PECVD silicon carbide as a chemically resistant material for micromachined transducers

Plasma enhanced chemical vapor deposited (PECVD) amorphous hydrogenated silicon carbide is a material with many potential applications for micromachined transducers. Specifically, its resistance to etching in a broad range of media such as sulfuric acid/peroxide, hydrofluoric acid and potassium hydroxide make it an excellent choice for use as an encapsulating material for media compatible transducers. This etch resistance also makes it useful as a masking material for intermediate processing steps. Despite this wet chemical resistance, it can be patterned easily in fluorine-based plasmas. A series of trials were undertaken in an attempt to correlate stress, resistivity and wet etch resistance with the following deposition parameters: pressure, CH4 flow rate, low frequency power, low frequency cycle time, high frequency power, and high frequency cycle time. Work to date has demonstrated a CMOS compatible, insulating thin film with a low stress (< 50 MPa) and high etch resistance. Four examples of its application are presented: an electrochemical probe, a fully packaged, encapsulated pressure sensor, a sealed and coated microfluidic channel, and deep-etched channels in glass.