Someone emailed me an Intel-related question - why are silicon wafers, used in chip production, round instead of squared or rectangular? The reasoning being, since the die pieces that are being cut out of the wafer are square, isn’t there waste at the edges? Couldn’t this be avoided with squared/rectangular wafers?
At one point in my Intel career, I knew the answer to this question. It was talked about during a fab tour soon after I was hired. But I’m a carpet-dweller, and far removed from the manufacturing process, so I’ve forgotten.
I’m sure this is a brain dead simple question for anyone who works in the fabs. So let’s have it? Why ARE wafers round?
TinyScreenfuls Feed (this blog)
Need to lighten up - I’m doing a "Twitter Boot Camp" with the ISN team in 1 hr. 
See http://www.ee.byu.edu/cleanroom/EW_formation.phtml for details on how silicon wafers are made. They start with a seed that is rotated along with the quartz heater; the rotation naturally produces a round shape — going with a rectangle would require cutting off more of the crystalline structure.
Round wafers, in addition to the process by which they are made, provide the most usable chips per area of wafer cross-section. Sure you lose some around the edges, but you would lose more with a rectangular or other shape. It’s pretty elementary.
Thank you Ben, this was the answer where I was looking for…
And thanks to Josh to post my question on your blog…
>Paul
Actually they aren’t completely round. They have a bit cut off on one side so that they can be aligned with the crystals in the proper direction. Look close and you can see it.
Apart from the already mentioned fact that they are round from the way they are produced, there are also practical problems of making some of the process steps on a square wafer. Even/homogenoues growth of films etc is a major problem as heat is not evenly spread on a wafer (cooler at the edges) and that there might be differences in strain. These problems can partly be dealt with, but using a square wafer would make an even distribution of temperature and stress across the wafer impossible.
A key process step that uses the round form of the wafer is photoresist application - this is done by spinning the wafer rapidly and dripping the liquid resist at the center; centrifugal force takes care of spreading it evenly.