Deposition of high-quality a-Si:H by suppressing growth of a-Si clusters in SiH₄ plasmas

The density of Si-particles in a small size range below 10nm (referred to as clusters) in SiH₄ capacitively-coupled high-frequency discharges amounts to 10¹¹cm^-3 even under deposition conditions of device-quality a-Si:H films. The results reported until now regarding the growth of such clusters are shown to be reasonably understood by taking into account the effects of gas flow on the growth. The SiH₂ bond formation in the a-Si films are found to be mainly contributed by incorporation of large clusters (clusters in a range above about 0.5 nm in size) rather than higher-order-silane (HOS) radicals [Si_nH_x (n<5, x<2n+2)] in the plasma. By employing the cluster-suppressed plasma CVD reactors, the remarkable decrease in SiH₂ bond density in the films is realized, leading to the deposition of a-Si:H films of less light-induced degradation. Based on the knowledge of cluster growth obtained until now, the reactor with a potentiality of high rate deposition of high-quality films is proposed and its preliminary results are presented.