IAN LANG ELECTRONICS
Czochralski's family had a chemist's business in Berlin, where he went to work. His ability soon outstripped pharmacy, and he became a leading figure in several laboratories and companies in Berlin and took his degree at Charlottenburg Polytechnic. In 1916 he noticed , during an experiment into crystallisation rates of metals, that a capillary dipped in a molten metal and slowly lifted above the liquid caused a slow solidification. He was able to make a needle of single crystal metal. In 1916 there was no practical use for this technology and it became largely a scientific curiosity. In 1950 Teal and Little from the Bell Laboratory applied Czochralski's method to germanium in the search for a better transistor and later it was used for silicon, giving the world a substrate for the very first integrated circuits in the 1960s. Czochralski, like many others featured here, follows the theme of an idea far ahead of its time.
Having achieved a goal of very nearly pure silicon, we now need to turn it into a material having a uniform crystal lattice if it is to be any good to us as a substrate for our integrated circuit. Below is a diagram of an apparatus set up to grow a rod using the Czochralski method:
The quartz crucible contains a measure of silicon and it is heated in the furnace whereupon the silicon melts. A single crystal or seed at the end of the puller rod is inserted into the melt. the puller rod is rotated at slightly less than 1 revolution per second and drawn upwards at about 2cm per hour, whereupon the molten silicon can solidify and the atoms align themselves in the same way as those of the seed. Eventually a solid cylinder of pure silicon is produced; it is known as a boule or an ingot.. In large commercial concerns, this can be up to 2m long and 30cm in diameter. Argon prevents chemical reaction taking place.
Why is this necessary? Because in a monocrystalline structure like this there are no grain boundaries , and thus there is no crystollographic defect which can have significant detrimental effects on the electrical properties of the material. Without crystalline perfection, the construction of very-large scale integration (VLSI) devices such as a computer processor would be at best extremely difficult, and system-on-a-chip constructions would be rendered impossible.