20 January 2015 Bilayer lift-off process for aluminum metallization
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Recently published reports in the literature for bilayer lift-off processes have described recipes for the patterning of metals that have recommended metal-ion-free developers, which do etch aluminum. We report the first measurement of the dissolution rate of a commercial lift-off resist (LOR) in a sodium-based buffered commercial developer that does not etch aluminum. We describe a reliable lift-off recipe that is safe for multiple process steps in patterning thin (<100  nm) and thick aluminum devices with micron-feature sizes. Our patterning recipe consists of an acid cleaning of the substrate, the bilayer (positive photoresist/LOR) deposition and development, the sputtering of the aluminum film along with a palladium capping layer and finally, the lift-off of the metal film by immersion in the LOR solvent. The insertion into the recipe of postexposure and sequential develop-bake-develop process steps are necessary for an acceptable undercut. Our recipe also eliminates any need for accompanying sonication during lift-off that could lead to delamination of the metal pattern from the substrate. Fine patterns were achieved for both 100-nm-thick granular aluminum/palladium bilayer bolometers and 500-nm-thick aluminum gratings with 6-μm lines and 4-μm spaces.
© 2015 Society of Photo-Optical Instrumentation Engineers (SPIE)
Thomas E. Wilson, Thomas E. Wilson, Konstantin A. Korolev, Konstantin A. Korolev, Nathaniel A. Crow, Nathaniel A. Crow, } "Bilayer lift-off process for aluminum metallization," Journal of Micro/Nanolithography, MEMS, and MOEMS 14(1), 014501 (20 January 2015). https://doi.org/10.1117/1.JMM.14.1.014501 . Submission:

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