Optical properties of isotropic and anisotropic films deposited by pulsed plasma

abstrakt

angličtina

Isotropic plasma-polymerized films were made from tetravinylsilane (TVS) monomer and its mixture with argon or oxygen gas. Films were deposited on polished silicon wafer (100) using plasma-enhanced chemical vapor deposition at pulsed RF plasma (13.56 MHz). The substrates were pretreated by argon plasma (10sccm, 5.7Pa, 5 W) for 10min to improve the film adhesion. The films were prepared at a total mass flow rate of 3.8 sccm (2.7 Pa), the content of argon or oxygen gas in a mixture ranging 0-92%, and the effective power operated from 2 to 250 W. The thickness of isotropic films was varied from 10 nm to 1 μm. An in-situ phase-modulated spectroscopic ellipsometer UVISEL (Jobin-Yvon) was employed to characterize the film thickness and optical properties of deposited films in the spectral range 250-830 nm. The dispersion dependence of the dielectric function was fitted using the five-parametric Tauc-Lorentz formula. We found out that optical parameters of deposited films are controlled by effective power and the band gap can be decreased from 2.8 eV (2 W) to 0.8 eV (250 W) if pure TVS was used. The refractive index at a wavelength of 633 nm was ranging 1.6-2.4 for films deposited from pure monomer and the range was similar (1.7-2.4) if TVS/Ar mixture was used, but was modified (1.5-2.2) if TVS/O2 mixture was applied. However, the power dependences of the refractive index differ according to the content of gas in mixture. Next, well-defined multilayer (anisotropic) films were deposited using pure monomer and its mixtures combining individual layers polymerized at different powers. A realistic model of the multilayer structure was used to analyze ellipsometric data and distinguish individual layers in the multilayered film, evaluate their thicknesses and optical constants. Dispersion dependences for the refractive index were well separated for each type of individual layer, if the thickness was decreased from 100-10 nm, and corresponded to those of the single layer.

thin films; optical properties; ellipsometry

KUCHARČÍK, J.; MISTRÍK, J.; ČECH, V.

15. 9. 2014

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