AVS 49th International Symposium
    Plasma Science Tuesday Sessions
       Session PS-TuP

Paper PS-TuP19
Ion Energy Distributions at the Substrate and Feature Charging During Plasma Etching

Tuesday, November 5, 2002, 5:30 pm, Room Exhibit Hall B2

Session: Plasma Applications
Presenter: A.E. Wendt, University of Wisconsin - Madison
Authors: A.E. Wendt, University of Wisconsin - Madison
R. Silapunt, University of Wisconsin - Madison
M. Patterson, University of Wisconsin - Madison
R. Ding, University of Wisconsin - Madison
Y.-H. Ting, University of Wisconsin - Madison
Correspondent: Click to Email
Substrate bombardment by energetic ions is a critical element of many plasma processes, and the magnitude of the ion energy is an important process parameter. However, the conventional sinusoidal bias voltage waveform generally leads to broad bimodal ion energy distributions (IED) at the substrate, and therefore cannot be used to take full advantage of ion bombardment as a means of controlling process results. By using a non-sinusoidal bias voltage waveform, we are able to produce a narrow IED at the substrate, with dramatic results that may help in meeting future IC manufacturing requirements. Our tailored bias voltage waveform has a periodic shape at the substrate consisting of a short spike in combination with a longer period of constant voltage. Most ions cross the sheath during the period of constant sheath voltage, resulting in a narrow IED. The height of the spike sets the magnitude of the ion energy. We have previously reported measurements of the sheath voltage waveform and etch selectivity on blanket films, confirming the effectiveness of this approach. This paper addresses the influence of the IED on feature charging during the etching of patterned dielectric films. In contrast to blanket films, in high-aspect-ratio features there is a greater shadowing effect for electrons than for ions. As a result, the feature bottoms will charge positive and deflect ions, and a steady state is reached when electron and ion fluxes balance. A limitation of a narrow ion energy distribution in that case is that the feature bottom must charge to a much higher potential in order to deflect the ions compared to the case of a bimodal distribution that includes some low energy ions, drastically reducing the energy of the remaining ions that do reach the feature bottom, affecting selectivity and etch rate. Proposed modifications of the tailored voltage waveform to address these issues will be presented. @FootnoteText@ @footnote 1@ Supported by SRC and NSF ECS-0078522.