Methods on Absorbing Films

• The following methods are combined:

Contents

1 Cases for reducing unknowns

1.1 Opaque Layer

1.2 Optical Constant Parameterization

1.3 Extrapolation from Transparent Region

2 Cases for adding information

2.1 SE + Transmission

2.2 Interference Enhancement

2.3 Multi-Sample Analysis

2.4 In-Situ

1. Cases for reducing unknowns

1.1 Opaque Layer

• Sample absorbs light in the entire measured range.
• Typical for metal substrates, thick metal films (>50-100nm)
• Model assumptions affect accuracies of final optical properties.
• Advantages:
  • Simplified data analysis – ignore the film thickness.
• Disadvantages:
  • Ignores surface films (oxide and/or roughness).
  • Opaque layer may have different “n,k” from thin layers.

1.2 Optical Constant Parameterization

• Use dispersion equations to describe sample optical properties.
• Often combined with other techniques
• Advantages:
  • Reduce # of Fit Parameters
  • Smooth, continuous curves for n,k that are often KK consistent
  • Work better for well-known and well-defined optical properties, such as a-Si or DLC
• Disadvantages:
  • By itself, results can often be correlated
  • Need to choose best of many different options.

1.3 Extrapolation from Transparent Region

• Sample is transparent in some measured region
  • Get thickness and n in the transparent region (k=0)
  • Extend to absorbing region to get n, k and thickness
• Correct model should fit both transparent and absorbing regions
• Advantages:
  • High sensitivity to thickness in transparent region.
  • Pt by pt fit quickly and easily extends into absorbing region.
  • Genosc models enhance KK consistency.
• Disadvantages:
  • Requires film to be transparent over some measured wavelengths.
  • Possible for NK to get lost in absorbing region
  • Complicated

2. Cases for adding information

2.1 SE + Transmission

• Advantages
  • Extra information from Intensity breaks correlation.
• Disadvantages:
  • Not for absorbing substrates.
  • Need accurate Intensity measurements.

2.2 Interference Enhancement

• Advantages:
  • Extra info. from multi-angle data.
  • Effective “substrate” features enhance sensitivity to correct film thickness/n,k.
  • Great method for absorbing substrates.
• Disadvantages:
  • Requires extra, thick dielectric layer.
  • Increases complexity

2.3 Multi-Sample Analysis

• Advantages:
  • More information about same material.
  • Easy to achieve from map of non-uniform sample.
• Disadvantages:
  • Requires consistent optical constants
  • In-situ requires ellipsometer integration into system.

2.4 In-Situ