Hard diamond like carbon (DLC) films with an addition of SiOx were deposited by capacitively coupled rf discharges from mixture of methane and hexamethyldisiloxane (HMDSO). The flow rate was changed in order to vary the SiOx content in the films. Thickness of the films was determined by ellipsometry. FTIR spectra showed presence of C-H bonds as well as silicon bonded to hydrogen and hydrocarbon groups. In the region 630-900 cm-1 normalized absorbance was computed. It is shown that the concentration of silicon containing bonds grows with the flow rate of HMDSO growing.