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 χ_O2(). It is found that the effect of oxygen fraction on films properties is related to O₂ 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 O₂ dissociation degree of 15% has been obtained for 50 sccm flow rate of O₂ (χ_O2=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 (χ_O2=0.38). The refractive index for deposited films from pure HMDSO (χ_O2=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 χ_O2=0.38.     

Active species characterization in RF remote oxygen plasma using actinometry OES and electrical probes

Actinometry optical emission spectroscopy (AOES), single cylindrical Langmuir probe and electrostatic planar probe were used to investigate the active species (electrons, ions and atomic oxygen) of remote oxygen plasma in an RF (13.56 MHz) hollow cathode discharge system, as a function of applied power and gas pressure. The electron density and electron temperature were determined from Langmuir probe. The atomic oxygen (AO) density was measured using argon actinometry method. Positive ion flux rate was estimated from the positive ion saturation current of the planar probe, and the combination of the planar and Langmuir probes enabled the determination of the negative ion fraction in the discharge. The explanation of the behavior of the different active plasma species was performed on the basis of the main kinetic reactions of oxygen plasma.     

Atomic oxygen in remote plasma of radio-frequency hollow cathode discharge source: Characterization and efficiency

Low-pressure, low-temperature remote oxygen plasma ignited by a radio-frequency (RF) hollow cathode discharge (HCD-L300) system is shown to be a powerful and effective source of neutral atomic oxygen (AO), useful in processing of polymeric materials. The density of AO was determined by a catalytic nickel probe as a function of pressure, RF power, oxygen flow rate and axial distance in the processing chamber. It was found to vary between ∼1×10¹⁹ to ∼1×10²⁰ atom m⁻³. The AO rich remote plasma-induced modification of wetting properties of polyimide (PI) and fluorinated ethylene propylene (FEP) surfaces has also been investigated. The wetting properties of the PI and FEP surfaces before and after exposure to the plasma were characterized by contact angle measurements and analysis. It was found that the influence of plasma surface treatment on wetting properties of FEP has an opposite effect to that of PI. On increasing the time of treatment, the surface of PI becomes more hydrophilic, whereas the hydrophobicity of FEP surface enhances. Moreover, a superhydrophobic FEP surface is produced at prolonged time of treatment. Changes in the surface morphology due to the plasma treatment were viewed under a scanning electron microscope (SEM).