Precise Damage Observation in Ion-Beam Etched MTJ

Abstract

Patterning damage at the sidewall in a magnetic tunnel junction (MTJ) was observed precisely using a rectangular MTJ where deterioration in crystallinity is easier to identify than in the case of a dot-shaped conventional MTJ. A 200–500 nm-square rectangular MTJ was patterned by a 200 eV ion beam (IB). Cross-sectional transmission electron microscopy was used for damage observation. A bright-field image showed that crystallinity deteriorated to a depth of $\sim 1.3$ nm in the MgO-barrier layer. A Fourier transform mapping image and a dark-field transmission electron microscopy image indicated the existence of an amorphous region at the patterning edge in the MgO layer. IB etching is one of the strong candidates for magnetic random access memory (MRAM) fabrication. However, a typical IB etching energy, e.g., 200 eV, introduces a damage depth of several monolayers at the patterned surface. Since nearly damage-free-patterned surface would be needed for high-density MRAM with nanoscale MTJs of $\sim 10$ nm in diameter, IB etching with much lower energy would be necessary for fabrication.