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Title: Penetration of plasma into the wafer-focus ring gap in capacitively coupled plasmas

Abstract

In plasma etching equipment for microelectronics fabrication, there is an engineered gap between the edge of the wafer and wafer terminating structures, such as focus rings. The intended purpose of these structures is to make the reactant fluxes uniform to the edge of the wafer and so prevent a larger than desired edge exclusion where useful products cannot be obtained. The wafer-focus ring gap (typically<1 mm) is a mechanical requirement to allow for the motion of the wafer onto and off of the substrate. Plasma generated species can penetrate into this gap and under the beveled edge of the wafer, depositing films and possibly creating particles which produce defects. In this paper, we report on a computational investigation of capacitively coupled plasma reactors with a wafer-focus ring gap. The penetration of plasma generated species (i.e., ions and radicals) into the wafer-focus ring gap is discussed. We found that the penetration of plasma into the gap and under the wafer bevel increases as the size of the gap approaches and exceeds the Debye length in the vicinity of the gap. Deposition of, for example, polymer by neutral species inside the gap and under the wafer is less sensitive to the sizemore » of the gap due the inability of ions, which might otherwise sputter the film, to penetrate into the gap.« less

Authors:
;  [1]
  1. Iowa State University, Department of Electrical and Computer Engineering, 104 Marston Hall, Ames, Iowa 50011 (United States)
Publication Date:
OSTI Identifier:
20979407
Resource Type:
Journal Article
Resource Relation:
Journal Name: Journal of Applied Physics; Journal Volume: 101; Journal Issue: 11; Other Information: DOI: 10.1063/1.2736333; (c) 2007 American Institute of Physics; Country of input: International Atomic Energy Agency (IAEA)
Country of Publication:
United States
Language:
English
Subject:
71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSICS; DEBYE LENGTH; DEPOSITION; ETCHING; IONS; MICROELECTRONICS; PARTICLES; PLASMA; POLYMERS; RADICALS; SUBSTRATES; WALL EFFECTS

Citation Formats

Babaeva, Natalia Y., and Kushner, Mark J. Penetration of plasma into the wafer-focus ring gap in capacitively coupled plasmas. United States: N. p., 2007. Web. doi:10.1063/1.2736333.
Babaeva, Natalia Y., & Kushner, Mark J. Penetration of plasma into the wafer-focus ring gap in capacitively coupled plasmas. United States. doi:10.1063/1.2736333.
Babaeva, Natalia Y., and Kushner, Mark J. Fri . "Penetration of plasma into the wafer-focus ring gap in capacitively coupled plasmas". United States. doi:10.1063/1.2736333.
@article{osti_20979407,
title = {Penetration of plasma into the wafer-focus ring gap in capacitively coupled plasmas},
author = {Babaeva, Natalia Y. and Kushner, Mark J.},
abstractNote = {In plasma etching equipment for microelectronics fabrication, there is an engineered gap between the edge of the wafer and wafer terminating structures, such as focus rings. The intended purpose of these structures is to make the reactant fluxes uniform to the edge of the wafer and so prevent a larger than desired edge exclusion where useful products cannot be obtained. The wafer-focus ring gap (typically<1 mm) is a mechanical requirement to allow for the motion of the wafer onto and off of the substrate. Plasma generated species can penetrate into this gap and under the beveled edge of the wafer, depositing films and possibly creating particles which produce defects. In this paper, we report on a computational investigation of capacitively coupled plasma reactors with a wafer-focus ring gap. The penetration of plasma generated species (i.e., ions and radicals) into the wafer-focus ring gap is discussed. We found that the penetration of plasma into the gap and under the wafer bevel increases as the size of the gap approaches and exceeds the Debye length in the vicinity of the gap. Deposition of, for example, polymer by neutral species inside the gap and under the wafer is less sensitive to the size of the gap due the inability of ions, which might otherwise sputter the film, to penetrate into the gap.},
doi = {10.1063/1.2736333},
journal = {Journal of Applied Physics},
number = 11,
volume = 101,
place = {United States},
year = {Fri Jun 01 00:00:00 EDT 2007},
month = {Fri Jun 01 00:00:00 EDT 2007}
}
  • Argon plasma characteristics in a dual-frequency, capacitively coupled, 300 mm-wafer plasma processing system were investigated for rf drive frequencies between 10 and 190 MHz. We report spatial and frequency dependent changes in plasma parameters such as line-integrated electron density, ion saturation current, optical emission and argon metastable density. For the conditions investigated, the line-integrated electron density was a nonlinear function of drive frequency at constant rf power. In addition, the spatial distribution of the positive ions changed from uniform to peaked in the centre as the frequency was increased. Spatially resolved optical emission increased with frequency and the relative opticalmore » emission at several spectral lines depended on frequency. Argon metastable density and spatial distribution were not a strong function of drive frequency. Metastable temperature was approximately 400 K.« less
  • Capacitively coupled plasma (CCP) discharges using high frequency (HF) and very high frequency (VHF) sources are widely used for dielectric etching in the semiconductor industry. A two-dimensional fluid plasma model is used to investigate the effects of interelectrode gap on plasma spatial characteristics of both HF and VHF CCPs. The plasma model includes the full set of Maxwell's equations in their potential formulation. The peak in plasma density is close to the electrode edge at 13.5 MHz for a small interelectrode gap. This is due to electric field enhancement at the electrode edge. As the gap is increased, the plasmamore » produced at the electrode edge diffuses to the chamber center and the plasma becomes more uniform. At 180 MHz, where electromagnetic standing wave effects are strong, the plasma density peaks at the chamber center at large interelectrode gap. As the interelectrode gap is decreased, the electron density increases near the electrode edge due to inductive heating and electrostatic electron heating, which makes the plasma more uniform in the interelectrode region.« less
  • The gap length effect on plasma parameters is investigated in a planar type inductively coupled plasma at various conditions. The spatial profiles of ion densities and the electron temperatures on the wafer level are measured with a 2D probe array based on the floating harmonic method. At low pressures, the spatial profiles of the plasma parameters rarely changed by various gap lengths, which indicates that nonlocal kinetics are dominant at low pressures. However, at relatively high pressures, the spatial profiles of the plasma parameter changed dramatically. These plasma distribution profile characteristics should be considered for plasma reactor design and processingmore » setup, and can be explained by the diffusion of charged particles and the local kinetics.« less