This paper describes the influence of H2O2 in HF solution on the surface roughness of bulk and silicon-on-insulator (SOI) wafers. Experiments are carried out for 0-, 2-, and 5 degrees-tilted bulk wafers with (100) surface orientation and various (100) SOI wafers. Atomic force microscopy images show that surface roughness is decreased by immersing the samples in an HF solution that includes H2O2. It has been found that the significant improvement of surface roughness is observed in separation by implanted oxygen (SIMOX) SOI substrates in comparison to bulk silicon wafers. From X-ray photoelectron spectroscopy analyses, in the case of bulk Si wafers, it has been shown that much oxygen adsorption and suboxides cover over the surfaces of Si wafers immersed in the HF solution with H2O2. The coverage rate of suboxides on bulk silicon wafers is related to the roughness of postcleaned surfaces. The suboxide on the postcleaned surface suppresses the degradation of surface roughness in the case of bulk wafers. In the case of SIMOX SOI wafers, surface suboxides are not left behind after immersion in HF solution with H2O2; a clean Si surface with a step and terrace structure is observed after immersion in the HF solution with H2O2. (c) 2005 The Electrochemical Society. [DOI: 10.1149/ 1.2133189] All rights reserved.