Impact of Post-deposition Plasma Treatment on Surface Passivation Quality of Silicon Nitride Films

Exposing a plasma-enhanced chemical vapor deposition-deposited silicon nitride (SiNx) film to an inert gasoxidizing plasma ambient results in a significant reduction in background plating in the case of electroplated Ni-Cu metallization on c-Si solar cells. However, plasma treatment of SiN
_x
is known to result in a degradation of the Si-SiNx interface. In this paper, we investigate the impact of an Ar/N
₂
O plasma treatment process on the surface passivation properties of SiN
_x
film. Following the plasma treatment, effective minority carrier lifetime (τ
_eff
) is seen to improve from 266 to 864 μs at a minority carrier density of 10
¹⁵
cm
^-3
. The interface-state density (Dit) at the Si-SiN
_x
interface also decreases by an order of magnitude, following the Ar/N
₂
O plasma treatment. Enhancement in τ
_eff
is found to be stable for annealing temperatures up to 450°C, which is typically used for Ni-Cu contact sintering. Substrate annealing during the post-deposition plasma treatment process is seen to play a major role in improving the τ
_eff
. Coupled with its potential for reducing the background plating, the proposed process is a promising candidate for developing the passivation layers for cell technologies with low-temperature metallization schemes.