Comparative study of PECVD deposited a-Si:H/SiNx:H double passivating layer on CZ crystalline si substrate

The effectiveness of hydrogenated amorphous layers for passivating crystalline silicon surfaces has been well documented in the literature for well over a decade. One limitation of such layers however has arison from their inability to withstand temperatures much above their deposition temperature without significant degradation. This limitation is of importance particularly with multicrystalline silicon materials where temperatures of at least 400°C are needed for effective hydrogenation of the crystallographic defects such as grain boundaries. To address this limitation, in this work the surface passivation quality and thermal stability of a-Si:H/SiNx:H passivating stack on p-type crystalline silicon wafers is studied for different deposition temperature of the capping SiNx:H layer. It is established that the as-deposited passivating quality of the stack highly depends on the deposition temperature of the SiNx:H layer and that the effectiveness of the passivation of the stack can be significantly enhanced after short term annealing at 400°C and even 450°C. It is also found there is an optimized a-SiNx:H deposition temperature for maximizing the effectiveness of both the surface passivation and stability of the amorphous silicon layer to elevated temperatures as high as 450°C for durations as long as 30 minutes. This provides the opportunity for such dielectric stacks to not only provide excellent surface passivation but to also participate as a hydrogen source for passivation of crystallographic defects within the silicon wafer at temperatures as high as 450°C, well above those normally able to be tolerated by surfaces passivated by amorphous silicon.