In Pecvd Preparation Of Ac: F: N Film Structure And Stability

a-C:F (fluorinated amorphous carbon) film is an important kind of low dielectric material used in ULSI (ultra-large scale integrated ) circuit. Its thermal stability temperature is required to meet the demand of damascene process (400℃). However, there exists a negative constrained relationship between the low dielectric constant and fine thermal stability of a-C:F film. Therefore, how to improve its thermal stability while keeping its low dielectric constant becomes a focus nowadays.In this thesis, two groups of multiplex gases (CF₄/CH₄/Ar and CF₄/CH₄/N₂) are used to prepare a-C:F and a-C:F:N films on polished silicon slices and quartz slices by PECVD method, and the prepared films are annealed. The thickness of the film before and after annealing is measured by ellipsometer. The thermal stability is expressed by the changing rate of thickness, which shows that the thermal stability of a-C:F film can be improved by changing deposition temperature, power of radio frequency and annealing temperature, but the alteration is very limited.This thesis mainly studies the influence of nitrogen incorporation on the thermal stability of a-C:F film. After being annealed, the thickness changing rate of a-C:F:N film is less than that of a-C:F film, which indicates that nitrogen incorporation is effective in improving the thermal stability of a-C:F film. The result of FTIR analysis shows that nitrogen doped a-C:F film forms the a-C:F:N film. Meanwhile, the FTIR and Raman analysis shows that the content of sp bond mode in the film obviously rises after nitrogen incorporation, which provides solid evidence that nitrogen incorporation actually improves the thermalstability of a-C:F film.The relationship between absorption coefficient (a) of a-C:F film and photon energy (hi)) is analyzed according to UV-VIS transmitted spectrum, and the optical bandgap is consequently aquired. The essential reason of changes of the optical bandgap is interpreted according to the cluster mode raised by Robertson. The relationship between optical bandgap and thermal stability of film is described, which shows that both rising deposition temperature and increasing flow rate can improve the thermal stability of films, but it will keep unchanging when the deposition temperature and flow rate rise to a certain level.