Impact of bottom electrode and SrxTiyOz film formation on physical and electrical properties of metal-insulator-metal capacitors

摘要

Metal-insulator-metal capacitors with Sr_xTi_yO_z (STO) dielectric films on TiN, Ru, and RuOx bottom electrodes with TiN top electrodes were studied. Metastable perovskite STO films with compositions in the Sr/(Sr+Ti) ~ 54-64 at. % range were obtained by crystallization at 600 ℃ in N_2 of dielectric stacks grown by atomic layer deposition consisting of Sr-rich STO films [Sr/ (Sr +Ti)~64 at. %] on thin interfacial TiOx layers. The significant decrease in equivalent oxide thickness (EOT) and STO lattice parameter observed with increasing TiOx thickness indicates full intermixing of the TiOx and STO layers during the crystallization anneal, which results in the formation of an STO layer with higher Ti content and higher dielectric constant. The Sr-rich STO on TiOx stacks crystallize with small grain size, favorable for low leakage (J_G). A significant improvement in J_G for e-injection from the bottom electrode is obtained when using RuOx, as compared to TiN or Ru. A milder J_G improvement with RuOx bottom electrode is also seen for e-injection from the top TiN electrode, indicating that higher quality perovskite STO films are formed on RuOx, or equivalently, that their trap density is lower. We propose oxygen scavenging from the STO by TiN or Ru electrodes, eliminated or reversed when using RuOx, as an explanation for the improvement. Using an optimized RuOx/TiOx/STO/TiN stack we obtained leakage of 10~7 A/cm~2 (at 0.8 V) and 0.4 nm EOT.