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Technology Stocks : Advanced Micro Devices - Moderated (AMD)
AMD 215.11+0.1%Dec 24 12:59 PM EST
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To: Neil Booth who wrote (50009)8/6/2001 3:04:30 PM
From: Paul EngelRead Replies (1) of 275872
 
Re: "why are wafers round? Why not square?"

Wafers are generally "grown" using a technique called Czochralski Growth.

In this technique, a Crucible containing molten Silicon (plus any doping elements)is used .

Above the molten silicon (all this is contained in an inert-gas atmosphere) on the end of a rod, a "seed" crystal of silicon (containing the same crystal orientation as the final desired cryatllographic orientation) is lowered into the molten silicon.

The seed crystal and rod are then slowly withdrawn (raised) from the molten silicon, being raised up from the surface as they are simultaneously ROTATED. This rotation and withdrawal "pull" the molten silicon out in a CYLINDRICAL pattern, and the molten silicon cools and crystallizes just above the surface.

During this process, the crucible itself is rotated in the OPPOSITE direction of the rotation of the seed rod being withdrawn and raised.

As the seed is further withdrawn, a cylindrical Boule of Silicon is formed - the rotation of the seed/Boule giving rise to a final cylindrical shape .

Following the growth of the boule, and after centerless grinding, the Boule is "sawn" with special diamond blades mounted on INTERNAL disks.

This results in round wafers - when the Boule is sawn much like a slice of baloney.
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