OPTIMIZATION OF Al_2O_3 FILMS OBTAINED BY ALD TO PASSIVATE P-TYPE C-SILICON WAFERS

摘要

Aluminum oxide (Al_2O_3) has emerged in recent years as a good candidate material to passivate both ptype and n-type substrates. The excellent surface passivation achieved can be attributed to both chemical and fieldeffect passivation provided by a large amount of fixed negative charge located at the c-Si/Al_2O_3 interface. The aim of this work is to optimize the film thickness and post-deposition annealing conditions, time and temperature, in order to get the best surface passivation. Al_2O_3 films were deposited by thermal Atomic Layer Deposition (ALD) at 150, 200 and 250°C. Double-side polished 4” FZ p-type (2.3 Ωcm ± 0.3) c-Si (100) wafers around 290 μm thick wafers were used in the study. We have analyzed systematically the surface passivation properties of different Al_2O_3 layers with different thicknesses (50, 25, 14, 6,5 and 1.4 nm) post-annealed in forming gas (N2/H_2) at temperatures ranging from 300 °C to 435 °C for different annealing times (5, 10, 20 and 30 min). An outstanding surface passivation, with an effective surface recombination velocity (S_(eff,max) ) below 10 cm/s has been achieved for an optimal post-deposition annealing temperature of 375 °C for t= 20 min, with Al_2O_3 layers thickness greater than 6.5 nm.