The use of non-standard materials (e.g. specific substrates shapes and dimensions or polymer materials) for MEMS applications imposed a requirement for the development of new techniques for even well-established processes. Acoustic energy in the MHz frequency range has been used in the semiconductor industry for various processes such as photoresist development, substrate cleaning and electro-plating enhancement. The work presented here is focusing on single wafer cleaning and on photoresist development.
The cleaning process developed addresses mainly wafer cleaning prior to wafer bonding processes, in which particle contamination is of crucial importance.
The photoresist development process was developed mainly for thick resist layers development (few hundreds of μm) in order to improve definition of high aspect ratio features but was used as well as a significant process time reduction factor for development of regular thickness resists (few μm).