The internal stress, film density and dynamic deposition rate of amorphous tin oxide (SnO 2 ) films were investigated as a function of the carbon dioxide (CO 2 ) gas flow ratio [CO 2 /(O 2 +CO 2 )] during sputter deposition. The internal stress and film density decreased with higher CO 2 gas flow ratios. The dynamic deposition rate increased 1.6-fold with increases in the CO 2 gas flow ratio. These results suggest that the stress relaxation of the SnO 2 films was induced to decrease the interatomic repulsive force with decreases in the film density. Therefore, using CO 2 gas was quite an effective method to reduce the compressive stress of the SnO 2 films.