Silicon Nitride Deposition: Impact on Lifetime and Light-Induced Degradation at Elevated Temperature in Multicrystalline Silicon

摘要

Light and elevated temperature induced degradation (LeTID) in multicrystalline (mc) silicon (Si) is known to be sensitive to the silicon nitride (SiNx:H) deposition and the firing, but the reason remains unknown. Three plasma-enhanced chemical vapor deposition (PECVD) tools are used to deposit five different layers, causing significant differences in the initial lifetimes before and after firing. The impact of the different depositions can be effectively compared by replacing the SiNx:H with well-passivating room-temperature iodine ethanol passivation (IE). The IE passivation reveals that the firing of SiNx:H and subsequent bulk hydrogenation leads to a lifetime increase only in the gettered samples. Although the PECVD temperature load affects the bulk lifetime, it does not cause LeTID without SiNx:H deposition. LeTID is only detected in samples fired with SiNx:H, but once the LeTID precursors have been activated, the PECVD layer can be etched and the wafer thinned down without affecting LeTID formation. No link is found between the LeTID defect density and the bulk-hydrogenated lifetime. Instead the LeTID defect density appears to decrease with decreasing PECVD deposition time and temperature.