PMMA-Assisted Plasma Patterning of Graphene

Michael Kaminski,Alfredo D Bobadilla,Jorge M Seminario,Anirudha V Sumant,Leonidas E Ocola

doi:10.1155/2018/8349626

Abstract

Microelectronic fabrication of Si typically involves high-temperature or high-energy processes. For instance, wafer fabrication, transistor fabrication, and silicidation are all above 500°C. Contrary to that tradition, we believe low-energy processes constitute a better alternative to enable the industrial application of single-molecule devices based on 2D materials. The present work addresses the postsynthesis processing of graphene at unconventional low temperature, low energy, and low pressure in the poly methyl-methacrylate- (PMMA-) assisted transfer of graphene to oxide wafer, in the electron-beam lithography with PMMA, and in the plasma patterning of graphene with a PMMA ribbon mask. During the exposure to the oxygen plasma, unprotected areas of graphene are converted to graphene oxide. The exposure time required to produce the ribbon patterns on graphene is 2 minutes. We produce graphene ribbon patterns with ∼50 nm width and integrate them into solid state and liquid gated transistor devices.

Highlights

Working with 2D materials such as graphene requires novel methods to fabricate ribbon patterns
Physical vapor deposition of the metal mask inherently involves high-temperature molecular events and strong binding of the metal to graphene. erefore, we opted for a poly methyl-methacrylate- (PMMA-)based mask, a polymeric material employed in e-beam lithography as a resist
We suggest this is an important factor for which PMMA can show an etching resistance to oxygen plasma as poor as that of graphene. erefore, to find conditions of improved etching resistance for PMMA and for selective patterning of graphene, we should decrease the energy and the number of oxygen ions that initiate the chain reaction

Summary

Introduction

Working with 2D materials such as graphene requires novel methods to fabricate ribbon patterns. Among the traditional methods are a metallic or resist mask to selectively protect graphene in plasma etch exposure [1,2,3,4,5] and focused ionbeam (FIB) etching [6, 7]. Major drawbacks of the traditional methods are the lack of adaptability of FIB for mass production of devices, the usage of harsh acid treatment to remove the HSQ resist [5] or metal mask [9, 11], and overetching of graphene from the edges underneath the metallic ribbon mask [9]. With a HSQ ribbon mask, the resultant width of graphene ribbon pattern is ∼10 nm smaller than the resist mask [8]. Despite its adoption to fabricate quantum dots, the PMMA resist mask has not been widely adopted to make patterns on graphene. A metallic mask is preferred instead of PMMA to make nanoscale patterns with widths or diameters smaller than 50 nm [9, 11, 15]

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