Greyscale Photolithography for Multilayer PZT Microelectromechanical Systems (MEMS) Device Applications

Report No. ARL-TR-8362
Authors: Delaney M Jordan, Robert R Benoit, Gabriel L Smith, Ronald G Polcawich
Date/Pages: May 2018; 26 pages
Abstract: We present development of a process to perform greyscale photolithography on a 2.55-μm 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-μm thickness or 0.5-μm 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 cure/bake temperature were optimized to produce the best greyscale profile through the thickness of the resist.
Distribution: Approved for public release
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Last Update / Reviewed: May 1, 2018