Boule (crystal)
Encyclopedia
A boule is a single-crystal
Single crystal
A single crystal or monocrystalline solid is a material in which the crystal lattice of the entire sample is continuous and unbroken to the edges of the sample, with no grain boundaries...

 ingot
Ingot
An ingot is a material, usually metal, that is cast into a shape suitable for further processing. Non-metallic and semiconductor materials prepared in bulk form may also be referred to as ingots, particularly when cast by mold based methods.-Uses:...

 produced by synthetic means. A boule of silicon
Silicon
Silicon is a chemical element with the symbol Si and atomic number 14. A tetravalent metalloid, it is less reactive than its chemical analog carbon, the nonmetal directly above it in the periodic table, but more reactive than germanium, the metalloid directly below it in the table...

 is the starting material for most of the integrated circuit
Integrated circuit
An integrated circuit or monolithic integrated circuit is an electronic circuit manufactured by the patterned diffusion of trace elements into the surface of a thin substrate of semiconductor material...

s used today.

In the semiconductor
Semiconductor
A semiconductor is a material with electrical conductivity due to electron flow intermediate in magnitude between that of a conductor and an insulator. This means a conductivity roughly in the range of 103 to 10−8 siemens per centimeter...

 industry, boules can be made by a number of methods, such as the Bridgman technique and the Czochralski process
Czochralski process
The Czochralski process is a method of crystal growth used to obtain single crystals of semiconductors , metals , salts, and synthetic gemstones...

, which result in a cylindrical rod of material.

In the Czochralski process
Czochralski process
The Czochralski process is a method of crystal growth used to obtain single crystals of semiconductors , metals , salts, and synthetic gemstones...

 a seed crystal
Seed crystal
A seed crystal is a small piece of single crystal/polycrystal material from which a large crystal of the same material typically is to be grown...

 is required to create a larger crystal, or ingot. This seed crystal is dipped into the pure molten silicon
Silicon
Silicon is a chemical element with the symbol Si and atomic number 14. A tetravalent metalloid, it is less reactive than its chemical analog carbon, the nonmetal directly above it in the periodic table, but more reactive than germanium, the metalloid directly below it in the table...

 and slowly extracted. The molten silicon grows on the seed crystal in a crystalline fashion. As the seed is extracted the silicon solidifies and eventually a large, cylindrical boule is produced.

A semiconductor crystal boule is normally cut with a diamond saw into circular wafer
Wafer (electronics)
A wafer is a thin slice of semiconductor material, such as a silicon crystal, used in the fabrication of integrated circuits and other microdevices...

s, and each wafer is polished to provide substrates suitable for the fabrication of semiconductor device
Semiconductor device
Semiconductor devices are electronic components that exploit the electronic properties of semiconductor materials, principally silicon, germanium, and gallium arsenide, as well as organic semiconductors. Semiconductor devices have replaced thermionic devices in most applications...

s on its surface.

The process is also used to create sapphire
Sapphire
Sapphire is a gemstone variety of the mineral corundum, an aluminium oxide , when it is a color other than red or dark pink; in which case the gem would instead be called a ruby, considered to be a different gemstone. Trace amounts of other elements such as iron, titanium, or chromium can give...

s, which are used for substrates in the production of blue and white LEDs, optical windows in special applications and as the protective covers for watches.
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