Nano-structured diffractive optical elements on SiN_X membrane for UV-visible regime applications

Silicon nitride (SiN_X) film is a commonly used material in silicon technology. In addition, it has excellent optical properties. It is transparent in both the UV and visible range, with a high refractive index of about 1.7-2. Owing to its superior mechanical and optical properties, we used a silicon nitride membrane as an optical phase element. We will fabricate nano-structured diffractive optical elements, such as wave-plate, polarizer, and polarized beam splitter on SiNXHY membrane by e-beam lithography for the UV-visible regime applications. The SiNXHY membranes were made from SiNXHY films deposited by an plasma enhanced chemical vapor deposition (PECVD) as an alternative method for low stress membrane fabrication used in UV-visible transmittance. The stress of silicon nitride film showed a change from compressive to tensile with increasing working pressure during film deposition. The UV-visible transmittance of the free standing membrane was measured, which showed that UV light is transparent at wavelength as short as 240nm. We will show the feasibility to fabricate nano-structured diffractive optical elements on the SiNXHY membrane combined with microoptoelectromechanical systems (MOEMS) technology for the application in the UV-visible regimes.