A technique is presented that provides planarization after a very deep etching step in silicon. This offers the possibility for not only resist spinning and layer patterning but also for realization of bridges and cantilevers across deep grooves or holes. The technique contains a standard dry film lamination step to cover a wafer with a 38 mu m thick foil. Next the foil is etched back to the desired thickness of a few micrometres. This thin film facilitates resist spinning and high-resolution patterning. The planarization method is demonstrated by the fabrication of aluminium bridges across a deep groove in silicon.
Spiering, V. L., Berenschot, J. W., Elwenspoek, M. C., & Fluitman, J. H. J. (1995). Sacrificial wafer bonding for planarization after very deep etching. Journal of microelectromechanical systems, 4(3), 151-157. https://doi.org/10.1109/84.465120