AVS 45th International Symposium
    Plasma Science and Technology Division Thursday Sessions
       Session PS-ThP

Paper PS-ThP3
Control of Ion Energy Distribution at Substrates During Plasma Processing

Thursday, November 5, 1998, 5:30 pm, Room Hall A

Session: Plasma Science and Technology Division Poster Session
Presenter: S.B. Wang, University of Wisconsin, Madison
Authors: S.B. Wang, University of Wisconsin, Madison
A.E. Wendt, University of Wisconsin, Madison
Correspondent: Click to Email
It is well-known that ion bombardment of the substrate is one factor that makes plasma processing indispensable in semiconductor fabrication. In an effort to understanding the factors governing selectivity in oxide etch processes, we examine the energy of ion bombarding the substrate. We start with a design study for an experimental system producing a narrow distribution of ion energies at the substrate. With fine control over the energy of the nearly monoenergetic ions, we can elucidate the effect of ion energy on selectivity. The ion energy distribution reaching the substrate has been investigated by a self-consistent spherical shell plasma model. The results show that the broadening of ion energy distribution depends on the area ratio of substrate to grounded wall which is varied by changing the radii of the two spherical shell electrodes. As the area ratio increases, the plasma potential is more strongly modulated by the rf potential on the powered electrode. Therefore, the ion energy, which is proportional to the difference between plasma potential and substrate potential, becomes narrower with increasing area ratio. This result suggests differences in processing performance between tools with similar plasma conditions but different effective grounded wall areas, such as ECR and inductively coupled plasmas. In addition, we show that the ion energy distribution can be controlled by modulation of the voltage waveform applied to the substrate electrode. In the simulation, the broadening shrinks as low as ~2T@sub e@(T@sub e@ is electron temperature in Volts) as compared to 20T@sub e@ or greater for a sinusoidal voltage waveform. In addition, the shape of the energy distribution is single peak rather than a saddle. This is a good tool for threshold energy studies. Based on these results, we have designed a system for experimental study of ion energy thresholds for selective etching. Experiments in ion energy control and selectivity improvement in experiment are currently underway. This work supported by NSF Grant #EEC8721545