THE INTERFACE STATES AT SiO2/POLYSILICON AND SiO2/MONOSILICON INTERFACE INFLUENCE ON N-POLYSILICON/OXIDE/N-MONOSILICON CAPACITANCE

The interface states have a very significant role in the components containing MOS structures. We study the interface states densities effect at SiO2/ Poly-silicon and SiO2/ mono-silicon surfaces on metal/poly-silicon /oxide/ mono-silicon capacitance. Then, a mono-dimensional simulation of capacitance-voltage characteristics of MSOS is presented [1]. The numerical solution of Poisson equation and the determination of the charge variation in the structure induced by an application of external bias (VG) allow us to simulate the capacitance-voltage MSOS characteristics. The geometrical model assumes that the poly-silicon layer is composed of a succession of defined mean grain size crystallites, separated by lateral grain boundary, which are parallel to the poly-silicon/ oxide interface. The interface states of mono-silicon/SiO2 shift the part of the curve that corresponds to the inversion of the substrate (mono-silicon) towards the negative voltage as it appears in Fig. 1. A shift towards the positive voltage of the inversion in poly-silicon layer for the interface states SiO2 / poly-silicon is shown in Fig 2-a. The Polycrystalline layer is in depletion. A peak appears at the level of the minimum corresponding Poly-silicon layer. If the Poly-silicon doping concentration is 10 cm, the effect of the interface states disappears, which is confirmed by Fig. 2-b. The density of the traps becomes negligible in front of the doping concentration. Our results are identical to those given by C. Leveugle on capacitances Poly-silicon/SiO2/ monosilicon [2]. -5 0 5 10 0,75 0,80 0,85 0,90 0,95 1,00