Jan Czochralski and His Method of Pulling Crystals
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HISTORICAL NOTE
Jan Czochralski and His Method of Pulling Crystals The most advanced factories, or “fabs,” in which integrated circuits are made use circular slices of silicon 300 mm in diameter. They are sliced from huge single crystals that are drawn from a molten silicon bath; these massive crystal ingots are rotated as they are slowly raised in synchrony with their growth rate, and the process has been perfected to the point where the dislocation population is about a million times lower than in a normal crystal. This procedure was initially developed by Gordon Teal and his colleagues at Bell Laboratories and then at Texas Instruments, from 1948 to 1952. However, the process was by no means entirely new. The scientist who discovered the process on which this modern procedure was based was Jan Czochralski (1885– 1953). According to one of his nephews, Czochralski (pronounced cho-HRALskee) based his experiment upon an accidental incident. One day, after melting some tin in a small dish with the intention of performing an experiment with it, Czochralski interrupted his work to write some notes. Absent-mindedly, he dipped his steel pen nib into the tin instead of the adjacent inkwell, then drew it out and found a thin filament of solid metal hanging from it; the slit in the nib had acted as a nucleating site for the solid. Instead of cursing, he perceived the significance of the accident and exploited it. In the middle of the First World War (1916), in Berlin, Czochralski designed a simple apparatus for measuring the crystal growth rate from the melt for a number of metals and submitted it in that year to the Zeitschrift für physikalische Chemie, which—slowed by the desperate circumstances of the time—delayed publication of the short paper until 1918. The apparatus (see Figure 1) consisted of a simple mechanism for dipping a fine glass tube (with a hook at the upper end, attached to a silk thread) into a bath of molten metal—starting with tin and going on to lead and zinc—and raising the tube, with a thin rod of solid metal hanging from it, at a steady (adjustable) rate using a clockwork mechanism. When the rate of ascent matched the natural rate of crystal growth near the melting temperature, a long single crystal of uniform diameter resulted. If the rate of raising was too small or too great, the solid rod either became thickened and short or attenuated and broke off. The single-crystal nature of the rod under ideal conditions was verified by etching. In later years, Czochralski applied the same method to several other metals.
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Main (which in due course became the leading German metallurgical firm), and 1939, when his research came to an end. He worked in Frankfurt until 1929, and among other achievements, he played a major role in creating the Zeitschrift für Metallkunde and later, the scientific society Deutsche Gesellschaft für Metallkunde. Throughout his years as a researcher and research director, Czochralski mixed
Jan Czochralski
Physical chemist and philosopher Michael Polanyi, in 1921–1922, also i
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