Protection of SrBi2Ta2O9 ferroelectric capacitors from hydrogen damage by optimized metallization for memory applications

Abstract

The degradation behavior of integrated Pt/SrBi2Ta2O9/Pt capacitors by hydrogen impregnation during the intermetal dielectric deposition and passivation is investigated. The hydrogen ions generated as a reaction byproduct from the SiH4-based deposition processes of the dielectric films induce reduction in the remanent polarization (Pr) as well as the imprint behavior of the small size capacitors (2×2 μm2). The degree of degradation is quite dependent on the size of the individual capacitors. The smaller capacitors underwent more serious degradation implying that the hydrogen ions impregnate into the SBT layer mainly along the etched side area of the capacitors not through the top Pt electrode. Metallization adopting TiN/Al/TiN/Ti multilayer is very effective in suppressing the hydrogen impregnation. In particular, the Ti layer appears to block the hydrogen penetration. Therefore, the optimized metallization scheme, wider metal lines than the top electrode area by 1 μm, successfully protects the integrated capacitors from the hydrogen damage. 12 μC/cm2 of 2Pr and 1.1 V of 2Vc (coercive voltage) with an imprinting voltage of 0.16 V were obtained from the passivated 2×2 μm2 array capacitors by the optimized metallization.