Crystallization of Silicon Ion Implanted LPCVD Amorphous Silicon Films for High Performance Poly-TFT

Abstract

AbstractThe mechanism of silicon ion implantation on the crystallization kinetics and the resulting grain sizes of LPCVD α-Si films have been studied by x-ray diffraction and transmission electron microscopy. The solid-phase crystallization was proceeded by random nucleation and growth from the Si/SiO2 interface. The most effective grain size enhancement was found by targeting the peak concentration of implanted siliconbeyond the Si/SiO2 interface, such that the maximum kinetic energy transfer occurred at that interface. The average grain size increases from ∼0.16 μm to ∼2.0 μm by a Si + implantation at 92KeV and a dose of 2X1015 cm-2 for 0.1 μm silicon film. X-ray diffraction intensities were analyzed to optimize implanting dose, beam current and energy for different film thickness. Grain size enhancement was achieved by retarding the random nucleation and increasing the nucleation activation barrier from ∼3.9eV to ∼4.9 eV for the implanted sample. The amorphous to crystalline growth activation barrier of ∼3.2 eV was not altered by Si+ implantation. The observed nucleation and growth kinetics change may be due to the chemical effect of the recoiled oxygen atoms from the substrate. The field-effect mobilities for both n- and p-channel TFTs increase by a factor of two with deep silicon implant.