Ellipsometric Diagnostic of Anisotropy Properties of Surface Layer of Silicon After Laser Treatment

Optical properties of non-treated silicon plates and Si plates modified by femtosecond laser irradiation have been investigated by ellipsometry. The samples of the nanostructured silicon as isolated cells were formed on the single-crystal silicon wafers by a method of the laser ablation. Laser beam scanning modes provide the synthesis of nanostructured silicon dioxide particles or silicon nanoparticles. It was established that the principal angle of incidence for the nanostructured silicon is significantly reduced in comparison to the one for monocrystalline silicon wafers of 12–21°. Moreover, the essential difference between the values of the cosΔ and tgΨ for two mutually perpendicular directions in own plane of the cell when ones were measured at single taken angle of light incidence \( \varphi \) = 53° was observed. Besides, for single cell it was found that the difference between the significances of the principal angle of incidence and ellipsometric parameter Ψ for two mutually perpendicular directions in own plane of the isolated cell of the nanostructured silicon is essential and equal to about 9° and more than 15° respectively. This means that the formed silicon nanostructures possess great optical anisotropy as a result of deformation influence of laser ablation and appearance of elastic stresses within the surface layer of the nanostructured silicon. The optical anisotropy was not found for silicon areas located between the cells of the nanostructured silicon.