A method of forming polycrystalline silicon film with large grains at a controlled location using a single irradiation of an excimer laser beam is proposed. The excimer laser beam is modified to have a specific spatial intensity profile, periodic spatial variation of intensity maxima ͑I max ͒ and minima ͑I min ͒, by means of a specially designed mask composed of transparent and opaque patterns. It is noted that the evolution of polycrystalline silicon microstructure is critically dependent on the melt depth of amorphous silicon at I min , which we categorized as "partial melting," "near-complete melting," and "complete melting" regimes. While the lateral grain growth of polycrystalline silicon increases in proportion to the fluence gradient as the energy density is increased, surprisingly we find that it decreases in the complete melting regime due to the "secondary nucleation" occurring at I max . By judicious selection of optimum intensity modulation and the spacing between I max and I min , we have obtained the maximum lateral grain size of 7.0 m at controlled position.

A new method to form polycrystalline silicon film with large grains at the controlled location by using a single irradiation of excimer laser beam is proposed for polycrystalline silicon thin film transistor. The excimer laser beam is modified to have a spatial intensity profile -periodic spatial variation of intensity maxima (I Max ) and minima (I Min ) -by the specially designed mask composed of the opaque and the transparent patterns where the opaque pattern size is less than the optical resolution of projection lens. Based on the melt depth of amorphous silicon at the location of I Min , one can obtain three different regimes, namely, the partial melting, the near-complete melting, and the complete melting. Polycrystalline silicon grains grow vertically and laterally from the seeds at the location of I Min to the complete molten region of I Max . The evolution of polycrystalline silicon microstructure is investigated and elucidated in each regime.