Ta2O5 films, 10 and 100 nm in thickness, directly deposited on a Si substrate were investigated by using transmission Fourier-transform infrared spectroscopy. The samples were annealed in dry oxygen, wet oxygen and nitrogen atmospheres. The Ta-O phonon peaks in the infrared absorption spectra appeared at 210, 510 and 570 cm(-1) in samples that were annealed at 700 and 800 degreesC for up to 4 h. We found that the 510/570 cm(-1) peak height ratio is larger for thicker Ta2O5 films annealed at higher temperatures. This implies that peak height ratios are directly related to Ta2O5 film quality, and we conclude that stronger lattice structures can be formed by annealing at higher temperatures.