction and temperature increase is completed, the temperature and pressure are kept constant at the third temperature and the fourth pressure for a time period of T2, and T2 is 110 hours. After the constant temperature and pressure are completed, a silicon carbide crystal with a low TED dislocation density is obtained.
[0053] Example 3
[0054] This embodiment provides a method for growing a silicon carbide crystal, the method comprising the following steps:
[0055] (1) Preparation stage: The silicon carbide raw material is loaded into the bottom of the crucible, the silicon carbide seed crystal is fixed on the crucible cover, the crucible is transferred to the single crystal growth furnace, and the single crystal growth furnace is evacuated and filled with argon. At the same time, the growth chamber is pressurized and heated, the pressure is raised to a first pressure, the first pressure is 200mbar, and the temperature is raised from room temperature 25°C to a first temperature, the first temperature is 1800°C. After the pressure increase and temperature increase are completed, the pressure is reduced and the temperature is raised, so that the pressure drops from the first pressure to the second pressure within 5 hours, the second pressure is 40mbar. At the same time, the temperature is raised from the first temperature to the second temperature, the second temperature is 2050°C. Among them, the TED dislocation density of the silicon carbide seed crystal is about 3000cm -2 .
[0056] (2) Buffering stage: After the decompression and temperature increase, nitrogen gas is introduced at a flow rate of 7 mlpm. Simultaneously, constant temperature decompression is performed at the second temperature for a time period T1, so that the pressure drops from the second pressure to the third pressure, the third pressure being 5 mbar, and T1 being 5 hours.
[0057] (3) Growth stage: After the constant temperature and pressure reduction is completed, the pressure is reduced and the temperature is increased, so that the pressure drops from the third pressure to the fourth pressure within 2 hours, and the fourth pressure is 3 mbar. At the same time, the temperature is increased from the second temperature to the third temperature, and the third temperature is 2250°C. After the pressure reduction and temperature increase is completed, the temperature and pressure are kept constant at the third temperature and the fourth pressure for a time period of T2, and T2 is 100 hours. After the constant temperature and pressure are completed, a silicon carbide crystal with a low TED dislocation density is obtained.
[0058] Example 4
[0059] The difference between this embodiment and embodiment 1 is that the second temperature is 2150° C., and the remaining growth methods and parameters are consistent with those in embodiment 1, so they are not described here in detail.
[0060] Example 5
[0061] The difference between this embodiment and embodiment 1 is that the third pressure is 3 mbar, and the remaining growth methods and parameters are consistent with those in embodiment 1, so they are not described here in detail.
[0062] The TED dislocation density of the silicon carbide substrate obtained after the growth process in the above embodiment was tested, and the test results are shown in Table 1:
[0063] Table 1
[0064] <![CDATA[Seed crystal dislocation density (cm -2 )]]> <![CDATA[TED dislocation density (cm -2 )]]> Example 1 1100 974 Example 2 2300 1320 Example 3 3000 1563 Example 4 1100 1891 Example 5 1100 2365
[0065] It can be seen from Examples 1 and 4 that if the temperature in the buffer stage (ie, the second temperature) is too high, the TED dislocation density of the silicon carbide crystal will increase significantly in the early growth stage.
[0066] It can be seen from Examples 1 and 5 that if the pressure in the buffer stage is gradually reduced to 3 mbar, that is, the third pressure is too low, the TED dislocation density of the silicon carbide crystal will also increase significantly in the early growth stage.
[0067] The applicant states that while the above-described embodiments illustrate the process of the present invention, the present invention is not limited to the above-described process steps, nor does it imply that the present invention must rely on the above-described process steps for implementation. Those skilled in the art will appreciate that any improvements to the present invention, equivalent substitutions for the raw materials used, additions of auxiliary components, and selection of specific methods, etc., fall within the scope of protection and disclosure of the present invention.
