Increasing fluorine concentration to control the microstructure from fullerene-like to amorphous in carbon films

Abstract

Fluorinated and hydrogenated amorphous carbon (a-C:H:F) films with increasing fluorine content are deposited using a pulsed direct current plasma enhanced chemical vapor deposition technique. The fluorine atomic concentrations of films deposited under CF₄/CH₄ gas with flow ratios of 2 : 1, 4 : 1, 5 : 1, 6 : 1 and 10 : 1 are 4.8%, 5.9%, 6.8%, 12.1% and 15.5%, respectively. As the F content increases, XPS analysis indicates that the C–C bonding structure transforms to form C–CF, C–F and –CF₂ groups. TEM images show that the microstructures of the films with lower fluorine contents are constituted by many discontinuous graphite-like and fullerene-like fragments. However, features like interlocking pores and amorphousness strongly prevail in the structures when the proportion of fluorine incorporated into the films increases. The slight increase in I_D/I_G and the up-shift of the G peak obtained from the Raman spectrum indicate the relative increase of the sp² configuration and the formation of sp²-hybridized carbon domains. A deposition mechanism is given to explain the microstructure evolution of the a-C:H:F films upon increasing the fluorine content.