RIE of SiO2 in doped and undoped fluorocarbon plasmas

Abstract SiO 2 and Si 3 N 4 on top of polycrystalline silicon, titanium silicide and gallium arsenide have been selectively etched by reactive sputter etching in glow discharges of CF 4 and CHF 3 . It is observed that for SiO 2 an infinite degree of selectivity can be obtained by admixing minor amounts of methane ( 3 . By a proper adjustment of the operating conditions, i.e. power, gas-flow, total pressure and the CH 4 to fluorocarbon ratio, we are able to control the rate of carbon deposition in such a way that etching takes place in exposed areas, releasing oxygen or nitrogen under the influence of energetic particle bombardment. The ion-assisted chemical reaction between oxygen or nitrogen and the polymerizing species, forming volatile products, together with the physical sputtering, makes these areas accessible to fluorine-containing species responsible for the chemical etching of SiO 2 . The importance of carbon deposition and oxygen release under energetic particle bombardment is demonstrated by resting the samples on different cathode materials and by sputter etching in an argon/methane atmosphere. These experiments confirm that prevention of carbon build-up by released oxygen is the main mechanism responsible for the high etch rate ratio between SiO 2 and Si in reactive ion etching.