Boule (crystal)

  A boule is a term used to describe a single-crystal ingot produced by synthetic means. This is the first of many steps to create an integrated circuit, as used by many today.

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In the semiconductor industry they can be made by a number of methods, such as the Bridgeman technique, or the Czochralski process. A cylindrical rod is produced. A semiconductor crystal boule is normally cut into circular wafers, and each wafer is polished to provide substrates suitable for the fabrication of semiconductor devices on its surface.

In the Czochralski process a seed crystal is required to create a larger crystal, or ingot. This seed crystal is dipped into the pure molten silicon and slowly extracted. The molten silicon grows on the seed crystal in a crystalline fashion. As the seed is extracted the silicon sets and eventually a large, circular boule is produced.

This boule is then cut with a diamond saw to produce the familiar wafers onto which the integrated circuits are etched.