PLASMA-ENHANCED CHEMICALLY VAPOR-DEPOSITED SI3N4 THIN-FILMS FOR OPTICAL WAVE-GUIDES

Silicon nitride films for applications in optical waveguides have been deposited by plasma-enhanced chemical vapour deposition (PECVD). Index of refraction, deposition rate, buffered HF etch rate and hydrogen content have been measured for different NH3-to-SiH4 ratios of precursor gases in the range 0.6-10. Results show that these magnitudes are nearly constant for 2 less-than-or-equal-to NH3:SiH4 less-than-or-equal-to 4. Thermal annealing of films deposited al high NH3:SiH4 ratios yields a large reduction (up to 70%) in the N-H bond concentration as well as a densification of the films. Finally, geometrical parameters necessary for the design of rib-type monomode optical waveguides based on the PECVD silicon nitride films were calculated.