Boule (crystal)

A boule is a single-crystal ingot produced by synthetic means. A boule of silicon is the starting material for most of the integrated circuits used today.

In the semiconductor industry, boules can be made by a number of methods, such as the Bridgeman technique and the Czochralski process, which result in a cylindrical rod of material.

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 solidifies and eventually a large, circular boule is produced.

A semiconductor crystal boule is normally cut with a diamond saw into circular wafers, and each wafer is polished to provide substrates suitable for the fabrication of semiconductor devices on its surface.