[13p-P5-1~64] 17 Nanocarbon Technology（Poster）

▲ [13p-P5-50] Formation of high quality Al₂O₃ gate dielectrics on epitaxial graphene using microwave-assisted annealing

〇(DC)KwanSoo Kim¹, GoonHo Park¹, Fukidome Hirokazu¹, Suemitsu Tetsuya¹, Otsuji Taiichi¹, Suemitsu Maki¹ (1.RIEC, Tohoku Univ.)

Keywords:Graphene, Microwave annealing

Epitaxial graphene on SiC is promising for fabrication of graphene field-effect transistors (GFETs) because it is formed by a direct growth on large size substrates and requires no transfer procedures. For development of high performance GFETs, it is essential to form a high quality gate dielectric layer without degrading the pristine properties of graphene. There are however several critical restrictions in the formation of gate dielectric layers on graphene, due, for instance, to generation of defects by plasma processing, onset of hole doping during high-temperature annealing, and a need for a surface modification before the ALD process. To overcome these limitations, we have been investigating a solution-based formation of an Al₂O₃ layer (sol-Al₂O₃). In the solution process, a thermal decomposition process is most important. If residual solvent or stabilizer fragments remain in the film, they can cause significant degradation of its dielectric properties. This is the reason why the thermal decomposition process is normally carried out at high temperature using furnace annealing. At these high temperatures, however, hole doping and mechanical modification of graphene will occur. In this study, we have examined a microwave annealing instead of the thermal annealing. We prepared EG on the Si-face of a 6H-SiC substrate by heating the sample under Ar atmosphere. After spin-coating a sol-Al₂O₃ layer on EG, we immediately exposed the samples to O₂ plasma to remove residual chemicals. We then annealed the sample using a household microwave oven at a fixed frequency of 2.45 GHz. We analyzed the peak positions of G and G’ bands of Raman scattering spectroscopy for various microwave-assisted annealing conditions after formation of a sol-Al₂O₃ layer, which conveys information on the hole doping concentration and the strain. Raman spectrum of the initial EG shows both G-band around 1596 cm^-1 and G’-band around 2714 cm^-1. After the microwave annealing at 1000 W, no change was observed in the doping concentration and in the strain. To evaluate the chemical composition of the Al₂O₃ films, we carried out an XPS analysis. We confirmed that hydroxyl- and carboxyl-related components are effectively eliminated by microwave-assisted annealing. MOS capacitors were also fabricated to evaluate the electrical properties. After the microwave-assisted annealing, we confirmed that the sol-Al₂O₃ layer shows sufficiently small leakage currents (~7.2x10^-10 A) and high dielectric constants (~7.5). Therefore, we conclude that the solution process combined with the microwave-assisted annealing is very effective in forming high quality sol-Al₂O₃ layer for EG-FETs.