Surface and bulk passivation of multicrystalline silicon solar cells by ...

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recombination in the SCR influences the magnitude of Seff, whereas, at high injection
levels, Seff is mostly determined by the recombination at the surface.
After plasma deposition, there is damage beneath the Si surface up to about 20 nm
deep [97, 98], which agrees well with the calculated L. Note that the major amount of
surface damage can be healed by the RTA process so that the width of the SCR will
subsequently be reduced. Therefore, a reduction of minority-carrier recombination in the
SCR is expected after the firing step for metallization of Si solar cells.
3.3 H Transportation Mediated by SiΝ :Η Layer
Based on the damaged layer and trapping/detrapping theory, a semi-quantitative
hydrogen transportation model is proposed which can be simply described in the
following steps:
(i) A large amount of the hydrogen atoms are trapped and "stored" in processinduced
traps (PITS) across the damaged region produced by the plasma process during
the nitride deposition.
(ii) In a rapid thermal annealing (RTA) step, H is released from the surface and
redistributed into the bulk region. Also, because the concentration of H in the damaged
region is higher than that in the SίΝx :H layer, some of the H may migrate into the nitride
layer.
(iii) H evolution from SiΝ :H layer thus occurs both ways: into the air and into Si.
The diffusion process of H into the bulk region and the out-diffusion into the ambient
occur simultaneously. As the H diffuses deeper into Si, it saturates the traps and other
defects, requiring less H for passivation. At the same time, the damage at the surface is