During reactive ion etching of tantalum silicide and polysilicon layers in a chlorine based chemistry it is observed that a film (15–20 nm) is deposited on vertical surfaces of etched structures. This film is even present after common resist strip processes. This film is analyzed by Auger electron spectroscopy and transmission electron spectroscopy, and the formation mechanism is investigated. It is shown it is composed of silicon dioxide sputtered from dielectric layers lying under the etched silicide and poly Si layers. Variables influencing the formation of the residual sidewall film are analyzed. It is demonstrated that the observed residual films are not involved in the anisotropic etch characteristics before the silicide or poly Si layer are etched through. It is further demonstrated that a carbon based polymer film or inhibition layer must be responsible for the anisotropic etch profile of the tantalum silicide layer. This second carbon based film is formed only with a sufficient amount of photoresist in the etching chamber.