An all-silica deca-dodecasil 3R (Si-DDR) zeolite with a pore size of 0.36*0.44 nm2 is highly desirable for membrane-based separation of CO2 from N2, which critical in the post-combustion carbon capture process, via molecular recognition of their slight size difference. For the first time, we acquired h0h-oriented, hydrophobic DDR zeolite films through epitaxial growth of a DDR seed layer with a structure directing agent of methyltropinium iodide. The degree of the out-of-plane orientation and inter-growth was increased with the secondary growth time, while reducing the defects that provide non-selective pathways. The resulting DDR membrane showed a CO2/N2 separation factor (SF) as high as 11.9 at 50°C under dry conditions. More desirably, it could achieve a much enhanced CO2/N2 SF of up to 15.9 at 50°C in the presence of H2O vapor.