The cost explosion is also primarily contributed by the
equipment cost, clean room facilities, and lithography process
complexity [8],[24]. Traditional top down silicon based
fabrication requires over 35 masks, and 700 steps for a 90
nm process [25]. The same trend is also stated in [26] for
DRAM process fabrication. To gain sufficient profits, [27]
states that on the average, DRAMs need 3000 to 5000 wafers
per mask set, 1500 for a microprocessors, and 500 or less
for ASICs and SOCs (Le. for 130 nm technology). Moreover,
design revisions cause a hike in mask cost, and reduction
in the number of wafer that can be produced in single
mask set. The mask contribution is becoming the dominant
factor in lithography costs, particularly as minimum feature
sizes fall below the exposure wavelength. These problems
lead to the combination of wafer production to the best
equipped foundaries [28].