Nickel ͑Ni͒ induced crystallization of amorphous silicon (a-Si) has been studied by selective deposition of Ni on a-Si thin films. The a-Si under and near the Ni-covered regions was found to be crystallized after heat treatment at 500°C from 1 to 90 h. Micro-Auger electron spectroscopy revealed that a large amount of Ni stayed in the region under the original Ni coverage, but no Ni was detected either in the crystallized region next to the Ni coverage or in the amorphous region beyond the front of the laterally crystallized Si. X-ray photoelectron spectroscopy revealed a nonuniform Ni distribution through the depth of the crystallized film under the original Ni coverage. In particular, a Ni concentration peak was found to exist at the interface of the crystallized Si and the buried oxide. It was found that a layer of 5-nm-thick Ni could effectively induce lateral crystallization of over 100 m of a-Si, but the lateral crystallization rate was found to decrease upon extended heat treatment. Transmission electron microscopy analysis showed that the crystallized film under the Ni coverage was composed of randomly oriented fine grains, while that outside the Ni coverage was mainly composed of large ͑110͒-oriented grains. A unified mechanism is proposed to explain the Ni induced crystallization of a-Si and possible reasons for the reduction in the lateral crystallization rate are discussed.

Compared to conventional solid phase crystallized (SPC) thin-film transistors (TFT's), metal induced laterally crystallized (MILC) TFT's exhibit significantly enhanced performance at reduced processing temperature. It is concluded that the major improvements in MILC-TFT's result from the growth of the crystal grains in a direction longitudinal to that of the current flow, whereas in SPC-TFT's, the grain boundaries are randomly oriented. It is also observed in this work that while the MILC-TFT's are less sensitive to short-channel effects (SCE's), their leakage current exhibits higher sensitivity to channel length reduction. These differences again can be traced to the different arrangements of the grain boundaries in the two types of devices.

Abstract-Process and material characterization of the crystallization of amorphous silicon by metal-induced crystallization (MIC) and metal-induced lateral crystallization (MILC) using evaporated Ni has been performed. An activation energy of about 2 eV has been obtained for the MILC rate. The Ni content in the MILC area is about 0.02 atomic %, significantly higher than the solid solubility limit of Ni in crystalline Si at the crystallization temperature of 500 C. A prominent Ni peak has been detected at the MILC front using scanning secondary ion mass spectrometry. The MIC/MILC interface has been determined to be highly defective, comprising a continuous grain boundary with high Ni concentration. The effects of the relative locations of this interface and the metallurgical junctions on TFT performance have been studied.Index Terms-Grain boundary, MILC, nickel, thin-film transistor.