Dynamics of Ions and Neutral Particles in the Sheath Region of Processing Plasmas

The path of ions traversing the sheath region of a radio frequency plasma is modelled using the Child-Langmuir approximation to the full sheath equation. The collective characteristics of many ions is obtained by Monte Carlo simulation, revealing structure in the relationship between many parameters. By performing a systematic calculation of ion impact energy versus initial energy and phase, a distinctive spiral shape has been observed. This provides additional insight into the mechanism that underlies the bimodal ion energy distributions that are widely reported in plasma processing systems. A further step has been taken from this observation, to see if it can be used to provide an analytic method for constructing ion energy distributions. A spiral shape that varies continuously across phase and initial ion energy space has been created, replicating that seen in Monte Carlo simulation. By sampling the result across the appropriate initial conditions, an ion energy distribution can be generated. A numerical solution to the full sheath equation has been implemented. This allows the inclusion of electrons into the area where the sheath region meets the plasma. It has been shown that this causes ions to follow a significantly different path through the sheath region. When an ion first enters the sheath region, it experiences a smaller force due to the reduction in electric field because of the presence of electrons. The effect of this propagates through to the ion energy distribution. Effects due to the high electric fields that are present in etched substrate features have been considered. Particles with an electric dipole moment are attracted along lines of increasing electric field strength under a mechanism called dielectrophoresis. An assessment of the significance of this force on neutral transport in substrate features has been made. It is found that particles with a typical dielectric moment are accelerated towards the central region of a trench and accelerated out of the trench in a fraction of time that it would take without a force due to dielectrophoresis