I'm not sure what it actually takes to manufacture them -- there's definitely some lithography that goes into it but I don't know much beyond that. You might be able to convert an existing microprocessor plant into a DNA microarray plant but i don't really know.

This is the one that I believe 23andme is purchasing in bulk -- or, at least it is the highest end microarray sold by the company 23andme gets their arrays from. http://www.illumina.com/pagesnrn.ilmn?ID=70