A novel low thermal budget technique is proposed for the preparation of thermally isolated silicon membranes. The selective formation of porous silicon in a p-type silicon wafer results in an undercut profile below the implanted n-type silicon regions. The sacrificial porous layer is subsequently removed in a dilute KOH solution. A non-stoichiometric LPCVD nitride layer combination forms the suspension of the single-crystalline silicon membranes. This technique eliminates the need for epitaxial substrates and backside alignment, and proves to be very efficient in the realization of a high-temperature micro-hotplate operating with minimum power consumption for the purpose of integrated gas sensors.
Ducso, C., Vazsonyi, E., Adam, M., Szabo, I., Barsony, I., Barsony, I., ... van den Berg, A. (1997). Porous silicon bulk micromachining for thermally isolated membrane formation. Sensors and actuators. A: Physical, 60(60), 235-239. https://doi.org/10.1016/S0924-4247(97)01384-8