Tantalum carbide(TaC) coating can solve the problem of crystal edge defects and improve the quality of crystal growth, which is one of the core technical directions of "fast growth, long thickness, and long growth".

1. Characteristics of tantalum carbide coating

TaC ceramics have a melting point of up to 3880 °C, high hardness (Mohs hardness 9~10), large thermal conductivity (22W•m-1•K−1), large flexural strength (340~400MPa), and small coefficient of thermal expansion (6.6×10−6K−1), and show excellent thermochemical stability and excellent physical properties, and graphite and C/C composites have good chemical compatibility and mechanical compatibility, so TaC coating is widely used in aerospace thermal protection, single crystal growth, energy electronics, and medical devices.

TaC-coated graphite has better chemical resistance than bare graphite or SiC-coated graphite, can be used stably at high temperatures of 2600°, does not react with many metal elements, and is the best performing coating in the third-generation semiconductor single crystal growth and wafer etching scenarios, which can significantly improve the control of temperature and impurities in the process to prepare high-quality silicon carbide wafers and related epitaxial wafers. It is especially suitable for the growth of GaN or AlN single crystals in MOCVD equipment and the growth of SiC single crystals in PVT equipment, and the quality of the single crystals grown has been significantly improved.

Second, the advantages of tantalum carbide coating devices

The use of tantalum carbide TaC coating can solve the problem of crystal edge defects and improve the quality of crystal growth, which is one of the core technical directions of "fast growth, long thickness, and long growth". Industry studies have also shown that tantalum carbide-coated graphite crucibles can be heated more uniformly, providing excellent process control for SiC single crystal growth, and therefore significantly reducing the probability of polycrystalline formation at the edge of SiC crystals. In addition, tantalum carbide graphite coating has 2 major advantages:

(1) Reduce SiC defects

In addition to optimizing growth parameters and high-quality source materials (e.g., SiC source powders), switching to tantalum carbide-coated graphite crucibles can also achieve good crystal quality.

Schematic diagram of conventional graphite crucible (a) versus TAC coated crucible (b).

 

According to the research of Eastern European University in Korea, the main impurity of SiC crystal growth is nitrogen, and tantalum carbide coated graphite crucible can effectively limit the nitrogen incorporation of SiC crystals, thereby reducing the generation of microtubules and other defects and improving crystal quality. The results show that under the same conditions, the carrier concentration in SiC wafers grown in traditional graphite crucibles and TAC coated crucibles is about 4.5×1017/cm and 7.6×1015/cm, respectively.

Comparison of SiC single crystal defects grown in conventional graphite crucibles (a) and TAC-coated crucibles (b).

(2) Improve the life of graphite crucibles

At present, the cost of SiC crystals has been high, of which the cost of graphite consumables accounts for about 30%. The key to reducing the cost of graphite consumables is to increase its service life. According to the United Kingdom research team, tantalum carbide coating can extend the service life of graphite parts by 30-50%. Based on this calculation, simply replacing tantalum carbide-coated graphite can reduce the cost of SiC crystals by 9%-15%.

Quoted from: WeChat Tansubang 2024-06-22