Dry and wet etch processes for NiMnSb Heusler alloy thin films

A variety of plasma etching chemistries were examined for patterning NiMnSb Heusler alloy thin films and associated Al2O3 barrier layers. Chemistries based on SF6, Cl-2, and BCl3 were all found to provide faster etch rates than pure Ar sputtering. In all cases the etch rates were strongly dependent on both the ion flux and ion energy. Selectivities of greater than or equal to 20 for NiMnSb over Al2O3 were obtained in SF6-based discharges, while selectivities less than or equal to 5 were typical in Cl-2, BCl3, and CH4/H-2 plasma chemistries. Wet etch solutions of HF/H2O and HNO3/H2SO4/H2O were found to provide reaction-limited etching of NiMnSb that was either nonselective or selective, respectively, to Al2O3.