VLSI - Lecture 4: Design Metrics

[@AdiTeman]

Corrections and Errata: @31:10, I say that 450mm is 15" - that should be 18", of course! (Thanks to @awuesiak)

[@awuesiak]

Great lecture, but one question about wafer sizes: shouldn't 450mm wafer be equivalent to 18 inches, not 15 inches?

[@AdiTeman]

Thanks for paying attention to this. This lecture has been out there a long time an no one has noticed this mistake yet 😆 I'm adding a pinned comment about this mistake.

[@netanellalazar3819]

hi adi, to your attention, this lecture is founded twice in the play list. thank you for the content it is excellent !

[@AdiTeman]

Thanks, I removed the duplicate from the playlist.

[@babaktorabi313]

Hey Professor, can you give a brief description on the sealring, scribe and die per reticle?

[@AdiTeman]

I guess just a word or two (there is a lecture that I plan to record at some time that goes a bit deeper into sign-off and chip finishing and contains a bit more detail about these). The seal ring is basically a structure you put around your chip to protect it during the dicing of the wafer. Therefore, it would contain guard rings (bulk contacts) or similar things to collect charge that may be produced during dicing. The scribe lines are just the area between dies that is left for dicing, so this is a wide area (so you don't cut a die itself) with nothing in it. Often, fabs will put test circuits and metrology in the scribe lines to test things at wafer level and these will be destroyed when cutting the wafer into dies. For the question of die per reticle, the issue is that the size of the mask is much smaller than the size of the whole wafer (taking into account the 4X optical reduction). So you need to move the wafer around and develop the mask onto it many times. I am not sure about the actual size of the photomasks, but most big chips are no larger than ~800mm^2, so I'm assuming this is about the size of the reticle (though I may be mistaken). There is a possibility to connect several reticles to make a single product, but this is quite rare, as it is tricky in the overlap and the price is huge. If you are interested in a very extreme and cool example, check out the company Cerebras, who recently announced a product that is the size of an entire wafer.

[@babaktorabi313]

@@AdiTeman Thanks for the explanation professor!