This paper presents a study of the process temperature dependence of $Al_2O_3$ film grown by thermal atomic layer deposition (ALD) as a passivation layer in the crystalline Si (c-Si) solar cells. The deposition rate of $Al_2O_3$ film maintained almost the same until $250^{circ}C$, but decreased from $300^{circ}C$. $Al_2O_3$ film deposited at $250^{circ}C$ was found to have the highest negative fixed oxide charge density ($Q_f$) due to its O-rich condition and low hydroxyl group (-OH) density. After post-metallization annealing (PMA), $Al_2O_3$ film deposited at $250^{circ}C$ had the lowest slow and fast interface trap density. Actually, $Al_2O_3$ film deposited at $250^{circ}C$ showed the best passivation effects, that is, the highest excess carrier lifetime (${ au}_{PCD}$) and lowest surface recombination velocity ($S_{eff}$) than other conditions. Therefore, $Al_2O_3$ film deposited at $250^{circ}C$ exhibited excellent chemical and field-effect passivation properties for p-type c-Si solar cells.