Claims
1. A method for growing silicon carbide crystals, characterized in that: The growth method comprises the following steps: (1) Preparation stage: SiC raw material is loaded into the bottom of the crucible, SiC seed crystal is fixed on the crucible cover, the crucible is transferred into the single crystal growth furnace, the single crystal growth furnace is evacuated and then filled with inert gas, and the growth chamber is pressurized and heated at the same time, the pressure is raised to a first pressure, and the temperature is raised to a first temperature; then the pressure is reduced and the temperature is raised, the pressure is reduced to a second pressure, and the temperature is raised to a second temperature; (2) Buffer stage: After reaching the second temperature, the doping gas is filled in, and the pressure is reduced at a constant temperature for a time period of T1 until the pressure drops to the third pressure; (3) Growth stage: After the constant temperature and pressure reduction is completed, the pressure is reduced to the fourth pressure and the temperature is increased to the third temperature; then, the temperature and pressure are kept constant at the third temperature and the fourth pressure for a time period of T2, and after the end, a silicon carbide crystal with a low TED dislocation density is obtained.
2. The growth method according to claim 1, characterized in that Step (1) The first pressure is 200-500 mbar; And / or, in step (1), the first temperature is 1600-1800°C.
3. The growth method according to claim 1, characterized in that: Step (1) the second pressure is 20-50 mbar; And / or, in step (1), the second temperature is 2000-2050° C.; And / or, the time for reducing pressure and raising temperature in step (1) is 1-5h.
4. The growth method according to claim 1, characterized in that: The inert gas in step (1) includes any one of helium, neon or argon, or a combination of at least two of them.
5. The growth method according to claim 1, characterized in that: The third pressure in step (2) is 5-10 mbar; And / or, the value range of T1 in step (2) is 1-5h.
6. The growth method according to claim 1, characterized in that: The doping gas in step (2) includes at least one of ammonia and nitrogen; And / or, the flow rate of the doping gas in step (2) is 1-7 mlpm.
7. The growth method according to claim 1, characterized in that: The time of reducing pressure and raising temperature in step (3) is 0.5-2h; And / or, the fourth pressure in step (3) is 1-5 mbar; And / or, the third temperature in step (3) is 2100-2300°C.
8. The growth method according to claim 1, characterized in that: The value range of T2 in step (3) is 100-150h.
9. The growth method according to claim 1, characterized in that: The growth method comprises the following steps: (1) Preparation stage: SiC raw material is loaded into the bottom of the crucible, SiC seed crystal is fixed on the crucible cover, the crucible is transferred into the single crystal growth furnace, the single crystal growth furnace is evacuated and then filled with inert gas, the inert gas includes any one of helium, neon or argon or a combination of at least two; at the same time, the growth chamber is pressurized and heated, the pressure is raised to a first pressure, the first pressure is 200-500 mbar, and the temperature is raised from room temperature 25°C to a first temperature, the first temperature is 1600-1800°C; after the pressure and temperature are raised, the pressure is lowered and the temperature is raised, so that the pressure drops from the first pressure to the second pressure within 1-5 hours, the second pressure is 20-50 mbar; at the same time, the temperature is raised from the first temperature to the second temperature, the second temperature is 2000-2050°C; (2) Buffering stage: After the pressure reduction and temperature increase, a doping gas is charged, wherein the doping gas includes at least one of ammonia and nitrogen, and the flow rate of the doping gas is 1-7 mlpm; at the same time, a constant temperature pressure reduction is performed at the second temperature for a time period of T1, so that the pressure drops from the second pressure to a third pressure, wherein the third pressure is 5-10 mbar, and the value range of T1 is 1-5 h; (3) Growth stage: After the constant temperature and pressure reduction is completed, the pressure is reduced and the temperature is increased, so that the pressure drops from the third pressure to the fourth pressure within 0.5-2 hours, and the fourth pressure is 1-5 mbar; at the same time, the temperature is increased from the second temperature to the third temperature, and the third temperature is 2100-2300°C; after the pressure reduction and temperature increase is completed, the third temperature and the fourth pressure are kept at a constant temperature and pressure for a time of T2, and the value range of T2 is 100-150 hours; after the constant temperature and pressure is completed, a silicon carbide crystal with a low TED dislocation density is obtained.
10. A silicon carbide crystal, characterized in that: The silicon carbide crystal is prepared by the preparation method according to any one of claims 1 to 9.