Silicon ingot

A silicon ingot, or boule, is a single crystal of silicon shaped like a long cylinder with a pointed end. Every atom in it lines up in one unbroken pattern from end to end. For leading chips, ingots are 300 mm across and can weigh a few hundred kilograms.

They are grown by the Czochralski process, named after Jan Czochralski, who discovered the method in 1916. Chunks of polysilicon are loaded into a crucible of pure quartz and melted at about 1,420 °C under argon gas. A tiny, measured amount of boron is added to the melt; this trace sets the crystal's electrical type, making it p-type. A small seed crystal is dipped into the surface and then slowly pulled up while seed and crucible rotate. Silicon freezes onto the seed, copying its atomic pattern. Careful control of speed and temperature sets the diameter as the crystal grows over a day or more.

A single crystal matters because boundaries between crystals would trap electrons and spoil transistors. The finished ingot is ground to an exact diameter and sliced into silicon wafers. Some ingots are doped with phosphorus instead, for n-type wafers.