Two-step laser recrystallization of poly-Si for effective control of grainboundaries

An excimer laser annealing method is proposed to increase the grain size an d control the microstructure of polycrystalline silicon thin film. The prop osed method is based on lateral grain growth during laser annealing. The la teral grain growth results when the lateral temperature gradient is larger than the vertical temperature gradient in molten a-Si. We designed a laser- masking window to maximize the lateral growth effect and affect the locatio n of grain boundaries. The masking window transmits the laser beam selectiv ely on a-Si film, so that the lateral temperature gradient is formed betwee n molten a-Si region and the cooler unmelted a-Si region. After the first l aser irradiation, a second laser irradiation without masking window is carr ied out to recrystallize the residual a-Si regions. Employing the proposed method, we obtained up to I mu m grain size with 80 nm thick a-Si film at 2 00 degrees C substrate temperature and also observed non-random grain bound aries by transmission electron microscopy (TEM). From observation with lase r energy variations, we found that the lateral growth takes place when the laser energy is greater than the full melt threshold. (C) 2000 Elsevier Sci ence B.V. Al rights reserved.