One of the simplest ways to measure the mechanical properties of a thin film is to deform it on a very small scale. Because indentation testing with a sharp indenter is one convenient means to accomplish this, nanoindentation, or indentation testing at the nanometer scale, has become one of the most widely used techniques for measuring the mechanical properties of thin films. Other reasons for the popularity of nanoindentation stem from the ease with which a wide variety of mechanical properties can be measured without removing the film from its substrate and the ability to probe a surface at numerous points and spatially map its mechanical properties. The utility of the mapping capability is illustrated in Figure 1, which shows several small indentations made at selected points in a microelectronic device. The hardness and modulus of the device were determined at each point. In addition to microelectronics, nanoindentation has also proved useful in the study of optical coatings, hard coatings, and materials with surfaces modified by ion implantation and laser treatment.

https://www.cambridge.org/core/services/aop-cambridge-core/content/view/S0883769400041634

Measurement of thin film mechanical properties using nanoindentation

Electromigration is an important concern in very large scale integrated circuits. In narrow, confined metal interconnects used at the chip level, the electromigration flux is resisted by the evolution of mechanical stresses in the interconnects. Solutions for the differential equation governing the evolution of back stresses are presented for several representative cases, and the solutions are discussed in the light of experimental as well as theoretical developments from the literature.

Stress evolution due to electromigration in confined metal lines

The influence of applied stress on the measurement of hardness and elastic modulus using nanoindentation methods has been experimentally investigated using special specimens of aluminum alloy 8009 to which controlled stresses could be applied by bending. When analyzed according to standard methods, the nanoindentation data reveal changes in hardness with stress similar to those observed in conventional hardness tests. However, the same analysis shows that the elastic modulus changes with stress by as much as 10%, thus suggesting that the analysis procedure is somehow deficient. Comparison of the real indentation contact areas measured optically to those determined from the nanoindentation data shows that the apparent stress dependence of the modulus results from an underestimation of the contact area by the nanoindentation analysis procedures.

https://www.cambridge.org/core/services/aop-cambridge-core/content/view/S0884291400022858

Influences of stress on the measurement of mechanical properties using nanoindentation: Part I. Experimental studies in an aluminum alloy

To measure nanomechanical properties of surface layers of bulk materials and thin films, depth-sensing nanoindentation measurement techniques are used commonly. The nanoindentation apparatus continuously monitors the load and the position of the indenter relative to the surface of the specimen (depth of an indent or displacement) during the indentation process. Indentation experiments can be performed at a penetration depth of as low as about 5 nm. This chapter presents an overview of various nanoindentation techniques, various measurement options, and data analysis. Data on elastic-plastic deformation behavior, hardness, elastic modulus, scratch resistance, film-substrate adhesion, residual stresses, time-dependent creep and relaxation properties, fracture toughness, and fatigue are presented.

Nanomechanical characterisation of solid surfaces and thin films

On the determination of residual stress and strain fields by sharp indentation testing.: Part I: theoretical and numerical analysis

Stress relaxation in aluminum films of several thicknesses was characterized by using both continuous indentation and x-ray diffraction techniques. Results of the indentation and x-ray stress measurements compare closely for films of small thicknesses. Indentation data from thicker films do not compare well to the x-ray data due to the presence of a residual stress distribution.

Residual stress measurements of thin aluminum metallizations by continuous indentation and x-ray stress measurement techniques

This work investigates thermal stress‐induced voiding, and void nucleation in particular, in narrow, passivated aluminum‐based metallizations on silicon substrates. After excursions to a higher temperature, the thermal stress is tensile, and increases during cooldown to room temperature, after which it relaxes with time. Experiments conducted on two aluminum alloy metallizations suggest that stress‐induced void nucleation is a one shot phenomenon during cooldown from the heat treatment temperature. Further, the high thermal stresses present, and the strong constraints against deformation provided by the substrate and passivation layer, make void nucleation unique in narrow passivated metallizations. Finally, voids always appear to be connected to grain boundaries. The above experimental evidence and theoretical considerations together suggest that grain boundary sliding is the main mechanism facilitating void nucleation in passivated aluminum alloy metallizations.

W. R. LaFontaine

Papers

Residual stress measurements of thin aluminum metallizations by continuous indentation and x-ray stress measurement techniques

Stress‐induced nucleation of voids in narrow aluminum‐based metallizations on silicon substrates