High rate anisotropic etching

High etch rate dry processes for several important materials including Si, SiO2, and Al have been developed using high pressure (> 100 Pa) processing. Etch rates can be made considerably faster than low pressure processes which are often reactant limited. The anisotropy is controlled by ion bombardment which will be shown to perform two roles: enchancement of the process or clearing of a passivant. A simple model of the potential distribution in the discharge will be discussed to aid in understanding the roles of excitation frequency and r.f. power in these processes. As device dimensions become smaller and wafer sizes larger, the need to precisely transfer resist patterns into underlying layers, uniformly and with individual wafer control are self evident. The need to do so in a cost effective way, has provided the pressure to develop high speed etching processes that make one at a time wafer handling a useful production technique. It is fortunate that the two requirements, high speed and anisotropy are mutually compatable and can be shown to have a positive corellation. In the past, considerable importance has been attached to the long mean free paths that exist at low pressures. Long paths are important for sputtering, to increase bombardment energy and reduce back scattering. However, if there are chemical reactions that produce stable, high vapor pressure products, high pressures can actually increase the rate of reaction, due to greater availability of reactant. That this can happen without a loss of dimensional control has not been generally appreciated.