Silicon ingots are round.

By: Mark (nothanks.delete@this.xxx.com), June 24, 2022 3:00 pm
Room: Moderated Discussions
Squarehead (squarehead.delete@this.fubar.com) on June 24, 2022 2:38 pm wrote:
> Mark Roulo (nothanks.delete@this.xxx.com) on June 24, 2022 2:29 pm wrote:
> > Doug S (foo.delete@this.bar.bar) on June 24, 2022 1:31 pm wrote:
> > > Why are wafers round? Since we make chips that are square or rectangular, making
> > > wafers square would minimize or totally avoid wasted silicon on the edges.
> > >
> > > I mean, I know that the first order is: they are round because all
> > > the equipment is designed to handle round wafers not square ones.
> > >
> > > But was any thought ever given to switching to square wafers when iterating from 100mm to 150mm to
> > > 200mm and 300mm wafers? Or is there some obvious reason why they must be round that I'm missing?
> >
> > Wafers are cut from grown silicon ingots.
> >
> > The silicon ingots are round.
> >
> >
>
> But one could grow a bigger boule of round silicon, slice it to have a square cross-section, and
> recycle the rest. Would this make sense? For a leading-edge wafer, what percentage of the wafer
> cost is the silicon itself? And how much more efficient could things get with square wafers?

I don't think you can re-use the silicon you cut away (though I'm not sure). The silicon is very pure and I don't know that it retains that property after you cut it.

I don't know what the cost of a bare 300mm wafer is.

I don't think the processing would be much more efficient. You don't lose all the silicon outside the central square (see below).


> I read that the shift from 200mm -> 300mm cost crazy amounts of $, so I'm guessing that
> even if square wafers made sense if you were starting from scratch, the cost to switch
> would make it a non-starter.
> But what were the biggest factors in the high cost of the 200mm->300mm transition? Is
> it possible that some of those costs would be more reasonable if one were thinking of
> 300mm round -> 300mm square?

The motivation for the increases in wafer size is that some manufacturing steps have a constant time regardless of the size of the wafer. Because of this you get more silicon processed in a given time if the wafers are larger.

Also, floor space in the fab is expensive and a tool that handles, say, 300mm wafers isn't 2x the size of a tool that handles 200mm wafers so you get some efficiencies there.

There WAS a push to go to 450mm wafers a while back, but that stalled out because there are costs as well and at the time Intel was pretty much the only fab customer that really wanted 450mm. There is currently no push for 450mm.

And, yes, because of path effects square wafers would be a big change.

Some steps, for example, *spin* the wafer. This works differently for square wafers than for round wafers. Those steps would need new tools that worked differently.

