In class, we briefly discussed wafer size and economics. Wikipedia has additional information on wafer preparation and how wafer size has increased over time: http://en.wikipedia.org/wiki/Wafer_%28electronics%29. 300mm is the current state-of-the-art wafer size, and 450mm wafers are in development.
What is the incentive to making larger and larger wafers? Economics!
Chris Mack at UT Austin has an excellent discussion of semiconductor manufacturing economics: https://www.youtube.com/watch?v=7igsP6Y-zEM&index=4&list=PLM2eE_hI4gSDjK4SiDbhpmpjw31Xyqfo_
The Wikipedia article on photomasks provides some context:
"The cost to set up a modern 45 nm process mask shop is $200–500 million ... The purchase price of a photomask can range from $1,000 to $100,000 for a single high-end phase-shift mask. As many as 30 masks may be required to form a complete mask set."