Numerical analysis on particle coating by the pulsed plasma process

초록

The a-Si thin-film growth on particles in the rotating pulsed SiH4 plasma process was analyzed numerically. The evolutions of chemical concentrations (SiH4, SiHx, SiHx+ and polymerized negative ions) in the pulsed plasmas have been shown during the plasma-on and -off. During plasma-on, SiH4 is consumed by the electron impact dissociative reactions, but, during plasma-off, the disappearance reaction of SiH4 stops because the electrons disappear in the plasma reactor. During plasma-on, SiHx and SiHx+ are generated quickly by a fast dissociative reaction of SiH4, but, during plasma-off, SiHx disappears rapidly by a reaction with hydrogen and also by the deposition onto the reactor wall and particles, and SiHx+ is consumed quickly by fast neutralization reactions with the negative ions. The negative ions are polymerized by the reactions with SiH4 during plasma-on, but, disappear by neutralization reactions during plasma-off. The growth rate of the film thickness profile depends on the SiHx concentration because the particles grow with the SiHx deposition. As the plasma-on time increases or as the plasma-off time decreases, the thin film thickness on the particles increases more quickly with faster SiHx deposition onto them. A fraction of the particles falling down in the gas phase (W-F P) increases as the rotation speed of the plasma reactor increases. As W-F P increases, as the particle concentration decreases, or as the particle diameter decreases, the film thickness on the particles increases more quickly because the flux of SiHx toward the particles increases. The pulsed plasma process can efficiently reduce the growth of polymerized negative ions and particles, both of which are not good for high-quality thin films. We showed that the high-quality thin films on the particles can be prepared successfully by deposition of low mass chemical precursors by pulsed plasma processes. (c) 2006 Elsevier Ltd. All rights reserved.

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