Although dedication of plasma etching equipment strictly to a single process is becoming a common practice in IC labs, a large number of older plasma systems (especially the barrel type) were designed and are still used for multiple processes such as thin film etching in CF4based plasma and photoresist striping in pure oxygen plasma. An investigation of a cross contamination effect is reported here. Silicon wafers coated with aluminum and exposed to a simulated oxygen plasma resist strip process were analyzed using Auger electron spectroscopy and x‐ray photoelectron spectroscopy. Relatively large amounts of carbon and fluorine were found to be present on the wafer surfaces. Wafers exposed to wet chemical treatments were analyzed for comparison. The C and F contamination is believed to be due to redeposition of a fluorocarbon compound on the wafer surface originating from the chamber walls, etc. ESCA examination of the samples resulted in similar observations but the chemical identification of the contamination could not be made.