No abstract

We investigated how the Pt capping layer affected perpendicular magnet anisotropy in magnetic-tunnel-junctions fabricated with a Ta electrode, a lower CoFeB layer, an MgO barrier, an upper CoFeB layer, and a Pt capping electrode, which was estimated by using an anisotropy constant multiplied by the upper CoFeB layer thickness (Ku * t). The maximum Ku * t was found at an annealing temperature of 300 °C for an magnetic tunnel junction with an upper CoFeB layer thickness of 0.9 nm, indicating a highly textured MgO (100) barrier of 1.0 nm with none of the remaining Pt inter-diffused in the upper CoFeB layer.

Recently, p-MTJ spin-valves with top Co 2 Fe 6 B 2 free layers have been widely studied. They potentially experience crystallinity degradation in the face-centered-cubic (fcc) structure of the MgO tunneling barrier as a result of the diffusion of Ta atoms and a significant amount of Fe atoms from the Co 2 Fe 6 B 2 free and pinned layers. A new design of the p-MTJ spin-valve using a nanoscale-thick W bridging and capping layer demonstrated the absence of significant crystallinity degradation in the fcc structure and showed a limited diffusion of Fe atoms, thus achieving a TMR ratio of~143% at an ex-situ annealing temperature of 400°C.

We have studied the characteristics of the mixture of HNO3 , HF , and H2O2 chemicals called the controlled slight etch (CSE) solution as an effective wafer cleaning solution. The silicon etch rate in the CSE solution was not dependent on HF concentration of the solution, while that in a mixture of HNO3 and HF was linearly dependent on HF concentration. The CSE solution reduced the surface concentrations of Fe and Cu ions below a concentration of 1010 normalatom/cm2 on the intentionally contaminated wafers and suppressed average surface microroughness increase in comparison to slight etch (SE) solution. X‐ray photoelectron spectroscopy (XPS) showed that the CSE cleaning does not leave chemical oxide on the surface. The average breakdown field for the CSE‐cleaned sample was 11.5MV/normalcm . We explained the etching mechanism that the H2O2 species in the CSE solution slows down the rate of oxidation reaction of the silicon wafer by interrupting autocatalytic reaction of HNO3 .