MEMS-CMOS integrated devices, and methods of integration at wafer level

A method for forming an integrated semiconductor device, comprising:

• providing a first wafer, the first wafer comprising a first substrate having a microelectromechanical system (MEMS) device layer, and at least one bonding pad on a surface of the MEMS device layer;
• providing a second wafer, the second wafer comprising a second substrate having at least one active device, at least one interconnect layer over the second substrate and having at least one conductive pad thereon, wherein the at least one interconnect layer in the second wafer comprises an interlayer dielectric (ILD) and at least one conductive structure embedded inside the ILD, and the at least one conductive structure is connected with the at least one conductive pad;
• bonding the first wafer over the second wafer so that the MEMS device layer is connected with the at least one interconnect layer, the at least one conductive pad on the second wafer is bonded with the at least one bonding pad on the surface of the MEMS device layer, and the at least one conductive structure embedded inside the ILD is connected with the at least one bonding pad on the surface of the MEMS device layer;
• etching the second substrate and the at least one interconnect layer to form a cavity extending from a surface of the second substrate to the MEMS device layer;
• and
• etching the first substrate and the MEMS device layer to form a MEMS device interfacing with the cavity extending from a surface of the second substrate to the MEMS device layer.