Investigation of TMAH for front-side bulk micromachining process from manufacturing aspect

An investigation on the influence of etchant concentration, dissolving silicon content and additives during silicon anisotropic etching in tetramethyl ammonium. hydroxide (TMAH) has been carried out. Based on the Taguchi method, the etch rates of Si, Al, and SiO2 were measured via under-etch experiments using the wagon-wheel mask pattern. The improvement on the surface quality was observed by agitating the solution under ultrasonic vibration in TMAH solutions with additives. Furthermore, a new approach is developed to reduce wet etching time and to control etched gap depth between the released micromembrane and the silicon substrate. This method employs a polysilicon or an amorphous silicon thin layer embedded between the micromembrane and silicon substrate as a sacrificial layer, then this layer would be fast isotropically etched away by TMAH solution. (C) 2001 Elsevier Science BN. All rights reserved.