NUMERICAL SIMULATION TO STUDY THE EFFECT OF BIASING AND TEMPERATURE ON CARBON DEPOSITION DURING GRAPHENE GROWTH USING Ar/C2H2/H2 IN PECVD

Abstract

Graphene is excellent material in sense of their wide range of applications in electronic devices as ultrafast transistors, electron field emitters, microelectrochemical systems, biochemical operations, optoelectronics, composite materials, photovoltaic cells, and energy storage etc. such extraordinary applications are due to unique geometry, high mechanical strength, high thermal and electrical properties, high chemical stability and impermeability. There are various synthesis techniques for the synthesis of graphene. The most commonly used and effective technique is chemical vapor deposition. Among various CVD techniques, Thermal Chemical Vapor Deposition and Plasma Enhanced Chemical Vapor Deposition are currently using throughout. Among these two CVD techniques, Thermal CVD systems are used at industrial level for large-scale synthesis of CNTs and Graphene. But there is one drawback with Thermal CVD is that the temperature in the chamber, especially near the substrate increase up to a very high value that the substrate decomposes thermally and left unusable for further use. In this case, Plasma Enhanced CVD techniques come into use as the temperature in the PECVD chamber does not exceed above 600oc. PECVD technique can be worked in low temperature while the deposition rate is equivalent to other CVD forms.

In this study, we have simulated the Plasma enhanced CVD to grow a horizontal planar layer of graphene on the substrate and vertically aligned graphene at the edges of the substrate. The graphene sheets were deposited on 200nm thick nickel catalyst sheet on a silicon substrate from 300K to 723K using acetylene (C2H2) as the carbon source in an argon V

(Ar) and hydrogen (H2) atmosphere. Ionization of Argon gas takes place by transformer action leading to the generation of plasma. Under the effect of the plasma, the carboncontaining gas goes through both ion-induced and thermal decomposition. The plasma also causes the nickel catalyst film to turn into nanoparticles, which acts as the active sites for carbon cluster or island formation. As the carbon fluxes reach the catalyst they diffuse into the catalyst nanoparticles and when they cool down, cluster or island formation occurs. The dispersion of these islands or cluster leads to the formation of the graphene layer. As the biasing of substrate increases from zero bias to -50 V DC the effective etching of catalyst surface increases, leading to decrease in thickness of planar graphene as well as a reduction in height of vertical graphene at the edges. Increase in temperature allows more carbon fluxes to diffuse into the catalyst nanoparticles, leading to increase in the thickness of planar graphene as well as vertically aligned graphenes at the edges.