Dependence of pyrocarbon microstructure on the substrate and annealing during the initial stage of chemical vapor deposition

Electron microscopic and electron spectroscopic techniques were applied to study interface properties, microstructure and texture of pyrolytic carbon obtained after short-time chemical vapor deposition (CVD) on planar Si substrates. The pyrolytic carbon was obtained in a hot-wall reactor from methane at a total pressure of 20 kPa and temperature of 1100 °C. Only short depositions between 2.5 and 240 min were performed. The carbon deposition starts with the nucleation of isolated islands. The increase of residence and deposition time leads to the formation of a continuous layer by larger island sizes and higher island densities, a transition from rough to smooth surfaces and formation of pores on smooth surfaces. An increased deposition rate during the first 15 min is observed which is correlated with a granular morphology of the carbon layer. Using BN-covered Si wafers with a surface roughness on a 100 nm scale reduces the texture degree in the vicinity of the interface and strengthens adhesion of the pyrolytic carbon compared to the smooth Si substrate. The texture of high-textured pyrolytic carbon is improved significantly by annealing at 1100 °C.