
Fab Implementation: MfD Response 179
by the overlay rules was conrmed by two independent approaches [27,28],
showing that the technology road map for equipment and mask manufactur-
ing indeed put similar emphasis on the CD and OL shrinkability. However,
the business aspect of providing tight OL solutions may in the future be
more critical than the one related to the CD shrink path, as tighter OL may
be required to take advantage of DPT in lieu of EUV or NIL.
To ensure low yield loss (e.g., below 10%) for a 40-mask process, CD and OL
tolerances of steppers and masks need to reect that the probability of geom-
etries on two design layers ...