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

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Technical Report,01 Jan 2017,30 Jun 2017

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US Army Research Laboratory Adelphi United States

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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 polymethyl 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.

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