Process-induced magnetic tunnel junction damage and its recovery for the development of spin–orbit torque magnetic random access memory

Abstract

The generation of torques in heterostructures of heavy metals and ferromagnets (HM / FM) in spin–orbit torque magnetic random access memory (SOT-MRAM) makes them interesting for the development of magnetic memory technology. Currently, the emerging SOT-MRAM technology faces major challenges in etching based on current manufacturing tools. In that respect, we experimentally investigate the two different etching recipes (namely, CF-Etch, & NH-Etch) of the reactive ion etching (RIE) process on the performance of a Ta/CoFeB/MgO/Ta (hard mask) magnetic film stacks to develop the SOT-MRAM technology. The experimental results demonstrate that CF-Etch etches Ta very fast, and MgO etches very slowly. In contrast, NH-Etch etches those two materials at a comparable rate. Both etches are terminated before MgO is removed. Based on the experimental results, we found that the CF-Etch reduces the interfacial anisotropy of CoFeB/MgO films. Moreover, the CF-Etch also destroys the magnetic moment of CoFeB film, which further deteriorates after the annealing process. In contrast, the magnetic properties of the stack are only slightly affected when the NH-Etch recipe is used. We also discuss the advantages and disadvantages of these two recipes based on the experimental study. Finally, we developed the SOT-MRAM devices based on these two etching recipes of the RIE process to improve the etching yield of this technology. The current SOT-MRAM fabrication process enables a uniform etch stop on the thin tunnel barrier layer and the Ta heavy metal layer (HM). A wafer-level statistical study of SOT switching characteristics, including tunnel magnetoresistance (TMR), SOT switching thresholds, and parallel/antiparallel state resistances (RP/RAP), has been performed.