Process Development for Reactive-Ion Etching of Molybdenum (MoS2) Utilizing a Poly(methyl methacrylate) (PMMA) Etch Mask

Report No. ARL-TR-8192
Authors: Alin Cristian Chipara; Alexander L Mazzoni; Robert A Burke; Barbara M Nichols; Matthew L Chin; Sina Najmaei; Eugene Zakar; Madan Dubey
Date/Pages: October 2017; 26 pages
Abstract: Previously we have relied on a carbon tetraflouride (CF4) + oxygen (O2) reactive-ion etching recipe (15 sccm CF4, 5 sccm O2, and 200 W) to etch molybdenum disulfide (MoS2). To define locations to be etched, the common electron beam lithography resist poly(methyl methacrylate) (PMMA) is used. However, we have observed that this process can leave a significant amount of PMMA residue on the substrate surface if the PMMA removal process is not aggressive enough. Additionally, this CF4 + O2 process etches silicon dioxide, which is typically used as both the substrate and back-gate dielectric of our 2-D field effect transistors. The PMMA residue tends to form a flap at the edge of the etched region instead of the PMMA particulate matter commonly reported in the 2-D literature. This report details the experiments performed to determine the source of the PMMA residue and the reasoning for switching to a chlorine + O2 process with a secondary, pure O2 step. This process development should be of use to others fabricating devices with 2-D materials or those using PMMA during reactive-ion etching.
Distribution: Approved for public release
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Last Update / Reviewed: October 1, 2017