Comparison of Cl₂ and F₂ based chemistries for the inductively coupled plasma etching of NiMnSb thin films

Abstract

Plasma etching chemistries based on BCl3/Ar, BCl3/H2 and NF3/Ar were studied for patterning NiMnSb Heusler alloys thin films and associated Al2O3 barrier layers in an inductively coupled plasma tool. Using BCl3/Ar discharges, high etch rates (≥ 1 μm/min) were achieved either at high source power [(1000 W) or high direct current (dc) self bias (-300 V)] and etch rates showed a strong dependence upon source power, ion energy, and gas composition. Hydrogen addition to the BCl3 created new species (HCl) in the plasma, leading to faster etch rates for NiMnSb than in the case of Ar addition. Selectivities of ≥8 for NiMnSb over Al2O3 were obtained in BCl3-based discharges. On the other hand, NF3/Ar discharges provided a narrow process window for the etching of NiMnSb and the etch rates were much lower compared to those with BCl3. The surfaces of NiMnSb etched with NF3/Ar was smoother (root-mean-square surface roughness of 1.4 nm measured by atomic force microscopy) than the surfaces produced with BCl3/Ar. In terms of near-surface chemistry, NF3/Ar produced Mn enrichment, indicating the existence of involatile Mn etch products, whereas Mn deficiency was obtained under the same conditions with BCl3/Ar. © 1999 American Vacuum Society.