High-Reliability Ta[sub 2]O[sub 5] Metal–Insulator–Metal Capacitors with Cu-Based Electrodes

The properties of tantalum oxide ( Ta 2 O 5 ) metal–insulator–metal (MIM) capacitors with Al ∕ Ta ∕ Cu ∕ Ta bottom electrodes were investigated. An ultrathin Al film successfully suppresses oxygen diffusion in the Ta 2 O 5 MIM capacitor with the Cu-based electrode. The electrical characteristics and reliability of Ta 2 O 5 MIM capacitors are improved by addition of ultrathin Al films. Ta 2 O 5 MIM capacitors have low leakage current density ( 1 nA ∕ cm 2 at 1 MV ∕ cm ) and high breakdown field ( 5.2 MV ∕ cm at 10 − 6 A ∕ cm 2 ). The decrease in leakage current is attributed to the formation of a dense and uniform Al 2 O 3 layer, which has self-protection property and stops further oxygen diffusion into the tantalum contact. The dominant conduction mechanism of leakage current is the Poole–Frenkel effect at electric fields above 1.5 MV ∕ cm .