Location control of crystal grains in excimer laser crystallization of silicon thin films for single-grain TFTs

Location of crystal grains is controlled in excimer laser crystallization (ELC) of amorphous Si (a-Si) thin films, aiming at a high-performance single-grain thin film transistor (TFT) whose channel is inside a single crystal grain with no grain boundary in the channel. The location control is achieved by manipulating seed-crystal forming sites in the starting thin film. The sites are small portions of the a-Si thin film, typically 1 μm in diameter, only in which nanometer-sized crystallites are embedded in the amorphous matrix. During the ELC, at least one crystallite survives the melting duration and serves as a seed crystal for the resolidification of the surrounding molten silicon. As a result, large crystal grains are formed at the predetermined sites. The TFTs whose channels are fabricated at the location-controlled crystal grains exhibit higher performance than the random polycrystalline Si (poly-Si) TFTs.