Silicon carbide resistance furnace heating body structure
By designing a heating element structure with gradually increasing graphite heating element thickness in a silicon carbide resistance furnace, the problem of uneven temperature gradient caused by traditional heating elements was solved, the quality of silicon carbide single crystals was improved, and crystal growth defects were reduced.
Patent Information
- Authority / Receiving Office
- CN · China
- Patent Type
- Utility models(China)
- Current Assignee / Owner
- LIAN KE BAN DAO TI YOU XIAN GONG SI
- Filing Date
- 2025-06-12
- Publication Date
- 2026-06-19
AI Technical Summary
In the existing silicon carbide single crystal growth process, the non-uniform axial temperature gradient inside the crucible caused by the traditional graphite heating element structure leads to crystal growth defects such as edge phase transitions, microtubes, and dislocations.
A heating element structure for a silicon carbide resistance furnace is designed, in which the thickness of the graphite heating element gradually increases from top to bottom, forming a constant and varying heat energy distribution. By changing the thickness of the graphite heating element, a constant temperature gradient is formed in the crucible, stabilizing the flow rate and crystallization rate of gaseous SiC.
This method achieves a constant temperature gradient per unit length between the seed crystal surface and the material surface temperature difference zone within the crucible, reducing edge phase transformations, microtubes, and dislocation defects during silicon carbide crystal growth.
Smart Images
Figure CN224382149U_ABST
Abstract
Description
Technical Field
[0001] This utility model relates to a heating element structure for a silicon carbide resistance furnace, specifically a heating element structure that improves the axial temperature gradient inside the crucible of a silicon carbide resistance furnace. Background Technology
[0002] Silicon carbide (SiC) is an excellent candidate for semiconductor devices due to its wide bandgap, high thermal conductivity, and high breakdown field. Among them, 4H-SiC, with its large bandgap (3.26 eV) and high electron mobility, is more widely used and popular in high-power, high-voltage electronic devices. Over the past decade, silicon carbide semiconductor technology has made significant progress, largely thanks to the high quality of silicon carbide single-crystal substrates. Therefore, producing higher-quality silicon carbide single-crystal substrates is crucial to further accelerating the development of silicon carbide devices.
[0003] To produce silicon carbide single crystal substrates with higher crystal quality, it is necessary to suppress growth defects. Currently, when using the most mainstream physical vapor transport (PVT) method to prepare 4H-SiC single crystals, the growth rate of SiC crystals, the crystal growth surface shape, and the axial temperature gradient in the crucible are closely related. The more uniform the temperature change gradient per unit distance (mm), the smoother the crystal growth surface shape and the more constant the crystal growth rate. This can suppress the generation of crystal edge phase transformations, microtubes, and dislocation defects to a certain extent, which is crucial for improving the quality of silicon carbide single crystals.
[0004] In existing technologies, resistance furnaces used for preparing 4H-SiC single crystals via physical vapor transport (PVT) primarily employ a cylindrical heating structure made of isostatically pressed graphite. A large DC or AC current is passed through the main heating element, generating high-density heat energy to continuously heat the SiC powder inside the crucible, causing it to sublimate into a gaseous state. This creates a temperature difference zone between the seed crystal surface and the material surface, with the temperature gradually decreasing upwards, forming an axial temperature gradient. This creates an upward airflow channel, allowing the gaseous SiC to flow upwards to the seed crystal surface and condense layer by layer into crystals. Traditional graphite heating elements have a constant resistance per unit length, resulting in uniform heat generation per unit length. However, within the temperature difference zone formed between the seed crystal surface and the material surface inside the crucible, the temperature gradient per unit length exhibits a curved pattern, causing inconsistencies in flow rate and crystallization rate at different locations. This can, to some extent, lead to defects such as phase transitions at crystal edges, microtubes, and dislocations. Utility Model Content
[0005] This invention proposes a heating element structure for a silicon carbide resistance furnace, which aims to overcome the above-mentioned shortcomings of the existing technology, achieve the generation of constant changing heat energy, and reduce defects such as phase transitions, microtubes, and dislocations at the edge of silicon carbide crystals.
[0006] The technical solution of this utility model is a heating element structure for a silicon carbide resistance furnace. The structure includes a graphite heating element, which is mounted on the outside of a crucible. A crucible lifting and rotating tray support assembly is connected to the bottom of the crucible. A heat insulation layer is provided on the outside of the graphite heating element, and the thickness of the graphite heating element gradually increases from top to bottom. Changing the thickness of the graphite heating element per unit height allows for a constant variation in heat energy, stabilizing the flow rate and crystallization rate of gaseous SiC and reducing defects such as edge phase transitions, microtubes, and dislocations during silicon carbide crystal growth.
[0007] Preferably, the longitudinal section of the graphite heating element is a right-angled trapezoid.
[0008] Preferably, or, the longitudinal section of the graphite heating body is composed of several right-angled trapezoids of equal height connected sequentially from top to bottom, with the right-angled legs of each trapezoid lying on a straight line, and the upper base of the lower right-angled trapezoid of two adjacent right-angled trapezoids being longer than the lower base of the upper right-angled trapezoid.
[0009] Preferably, the length difference between the upper and lower bases of each right-angled trapezoid in the graphite heating element is equal.
