PLASMA AND SURFACE-REACTIONS DURING A-SI-H FILM GROWTH

The mechanisms of a-Si:H film deposition from SiH4 glow discharges are analyzed. Recent progress in modeling and diagnostic of electrical power dissipation in DC and RF discharges revealed the importance of electron attachment and powder formation from negative ions. In conventional deposition conditions of optoelectronic-grade a-Si:H, the plasma chemistry favors SiH3 radicals which combine a low sticking probability and a high surface mobility on the H-covered film surface. Low SiH4 pressure discharges involves a large fraction of non mobile species such as SiH m less-than-or-equal-to 2 radicals, but also a high flux of positive ions which can enhance surface mobility and structural rearrangement by momentum transfer (ion kinetic energy). Surface reactions can be also controlled by electronic energy transfer (neutralization of ions, deexcitation of metastables, photon irradiation, radical recombination). H atoms induce microcristalline silicon growth by combining the effects of chemical etching and annealing of the growth zone and H-coverage of the surface.