Semiconductor device and manufacturing method thereof

A semiconductor device, comprising:

• a first wafer;
• a second wafer over the first wafer, wherein the second wafer comprises:
• a substrate;
• an isolation structure in the substrate;
• a first transistor and a second transistor adjacent the isolation structure;
• and
• an interconnect structure between the substrate and the first wafer;
• a power via penetrating the substrate and the isolation structure to the interconnect structure, and the isolation structure is at opposite sides of the power via in a cross-sectional view;
• and
• a signal via penetrating the substrate to the interconnect structure, wherein the signal via is between the first transistor and the second transistor but spaced apart from the isolation structure, and an area of the signal via interfacing with the interconnect structure is less than an area of the power via interfacing with the interconnect structure;
• and
• a liner layer wrapped around the power via, wherein the isolation structure is in contact with a first side and a second side of the liner layer in a cross-section view, and the first side is opposite to the second side.