The postdeposition thermal effect on different silicon oxide-based multilayers is investigated using x-ray photoelectron spectroscopy (XPS) depth profiling. A multilayer consisting of borophosphosilicate glass (BPSG) and germophosphosilicate glass (GPSG), used frequently as cladding and core layers in silica waveguides, is investigated. XPS depth profile results indicate that diffusion of Ge and B into both BPSG and GPSG, even with 30 min of annealing at 800 degrees C, makes two layers of germoborophosphosilicate glass (GBPSG) at the interfacial region, with considerable refractive index changes as compared with the initial GPSG material. During annealing, the dopants diffuse as neutral species rather than in oxide/suboxidized form. XPS depth profiling is also carried out using nondoped silicate glass or phosphosilicate glass as a diffusion blocking layer. The results show that both Ge and B diffuse less than in BPSG and GPSG. Based on this investigation, waveguide structures are proposed which can compensate the dopant diffusion that is caused by post-thermal treatment.