Investigation of postoxidation thermal treatments of Si/SiO2 interface in relationship to the kinetics of amorphous Si suboxide decomposition

Abstract

Interfacial Si suboxides (SiOx, x<2) are detrimental to transistor performance and are typically minimized during postoxidation anneals. To study the kinetics of SiOx decomposition, thick films (∼2000 Å) of amorphous Si:O:H alloys (0.7<x<1.4) were deposited by remote plasma enhanced chemical vapor deposition and subjected to rapid thermal anneals. Films were characterized by Fourier transform infrared spectroscopy, Raman spectroscopy, ellipsometry, photoluminescence (PL), and transmission electron microscopy. At temperatures >500 °C initially there is a rapid segregation into amorphous Si (a-Si) surrounded by a SiO2 shell which acts as a diffusion barrier decelerating the reaction. Phenomenological modeling of kinetics with a one-dimensional Avrami–Erofe’ve treatment gives an upper limit for a-Si lateral growth rates of 1.2 Å/s at 900 °C with an activation energy of 120 kJ/mol. PL, Raman, transmission electron microscopy and ellipsometry confirm this segregation model in the amorphous state. Due to the rapid initial decomposition and relatively large diffusion coefficients, a simple kinetic hindrance explanation for the 4–8 Å of SiOx at the SiO2/Si interface is unlikely.