High Throughput ALD of Al2O3 layers for Surface Passivation of Silicon Solar Cells

A high-throughput ALD system based on wafer transport in an atmospheric gas bearing was developed. Line-shaped TMA and H2O precursor zones are present in the direction perpendicular to transport takes place. Thin Al2O3 films of 4-24 nm were deposited at wafer speed of 160-230 mm/s (corresponding to a throughput of 2400 - 3600 wph). After annealing and firing the films show good passivation. Effective minority carrier lifetimes measured on 2.3 Omega cm p-type c-Si wafers at excess carrier density of 1E15 cm(-3) reach values of 0.3-2.5 ms depending on surface preparation, annealing steps and film thickness. No degradation of films during firing was observed and the lifetime values remain stable in time. The Levitrack system presented in this paper is expected to meet the requirements of the PV industry.