The effects of forming gas anneal on the electrical characteristics of Ir-electroded BST thin film capacitors

The effect of various temperature nitrogen anneals prior to top electrode deposition on the ability of Ba0.7Sr0.3TiO3 (BST) thin-film capacitors with both Ir and Pt top electrodes to withstand hydrogen damage was investigated. Experimental results show that samples that underwent a 750 degrees C N-2 pre-top electrode anneal exhibited the lowest leakage current density at positive bias for both Ir- and Pt-electroded devices after forming gas anneal. It was also found that DRAM polarization values decreased slightly after forming gas anneal. Also, a post-top electrode deposition 550 degrees C O-2 anneal improved both electrical characteristics (lowered leakage and increased DRAM polarization) of these devices. Complete recovery of the leakage level prior to hydrogen damage was obtained after a 550 degrees C N-2 recovery anneal for some devices independent of the pre-top electrode anneal. Ir- and Pt-electroded BST (40nm) capacitors have been shown to meet the 1 giga-bit DRAM leakage current requirement of 10(-8) A/cm(2) at 1.7 V. These Ir- and Pt-electroded BST devices achieved capacitance density levels of approximately 50 fF/mu m(2).