Surface roughness of SiO2 from a remote microwave plasma enhanced chemical vapor deposition process

Abstract

We have investigated the roughness of the top surface of silicon dioxide deposited via a remote plasma enhanced chemical vapor deposition (RPECVD) process in a microwave reactor. We find a roughening transition at a deposition temperature of approximately 250 °C. Above this temperature, the surface is fairly smooth (root mean square roughness ∼0.3 nm). Below this deposition temperature, the oxide surface becomes extremely rough. Rapid thermal annealing at 900 °C does not eliminate this roughness, which is very nonuniform at the nanometer scale. For very thin RPECVD oxide applications, oxide surface roughness could be a limitation. We have used our three-dimensional Poisson solver in order to investigate the effects of oxide surface roughness taken from actual atomic force microscopy measurements on the confining potential within the silicon inversion layer of a metal–oxide–semiconductor (MOS) field effect transistor. In order to assess the quality of our process and system, oxides are characterized electrically with MOS capacitors, and structurally with Fourier transform infrared spectroscopy, high-resolution cross-sectional transmission electron microscopy, and etch rates in HF containing solutions.