Volume 2, Issue 2 (March 1974)
Sources and Magnitude of Errors in the Measurement of Coating Thickness with the Double-Beam Interference Microscope
An analysis was made of three factors (fringe width, phase change, and surface roughness) which contribute to errors in measurement of coating thickness with a double-beam interference microscope. Excluding any unpredictable contributions made by surface roughness, a theoretical analysis based on a literature search revealed that the total of the two remaining errors will not exceed ±0.19 μm (±0.0076 mil) if either the coating or its substrate is a metal. If both are metals, the error will not exceed ±0.12 μm (±0.0048 mil). Measurements were made on a few samples of common coating systems. The errors experienced were much less than the above theoretical values, and would not normally contribute significantly to measurements with the double-beam interference microscope.