Near-Ideal Si-SiO2 Interfaces

Abstract

The Si-SiO 2 interface plays a key role in insulated-gate field-effect transistors (IGFETs). Of principal concern are the interface charge density Q ic and the fast-state density N fs . These properties can be optimized by eliminating the transition region and creating an abrupt interface. Our work with the chemical vapor deposition (CVD) of SiO 2 using a CO 2 -SiH 4 -H 2 system in the presence or absence of trace amounts of HCl gas at 1000°C has demonstrated that unannealed CVD SiO 2 on (100) Si using a vertical-cold-wall reactor has properties similar to those of unannealed SiO 2 on (100) Si formed by the usual thermal oxidation procedure. In addition, using only 2.27 vol% HCl, we have produced films of SiO 2 on (111) Si that are better than their thermal counterparts, unannealed or annealed; i.e., Q ic ≈ 5 × 10 10 cm −2 and N fs ≈ 10 10 cm −2 -eV −1 . We attribute these results, at least in part, to an abrupt interface between the CVD SiO 2 and Si. Deposition rates of 10–20 nm/min were used to reproducibly deposit 30–50 nm of SiO 2 . The CVD SiO 2 films also show a significantly lower standard deviation in the breakdown fields (±1.5%) and the mobile charge densities (±5%) than their thermal counterparts. In general, N fs was independent of Q ic .