Tunable Fabry-Pérot cavities fabricated from PECVD silicon nitride employing zinc sulphide as the sacrificial layer

Abstract

The construction of self-supporting and suspended structures is one of the fundamental challenges of microelectromechanical systems (MEMS). Many technologies have been developed for the fabrication of such structures, which can be categorized into bulk or surface micromachining. Generally surface micromachining techniques rely on a high-temperature deposition process such as low pressure chemical vapour deposition to produce high-quality films. Plasma enhanced chemical vapour deposition (PECVD) can be used to deposit films at temperatures less than 300 • C. PECVD of silicon nitride has not been used extensively in MEMS structures due to the material limitations created via the deposition technique, primarily controllability of the intrinsic stress and etch selectivity of the deposited film. We show here that PECVD silicon nitride can be used successfully in MEMS structures, and that the intrinsic stress is controllable through variations in the PECVD deposition parameters. A MEMS-based Fabry-Pérot cavity has been fabricated using PECVD silicon nitride as the membrane layer with ZnS as the sacrificial material. Devices with an initial 1 µm cavity length typically provide a displacement of 240 nm across a 380 µm membrane span for an applied bias of only 1.6 V.

Silicon Nitride Films Deposited by RF Sputtering for Microstructure Fabrication in MEMS

“…4,5 More recently, the application of silicon nitride films has been extended to structural materials in microelectromechanical system (MEMS) devices. [6][7][8][9] Silicon nitride films can be prepared by a variety of methods such as low-pressure chemical vapor deposition (LPCVD), 10,11 plasma-enhanced CVD (PECVD), 12,13 pulsed laser ablation, 14 reactive evaporation, 15 and sputtering. 16,17 Conventionally, high-quality stoichiometric silicon nitride films are obtained by the LPCVD process at temperatures in excess of 700°C.…”

Effect of deposition conditions on mechanical properties of low-temperature PECVD silicon nitride films

“…More recently, the application of silicon nitride thin films has been extended to structural materials in micro-electro-mechanical systems (MEMS) devices, e.g., support structures for tunable mirrors in Fabry-Perot filters [3,4]. PECVD processes enable the deposition of silicon nitride thin films at much lower temperatures than those deposited by low-pressure chemical vapor deposition (LPCVD).…”

Properties of Rf Plasma Nitrided Silicon Thin Films at Different Rf Plasma Processing Powers

“…The decreasing refractive index with increasing rf plasma processing power is likely to be caused by an increase of the band gap (E g3 ) as well as by a change in the bucking density. This study showed that it is possible to transform Si thin films gradually into nitrides compound thin films, as important materials for both microelectronics and integrated optics such as thin windows for biomedical microdevices [40], blocks for integration of rf devices [41] and microelectromechanical systems [42], by controlling the rf plasma processing power.…”