STUDIES OF REACTIVE ION ETCHING USING COLUTRON HOT-FILAMENT DC PLASMAION SOURCES

In a study of reactive ion etching of silicon, Colutron hot filament d c plasma ion sources were used for halocarbon ion production. Mass spe ctrometric analyses of ions extracted from such sources showed that th e ion population was very sensitive to the ion source materials. When CF4 was admitted to a regular Colutron ion source in which the hot fil ament 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) w as found as a result of reactions in the ion source. When quartz was r eplaced by boron nitride, BF(n)+ species with small amounts of CF(n)were generated. The most effective way to enhance CF(n)+ production se ems to be the covering of the quartz chamber with a graphite inner jac ket. In the study of CCl2F2 plasma, Cl+ was found to be the main speci es regardless of the chamber materials. The bombardment reactions of t hese ions with silicon were studied by mass separation of the ion spec ies and by analyzing the bombarded surfaces with X-ray photoelectron s pectroscopy. 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 format ion. Both the CF(n)+ and COF(n)+ bombardment moved the Fermi level of the silicon surface close to the conduction band maximum. In compariso n, BF2+ bombardment at < 300 eV gave a boron overlayer and a p+ silico n surface.