[0010] The advantages of this invention are: reasonable structural design, which can generate constant heat energy by changing the thickness of the graphite heating element within a unit height; during operation, the temperature gradient per unit length in the temperature difference zone formed by the seed crystal surface and the material surface in the crucible is constant, and the flow rate and crystallization rate of each interval tend to be consistent; it can reduce defects such as phase transformation, microtubes and dislocations at the edge of silicon carbide crystals. Attached Figure Description
[0011] Figure 1 This is a schematic diagram of the first embodiment of the heating element structure of the silicon carbide resistance furnace of this utility model.
[0012] Figure 2 This is a schematic diagram of the second embodiment of the heating element structure of the silicon carbide resistance furnace of this utility model.
[0013] Figure 3 This is a schematic diagram of the silicon carbide resistance furnace containing the heating element structure of the silicon carbide resistance furnace of this utility model.
[0014] In the figure, 1 is the heat insulation layer, 2 is the graphite heating element, 3 is the crucible, and 4 is the crucible lifting and rotating tray support assembly. Detailed Implementation
[0015] The present invention will be further described in detail below with reference to embodiments and specific implementation methods.
[0016] like Figure 1 As shown in the figure, in one embodiment, the longitudinal section of the graphite heating element is a right trapezoid, that is, the thickness of the graphite heating element gradually increases from top to bottom.
[0017] This causes the heat energy generated by the graphite heating element per unit height to change linearly with the increase of thickness. During operation, the temperature gradient per unit length in the temperature difference zone formed by the seed crystal surface and the material surface in the crucible can be kept constant, and the flow rate and crystallization rate of gaseous SiC tend to be stable.
[0018] like Figure 2 As shown, in another embodiment, the longitudinal section of the graphite heating body is composed of several right-angled trapezoids of equal height connected from top to bottom, and the right-angled legs of each right-angled trapezoid are on a straight line. The upper base of the lower right-angled trapezoid of two adjacent right-angled trapezoids is longer than the lower base of the upper right-angled trapezoid, and the length difference between the upper and lower bases of each right-angled trapezoid is equal.
[0019] The above structure also allows the thickness of the graphite heating element to gradually increase from top to bottom. Specifically, the thickness of the graphite heating element increases with a fixed height, forming several steps, so that the heat energy generated by the graphite heating element per unit height also changes stepwise with increasing height. During operation, the temperature gradient per unit length in the temperature difference zone formed by the seed crystal surface and the material surface in the crucible exhibits multiple constant changes, and the flow rate and crystallization rate of gaseous SiC tend to stabilize.
[0020] like Figure 3 As shown, the graphite heating element 2 is covered on the outside of the crucible 3, and the bottom of the crucible 3 is connected to the crucible lifting and rotating tray support assembly 4. The graphite heating element 2 is covered with a heat insulation layer 1.
[0021] As one example, the production process includes the following steps:
[0022] 1) According to the process ratio, place the silicon carbide powder (e.g., 4kg of 8-20 mesh SiC powder and 1kg of 20-40 mesh SiC powder) in layers in the crucible and flatten them; then put in the porous plate and a certain amount of tantalum particles;
[0023] 2) Then install the graphite ring for the crystal growth area and the graphite cap with the seed crystal attached;
[0024] 3) Place the crucible in Figure 3 In the thermal field shown;
[0025] 4) The silicon carbide crystal growth furnace is evacuated for 2-3 hours at the beginning, and then argon gas is quickly introduced to the furnace cavity pressure of 500 mbar. The evacuation and argon gas filling can be repeated.
[0026] 5) After cleaning the furnace cavity, fill it with the required ratio of nitrogen and argon under vacuum pressure, and start heating according to the set power gradient or temperature gradient. Monitor the crystal growth temperature of the crucible to reach the target value (e.g., 2100-2150℃) and maintain the temperature stable.
[0027] 6) The silicon carbide powder inside the crucible begins to sublimate and crystallizes on the seed crystal surface under the pull of the axial temperature gradient. An image of the axial temperature gradient inside the crucible is collected under thermal field simulation, and the temperature layers in the image are clearly defined.
[0028] All of the components described above are existing technologies, and those skilled in the art can use any model and existing design that can achieve their corresponding functions.
[0029] The above description is only a preferred embodiment of the present utility model. It should be noted that for those skilled in the art, several modifications and improvements can be made without departing from the inventive concept of the present utility model, and these all fall within the protection scope of the present utility model.
Claims
1. A silicon carbide resistance furnace heating element structure, characterized by, It includes a graphite heating element, which is covered on the outside of the crucible. The bottom of the crucible is connected to the crucible lifting and rotating tray support assembly. The outside of the graphite heating element is covered with a heat insulation layer, and the thickness of the graphite heating element gradually increases from top to bottom.
2. A silicon carbide resistance furnace heater structure as set forth in claim 1, characterized by The longitudinal section of the graphite heating element is a right-angled trapezoid.
3. The structure of the SiC resistance heater of claim 1, wherein The longitudinal section of the graphite heating element is composed of several right-angled trapezoids of equal height connected sequentially from top to bottom, with the right-angled legs of each trapezoid lying on a straight line, and the upper base of the lower right-angled trapezoid of two adjacent right-angled trapezoids being longer than the lower base of the upper right-angled trapezoid.
4. A silicon carbide resistance heating element structure as claimed in claim 3, wherein The difference in length between the upper and lower bases of each right-angled trapezoid in the graphite heating element is equal.