Thermodynamic assessment and experimental verification of reactive ion etching of magnetic metal elements

Abstract

A thermodynamic analysis of etch chemistries for Co, Fe, and Ni using a combination of hydrogen, oxygen, and halogen gases suggested that a single etchant does not work at 300 K; however, a sequential exposure to multiple etchants results in sufficiently high partial pressure of the reaction products for the process to be considered viable. This sequential dose utilized the two reactions, a surface halogenation followed by the secondary etchant exposure. (MX2 (c) + 3Y →MY(g) + 2XY(g), where M = Co, Fe, Ni; X = F, Cl, Br; Y = O, H) The volatilization reaction induced by sequential plasma exposure changed the equilibrium point, increasing the partial pressure of the etch product. Amongst all combinations, Cl2 or Br2 plasmas followed by H2 plasma were the most effective. From both the gas phase diagnostics and surface composition analysis, H2 plasma alone could not etch metallic Co, Fe, and Ni films but alternating doses of Cl2 and H2 plasmas resulted in more effective removal of chlorinated metals and increased the overall etch rate.