Silicon oxynitride: a versatile material for integrated optics application

Silicon oxynitride is a very attractive material for integrated optics application, because of its excellent optical properties (e.g., optical loss below 0.2 dB/cm), the large refractive index range (between 1.45 for silicon oxide and 2.0 for silicon nitride), and last but not least, the availability of reliable, low-cost fabrication technologies. Since good uniformity and reproducibility of the layers is extremely important for integrated optics applications, we have optimized the plasma-enhanced chemical vapor deposition and low-pressure chemical vapor deposition technologies of silicon oxynitride with respect to these requirements. Over a 50× 50 mm area on a 3 in. wafer, an inhomogeneity of the refractive index of Deltan<5×10–4 and a nonuniformity of the layer thickness of deltad<1% can be obtained. Furthermore, new challenges such as the conditioning of the reactor, in order to guarantee process reproducibility in the same order of magnitude, are discussed. The high optical loss of silicon oxynitride in the third telecommunication window (wavelength range lambda= 1530-1605 nm), which is caused by the overtones of the Si[Single Bond]H and N[Single Bond]H bonds, was decreased by thermal treatment. Silicon oxynitride waveguides having a refractive index of 1.48 and an optical loss below 0.2 dB/cm (at lambda>=1550 nm) were realized.