Hard mask etch process development for patterning 60nm magnetic tunnel junction

Magnetic random access memory (MRAM) is one of the most promising solution for the non-volatile memory in the post-Moore era. Its core feature is the magnetic tunnel junction (MTJ), which determines the performance of the device. The main constituency materials of the MTJ are metallic elements such as Ta, Fe, Co, Mg, etc. They generally form a multilayer stack which contains many single-layer material in nanometer scale. The challenges for the plasma etching, which is typically done in an ICP etcher in one pass, mainly include accurate transfer of the etching topography and control of non-volatile metal etching by-products. This paper proposes following solutions to address above challenges: 1. Introduce HBr curing to harden the incoming photoresist surface to reduce the mask shape deformation; 2. Use CF4 gas in the plasma strip step to clean the metal oxide polymer.