Raman spectroscopy investigation on excimer laser annealing and thickness determination of nanoscale amorphous silicon

Raman spectroscopy was used to investigate excimer laser annealing and thickness determination of amorphous silicon (a-Si) layers which are less than 20 nm thick. The a-Si layers were produced on silicon (Si) substrates using Si⁺ ion implantation with an energy of 10 keV and a dose of 1 × 10¹⁵ cm^-2. Excimer laser annealing was applied to re-crystallize the a-Si layers. The dependence of re-crystallization on laser fluence was investigated using Raman spectroscopy. A threshold laser fluence of 0.4 J cm^-2 was required to re-crystallize the a-Si layers. In Raman spectroscopy, the Raman intensity shows a periodical variation with a period of 90° as a function of the angle between the Si orientation and the laser polarization. Based on this phenomenon, a method to determine nanoscale a-Si film thickness was proposed in two ways. One way was carried out without sample rotation to determine the a-Si thickness provided that the reference c-Si and a-Si/c-Si samples are in the same crystal orientation. The other way was carried out with sample rotation to determine the a-Si thickness without knowing the crystal orientation beforehand.