David J. Dingley

Analysis of grain-boundary structure in Al–Cu interconnects

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...

Determination of crystal phase from an electron backscatter diffraction pattern

Electron backscatter diffraction (EBSD) is a scanning electron microscope-based technique principally used for the determination and mapping of crystal orientation. This work describes an adaptation of the EBSD technique into a potential tool for crystal phase determination. The process can be distilled into three steps: (1) extracting a triclinic cell from a single EBSD pattern, (2) identifying the crystal symmetry from an examination of the triclinic cell, and (3) determining the lattice parameters. The triclinic cell is determined by finding the bands passing through two zone axes in the pattern including a band connecting the two. A three-dimensional triclinic unit cell is constructed based on the identified bands. The EBSD pattern is indexed in terms of the triclinic cell thus formed and the crystal orientation calculated. The pattern indexing results in independent multiple orientations due to the symmetry the crystal actually possesses. By examining the relationships between these multiple orientations, the crystal system is established. By comparing simulated Kikuchi bands with the pattern the lattice parameters can be determined. Details of the method are given for a test case of EBSD patterns obtained from the hexagonal phase of titanium.

ADVANCED SOFTWARE CAPABILITIES FOR AUTOMATED EBSD

Venables (1973) coined the term electron backscatter diffraction (EBSD) to describe backscatter Kikuchi diffraction in the scanning electron microscope (SEM). The first commercial system was produced by Moon and Harris of Custom Camera Designs in 1984 and was an outgrowth of the system designed by Dingley at the University of Bristol. This design was later provided to both Oxford Instruments and Ris0 National Laboratory out of which the OPAL™ and HKL™ systems evolved. The first fully automated EBSD system capable of automatic indexing of EBSD patterns and subsequent mapping of the spatial distribution of crystallographic orientation was introduced by Wright (1992). The term Orientation Imaging Microscopy or OIM™ was coined to describe this automated technique for forming images by mapping orientation data obtained from automated EBSD (Adams et al., 1993). Dingley and Adams co-founded TSL (or TexSEM Laboratories) in 1994 to produce the first commercial automated EBSD system based on the system developed by the group at Yale University (Adams, Wright, and Kunze). TSL adopted the name OIM™ for its automated EBSD products. Much of what was included in the original TSL system has become a standard for modern EBSD systems.

Extension of Orientation Mapping to the Transmission Electron Microscope

This paper describes progress in improving the spatial resolution of the well-established Orientation Imaging Microscopy technique, OIM, by developing an analogous procedure for the transmission electron microscope. The transmission orientation micrographs are obtained by recording a large series of dark field micrographs taken from the chosen area in the specimen. This area is selected so that it contains all of the grains of interest and is imaged at sufficiently high magnification to yield the spatial resolution required. The changing intensity of each pixel in different dark field micrographs permits the equivalent of a diffraction pattern for that pixel to be constructed. This enables determination of the lattice orientation of small volumes in the sample corresponding to that imaged in each individual pixel. Experimentation has shown that problems arise however, that decrease the fraction of correctly measured points due to ambiguities in determining the index of higher order reflections, especially when the total number of reflections observed is small. The solution has been to both modify the indexing procedure and to sum the diffraction vectors observed within a single grain. The paper concentrates on a detailed analysis of a heavily deformed aluminium sample, chosen because of the fragmentation of the structure.