Influence of O2 Gas on Etch Profile of Magnetic Tunnel Junction Stacks Etched in a CH4/O2/Ar Plasma

Abstract

The etch characteristics of magnetic tunnel junction (MTJ) stacks patterned with W/TiN films were examined using an inductively coupled plasma of a CH4/O2/Ar gas mix. The effect of the O2 concentration on the etch rate, etch selectivity and etch profile of the MTJ stacks was examined. The etch profile of the MTJ stacks in 60% CH4/Ar gas appeared to be the best. The addition of 10% O2 gas in CH4/Ar gas led to an improved etch profile with less redeposition on the sidewall of the MTJ stacks. This was attributed to the increase in [H]/[Ar] and [O]/[Ar] intensity ratios with increasing O2 concentration to 20%. Transmission electron microscopy of the etched MTJ stacks revealed redeposited materials on the sidewall of the MTJ stacks etched in CH4/Ar gas that were indentified to be mainly Pt, Mn, Co, Ru and Ti. On the other hand, the amount of redeposited materials decreased significantly with the addition of 10% O2 in CH4/Ar gas. The formation of metal oxides and protection layer in CH4/O2/Ar gas mix resulted in a high degree of anisotropy without redeposited materials in the etch profile of MTJ stacks.