Smoothing single-crystalline SiC surfaces by reactive ion etching using pure NF₃ and NF₃/Ar mixture gas plasmas

In pure NF₃ plasma, the etching rates of four kinds of single-crystalline SiC wafer etched at NF₃ pressure of 2 Pa were the highest and it decreased with an increase in NF₃ pressure. On the other hand, they increased with an increase in radio frequency (RF) power and were the highest at RF power of 200 W. A smooth surface was obtained on the single-crystalline 4H-SiC after reactive ion etching at NF₃/Ar gas pressure of 2 Pa and addition of Ar to NF₃ plasma increased the smoothness of SiC surface. Scanning electron microscopy observation revealed that the number of pillars decreased with an increase in the Ar-concentration in the NF₃/Ar mixture gas. The roughness factor (R_a) values were decreased from 51.5 nm to 25.5 nm for the As-cut SiC, from 0.25 nm to 0.20 nm for the Epi-SiC, from 5.0 nm to 0.7 nm for the Si-face mirror-polished SiC, and from 0.20 nm to 0.16 nm for the C-face mirror-polished SiC by adding 60% Ar to the NF₃ gas. Both the R_a values of the Epi- and the C-face mirror-polished wafer surfaces etched using the NF₃/Ar (40:60) plasma were similar to that treated with mirror polishing, so-called the Catalyst-Referred Etching (CARE) method, with which the lowest roughness of surface was obtained among the chemical mirror polishing methods. Etching duration for smoothing the single-crystalline SiC surface using its treatment was one third of that with the CARE method.