Application of Silicon Carbide Powder in the Production of Silicon Carbide Wafers

The production of silicon carbide wafers requires the preparation of silicon carbide substrates. Currently, the improved Lely method, high-temperature CVD method, and solution method are commonly used for their preparation, with the improved Lely method being the mainstream.
The Lely method, also known as sublimation method, is based on the principle that in a hollow cylindrical graphite crucible (the outermost graphite crucible with a built-in porous graphite ring), industrial grade silicon carbide powder is placed between the crucible and the porous graphite ring and heated to 2500 ℃. At this temperature, silicon carbide decomposes and sublimates, producing a series of gas-phase substances such as silicon single crystals, Si2C, and SiC2. Due to the temperature gradient between the inner wall of the crucible and the porous graphite ring, these gaseous substances randomly generate crystal nuclei on the inner wall of the porous graphite ring. However, the Lely method has low yield, difficult to control crystal nuclei, and can form different structures with limited size.
With the deepening of research, researchers have proposed an improved Lely method, also known as the Physical Vapor Transport (PVT) method. Based on the Lely method, seed crystals are introduced into the sublimation growth furnace, and appropriate temperature gradients are designed to control the material transportation from SiC sources to seed crystals. This method can control the crystal nucleus and orientation. This method can obtain SiC crystals with larger diameter and lower expansion defect density. With the continuous improvement of the growth process, companies that have adopted this method to achieve industrialization include Cree, Dow Corning, II-VI from the United States, SiCrystal from Germany, NipponSteel from Japan, Shandong Tianyue, Tianke Heda from China, and others.
In the PVT method, there are many factors that affect the synthesis of SiC crystals, among which SiC powder as a raw material directly affects the growth quality and electrical properties of SiC single crystals. Therefore, in recent years, the preparation of high-purity SiC powders has gradually become a research hotspot in the field of SiC single crystal growth. At present, there are three main methods for synthesizing SiC powders in the industry: the first is the solid-state method, with Acheson method and self-propagating high-temperature synthesis method being the most representative among the solid-state methods; The second is the liquid phase method, the most representative of which are the sol gel method and the polymer thermal decomposition method; The third type is the gas phase method, among which the most representative are the chemical vapor deposition method and the plasma method.