Spectroscopic investigation of thermally induced structural evolution of a-C:H:Si film

Temperature-induced evolution of Si-doped hydrogenated amorphous carbon films on Silicon was monitored using Raman, X-ray photoelectron spectroscopy (XPS) with depth profiling, and electron microscopy. XPS showed that carbon on the surface of as-deposited films is present as sp² > SiC > SiC_xO_y > sp³ > C[sbnd]O > C[dbnd]O > COOR. sp² and sp³ carbon decrease with depth and are stable until 600 °C when they evaporate. Carbon rich SiO_xC_y is higher deeper in the sample and is stable up to 450 °C, after which SiO₂ and intermediate oxidation states of Si start to form. SiC is present evenly throughout the film and is stable until 600 °C. After 600 °C nearly all carbon in the film evaporates from the surface to a depth of 63 nm. The ratio of sp² to sp³ is lower on the surface and is constant with temperature until 600 °C. Other carbon oxygen species form as the temperature is increased to 400 °C, above which they evaporate. Carbon atoms leave the surface by gasification between 600 and 750 °C. Raman data strongly supports the XPS conclusions. Optical and electron microscopy shows that at 750 °C the surface of the film is optically different and cracked. The fact that the films were stable up to 600 °C demonstrates the great potential of Si-doped coatings for high-temperature applications.