Incidence Angle Dependence of the Silicon Near-Surface Contamination Caused by CF4 Reactive Ion Beam Etching

The incidence angle dependence of silicon near-surface contamination caused by CF4 Reactive Ion Beam Etching was studied using on-line variation of SiF4 partial pressure and Auger Sputter Profiling. Initial and steady state etch rates both vanish at grazing incidence and have a smooth maximum at 20–30 deg. It is shown that whatever is the incidence angle, a C, F-blocking overlayer grows involving an etch rate attenuation by a factor which is only slightly dependent on the incidence angle. As the angle increases, with a 500 eV beam, the thickness of the C, F contamination layer decreases monotonically from 1.9 nm down to a constant value of about 1nm achieved beyond a critical angle of 45 deg. Then a “C, F-reactive mixed layer” is seen over the silicon the etching of which is dominated by surface mechanisms. Conversely with the lower angles, the thickness of the “carbonaceous incorporated layer” becomes larger than that of the mixed layer, and volume mechanisms dominate the silicon removal.