AVS 58th Annual International Symposium and Exhibition
    Plasma Science and Technology Division Wednesday Sessions
       Session PS+SS-WeM

Paper PS+SS-WeM6
Near-Threshold Ion-Enhanced Silicon Etching

Wednesday, November 2, 2011, 9:40 am, Room 202

Session: Plasma Surface Interactions (Fundamentals & Applications) I
Presenter: Hyungjoo Shin, University of Houston
Authors: H. Shin, University of Houston
W. Zhu, University of Houston
V.M. Donnelly, University of Houston
D.J. Economou, University of Houston
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Nearly mono-energetic ion energy distributions (IED) were obtained on the substrate electrode in a Faraday-shielded inductively couple plasma. This was accomplished by pulsing the plasma, and applying a synchronous DC bias on a “boundary” electrode, during a specified time window in the afterglow. Both the peak ion energy and the width of the IED could be controlled.[1] The ability to precisely control the IED enabled a study of ion-enhanced etching of silicon with chlorine, at near-threshold ion energy. Unlike “beam” experiments, where there is no plasma over the substrate, this work involves etching under “realistic” plasma conditions. The progress of etching in an argon-diluted chlorine plasma was monitored as a function of pressure and ion energy using optical emission spectroscopy. The silicon etch rate was measured using infrared laser interferometry. The etch rate of a p-type blanket silicon substrate was proportional to Cl-atom density, but did not depend on ion energy for sub-threshold (less than ~ 20 eV) ions. Under these conditions, however, the etch rate was much higher than that expected based on reported experiments in downstream plasmas where the surface is exposed to Cl atoms alone. Above threshold, the etch rate increased with the square root of ion energy. A comparison with n-type silicon substrate was also made. The carrier-mediated mechanisms of p-type Si etching in a plasma under very low energy ion bombardment will be proposed and discussed.

Work supported by the DoE Plasma Science Center and NSF.

[1] H. Shin et al., to appear in Plasma Sources Science and Technology.