Properties of thin films deposited from HMDSO/O 2 induced remote plasma: Effect of oxygen fraction

Abstract

Thin films deposited from Hexamethyledisiloxane (HMDSO)/O 2 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 χ O 2 ( χ O 2 = 0 , 0.38 , 0.61 , 0.76 and 0.90 ). It is found that the effect of oxygen fraction on films properties is related to O 2 dissociation degree ( α d) behavior in pure oxygen plasma. α d has been investigated by actinometry optical emission spectroscopy (AOES) combined with double Langmuir probe measurements, a maximum of O 2 dissociation degree of 15% has been obtained for 50 sccm flow rate of O 2 ( χ O 2 = 0.61 in HMDSO/O 2 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 O 2 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/O 2 ( χ O 2 = 0.38 ). The refractive index for deposited films from pure HMDSO ( χ O 2 = 0 ) has been found to be higher than that of films deposited from HMDSO/O 2 mixture. In HMDSO/O 2 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 O 2 to HMDSO plasma, and it is minimum for χ O 2 = 0.38 .