Reliable processing of graphene using metal etchmasks

Abstract

Graphene exhibits exciting properties which make it an appealing candidate for use in electronic devices. Reliable processes for device fabrication are crucial prerequisites for this. We developed a large area of CVD synthesis and transfer of graphene films. With patterning of these graphene layers using standard photoresist masks, we are able to produce arrays of gated graphene devices with four point contacts. The etching and lift off process poses problems because of delamination and contamination due to polymer residues when using standard resists. We introduce a metal etch mask which minimises these problems. The high quality of graphene is shown by Raman and XPS spectroscopy as well as electrical measurements. The process is of high value for applications, as it improves the processability of graphene using high-throughput lithography and etching techniques.

Figure 1

Characterisation of as transferred graphene on SiO₂ substrates. On left XPS spectrum shows good quality graphene, on right AFM image shows presence of large flakes of graphene with some contamination (marked by circles) and cracks (marked by rectangles). The Raman spectrum of monolayer graphene obtained from the sample is shown in inset.

Figure 2

Schematic of processing for graphene. In first step, graphene is transferred on to suitable substrates and Ni etch mask is created on it in second step. Plasma etching and removal of Ni produced patterned graphene, which is then contacted in the last step using standard liftoff process.

Figure 3

On the right severe delamination of graphene caused by resist (blue) removal. With metal mask no delamination occurs as shown on left (scale bar represents 10 μm). The inset shows typical Raman spectrum of etched graphene, note the smaller barely noticeable D peak (approx. 1350 cm^-1) compared to Figure 1.

Figure 4

Graphene ribbons contacted from top on Al₂O₃ substrates with nickel contacts. The FET measurements were taken between two inner electrodes as source and drain, and substrate was gated from back. On the right, an I_sd - V_g characteristic of the device is shown at V_sd of 50 mV.