Measured Ellipsometry

The Measured Ellipsometry window brings a spectroscopic ellipsometer’s Ψ and Δ into a design. Import reads the pair from an instrument file and stores it on the design; Export writes either your imported curves or the design’s own calculated Ψ/Δ to CSV.

Ellipsometric curves live apart from the photometric ones in Measured Spectra, and for good reason: they carry no percent scale, there is no polarization to choose, they mean nothing without an angle of incidence, and their Δ carries a sign convention that differs between instruments. A Ψ/Δ pair imported here is what n,k Characterization reads to derive a film’s constants.

What kind of measurement this takes

Reflection ellipsometry on an isotropic sample. Ψ and Δ are defined here from the reflected amplitude ratio,

ρ = r_p / r_s = tan(Ψ) · exp(i Δ)

which is the same definition Ellipsometry computes the design’s own curves from. So a measurement imports and fits when it is a Ψ and Δ pair, in degrees, against wavelength, taken in reflection at a stated angle.

These are outside that, and none of them is read:

Not supported	What to do instead
Transmission ellipsometry. The model is the reflected pair; a measurement made through the sample is a different quantity.	Measure the same sample in reflection.
Generalised or Mueller-matrix ellipsometry, and any anisotropic or depolarising sample.	Nothing here covers it. The film is isotropic.
Is, Ic and Ic′, the native quantities a phase-modulated ellipsometer writes.	Export the measurement as Ψ and Δ from the instrument’s own software.
tan Ψ and cos Δ rather than degrees. Some exports write these under headings that say PSI and DELTA.	Convert to degrees before importing. The window detects the Δ column and warns rather than fitting them.
An angle sweep at one wavelength.	Curves here are functions of wavelength. Use Ellipsometry in angular mode to compare a design against one.

Which instrument exports have been read end to end, and which have not, is in Ellipsometry files.

Import

Press Open file… and pick a file. What the importer reads, and which instrument exports have been checked against it, is on the Ellipsometry file formats section of the formats page.

Measurement conditions

Set these before adding a curve. They are stored on each curve and can be corrected afterwards on the curve’s own card.

• Angle of incidence. The angle the instrument measured at, and the one setting a Ψ/Δ pair cannot be read without. At normal incidence there is no p-versus-s distinction left to measure, so any film gives Ψ = 45° and Δ = 180° and the pair says nothing about the coating. A fit refuses a curve that arrives at 0°.

  The window starts at 70°, which is where most fixed-angle instruments sit, near the principal angle of silicon. If the file states its angle it is read from the file instead; many do not, so check it.

• Δ convention. Two are offered:

  Setting	What it means
  Azzam–Bashara	What measurement files carry. This is the default and the one to leave alone unless you know otherwise.
  360° − Δ	Δ with the opposite sign, for data written in the other time convention. Ψ is the same either way.

  The same choice appears in Ellipsometry for the calculated curves, and the two have to agree or the comparison is meaningless. If an imported Δ looks like a mirror image of the design’s, this is the setting to change.

• Incidence side. Which face of the sample the beam entered.

Configuring the columns

The panel reports what was parsed and lets you correct it before anything is added: the wavelength unit, which column to take, whether it is Ψ or Δ, and the curve’s name. The preview beside it plots the column you are configuring, and goes back to a curve on the design when you click one.

Ψ and Δ are told apart from the values, not from the column order. Ψ is the arctangent of a magnitude ratio, so it cannot leave 0 to 90 degrees, while Δ runs over a full turn. A column that goes above 90 or below zero is therefore Δ and cannot be Ψ. Where that settles nothing the file order stands, and one click swaps them. A column the file names Psi or Delta is taken at its word.

Add this column adds the one you configured. Add all typed columns adds every column that has a quantity, which is what a two-column Ψ/Δ file wants.

What is on the design

Curves are grouped by angle and side, because a fit needs both halves of one measurement. A group missing its partner says so rather than sitting in a flat list looking usable. Each card carries the curve’s colour, name, quantity, angle, side, Δ convention and point count, and all of them stay editable.

A Δ column that never leaves −1 to 1 is flagged. At least one instrument writes tan Ψ and cos Δ under headings that say PSI and DELTA; read as degrees those numbers are legal and the mistake is invisible, so the window says so instead of letting a fit run on them. Convert such a file to degrees before importing it.

Export

Measured writes the curves on the design, with a checkbox per curve.

Calculated from the design writes the design’s own Ψ and Δ over a wavelength range and step you choose, at an angle you choose. Use it to hand a target to an instrument’s own software, or to produce a reference file. Δ is written in the convention selected in the Import tab, which is stated under the button.

The X axis of either export can be nanometres, micrometres, or photon energy in eV.

A round trip worth doing once

Exporting a design’s calculated Ψ/Δ and importing it straight back is the quickest way to satisfy yourself that the conventions on both sides line up. Fit it in n,k Characterization and you should get the film you started from, with a residual near zero. A 500 nm TiO₂ layer put through that loop comes back at 499.9 nm with residuals of 0.008° in Ψ and 0.05° in Δ. If your own loop does not close, the Δ convention or the angle of incidence is the first thing to check.