Oxide thickness & dispersion

Measuring both thickness and dispersion of an oxide is common because optical properties depend on deposition conditions. A known-dispersion oxide such as thermal SiO₂ is a simple case, but SiOx comes in many stoichiometries with different dispersions, so thickness and dispersion must be measured together. The approach: fit with standard SiO₂ and check for a good fit (a poor fit means the dispersion doesn't match), then use a Cauchy representation with thickness and Cauchy coefficients as free parameters - preferably on a thicker film (> 400 nm). Adding a "scale" parameter corrects for intensity differences between calibration and measurement. Once a good fit fixes the dispersion, thinner samples measure thickness alone; a correct dispersion gives good fits for both thick and thin films.

Measurement workflow

1. Fit the measurement using standard SiO₂ dispersion and check whether a good fit can be achieved.
2. If dispersion does not match, use a Cauchy representation of SiO₂ and set both thickness and Cauchy coefficients as calculation parameters. Thicker available films, preferably above 400 nm, give the best results.
3. Add the scale parameter and recalculate. Scale corrects for small light-intensity differences between calibration and measurement configuration.
4. After a good fit is obtained, fix the measured dispersion. Other, thinner samples can then be measured using that dispersion, with only thickness and scale as measured parameters.
5. Check the result by confirming that the same dispersion gives a good fit for both thick and thin films.

Why use MProbe 40 Vis?

• Small-spot measurement helps select the exact measurement area.
• Live camera image with reticle helps position the measurement on the sample.
• Different objectives can be selected based on spot-size requirements.
• MProbe 40 Vis has the same performance as MProbe 20 Vis, with small-spot capability added.

Basic specification

Measured with: MProbe 40 Vis (MProbe 40).