Plasma deposition of fluorocarbon thin films from $c-C4F8$ using pulsed and continuous rf excitation

Fluorocarbon films of varying composition have been deposited from pulsed and continuous plasmas of octafluorocyclobutane $(c-C4F8)$ and $c-C4F8$/Ar. Continuous plasma deposition rates are a very weak function of applied rf power (may be within experimental error). Pulsed plasma deposition rates are significantly lower than continuous plasma rates at the same average power. The pulsed plasma deposition rates can be attributed almost entirely to the plasma on time during the pulse, but there is a slight dependence on pulse off time. Ar addition affects the deposition rates through a residence time effect, but also affects the deposition chemistry by reducing the degree of $C4F8$ dissociation, resulting in more fluorinated films. Refractive indices for all films increase approximately linearly with applied rf power, with the pulsed plasma-deposited films falling on the same curve. Carbon $1s$ x-ray photoelectron spectroscopy shows that the continuous plasma-deposited films become increasingly fluorinated as the rf power is decreased. Pulsed plasma films are more fluorinated than similar average power continuous plasma films: 44% $CF2$ for 10/50 (400 W on time, 67 W average power) versus 37% for 50 W continuous. Literature and preliminary gas-phase measurements suggest that the $C4F8$ is not fully dissociated in either plasma system and that larger species in the gas phase may play a significant role in the deposition mechanisms.