Next, an IMD layer 24 is formed on the IMD layer 20 and the metal interconnections 22, a first patterned mask 26 is formed on the IMD layer 24, and then a second patterned mask 28 is formed on the first patterned mask 26. In this embodiment, the first patterned mask 26 preferably includes a metal mask which could include titanium (Ti) and/or titanium nitride (TiN) while the second patterned mask 28 preferably includes a patterned resist.

It should be noted that the first patterned mask 26 is preferably made of a plurality of rectangular patterns extending along a first direction such as X-direction in FIG. 1 and the plurality of rectangular patterns of the first patterned mask 26 include a plurality of first openings or slots 30 therebetween also extending along the same first direction or X-direction, in which the edges of the first slots 30 are preferably aligned with the edges of the metal interconnections 22 embedded in the IMD layer 20 underneath. The second patterned mask 28 on the other hand is made of a plurality of rectangular patterns extending along a second direction such as Y-direction in FIG. 1 and the plurality of rectangular patterns of the second patterned mask 28 includes a plurality of second slots 32 therebetween, in which the second slots 32 are also extending along the same second direction such as Y-direction and intersecting the first slots 30.