We have used x-ray photoelectron spectroscopy (XPS) to study the chemical constituents present on the surfaces after etching of poly-Si features masked with photoresist or oxide patterns. The wafers were etched in a low pressure, high density plasma, helicon source using a HBr/Cl2/O2 gas mixture. The O2 gas flow rate was tuned to obtain anisotropic etching profiles by forming an SiO2 like layer on the sidewalls of the features and maximizing the polysilicon/gate oxide selectivity. Electrostatic charging of insulating surfaces and geometric shadowing of photoelectrons by adjacent photoresist lines were performed to differentiate the photoemission signals from the tops, sidewalls, and bottoms of the features. XPS analyses have shown that the passivation layer formed on the polysilicon sidewalls during etching is a chlorine rich silicon oxide film with both type of masks. This film contains a low carbon concentration when resist is used as a mask. The similar thickness and constitution of the sidewall for oxide and photoresist masked poly-Si samples indicate that the nature of the mask material has no significant effect on the sidewall passivation mechanism. © 1997 American Vacuum Society.