Silicon ingots are round.

By: Adrian (a.delete@this.acm.org), June 24, 2022 11:34 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 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?
>
>
>

Only a few of the semiconductor devices have huge dies, like the largest CPUs and GPUs.

Most cheap devices have areas of at most a few square mm. For such devices the circle segments that would be removed when cutting a circle into a square would contain thousands of devices.

It would be pretty stupid to reduce the production capacity per wafer in this way.

Moreover, there are many technological steps where it is desirable to rotate the wafer and which is circular form is more convenient. The most important is depositing photoresist as a thin uniform layer on the wafer, which is done by spinning the wafer extremely fast, so that the photoresist will be spread by the centrifugal forces.


Also, silicon is fragile. Handling the wafers, either manually or automatically must be done with extreme care, to avoid breaking the wafers. If a wafer had corners, they would be much more prone to breaking during handling.

Nowadays, I suppose that wafers are almost never handled manually, but many years ago, when the wafers were smaller and it was not unusual to handle them manually with Teflon pincers, for various experiments and tests, I have broken a few wafers, so I am well aware of the fragility problem.

< Previous Post in ThreadNext Post in Thread >
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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