Etching of ruthenium coatings in O ₂- and Cl ₂- containing plasmas

Ruthenium (Ru) film etching has been studied with O2 - and Cl2 -containing inductively coupled plasmas to understand the etching mechanism and the relationship between plasma characteristics and the competition between the wall deposition of etch by-products and the creation of volatile etch by-products that flow into the downstream. The ICP was characterized by multiple in situ diagnostic tools. Ru films were etched either from 6-in. wafers placed on a rf-biased substrate or from Ru-coated QCMs without a Ru-coated wafer present. Ru etches readily in O2 -containing plasma. Cl2 addition resulted in significant changes in etch rate, wall deposition behavior, and the downstream etch product composition. When Ru was etched by Ar O2 plasmas, a positive wall deposition rate was observed and no Ru O4 was observed in the foreline. The etching rate correlated well with the oxygen radical density. With Cl2 addition, our observations included the significantly increased etching rate, the detection of Ru O4 downstream by FTIR, the detection of Ru Ox Cly ions in the plasma, and virtually zero wall deposition. The increased etch rate with Cl2 addition was not solely due to an increase in O atom concentration, plasma density, plasma potential or the electron energy distribution. It is believed that both O- and Cl-containing species (ions and/or neutrals) are necessary to explain the different behavior in Ru etching by using Cl2 and O2 -containing plasmas.