Reflection of infrared radiation from lamellar gratings on a silicon wafer

Infrared reflectance spectra in the spectral range from 1.5 to 14 mu m of a smooth-surface silicon sample cut from a Si wafer and grating structures f abricated on the same wafer have been measured and analyzed theoretically. The structural dimensions of the gratings are in the range of the radiation wavelengths. Two types of experiments have been conducted. In the first ex periment we investigated specular reflectance. The results show that the re flectance spectra depend on the mounting type: planar- or conical-diffracti on mounting, and on the side of the sample which is irradiated. The differe nces become very pronounced for wavelengths larger than the grating period. For the reflection spectra in the case of conical-diffraction mounting, re asonably good agreement between experimental spectra and theoretical zero-o rder efficiency spectra is obtained. In the case of planar- diffraction mou nting an agreement between theory and experiment is achieved only if we ass ume an admixture of the higher diffraction orders. In the second experiment we studied the angular diffraction pattern from the different gratings in planar- diffraction mounting. We found that it depends strongly on the radi ation incidence angle, the radiation wavelength and grating parameters. It is observed and confirmed by simulation that the reflection dip at about 9 mu m due to vibrational transition in complex Si-interstitial O-2 is enhanc ed by the grating structure. (C) 1999 American Institute of Physics. [S0021 -8979(99)07711-7].