Trench isolation connectors for stacked structures

A method for forming a wafer-on-wafer stack comprising:

• performing front-end-of-line processing on a first wafer and a second wafer, wherein the first wafer includes a first trench isolation structure disposed in a first substrate, the second wafer includes a second trench isolation structure disposed in a second substrate, the first trench isolation structure surrounds a first device of the first wafer, and the second trench isolation structure surrounds a second device of the second wafer;
• forming a first trench isolation connector in the first trench isolation structure and a second trench isolation connector in the second trench isolation structure;
• after forming the first trench isolation connector and the second trench isolation connector, forming a first frontside interconnect that connects the first trench isolation structure to the first device and a second frontside interconnect that connects the second trench isolation connector to the second device;
• and
• after forming the second frontside interconnect and exposing a backside of the second trench isolation connector, attaching the first wafer to the second wafer, wherein the second trench isolation connector is connected to the first device and the second device.