Raman spectroscopy for evaluating laser annealed silicon layers

Abstract

This paper reports on the results of applying ordinary Raman spectroscopy and a new narrow probing laser source to determine the degree of crystallinity obtained after laser annealing of amorphous silicon. Ordinary Raman spectroscopy over a large area annealed by multiple laser scans has been found to result in Raman spectra of variable band shapes and frequencies. These may be interpreted as superposition of amorphous (broad band centered around 480cm-1) and single crystal silicon spectra (sharp band centered at 523 cm-1) from the partially recrystallized regions. Probing selected locations in the annealed regions with a 1µm spot size laser source (using a Molecular Optical Laser Examiner, MOLE) has shown, for the first time, sharp bands being produced as low as 512 cm-1. Further annealing moved the narrow bands towards 523 cm-1, the centre frequency typical for ordinary Raman spectroscopy on single crystal silicon. Thus a combination of the two approaches allows examination of the effectiveness of laser annealing at both the macroscopic and microscopic level.