On annealing twins and CSL distributions in F.C.C. polycrystals

Electrical, Magnetic and Mechanical Properties of Nanocrystalline Nickel

The electrical, magnetic and mechanical properties of bulk nanocrystalline nickel produced by pulse-electrodeposition are reviewed and discussed in the context of nanoprocessing as a distinct form of grain boundary engineering to develop soft magnetic materials with improved performance characteristics.

Characterization of Textured Aluminum Lines and Modelling of Stress Voiding

It is well known from studies of individual interfaces that grain boundaries exhibit a spectrum of properties because their structure is misorientation dependent. Usually this variability is neglected and properties are modeled using a mean field approach. The limitations inherent in this approach can be overcome, in principle, using a combination of experimental techniques, theory and modeling. The bamboo structure of an interconnect is a particularly simple polycrystalline structure that can now be readily characterized experimentally and modeled in the computer. The grain misorientations in a [111] textured aluminum line have been measured using the new automated technique of orientational imaging microscopy. By relating boundary angle to diffusivity the expected stress voiding failure processes can be predicted through the link between misorientation angle, grain boundary excess free energy and diffusivity. Consequently it can be shown that the high energy boundaries are the favored failure sites thermodynamically and kinetically.

Toward Realizing the Structure-Property Link in Polycrystalline Thin Films

Many materials for engineering applications are used in polycrystalline form and contain grain boundaries with a range of structures and properties. However, most research on grain boundaries to date has focussed exclusively on symmetric coincidence site lattice interfaces. To go beyond descriptions for these simple interfaces and thence to an aggregate of grains and grain boundaries in a polycrystal will require a new approach. Here we discuss two models for properties of polycrystalline materials, including their advantages and drawbacks, and indicate the microstructural variables available to optimize properties.

A Grain Boundary Engineering Approach to Materials Reliability

Intergranular degradation processes, (e.g., corrosion, stress corrosion, cracking, creep cracking) are a frequent cause of premature and unpredictable service failure of engineering components. Recent advances in (1) understanding structure-property relationships for grain boundaries, and (2) characterization techniques for grain boundaries in polycrystalline materials, have provided the means for improved component lifetime prediction, and the opportunity to engineer intergranular-degradation resistant microstructures.

In this work, we present our previously developed geometric models for grain boundary structure and grain size effects on intergranular degradation susceptibility. Specific examples are presented of the successful application of the ‘grain boundary engineering’ approach to the prediction and mitigation of intergranular corrosion, stress corrosion cracking, and creep cracking in Ni-based materials.

Impact of trench aspect ratio on microstructure variation in as-deposited and annealed damascene Cu interconnect lines

Microstructure variation with trench aspect ratio has been investigated in both as-deposited and annealed damascene Cu interconnect lines using Orientation Imaging Microscopy (OIM). The microstructure was characterized by measuring mean grain size, grain size and grain boundary distribution and grain aspect ratio. Since the lines were highly twinned, the mean grain size was measured both before and after neglecting the presence of Sigma3 boundaries. The mean grain size was higher for the annealed lines compared to as-deposited lines and increased proportionally with decreasing trench aspect ratio in the annealed Cu lines with higher aspect ratio. The distribution of coincident site lattice (CSL) boundaries revealed a higher fraction of Sigma3 boundaries in all the lines; their increase upon annealing in the majority of the specimens was accompanied by a decrease of Sigma9 CSL boundaries. The fraction of CSL boundaries was higher in the lines with higher aspect ratios and increased upon annealing in most of the lines. The role of pitch distance (line spacing) in influencing the mean grain size and CSL boundary distribution was identified. Additionally the microstructure was characterized by measuring the grain boundary misorientation distribution. The grain shape was characterized by measuring the grain aspect ratio. Strain distribution in the lines was examined using the Image Quality (IQ) parameter.