Thick-film doped-oxide deposition processes for applications in planar lightwave circuit fabrication

Abstract

Plasma enhanced chemical vapour deposition (PECVD) was used in the development of silica layers for use in planar lightwave circuit fabrication. These high-rate (>200 nm/min) processes are tailored specifically for the thick-film (5/spl sim/15 /spl mu/m) films required for these applications A GeH/sub 4/ addition to the process was used to deposit the core layer, controlling the core-clad refractive index (RI) difference in the range of 0.2%-1.65%. Undoped SiO/sub 2/ and Ge-doped SiO/sub 2/ films up to 10 /spl mu/m have been deposited on to 4" Si <100> wafers. The 'as deposited' and 'annealed' film properties: film uniformity, RI, RI uniformity and stress have been compared. The upper cladding layer in an optical planar waveguide is typically formed using boron and phosphorus doped films (BPSG) which provides the necessary reflow characteristics. Refractive index uniformity of /spl plusmn/0.0003 across 4" silicon wafers was achieved on all films after annealing. The core layer was shown to be capable of producing optical losses of <0.1 dB/cm when processed into a waveguide.