We investigated the effects of moisture on the deposition behavior of the MnOx diffusion barrier layer on TEOS-oxide substrates. The moisture effects were investigated in two ways: (1) with and without the introduction of H2O gas in the reaction chamber and (2) with and without pre-annealing of the TEOS-oxide substrates without introducing H2O gas. A thick crystalline MnOx layer was formed under the presence of H2O gas. A thin amorphous MnOx layer was formed without H2O gas. Without H2O gas in the reaction chamber, the thickness of the MnOx layer was slightly thinner on the substrate with pre-annealing than on the substrate without annealing.