c-Si based carrier selective contact solar cells are achieving high efficiency with a crucial step of silicon surface passivation, reducing the electronic recombination losses occurring at the interface of Si and the passivation layer. The ultrathin passivation layers of Al₂O₃ are deposited by atomic layer deposition (ALD), known for its conformance and homogeneity. ALD is an attractive technique for low-temperature deposition of layers required for the development of c-Si carrier selective contacts and passivation. The deposition temperature is fixed at 200 °C, which lies in the ALD window for Al₂O₃ films. In this study, deposition of Al₂O₃ films is done by thermal ALD process where the growth per cycle of the film is calculated to be 0.1 ± 0.01 nm using spectroscopic ellipsometry. Al₂O₃ films were deposited on n-type CZ Si (111) (2 Ω cm) wafers of thickness 170 μm after processing with saw damage removal, standard RCA clean, and HF dip. Post-deposition annealing was done in forming gas environments at various temperatures to probe the passivation quality. A monotonic improvement was obtained with annealing in such an environment, reaching an excellent lifetime of about 1.24 ms (measured by WCT-120 Sinton lifetime tester) at a minority carrier concentration of 1 × 10¹⁵ cm⁻³ for samples annealed in forming gas environment at 310 °C. This is an excellent value for an industrial-type CZ wafer with a measured bulk lifetime of only ~ 3 ms. The corresponding effective surface recombination velocity obtained is 3.7 cm/s. An implied open-circuit voltage (iV_OC) of 0.704 V is achieved for the same. These results demonstrate that the passivation obtained here is of device quality for CZ Si wafers and facilitates the development of high-efficiency Si heterojunction (SHJ) solar cells.