RGB-Color Image Analysis for Determination of Birefringence of Micro-Films and Columnar Coatings

The birefringence analysis of thin approximate to 1 mu$\approx 1\hspace*{3.33333pt}\umu $m SiO2 films deposited via evaporation at a glancing angle of 70 circle$\hspace*{3.33333pt}{70}<^>{\circ}$ to the normal on resist pillar arrays on Si and nanopatterned SiO2 substrates is carried out by spectral and color (red-green-blue [RGB]) imaging modes. Retardance and birefringence of the films deposited over flat and structured regions can be distinguished with only approximate to 1% difference between neighboring regions for the visible spectral range using RGB numerical analysis of images. The Michel-Levy color map is used for color rendering of birefringence to make quantitative measurements by numerical RGB color filtering. It is shown that by using lambda/2$\lambda /2$ at 530 nm waveplate inserted at pi/4$\pi /4$ angle to the cross polarizer-analyzer setup, the range of changes in chromaticity xy-coordinates expands approximately twice upon angular rotation of a birefringent sample. This facilitates a better signal-to-noise determination of birefringence. The proposed method with lambda/2$\lambda /2$-plate color shifting can be directly used to determine birefringence from step-like spectral features in reflection and transmission polariscopy. Direct measurement of birefringence (Delta n=0.023${\Delta}n=0.023$) and retardance of SiO2 chevron film is carried out using Berek compensator as a benchmark.

Automated summary

The birefringence analysis of SiO2 films deposited at a glancing angle of 70° on resist pillar arrays and nanopatterned SiO2 substrates is carried out using spectral and color imaging modes. The films can be distinguished based on retardance and birefringence using RGB numerical analysis. By inserting a λ/2 waveplate and rotating the birefringent sample, the range of chromaticity xy-coordinates is increased, facilitating a better determination of birefringence.