Crystallization Study by Transmission Electron Microscopy of SrTiO_3 Thin Films Prepared by Plasma-Assisted ALD

摘要

The crystallization behavior of thin strontium titanate (SrTiO_3> STO) films with ~15 nm thickness was studied by Transmission Electron Microscopy (TEM). Amorphous STO films with [Sr]/([Sr]+[Ti]) ratio ranging from 0.50 to 0.63 were deposited at 350°C by plasma-assisted ALD and subsequently treated by rapid thermal annealing in flowing N_2 for crystallization. Different temperatures and annealing durations were employed to fully characterize the crystallization process. TEM analysis showed that transrotational crystals were formed and evidenced the influence of the STO composition and of the thermal budget applied on the grain size, crack and void formation. In particular, Sr-rich layers ([Sr]/([Sr]+[Ti] > 0.59) showed a finer crystalline structure which was imputed to a higher nucleation probability at the onset of the crystallization process. Crystallization into the perovskite structure was confirmed for all the film compositions studied. By tuning the STO composition and the thermal budget of the annealing step it was demonstrated that it is possible to control the microstracture of the crystallized film as a further step in optimizing the STO film properties.