Epifilm thickness measurements using Fourier transform infrared spectroscopy: Effect of refractive index dispersion and refractive index measurement

Procedures and results of refractive index measurements using a Fourier transform infrared spectrometer are reported. These measurements were performed on both lightly and heavily doped silicon samples over the midinfrared (2.5–25 μm) spectrum region. A strong dependence of refractive index as a function of substrate dopant concentration was observed. Moreover, it was observed that the refractive index of heavily doped silicon also varies significantly with wavelength. Furthermore, it was also observed that the refractive index of silicon decreases with increasing wafer temperature for long wavelengths. Finally, the effect of refractive index dispersion on epifilm thickness measurement was examined. The results suggest that the spectral dispersion of the refractive index cannot be neglected for epifilm thickness measurements.