Inductively coupled plasma etch processes for NiMnSb

Abstract

Plasma chemistries based on SF6, NF3, or CH4/H2 were investigated for inductively coupled plasma (ICP) etching of NiMnSb Heusler alloy thin films. The resulting etch rates were a strong function of ion energy, ion flux, and plasma composition. In SF6/Ar discharges, the etch rates increased from 100 to 300 Å min−1 under conventional reactive ion etch conditions to >10 000 Å min−1 with the addition of even relatively small amounts (200 W) of ICP source power. The etched surface becomes enriched in Mn under these conditions. In NF3/Ar discharges the etch rates actually decrease as ICP source power is increased, leading to net deposition at either high NF3 percentages or high ICP powers. The etched surface is also enriched in Mn under these conditions, with a Sb-deficient region underneath. In CH4/H2/Ar discharges, the etch rates are slower than with pure Ar and show no evidence of a chemical component in the etch mechanism. Since the etch rates are so high in ICP SF6/Ar discharges, it is necessary to pay careful attention to removal of the native oxide on NiMnSb, which prevents etching while it is present, and thus may cause extremely rough surfaces if it not uniformly removed.