SMOOTHING OF THE SI SURFACE USING CF4 O2 DOWN-FLOW ETCHING/

Changes in surface morphology have been studied for Si surfaces treate d with CF4/O2 down-flow etching. It has been found that rough Si surfa ces can be smoothed and Si trench comers can be rounded off using this CF4/O2 down-flow etching. A SiFxOy layer is formed on the Si surface etched by a down-flow discharged CF4/O2 gas mixture in high O2 concent ration. A thick SiFxOy layer is formed at the concave part of the surf ace, which prevents fluorine atoms from reacting with Si. On the other hand, Si etching proceeds fast at the convex part covered with a thin SiFxOy layer. As a result, a rough Si surface is smoothed and trench comers are rounded off. By applying this treatment to a polycrystallin e silicon surface, the leakage current of a SiO2 film grown on it is m uch reduced,