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.

Thermal Atomic Layer Etching of Nickel Using Sequential Chlorination and Ligand-Addition Reactions

“…Other plasma etch methods for nickel involve sequential doses of reactants to control the etch rate. One sequential plasma process used Cl 2 plasma to form NiCl 2 and then H 2 plasma to produce gaseous nickel hydride . The etch rate observed for nickel under the Cl 2 and H 2 plasma conditions was 57 Å/cycle .…”

Suboxide/subnitride formation on Ta masks during magnetic material etching by reactive plasmas

“…Also, for magnetic metals, there have been various attempts to devise efficient RIE processes for their smallscale patterning. For example, etching of magnetic materials by Cl 2 based plasmas has been proposed, [5][6][7][8] but under typical conditions of chlorine etching of magnetic materials, metal chlorides are not volatile and corrosion occurs on etched metal surfaces.…”

Progress and prospects in nanoscale dry processes: How can we control atomic layer reactions?

“…Kim et al have developed an approach to the plasma etching of magnetic materials that uses a combination of thermodynamic assessment and experimental validation. 92) Potential reactions between the dominant vapor phase and condensed species at the surface were considered under various process conditions. The volatility of the etching products was calculated to aid the selection of patterning chemistries, and this approach has been demonstrated successfully for test cases involving both halogen and organic etching chemistries.…”