An integrated circuit structure includes a first, a second and a third metallization layer. The first metallization layer includes a first dielectric layer having a first k value; and first metal lines in the first dielectric layer. The second metallization layer is over the first metallization layer, and includes a second dielectric layer having a second k value greater than the first k value; and second metal lines in the second dielectric layer. The third metallization layer is over the second metallization layer, and includes a third dielectric layer having a third k value; and third metal lines in the third dielectric layer. The integrated circuit structure further includes a bottom passivation layer over the third metallization layer.