We have examined the influence of bonded hydrogen on the losses in silicon oxynitride (SiON) planar optical waveguides on silicon substrates having a silicon dioxide buffer layer. In the SiON layer grown by plasma enhanced chemical vapour deposition, hydrogen was mainly bonded to silicon as evidenced by strong absorption at 2160 cm-1. The concentration of bonded hydrogen was reduced from 1.2×1022 cm-3 to 5×1021 cm-3 as the substrate temperature was raised from 100 to 300 °C. The corresponding change in the loss was from 1.5 to 1.2 dB cm-1 at 632.8 nm.
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