Enhancing interface doping in graphene-metal hybrid devices using H₂ plasma clean

Synthetic graphene suffers from surface contamination after the removal of transfer polymer. This impacts the chemical and electronic properties at the interface of graphene-metal structures. Hydrogen plasma treatment is promising to effectively clean, dope and pattern graphene. However, it also causes irreversible damage to the graphene lattice or reversible graphene hydrogenation which primarily depends on the flux and energy of plasma radicals/ions. Here, we optimize a downstream Ar/H₂ plasma with moderate flux and low energy thermal H radicals to eliminate polymer residues and enhance the charge transfer at the graphene-metal interface. A systematic study is carried out to evaluate the plasma-induced doping and defectivity in ruthenium capped graphene devices. Single layer graphene is found to be n-doped after plasma treatment accompanied by an increase in defect density. Similarly, bilayer graphene (BLG) also undergoes n-doping but does not incur significant plasma-induced damage. Sheet resistance of Ru capped plasma cleaned BLG is found to decrease by 18%. After device fabrication, a final plasma clean reduces the surface roughness of the capping metal, and further improves the electrical conductivity. This study provides a viable basis to effectively clean and dope graphene-metal interface with a fab-compliant plasma technique while preserving the high quality of graphene.