Reduction of hydrogen-induced optical losses of plasma-enhanced chemical vapor deposition silicon oxynitride by phosphorus doping and heat treatment

Abstract

Plasma-enhanced chemical vapor deposition phosphorus-doped silicon oxynitride (SiON) layers with a refractive index of 1.505 were deposited from N2O, 2% SiH4∕N2, NH3, and 5% PH3∕Ar gaseous mixtures. The PH3∕Ar flow rate was varied to investigate the effect of the dopant to the layer properties. We studied the compositions and the chemical environment of phosphorus, silicon, oxygen, nitrogen, and hydrogen in these layers by using x-ray photoelectron spectroscopy and Fourier transform infrared spectroscopy. The number of N–H and O–H bonds, which are responsible for optical losses around 1.55 and 1.3μm, decreases in the as-deposited layers with increasing phosphorus concentration. Furthermore, the bonded hydrogen in all P-doped layers has been eliminated after annealing at a temperature significantly lower than required for undoped silicon oxynitride layers, that is to say 1000°C instead of 1150°C. The resulting optical loss in the entire third telecommunication window was well below 0.2dB∕cm, making P-doped SiON an attractive material for demanding integrated optics applications.