AVS 52nd International Symposium
    Plasma Science and Technology Thursday Sessions
       Session PS+MS-ThM

Paper PS+MS-ThM6
Effect of Reactor Geometry on Ion Energy Distributions for Pulsed Plasma Doping (P@super 2@LAD)@footnote 1@

Thursday, November 3, 2005, 10:00 am, Room 302

Session: Process Equipment Modeling
Presenter: A. Agarwal, University of Illinois at Urbana-Champaign
Authors: A. Agarwal, University of Illinois at Urbana-Champaign
M.J. Kushner, Iowa State University
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Ultra-shallow junctions (USJ) are required for fabrication of sub-0.1 µm transistors in semiconductor integrated circuits. Plasma implantation methods such as pulsed plasma doping (P@super 2@LAD) present simple, low cost alternatives to beam line technologies. P@super 2@LAD is capable of delivering high dose rates at ultra-low energies (0.02-20 keV) using conventional plasma processing technologies.@footnote 2@ In this talk, results from a computational investigation of P@super 2@LAD using different reactor geometries will be discussed. The investigation was performed using a modified version of the Hybrid Plasma Equipment Model to address quasi-dc pulsed biases.@footnote 3@ An inductively coupled plasma is used to generate ions in pressures of 10s mTorr. A quasi-dc pulsed bias is applied to the substrate to accelerate ions. Typical bias pulse lengths range between 5 and 50 µs and bias voltages are up to 20 kV. Results will be presented for Ar/NF@sub 3@ (a surrogate for Ar/BF@sub 3@) gas mixtures. The large bias voltages and long pulse lengths result in there being considerable thickening of the sheath during the pulse. Sufficient charge is extracted during the pulse that some amount of depletion of ions results. Non-uniformities in plasma density as the sheath extends into the plasma or the ability of the plasma to repopulate depleted charge can have a significant effect on the ion energy distributions (IEDs) to the substrate, which influences the doping profiles. For example, at sufficiently high biases (>2 kV), the IEDs can be skewed in the direction of the source of ion production with the result that the ions approach the substrate preferentially from one direction. As the sheath expands into the center of the reactor where the plasma density is higher, the rate of expansion slows. The result can be a laterally dependent sheath thickness which in turn affects the collisionality of ions crossing the sheath. The consequences of varying reactor aspect ratios and positioning of coils on IEDs will be discussed. @FootnoteText@ @footnote 1@ Work supported by VSEA, Inc. NSF (CTS03-15353) and SRC. @footnote 2@ S. B. Felch, B. -W. Koo, R. B. Liebert, S. R. Walther, and D. Hacker, Surf. Coatings Technol., 156, 229 (2002) @footnote 3@ A. Sankaran and M. J. Kushner, J. Vac. Sci. Technol. A, 22, 1242 (2004)