A study of reactive sputter etching by directed ion beams and R.F. plasmas.

This work compares the alternative methods of etching silicon semiconductor materials. Conventional methods of pattern delineation using aqueous etchants are being replaced for some applications by dry processing. The reasons for the move towards plasma and ion beam etching are examined particularly in relation to very large scale integration (VLSI) technology and the required reduction in feature size. A review of the published information on the use of reactive gas plasmas shows that this etching process is capable of producing vertical profiles without loss of pattern definition in lum. features.
Noble gas ion beam sputtering, another alternative dry etching process, has some advantages over plasma etching but does not compare favourably in terms of material etch-rate selectivity and profile replication.
Reactive ion beams produced by heated filament sources etch silicon compounds more rapidly than argon beams, but undesirable topographical features such as "facets" and "trenches" may be observed after beam energies greater than about 1 keV have been used.
The total beam current and current distribution have been determined for a medium sized (B93) Saddle-Field source. The etch rates of several materials were greater with a fluorocarbon beam than with an argon beam produced by this source.
Examination of profiles produced by etching silicon dioxide with beams from the B93 source injected with either CHF3 or CF4 showed no evidence of sputtering induced artefacts or lateral attack due to the diffusion of chemically reactive fragments. The results of reactive ion beam etching (RIEB) with a Saddle-Field source suggest that chemical attack predominates over sputtering. A two stage mechanism is proposed in which the incident particles cause bond cleavage at the surface followed by addition and abstraction reactions, leading ultimately to the formation of volatile products.
The possible commercial applications of RIBE with Saddle-Field sources are discussed, and suggestions are advanced for further work in this area.

A thesis submitted in partial fulfilment of the requirements for the degree of Doctor of Philosophy of the Council for National Academic Awards.