Thermal stabilities of metal bottom electrodes for Ta2O5 metal-oxide-metal capacitor structure

Thermal stabilities of various metal bottom electrodes were examined by using a Ta2O5 metal-oxide-metal (MOM) capacitor structure. After depositing 10-nm thick Ta2O5 on metal-electrode/poly-Si, we performed rapid thermal oxidation (RTO) at 850 °C for 60 s in an O2 ambient. A chemical-vapor-deposition (CVD) WSi2 electrode showed satisfactory thermal stability after the RTO, while other examined electrode materials exhibited thermal degradation caused by oxidation failure or interfacial reaction between the substrate poly-Si and the Ta2O5. After post-annealing at 650 °C for 30 min (in N2 condition) with CVD TiN top electrode, an effective oxide thickness (Tox) of ∼32 Å and a leakage current density of ∼107 A/cm2 at 1.25 V were obtained from the MOM capacitor with the WSi2 bottom electrode. Other electrode materials, such as TiN, TiSix, WNx, W, and Ta, were severely oxidized during the RTO in the MOM structures, and very poor capacitor properties were obtained in terms of Tox and leakage current.