Semiconductor devices, methods of manufacture thereof, and IMD structures are disclosed. In some embodiments, a semiconductor device includes an adhesion layer disposed over a workpiece. The adhesion layer has a dielectric constant of about 4.0 or less and includes a substantially homogeneous material. An insulating material layer is disposed over the adhesion layer. The insulating material layer has a dielectric constant of about 2.6 or less. The adhesion layer and the insulating material layer comprise an IMD structure.