Study of oxygen vacancy in high-k gate dielectric by charge injection technique

A new technique by charge injection is introduced to investigate the charging effect on weak oxide in the gate stack of high-k metal gate process. The oxide with extra oxygen vacancy is more vulnerable to process charging, as verified by the correlation of Vt vs. subthreshold swing degradation, SILC spectrum, and chemical bonding state analysis using X-ray photoelectron spectroscopy (XPS) and electron energy loss spectroscopy (EELS). Degradation of pFET threshold voltage (Vt) shift by gate injection under Source/Drain (S/D) floating condition is observed, this is attributed to the oxide damage by the accelerated carriers from S/D reverse bias. The convolution of “random dopant fluctuation (RDF) + charging effect” is expected to magnify devices Vt shift, especially for those worse bit cells with high Vt as verified by the Monte-Carlo simulation. We further demonstrate that process with tighten Vt distribution, such as FinFET technology with less implant process and better charge release immunity, is less vulnerable to the charging induced Vt shift.