The Si(1 1 1) wafer surface roughening caused in NH4OH:H2O2:H2O (SC-1) step and flatting the rough surface have been investigated, using ex situ atomic force microscopy (AFM). We have demonstrated that the formation of a large number of etch pits in depth of 2.5-3.5 nm on Si(1 1 1) wafer during SC-1 treatment is responsible for the wafer roughening. In order to completely remove the etch pits on the wafer surface, a simple but powerful cleaning procedure, consisting of (H2SO4:H2O2) oxidation step and subsequent HF dip step, has been applied to the Si wafer. By AFM section analysis, a thickness of 0.8-1 nm of Si oxide layer can be removed by applying the above cleaning procedure one time. Therefore, after running the cleaning procedure three or four times, all the etch pits can be completely removed from the Si wafer. Atomically flat Si(1 1 1) surface with root mean square (RMS) roughness of similar to0.15 nm/mum can be finally obtained. (C) 2003 Elsevier B.V. All rights reserved.