Study on the Crucial Factors for Deposition Rate in the High-rate Deposition Process of Polycrystalline Silicon Films by Atmospheric Pressure Plasma CVD

Abstract

Using the atmospheric pressure plasma CVD (AP-PCVD) technique, polycrystalline silicon (poly-Si) films were deposited at high rates ranging from 0.4 to 7.6 nm/s. In order to clarify the deposition process of poly-Si films, the influences of VHF power, concentration of the reactive gases (H 2 , SiH 4 ), substrate temperature (T sub ) and deposition gap on the deposition rate were studied. Simultaneously increasing VHF power and hydrogen dilution ratio of SiH 4 (H 2 /SiH 4 ratio) was found to be the crucial method to improve the crystallinity and also to increase the deposition rate of the film. In addition, it was found that L P was sensitive to H 2 concentration in the plasma atmosphere, while it was not affected by SiH 4 concentration within the present deposition conditions. These facts suggested that supplying sufficient VHF power enhanced dissociation of H 2 molecules, which leaded to effective generation of atomic hydrogen in the plasma, and that the atomic hydrogen played important roles in both dissociation of SiH 4 molecules and crystalline Si film growth. It became clear that the deposition rate had positive temperature dependence with extremely small activation energy of 0.036eV. Additionally, the extremely small activation energy implied that a T sub -independent process partly contributed to the surface reaction. It was also revealed that the deposition rate increased exponentially with decreasing the deposition gap, indicating that the deposition precursors were supplied to the surface by diffusion.

Growth of high-crystallinity silicon films by a combination of intermittent pulse heating and plasma-enhanced chemical vapor deposition

“…6) Consequently, research on forming polycrystalline semiconductor layers on the gate oxide films of BG-TFTs has been attempted for many years. Methods for forming polycrystalline Si (poly-Si) films have been studied, such as, lowpressure chemical vapor deposition (CVD), 7,8) plasma-enhanced CVD (PECVD), [9][10][11][12] and reactive thermal CVD, 13,14) where crystalline-Si is directly deposited on an insulator. However, these methods are prone to problems such as the difficulty of suppression of the amorphous incubation layer during the initial stage of growth just above the insulating layer and no increase in mobility because the amorphous layer becomes the channel of the BG-TFT.…”