Anodic Silicon Dioxide as a Mask Material for the Fabrication of Microstructures in Surfactant Added TMAH

In the microelectromechanical system (MEMS) fabrication, silicon dioxide (SiO2) thin films are most widely used for different applications such as etch mask, structural and sacrificial layers. One of the widespread applications is etch mask in alkaline etchants. In the synthesis of silicon dioxide thin films anodic oxidation method offers several advantages over the conventional deposition techniques such as room temperature deposition, low cost, simple experiment setup, etc. The present work aims to explore anodic SiO2 thin films as etch mask material in surfactant added tetramethylammonium hydroxide (TMAH) solution for the fabrication of MEMS structures with sharp convex corners. Anodic oxidation of silicon is employed to grow oxide thin films at wafer-scale at room temperature. Thickness uniformity and refractive index are measured using ellipsometry. Etch rate of the oxide is investigated in 0.1% v/v of surfactant (Triton X-100) added 25 wt% TMAH at three different temperatures. Furthermore, the etch rate, etched surface morphology and undercutting at convex corner of {100} silicon wafer are investigated. Optical microscope is employed to inspect the etched surface morphology of {100} silicon and also to check the quality of the etched oxide surface. Undercutting and etch depth are measured using a 3D measuring laser microscope