I generated 2 spef files
1) with out metal fill
2) with metal fill
both after routing and when i ran ETS (STA) for timing I see that there is no much effect on timing for in2reg but a few ps on reg2out. Could some one please tell me wat timing is majorly effected by metal fill ..or please point me 2 to the docs that I can read .
Metal fill is not limited to a certain path group for timing impact, it can affect all timing groups. Generally, if your design is reasonably utilized then metal should not have significant impact on timing because on most layers there should be a sufficient amount of metal already, so the addition of metal fill is minimized. If however, you design has low utilization and thus low amount of routing, then metal fill will change timing dramatically.