Structural and electrical studies on fluorinated amorphous carbon films as intermetal dielectric layer in ULSI devices

Fluorinated amorphous carbon (a-C:F) films were deposited on a p-type Si(100) substrate by using an inductively coupled plasma chemical vapor deposition (ICPCVD) system with a mixture of carbon fluoromethane (CF4) and methane (CH4) gases. X-ray photoelectron spectroscopy was used to investigate the various bonding species such as –CF–, –CF2– and –CF3 bonds present in the film. The concentrations of the C–F2 and the C–F3 bonds in a-C:F film increased at the higher CF4/(CH4 + CF4) flow rate ratios of 70% and 75%. Therefore, we can infer that the greater incorporation of fluorine with carbon is associated with higher binding energy, since more energy is required to take out the electron of the core level due to higher electronegativity of fluorine. The C–V characteristics of an as-deposited film show that the film contains either interface trapped charges or bulk traps and that of annealed film have the interface trapped charges rather than the bulk traps. The lowest dielectric constant of as-deposited and annealed a-C:F films are found to be 2.5 and 2.6 for the CF4/(CH4 + CF4) flow rate ratio of 75%, which shows that the greater incorporation of fluorine in the films helps in decreasing the dielectric constant.