The atomic layer deposition (ALD) of Ta2O5 and TaSiOx from TaCl5, SiCl4, and H2O is reported. Both processes are influenced by the concomitant etching of Ta2O5 and TaSiOx by TaCl5. The optimum deposition temperature is found to be 250 °C for both Ta2O5 and TaSiOx. For lower deposition temperatures, the large Cl contamination leads to poor dielectric properties of the films, whereas higher temperatures lead to poor within-wafer (WiW) thickness non-uniformity due to etching. Si incorporation is limited to Si/(Si + Ta) ∼ 0.65 because of the slow adsorption kinetics of SiCl4 on SiOH-terminated surfaces. Under optimum conditions, amorphous films with good dielectric quality are obtained.