page_title: Czochralski method
section_title: Crystal sizes
hierarchical_section_title: Czochralski method / Crystal sizes
caption_attribution_description: English: A silicon crystal being grown by the Czochralski process at the Raytheon Corp. semiconductor plant in Newton, Massachusetts, USA, in 1956 for use in the first silicon transistors. The transistor was invented in 1946, and the Czochralski process was first used to grow silicon crystals to make the first silicon transistors at Bell Labs in 1953, so this is one of the earliest silicon crystal production plants. The induction heating coil visible around the crucible carries a radio frequency current, and the heat induced melts the pure silicon in the crucible at a temperature of 2650°F. A seed crystal of solid silicon is attached to the rod and is lowered into the tube to touch the surface of the melted silicon. By carefully controlling the temperature distribution using the induction heater, the melted silicon is induced to crystallize on the seed, adding to the crystal. The seed is slowly pulled up from the melt, and the silicon freezes onto the end, creating a solid rod of monocrystal silicon. Here the process has just begun, and the tapered end of the crystal is visible just below the rod. In this early device the silicon crystal was only 1 inch wide. The woman is measuring the temperature of the melt with an optical pyrometer. This device has a filament attached to a calibrated current source inside the viewing tube, which appears silhouetted in front of the hot silicon. The technician turns up the current until the luminous filament just disappears against the background of the glowing silicon. This means the filament and the silicon are at the same temperature. The current knob (bottom) is calibrated in temperature, so she can read the temperature of the silicon off the knob. Alterations to image: Cropped out portions of magazine cover containing text, straightened, removed obvious dirt and damage.
context_page_description: The Czochralski method, also Czochralski technique or Czochralski process, is a method of crystal growth used to obtain single crystals of semiconductors, metals, salts and synthetic gemstones. The method is named after Polish scientist Jan Czochralski, who invented the method in 1915 while investigating the crystallization rates of metals. He made this discovery by accident: instead of dipping his pen into his inkwell, he dipped it in molten tin, and drew a tin filament, which later proved to be a single crystal.
  The most important application may be the growth of large cylindrical ingots, or boules, of single crystal silicon used in the electronics industry to make semiconductor devices like integrated circuits. Other semiconductors, such as gallium arsenide, can also be grown by this method, although lower defect densities in this case can be obtained using variants of the Bridgman–Stockbarger method.
  The method is not limited to production of metal or metalloid crystals. For example, it is used to manufacture very-high purity crystals of salts for use in particle physics experiments, with tight controls on confounding metal ions and water absorbed during manufacture.
context_section_description: Due to efficiencies of scale, the semiconductor industry often uses wafers with standardized dimensions, or common wafer specifications. Early on, boules were small, a few cm wide. With advanced technology, high-end device manufacturers use 200 mm and 300 mm diameter wafers. Width is controlled by precise control of temperature, speeds of rotation, and the speed at which the seed holder is withdrawn. The crystal ingots from which wafers are sliced can be up to 2 metres in length, weighing several hundred kilograms. Larger wafers allow improvements in manufacturing efficiency, as more chips can be fabricated on each wafer, with lower relative loss, so there has been a steady drive to increase silicon wafer sizes. The next step up, 450 mm, is currently scheduled for introduction in 2018. Silicon wafers are typically about 0.2–0.75 mm thick, and can be polished to great flatness for making integrated circuits or textured for making solar cells.
  The process begins when the chamber is heated to approximately 1500 degrees Celsius, melting the silicon. When the silicon is fully melted, a small seed crystal mounted on the end of a rotating shaft is slowly lowered until it dips just below the surface of the molten silicon. The shaft rotates counterclockwise and the crucible rotates clockwise. The rotating rod is then drawn upwards very slowly—at about 25 mm per hour when making a crystal of ruby—allowing a roughly cylindrical boule to be formed. The boule can be from one to two metres, depending on the amount of silicon in the crucible.
  The electrical characteristics of the silicon are controlled by adding material like phosphorus or boron to the silicon before it is melted. The added material is called dopant and the process is called doping. This method is also used with semiconductor materials other than silicon, such as gallium arsenide.
caption: Silicon crystal being grown by the Czochralski method at Raytheon, 1956. The induction heating coil is visible, and the end of the crystal is just emerging from the melt. The technician is measuring the temperature with an optical pyrometer. The crystals produced by this early apparatus, used in an early Si plant, were only one inch in diameter.
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