Modulation of the effective work function of TiN metal gate for PMOS application

It is important to find a way to modulate the work function of TiN metal gate towards the valence band edge of Si, which can meet the lower threshold voltage requirement of p-type metal-oxide-semiconductor (MOS) transistor. In this work, effects of TiN thickness, post-deposition annealing (PDA), oxygen incorporation and N concentration variation on the work function of TiN metal gate in MOS structures are systematically investigated. It can be found that the work function positively shifts at the initial stage as the thickness of the TiN layer increases and stabilizes at such a thickness. PDA at N-2 ambience with a trace of O-2 can also cause a positive shift in the work function of TiN metal gate. The same tendency can be observed when oxygen is incorporated into TiN. Finally, increasing the N concentration in TiN can also positively shift the work function. All these measures are effective in modulating the TiN metal gate so that it is more suitable for PMOS application.