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2016 © Plasmetrex GmbH

LARGE AREA UNIFORMITY SIMULATION for a-Si LAYER THICKNESS


  The uniformity of the plasma is determined through three major effects:

  • 1. The density of reactive species depending on the gas flow distribution.
  • 2. RF standing wave effect providing usually a maximum deposition rate in in the center.
  • 3. RF skin effect causing a increased deposition rate at the substrate edges.
  • Standing wave and skin effect depend mainly on plasma parameters and gas temperature.
    • Real RF power in the plasma ↔ Layer thickness Uniformity
    • Pressure
    • Temperature influence
    • Chamber conditioning
Pressure

  Plasma process models save development costs:

  • Test panels
  • Tool time used for development
  • Consumables (like gas, pumps, ...)

Tool for Deposition in Solar Cell Manufacturing

Schematical setup of plasma deposition tool 
for PECVD in Solar Cell Manufacturing

a-Si layer thickness

RF power distribution

Measured Sheath Thickness

Measured Sheath Thickness

Ariel Ben-Porath, Benny Shoham, BrightView systems
'Increasing cell efficiency and optimizing productivity using wide area metrology'
Photovoltaics World, March/April 2010  

Simulation: Plasmetrex GmbH

Performance:

Large area plasma modelling (Solar cell manufacturing)

Approach

  • Target: Plasma parameters and their uniformity
  • Ansatz: RF field simulation in plasma (Maxwell Equations, Poisson Equation)
  • Fluid model with first two moments of Boltzmann Equation
  • Need analytical solution for complex Helmholtz equation, provides also the
    basement of a nonlonear and robust sensor model for measured harmonics in the RF discharge current

Large electrode area

  • up to 2200 mm x 2600 mm
  • Typical electrode gap: 15 mm
  • Wall temperature: 175 C
  • Process gases: SiH4, H2, ...+PH3, NF3 for chamber cleaning

Expected results

  • Large area plasmas show special effects
  • Standing plasma wave, no vacuum wave
  • Skin effect in plasma

Results

  • Axial and radial RF current is non-uniform, depending on plasma parameters.
  • Spatially varying RF power dissipation in plasma bulk (electrons - chemistry) and boundary sheath (ion - physics)
  • Non-uniformity of deposition rate and layer structure