Relationship between Thin-Film Transistor Characteristics and Crystallographic Orientation in Excimer-Laser-Processed Pseudo-Single-Crystal-Silicon Films

The characteristics of thin-film transistors (TFTs) fabricated on pseudo-single-crystal (PSX)-Si thin films were examined. The variations of mobility were more than the theoretical values derived from the crystallographic orientation dependence of a bulk Si metal--oxide--semiconductor (MOS) transistor. To clarify the origin of this discrepancy, the relationships between the TFT characteristics and the crystallographic orientation of Si films in the channel region were investigated by using an electron backscattering pattern (EBSP) method. It was found that the surface orientation dependence for the PSX-Si TFT was different from that for a bulk Si MOS transistor, especially for the p-channel mode. A group of TFTs having a nearly {100}-oriented nucleus had a mobility close to those of simultaneously processed silicon-on-insulator (SOI) devices in the p-channel mode as well as in the n-channel mode. In contrast, a group of TFTs having a nearly {110}-oriented nucleus had a low and widely scattered mobility. The reason for these results is that twin boundaries with dislocations are easily generated in a grain grown from a {110}-oriented nucleus in order to compensate for the difference of the growth rates in different directions.