Dummy pattern and method for forming same

The invention discloses a dummy pattern and a method for forming the same. The method comprises the following steps of: supplying an arrangement region, wherein the arrangement region comprises an arrangement pattern which has a first density; a plurality of first dummy patterns are inserted into the arrangement pattern and have second densities; the second densities correspond to the first density; the arrangement region is partitioned to define a plurality of sub regions; the sub regions have third densities; the sizes of the first dummy patterns are adjusted according to differences between the third densities and the second densities; and the arrangement pattern and the first dummy patterns are output to an optical mask.