Effect of thin Si insertion at metal gate/high-k interface on electrical characteristics of MOS device with La₂O₃

The effect of a thin Si layer insertion at W/La₂O₃ interface on the electrical characteristics of MOS capacitors and transistors is investigated. A suppression in the EOT increase can be obtained with Si insertion, indicating the inhibition of diffusion of oxygen atoms into La ₂O₃ layer by forming an amorphous La-silicate layer at the W/La₂O₃ interface. In addition, positive shifts in V _fb and V_th caused by Si insertion implies the formation of amorphous La-silicate layer at the top of La₂O₃ dielectrics reduces the positive fixed charges induced by the metal electrode. Consequently, a large improvement in mobility has been confirmed for both at peak value and at high E_eff of 1 MV/cm with Si inserted nFETs. Although a degradation trend on EOT scaling has been observed, the insertion of thin Si layer is effective in pushing the scaling limit.