Near-Ideal Si-SiO2 Interfaces

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
.