Microelectromechanical systems (MEMS) device manufacturers today are faced with the challenge of protecting electronic circuitry and other sensitive device structures during deep silicon wet-etch processes. Etch processes of this nature require prolonged exposure of the device to harsh corrosive mixtures of aqueous acids and bases at higher than ambient temperatures. A need exists for a spin-applied polymeric coating to prevent the exposure of such circuitry against the corrosive etchants. The challenge exists in developing protective coatings that will not decompose or dissolve in the etchants during the etch process. Such coatings require superior adhesion to the substrate without destroying the sensitive features below. Brewer Science, Inc., has developed a multilayer coating system for basic etchants which is compatible with a variety of semiconductor materials and offers protection against concentrated potassium hydroxide (KOH) etchants at prolonged exposure times of more than 8 hours. In addition, a second multilayer coating system is being developed for use with strong hydrofluoric and other various mixed acid etchants (MAEs) for exposures of 30 minutes or longer. These materials are specifically designed to protect circuitry subjected to concentrated MAEs during the wafer thinning processes used by MEMS device manufacturers.
A need exists for spin-applied polymeric coatings to protect electronic circuitry and other sensitive structures on MEMS devices during deep silicon wet etching processes involving corrosive mixtures of aqueous acids and bases. The challenge exists in developing protective coatings that do not decompose or dissolve in the harsh etchants and, more importantly, that maintain good adhesion to the substrate during the sometimes long etching processes. We have developed a multilayer coating system that is stable and adheres well to silicon nitride and other semiconductor materials and affords chemical protection for at least eight hours in hot potassium hydroxide etchant. The same coating system is also compatible with concentrated hydrofluoric acid etchants, which can diffuse rapidly through many polymeric materials to attack the device substrate.