Conductive Atomic Force Microscopy Analysis for Local Electrical Characteristics in Stressed SiO₂ Gate Films

Abstract

We have investigated microscopically the current leakage characteristics of SiO 2 gate films in metal-oxide-semiconductor structure capacitors subjected to the Fowler-Nordheim (FN) constant current stress using a conductive atomic force microscope (C-AFM). Current images of C-AFM clearly reveal the leakage current spots in the samples in which the stress induced leakage current was confirmed by the macroscopic current-voltage (I-V) measurement. On the other hand, in the sample after the repeated macroscopic I-V measurement, there is a shift in threshold voltage for the appearance of current spots and its value directly corresponds to the voltage shift observed in the macroscopic capacitance-voltage measurements for this sample. The total number of current spots observable in the C-AFM scanned area critically depends on the substrate voltage: the spot number initially increases with the voltage to a certain value then decreases. The visibility of the current spot is well explained by the holes trapped locally at defect sites created in the stressed SiO 2 .

Advances in AFM for the electrical characterization of semiconductors

“…Thickness fluctuations represent only one of the possible causes of current leakage through gate oxides. For electrically stressed oxides, charge trapping at the oxide/silicon interface may lead to weak spots at which leakage currents are enhanced [156]. Using TUNA, such weak spots may be identified as regions of higher current flow in current maps, and I -V curves may be taken at these points.…”

Behavior of Local Charge-Trapping Sites in La2O3–Al2O3 Composite Films under Constant Voltage Stress

“…10) The distribution of trapped holes and their trapping and detrapping phenomena have been revealed by observing the time dependence of local leakage current of the gate SiO 2 films by C-AFM. [11][12][13] The influence of trapped holes on the breakdown processes has been also clarified. 14) La 2 O 3 -Al 2 O 3 composite films are one of the promising candidates for next-generation gate high-k films because of their comparatively large dielectric constants and electron barrier height for Si.…”

Local Current Leakage Characterization in La2O3-Al2O3 Composite Films by Conductive Atomic Force Microscopy

“…Conductive atomic force microscopy (C-AFM) is a powerful tool to analyze the local morphological and electrical properties in gate dielectric films [1,2] . We have elucidated thus far local current leakage and degradation processes in stressed SiO 2 films using C-AFM [3][4][5][6][7] .…”