Research On Hydrogenated Amorphous Carbon Films

Amorphous carbon films were hygrogenated amorphous and microcrystal carbon films composed of sp2C and sp3C. Amorphous carbon films attracted extensive attention for its outstanding properties such as high hardness, anti wear-resistance, low friction coefficient, optical transparency and chemical inertness. It has widespread applications, for example, protective coatings, wear coatings, optical windows, magnetic storage devices, field emission and solar cell. In this thesis, amorphous carbon films were deposited on silicon (111) substrate by microwave plasma chemical vapor deposition with a mixture of acetylene and hydrogen. Effects of flow ratios, microwave power and deposition pressure on surface morphology, structure and growth rate of amorphous carbon films were studied. Finally, the thermal stability of amorphous carbon films was investigated by annealing disposal. X-ray diffraction and Raman spectroscopy were used to detect the structure of the films. Scan probe microscopy and Surface profiler were used to analyze the surface morphology and the thickness of the films.Our results indicate that flow ratios can greatly affect the properties of amorphous carbon films deposited by microwave plasma chemical vapor deposition. Hydrogen in the reactive gas plays a crucial role in the deposition of amorphous carbon films. Proper amount of hytrogen can improve the density of grains and increase the deposition rate. Excessive hydrogen will form polymeric hydrocarbon clusters in the films and reduce deposition rate. By changing the flow ratios (H2/C2H2), we can obtain the three-phase amorphous carbon films of graphite-like, diamond-like and polymer-like. With the increase of flow ratios, amorphous carbon films can change from graphite-like phase to diamond-like phase, and finally, to polymer-like phase. Different kinds of amorphous carbon films have different sp3C contents, films hardness, internal stress and optical gaps. Therefore, this experimental result has an important significance for industrial applitcations.With the microwave power increase, the energy of plasma and the ionized degree of reactive gas increase. So deposition rate increases at the high density of plasma. More and more particles were deposited and formed together. Thus, surface morphology of amorphous carbon films exhibits as plate and smooth. Lots of particles combine and clusters appear when the power increases.When we increase the deposition pressure, the diameter of the plasma ball becomes smaller. The density and the number of particle improve in identity time and area. This means that more and more particles can deposit on the substrate and deposition rate increases. Annealing does not seem to change the surface morphology or the film structures. The phase transitions are not found during the different annealing temperatures. Amorphous carbon films show a good thermal stability.