The effects of hydrogen on aluminum-induced crystallization of sputtered hydrogenated amorphous silicon

The effects of hydrogen on aluminum-induced crystallization (AIC) of sputtered hydrogenated amorphous silicon (a-Si:H) were investigated by controlling the hydrogen content of a-SiH films. Nonhydrogenated (a-Si) and hydrogenated (a-Si:H) samples were deposited by sputtering and plasma-enhanced chemical vapor deposition (PECVD). All aluminum films were deposited by sputtering. Hydrogen was introduced into the sputter-deposited a-Si films during the deposition. After deposition, the samples were annealed at temperatures from 200°C to 400°C for different periods of time. X-ray diffraction (XRD) patterns were used to confirm the presence and degree of crystallization in the a-Si:H films. For nonhydrogenated films, crystallization initiates at a temperature of 350°C. The crystallization of sputter-deposited a-Si:H initiates at 225°C when 14% hydrogen is present in the film. As the hydrogen content is decreased, the crystallization temperature increases. On the other hand, the crystallization initiation temperature for PECVD a-Si:H containing 11at.%H is 200°C. Further study revealed that the crystallization initiation temperature is a function, not only of the total atomic percent hydrogen in the film, but also a function of the way in which the hydrogen is bonded in the film. Models are developed for crystallization initiation temperature dependence on hydrogen concentration in a-Si:H thin films.