Detection of defect states responsible for leakage current in ultrathin tantalum pentoxide (Ta2O5) films by zero-bias thermally stimulated current spectroscopy

Defect states responsible for leakage current in ultrathin (physical thickness <10 nm) tantalum pentoxide $({\mathrm{Ta}}_{\mathrm{2}}{\mathrm{O}}_{\mathrm{5}})$ films were measured with a novel zero-bias thermally stimulated current technique. It was found that defect states $\mathrm{A,}$ whose activation energy was estimated to be about 0.2 eV, can be more efficiently suppressed by using ${\mathrm{N}}_{\mathrm{2}}\mathrm{O}$ rapid thermal annealing (RTA) instead of using ${\mathrm{O}}_{\mathrm{2}}$ RTA for postdeposition annealing. The leakage current was also smaller for samples with ${\mathrm{N}}_{\mathrm{2}}\mathrm{O}$ RTA than those with ${\mathrm{O}}_{\mathrm{2}}$ RTA for postdeposition annealing. Hence, defect states $A$ are quite likely to be important in causing leakage current.