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To: Neil Booth who wrote (50009)	8/6/2001 6:57:29 AM
From: Yousef	Read Replies (2) \| Respond to of 275872

Neil, Re: "If it's not a dumb question, why are wafers round? Why not square?" I can hardly wait for Dan3's answer ... This should be "classic". BTW, do you know how many AMD engineers it takes to "screw in a light bulb"?? Make It So, Yousef

To: Neil Booth who wrote (50009)	8/6/2001 6:58:26 AM
From: Dan3	Read Replies (1) \| Respond to of 275872

Re: why are wafers round? Why not square? There are others who can answer that question better than I can. I can speculate that rotary polishing tools do a lot better when there aren't any corners. The silicon is "grown", but it should be possible to grow a shape other than a cylinder.

To: Neil Booth who wrote (50009)	8/6/2001 3:04:30 PM
From: Paul Engel	Read Replies (1) \| Respond to 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 The seed crystal and rod are then slowly withdrawn (raised) from the molten silicon, being raised up from the surface as they are simultaneously ROTATED.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 During this process, the crucible itself is rotated in the OPPOSITE direction of the rotation of the seed rod being withdrawn and raised. As the seed is further withdrawn, a cylindrical Boule of Silicon is formed - the rotation of the seed/Boule giving rise to a final cylindrical shape .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.