The term ingot ( English. for, bullion ') is used in English only in a special meaning: It refers to a block of semiconductor material such as silicon. Ingots can be constructed monocrystalline or polycrystalline.
Monocrystalline ingots can be produced by different crystal growing process. In general, the growth from the melt, wherein the Czochralski method is usually employed in silicon and other semiconductor materials. The Czochralski method (in short: CZ process ), the preparation of the ingot by dipping a seed crystal as a seed crystal serving in a melt of the Halbleitermatrials. By slow precise handling under rotation (so-called drawing) one obtains the characteristically shaped round columns (ingots ), which in the case of silicon today typically have a diameter of about 200 or 300 mm and 2 m height have (pictured right). Silicon here represents a special case; Ingots from other semiconductor materials are significantly smaller in the rule, even today. The reason for this is primarily the far less need for other semiconductor materials, which makes unnecessary such large crystals, and if necessary, technical problems in manufacturing.
Polycrystalline ingots (also known as multicrystalline ingots) are formed as rectangular blocks, when the silicon raw material (left) is melted and poured into the typical rectangular shape. They are mainly used in photovoltaic solar cells and for the production of the micromechanics.
Due to the variety of semiconductor materials, crystal growth method and of course applications, there are also major differences in the manufacturing objectives of ingots. Generally, however, there may be mentioned the following objectives:
- Purification of the material through removal of the impurities during the crystallization
- Setting the basic electrical conductivity of the semiconductor material by doping (English: doping ). , For example, in the case of silicon by the incorporation of boron and / or phosphorus atoms for the production of (weak) p-and n -doped substrates The installation can not be completely prevented, and is therefore generally set to a defined level, but which usually can have a slight gradient and within the longitudinal axis of the ingot in some manufacturing processes.
- Rectangle cutting or milling the ingots for high yield of ingots suitable for further processing ( cut in state as a Brick ( Brick ) refers )
- Minimize material displacements and lattice defects
- ( Avoid stress formation during cooling ) avoidance of thermally induced mechanical stress
- Surface treatment (grinding)
And column blocks are then clamped in sawing machines and several hours by using a slurry (slurry) of very fine silicon carbide crystals, which are used as an abrasive, into slices (wafer) cut.