Defects and Diffusion in Silicon Technology
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Diffusion in Silicon Technology Tony E. Haynes, Guest Editor
The silicon at the heart of highperformance integrated circuits (ICs) is the most precisely engineered material in mass production today. Crystalline silicon, purified to the level required for manufacturing modern, high-performance microelectronics (better than parts-per-billion purity), is arguably the most perfect material known. It is produced in large quantities and very economically. Continuing progress in basic silicon materials science has been central to this achievement. At the same time, access to such a perfect material and detailed knowledge of silicon’s properties have provided the experimentalist with excellent opportunities to devise rather elegant experiments in which the parameters can be controlled very precisely. Silicon has similarly provided condensed-matter theorists with a nearly ideal test bed for new theoretical approaches. This issue of MRS Bulletin is dedicated to the materials physics that has both enabled the development of such a highly perfect material and benefited from its availability. The stringent constraints placed on the properties of the silicon used in microelectronics pose a number of challenging problems for the materials scientist. Many of these demands come from the push for continually improving performance that drives the IC market. For instance, operation at higher frequencies with lower power consumption and in smaller packages constantly challenges our ability to control the placement of the dopant atoms that determine the operational characteristics of individual transistors. Other considerations are related to more practical matters of economy and reliability, which drive us toward improved strategies for reducing the number of manufacturing steps and increasing the manufacturing yield, that is, the fraction of completed devices that meet operating specifications. Solutions must also be found for control14
ling grown-in crystalline defects as well as defects and contaminants that are introduced into the silicon during manufacturing. The contributors to this set of articles have provided a survey of the current status of some of the most interesting materials-science problems that lie below the silicon surface. The first article, by Paul Packan, provides an appreciation for the magnitude of the research challenges in today’s silicon materials science by describing the critical link between materials-research needs and the limitations on continuing improvements in device performance. Calculations of the electrical properties of model transistors dramatically demonstrate how performance is limited by dimensional scalability. Extrapolation of current scaling trends shows that the continued success of scaling will depend very soon on the elimination of nonequilibrium dopant diffusion and electrical activation of supersaturated dopant concentrations. These considerations lead naturally into a discussion of the properties of point defects in silicon, which control diffusion and impurity clustering. Hartmut Br
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