As the volatile dynamic random access memory (DRAM) device faces a physical limitation, new memory devices are actively investigated to solve this problem. Among them, spin transfer torque magnetic random access memory (STT-MRAM) has received a lot of attention because of its very high speed of device, endurance, low power consumption of device, and high density memory cell in addition to the non-volatility of information. Especially, the MTJ memory elements which consist of Co_xFe_yB_z/MgO/Co_xFe_yB_z multilayer structure are the critical building blocks for high density magnetic random access memory with high tunneling magnetoresistance(TMR). However, the dry etching of MTJ stack with sub 70 nm is a challenging step in the fabrication of STT-MRAM. The etching of nanoscale MTJ induces oxidation in magnetic layer, pattern degradation and damage or sidewall redeposition at patterned MTJ sidewall especially.

In this study, for successful etching of MTJ and MTJ related materials, RIB (reactive ion beam) etching using NF₃, CH₃OH, and CO/NH₃ gas mixture and ICP etching using Ar, He, CO/NH₃ and so on were conducted. Etch characteristics of magnetic tunnel junction (MTJ) stacks masked with W were investigated precisely using field emission scanning electron microscopy (FE-SEM) and TEM (Transmission electron microscopy). Simulation of MTJ material and hardmask material was conducted with SRIM simulation to observe tendency with etch process of blank unit thin film samples. In addition, the magnetic hysteresis curves were analyzed by a vibrating sample magnetometer (VSM). The results showed that, among the various gas combinations, the use of He gas improved etch selectivity of MTJ materials over W and also improved the etch profile of MTJ features. Also the He etch gas could be beneficial in reducing damage. The detailed etch mechanism and results on the etching of MTJ materials will be presented.