Gas phase particulate formation in radiofrequency fluorocarbon plasmas

The production, suspension and transport of fluorocarbon particulates in capacitively coupled radiofrequency discharges are studied using in situ laser light scattering and ex situ chemical analysis. The time evolution of the spatial distribution of suspended palticles is obtained by two-dimensional imaging of the scattered light. The chemistry of the discharge is varied by use of a range of pure fluorocarbon gases and mixtures with argon, oxygen and hydrogen-containing molecules. Addition of hydrogen to a fluorocarbon discharge increases the rate of formation of particles although these powders are found by Fourier transform infrared measurements to contain negligible amounts of hydrogen. Particle formation rates correlate with polymer deposition rates and are independent of apparatus history. It is proposed that this is a, clear example of gas phase rather than surface processes leading to particle nucleation and growth.