Naoya Yamamoto

Pulsed Green-Laser Annealing for Single-Crystalline Silicon Film Transferred onto Silicon wafer and Non-alkaline Glass by Hydrogen-Induced Exfoliation

A single-crystalline Si film was transferred onto a Si wafer and non-alkaline glass by hydrogen-induced exfoliation and the effect of pulsed green-laser annealing was investigated. Above a laser energy of 1285 mJ/cm2, the crystallinity of the Si film was recovered both on the Si wafer and the glass. The linewidth of micro-Raman spectra of the Si film on the Si wafer was constant at about 3.9 cm-1 which was close to that for commercial silicon-on-insulator (SOI) wafer. On the other hand, the linewidth of the Si film on the glass was constant at about 4.1 cm-1. A Raman peak shift toward a lower frequency was observed on the Si film on the glass; it was assumed that the difference of the linewidth on the Si wafer and that on the glass originated from the tensile stress in the Si film due to the difference of thermal expansion coefficients. The results of numerical simulation suggested that the thickness of the region damaged by hydrogen ion implantation was greater than 300 nm; the damaged region had to be melted and resolidified to obtain the recovered single-crystalline silicon upon pulsed laser annealing.

Orientation Dependence of Silicon Oxidation Ratio in High-Pressure Water Vapor

We investigated the relative oxidation rates of single-crystalline Si substrates with various orientations to study the formation of thermally grown oxide films on multicrystalline Si at low temperatures in high-pressure water vapor. The oxidation rates depended greatly on the Si substrate orientation, but the increasing pressure did not change the proportion of their relative oxidation ratio even though the oxidation rate was accelerated by the pressure. On the basis of our modeling of the Si surface structure, we consider that the dependence of oxidation ratio on substrate Si orientation depends in turn on interface atomic density for a structure that has one or two Si–O bonds.

Improvement in Characteristics of Thin Film Transistors upon High-Pressure Steam Annealing

Low-temperature (350 °C) and high-pressure (1 MPa) steam annealing is effective for improving the characteristics of low-temperature-processed polycrystalline silicon thin film transistors (LTPS-TFTs) and their uniformity. We developed high-pressure annealing systems for 600×720 and 400×500 mm2 glass substrates, and investigated the annealing effects on the electrical properties of n-channel TFTs. The TFTs fabricated without high-pressure annealing have a low saturation mobility caused by the large amount of fixed oxide charge in SiO2, and a high threshold voltage (Vth) caused by the high trap density at the SiO2/Si interface. High-pressure steam annealing effectively reduces the amount of fixed oxide charge and the number of interface traps, resulting in the improvement of TFT properties. The crystal orientation of poly-Si strongly affects the interface trap density, which causes the nonuniformity of the TFT characteristics. High-pressure annealing also decreases the deviation of the trap density caused by the crystal orientation, and uniform electrical properties are achieved.