Polycrystalline Silicon Thin Film Transistors Fabricated by Employing Selective Self Ion-Implantation and Excimer Laser Annealing

Abstract

Polycrystalline silicon thin film transistors (poly-Si TFT’s) fabricated by excimer laser annealing (ELA) are promising devices for active-matrix liquid-crystal display (AMLCD) due to their high field-effect mobilities and low thermal budgets [1,2]. It is well known that the electrical characteristics of poly-Si TFTs depend on the grain size and the defect density of the poly-Si film. In the fabrication of low temperature poly-Si TFT’s, excimer laser annealing is considered as most a promising tool for preparing poly-Si films with low defect densities. However, grain size is very sensitive to the laser energy density, and nucleation takes place randomly [3,4]. Selective self ion-implantation (Si+) has also been reported as a tool for artificial nucleation prior to thermal annealing. If high-energy ion-implantation is employed, high-density defects and high-density nucleation can be provided artificially in amorphous silicon films [5]. In this paper, we propose a novel method to prepare good quality poly-Si films by employing selective self ionimplantation and ELA. We fabricated poly-Si TFT’s by employing the proposed method and confirmed the improved electrical characteristics of poly-Si films in both the onand the off-state through measurements of the TFT characteristics.