Wide-spectral range DUV – MIR spectroscopic ellipsometry study of PECVD-grown silicon oxide and nitride thinfims: Wide-spectral range DUV – MIR spectroscopic ellipsometry study of PECVD-grown silicon oxide and nitride thinfims

Thin-film silicon oxide (SiO2), nitride (Si3N4) and silicon oxynitrides (SiOxNy) are the most commonly used materials for photonic integrated circuits, electronics and MEMS devices. Two conventional techniques for thin-film growth of oxides and nitrides include low-pressure chemical vapour deposition (LPCVD) and plasma-enhanced chemical vapour deposition (PECVD). Although LPCVD can provide good quality thinfilms with low-optical-losses, however, the deposition process requires a high temperature (i.e 700 °C), which is not compatible with many electronic, photonic and MEMS devices. Furthermore, the high-temperature process also limits the film thickness due to the increase of tensile stress during the deposition1. PECVD with a low operation temperature (i.e 300 °C) can be a good alternative process for growing CMOS-compatible thin-film oxides and nitrides. In photonic applications, most critical property of thin-film oxides and nitrides is the low-optical-loses, which are intrinsically attributed to interband transitions in the range from deep ultraviolet (DUV) to near infrared region (NIR) and functional bonds (Si-H, N-H) and oxide and nitride phonons (Si-O, Si-N) in the mid-infrared region (MIR). In this study, by mean of comprehensive spectroscopic ellipsometry study in a wide-spectral range covering from DUV (starting from 0.193 µm) to MIR region (25 µm), we experimentally study and optimize low-optical-loss thin-film silicon oxides and nitrides grown by PECVD technique. Complete absorption losses due to interband transitions (modelled by Tauc-Lorentz combined with Gauss oscillators) and chemical bonds and phonons (modelled by Brendel-Borman oscillators2) are simultaneously modelled, providing a full information of complex optical properties of silicon oxide and nitride films. Further rapid thermal annealing (RTA) process from 500 ℃ to 1000 ℃ in ambient gases (N2, Ar) is also extensively investigated to improve optical properties and thinfilm mechanical stress. The results achieved in this study provide an alternative low-optical-loss and low-stress dielectric thinfilm platform for applications in electronic, photonic and MEMS devices.