Why are processor wafers round?
One question has bugged me for a long while: why are processor wafers round? After all, it doesn’t really make a lot of sense when those wafers are sliced and diced into square processor cores. As you can see from the photo above, it means the cores around the outer edges of the wafer are incomplete, creating waste.
Finally, at Intel’s European Research showcase this week, I got the answer.
Processor wafers are made out of silicon, or more precisely melted sand, which according to Intel has a “high percentages of silicon in the form of silicon dioxide”. The sand is melted in a huge vat and once it reaches the necessary temperature, a seed crystal is dropped into the melt and crystal growth begins around the seed. As the growth continues the seed is slowly rotated, gradually forming a solid, round ingot.
Each ingot weighs about 100kg and has a “silicon purity of 99.9999999%”, according to Intel. Those enormous silicon ingots are then sliced into individual wafers, each only 1mm thick.
And that, in a nutshell, is why silicon wafers are circular. “Nature wants to build them round,” said Intel fellow, Jose Maiz. Although I still prefer the explanation offered by one of my colleagues. “They just want pretend they’re rock stars with gold discs”.