The chemical vapor deposition of tantalum oxide thin films from pentaethoxy tantalum on to trench structures was conducted to investigate experimentally the step coverage and to compare these results with simulated findings. The dependence of the step coverage on the substrate temperature and the type of carrier gas was evaluated experimentally, and the sticking coefficient was determined from the comparison of the experimental results with the simulation. Deposition at low temperatures using He carrier gas gives better step coverage with the tantalum oxide thin film. A comparison of the activation energy associated with the sticking coefficient with the activation energy associated with the deposition rate on a blank wafer surface using He and Ar carrier gases was made. The step coverage with He was determined from the deposition rate, while the step coverage with Ar was determined using the Knudsen diffusion rate of reactant inside the trench.