Surface Fluorination of Polyimide Thin Films by CF4 + O2 Reactive Ion Beam Etching

Surface fluorination of polyimide thin films during CF4 + O2 reactive ion beam etching (RIBE) was investigated. The removal of the fluorinated layer by a subsequent oxygen ion beam etch was also studied. Electron spectroscopy for chemical analysis (ESCA) and Rutherford backscattering spectrometry (RBS) detected a fluorinated surface layer on the order of 100 A thick. Fluorine atom concentration in the surface of the film (as measured by RBS) and the etch rate of the film were measured as a function of several experimental parameters: ion energy, ion current density, etch time, and gas composition. The results are compared with theoretical predictions of the total number of fluorine atoms retained in the film after etching.