Temperature dependence of leakage currents in Ti-doped Ta2O5 films on nitrided silicon

Conduction mechanisms and electrically active defects in rf sputtered Ti doped Ta2O5 thin films have been investigated by analysing the impact of temperature on the I-V curves. The films (about 6 nm thick) were grown on silicon substrates nitrided in N2O or NH3 ambient. Two different methods of Ti incorporation were used-a surface doping, where a thin Ti layer is deposited on the top of Ta2O5, and a bulk doping, where the Ti layer is sandwiched between two layers of Ta2O5. The I-V characteristics were measured in a temperature range from 30 to 100 0C. Current is found to be governed mainly by the modified Poole-Frenkel (PF) effect, with a temperature dependent degree of compensation. Two types of trap centres involved in the PF conduction process have been identified: shallow traps located at about 0.3-0.4 eV below the conduction band edge of the dielectric, present in all doped films, and deeper centres at 0.65 eV, present only in the bulk-doped films. The origin of these trap centres is also discussed.