Characterisation of thin LPCVD silicon-rich oxide films

Thin silicon rich oxide (SiO x) films were deposited using the LPCVD (Low Pressure Chemical Vapour Deposition) method. Silane diluted in argon and oxygen were used as the reactant gasses, and the deposition temperature was kept constant at 570 °C. The films were deposited on silicon (111) and on fused silica substrates. Films with the different values of the oxygen content were deposited by varying the ratio of the flows of oxygen and silane in the horizontal tube reactor. The films were characterized in terms on the surface quality (by X-ray specular reflectivity and scanning electron microscopy) and in terms of the oxygen content x (by time of flight elastic recoil detection analysis). The films were found to have a very smooth, homogeneous surface and the oxygen content was found to vary from x=0 to x=2 in dependence on the deposition parameters. The refractive indices of the films were measured both in the visible (405 nm) and in the infrared (1319 nm and 1542 nm), compared to the values which the Bruggeman's effective medium theory predicts for such thin films, and were found to be in good agreement. The position of the Si-O stretching peak in the infrared absorption spectra was used to draw some conclusion about the distribution of the silicon and oxygen atoms inside the amorphous SiO x matrix. The atoms were found to be inhomogeneously distributed inside the amorphous matrix, with the average number of oxygen atoms in the vicinity of a given silicon atoms being lower than x.