Hi Prashant,Originally posted in cdnusers.org by EngHan
I prefer to add std filler cell after routing if possible. It is not possilbe if there are metal blockage in the filler cell except at the power rail. Most of the std fiiller cell I worked with does not have metal blockage that will affect detailed routing.
However, it is better to add pad filler before rouitng as the router can use those space for routing if it is not fill by pad filler.
Advantage of adding filler cell later is database size. The number of std filler can be several time of the other logic cell. The overhead is not small. I can't think of disadvantage, except that you have to be sure that the filler does not have blockage that will affect routing.
Nowsaday all P&R tool can remove and add filler cells after detailed rouitng to fix timing or crosstalk. However, with nanometer process, adding of std filler cell can take awhile. So it is ready good if you can add the std filler cell just before performing full DRC.