Packaged semiconductor devices including backside power rails and methods of forming the same

A device comprising:

• a first integrated circuit device comprising:
• a first substrate;
• a first device layer over the first substrate, the first device layer comprising a first transistor structure;
• and
• a first interconnect structure over the first device layer, the first interconnect structure comprising a first power rail on a backside of the first device layer, the first power rail being electrically coupled to a first source/drain region of the first transistor structure through a first backside via;
• and
• a second integrated circuit device comprising:
• a second substrate;
• a second device layer over the second substrate, the second device layer comprising a second transistor structure;
• and
• a second interconnect structure over the second device layer, wherein the second interconnect structure is bonded to the first interconnect structure by dielectric-to-dielectric and metal-to-metal bonds.

A method comprising:

• forming a first transistor on a first substrate;
• forming a first interconnect structure over the first transistor;
• exposing a first source/drain region of the first transistor, wherein exposing the first source/drain region comprises thinning the first substrate;
• after exposing the first source/drain region, forming a second interconnect structure over the first transistor opposite the first interconnect structure, wherein forming the second interconnect structure comprises:
• depositing a first dielectric layer over the first transistor;
• forming a first backside via through the first dielectric layer and electrically coupled to a first source/drain region of the first transistor;
• and
• forming a first conductive line electrically connected to the first backside via;
• and
• bonding a first integrated circuit device to the first interconnect structure, wherein bonding the first integrated circuit device to the first interconnect structure comprises forming dielectric-to-dielectric bonds between the first integrated circuit device and the first interconnect structure.