DEPOSITION OF THICK SILICA TITANIA SOL-GEL FILMS ON SI SUBSTRATES

A process for production of thick (> 10 mum) titania-doped silica film s on Si substrates by repetitive spin-coating of sol-gel material and rapid thermal annealing for 10 s in the range 800-1200-degrees-C is de scribed. The dependence of overall thickness and etch rate in buffered HF on annealing temperature is described, and it is shown that films annealed at low (< 1175-degrees-C) temperatures have a relatively larg e thickness and etch rate. However, films having the properties of ful ly densified material (minimum thickness and etch rate) can be produce d by subsequent consolidation. The film stress characteristics are sim ilar to those of phosphosilicate glass formed by the same process: fil ms annealed below a critical temperature (< 1075-degrees-C) are under tensile stress at the annealing temperature, and crack before a thick film can be built up. Refractive index data are given; these show that only fully consolidated films have the refractive index expected from their SiO2 and TiO2 compositions. Finally, discrepancies in results f or thicknesses of unconsolidated single-layer and multilayer films are explained using a simple model that accounts for the effect of cumula tive densification.