Relative merits of [formula omitted] and [formula omitted] plasma chemistries for dry etching of magnetic random access memory device elements

Abstract

A typical magnetic random access memory stack consists of NiFe/Cu/NiFeCo multilayers, sandwiched by contact and antioxidation layers. For patterning of submicron features without redeposition on the sidewalls, it is desirable to develop plasma etch processes with a significant chlorinated etch component in addition to simple physical sputtering. Under conventional reactive ion etch conditions with [formula omitted]-based plasmas, the magnetic layers do not etch because of the relatively involatile nature of the chlorinated reaction products. However, in high ion density plasmas, such as inductively coupled plasma, etch rates for NiFe and NiFeCo up to ∼700 Å min−1 are achievable. The main disadvantage of the process is residual chlorine on the feature sidewalls, which can lead to corrosion. We have explored several options for avoiding this problem, including use of in situ and ex situ cleaning processes after the [formula omitted]-etching, or by use of a noncorrosive plasma chemistry, namely [formula omitted] In the former case, removal of the chlorine residues with in situ [formula omitted] plasma cleaning (to form volatile HCl that is pumped away), followed by ex situ solvent rinsing, appears effective in preventing corrosion. In the latter case, the [formula omitted] plasma chemistry produces metal carbonyl etch products, that are desorbed in the simultaneous presence of an ion flux. The etch rates with [formula omitted] are much lower than with [formula omitted] over a broad range of source powers (0–1500 W), radio frequency chuck powers (50–450 W), pressures (1–30 mTorr) and plasma compositions. We have tried substitution of [formula omitted] for CO, and addition of Ar to produce faster etch rates, without success. Maximum rates of ∼300 Å min−1 for NiFe and NiFeCo were obtained with [formula omitted] under optimum conditions. The etched sidewalls tend to be sloped because of mask erosion during plasma exposure, in contrast to the case of [formula omitted]-based chemistries where the sidewalls are vertical. © 1999, American Institute of Physics. All rights reserved.