Role of Hydrogen in Polycrystalline Si by Excimer Laser Annealing
The role of hydrogen in the Si film during excimer laser annealing (ELA) has been successfully studied by using a novel sample structure, which is stacked by a-Si film and SiN film. Hydrogen contents in the Si films during ELA are changed by preparing samples with hydrogen content of 2.3-8.2 at.% in the SiN films with a use of catalytic (Cat)-CVD method. For the low concentration of hydrogens in the Si film, the grain size increases by decreasing hydrogen concentration in the Si film, and the internal stress of the film decreases as increasing the shot number. For the high concentration of hydrogens in the Si film, hydrogen burst was observed at 500 mJ/cm 2 and the dependence of the internal stress on the shot number becomes weak even at 318 mJ/cm 2 . These phenomena can be understood basically using the secondary grain growth mechanism, which we have proposed.
Crystal Growth of Low-Temperature Processed Poly-Si by Excimer Laser Annealing - Dependences of Poly-Si Grain on Energy Density and Shot Number -
This paper examines the characteristics of the poly-Si grains formed by ELA with the energy density from 75 mJ/cm2 to 400 mJ/cm2, and discusses the change of the crystal growth mechanism of the recrystallized poly-Si dependent on the energy density. For the energy density from 250 mJ/cm2 to 350 mJ/cm2, the disk-shaped grains are observed. The dependences of the area ratio of disk-shaped grain both on the energy density and on the shot number are examined. From these results, the role of the disk-shaped grains for the change of the crystal growth mechanism dependent on the energy density is clarified.
Recrystallization processes in polycrystalline silicon
Recrystallization processes in polycrystalline silicon made by a chemical vapor deposition technique have been investigated. Primary recrystallization has been observed between 1150 and 1250 °C, secondary recrystallization occurred above 1350 °C. By this procedure, grains of about 100 μm have been obtained. Recrystallized silicon can in principle be used as a substrate for making relatively inexpensive solar cells.