Mixed-phase Ni–Al as barrier layer against perovskite oxides to react with Cu for ferroelectric memory with Cu metallization

Abstract

The microstructures, interfaces, and physics properties of the devices with multifunctional barrier materials are investigated to achieve integration of perovskite oxide films with Cu film on Si for the application in nonvolatile Si-based ferroelectric random access memories (FeRAMs) with the on-chip copper metallization of advanced microelectronic devices. La0.5Sr0.5CoO3/Pb(Zr0.4Ti0.6)O3/La0.5Sr0.5CoO3 (LSCO/PZT/LSCO) capacitors have been successfully fabricated on the Cu/Ni–Al/SiO2/Si stack structure for Cu interconnects using an amorphous Ni–Al (a-Ni–Al) film as the barrier layer for the Cu/SiO2 interface and a mixed-phase nanocrystalline Ni–Al (n-Ni–Al)/a-Ni–Al ((n+a)-Ni–Al) bi-layer-like film as the oxygen diffusion barrier layer for the LSCO/Cu interface, respectively. The perfect structure compatibility and clear interfaces between thin films are achieved. Excellent physical properties of the capacitor, such as high remnant polarization (∼26 μC/cm2), good reliability and dielectricity, powerfully confirm that Ni–Al film can be used as the barrier layer between Cu and SiO2 or LSCO. The barrier properties of the (n+a)-Ni–Al can be understood as two aspects: n-Ni–Al component can level up the roughness of Cu/barrier/SiO2/Si surface and relax stresses in the multilayer stack heterostructure, and a-Ni–Al can inhibit oxygen penetration. Compared to the (n+a)-Ni–Al, only n-Ni–Al film without a-Ni–Al layer couldn't prevent Cu oxidation due to oxygen penetration leading to the failure of devices, whose failure mechanism can be ascribed to the reactions between Cu and complex oxides. The results fully illustrate the viability of the lead-based ferroelectric capacitors grown on Cu/Barrier/SiO2/Si stack structure with Ni–Al barrier for the future ferroelectric capacitor based devices with Cu metallization.