Effect of the Annealing Temperature of the Seed Layer on the Following Main Layer in Atomic-Layer-Deposited SrTiO3 Thin Films

Abstract

SrTiO3 (STO) films are grown via atomic layer deposition at 370 degrees C with a two-step growth method. A 5-nm-thick seed layer is first deposited and annealed via rapid thermal annealing (RTA) at temperatures ranging from 450 to 650 degrees C, and the main layer is subsequently grown on the annealed seed layer for in situ crystallization. When the RTA temperature is 500 degrees C or lower, the seed layer remains amorphous, and the main layer is also grown in the amorphous phase. At the 550 degrees C seed annealing temperature, the STO film is partially crystallized, and at the higher annealing temperature, the STO main layer is fully crystallized. The oxygen diffuses through the vertically aligned grain-boundaries during the crystallized film growth, which induces the oxidation-reduction reaction of the underlying Ru substrate. This reaction causes a higher growth rate in the crystalline phase. The large growth rate difference between the amorphous and crystalline regions induces a severe roughening of the main layer. When RTA is done at 600 degrees C, the film is mostly crystallized, and the main layer becomes smooth again. Consequently, a 0.52nm equivalent oxide thickness is achieved with the low leakage current of 2.5x10(-8)Acm(-2) at the 0.8V applied bias.