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.