Mechanical Properties in Small Dimensions: Comments from Industry
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Mechanical
Properties in Small Dimensions: Comments from Industry
The following are commentaries provided by representatives from industry. These short articles lend an additional context in which to appreciate the importance of the issues and mechanisms discussed in the technical articles. The authors of the commentaries point out that the basic principles that underlie the influence of scale on material behavior are not only interesting in their own right, but also are directly applicable to issues of great significance to designers and manufacturers of small-scale devices and structures. In addition, directions for future emphasis are suggested. Richard P. Vinci Shefford P. Baker Guest Editors
Control of Stresses in Silicon-Device Manufacturing In the development and manufacturing of silicon devices, the control of thin-film stresses continues to be a major challenge. High stresses can cause deformation, delamination, cracking, and void formation. They may also directly affect device characteristics. In multilevel interconnections now being developed, low-dielectric-constant insulators are being introduced that have drastically weaker mechanical properties than the glassy SiO2 used for decades. These factors, together with rapidly decreasing dimensions, require a greater understanding of the origins of thin-film stresses. High stresses are created by thermal-expansion mismatch during the heating cycles required for fabrication, and they are also a by-product of the film microstructure. These microstructureinduced stresses are referred to as “intrinsic” stresses and are the subject of the article by Floro et al. in this issue.
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The article provides a discussion of several prior models and mechanisms related to thin-film stresses and gives enough detail to examine the differences experimentally. Since many of the thin films used in silicon devices, such as contacts and diffusion-barrier layers, are barely thicker than their coalescence thickness, a careful evaluation of the mechanisms described by Floro et al. may help to control their properties to even smaller dimensions. James M.E. Harper Manager, Thin-Film Metallurgy and Interconnections IBM T.J. Watson Research Center
Fracture in Small Dimensions Ensuring long-term integrated-circuit interconnect reliability has always been challenging, given that a single electrical failure of an individual interconnect line or via, among millions of such microfeatures, can destroy the whole chip. Furthermore, a crack need only be
of the order of 1 m in size to cause such a failure. Traditionally, this problem was addressed in two ways: by modifying materials in order to enhance thin-film strength and interface adhesion as well as to reduce various stresses, and by rigorous reliability testing to reveal any weak links that can be fixed by altering local structures. While these approaches were not systematic, they did apply thin-film fracture mechanics empirically or intuitively. In fact, because fracturerelated failures were often observed to occur after exposure t
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