C. Vallee, A. Goullet, A. Granier, A. van der Lee, J. Durand, C. Marliere

Inorganic to organic crossover in thin films deposited from O₂/TEOS plasmas

Journal of Non-Crystalline Solids 272 (2000) 163–173

The structure of thin films prepared from O₂/TEOS plasmas in an rf helicon reactor has been investigated using in situ UV-visible spectroscopic ellipsometry and ex situ X-ray, reflectivity, Fourier transform infrared, photoelectron and Rutherford backscattering spectroscopy. It is shown how the structure of the films evolves from an inorganic silica-like structure towards an organic SiO_xC_yH_z framework when the relative proportion of TEOS in the plasma increases. On the one hand, the structure and properties of the silica-like films are shown to be very close to those of a thermal oxide. On the other hand, the organic films have larger refractive index and extinction coefficient but are less dense than the SiO₂-like films. It is shown that the increase in the refractive index and extinction coefficient is correlated to the carbon incorporation into the film. It is further established that the O/Si content ratio is enhanced from about 2 to 2.5 with increasing TEOS volume fraction. This evolution is explained by the increasing number of Si-O-H and Si-O-C_xH_y. bonds in the material at the cost of the number of -Si-O-Si- bonds. It is furthermore shown that the abrupt character of the transition between silica-like and organic films is likely to be correlated to the depletion in oxygen atoms in the plasma.

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