Submicron-scale characterization of poly-Si thin films crystallized by excimer laser and continuous-wave laser

Abstract

Stress and defects in polycrystalline silicon (poly-Si) for thin-film transistor (TFT) were investigated on the aspect of difference of techniques between excimer laser annealing (ELA) with extremely short pulse duration and continuous-wave laser lateral crystallization (CLC). Micro-Raman spectroscopy was used for characterization. Mapping measurements with high spatial resolution were carried out for the optical-phonon mode at ∼520 cm−1 to observe distribution of stress and defects. Defects were characterized also by local-vibration modes (LVMs) in ∼2000 cm−1 region, where LVMs were induced by terminating dangling bonds at defects with hydrogen atoms. Significant tensile stress was found for both ELA and CLC, which magnitude is dominated by the thermal stress. The stress in ELA poly-Si tends to relax in the vicinity of grain boundaries. Densities of defects in grains and dangling bonds at grain boundaries in CLC poly-Si films were apparently smaller than those in ELA films. Those differences are attributed to cooling rates of ELA and CLC. The defects in CLC poly-Si distribute extending along the laser scan direction parallel to TFT channel current, which is effective to prevent the deterioration of TFT characteristics by residual defects.