Mechanical stresses studied by optical methods in diamond-like carbon films containing Si and O

In this paper the quantitative dependence of the mechanical stress inside diamond-like carbon films containing Si and O atoms on a flow rate ratio of methane CH4 and hexamethyldisiloxane C6H18Si2O in the deposition mixture is determined. For this purpose the modified Stoney's formula is employed. The important quantities taking place in this formula, i.e. the radius of curvature of the spherical surface of a deformed silicon substrate because of the film stress and the film thickness, are determined using the combined optical method based on two-beam interferometry, variable angle spectroscopic ellipsometry and near-normal spectroscopic reflectometry. It is shown that the influence of the flow rate ratio on the values of the mechanical stresses taking place inside these films is negligible within the experimental accuracy achieved for determining these stresses if the total flow rate of gases used to be constant in the deposition mixture. A discussion of this fact is also performed. The film studied were prepared using the plasma enhanced chemical vapor deposition.