But note that none of this matters if you can't re-use the silicon that you threw away when you cut the round ingot into square wafers. If you can't re-use that then you might as well go with round wafers because you don't actually lose the silicon outside the central "square" ... you can still fit die into some of the area on the left, right, top and bottom of the square. You can play around with how many 10x10 die you can fit onto a 300 mm wafer. It is non-trivially more than you can fit onto a 212x212 square wafer.
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TopicPosted ByDate
OK dumb question timeDoug S2022/06/24 01:31 PM
  OK dumb question timeanon52022/06/24 01:38 PM
  Silicon ingots are round.Mark Roulo2022/06/24 02:29 PM
    Silicon ingots are round.Squarehead2022/06/24 02:38 PM
      Silicon ingots are round.Mark2022/06/24 03:00 PM
        Silicon ingots are round.Gary Kopp2022/06/24 03:20 PM
      Silicon ingots are round.Adrian2022/06/24 11:34 PM
    Silicon ingots are round.tarlinian2022/06/24 03:38 PM
      Silicon ingots are round.Doug S2022/06/24 11:13 PM
        Silicon ingots are round.anon2022/06/25 11:34 AM
          Silicon ingots are round.Doug S2022/06/25 11:39 AM
            Silicon ingots are round.Groo2022/06/26 09:41 AM
              Silicon ingots are round.Doug S2022/06/26 12:05 PM
                Silicon ingots are round.Gtoo2022/06/26 02:55 PM
          Silicon ingots are round.rwessel2022/06/25 11:43 AM
            Not reallyGroo2022/06/26 09:39 AM
              Not reallydmcq2022/06/26 10:56 AM
                Not reallyGroo2022/06/26 02:58 PM
              Not reallyanon22022/06/26 05:22 PM
              Why not triangles? Anon2022/06/27 03:34 AM
                Why not triangles? Math Nerd2022/06/27 04:52 AM
                Why not triangles? Math Nerd2022/06/27 05:45 AM
                  Don't forget Penrose Tiling (NT)ananon2022/06/27 06:06 AM
                  Why not triangles? Doug S2022/06/27 07:43 AM
                  Why not triangles? Anon2022/06/27 08:33 AM
                    Die shape that minimizes wasted area on circular wafersMath Nerd2022/07/01 09:20 PM
                      Die shape that minimizes wasted area on circular wafersBrett2022/07/02 02:35 PM
                        Die shape that minimizes wasted area on circular wafersMath Nerd2022/07/02 04:15 PM
                        Die shape that minimizes wasted area on circular wafersMark Roulo2022/07/02 04:41 PM
                          Die shape that minimizes wasted area on circular wafersDoug S2022/07/02 06:44 PM
                          Die shape that minimizes wasted area on circular wafersBrett2022/07/03 12:31 AM
                            Die shape that minimizes wasted area on circular wafersAdrian2022/07/03 10:25 PM
                              Die shape that minimizes wasted area on circular wafersanon22022/07/03 11:33 PM
                                Die shape that minimizes wasted area on circular wafersBrett2022/07/04 12:45 AM
                                  Die shape that minimizes wasted area on circular wafersdmcq2022/07/04 06:09 AM
                                    Die shape that minimizes wasted area on circular wafersJames2022/07/04 09:52 AM
                                      Die shape that minimizes wasted area on circular wafersdmcq2022/07/04 10:26 AM
                                        Die shape that minimizes wasted area on circular wafersAdrian2022/07/05 03:28 AM
                                      Cannon Lake vs Kaby LakeMark Roulo2022/07/04 10:30 AM
                                        C-class bonusesblue2022/07/04 12:27 PM
                                          C-class bonusesanonymou52022/07/04 03:23 PM
                                  Die shape that minimizes wasted area on circular wafersanon22022/07/04 06:53 AM
                                    Die shape that minimizes wasted area on circular wafersBrett2022/07/04 12:32 PM
                                      Die shape that minimizes wasted area on circular wafersFoyle2022/07/04 01:30 PM
                                        Die shape that minimizes wasted area on circular wafersAnon2022/07/04 01:37 PM
                                          What is a mirrored die?Mark Roulo2022/07/04 02:59 PM
                                            What is a mirrored die?Brett2022/07/04 03:32 PM
                                              What is a mirrored die?Doug S2022/07/04 10:08 PM
                                        Die shape that minimizes wasted area on circular wafersanonymou52022/07/04 03:12 PM
                                          Die shape that minimizes wasted area on circular wafersFoyle2022/07/05 10:41 AM
                                      Die shape that minimizes wasted area on circular wafersanon22022/07/04 04:52 PM
                                        Die shape that minimizes wasted area on circular wafersUngo2022/07/05 06:24 PM
                                          Die shape that minimizes wasted area on circular wafersBrett2022/07/05 07:56 PM
                                            Die shape that minimizes wasted area on circular wafersanonymou52022/07/06 05:46 AM
                                              Die shape that minimizes wasted area on circular wafersdmcq2022/07/06 02:55 PM
                                                Die shape that minimizes wasted area on circular wafersMark Roulo2022/07/06 04:09 PM
                                                Die shape that minimizes wasted area on circular wafersDoug S2022/07/06 05:31 PM
                                      Example of mirrored wafer?Mark Roulo2022/07/04 06:01 PM
                                  Not the same as 3-core CPU from a 4-core dieMark Roulo2022/07/04 09:31 AM
                                Wafer probingAdrian2022/07/05 03:08 AM
                                  Great comment, thank you (NT)anon22022/07/06 12:00 AM
                crystal latticehobold2022/06/27 12:09 PM
                  crystal latticedmcq2022/06/27 03:58 PM
                  Given path dependency I doubt it ...Mark Roulo2022/06/27 06:02 PM
                    Given path dependency I doubt it ...Adrian2022/06/27 10:01 PM
              Hexagonal DieMath Nerd2022/06/27 05:05 AM
                Hexagonal DieAdrian2022/06/27 10:24 PM
                  Hexagonal Diedmcq2022/07/06 03:00 PM
          Silicon ingots are round.dmcq2022/06/25 02:38 PM
            Silicon ingots are round.dmcq2022/06/25 02:43 PM
          Silicon ingots are round.aaron spink2022/06/25 03:05 PM
      Notch on Silicon WafersEric P2022/07/01 04:07 PM
        Still there, I think ...Mark Roulo2022/07/01 04:47 PM
          Still there, I think ...Eric P2022/07/01 05:26 PM
            Still there, I think ...tarlinian2022/07/01 06:50 PM
              Still there, I think ...David Kanter2022/07/02 09:14 AM
            Still there, I think ...Mark Roulo2022/07/01 09:31 PM
              Still there, I think ...Eric P2022/07/02 12:10 AM
  OK dumb question timeanonymouse2022/06/24 03:47 PM
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