Fabrication of buried channel waveguides on silicon substrates using spin-on glass

A new process for the deposition of thick (≈10-µm) films of silica and titania-doped silica on silicon substrates is described. Films are built up by repetitive operation of a simple process cycle in which a layer of sol-gel material is deposited by spin coating, then densified by rapid thermal annealing. Stressfree layers are obtained through careful choice of the anneal temperature. Bilayer structures suitable for waveguide fabrication may also be constructed by performing two successive deposition runs using sol-gel precursors with different titania concentrations. These bilayers may be patterned topographically into ridges by using reactive ion etching, and the ridges may be planarized by applying additional layers of sol-gel material to form buried channel waveguides.