Plasma–induced damage in magnetic tunneling junctions

Abstract

Plasma–induced damage (PID) in the fabrication of magnetic tunnel junction (MTJ) based magnetic random access memory (MRAM) is studied after the formation of MTJ devices, which excludes process effect directly from the ion beam etching and protection layer deposition. Large degradation in coercivity (Hc) of MTJs is found in comparison with that measured just after the top metal （TM） was formed, which heavily deteriorates MRAM performances. This Hc degradation is found to be mainly introduced in plasma-enhanced chemical vapor deposition (PECVD) for passivation (PA) film after TM formation. The amplitude of the degradation depends on plasma power, but independent of the composition of the PA film. Hc reduction is observed once the plasma is turned on even though no PA deposition is performed. These results suggest that the observed Hc degradation is from PID effect most likely due to the plasma charge damage (PCD) induced in the PECVD process as no direct plasma contact with MTJ devices is involved in the process. It is argued that this PCD effect is due to the charge accumulations at the interface between the free layer and MgO barrier based on electric field–modulated magnetic anisotropy effect. This is further confirmed by an experiment in which Hc degradation is largely cured through partially removing the trapped charges by an annealing process.