Fabrication of thick silicon dioxide layers using DRIE, oxidation and trench refill

This paper reports a new method of fabricating very thick (10-100 /spl mu/m) silicon dioxide layers without the need for very long deposition or oxidation. DRIE is used to create high aspect ratio trenches and silicon pillars, which are then oxidized and/or refilled with LPCVD oxide to create layers as thick as the DRIE allows. Stiffeners are used to provide support for the pillars during oxidation. Thermal tests show that such thick silicon dioxide diaphragms can effectively thermally isolate heated structures from neighboring structures within a distance of hundreds of microns. The thermal conductivity of the thick SiO/sub 2/ is measured to be /spl sim/1.1 W/(m/spl middot/K). Such SiO/sub 2/ diaphragms of thickness 50-60 /spl mu/m can sustain an extrinsic shear stress up to 3-5 MPa.