MadSci Network: Computer Science

Re: Why is a wafer for semiconductor manufacturing round and not square?

Date: Thu Oct 29 11:52:32 1998
Posted By: Frank Berauer, Technology Transfer Engineer Microelectronics
Area of science: Computer Science
ID: 909437226.Cs

The ultra-pure silicon for wafers is grown in huge round rods that
are then sliced into wafers. The round shape comes naturally with
the growth process. Making the slices square-shaped would be more
work and waste material.
The yield is lower near the edge of the wafer, because it is more
difficult to control processes there. A circle has the lowest edge-
to-area-ratio of all shapes and thus offers the highest possible
yield. Some of the processes in a wafer fab, e.g. coating with
photoresist by dripping on a spinning wafer, even make use of the
round shape for process uniformity and would not work well with
square wafers.

Greetings from Singapore,
	Frank Berauer

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