ARL-TR-8362 - Greyscale Photolithography for Multilayer PZT Microelectromechanical Systems (MEMS) Device Applications | U.S. Army Research Laboratory

摘要

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.