A simple method for effectively restrain electrochemical corrosion of polycrystalline silicon by HF-based solutions

A simple method is described to protect polycrystalline silicon (polysilicon) from electrochemical corrosion which often happens when the Micro-Electro-Mechanical systems (MEMS) device is released in HF-based solutions, especially when the device contains noble metal. We propose to employ a photoresist (PR) layer to cover the noble metal layer, which electrically contacts with the underlying polysilicon layer. This PR cover can prevent HF-based solution from diffusing through and arriving at the surface of the noble metal, thus cut off the electrical current of the electrochemical corrosion and thus protect the polysilicon layer intact. The polysilicon layer can be protected longer than 80 min in 49% HF solutions by 3 μm thick AZ6130 photoresist. This approach is not only simple, effective, IC technology compatible, and suitable for batch fabrication, but also can significantly improve the performance of MEMS devices.