Plasma irradiation damages to magnetic tunneling junction devices

Abstract

We exposed magnetic tunneling junction (MTJ) devices—fabricated using Ar-ion milling—to the reactive plasma commonly used in etching to determine the mechanism of the damage caused by the exposure. Exposing MTJ devices to the conventional continuous-wave (CW) plasma widely used in plasma etching significantly degrades their magnetic characteristics. However, exposure to a pulse-time-modulated (TM) plasma does not degrade the MTJ devices’ magnetic characteristics. Analysis of transmission electron microscopy cross sections of the MTJ device structures revealed that the structure of the CoFe pinned layer was damaged in the MTJ devices exposed to a conventional CW plasma. This structural damage degraded the MTJ devices’ magnetic characteristics. No damage to the structure of the MTJ devices was seen in those exposed to a TM plasma. Therefore, using the TM plasma offers an effective, damage-free method of etching MTJ devices as part of their manufacturing process.