A bilayer porous low dielectric constant (low-k) interconnect structure and methods of fabricating the same are presented. A preferred embodiment having an effective dielectric constant of about 2.2 comprises a bottom deposited dielectric layer and a top deposited dielectric layer in direct contact with the former. The bottom layer and the top layer have same atomic compositions, but a higher dielectric constant value k. The bottom dielectric layer serves as an etch stop layer for the top dielectric layer, and the top dielectric layer can act as CMP stop layer. One embodiment of making the structure includes forming a bottom dielectric layer having a first porogen content and a top dielectric layer having a higher porogen content. A curing process leaves lower pore density in the bottom dielectric layer than that left in the top dielectric layer, which leads to higher dielectric value k in the bottom dielectric layer.