Fabrication of thick SiO 2 block with dry-released underneath cavity in silicon for RF MEMS

A so-called SiDeox new technology to fabricate a thick silicon oxide layer with an underneath cavity for applications in RF MEMS devices is presented. Photolithography was performed on the silicon substrate with 1.8 µm patterns. Deep reactive ion etching (DRIE) using Alcatel A601E ICP etcher was performed to form 34 µm deep trenches in the silicon substrate. Subsequently, the sidewalls of trenches were passivated in situ and isotropic silicon etching was performed in the ICP chamber to release silicon trenches from the silicon substrate to form an 8 µm cavity. A DRIE etched silicon wafer was then thermally oxidised in the thermal furnace. Silicon beams with width of 1.8 µm were completely oxidised and 2.2 µm trenches were filled with silicon oxide. A silicon oxide block as thick as 36 µm was fabricated with an underneath cavity of 6 µm. There is potential to build RF devices on such a silicon oxide block as substrate to achieve a better quality factor by reducing electric loss.