Gate oxide thickness dependence of the leakage current mechanism in Ru/Ta_2O_5/SiON/Si structures

摘要

Leakage conduction mechanisms in Ru/Ta_2O_5/SiON/Si structures with rf-sputtered Ta_2O_5 with thicknesses ranging from 13.5 to 1.8 nm were systematically studied. Notable reaction at the Ru/Ta_2O_5 interface was revealed by capacitance-voltage measurements. Temperature-dependent current-voltage characteristics suggest the bulk-limited conduction mechanism in all metal-oxide-semiconductor structures. Under gate injection, Poole-Frenkel emission was identified as a dominant mechanism for 13.5 nm thick Ta_2O_5. With an oxide thickness decreasing down to 3.5 nm, the conduction mechanism transforms to thermionic trap-assisted tunnelling through the triangular barrier. Under substrate injection, the dominant mechanism gradually changes with decreasing thickness from thermionic trap-assisted tunnelling to trap-assisted tunnelling through the triangular barrier; Poole-Frenkel emission was not observed at all. A 0.7 eV deep defect level distributed over Ta_2O_5 is assumed to be responsible for bulk-limited conduction mechanisms and is attributed to H-related defects or oxygen vacancies in Ta_2O_5.