Plasma chemistry and dust-particle generation in pure methane plasma: Influence of the RF electrode cleanliness

Hydrocarbon dust-particles are formed and grown to a large size (around 1 μm) in a low pressure capacitively coupled radio frequency discharge in methane. The methane decomposition leads to the formation of both spherical dust-particles in the plasma bulk and coating on the electrodes. Under ion bombardment, the coating on the biased top electrode peels off, leading to the fall of flakes. To better understand the role played by the electrode surface state on the plasma chemistry and on the dust-particle growth, experiments are carried out in two different initial conditions for the electrodes: (i) without any coating and (ii) with a homogeneous hydrocarbon coating. Spherical dust-particle growth is followed using the temporal evolution of the DC self-bias voltage. At the end of the experiment, dust-particles and flakes are collected and observed by scanning electron microscopy. Using mass spectrometry, temporal evolutions of neutrals, ionic species, and positive ion energies are investigated. Between the two experimental conditions, no strong differences were observed on the plasma chemistry. However, the self-bias voltage is strongly modified as well as the dust-particle growth and dynamics.Hydrocarbon dust-particles are formed and grown to a large size (around 1 μm) in a low pressure capacitively coupled radio frequency discharge in methane. The methane decomposition leads to the formation of both spherical dust-particles in the plasma bulk and coating on the electrodes. Under ion bombardment, the coating on the biased top electrode peels off, leading to the fall of flakes. To better understand the role played by the electrode surface state on the plasma chemistry and on the dust-particle growth, experiments are carried out in two different initial conditions for the electrodes: (i) without any coating and (ii) with a homogeneous hydrocarbon coating. Spherical dust-particle growth is followed using the temporal evolution of the DC self-bias voltage. At the end of the experiment, dust-particles and flakes are collected and observed by scanning electron microscopy. Using mass spectrometry, temporal evolutions of neutrals, ionic species, and positive ion energies are investigated. Between the ...