Jeremy Thurn

Evaluation of film biaxial modulus and coefficient of thermal expansion from thermoelastic film stress measurements

The so-called “double-substrate technique,” a popular method for determining thermoelastic properties of films, involves deposition of a film on two (or more) substrates of differing coefficient of thermal expansion (CTE) and measuring the elastic stress response to thermal cycling to determine the film biaxial modulus and CTE. However, the substrate CTE variation with temperature is often neglected. As an unintended consequence, the calculated film properties will depend on the temperature range used during thermal cycling and data analysis. An analysis technique that allows the film CTE to vary with temperature is proposed, ensuring that the calculated film properties are independent of the temperature range used during thermal cycling. The technique is demonstrated for a NiFe (permalloy) film electroplated on Al2O3–TiC, Si, and glass substrates.

Thermally induced stress hysteresis and co-efficient of thermal expansion changes in nanoporous SiO2

The thermomechanical response of electron beam deposited nanoporous silicon dioxide is examined using substrate curvature measurements and nanoindentation. Analysis of the thin film bond angle strain distributions versus temperature indicates that low temperature ( T< 100 ◦ C) stress hysteresis and tensioning are primarily attributed to hydrogen bonded water desorption. However, at higher temperatures, the absence of water desorption suggests that the thermomechanical behaviour is related to thermally induced bond angle strain redistributions towards the local bonding environment of quartz and thermally grown silicon dioxide. This is supported by the co-efficient of thermal expansion data that trend lower with higher annealing temperatures. The re-absorption of water into the thin film accounts for the reproducibility of the open-loop stress hysteresis and tensioning observations. (Some figures in this article are in colour only in the electronic version)

Comparison of depth-sensing indentation at ultramicroscopic contacts by single- and multiple-partial-unload cycles

Abstract Thin films typically exhibit variations in modulus and hardness with increasing indentation depth during depth-sensing indentation experiments at ultramicroscopic contacts (“nanoindentation”) because the measured stiffness response is affected by the substrate. There are three techniques commonly used to sample this variation in properties with depth: multiple indentations with increasing peak load, a single indentation with multiple-partial-unload cycles, and continuous stiffness measurement during a single indentation event. Experiments using the first two options were performed on a series of thin film systems and the method of multiple-partial-unloading found to have significant drawbacks when used at the sub-micron length scale that lead to erroneous conclusions.