Characterization of hydrogenation and dehydrogenation of post-plasma treated low-pressure chemical-vapor-deposited amorphous silicon films

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Abstract
Utilizing infrared spectroscopy, secondary ion mass spectroscopy, photoluminescence (PL), and electron-spin resonance measurements, we have characterized low-pressure chemical vapor deposition amorphous silicon films (a-Si) post-hydrogenated under various plasma treatment conditions, and annealed ones at various temperatures after plasma treatment. The amount of the total bonded hydrogen (NT,H) in the film brought about by hydrogen plasma varied with radio-frequency power, temperature, and exposure time. The depth of the bonded hydrogen layer increased according to the increase in NT,H, with increasing surface hydrogen concentration in the small NT,H region, and it almost kept the surface saturation of the hydrogen concentration in the larger NT,H region. The PL intensity increased in proportion to the increase of NT,H; it changed sharply at small NT,H, and then slowly at large NT,H. Two peaks appeared in the hydrogenated sample, the origin of which was explained by two differently strained states. The defect number decreased according to the increase of NT,H. However, a considerable amount of Si–Si bonds (300–700 bonds) was cleaved for annihilation of one defect by the hydrogenation. Annealing the post-hydrogenated samples above 400 °C caused a decrease of NT,H, regrowth of the defects, and an increase of Si–Si bond strain.