Etching characteristics of magnetic materials (Co, Fe, Ni) using CO/NH 3 gas plasma for hardening mask etching

Abstract

Etching of magnetic materials, NiFe, CoFe, and Fe, has been studied with a high-density helicon plasma source using non-corrosive CO/NH 3 gas. High etch rates, ranging from 45 to 130 nm/min, were achieved. The etch rate strongly depended on both plasma density and ion energy. The main etching mechanism is interpreted as physical sputtering rather than as chemical reaction. A high selectivity of 6–16 was achieved by using hard masks of Ti or Ta. This is attributed to the hardening surface layer of the masks by nitradation, carbonization, or oxidation in CO/NH 3 gas plasma. This etching process is named as hardening mask etching. This etching process was also applied for tunneling magneto-resistive (TMR) multi-layers that uses magnetic random access memory with a Ta mask. A high anisotropy of about 80° was obtained without residues, sidewall deposition, and corrosion. This process is potentially applicable to the etching of thin magnetic materials in TMR stacks, patterned media, and read/write head.