Ingot

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Monocrystalline silicon column

The term ingot ( English for ' bar ') is only used in German with a special meaning: it is understood to be a block made of a semiconductor material such as silicon . Ingots can be monocrystalline or polycrystalline . Polycrystals are divided into disordered and directed crystallization.

Monocrystalline ingots

Silicon raw material can be melted into ingots

Monocrystalline ingots can be produced using different crystal growing methods. Growing generally takes place from the melt , the Czochralski process usually being used for silicon and other semiconductor materials. When Czochralski method (in short: CZ method), the preparation of the ingot by a as a seed crystal serving seed crystal is dipped into a melt of the semiconductor material. Slow, controlled lifting while rotating (so-called pulling ) produces the characteristically shaped round columns (ingots), which in the case of silicon today usually have a diameter of approx. 200 or 300 mm and a height of 2 m (right picture). Silicon is a special case here; Ingots made from other semiconductor materials are usually still much smaller today. The main reason for this is the far lower demand for other semiconductor materials, which makes such large crystals unnecessary, and possibly technical problems in production.

Polycrystalline ingots

Polycrystalline ingots (also known as multicrystalline ingots ) are created as angular blocks when the silicon raw material (picture left) is melted down and poured into the typical cuboid shape. They are mainly used in photovoltaics for the production of solar cells and in micromechanics .

aims

Due to the multitude of semiconductor materials, crystal growing processes and of course applications, there are also greater differences in the production goals of ingots. In general, however, the following goals can be mentioned:

  • Purification of the starting material by separating the impurities during crystallization
  • Adjusting the electric conductivity of the basic semiconductor material by dopant (engl .: doping ), for example in the case of silicon, by the incorporation of boron - and / or phosphorus -atoms for the preparation of (weak) p- and n-doped substrates. The installation cannot be completely prevented in some manufacturing processes and is therefore usually set to a defined dimension, which, however, can usually also have a slight gradient within the longitudinal axis of the ingot.
  • Rectangular cutting or milling of the raw blocks for the highest possible yield of suitable ingots for further processing (in the cut state also referred to as brick)
  • Minimize material shifts and lattice errors
  • Avoidance of thermally caused mechanical stress (avoid stress formation during cooling)
  • Surface treatment (grinding)

Columns and blocks are then clamped in sawing machines and using several hours of a slurry ( slurry ) of very fine silicon carbide crystals, as grinding agents serve into slices ( wafers sawed).

literature

Individual evidence

  1. ↑ Entry multicrystalline ingot = multisilicon in the glossary ( memento of August 11, 2011 in the Internet Archive ) on silicon wafer production by Swiss Wafers, accessed on April 16, 2010.