Theoretical and experimental investigation of ultrathin oxynitrides and the role of nitrogen at the Si-SiO2 interface

We investigate microscopic properties of ultrathin oxynitride gate dielectr ics using a combination of first principles electronic structure methods an d the attenuated total reflection (ATR) infrared spectroscopy. We use a the oretical structural model based on the Si-SiO2 interface. The quantum molec ular dynamics simulations suggest that N accumulates at the interface. We h ave generated samples with the nitrogen concentrations from 1.69x10(14) to 6.78x10(14) cm(-2). The analysis of nitrogen containing cells indicates a s ignificant structural improvement of the oxide layer and the strain reducti on at the interface. We have performed a calculation of the vibrational den sity of states. The experimental infrared ATR data is in qualitative agreem ent with the calculation. The valence band offset is estimated with two dif ferent theoretical methods. Calculations reveal a close agreement between a reference energy level based method and a direct estimate based on the den sity of states analysis. For the highest nitrogen concentration considered we find a 0.3 eV increase of the valence band offset due to nitrogen at the interface. The leakage current is studied using the Landauer theory to mod el the conductance through the gate dielectric. (C) 2000 American Vacuum So ciety. [S0734-211X(00)01505-5].