Optical investigations of layered plasma-polymerized TVS/O2 films

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angličtina

Thin films with layered structure were prepared from tetravinylsilane (TVS)/oxygen gas mixture using plasma polymerization technique. The films were deposited on one-side polished IR transparent Si (100) wafers that were pretreated by oxygen plasma. The thickness of layered structure was about 1 micron and deposition was carried out in pulsed RF helical coupled plasma system at different RF effective power and O2/(TVS + O2) flow rate ratio. Particular sublayers of the layered structure were constructed at different deposition conditions (effective power, oxygen content). Deposited films were formed by a-SiC polymer network with incorporated oxygen atoms and side vinyl, hydroxyl and carbonyl groups [1]. A layered structure of the films, optical constants of sublayers, interdiffusion of oxygen between the sublayers with different oxygen content, and ageing effects were studied by spectroscopic ellipsometry. Ellipsometric spectra of deposited films were recorded using phase-modulated spectroscopic ellipsometer (UVISEL, Jobin Yvon) in the range from 1.5 to 5 eV. Each sample was investigated as prepared and repeatedly in specific time intervals. The spectra were analyzed using an optical model consisting of the substrate with native silicon oxide layer, planparallel sublayers, and an overlayer included to evaluate effects of air exposure and film ageing. The dispersion dependence of the dielectric function was fitted using the five-parametric Tauc-Lorentz formula, which was derived for the parameterization of the opto-electrical response of amorphous dielectrics [2]. Comparing ellipsometric measurements recorded immediately after the deposition with those recorded later, we were able to observe changes in optical constants at interfaces probably due to diffusion of oxygen atoms from the oxygen-rich sublayer to the originally oxygen-free sublayer. The polymer behaved like a dielectric in the visible region and the refractive index of plasma polymer decreased with enhanced oxygen content.

plasma polymerization, spectroscopic ellipsometry, tetravinylsilane

ČECHALOVÁ, B.; STUDÝNKA, J.; MISTRÍK, J.; ČECH, V.

2007

13. 12. 2007

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