Electrical Properties of Al-Doped SrTiO3 Films Grown Via Atomic Layer Deposition on Ru Electrodes

Abstract

Atomic layer deposition (ALD) of Al2O3-inserted SrTiO3 (STO) dielectric thin films were investigated in metal-insulator-metal capacitors for dynamic random access memory. STO thin films exhibit much higher dielectric constant compared with currently used ZrO2-based films, but the leakage current density is generally higher due to their low band-gap. To decrease the leakage current density, insertion of the ALD-Al2O3 could be adopted as for the current ZrO2-Al2O3-ZrO2 dielectric layer. One ALD cycle of the Al2O3 film was performed during the ALD of the bottom region of the STO film. As a result, the leakage current of the STO thin film with a thickness of 8nm decreased from 8.1 X 10-6 A/cm2 to ~2.8 X 10-8 A/cm2 at 0.8V, whereas the equivalent oxide thickness (EOT) of the (top) RuO2/STO/Ru (bottom) capacitor slightly increased from 0.8nm to 0.9nm. Al2O3 can exhibit a sufficient leakage current reduction effect at a small insertion ratio, but the increased Al portion deteriorates the dielectric constant and leakage current due to the inhibited crystallization. The lower crystallization during the ALD requires higher annealing temperature, which caused the nano- or micro-cracks in the film and consequent increase in the leakage current. Therefore, careful optimization of the Al insertion was performed to improve the leakage current performance while maintaining the high dielectric constant. Figure 1