1. Introduction and overview 2. Film stress and substrate curvature 3. Stress in anisotropic and patterned films 4. Delamination and fracture 5. Film buckling, bulging and peeling 6. Dislocation formation in epitaxial systems 7. Dislocation interactions and strain relaxation 8. Equilibrium and stability of surfaces 9. The role of stress in mass transport.

Thin Film Materials: Stress, Defect Formation and Surface Evolution

Electromagnetic Response and Energy Conversion for Functions and Devices in Low‐Dimensional Materials

A theory is developed which allows one to discuss the stability of multiply-twinned particles and to calculate critical sizes for stable and quasi-stable states. An icosahedral particle is essentially stable for r ≦ r i w * , quasi-stable for r i w * r i t 0 where r is an edge length of the particle, while a decahedral particle is not essentially stable but quasi-stable for r ≦ r d t 0 and unstable for r > r d t 0 . The critical sizes r i w * , r i t 0 and r d t 0 are formulated as functions of the specific surface energy γ h k l , the twin boundary energy γ t , the elastic strain energy W and the adhesive energy γ a to the substrate. Calculated critical diameters 2 r i w * ,2 r i t 0 and 2 r d t 0 for the particles grown in free space for several elements range between 15.5A and 106.8A, between 109.8A and 486.1A and between 725A and 3961A, respectively. These values are in good agreement with experimental results.

Stability of Multiply-Twinned Particles

The behavior of electromigration‐induced voids in narrow, unpassivated aluminum interconnects is examined, using scanning electron microscopy. Some electromigration tests were interrupted several times in order to observe void nucleation, void growth, and finally the failure of the conductor line. It is found that voids which opened the line have a specific asymmetric shape with respect to the electron flow direction. Besides void nucleation and void growth, void shape changes can consume a major part of the lifetime of the conductor line. A first attempt to model these processes on the basis of diffusion along the void surface shows that voids with a noncircular initial shape tend to produce the fatal asymmetry due to electron wind effects, with the anisotropy of surface energy possibly playing only a minor role.

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Electromigration failure by shape change of voids in bamboo lines

Motions of Microscopic Surfaces in Materials

We report the morphology of electromigration induced transgranular slit‐like voids in Al and Al‐2% Cu thin‐film interconnects with near bamboo microstructures. The grain structure surrounding fatal voids was determined from images produced by scanning electron and focused ion beam microscopy. Fatal voids were seen to traverse grains near to, but apart from, bamboo boundaries or grain triple points, and often appear to emanate from small wedge‐shaped voids at the interconnect edge. The small volume slit voids are consistent with an observed decrease in fatal void volume with reduced linewidth/grain size ratio. However, the transgranular void pathway represents a new failure mechanism responsible for reduced reliability in the narrow interconnects which are more relevant for advanced integrated circuit technologies. The conditions for stress‐induced transgranular slit voiding are briefly discussed.

Electromigration induced transgranular slit failures in near bamboo Al and Al‐2% Cu thin‐film interconnects

Detailed transmission and scanning electron microscopic images of electromigration‐induced open circuit failures are presented for fine line aluminum alloy thin film interconnects. A characteristic slit open circuit, similar to stress migration open circuits in narrow interconnects, is shown for various film compositions, processing, and deposition conditions. It is suggested that slit failure morphology is more generally observed for low (≊1) ratios of conductor line width to film grain size. The slit failures observed often occur near copper rich precipitates. The morphology of several slit voids suggests that they are transgranular across the linewidth, consistent with other recent reports of electromigration induced damage in single crystal interconnects.

Slit morphology of electromigration induced open circuit failures in fine line conductors

The role of crystallographic texture in electromigration resistance of interconnect lines is well documented. The presence of a strong (111) fiber texture results in a more reliable interconnect structure. It is also generally accepted that grain-boundary diffusion is the primary mechanism by which electromigration failures occur. It has been difficult to this point, however, to obtain statistically reliable information of grain-boundary structure in these materials as transmission electron microscopy investigations are limited by tedious specimen preparation and small, nonrepresentative, imaging regions. The present work focuses upon characterization of texture and grain-boundary structure of interconnect lines using orientation imaging microscopy, and particularly, upon the linewidth dependence of these measures. Conventionally processed Al–1%Cu lines were investigated to determine the affects of a postpatterning anneal on boundary structure as a function of linewidth. It was observed that texture tende...

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Analysis of grain-boundary structure in Al–Cu interconnects

Using off-axis electron holography under Lorentz microscopy conditions to experimentally determine the magnetization distribution in individual cobalt (Co) nanowires, and scanning precession-electron diffraction to obtain their crystalline orientation phase map, allowed us to directly visualize with high accuracy the effect of crystallographic texture on the magnetization of nanowires. The influence of grain boundaries and disorientations on the magnetic structure is correlated on the basis of micromagnetic analysis in order to establish the detailed relationship between magnetic and crystalline structure. This approach demonstrates the applicability of the method employed and provides further understanding on the effect of crystalline structure on magnetic properties at the nanometric scale.

John E. Sanchez

Papers

Electromigration failure by shape change of voids in bamboo lines

Electromigration induced transgranular slit failures in near bamboo Al and Al‐2% Cu thin‐film interconnects

Slit morphology of electromigration induced open circuit failures in fine line conductors

Analysis of grain-boundary structure in Al–Cu interconnects

Mapping the magnetic and crystal structure in cobalt nanowires