Importance of Annealing Step on Dielectric Constant of ZrO2 Layer of MIM Capacitors with Al2O3/ZrO2 and ZrO2/Al2O3 Stack Structures

Abstract

We investigated characteristics of ZrO2/Al2O3 (ZA) and Al2O3/ZrO2 (AZ) insulators after two annealing step such as post-deposition annealing (PDA) at 600°C before TiN top electrode (TE-TiN) deposition and post-metallization annealing (PMA) at 600°C after TE-TiN deposition. The ZrO2 layers (2.9-5.7 nm) and Al2O3 layer (2.0 nm) were deposited by atomic layer deposition at 300°C. ZrO2 layer had a polycrystalline structure while Al2O3 layer had an amorphous structure. The capacitance of the AZ capacitors after PDA or PMA reasonably decreased as ZrO2 thickness increased. On the other hand, the ZA capacitors after PDA (ZA wPDA) exhibited almost similar capacitance while the ZA capacitors after PMA decreased as well as the AZ capacitor. The dielectric constant (k) of the ZA wPDA drastically increased to 44 compared to other capacitors (30-37) in the ZrO2 thickness region of over 4.9 nm. This is because the ZrO2 layer was annealed with an asymmetric structure sandwiched between Al2O3 and TiN with different coefficients of thermal expansion during PDA. Furthermore, the ZA wPDA with the ZrO2 layers (4.9-5.7 nm) exhibited superior characteristics satisfying a high k-value and a high electric filed value at J = 1 × 10-5 Acm-2. These indicated that PDA treatment should perform after 1st-ZrO2/Al2O3 layer deposition to obtain ZrO2 layer with high k-value.