ELECTRICAL AND CHEMICAL PROPERTIES OF ULTRATHIN RT-MOCVD GROWN Ti-DOPED Ta_2O_5

摘要

Recent results suggested that doping Ta_2O_5 with a small amount of TiO_2 using standard ceramic processing techniques can increase the dielectric constant of Ta_2O_5 significantly. In this paper, this concept is studied using RTCVD. Ti-doped Ta_2O_5 films are deposited using TaC_(12)H_(30)O_5N, C_8H_(24)N_4Ti, and O_2 on both Si and NH_3-nitrided Si substrates. An NH_3-based interface layer at the Si surface is used to prevent interfacial oxidation during the CVD process and post deposition annealing is performed in H_2/O_2 ambient to improve film quality and reduce leakage current. A sputtered TiN layer is used as a diffusion barrier between the Al gate electrode and the TaTi_xO_y dielectric. XPS analyses confirm the formation of a (Ta_2O_5)_(1-x)(TiO_2)_x composite oxide. A high quality TaTi_xO_y gate stack with EOT = 7 A and leakage current J_g = 0.5 A/cm~2 @ V_g = -1.0 V has been achieved. We have also succeeded in forming a TaTi_xO_y composite oxide by rapid thermal oxidation of the as-deposited CVD TaTi films. The electrical properties and J_g-EOT characteristics of these composite oxides are remarkably similar to that of RTCVD Ta_2O_5, suggesting that the dielectric constant of Ta_2O_5 is not affected by the addition of TiO_2.