Rapid dual-wavelength imaging ellipsometric system with stroboscopic illumination technique

Dual-wavelength light sources with stroboscopic illumination technique were applied in photoelastic modulated ellipsometry to retrieve two-dimensional ellipsometric parameters of thin films on a silicon substrate. Two laser diodes are alternatively switched on and modulated by a programmable pulse generator for triggering four short pulses at their specific temporal phase angle of a modulation cycle, and short pulses are used to freeze the intensity variation of the PEM modulated signal that images can be captured by a charge-coupled device. Although the phase retardation of a photoelastic modulator is related to the light wavelength, we employed an equivalent temporal phase shift technique to avoid any setting from the photoelastic modulator. As a result, ellipsometric parameters of different wavelengths can be rapidly obtained from this dual-wavelength ellipsometric system every 10s. Both static and dynamitic experiments were demonstrated in this work.