Difficulties in Preparation Technology of Silicon Carbide Single Crystal

The preparation technology of silicon carbide single crystals includes PVT method (physical vapor transport method), solution method, and high-temperature vapor chemical deposition method. Currently, commercial silicon carbide single crystal growth uses PVT method. The difficulty of preparing silicon carbide single crystals by PVT method lies in:
① Design and manufacturing technology of silicon carbide single crystal growth equipment. The silicon carbide long crystal furnace is the carrier for crystal preparation and an important component of the thermal field and process in the core technology of crystal growth. For silicon carbide single crystal substrates with different sizes and conductivity, the silicon carbide long crystal furnace needs to achieve various performance indicators such as high vacuum degree and low vacuum leakage rate, providing suitable thermal field conditions for high-quality crystal growth.
② There are many environmental impurities in the synthesis process of silicon carbide powder, making it difficult to obtain high-purity powder; Incomplete reaction between silicon powder and carbon powder as the reaction source can easily cause Si/C ratio imbalance; The crystal form and particle size of synthesized silicon carbide powder are difficult to control.
③ Silicon carbide single crystals undergo a "solid gas solid" transformation and recrystallization process in a sealed graphite chamber at temperatures above 2300 ° C. The growth cycle is long, the control is difficult, and defects such as microtubules and inclusions are prone to occur.
④ Silicon carbide single crystal includes more than 200 different crystal forms, but generally only one crystal form is required for production. During the growth process, it is easy to produce crystal form transformation, resulting in multi-type inclusion defects. It is difficult to stably control a single specific crystal form during the preparation process, such as the current mainstream 4H type.
⑤ There is a temperature gradient in the thermal field of silicon carbide single crystal growth, which leads to the presence of primary internal stress and defects such as dislocations and stacking faults during the crystal growth process.
⑥ During the growth process of silicon carbide single crystals, it is necessary to strictly control the introduction of external impurities in order to obtain highly pure semi insulating crystals or directionally doped conductive crystals. For semi insulating silicon carbide substrates used in RF devices, electrical performance needs to be achieved by controlling the extremely low impurity concentration and specific types of point defects in the crystal.
⑦ As a high hardness brittle material with a Mohs hardness of 9.2, silicon carbide substrate is prone to cracking during processing, and the substrate after processing is prone to quality issues such as warping; In order to achieve the quality level of downstream epitaxial open box use, it is necessary to perform ultra precision machining on the surface of silicon carbide substrate to reduce surface roughness, flatness, and meet strict metal and particle control requirements.
The high difficulty of silicon carbide single crystal preparation technology undoubtedly limits product yield, increases production costs, and thus affects its final price. This is also the main reason why the price of silicon carbide devices remains high.