Annealing and oxidation of silicon oxide films prepared by plasma-enhanced chemical vapor deposition

X.Y. Chen, National University of Singapore
Yongfeng Lu, University of Nebraska - Lincoln
L.J. Tang, Institute of Microelectronics, 11 Science Park Road, Singapore 117685, Singapore
Y.H. Wu, National University of Singapore
B.J. Cho, National University of Singapore
X.J. Xu, National University of Singapore
J.R. Dong, Institute of Materials Research and Engineering, 3 Research Link, Singapore 117602, Singapore
W.D. Song, Data Storage Institute, 5 Engineering Drive 1, Singapore 117608, Singapore

Document Type Article

Published in JOURNAL OF APPLIED PHYSICS 97, 014913 (2005). © 2005 American Institute of Physics. Used by permission.

Abstract

We have investigated phase separation, silicon nanocrystal (Si NC) formation and optical properties of Si oxide (SiO_x, 0,x,2) films by high-vacuum annealing and dry oxidation. The SiO_x films were deposited by plasma-enhanced chemical vapor deposition at different nitrous–oxide/silane flow ratios. The physical and optical properties of the SiO_x films were studied as a result of high-vacuum annealing and thermal oxidation. X-ray photoelectron spectroscopy (XPS) reveals that the as-deposited films have a random-bonding or continuous-random-network structure with different oxidation states. After annealing at temperatures above 1000 °C, the intermediate Si continuum in XPS spectra (referring to the suboxide) split to Si peaks corresponding to SiO₂ and elemental Si. This change indicates the phase separation of the SiO_x into more stable SiO₂and Si clusters. Raman, high-resolution transmission electron microscopy and optical absorption confirmed the phase separation and the formation of Si NCs in the films. The size of Si NCs increases with increasing Si concentration in the films and increasing annealing temperature. Two photoluminescence (PL) bands were observed in the films after annealing. The ultraviolet (UV)-range PL with a peak fixed at 370–380 nm is independent of Si concentration and annealing temperature, which is a characteristic of defect states. Strong PL in red range shows redshifts from ~600 to 900 nm with increasing Si concentration and annealing temperature, which supports the quantum confinement model. After oxidation of the high-temperature annealed films, the UV PL was almost quenched while the red PL shows continuous blueshifts with increasing oxidation time. The different oxidation behaviors further relate the UV PL to the defect states and the red PL to the recombination of quantum-confined excitions.