1.6 Ingots and Wafers

• ICs originate with the growth of single crystals of silicon and gallium arsenide
• The crystals are grown from the melt with the melting temperatures Tm(Si)=1414 C, Tm(GaAs)=1238 C
• In Czochralski technique:
1. the melt is contained in a crucible, quartz (crystalline SiO2) for Si or graphite (carbon) for GaAs, and is kept in a molten state by RF inductive heating
2. Liquid-encapsulated Czochralski (LEC) uses a capping layer of an inert liquid (usually boron trioxide) to cover the exposed melt
3. For growth, a seed crystal is inserted into the melt and then slowly withdrawn
4. Crystal growth occurs by freezing at the interface between the solid seed and melt
5. Crystal growth proceeds by the successive additions of layers of atomic planes at the liquid-solid interface 
• After growth and surface finishing, the ingot is cut on a diamond-tipped  saw into slices or wafers 100 - 250 thick ( depending on wafer diameter)
• The wafers are evaluated for dislocation content and resistivity
• The wafers are etch polished on one surface and then place in individual slots in plastic trays for delivery to the fabrication lines