18 May 2009 Silicon oxide sacrificial layers deposited by pulsed-DC magnetron sputtering for MEMS applications
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Abstract
Surface micromachining requires the use of easily-removable sacrificial layers fully compatible with all the materials and technological processes involved. Silicon dioxide films, thermally grown on silicon substrates or deposited by CVD, are commonly used as sacrificial layers in surface micromachining technologies, despite their low lateral etch rate in conventional fluorinate solutions. The development of silicon oxide layers with high etch rates poses a great technological challenge. In this work we have investigated the possibility of obtaining easily removable silicon oxide layers by pulsed-DC magnetron reactive sputtering. We have carried out a comprehensive study of the influence of the deposition parameters (total pressure and gas composition) on the composition, residual stress and lateral etch rate in fluorine wet solutions of the films. This study has allowed to determine the sputtering conditions to deposit, at very high rates (up to 0.1 μm/min), silicon oxide films with excellent characteristics for their use as sacrificial layers. Films with roughness around 5 nm rms, residual stress below 100 MPa and very high etch rate (up to 5 μm/min in the lateral directions), around 70 times greater than for thermal silicon oxide, have been achieved. The structural characteristics of these easily removable silicon oxide layers have been assessed by infrared spectroscopy and atomic force microscopy, which have revealed that the films exhibit some kind of porous structure, related to very specific sputter conditions. Finally, the viability of these films has been demonstrated by using them as sacrificial layer in the fabrication process of AlN-based microresonators.
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Sheila González-Castilla, Sheila González-Castilla, Jimena Olivares, Jimena Olivares, Marta Clement, Marta Clement, Lucía Vergara, Lucía Vergara, Laura Pulido, Laura Pulido, Enrique Iborra, Enrique Iborra, Jesús Sangrador, Jesús Sangrador, } "Silicon oxide sacrificial layers deposited by pulsed-DC magnetron sputtering for MEMS applications", Proc. SPIE 7362, Smart Sensors, Actuators, and MEMS IV, 73620X (18 May 2009); doi: 10.1117/12.821485; https://doi.org/10.1117/12.821485
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