In situ observation and analysis of wet etching process for micro electro-mechanical systems

Details of the etching of polysilicon sacrificial layers using a KOH etching solution have been studied. Etching rates showed strong dependence on KOH concentration and the structure pattern of the layers. For the clarification of the etching process, in situ observation of an etching process for various micro-membrane structures with polysilicon sacrificial layers has been done. Etching observation equipment was created for this purpose. The equipment is capable of monitoring and recording the etching process in situ under various etching conditions such as temperatures, flow rates and concentrations. It is shown from in situ observation that hydrogen bubbles play an important role in supplying fresh etching solution to the surface to be etched away. Repeated accumulation and exhaust of hydrogen bubbles cause strong oscillatory movement of the membrane structures. This movement results in the fracture of the membrane due to the increase in membrane stress. Based on these results, a system for in situ observation and stress analysis of a wet etching process is proposed