Plasma etching of refractory metals (W,Mo, Ta) and silicon in SF6 and SF6-O2. An analysis of the reaction products

The etching rates and reaction products of refractory metals (W, Mo, and Ta) and silicon have been studied in a SF₆-O₂ r.f. plasma at 0.2 torr. The relative concentrations of WF₆ and WOF₄ and the intensities of the WF_n⁺ (n=3–5), WOF_m⁺ (m=1–3), MoF_n⁺, and MoF_m⁺ ions have been measured by mass spectroscopy. An analysis of the neutral composition of the plasma during etching of these metals and a comparison with the results obtained for silicon show that at least two species are involved for W and Mo etching: fluorine and oxygen atoms. A reaction scheme is proposed.