Novel Electrode Barriers for High Density Ferroelectric Nonvolatile Memories

In this paper, we propose a new electrode-barrier structure for direct integration of lead zirconate titanate (PZT) based capacitors onto polysilicon plug for high density FRAM applications. The electrode-barrier structure is based on noble metal alloys (e.g. Pt–Rh, Pt–Ir, Pt–Ru) and their oxides (e.g. PtRhOx) which satisfy the needs for an excellent diffusion barrier as well as a high conducting electrode. It has been found that the PtRhOx/PtRh/PtRhOx electrode-barrier structure acts as a very good bottom electrode on poly-silicon plug. The bottom PtRhOx layer has shown excellent diffusion barrier properties for lead, oxygen and silicon up to processing temperatures of 700 °C as established by Auger electron spectroscopy and Rutherford backscattering spectroscopy studies. The electrode barriers showed no hillock formation and PZT films deposited on this structure crystallized predominantly in the perovskite phase. The capacitors exhibited very good hysteresis properties with remnant polarization (Pr) of 16 μC/cm2, a coercive field (Ec) of 32 kV/cm, extremely low fatigue (after 1×1010 cycles) of 3–4%, imprint (after 3.3×109 cycles) of 8–12%, retention (after 1×105 s) of 2–3% and leakage current density (at 100 kV/cm) less than 10—8 A/cm2. These electrode barriers hold excellent promise for application in high density FRAM capacitor over bit line (COB) structure.