A low energy hydrogen-argon plasma was applied to clean silicon (100) surface. In situ spectroscopic ellipsometry in the UV-Vis range was used to characterise the morphology and etching damage in dependence on the substrate temperature. Ex situ atomic force microscopy and in situ reflection high-energy electron diffraction was used to characterise complementary the surface morphology and surface structure. In dependence of the substrate temperature two types of surface morphologies could be classified. Using spectroscopic ellipsometry the optimum conditions for the silicon surface cleaning were determined. (C) 2003 Elsevier B.V. All rights reserved.