Optical properties of nitride-rich SiNx and its use in CMOS-compatible near-UV Bragg filter fabrication

Nitride-rich silicon-nitride (SiN${}_x$) is being explored for its potential as a suitable optical material for use in microsystems operating in the near-UV spectral range. Although silicon-rich SiN${}_x$ is widely accepted as a CMOS-compatible dielectric and micromechanical material, its optical absorption limits application to the visible to near-IR spectral range. However, this work shows that a balance can be achieved between a sufficiently high index of refraction ($n>$ 2) and an acceptable optical loss ($k<10^{-3}$) in nitride-rich SiN${}_x$ of appropriate composition ($x\sim 1.45$). Bragg reflectors with a design wavelength at ${\lambda }_o$= 330 nm are used for validation. PECVD is used for sample preparation and experiments confirm that the spectral range available for use of SiN${}_x$-based optical microsystems extends to wavelengths as low as 300 nm.