What should we pay attention to when preparing high-quality silicon carbide single crystals?
The current methods for preparing silicon carbide single crystals mainly include: physical vapor transport (PVT), top seed solution growth (TSSG), and high temperature chemical vapor deposition (HT-CVD).
Among them, the PVT method has the advantages of simple equipment, easy operation control, low equipment price and operating cost, and has become the main method used in industrial production.
1. Silicon carbide powder doping technology
Doping an appropriate amount of Ce element in silicon carbide powder can achieve the effect of stable growth of 4H-SiC single crystal. Practice has proved that doping Ce element in powder can increase the growth rate of silicon carbide crystals and make the crystals grow faster; it can control the orientation of silicon carbide, making the crystal growth direction more single and more regular; inhibit the generation of impurities in the crystal, reduce the generation of defects, and make it easier to obtain single crystal crystals and high-quality crystals; it can inhibit the corrosion of the back of the crystal and increase the single crystal rate of the crystal.
2. Axial and radial temperature field gradient control technology
The axial temperature gradient mainly affects the crystal growth form and crystal growth efficiency. Too small temperature gradient will lead to the appearance of impurities during the crystal growth process, and will also affect the transport rate of gas phase substances, resulting in a decrease in the crystal growth rate. Appropriate axial and radial temperature gradients help the rapid growth of SiC crystals and maintain the stability of crystal quality.
3. Basal plane dislocation (BPD) control technology
The main reason for the formation of BPD defects is that the shear stress in the crystal exceeds the critical shear stress of the SiC crystal, resulting in the activation of the slip system. Because BPD is perpendicular to the crystal growth direction, it is mainly generated during the crystal growth process and the later crystal cooling process.
4. Gas phase component ratio adjustment control technology
In the crystal growth process, increasing the carbon-silicon ratio gas phase component ratio in the growth environment is an effective measure to achieve stable growth of a single crystal. Because a high carbon-silicon ratio can reduce large step aggregation and maintain the inheritance of growth information on the surface of the seed crystal, it can inhibit the generation of polymorphs.
5. Low stress control technology
During the crystal growth process, the presence of stress will cause the internal crystal plane of the SiC crystal to bend, resulting in poor crystal quality or even crystal cracking, and large stress will lead to an increase in the basal plane dislocation of the wafer. These defects will enter the epitaxial layer during the epitaxial process and seriously affect the performance of the later device.
Looking ahead, high-quality SiC single crystal preparation technology will develop in several directions:
Large-size
The preparation of large-size silicon carbide single crystals can improve production efficiency and reduce costs, while also meeting the needs of high-power devices.
High-quality
High-quality silicon carbide single crystals are the key to achieving high-performance devices. At present, although the quality of silicon carbide single crystals has been greatly improved, there are still some defects, such as micropipes, dislocations, and impurities. These defects will affect the performance and reliability of the device.
Low-cost
The preparation cost of silicon carbide single crystals is high, which limits their application in some fields. The preparation cost of silicon carbide single crystals can be reduced by optimizing the growth process, improving production efficiency, and reducing raw material costs.
Intelligent
With the development of technologies such as artificial intelligence and big data, silicon carbide crystal growth technology will gradually become intelligent. The growth process can be monitored and controlled in real time through sensors, automatic control systems and other equipment to improve the stability and controllability of the growth process. At the same time, big data analysis and other technologies can be used to analyze and optimize growth data to improve the quality and production efficiency of crystals.
The preparation technology of high-quality silicon carbide single crystals is one of the hot spots in current semiconductor material research. With the continuous advancement of science and technology, silicon carbide crystal growth technology will continue to develop and improve, providing a more solid foundation for the application of silicon carbide in high temperature, high frequency, high power and other fields.