Some Chemical Aspects of the Fluorocarbon Plasma Etching of Silicon and Its Compounds

Mass spectrometric sampling of fluorocarbon glow discharges and in situ measurements of the etch rate of Si and SiO
2
with quartz crystal microbalances have been used to provide additional insight concerning the chemistry involved when additive gases such as O
2
, H
2
, N
2
, H
2
O, and C
2
F
4
are injected into a CF
4
glow discharge. The results obtained in our low-pressure, long-residence-time system indicate that the etching behavior of the discharge is not significantly influenced by the molecular structure of the injected gas molecules but is determined primarily by the elemental composition of the glow discharge. This phenomenologically observed result can be used to predict qualitatively the relative etching behavior of a large class of gaseous etchant mixtures as well as the role of various electrode or wall materials in the plasma etching process. Although this oversimplified interpretation should not be extended to short-residence-time plasma systems, it is believed to be valid for some of the configurations used in plasma etching and reactive ion etching.