Gas pressure dependence of optical and mechanical properties in a SiCO thin film for optical waveguide by reactive sputtering method

Abstract

In this study, the gas pressure dependence of optical and mechanical characteristics in reactive sputtered SiCO thin films for optical guided-wave pressure sensors was experimentally investigated. Thin films were fabricated by varying the gas pressure from 0.3 to 1.0 Pa at an oxygen flow ratio of 6%, and the gas pressure dependences was clarified. As the gas pressure increased, the optical bandgap of the SiCO thin film increased, resulting in a transparent SiCO films. On the other hand, the refractive index, young's modulus, and hardness decreased with increasing gas pressure. Combining this dependence with the oxygen inflow ratio dependence of the previous study, the first-order approximation formula for the gas pressure and oxygen flow rate ratio for various film characteristics was obtained. Based on this equation, trajectories of equal bandgaps and equal young's moduli on the oxygen flow ratio—gas pressure plane were created on the oxygen influx ratio-gas pressure coordinates, making it easy to fabricate waveguides with desired characteristics.