Groove depth dependence of IR transmission spectra through silicon gratings: experiment versus theory

Infrared normal transmission through diffraction gratings micromachined on (1 1 0) silicon wafer with differing periods, groove widths and groove depths was experimentally and theoretically studied. Numerical simulations using rigorous electromagnetic theory of gratings, and a method of smoothing the substrate-derived interference fringes in the simulated spectra were carried out to account for the measured spectra. High sensitivity of the spectra at wavelengths smaller than the grating period to the precise value of the groove depth was studied. By adjusting the groove depth values input in the simulations, a fair agreement between theory and experiment was achieved. The results of the study suggest a possibility of an all-optical method of checking the depth of lamellae obtained in a non-self-stopping etch process, or of measuring in-depth structural dimension during microelectronic fabrication.