Pure and PDMS contaminated PS oligomers films were investigated both by time-of-flight static secondary ion mass spectrometry (TOF-SSIMS) and X-ray photoelectron spectroscopy (XPS). The secondary ion spectra from the PDMS contaminated PS oligomers were almost completely related to PDMS. XPS revealed a PDMS contamination characterized by a silicon surface concentration of 6 at.%. Obviously siloxane contaminants existing on the surface of a silicon wafer may diffuse towards the PS oligomers outermost surface resulting in a rather high PDMS surface concentration of about 85%. Due to the known differences in the information depth and sensitivity of SSIMS and XPS very different detection limits are to be considered. In elimination of siloxane contaminants by ultrasonication in hexane was found to be an effective way. Another common organic cleaning procedure, which is ultrasonication in trichloroethylene (TCE), subsequently in isopropanol and finally in acetone was found to be ineffective for cleaning of PDMS contaminated silicon wafers. (C) 2003 Elsevier B.V. All rights reserved.