Properties of thin films deposited from HMDSO/O2 induced remote plasma: Effect of oxygen fraction

Thin films deposited from Hexamethyledisiloxane (HMDSO)/O2 mixture excited in a radio-frequency hollow cathode discharge system have been investigated for their structural, optical and corrosive properties as a function of oxygen fraction χO2χO2(χO2=0,0.38,0.61,0.76and0.90). It is found that the effect of oxygen fraction on films properties is related to O2 dissociation degree (αd) behavior in pure oxygen plasma. αd has been investigated by actinometry optical emission spectroscopy (AOES) combined with double Langmuir probe measurements, a maximum of O2 dissociation degree of 15% has been obtained for 50 sccm flow rate of O2 (χO2=0.61χO2=0.61 in HMDSO/O2 plasma). Fourier transform infrared spectroscopy (FTIR) and optical measurements showed that the behavior of both identified IR group densities and deposition rate as a function of oxygen fraction is similar to that of O2 dissociation degree. The inorganic nature of the films depends significantly on oxygen fraction, the best inorganic structure of deposited films has been obtained for 62% HMDSO content in the mixture HMDSO/O2 (χO2=0.38χO2=0.38). The refractive index for deposited films from pure HMDSO (χO2=0χO2=0) has been found to be higher than that of films deposited from HMDSO/O2 mixture. In HMDSO/O2 plasma, it has a behavior similar to that of deposition rate, and it is comparable to that of quartz. The effect of oxygen fraction on the corrosive properties of thin films deposited on steel has been investigated. It is found that the measured corrosion current density in 0.1 M KCl solution decreases with the addition of O2 to HMDSO plasma, and it is minimum for χO2=0.38χO2=0.38.