The Effects of Postdeposition Anneal and Postmetallization Anneal on Electrical Properties of TiN/ZrO2/TiN Capacitors

Abstract

Metal–insulator–metal (MIM) capacitors based on zirconia (ZrO2) are widely used in dynamic random access memories (DRAMs). As the smaller and smaller feature size in DRAM chips requires higher and higher capacitance density, it is necessary to minimize the equivalent oxide thickness (EOT) of ZrO2, or maximize its dielectric constant ( <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">${k}$ </tex-math></inline-formula> ) while maintaining low leakage currents. Annealing is an effective method to achieve high <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">${k}$ </tex-math></inline-formula> -values. In this article, we report the impact of two mainstream annealing methods on the electrical properties of ZrO2-based MIM capacitors. The results showed that the dielectric constant of ZrO2 reached 41.5 after postdeposition anneal (PDA) at 350 °C, while grazing incidence X-ray diffraction (GIXRD) measurements indicated the formation of high- <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">${k}$ </tex-math></inline-formula> tetragonal phase. In contrast, similar dielectric constant enhancement requires much higher temperature (450 °C) for postmetallization anneal (PMA). When similar high- <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">${k}$ </tex-math></inline-formula> value was reached, the leakage current density of PDA samples was three orders of magnitude lower than that of PMA ones at 0.8 V. Additionally, lower annealing temperature also decreases the parasitic EOT at the interface, which was formed by the interaction of ZrO2 and TiN electrodes. Overall, we found PDA is more beneficial for achieving a higher dielectric constant (>40), lower leakage currents, and lower EOT at lower temperatures compared with PMA, and potentially more suitable for industrial DRAM fabrication process.