THE EVOLUTION OF PLASMA ETCHING IN INTEGRATED CIRCUIT MANUFACTURING

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THE EVOLUTION OF PLASMA ETCHING IN INTEGRATED
CIRCUIT MANUFACTURING

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Abstract author J.W. Coburn Dept. of Chemical
Engineering University of California

• Presented by Wei Yan

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Introduction

• Plasma etching is currently widely used in the
  fabrication of silicon-based integrated circuits.
  
• The process is used to produce high-resolution
  patterns in many of the thin layers of the
  circuits and to selectively remove masking layers
• This paper describe the evolution of plasma
  etching in integrated circuit manufacturing from
  many different aspects

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Plasma system

• Early 1970s plasma equipment
• atoms or radicals,created in a reduced pressure
  glow discharge, were used to react with solids to
  form volatile products.
• typically did not cause extensive energetic ion
  bombardment of the wafer surface

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Plasma system(contd)

• Capacitively coupled planar diode systems
• Symmetric systems (area of the powered electrode
  is comparable to the area of grounded surface in
  contact with the plasma)have large plasma
  potentials
• A more spatially uniform plasma density is
  obtained when the gap between the electrodes is
  much less the the electrode diameter
• Grounded wafer chucks.
• Capacitively coupled cylindrical diode (hexode)
• Spatially uniform plasma with a low plasma
  potential
• Solve the micro-roughness of the etched surface
  problem
• Wafer area(inner cylinder or hexode) is always
  less than the area of the grounded outer
  cylinder(wall) resulting in a low plasma potential

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Plasma system(contd)---Independent control of
the ion energy and ion current density

• Planar triode etchers
• Fast etch rates with lower ion energies
• Single frequency triode involves energetic ion
  bombardment of both powered electrodes at lower
  pressures, causes micro-roughness
• Dual frequency triode/dual frequency diode
  systems
• Solve the micro-roughness problem
• Inductively powered sources , combined with
  capacitively powered wafer chucks
• Generated higher density plasma
• Provide the optimum ion energy

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Some Plasma equipment Illustrations

• CCP-Capacitively coupled plasma
• ICP - Inductively coupled plasma

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Illustration of Inductively coupled plasma


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Chemistry in Plasma Etching

• Fluorine-deficient (polymerizing) chemistry
  (first used to etch siO2 selectively to Si)
• Polymerizing chemistries in controlling the
  undercut (sidewall passivation)
• Use of halocarbon feedgases, CF4 was the most
  common

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Study of the Process in Surface Science Aspects

• Directed beam simulations of the plasma etching
  (late 1970s)
• Confirm the importance of the energetic ion
  bombardment in increasing the reaction
  probability of neutral species with solid
  surfaces.

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Cooling

• Inject some helium between the wafer chuck and
  the backside of the wafer

• Peripheral clamping of the wafer to the chuck
• Often lead to a redial dependence of the wafer
  temperature causing a radial dependence of the
  etching rate.
• address schedule implications
• Use electrostatic clamping of the wafer(ECE)
• i.e. the wafer serves as one electrode of a
  planar capacitor
• Provides a uniform clamping force over the wafer
  surface
• Controlled and uniform wafer temperatures can be
  obtained in plasma etching environments

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Wall-catalysed Recombination

• Limiting factor in the transport of atoms and
  radicals at low pressures.
• Recombination of atoms/radicals on surfaces
  immersed in a plasma can greatly influence the
  steady state concentration of the atoms/radicals
  and the resulting etch behavior
• The efficiency of this recombination process
  depends on
• the surface material
• the surface temperature
• the nature of the gas phase species