Cpu wafer production

[adaman2576]

This might be an oddball question to ask... When cpu manufactures make wafers that get cut into separate cpu chips, why do they make the wafers round? From what I know about the way cpu cores are set up, the chips are usually square or rectangular in shape. This means that there are quite a few wasted cores at the edges of the circle wafer that are cut off. Wouldn't it make more sense to make the wafers square or rectangular shape?
Adaman

 

[ghnader hsmithot]

This might be an oddball question to ask... When cpu manufactures make wafers that get cut into separate cpu chips, why do they make the wafers round? From what I know about the way cpu cores are set up, the chips are usually square or rectangular in shape. This means that there are quite a few wasted cores at the edges of the circle wafer that are cut off. Wouldn't it make more sense to make the wafers square or rectangular shape?
Adaman

I love cpu questions!!

Once the melt has reached the desired temperature, we lower a silicon seed crystal, or "seed" into the melt. The melt is slowly cooled to the required temperature, and crystal growth begins around the seed. As the growth continues, the seed is slowly extracted or "pulled" from the melt. As the the ingot is pulled it is slowly rotated. This is done to help normalize any temperature variations in the melt. The temperature of the melt and the speed of extraction govern the diameter of the ingot, and the concentration of an electrically active element in the melt governs the electrical properties of the silicon wafers to be made from the ingot. This is a complex, proprietary process requiring many control features on the crystal-growing equipment. The crystals naturally tend to a circular shape due to the crystal structure itself, and the surface tension on the liquid.
http://www.cpushack.com/MakingWafers.html

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.

Read more: Why are processor wafers round? | PC Pro blog http://www.pcpro.co.uk/blogs/2010/05/06/why-are-processor-wafers-round/#ixzz1NxOMMTMR
http://www.pcpro.co.uk/blogs/2010/05/06/why-are-processor-wafers-round/

The method of growing silicon crystals (which is a seed crystal rotating in molten silicon) leads to round ingots. A square process would be hard because squares do not have a constant radius so cooling won't be uniform.

You could make the ingot to be square but this makes polishing the surface and edges difficult because of the corners, not to mention you aren't actually gaining any additional area.

Solar cells are made from square wafers where the corners of the square are sliced off.Impurity seems to be existent on the most edge.

 

[ghnader hsmithot]

i was wondering this a while ago, except i just googled it and found out . but yeah the explaination above by ghnader Hsmithot, explains the reason behind your question quite well.

You could give him a better answer.He might give select you as the best answer.

 

[adaman2576]

Thanks for the quick explanations. I supposed i could of just googled it but, i figured i would get a better explanation here.
Adaman

 

[adaman2576]

Best answer selected by adaman2576.

 

[ghnader hsmithot]

Thanks for the quick explanations. I supposed i could of just googled it but, i figured i would get a better explanation here.
Adaman

No worries at all.If there are more cpu questions i might be able to answer it if not some of the other members are more than capable.