iTF - Intrinsic Thin Film Mechanical Property Solution
Enabling Quantitative Mechanical Property Measurements of Ultra-Thin Films
Interpreting nanoindentation results on thin films can be complicated due to the effect of the substrate on the test results, where the elastic response of the contact is a combined response of the tip, the film and the substrate. A 10% “rule” has been widely used during nanoindentation to estimate the intrinsic thin film modulus, where at <10% of the film thickness the substrate effect is assumed to be diminished. However the 10% rule fails to estimate thin film modulus when the film is stiffer than the substrate, as well as when the elastic mismatch between the film and the substrate is large. Significantly shallower indents have to be performed to obtain film modulus for these systems. The thinner the film becomes, the more difficult it is to measure intrinsic film properties. Additionally, nonlinear elastic behavior, anisotropy, and local hardening also affect the results of nanoindentation on layered materials.
Hysitron utilizes patented iTF (Intrinsic Thin Film Mechanical Property Solution) models to provide intrinsic, quantitative elastic properties of thin films and layered structures. iTF is based on Yu’s elastic indentation on layered materials solution and expands to plastic indentation by introducing plasticity parameter – a variable along with thin film modulus can be calculated through series of numerical calculations. To use iTF for intrinsic thin film modulus analysis, stiffness of the layered thin film system is obtained as function of indentation depth. Using the depth profiles of the stiffness as well as the load, iTF generates stiffness-contact radius curves both from Yu’s solution and from area function obtained by the user. This is with known substrate modulus and initially assumed film modulus and plasticity parameter. Then the sum of error between the two curves at each assumed film modulus and plasticity parameter combination is plotted in an error matrix. The minimum error provides the correct combination of calculated film modulus and plasticity parameter. Hysitron’s iTF has successfully been proven to analyze the thin film intrinsic modulus with less than 2nm film thickness.
Hysitron’s iTF Features
- Patented models to provide intrinsic, quantitative elastic properties of thin films and layered structures
- Based on Yu’s elastic indentation solution and expanded to plastic indentation by introducing a plasticity parameter
- Experimental determination of intrinsic elastic properties and plasticity parameter calculations integrated into Hysitron software
References: H. Li, J. J. Vlassak, Determining the elastic modulus and hardness of an ultra-thin film on a substrate using nanoindentation. J Mater Res 24, 1114 (Mar, 2009). US Patent Number 8,265,884.