Evolution of Etch Profile of Magnetic Tunnel Junction Stacks Etched in a CH3OH/Ar Plasma

Abstract

Etch characteristics of magnetic tunnel junction (MTJ) stacks masked with W/TiN films were investigated using an inductively coupled plasma reactive ion etching in a CH3OH/Ar gas. The effect of CH3OH concentration on the etch rate, etch selectivity and etch profile of MTJ stacks was examined. The high degree of anisotropy of etched MTJ stacks at high CH3OH concentrations resulted from the high etch selectivity of MTJ stacks to hard mask which was closely related with the high ratio of [H]/[Ar] peaks obtained by optical emission spectroscopy. The evolution of etch profile of MTJ stacks was examined to elucidate the etch mechanism in a CH3OH/Ar gas. Transmission electron microscopy of the etched MTJ stacks revealed the redeposition on the sidewall of MTJ stacks occurred during the early stage of etching and the gradual sputtering-off of the redeposited materials during further etching, resulting in a high degree of anisotropy. In addition, the redeposited materials turn out to be mainly Pt and Mn with low levels of Co and Fe by using energy dispersive X-ray spectroscopy