Evaluation of depth distribution and characterization of nanoscale Ta/Si multilayer thin film structures

Abstract

A multilayer thin film structure of ten alternate Ta and Si layers with approximately 18nm thickness for the combined (Ta+Si) layer, was evaluated to explore the individual layer thickness and the interface mixing behavior using different surface characterization techniques like Time-of-Flight Secondary Ion Mass Spectrometry (TOFSIMS), X-ray Reflectometry (XRR) and Kelvin Probe Force Microscopy (KPFM). These results were compared with measurements performed earlier using cross section Transmission Electron Microscopy (TEM). The TOFSIMS depth profile results indicate the individual thickness of Si and Ta layers to be 8.1nm and 5.9nm respectively which are less than the corresponding actual thickness measured by cross section TEM as 10.5nm and 7.5nm. The difference in thickness measurement has been explained in the light of ion bombardment induced atomic mixing in the interface during sputter depth profiling. A scanning electron micrograph shows the actual crater and its edges created due to the sputtering including the multilayer for real view of the structure. The XRR observations however reveal better agreement with the cross section TEM data, both being non-destructive in nature. Attempts were made to characterize the multilayer using KPFM technique which clearly elucidated the grating type cross section of the structure.