Crystallinity Evaluation of Low Temperature Polycrystalline Silicon Thin Film Using UV/Visible Raman Spectroscopy

Abstract

Low temperature poly-Si (LTPS) is one of the most important high mobility channel materials for thin film transistors (TFTs). However, the improvement of the LTPS TFT performance is limited by the grain size and crystallinity variation. Thus, advanced nondestructive and high-resolution evaluation techniques are needed for LTPS thin film to monitor its crystallinity and grain size distribution. We evaluated the crystallinity of LTPS thin film during the fabrication process with various conditions using UV/visible Raman spectroscopy. As a result, we confirmed from Raman imaging measurements that a-Si deposited at higher temperature and lower pressure is crystallized rapidly. It can be considered that slow crystallization is caused by strong tensile strain and high hydrogen concentration in LTPS thin films. Furthermore, good crystallinity can be obtained with increasing annealing duration and deposition temperature of a-Si. In conclusion, we believe Raman spectroscopy, especially when used as imaging technique, is useful for in-line process evaluation.