Atomic structure in SiO2 thin films deposited by remote plasma-enhanced chemical vapor deposition

Abstract

We have studied selected structure-dependent properties of thin films of SiO2 prepared by remote plasma-enhanced chemical vapor deposition (remote PECVD) and thermal oxidation of crystalline silicon, and have identified process-dependent differences in their local atomic structures. We have determined the frequency ν and linewidth Δν of the Si–O bond-stretching infrared-active vibration near 1075 cm−1, and have found that all relatively thick oxide films, t>1000 Å, prepared by either of these two techniques display the same linear relationship between Δν and ν. This behavior has been interpreted in terms of a central force model that gives the average bond angle 2θ at the oxygen atom sites, and attributes the linewidth to a distribution of vibration modes associated with a ±30° spread in 2θ. We have determined that (i) in remote PECVD films deposited at temperatures (Ts ) between 200 and 350 °C, 2θ varies between 140° and 144°; (ii) in thermal oxides grown over a temperature range (Tox ) between 800 and 1150 °C, 2θ varies from about 147° to 150°; and (iii) in thick oxide films, independent of the preparation method, Δθ/θ is equal to 0.21±0.01. We have compared other oxide properties as well: (a) the optical index of refraction n at 632.8 nm, (b) the intrinsic stress σi, and (c) the etch rate in buffered HF (6:1). In addition, we discuss the electronic properties of remote PECVD and thermally grown SiO2 films in metal–oxide–semiconductor (MOS) structures, where we have observed that the same device quality MOS properties can be obtained in structures employing both types of oxide films. Finally, we compare stress and strain in the remote PECVD and thermal oxides in the immediate vicinity of the Si/SiO2 interface, and the bulk of the oxide films, and correlate the differences we observe with fundamental differences in the two thin-film formation processes.