Optimization of a Concentrated Chloride-Based CVD Process for 4H-SiC Epilayers.

Concentrated homoepitaxial growths of 4H-SiC was performed using a chloride-based chemical vapor deposition (CVD) process on different off-angle substrates (on-axis, 4 and 8° off-axis toward the [1120] direction). A suitable combination of gas flow and process pressure iṡ needed to produce the gas speed that yields an optimum cracking of the precursors and a uniform gas distribution for deposition over large areas. The use of low pressure and the addition of chlorinated precursors bring the added benefit of achieving higher growth rates. A systematic study of the gas speed's effect on the growth rate, uniformity, and morphology on the 4H-SiC epitaxial layers was performed. Growth rates in excess of 50 μm/h were achieved on 50 mm diameter wafers with excellent thickness uniformity (below 2% σ/mean without rotation of the substrate) and smooth morphology using only 1/10 of the typical gas carrier flow and process pressure demonstrating the feasibility of a concentrated chloride-based CVD process for 4H-SiC. Thermodynamic calculations showed that the improved thickness uniformity could be due to a more uniform gas phase composition of the silicon intermediates. The concentration of the SiCl₂ intermediate increases by a factor of 8 at a reduced carrier flow, while all the other hydrogenated silicon intermediates decrease. [ABSTRACT FROM AUTHOR]