Dose dependence of the silicon near-surface modifications caused by CF4 reactive ion-beam etching

The ion dose dependence of the silicon near-surface modifications caused by CF4 reactive ion-beam etching was studied using on-line variation of SiF4 partial pressure, ellipsometry, and Auger electron spectroscopy. The existence of two critical doses is demonstrated. Beyond the lower critical dose, of about 5 x 1016 cm-2 according to the beam parameters, the steady state of the carbonaceous overlayer is reached, and the overlayer can be removed effectively by a simple dip in concentrated HF for 60 s, thus allowing the diagnostics of the damage of the underlying silicon. On the other hand, the silicon near surface is still modified up to a second critical dose, for which the steady state of both the overlayer and Si subsurface is then reached. Likewise, the conditions to minimize the contamination of the underlying crystal, as a function of the ion dose, are achieved