RECRYSTALLIZATION OF LPCVD AMORPHOUS SI FILMS USING F+ IMPLANTATION

Abstract

The recrystallization behavior of low pressure chemical vapour deposition amorphous Si films by implanting F-19+ with various energies and doses and by annealing at 600-degrees-C has been investigated by X-ray diffraction, transmission electron microscopy, and Raman spectroscopy. The electrical properties of these films have been studied by fabricating n-channel (n-ch) thin film transistors with these films. The grain size of 150 nm thick Si films increased from about 0.3 mum to about 2.5 mum with increasing F+ dose. The grain size enhancement was more effective, when the projection range of the fluorine ion was placed at the Si/SiO2 interface. This enhancement was attributed to the retardation in the nucleation rate owing to the higher degree of disorder at the Si/SiO2 interface by F+ implantation. A heavy dose of fluorine ions caused the increase in the threshold voltage of n-ch thin film transistor, suggesting fluorine is a hole generator owing to its large electronegativity. The field effect mobility increased as the grain size increased. The maximum field effect mobility obtained without hydrogen passivation was about 23 cm2 V-1 s-1 when the dose was 2 x 10(15) cm-2 and the projection range was targeted at the Si/SiO2 interface. It was found that the field effect mobility values mainly depended on the grain size and that the grain boundary passivation by fluorine atom seemed ineffective.