Ever Wonder…?

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Why Are Silicon Wafers Round, Instead Of Rectangular?

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Why are silicon wafers, used in chip production, round instead of squared or rectangular? The reasoning being, since the die pieces that are being cut out of the wafer are square, isn’t there waste at the edges? Couldn’t this be avoided with squared/rectangular wafers?

Processor wafers are made out of silicon, or more precisely melted sand, which according to Intel has a “high percentages of silicon in the form of silicon dioxide”. The sand is melted in a huge vat and once it reaches the necessary temperature, a seed crystal is dropped into the melt and crystal growth begins around the seed. As the growth continues the seed is slowly rotated, gradually forming a solid, round ingot.

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Each ingot weighs about 100kg and has a “silicon purity of 99.9999999%”, according to Intel. Those enormous silicon ingots are then sliced into individual wafers, each only 1mm thick.

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A Textbook Explanation: Silicon Fabrication

The reason of the circular, cylindrical shape, is a by-product occurrence of the process with which Silicon wafers are grown.

Industry regularly uses a Silicon Growth Method that is named “The Czochralski Growth Method.” This method grows Silicon crystal by solidifying a Crystal-Liquid into a solid.

A Silicon molecule or more is attached to a mechanical device, which is then dipped into a pool of liquid Silicon-crystal Melt. To start the growth, the Mechanical Device rotates one direction in the pool of Crystal Liquid.

The Liquid melt is rotated the OPPOSITE direction of the mechanical device. Little-by-little, the crystal starts to grow from this smaller piece. As the crystal grows, the two rotations keep happening, while the mechanical device is very slowly lifted out of the pool of Crystal Liquid.

So, that’s why wafers are circular. When they grow Silicon crystal, it starts as a liquid, and rotates its way out as it becomes a solid.

So there you have it!  We now know why Silicon Wafers are round, instead of rectangular.
Pretty simple, I guess.
 


Watch Silicon Wafer Production – You Tube