Monomer deficient conditions used to control physical properties of plasma polymer films in wide ranges by RF power

abstract

English

We found out that the monomer deficient conditions enable to control mechanical and optical properties of plasma polymer films by RF power using plasma-enhanced chemical vapor deposition. The monomer deficient conditions may be characterized by the plasma process pressure (plasma switched on) lower than the basic process pressure (plasma switched off), which means that the concentration of reactive species is not insignificant or is even comparable with the concentration of monomer molecules. The monomer deficient conditions are achieved at lower monomer flow rates (0.5-10 sccm) operated at lower basic process pressures (1-5 Pa). In this study, we plasma polymerized tetravinylsilane at a mass flow rate of 3.8sccm operated at a basic process pressure of 3.0 Pa, and RF power ranging 10-70 W using continuous wave. The plasma process pressure decreased from 1.7 Pa (10 W) to 1.1 Pa (70 W) at enhanced power. The plasma species were monitored by mass spectrometry and correlated with chemical properties of deposited films and the deposition rate at a given RF power. The organic/inorganic character (C/Si ratio) of plasma polymer was varied from 4.6 to 7.3 with enhanced power. Optical properties of plasma polymer were analyzed by spectroscopic ellipsometry in the range 250-830 nm. The refractive index was 1.7 (10 W)-2.1 (70 W) for a wavelength of 633 nm, the extinction coefficient was 0.18 (10 W)-0.30 (70 W) for a wavelength of 250 nm, and the band gap was controlled by RF power in range 2.0 (10 W)-1.2 eV (70 W). The Young’s modulus and hardness of plasma polymer could be varied from 12GPa (10 W) to 81 GPa (70 W) and from 0.84 to 8.8GPa, respectively, as was determined from nanoindentation measurements. The physical properties of plasma polymer are related to increased polymer cross-linking expressed via the density 1.5 (10 W)-1.8 g cm-3 (70 W). The RF power may be considered as an effective tool for tailoring of plasma polymer with respect to its application.

thin films; plasma polymerization; optical properties; mechanical properties

ČECH, V.; HOFEREK, L.; TRIVEDI, R.; KONTÁROVÁ, S.

15. 9. 2014

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