Wet Etching Studies of PECVD Silicon Nitride Films in Doped TMAH Solutions

Abstract

It has been reported that the etch rate of exposed aluminum lines and pads on MEMS chips can be significantly reduced by dissolving an appropriate amount of silicon (or silicic acid, water glass) and ammonium persulfate (AP) in TMAH solution. However the etch rates of the PECVD silicon nitride films，which is usually underlying aluminum lines and pad, were rarely reported in previous literatures. In this paper, silicon nitride films of high compressive stress, low compressive stress, micro-stress, low tensile stress and high tensile stress are prepared by adjusting the flow ratio of SiH4 to NH3 and plasma power. Then the films are etched in four kinds of previously reported doped TMAH solutions. The experimental results show that silicon nitride films depositing at low flow ratio of SiH4 to NH3 and lager RF power were etched more slowly in doped TMAH solution than that of depositing at high flow ratio of SiH4 to NH3 and low RF power.