Optimization of PECVD boron-phosphoros doped silicon oxynitride for low-loss optical waveguides

Boron phosphorus-doped silicon oxynitride layers for integrated optics applications have been deposited from 2% SiH4/N2 + N2O + 5% PH3/Ar and 5% B2H6/Ar. The influence of boron and phosphorus-doping to the PECVD SiON layer properties has been investigated. The boron concentration was found to increase steadily with the diborane flow rate. Special attention has been given to the reflow properties and the presence of hydrogen bonds that lead to unwanted optical absorption in telecommunication applications. The reflow properties of P-doped SiON layers have been improved by B-doping. A significant material reflow was obtained for BP-doped SiON containing ~ 3 at% P and ~ 5 at% B by heat treatment at 1000°C in N2 atmosphere for 17 hours. Also the sidewall surface roughness of the BP-doped channel waveguides with a refractive index up to 1.51 has been smoothed. Moreover, the hydrogen induced losses have been eliminated at 1000 °C. In that case, the optical losses in the entire range from 1300 to 1600 nm (including the third telecommunication window) are reduced to below 0.2 dB/cm for slab-type BP-doped SiON waveguides. It therefore can be concluded that this material is very promising for applications in low-loss integrated optical devices.