Plasma etching of NiFe/Cu and NiMnSb/Al₂O₃ multilayers for sub-micron pattern definition

Abstract

A number of different plasma chemistries have been investigated for pattern transfer in NiFe/NiFeCo/Cu multilayer stacks and NiMnSb/Al2O3 structures. For NiFe alloy/Cu films, achievement of a high etch rate depends upon balancing atomic Cl neutral flux with a coincident Ar+ ion flux. The chloride etch products are generally not volatile in conventional systems, leading to formation of a thick selvedge layer that prevents etching. However, at high ion flux (>1011 cm-3) conditions in plasma sources such as electron cyclotron resonance (ECR) or inductively coupled plasma (ICP), these etch products can be desorbed by ion assistance, preventing formation of the selvedge layers. For NiMnSb thin films, SF6-based plasmas produce etch rates above 10,000 angstroms min-1 in both ECR and ICP tools. Sub-micron features with excellent sidewall anisotropy and smoothness have been produced in both materials.