Novel Polymeric Protective Coatings for Hydrofluoric Acid Vapor Etching During MEMS Release Etch

摘要

MEMS release etching of a sacrificial oxide layer plays an important role in fabricating moving parts in MEMS devices. Traditionally, wet chemistries have been used in order to achieve release etching, but their use can create surface tension issues that can cause the MEMS microstructures to stick together. It has been demonstrated that using hydrofluoric acid (HF) vapor release etching can efficiently circumvent the stiction phenomenon because it substantially eliminates surface tension. Inorganic-based films such as silicon nitride, alumina, SiC, polysilicon, etc., have been used as masking materials that are resistant to vapor HF. These materials require very-high-temperature vacuum deposition techniques that are often lengthy, complicated, and costly. This paper presents novel spin-on polymeric HF-resistant blanket coating materials that protect silicon oxide or metals against HF attack during HF vapor etching. These newly developed polymeric coatings can be processed at lower temperatures (< 250°C) and are applied as thin films (10-15μm) for extended HF vapor etching periods (longer than 1 hour). Hence, these HF vapor-resistant materials will enable the MEMS industry to significantly lower the cost of manufacturing MEMS devices and will significantly simplify the manufacturing process as well.