Resolving nanoscale mechanical properties of multi-layered low-k dielectric films by contact resonance atomic force microscopy

The continuous advances in semiconductor device fabrication demand various characterization techniques capable of proving quantitative measurements at the nanoscale. A prominent scanning probe-based technique for nanoscale elastic property measurements is contact resonance atomic force microscopy (CR-AFM). CR-AFM uses the sensitivity of the eigenmodes of an AFM cantilever to the contact mechanics established between the apex of the AFM probe and the sample tested. While the applicability of CR-AFM has been examined on a large variety of compliant and stiff materials, new methodological approaches are expected to improve its measurement accuracy and ease of applicability. This is especially relevant to single and multi-layered coated specimens that are part of advanced semiconductor devices. In this work we examined CR-AFM measurements on a series of thin low-k dielectric films assembled in a stiff/compliant/substrate structure. The thickness of the top layer was used as a control parameter to vary the structural complexity and mechanical stiffness of the system. The measurements were analyzed both by analytical models and finite element analysis to observe the contributions of various geometrical factors and approximations that usually are mitigated by calibration procedures. It was found that the finite element analysis provides a more detailed yet inclusive analysis of the mechanics of the system and can be used to separate among the mechanical properties of layered structures.