Wafer Formation :

After the single crystal ingot is grown it is then mechanically processed to manufacture wafers. The first step involves the mechanically grinding in which the more or less cylindrical ingot is converted into perfect cylinder with controlled diameter. Next, the Si cylinder is sawed into individual wafers about 775 mm thick by using a diamond-tipped inner hole blade saw or wire saw. The resulting wafers are then mechanically lapped and ground on both sides to achieve a flat surface and to remove the mechanical damage due to sawing.

The Si wafers are then “chamfered” along the edges to minimize the likelihood of chipping the wafers during processing. Finally, the wafer undergo chemical mechanical polishing using a slurry of very fine SiO 2 particles in a basic NaOH solution to give the front surface of the wafer a mirror like finish. The wafers are now ready for Integrated circuit fabrication.

To change the conductivity of Si wafer, we can add intentional impurities or dopants to the silicon melt to change its electronic properties. If donor impurities are added in the melt before solidifying then after crystal growth and sawing the ingot, n-type wafers are created. Similarly if acceptor impurity atoms are added in the Si melt then after crystal growth and sawing the ingot, p-type wafers are created. The wafers in a quartz carrier are shown in Figure below.


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