Silicon wafers - why are they round?

[AmberClad]

Like the title says, I was wondering why those big silicon wafers that Intel and AMD like to show off are always round. Isn't it extremely wasteful to have all those dies on the edges that are unusable? Do they have to be round due to the fabrication process?

 

[OS]

part of the manufacturing process, the wafers are cut from basically a giant crystal that is grown in the shape of a giant turd.

A seed crystal is spun at the surface of a giant vat of molten silicon so it naturally takes a circular profile.

 

[OS]

http://en.wikipedia.org/wiki/Czochralski_process

 

[AmberClad]

Originally posted by: OS

part of the manufacturing process, the wafers are cut from basically a giant crystal that is grown in the shape of a giant turd.

A seed crystal is spun at the surface of a giant vat of molten silicon so it naturally takes a circular profile.

Ack, I almost gagged on my coffee when I read your description 😛. Thanks for the link.

 

[CycloWizard]

Like OS said, it's a spinning process. The crystallization process is controlled using Marangoni flows (i.e. flows that are dominated by surface tension forces).

 

[thereaderrabbit]

There are lots of reasons, but simply put most chip manufacturers make lots of chips of different sizes and wasting silicon is a big deal...

So there is no good square one size fit's all shape, photo lithography tools loose their efficiency radially as you move from the center of a wafer (so doing corners would be wasteful) and the circular shape gives you the most efficiency (lease Si waste) as far as the area over diameter ratio is concerned. Yes, the Czochralski also drives the industry towards this shape, but the reason I just stated above is why industry doesn't care to change the process or later cut them into squares.

 

[firewolfsm]

thereaderrabbit, I'm almost sure that one wafer can only have one type of chip on it. If a company produces more than one kind of processor then they have to manufacture them separately.

 

[TuxDave]

Originally posted by: firewolfsm
thereaderrabbit, I'm almost sure that one wafer can only have one type of chip on it. If a company produces more than one kind of processor then they have to manufacture them separately.

For small chips, they can share a mask and therefore get different chips on the same wafer. When ST Microelectronics helped me fabricate my chip for my thesis, we were waiting for a tape out schedule that we could squeeze our chip in. Of course all ST Microelectronic chips got first dibs and all remaining space went to us. And if there wasn't enough to fill a mask they cancelled that tape out. And we're talking about like a 50mm by 50mm chip here.

But if you're talking about the main fabrication like the style of the Core2Duos and whatnot, the wafers will carry only one chip.

 

[silverpig]

Originally posted by: TuxDave

Originally posted by: firewolfsm
thereaderrabbit, I'm almost sure that one wafer can only have one type of chip on it. If a company produces more than one kind of processor then they have to manufacture them separately.

For small chips, they can share a mask and therefore get different chips on the same wafer. When ST Microelectronics helped me fabricate my chip for my thesis, we were waiting for a tape out schedule that we could squeeze our chip in. Of course all ST Microelectronic chips got first dibs and all remaining space went to us. And if there wasn't enough to fill a mask they cancelled that tape out. And we're talking about like a 50mm by 50mm chip here.

But if you're talking about the main fabrication like the style of the Core2Duos and whatnot, the wafers will carry only one chip.

Couldn't you have just done that single chip via ebeam?

 

[dantonic]

ROFL
A Giant "Turd" I'm still laughing.

 

[PottedMeat]

Originally posted by: TuxDave

For small chips, they can share a mask and therefore get different chips on the same wafer. When ST Microelectronics helped me fabricate my chip for my thesis, we were waiting for a tape out schedule that we could squeeze our chip in. Of course all ST Microelectronic chips got first dibs and all remaining space went to us. And if there wasn't enough to fill a mask they cancelled that tape out. And we're talking about like a 50mm by 50mm chip here.

But if you're talking about the main fabrication like the style of the Core2Duos and whatnot, the wafers will carry only one chip.

50mm by 50mm? Isn't that a huge chip?

 

[dude]

Squares mean cutting off the edges = wasteful

Nothing goes to waste these days. Most of the pot scrap and sliced off tops and tails are sent to recycle nowadays. There is too many companies needing wafers and not enough to go around, so believe it or not, this past year, wafer prices has sky-rocketed!

Most wafers are keyed, with a flat cut at one edge. What I'm wondering is why do they etch numbers or bar codes on the chips themselves in the old days? THAT is wasteful! However, they usually laser imprint it on the edge, where no etching is done.

On a side note, I recycle wafers and scrap silicon. If anyone has any or some sort of source for them, I will gladly pay you for sources or for percentages of the price! My email is in my profile.

Thanks!

 

[TuxDave]

Originally posted by: PottedMeat

Originally posted by: TuxDave

For small chips, they can share a mask and therefore get different chips on the same wafer. When ST Microelectronics helped me fabricate my chip for my thesis, we were waiting for a tape out schedule that we could squeeze our chip in. Of course all ST Microelectronic chips got first dibs and all remaining space went to us. And if there wasn't enough to fill a mask they cancelled that tape out. And we're talking about like a 50mm by 50mm chip here.

But if you're talking about the main fabrication like the style of the Core2Duos and whatnot, the wafers will carry only one chip.

50mm by 50mm? Isn't that a huge chip?

Errr... 5mm by 5mm. ^_^