Abstract
In the last two decades, MEMS products have deeply permeated our ordinary lives, investing a multitude of markets.
Contemporary world is the answer to Richard Feynman’s question “Which are the possibilities of small but moveable machines?” It was 1959 when he asked this question during one of his famous conferences held at Los Angeles High School, trying to imagine the realization of infinitesimal machines (Feynman R, Plenty of room at the bottom. Talk given to American Physical Society in Pasadena, CA. https://web.pa.msu.edu/people/yang/RFeynman_plentySpace.pdf, 1959). The revolution he imagined has later been driven by MEMS device realization enabled by a new technology: the MEMS micromachining technology.
In MEMS sensors or actuators devices, 3D structures are realized through silicon that can be movable or fixed, as described in Part III and Part IV of the present book. The main geometrical features make the world of MEMS a new one: depths ranging from 1 μm to full wafer thickness (725 μm), in-plane sizes spanning from nanometers to centimeters, ratios between etch depth and feature width reaching up to 70:1 – that is what high Aspect Ratio (AR) means. The silicon patterning must be anisotropic to guarantee a tight CD control, perpendicular to the silicon surface to allow the best device functionality and free from morphological defectiveness. The “carving” approach which fulfills all these requirements is called Dry Deep Silicon Etch.
Two main techniques have been developed to “carve” silicon: Cryogenic (Tachi S, Tsujimoto K, Okudaira S, Appl Phys Lett 52:616–618, 1988 February) and Bosch (Laermer F, Schilp A, Method of anisotropically etching silicon. German Patent No DE4241045, 1993 (US Patent No 5501893, Mar. 26, 1996)), the second one proving to be more versatile and reliable and therefore adopted by ST MEMS R&D Group in Italy since the very beginning of the first ST MEMS platform development.
ST’s deep silicon etch story begins in 1999 with the installation of one of the most innovative 6″ plasma tools developed by STS (Surface Technology System) in partnership with Bosch. Since then, MEMS market has widened its product portfolio and more suppliers appeared on the stage. A lot of development has been done in terms of equipment to follow the continuous demand for plasmas with higher precision and resolution to enhance sensors and actuators performances.
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Alessandri, A., D’Ercoli, F., Petruzza, P., Sciutti, A. (2022). Deep Silicon Etch. In: Vigna, B., Ferrari, P., Villa, F.F., Lasalandra, E., Zerbini, S. (eds) Silicon Sensors and Actuators. Springer, Cham. https://doi.org/10.1007/978-3-030-80135-9_5
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