Gettering Effects of Silicon Nitride Films From Various Plasma-Enhanced Chemical Vapor Deposition Conditions

This paper investigates and compares the impurity gettering effects of silicon nitride (SiN
_x
) films that are synthesized by plasma-enhanced chemical vapor deposition (PECVD) under various conditions. Both industrial- and laboratory-scale PECVD systems are employed to deposit SiN
_x
films with a wide range of properties (with refractive indices from 1.93 to 2.45 at 632 nm), which covers the entire range of SiN
_x
used for silicon solar cells. The gettering effects are quantified by monitoring the reduction kinetics of the interstitial iron concentration in the silicon wafer bulk as iron becomes gettered to the surface SiN
_x
layers during cumulative annealing at 400 °C. The results show that the very different SiN
_x
films generate similar gettering kinetics, indicating that the impurity gettering effect is likely present in most PECVD SiN
_x
films for silicon solar cells. The gettering kinetics and the SiN
_x
film properties of refractive index, Si–N, Si–H, N–H bond densities, and H content, are found to have no clear correlations.