Studies of reactive ion etching using Colutron hot filament dc plasma ion sources

Abstract

In a study of reactive ion etching of silicon, Colutron hot filament de plasma ion sources were used for halocarbon ion production. Mass spectrometric analyses of ions extracted from such sources showed that the ion population was very sensitive to the ion source materials. When CF 4 was admitted to a regular Colutron ion source in which the hot filament dc plasma was confined by a small quartz chamber, instead of the anticipated CF n + ions, a mixture of COF n + and SiF n + ( n = 0–3) was found as a result of reactions in the ion source. When quartz was replaced by boron nitride, BF n + species with small amounts of CF n + were generated. The most effective way to enhance CF n + production seems to be the covering of the quartz chamber with a graphite inner jacket. In the study of CCl 2F 2 plasma, Cl + was found to be the main species regardless of the chamber materials. The bombardment reactions of these ions with silicon were studied by mass separation of the ion species and by analyzing the bombarded surfaces with X-ray photoelectron spectroscopy. It was found that CF n + bombardment of silicon resulted in the formation of a fluorocarbon polymer overlayer. The oxygen atom carried by COF n + reduced the fluorocarbon buildup by carbonyl formation. Both the CF n + and COF n + bombardment moved the Fermi level of the silicon surface close to the conduction band maximum. In comparison, BF 2 + bombardment at < 300 eV gave a boron overlayer and a p + silicon surface.