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

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 SiOxCyHz 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–CxHy 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.