Charging, transport and heating of particles in radiofrequency and electron cyclotron resonance plasmas

Once particles are formed or injected into plasmas used for materials processing, such as in plasma etching, plasma-assisted chemical vapour deposition or sputtering plasma systems, the nature of particle transport will largely determine whether a processing surface will be contaminated. We investigate the situation in which the particle density is low enough to ignore particle-particle and particle-plasma interactions. Emphasis is placed on obtaining expressions for the forces experienced by particles. These expressions depend on the local plasma condition: plasma density, electron temperature, positive ion directed and random kinetic energies, electric field and ion mass. We apply a model of an electron cyclotron resonance discharge to prediction of the existence and nature of particle trapping. Model predictions indicate that a high-density source such as an electron cyclotron resonance discharge is unlikely to trap particles mainly because of the large ion drag force sweeping particles out of the discharge. Finally, we present a model of particle heating in discharges. Under typical radiofrequency discharge conditions, particles are generally predicted to be near the neutral gas temperature in the discharge. We have conducted experiments and found results in agreement with these predictions. However, under conditions typically encountered in high-density plasma sources such as an electron cyclotron resonance source, the model predicts that particles may be heated to temperatures of two to three times room temperature.