GRAIN-GROWTH OF LASER-RECRYSTALLIZED POLYCRYSTALLINE AND AMORPHOUS-SILICON FILMS

Abstract

The grain growth mechanisms of polycrystalline and amorphous silicon films on SiO2 have been studied using continuous wave (CW) CO2 laser system under different laser powers. A solid-phase grain growth mechanism was observed at laser powers ranging from 5 W to 15 W. In this power region, the grain growth of the amorphous silicon specimens was more significant than that of the polycrystalline silicon ones. Dramatic grain growth was obtained as the laser power increased from 17.5 W to 22.5 W for both specimens. The liquid-phase grain growth mechanism could be used to explain this phenomenon. In the solid-phase grain growth regime, the [110] texture was dominant for the polycrystalline silicon samples and a stronger [100] texture was observed for the amorphous specimens. However, X-ray diffraction revealed a [100] preferred orientation for both the laser-recrystallized polycrystalline and amorphous silicon films in liquid-phase growth regime. Furthermore, thin film transistors fabricated with these recrystallized films were also demonstrated. TFTs with an on/off current ratio of 1.58 x 10(8) and an effective mobility as large as 200 cm(2) V-1 s(-1) could be achieved for silicon films laser-recrystallized in the liquid-phase growth regime due to the large grain size.