Conductive-atomic force microscopy characterization of Ta_2O_5/SiO_2 stacks and the effect of microwave irradiation

摘要

The local electrical properties of ultrathin (4 nm) sputtered Ta_2O_5 on Si was studied by the conductive atomic force microscopy (C-AFM) technique. A current degradation during the repeatedly applied ramped voltages on the same dielectric point was observed, and the current increase was interpreted as stress-induced leakage current. With increasing applied voltages the impact of more leaky regions in the current map is stronger due to defect generation and the start of trapping/detrapping processes in these defects. Short exposure (seconds) to microwave irradiation acts as an annealing process of nanoscale level electrically active centres. The individual effect of both interfacial SiO_2-like and bulk Ta_2O_5 layers on the current-voltage (I-V) characteristics, and the difficulties in the data interpretation when using the known methods typical of macroscopic measurements were discussed. If the stack parameters used in the I-V curves fitting procedure are not known accurately the conclusion on the mechanism of conductivity is uncertain. Therefore, C-AFM as a novel characterization technique should be further developed to make it adequate for high-k stacks I-V data interpretation.