Barrier layers for interconnects in bonded wafers

A method for fabricating a semiconductor device, comprising:

• bonding a top wafer to a bottom wafer, wherein the top wafer comprises a first metal interconnection comprising a first barrier layer, an interlayer dielectric layer and an inter-metal dielectric layer, wherein an interface is present between the inter-metal dielectric layer and the interlayer dielectric layer, and a bottom surface of the first barrier layer is even with the interface;
• forming a dielectric layer on a bottom surface of the top wafer;
• and
• forming a second metal interconnection in the dielectric layer and the top wafer and connected to the first metal interconnection, wherein the second metal interconnection comprises a second barrier layer.