Smoothing of the Si surface using CF4/O2 down-flow etching

Abstract
Changes in surface morphology have been studied for Si surfacestreated with CF4/O2 down‐flow etching. It has been found that rough Si surfaces can be smoothed and Si trench corners can be rounded off using this CF4/O2 down‐flow etching. A SiF x O y layer is formed on the Si surfaceetched by a down‐flow discharged CF4/O2 gas mixture in high O2 concentration. A thick SiF x O y layer is formed at the concave part of the surface, which prevents fluorine atoms from reacting with Si. On the other hand, Si etching proceeds fast at the convex part covered with a thin SiF x O y layer. As a result, a rough Si surface is smoothed and trench corners are rounded off. By applying this treatment to a polycrystallinesiliconsurface, the leakage current of a SiO2 film grown on it is much reduced.