Quantitative assessment of mobility degradation by remote Coulomb scattering in ultra-thin oxide MOSFETs: measurements and simulations

In this paper, we report measurements of electron effective mobility (/spl mu//sub eff/) in ultra-thin (UT) pure SiO/sub 2/ bulk MOSFETs. A low substrate doping was intentionally used to better detect a possible /spl mu//sub eff/ degradation at small T/sub ox/. New quantitative criteria were developed and used to obtain /spl mu//sub eff/ measurements unaffected by either gate doping penetration or gate oxide leakage. Mobility simulations, based on an improved and comprehensive remote Coulomb scattering (RCS) model, exhibit a good agreement with the experimentally observed mobility reduction at small T/sub ox/. Our results indicate that polysilicon screening is an essential ingredient to reconcile the RCS models with the experiments.

I. Introduction

The RCS with the ionized impurities in the polysilicon has been regarded as the possible origin of the degradation of effective mobility in Ultra-Thin (UT) gate oxide MOSFETs [1], [2], and its quantitative understanding is also very important to assess the effect on of the fixed charges in the stacks of High-K gate dielectrics [3].