Fabricating processes of free-standing silicon nitride thin film for MEMS devices

In this paper, experiments were carried out to fabricate a kind of free-standing silicon nitride thin film which was applied to many MEMS devices, especially for the gas flow sensors and Pirani. A series of manufacturing processes were researched and optimized to obtain perfect experimental results. LPCVD silicon nitride, dry etching silicon nitride and wet etching silicon were carefully studied in the experiments.1 um thick SiN layer was deposited on the double-sides polished silicon wafer. ICP was employed to obtain the corrosion windows. Results showed that etching rates of the SiN and Si are 0.17 um/min and 1.18 um/min respectively. Wet etching process with the conditions of 30% KOH solution at 85°C was applied to release the SiN films from the substrate. Wet etching rate was about 0.817 um/min. The chromium (50nm) and platinum (200nm) layers were sputtered onto the SiN layer which acted as resistances in the test circuits. Finally, many ideal metallized free-standing silicon nitride films were fabricated on the single wafer surface. Without doubt, it may have a long-term positive impact on MEMS development and applications.