X-ray Photoelectron Spectroscopy Study of Optical Waveguide Glasses

This paper describes the characterization by x-ray photoelectron spectroscopy (XPS) of several Ge-doped silica glasses before and after reactive ion etching (RIE) in sulphur hexafluoride (SF6). These glasses have been commonly used in the production of optical waveguides, with varying amounts of GeO2 dopant. Surface composition modifications as a function of etching conditions and rate were studied, with the modified Auger parameter α′ utilized as a tool for detecting small chemical shift changes. Both the Ge LMM energy and values for α′ indicated that the RIE process modified the GeO2, involving partial reduction to GeO along with a possible associated chemical reaction with residue material. It was observed that in all instances the surface stoichiometry was significantly different to the bulk composition. Material grown using two processes, flame hydrolysis deposition (FHD) and plasma-enhanced chemical vapour deposition (PECVD), exhibited very different etching characteristics. The deposition of fluorine reaction products on the glass surface as a result of the etching is also discussed.