Energy dependence of ion-assisted chemical etch rates in reactive plasmas

In a highly cited paper, Steinbruechel [C. Steinbruechel, Appl. Phys. Lett. 55, 1960 (1989)] has demonstrated that in the sub-keV region the etch yield scales like the square root of the ion energy. Based on this result, many authors have subsequently applied this specific energy dependence to ion-assisted chemical etch rates of various materials in different etch tools. In this work, it is demonstrated that in contrast to the etch yield, the etch rate cannot universally be modeled by a simple square-root energy dependence. A novel model accounting for the correct energy dependence of ion-assisted chemical etch rates is therefore proposed. Application of this model to the etching of SiO2 and ZnO in halogenated plasma chemistries provides a quantitative description of the simultaneous dependence of the etch rate on ion energy and on ion and reactive neutral fluxes