Understanding the materials, electrical and reliability impact of Al-addition to ZrO2 for BEOL compatible MIM capacitors

As operating frequency and circuit density of VLSI systems continue to increase, the L*di/dt induced voltage fluctuations in the power grid increasingly becomes a source of voltage/timing problems. On-chip decoupling capacitors, placed in close proximity to the power grid conductors, can offset parasitic inductances and thereby reduce the high frequency noise. High capacitance density MIM capacitors, placed between the last two metal layers, have been shown to be effective in achieving on-chip decoupling in high performance processors. There have been many reports in the literature on the use of high-k material such as Ta₂O₅, HfO₂, ZrO₂ for MIM capacitors [1-5]. A large number of reports of high-k MIM are focused on DRAM rather than decoupling capacitors applications [2-4]. One important difference between the DRAM capacitor module and decoupling capacitors is the thermal budget requirement. DRAM capacitors allow a higher thermal budget (~700°C) compared to embedded decoupling capacitors which must meet the BEOL thermal budget requirement (~400°C). We have recently reported an improved reliability by addition of Al into ZrO₂ [6]. In this work, we report detailed material, electrical and further reliability characterization of ZrO₂-based MIM capacitor capable of meeting stringent reliability requirement while maintaining compatibility with the backend processing thermal budget. A capacitor with >20fF/μm² capacitance density and leakage current density <;100nA/cm² meeting lifetime target (operated on both polarities) is demonstrated.