Intrinsic Point Defects and Their Control in Silicon Crystal Growth and Wafer Processing
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Defects and Their Control in Silicon Crystal Growth and Wafer Processing R. Falster and V.V. Voronkov
Introduction Silicon produced for the microelectronics industry is far and away the purest and most perfect crystalline material manufactured today. It is fabricated routinely and in very large volumes. Many of the advances in integrated-circuit (IC) manufacturing achieved in recent years would not have been possible without parallel advances in silicon-crystal quality and defect engineering. Transition-metal contamination is a case in point. Essentially all practical problems (minority carrier lifetime, metal precipitation, stacking faults, etc.) associated with metal contaminants have largely been solved through advances in crystal purity. Today, silicon technology faces two main defect challenges, neither of which can be solved simply by increasing the level of crystal purity, as was the case in the transition-metal problem. So important are these problems that they in fact challenge the very status of the traditional, polished, Czochralski-grown silicon wafer (as opposed to the much costlier epitaxial silicon substrate) as a suitable material for the coming generations of advanced IC processes. One of these challenges arises from the intrinsic, or native, point defects, lattice vacancies, and silicon self-interstitials, and the other from the most important extrinsic point defect in Czochralski-grown silicon: oxygen. Large advances have been made recently in these areas, producing solutions to these engineering problems. Although the solutions to these two problems are completely separate (one is imposed on
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the crystal-growth process and the other on wafer heat-treating), they are related; the underlying science is shared by both and is common to the range of topics covered in this issue. In particular, studies of point defects from the point of view of crystal growth and oxygen-precipitation control can give new insights into the elusive properties of these defects. This article summarizes these advances in silicon science and engineering.
Vacancies and Interstitials and Their Agglomerates in Silicon Crystals Microdefects in silicon related to intrinsic point defects were first observed in the early 1960s—ironically, almost immediately after the main silicon-crystal problem of the day was solved, that of dislocation-free growth. Eliminating dislocations from silicon crystals simultaneously eliminated an important distributed sink for “grown-in” intrinsic point defects, thus allowing them to homogeneously agglomerate. One problem solved, another created. It was not, however, until recent years that demands for crystal perfection reached such extremes that specific problems associated with these defect types were identified, and urgent solutions were demanded. The study of these microdefect agglomerates and their related effects on crystal growth has yielded a rich array of information on the properties of intrinsic point defects at high temperatures. The incorporation of intrinsic point defects into a
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