Cycle-time reduction is of great importance to semiconductor manufacturers.
Photolithography, being one of the most repeated processes, is an area whe
re substantial improvements can be made. We investigate the effects of vari
ous process control mechanisms for photolithography on the cycle-time at th
e process and at the overall fab via a simulation study. Test run policy at
the photolithography station, test run frequency, duration of inspection,
and machine dedication policy for the equipment are the factors we consider
. Equipment down time due to preventive or breakdown maintenance and rework
rates are also taken into account. Parallel testing, where test wafer is i
nspected while the lot is being processed, is the best policy in terms of c
ycle-time performance. Long inspection time and infrequent, long down times
have the most adverse effects, but flexible machine assignment may reduce
the impact of down times, Test run frequency is only significant for serial
testing, where processing of the lot is not finished until the failed test
wafer is stripped and reworked.