By Aude Rothschild, IMEC; Bart Vermang, IMEC; Hans Goverde, IMEC
Al2O3 deposition has received a lot of attention in the last few years for its attractive passivation properties of c-Si surfaces. Within the local Al back-surface field (BSF) cell concept, we considered several avenues of study: surface preparation, thermal stability, charge investigation and the ‘blistering’ phenomenon. The investigations converged on a passivation stack that includes a thin interfacial SiO2 like layer and a thin Al2O3 layer (~10nm), which undergoes a high-temperature anneal (> 600°C). In order for a surface passivation with Al2O3 to be a cost-effective step for the PV industry, a high Al2O3 deposition rate is required. Compared to the different high-throughput tools that have recently emerged on the PV market, such as atomic layer deposition (ALD) and plasma-enhanced chemical vapour deposition (PECVD), our tool screening revealed quite similar results. The differences therefore seem to have an origin primarily in the tool specifications rather than in the achievable Al2O3 material properties.
