Monocrystalline Silicon

Summary based on wikipedia page

Czochralski Method

The Czochralski method (CZ) is a versatile technique that can be used to grow macroscopic monocrystals of various elements, minerals, and compounds. It was invented in 1915 by Jan Czochralski a Polish scientist working in Germany who accidentally discovered it while conducting research into metal crystallization rates. He apparently absentmindedly dipped his fountain pen into a container of molten tin instead of an inkwell and drew a filament of tin which a later investigation proved to be monocrystalline.

While inception of the method occurred in 1915, it would not be until 1937 that maturity of the process was reached. In that year Henry Walther at Bell Telephone Labs added mechanical and thermodynamic methods to compensate for nonuniform thermal stress that affected crystal quality in the older method. The innovations consisted of crystal rotation and dynamic gas stream cooling that allowed the user to control for crystal shape and diameter of bulk crystals.

With the advent of the semiconductor revolution, CZ underwent rapid deployment in the United States during and after WWII. Many refinements were added to control for evaporative loss, enable continuous production and improved diameter control of the produced crystal over the next thirty years. These refinements extended both the scope of use, quality and production rate of the process that the current industrial process possesses.

A factor driving selection of a method to grow monocrystals (MGM) is the crystal lattice defect density of the final product. Other approaches such as Bridgman-Stockbarger method (BSM) and physical vapour support (PVS) are competitors. For some materials, alternative methods may be more effective than CZ, but CZ is currently the dominant method for economic production of monocrystalline silicon (mono-Si) feedstock for se miconductors. mono-Si grown using CZ is called monocrystalline CZ silicon (CZ-Si).

The Method

The raw feedstock is semiconductor-grade silicon (silicon containing O(ppm) impurity, usually quartz) that is melted at 1425C in a silica crucible. Dopants are mixed in as needed for the application. A rod-mounted seed crystal is dipped into the melt and rotated and retracted at a rate to extract the coalescing crystal from the melt. Temperature, retraction rate, rotation rate are regulated by controller that observes temperature and velocity field such that a monocrystalline cylindrical ingot is produced. The crucible walls gradually melt as the process proceeds, introducing oxygen as an impurity. This effect of this impurity has been studied in depth and can have beneficial or detrimental effects on the crystal produced. Utility is dependent on the intended use of the crystal produced. For example, oxygen impurities can improve mechanical strength but can also degrade electronic performance.