Gas species dependent charge build-up in reactive ion etching

The effects of gas species on the charge build-up in reactive ion etching (RIE) have been investigated. The charge build-up was evaluated using metal/nitride/oxide/silicon (MNOS) capacitors and metal/oxide/silicon (MOS) capacitors. It was found that etching with electronegative gases such as O₂ and CF₄ results in considerable charge build-up. The spatial distribution of plasma parameters was diagnosed using a Langmuir probe. It was found that the spatial distribution of plasma parameters is non-uniform in plasmas of negative gases,while it is uniform in H₂, He, Ar, and Xe gas plasmas. The results suggest that we must take the effect of the gas species into consideration for the nonuniformity in a plasma, which causes the significant charge build-up. Models that can be used to explain the effect of gas species are discussed. It was also found that the charge build-up can be drastically reduced by adding H₂ gas to negative gases.