Spectroscopic Ellipsometry Principles

Ellipsometry is a versatile thin film characterization technique that has applications in many different fields. This sensitive measurement technique provides unequalled capabilities for thin film metrology, and provides thin film thickness with angstrom resolution. As an optical technique, spectroscopic ellipsometry is non-destructive and contactless.

Which Thin Film Properties are Characterized by Spectroscopic Ellipsometers ?

Through an analysis of the state of polarization of the light that is reflected from the sample the technique allows the accurate characterization of a range of properties including the layer thickness, optical constants, chemical composition, crystallinity, anisotropy and uniformity. Thickness determinations ranging from a few angstroms to tens of microns are possible for single layers or complex multilayer stacks.

Optical

Ellipsometry Equation

Ellipsometry consists of the measurement of the change in polarization state of a beam of light upon reflection from the sample of interest. The exact nature of the polarization change is determined by the sample's properties (thickness and refractive index). The experimental data are usually expressed as two parameters Ψ and Δ. The polarization state of the light incident upon the sample may be decomposed into an s and a p component (the s-component is oscillating parallel to the sample surface, and the p-component is oscillating parallel to the plane of incidence). The intensity of the s and p component, after reflection, are denoted by Rs and Rp. The fundamental equation of ellipsometry is then written:

Thus, tanΨ is the amplitude change upon reflection, and Δ is the phase shift. Since ellipsometry is measuring the ratio of two values (rather than the absolute value of either), it is very robust, accurate (can achieve angstrom resolution) and reproducible. For instance, it is insensitive to scatter and fluctuations, and requires no standard or calibration.

Ellipsometry Advantages

  • Non-destructive and non-contact technique
  • No sample preparation
  • Solid and liquid samples
  • Fast thin film thickness mapping
  • Single and multi layer samples
  • Accurate measurement of ultra-thin films of thickness < 10nm