Paper TF-ThP41
The Leakage Current Reduction in Atomic Layer Deposition Of Al₂o₃-Inserted Srtio₃ Films for Metal-Insulator-Metal Capacitors

Thursday, November 2, 2017, 6:30 pm, Room Central Hall

The characteristics of 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 energy. To decrease the leakage current density, ALD-Al₂O₃ cycles were included in the STO ALD at different positions of the stack. 1 to 5 cycles of Al₂O₃ were inserted in the top, bottom, or middle of the STO film. As a result, the leakage current of the STO thin film with a thickness of 8nm decreased from 10^-6 A/cm² to 10^-8 A/cm² at 0.8V. This improved the minimum attainable equivalent oxide thickness (EOT) of the (top) RuO₂/STO/Ru (bottom) capacitor from 1.0nm to 0.68nm, with an acceptable leakage current density (~8 X 10^-8A/cm²). The degree of leakage current decrease was dependent on the locations of Al₂O₃ insertion into the STO thin film during the ALD. The leakage current reduction was more effective when Al₂O₃ was deposited at the top portion of the STO film than when it was deposited at the bottom portion. Only one cycle of Al₂O₃ at the bottom location significantly decreased the crystallinity of the STO layer grown on top, and thus, the higher post-annealing temperature was required to achieve high crystalline quality, which simultaneously increased the leakage by possibly involving nano- and micro-cracks. The Al₂O₃ at the top location did not induce such adverse effect while leakage current suppression effect was achieved.