In this study, the atomic-scale roughness and uniformity of SiO2 thermally grown on an atomically flat Si surface were investigated. The SiO2 surface roughness increased with increasing oxide thickness in the initial rapid oxidation region of the Deal Grove model. This roughness growth was a result of reoxidation of SiO species near the SiO2 surface, which were emitted from the Si/SiO2 interface during oxidation. However, the surface roughness growth is saturated in the linear-rate oxidation region. This is because the emitted SiO species within the SiO2 were reoxidized without thickness increment, and the generated oxidation stress was absorbed within the film. Although the amount of the emitted SiO decreases by the surpassing relaxation effect, the surface roughness is kept without shrinking. An incubation period before the onset of roughening was found, during which the surface roughness remained unchanged. (C) 2009 The Electrochemical Society. [DOI: 10.1149/1.3236631] All rights reserved.