Hard Substrate System Research Articles

A novel approach to extracting hardness of copper/niobium (Cu/Nb) multilayer films by removing the substrate effect

This article presents a novel method to eliminate the substrate effect in soft thin film on hard substrate by correcting the projected contact area in nanoindentation test. The hardness of sputtered Cu/Nb multilayer films on silicon substrate with different individual layer thickness was measured by nanoindentation in continuous stiffness mode (CSM) and was shown to be influenced by both indentation size effect (ISE) and substrate effect. Finite element modeling (FEM) and atomic force microscope (AFM) were used to investigate the influence of substrate to the hardness measurement, and the results showed that the hardness deviation induced by the substrate effect resulted from the pile-up can be reasonably removed. Silicon substrate was found to be crucial for the pile-up formation, as the vertical plastic flow of soft Cu/Nb film was restrained by hard silicon substrate with the increase of indentation depth. After applying our pile-up correction and revised Nix-Gao fitting, the hardness curves show a depth independent relation, which fulfills the requirement for accurate hardness measurement. We showed that the hardness deviation due to pile-up is about 14%. Meanwhile, some vague issues like the plateau region and “one-tenth rule” applied in many studies were discussed and clarified basing on our experimental and modeling results. The correcting methods and simulation results could be instructive and significant for nanoindentation hardness test of similar soft film on hard substrate system.

A new approach to determine wedge-indented interfacial toughness in soft-film hard-substrate systems with application to low-k films on Si substrate

Abstract

Plastic Domain Microstructure and Hardness Analysis of Indented Layered Composite

The size dependent hardening in Al-4wt%Cu thin film on Si substrate has been investigated by the numerical calculation of indentation stress field and the observation of plastic zone microstructure of indented film. Distribution of internal stress predicted by triangular dislocation loop (TDL) model shows no size dependency with the different number of dislocations when the constant line density is assumed at the contact surface. TEM cross-sectional observation reveals that the plastic deformation is dominantly induced inside the film, and the growth of plastic zone is restricted at the interface of hard Si substrate. The size dependent hardening in soft film and hard substrate system is discussed from the change in dislocation density with respect to the plastic zone microstructure.

INVESTIGATION OF INDENTATION METHODS FOR PROPERTIES DETERMINATION IN HARD FILM – SOFT SUBSTRATE SYSTEMS

ABSTRACTElastic modulus values of the thin films utilized in three different hard film- soft substrate systems were measured using a combination of traditional and continuous stiffness indentation. These systems were chosen to represent typical systems currently utilized in MEMS and included Si/SU8/W, Si/SiO2/Ti/Pt/PZT, and Si/SiO2/Ti/Pt. The last system was coated with either a compressive or nonstressed Cr film. By taking into account ratio between the creep due to the polymer substrate, SU8, to the unloading rate, the modulus of W was measured to be 400 GPa. The modulus of the SU8 was also determined to be 6 GPa. Comparing both the CSM and traditional indentation for the Si/SiO2/Ti/Pt/PZT system showed that the dynamic motion of the indenter caused pile-up in the PZT and resulting in the overestimation of the PZT modulus. This pile-up is a function of the sinusoidal loading frequency. Instead, the modulus of the PZT was measured by shallow depths of traditional indentation that resulted in the PZT modulus of 100 GPa. The hard film-soft substrate systems were show to follow the same trend as stressed soft-film hard-substrate systems with residual stress. The modulus was over estimated for compressively stressed Cr films.

Substrate effects on nanoindentation mechanical property measurement of soft films on hard substrates

Substrate effects on the measurement of thin film mechanical properties by nanoindentation methods have been studied experimentally using a model soft film on hard substrate system: aluminum on glass. The hardness and elastic modulus of aluminum films with thicknesses of 240, 650, and 1700 nm sputter-deposited on glass were systematically characterized as a function of indenter penetration depth using standard nanoindentation methods. Scanning electron and atomic force microscopy of the hardness impressions revealed that indentation pileup in the aluminum is significantly enhanced by the substrate. The substrate also affects the form of the unloading curve in a manner that has important implications for nanoindentation data analysis procedures. Because of these effects, nanoindentation measurement techniques overestimate the film hardness and elastic modulus by as much as 100% and 50%, respectively, depending on the indentation depth. The largest errors occur at depths approximately equal to the film thickness.

Nanoindentation of Soft Films on Hard Substrates:The Importance of Pile-Up

AbstractNanoindentation is a common technique for measuring the mechanical properties of thin films. Here, we address the potential measurement errors caused by pile-up when soft films deposited on hard substrates are tested by nanoindentation methods. Pile-up is exacerbated in soft film / hard substrate systems because of the constraint the substrate exerts on plastic deformation of the film. To experimentally examine pile-up effects, aluminum films with thicknesses of 240 and 1700 nm were deposited on hard glass substrates and tested by standard nanoindentation techniques. The aluminum/glass system is interesting because the film and substrate have similar elastic moduli; thus, any unusual behavior in the nanoindentation results may be attributed to differences in the plastic flow characteristics alone. A detailed scanning electron microscopy examination of nanoindentation hardness impressions in the film revealed that common methods for analyzing nanoindentation data underestimate the true contact areas by as much as 80%, which results in overestimations of the hardness and modulus by as much as 80% and 35%, respectively. The sources of these errors and their influence on the measurement of hardness and elastic modulus are discussed, and a simple model for the composite hardness of the film/substrate system is developed. The model could prove useful in measuring the hardness and elastic modulus of soft-film / hard substrate systems when it is not possible to make indentations shallow enough to avoid the substrate influences.