PLASMA-ENHANCED CHEMICAL VAPOR-DEPOSITION OF LOW-LOSS SION OPTICAL WAVE-GUIDES AT 1.5-MU-M WAVELENGTH

Good optical-quality SiON layers deposited upon a SiO2 buffer layer placed upon silicon wafers have been obtained by using plasma-enhanced chemical vapor deposition from SiH4, NH3, and N2O. Optical planar waveguides with a thickness of 5-mu-m and a refractive index of 1.470 have been deposited and investigated in the wavelength region of 1.3-1.6-mu-m. Three absorption bands at 1.40, 1.48, and 1.54-mu-m have been detected and interpreted as Si-OH, N-H, and Si-H vibrational modes, respectively. Absorption losses of 3.8 dB/cm at 1.4-mu-m and 3.2 dB/cm at 1.51-mu-m have been measured. A mild annealing at approximately 800-degrees-C completely removes the band at 1.40-mu-m, whereas strong reduction of absorption at 1.51-mu-m requires 3 h of annealing at 1100-degrees-C. As a result, propagation losses of 0.36 to 0.54 dB/cm have been measured at 1.54-mu-m wavelength.