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

Abstract

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.