Towards the sub-50 nm magnetic device definition: Ion beam etching (IBE) vs plasma-based etching

Conventionally, the tunneling magneto resistive (TMR) devices for both hard drive and magnetic random access memory (MRAM) are defined via photolithography and subsequent ion mill processes. Due to non-volatility of ion milling byproducts, re-deposition of device materials across the tunneling barrier will increase the critical dimension (CD) and reduce the pattern transfer fidelity; moreover, it causes electrical shunting and TMR ratio drop. Therefore, either relatively large angle primary or two-step mill with a subsequent large angle side mill is required to clean-up such re-deposition across the barrier. Such primary milling angle and side milling time at a fixed primary mill angle have been determined experimentally to be ∼20–30° and above 30 s, respectively, in this study. However, it was found that extended side milling can cause substantial damage for sub-∼30 nm. We also investigated the plasma-based etching of such TMR devices using various chemistries and presented optical emission spectrum of such chemistries. The plasma etched TMR device profile and the possible interaction between the chemistry with the MgO barrier was also discussed.