Surface Nonuniformity-Induced Frequency Dispersion in Accumulation Capacitance for Silicon MOS(n) Capacitor

Abstract

Frequency dispersion in accumulation capacitance is observed in Al/SiO2/n-Si structured MOS with an ultrathin oxide layer (2.8 nm) grown on roughened silicon surface. The measured accumulation capacitance shows a 14.9% (26.9%) decrease at 1-kHz measurement frequency, and a 50.3% (69.2%) decrease at 10-kHz measurement frequency for partially nonuniform (fully nonuniform) sample. This phenomenon can be attributed to the lateral series resistance in the surface accumulation layer due to the interaction between nonuniformly distributed electrons. By taking into account the effect of nonuniformity-induced lateral series resistance, the accumulation C-V can be reproduced from a simplified model with a carefully chosen effective series resistance Rs,eff. The extracted Rs,eff is found to be frequency dependent and the value increases with a larger percentage of the nonuniform area. On the other hand, for p-type MOS, inconspicuous frequency dispersion in accumulation capacitance but apparent distortion in C-V profiles is observed. The possible mechanisms for the phenomenon are discussed.