Optimization of ICPCVD Amorphous Silicon for Optical MEMS Applications

• Published in: Journal of microelectromechanical systems Vol. 24; no. 6; pp. 1998 - 2007
• Main Authors: Tripathi, Dhirendra Kumar, Fei Jiang, Martyniuk, Mariusz, Antoszewski, Jarek, Dilusha Silva, K. K. M. B., Dell, John M., Faraone, Lorenzo
• Format: Journal Article
• Language: English
• Published: New York IEEE 01-12-2015; The Institute of Electrical and Electronics Engineers, Inc. (IEEE)
• Subjects: distributed Bragg reflector (DBR); Integrated optics; Iterative closest point algorithm; Microelectromechanical systems; optical constants; Optical device fabrication; Optical microelectromechanical systems (MEMS); Optical refraction; Optical variables control; Quality; Refractive index; Silicon; silicon-hydrogen bonding; Thin films; optical constants; Optical microelectromechanical systems (MEMS); distributed Bragg reflector (DBR); silicon-hydrogen bonding
• ISSN: 1057-7157; 1941-0158
• DOI: 10.1109/JMEMS.2015.2459066

In this paper, we present the optimization of optical and mechanical properties of inductively coupled plasma chemical vapor deposited (ICPCVD) amorphous silicon thin films for fabrication of high-quality optical microelectromechanical systems-based devices operating from visible to short-wave infrared wavelengths (450-3000 nm). Our results indicate that, at relatively high deposition temperatures for plasma CVD, a decrease in the ICP power results in films with lower tensile stress, higher refractive index, and lower extinction coefficient. We show that hydrogen concentration alone is not a sufficient parameter for controlling optical and mechanical quality of the films. In particular, both the hydrogen concentration and the hydrogen-silicon bonding nature together play a vital role in determining the optical and the mechanical quality of the silicon thin films. As a demonstration vehicle, three layer silicon-silicon oxide-silicon-based distributed Bragg reflectors were fabricated for the visible (500-700 nm), near infrared (700-1000 nm), and short-wave infrared (2000-3000 nm) wavelength ranges using an optimized silicon fabrication recipe. The measured optical transmission spectra show close to 90% peak reflectivity. Finally, stress optimization was evaluated by fabricating 270-μm diameter circular suspended silicon membranes, which demonstrate a flatness variation on the order of <;6 nm across the entire lateral dimension.