Effect of RF pulsing biasing on the etching of magnetic tunnel junction materials using CH₃OH

The magnetic tunnel junction (MTJ)-related materials such as CoFeB, CoPt, MgO, and Ru, and W were etched using CH₃OH in a pulse-biased inductively coupled plasma system and the effect of bias pulsing (100% ∼ 30% duty percentage) on the etch characteristics of the MTJ-related materials was investigated at the substrate temperature of 200°C. The etch selectivity of MTJ-related materials over W was improved by using pulse-biasing possibly due to the formation of more stable and volatile etch products during the pulse-off time and the removal of the compounds more easily on the etched CoFeB surface during the pulse-on time. X-ray photoelectron spectroscopy also showed that the use of lower duty percentage decreases the residue thickness remaining on the etched MTJ materials indirectly indicated the higher volatility of the etch products by the bias pulsing. The etching of nano-patterned CoFeB masked with W also showed more anisotropic etch profile by pulse-biasing probably due to the increased the etch selectivity of CoFeB over W and the decreased redeposition of etch products on the sidewall of the CoFeB features. The most anisotropic CoFeB etch profiles could be observed by using CH₃OH gas in the pulse biasing of 30% duty ratio.