Lateral Diffusion of Phosphorous Induced by Excimer Laser Irradiation of Silicon Thin Film for Formation of Gradual Lightly Doped Region in Polycrystalline Silicon Thin Film Transistors

Abstract

A gradual lightly doped region was fabricated in a polycrystalline silicon (poly-Si) film by the lateral diffusion of dopants induced by excimer laser annealing. The lateral diffusion of phosphorous induced by excimer laser irradiation was verified, and the lateral diffusion length was measured by electrostatic force microscopy (EFM). The graded lateral diffusion profile was also observed by EFM. The lateral diffusion length from a heavily doped Si region to the intrinsic Si region was varied from 1.35 to 4.28 µm depending on the excimer laser energy density and irradiation number. The experimental results indicate that a lightly doped drain (LDD) structure can be fabricated in poly-Si thin film transistors (TFTs) by the lateral diffusion of dopants without the need for any additional mask.