Radical nitridation of Al films for the barrier formation in ferromagnetic tunnel junctions

Nitridation process of Al films using microwave-excited plasma was investigated to realize highly qualified Al-N barrier for magnetic tunnel junctions (MTJs), in comparison with reactive deposition process of Al-N films. The MTJs fabricated by the plasma nitridation method with Kr+N2 or Ar+N2 mixed gas showed larger values of tunnel magnetoresistance (TMR) ratio and resistance-area product (R×A) than those of the MTJs fabricated with He+N2 plasma. The MTJs with reactive-deposited Al-N showed relatively small values of TMR ratio and R×A. From the optical emission spectroscopy of the respective plasma, we concluded that N2 ion in the plasma is a responsible factor for lowering the barrier height of Al-N and that radical nitridation process is suitable to form the barriers without inducing defects.