Ellipsometer (Woollam) - Measuring thin dielectrics with Native Oxide pre-measurement

To measure very thin (<<30nm) transparent dielectric (ie. glass/oxide) films on a Silicon witness sample, you need to account for the Native Oxide already present on the Silicon wafer. This is because the refractive index of those films is somewhat similar to the native oxide, so the optical measurement can't distinguish it. In addition, ellipsometry can't measure refractive index for films <20nm, further compounding the problem.

(You can optionally HF-etch the oxide prior to deposition to remove it - it typically takes hours to regrow to measurable thicknesses.)

The method is very similar to Example B in the SOP, or the method for measuring thin metals - you just

• Pre-measure the native oxide on the silicon witness before the primary deposition. Save the Snapshot and/or Data of this measurement.
• Perform your deposition step.
• Measure again, but utilize your previously measured layer as a "frozen" (non-fitting) layer, so you are only measuring the newly deposited film.

Detailed steps can be found in Ellipsometer (Woollam) - Measuring thin metals with oxide pre-measurement, but instead of a ~500nm Thermal oxide pre-measurement, you are measuring the native oxide (~2nm) on the silicon substrate. Other steps for saving/re-fitting data are the same.