IUVSTA 15th International Vacuum Congress (IVC-15), AVS 48th International Symposium (AVS-48), 11th International Conference on Solid Surfaces (ICSS-11)
    Plasma Science Thursday Sessions
       Session PS-ThP

Paper PS-ThP3
Reduction of Plasma-Induced Damage through Ion-Ion Synchronous Bias

Thursday, November 1, 2001, 5:30 pm, Room 134/135

Session: Plasma Etching Poster Session
Presenter: L.J. Overzet, University of Texas at Dallas
Authors: L.J. Overzet, University of Texas at Dallas
S.K. Kanakasabapathy, University of Texas at Dallas
K.P. Cheung, Agere Systems
M.V. Malyshev, Agere Systems
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Electron-shading induced differential-charging of anisotropic etch structures has been shown to be a cause of plasma process induced-damage.@footnote 1@ It is due to a disparity in the angular velocity distributions of negative and positive species in conventional electron-ion plasmas. Electron-free plasmas, also known as negative-ion/positive-ion (ion-ion) plasmas can be made devoid of this disparity. The comparable masses and average energies of negative and positive ions in the center of an ion-ion glow allow nearly equal anisotropy to be produced in their velocity distributions when biased. Ion-ion plasmas can be formed by extinguishing the plasma power and waiting an appropriate time. For example: electrons are lost rapidly (~10's of µsec) to attachment in the afterglow of pulsed Cl@sub 2@ discharges leaving behind an ion-ion plasma that lasts for ~100's of µsec. Alternating fluxes of high kinetic energy positive-ions and negative-ions can then be produced by applying a low-frequency AC bias to the processing substrate. When this AC bias is pulsed synchronously with the plasma power and phase locked to the ion-ion plasma, it can produce alternating fluxes of positive-ions (Cl@sub 2@@super +@) and negative-ions (Cl@super -@).@footnote 2@ This ion-ion `synchronous bias' is superior for extracting negative-ions compared to an `asynchronous bias' due to the low DC self-bias it induces. We have demonstrated a reduction in electron-shading induced potentials for ion-ion synchronous bias using in-situ charge-monitoring circuitry. We have also compared some cross-sectional micrographs of etched polysilicon lines on oxide. Our limited results indicated an improvement in etch profiles for ion-ion synchronous bias at the smallest linewidth of 0.45µm. @FootnoteText@ @footnote 1@ G.S. Hwang and K.P. Giapis J. Appl. Phys., 82, 566(1997) @footnote 2@ S.K. Kanakasabapathy, L.J. Overzet, V. Midha and D.J. Economou, Appl. Phys. Lett., 78, 22(2001).