Study On Structure And Properties Of Fluorinated Diamond-Like Carbon Films Prepared By Reactive Magnetron Sputtering

With many excellent properties such as highly hardness and thermal stability and high-insulated properties, the hydrogenated diamond-like carbon films have been studied for many years. If the hydrogen atom is replaced by fluorine atom, fluorinated diamond-like carbon (F-DLC) films may be prepared. Because the fluorine element is strong negative-dielectric and the fluorinated chemical bonds have low dielectric polarizability and may reduce the films dielectrics constant, the fluorinated diamond-like carbon films may be used for low k dielectric material in micro-electronic device. The fluorinated material may have a useful application into protective films because of its hydrophobic property and low friction factor. More real and perceived concerns about the F-DLC films have to be paid such as the structure and its new properties of the F-DLC films while some of the best qualities of DLC films are preserved. The F-DLC films were prepared by reactive magnetron sputtering using trifluoromethane (CHF3) and Argon as source gases and pure graphite as a target. The DLC feature of the films has been affirmed by Raman spectroscopy and its structural evolutions with the different deposition conditions studied. The XRD spectroscopy shows that the F-DLC films are amorphous. The cluster sizes of F-DLC films have been estimated by SEM photo and intensity ratio ID/IG of the D and G modes of their Raman spectroscopy. The process of preparing F-DLC films by reactive magnetron sputtering method is very complicated, involving sputter of graphite target, dissociation of source gases, film growth and etch effect of F atoms in the discharge area to the deposited film. The influence of deposition parameters such as pressure, source gas flow ratios Ar/CHF3 and RF input power on deposition rate of F-DLC films has been studied. The experiment results show that deposition rate of F-DLC films ranges from 0.8 to 3.5 nm/min on the conditions of pressure of 0.5—6Pa, RF input power of 60-320W and Ar/CHF3 of 1:2 –8:1. The mechanical properties of F-DLC films such as hardness and elastic modulus have been measured and the influence of deposition parameters on those mechanical properties are also been analyzed. The hardness and elastic modulus of F-DLC films ranges from 0.7 to 2.4GPa and 9 to 40GPa respectively. The results of Raman scatting show that sp2/sp3 hybrid ratios of F-DLC films could be modified by controlling the deposition condition. The chemical components of F-DLC films have been studied. The FTIR spectra corresponding to different deposition parameters shows that the films contain little hydrogen or the films are hydrogen-free. The frames of films are made up of aromatic rings with fluorine atom attached and some aromatic rings without fluorine atom attached. The fluorine atom was bond to skeletons of aromatic rings in modes of –CF2 symmetric stretch vibration, HFC=C< and C-F stretch vibration, –CF2 chains, F2C=C< vibration and F2C=CF vibration. The fluorine and carbon content of F-DLC films deposited at different parameter were measured by XPS spectroscopy. The results show that fluorine content of F-DLC films ranged from 23 to 37at.% and confirm that the skeleton of F-DLC films are aromatic rings with fluorine atom attached and the films contain some aromatic rings without fluorine atom attached. The dominant bonding state of C-Fx is CF2. The result reveals that the films prepared at RF input power of 60W and pressure of 2Pa and Ar/CHF3 of 2:1 have the highest fluorine content of 37at.% and have good stability. The optical properties of F-DLC films were measured by UV-VIS, and optical band gaps of F-DLC films deposited at different parameters were obtained by analysis related to UV-VIS. The results show that the F-DLC films'transmission properties to ultraviolet and visible light depended on deposition conditions. The optical band gaps of F-DLC films are about 1.37—2.64eV, which depend not only on the content of fluorine atoms in the films but also on C-Fx bonding configurations and C-Fx bond distribution. The dielectric properties of F-DLC films were measured by analyzing their C-V characteristics of MIS structure. The dielectric constant of F-DLC films ranged from 1.77 to 3.25. The lowest dielectric constant of 1.77 was obtained at RF input power of 60W and pressure of 2Pa and Ar/CHF3 of 2:1 and the results from annealing of the F-DLC filmsshow that the films have good thickness and optical band gaps stability under those deposition conditions. It is believed that F-DLC films prepared at those deposition conditions should have promising applications in the field of low k materials and optical coating.