Fabrication of suspended membranes for thermal sensors using high-density plasma etching

In this work, we describe a front-side Si micromachining process for the fabrication of suspended membranes for thermal sensors. Membrane release is achieved by means of lateral isotropic etching of the bulk silicon substrate, the etching being optimised for high rates and high selectivity with respect to the membrane material and the photoresist that is used to protect the device. Lateral Si etch rates of the order of 6-7 mum/min have been achieved in a high-density F-based plasma, which permit a reasonable etching time for the release of the membrane and the simultaneous formation of the cavity underneath that ensure thermal isolation of the final device.