We investigate the thermal stability of silicon surface passivation provided by aluminium oxide (Al2O3) films deposited using atmospheric pressure chemical vapour deposition (APCVD) and fired in a belt furnace at a peak temperature of similar to 810 degrees C. Firing stability is investigated for p- and n-type substrates as a function of Al2O3 film thickness both with and without a plasma-enhanced chemical vapour deposition (PECVD) SiNx capping layer, and for boron-diffused surfaces with a similar to 10 nm Al2O3 film only. Excellent thermal stability of the passivation is demonstrated, with effective carrier lifetimes in n-type silicon wafers remaining stable or even improving after firing, and lifetimes in p-type wafers initially degrading slightly but recovering to above their initial values following similar to 10 min illumination by a halogen lamp at similar to 20 mW/cm(2). Film thickness appears to be unimportant to stability, as does the presence of the capping layer. Surface recombination velocities of less than 3 cm/s for 1.35 Omega cm p-type and less than 2 cm/s for 1.2 Omega cm n-type substrates are measured after firing and illumination. The passivation of boron-diffused surfaces is also shown to improve slightly following firing, with a post-firing saturation current density of 42 fA/cm(2) on a diffusion with a sheet resistance of 100 Omega/square and surface dopant concentration of similar to 1.3 x 10(19) cm(-3). Capacitance-voltage (C-V) measurements show that short firing times result in an initial reduction of the interface defect density D-it and a slight increase of the negative insulator fixed charge density Q(f), while longer firing results in a substantial increase in both Q(f) and D-it. (C) 2013 Elsevier B.V. All rights reserved.