Identifying the Measured Interface in Optical Film Profiling

A transparent film can present more than one optical interface to a surface profiler. Before treating a height map as the coating surface or film thickness, confirm what the analysis selected. This is especially important when a protective film sits on a textured or patterned substrate.

Describe the complete optical stack

Zygo’s thick-film analysis explanation distinguishes signals from the film surface and substrate and uses film optical information in its analysis. This supports identifying the selected interface rather than assuming every apparent height belongs to the outer surface.

Record film identity, substrate, nominal construction and any known optical data required by the chosen method. Include whether the measurement is intended to obtain topography, thickness or both. Those outputs should have explicit names in the report.

Review the method’s suitability

Ask the laboratory how it handles areas where the method cannot separate or confidently evaluate the interfaces. Missing or invalid data should remain identified, rather than being silently filled into a smooth-looking map.

Use a representative verification feature

Where practical, include a known construction or an independently characterized location to verify interpretation. Agree on the reference before evaluating the unknown sample. A convenient unrelated glass standard may verify instrument operation without validating the specific film model.

For example, a textured substrate can contribute structure that remains visible through a coating. A map resembling that texture should prompt review of interface selection before concluding that the coating reproduced the same topography.

Retain the original dataset and analysis configuration. If optical inputs are revised, issue a documented reanalysis and identify which outputs changed. Do not overwrite the earlier result without preserving the reason for correction.

Keep stitching and any excluded border regions documented when several fields are combined. A seamless-looking image should still reveal which locations were directly measured and which portions could not support the required interface analysis.

Report the property actually established

Label top-surface height, substrate height and film thickness separately. State the measurement area and any excluded regions. A thickness map does not independently prove cure, adhesion or absence of every coating defect.

Use complementary inspection when the product requirement extends beyond the optical method’s valid scope. Plan destructive verification carefully so it can be connected to the same mapped location.

The roughness-analysis guide addresses filtering of a measured surface, while contact-angle review covers a different property of the exposed film.