The exposed silicon oxide layer is dry etched (AMI ETCH P-5000). Then, with the photoresist and silicon oxide masks, the underneath silicon is etched (~2.12 µm DRIE Alcatel 601E) by using a quasi-isotropic etching recipe to define the pillars. Once defined the structures, the photoresist is removed. Finally, the wafer is 1.5-µm-thick thermally oxidized to convert the silicon anchoring structures onto silicon oxide structures.