Greyscale Photolithography for Multilayer PZT Microelectromechanical Systems (MEMS) Device Applications
Technical Report,01 Oct 2016,31 Aug 2017
US Army Research Laboratory Adelphi United States
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We present development of a process to perform greyscale photolithography on a 2.55-m thick photoresist in order to transfer tiered and sloped structures into multilayer thin films using a single-ion mill etch. Applications include access to buried layers, such as electrodes in a stack of multilayer lead zirconate titanate PZT, or ramps for routing signal lines over large step heights. Current state-of-the-art processing requires a separate photolithography step and an ion mill etch for each layer of the substrate, which can be costly and time-consuming. The greyscale process was tested on three silicon wafers with a stack of four PZT thin film layers of either 0.25-micrometer thickness or 0.5-micrometer thickness per layer, with platinum or iridium oxide IrO2 electrodes above and below each layer. Process variables including resist rehydration, focus of the exposure, and UV curebake temperature were optimized to produce the best greyscale profile through the thickness of the resist.
- Fabrication Metallurgy