Excellent Passivation of n-Type Silicon Surfaces Enabled by Pulsed-Flow Plasma-Enhanced Chemical Vapor Deposition of Phosphorus Oxide Capped by Aluminum Oxide

Abstract

Phosphorus oxide (POx) capped by aluminum oxide (Al2O3), prepared by atomic layer deposition (ALD), has recently been introduced as a surface passivation scheme for planar n-type FZ silicon. In this work, a fast pulsed-flow plasma-enhanced chemical vapor deposition (PECVD) process for the POx layer is introduced, making it possible to increase the POx deposition rate significantly while maintaining the POx/Al2O3 passivation quality. An excellent surface passivation is realized on n-type planar FZ and Cz substrates (J0 = 3.0 fA cm−2). Furthermore, it is demonstrated that the POx/Al2O3 stack can passivate textured surfaces and that the application of an additional PECVD SiNx capping layer renders the stack stable to a firing treatment that is typically used in fire-through contact formation (J0 = 12 fA cm−2). The excellent surface passivation is enabled by a high positive fixed charge density (Qf ≈ 4 × 1012 cm−2) and an ultralow interface defect density (Dit ≈ 5 × 1010 eV−1 cm−2). Finally, outstanding passivation is demonstrated on textured silicon with a heavy n+ surface doping, as is used in solar cells, on par with alnealed SiO2. These findings indicate that POx/Al2O3 is a highly suited passivation scheme for n-type silicon surfaces in typical industrial solar cells.