Evaluation of strain-induced mobility variation in TiN metal gate SOI n-MOSFETs

In this paper, the influence of the strain induced by a TiN metal gate in the channel of n-MOS SOI transistors is investigated. Mechanical simulation has been used to calculate the strain components, which are found to show strong variations near the gate edge and a rather constant level under the gate. The influence on electron mobility has been calculated using the deformation potential theory, in its general formulation, as channel strain is neither purely biaxial nor uniaxial. It is found that electron mobility is more degraded by TiN-induced strain as the gate length becomes smaller. However, this degradation can be maintained below 10% for a [110]-oriented channel, provided that the residual stress in the 10 nm TiN layer is smaller than about 2.5 GPa.