The most common method to precisely measure the thickness of anti-reflection coatings is using ellipsometry which looks at the way polarized light is reflected.
A simple method to measure anti-reflection coating is by simply looking at the film colour.1
The color of the film is affected by the thickness as well as the refractive index so the film color is merely a rough guide to thickness. There are multiple tables for determining the films thickness for films of silicon dioxide or silicon nitride such as those shown below. It is common to fabricate film standards so that variations in process conditions can be quickly detected by comparing samples to the standard.
Color Chart for Films of Silicon Dioxide (SiO2) under fluorescent lighting2
|Colour and Comments|
|0.10||Dark violet to red violet|
|0.15||Light blue to metallic blue|
|0.17||Metallic to very light yellow green|
|0.20||Light gold to yellow; slightly metallic|
|0.22||Gold with slight yellow orange|
|0.25||Orange to melon|
|0.30||Blue to violet blue|
|0.32||Blue to blue green|
|0.35||Green to yellow green|
(actually at times appears to be light creamy gray or metallic)
|0.58||Light orange or yellow to pink borderline|
|0.68||"Bluish" (actually appears more like a mixture between violet red and blue green and looks grayish)|
|0.72||Blue green to green (quite broad)|
|0.80||Orange (rather broad for orange)|
|0.85||Dull, light red violet|
|0.95||Dull yellow green|
|0.97||Yellow to "yellowish"|
|1.24||Carnation pink to salmon|
|1.32||Sky blue to green blue|
|1.54||Dull yellow green|
- 1. , “Electronic color charts for dielectric films on silicon”, Optics Express, vol. 12, pp. 1464–1469, 2004.
- 2. , “Nondestructive determination of thickness and refractive index of transparent films”, IBM Journal of Research Devices, vol. 8, pp. 43–51, 1964.