Integrated circuit devices including stacked elements and methods of forming the same

A method of forming an integrated circuit device, the method comprising:

• providing a first structure and a second structure, wherein the first structure comprises a transistor, a first bonding pad on a first side of the first structure, a first substrate extending between the transistor and the first bonding pad, and the second structure comprising a second substrate, a second bonding pad on a first side of the second structure, and a second contact plug;
• forming a back-end metal structure on a second side of the first structure that is opposite the first side thereof;
• forming a portion of a passive device in the second substrate;
• attaching the first side of the first structure to the first side of the second structure, wherein, after attaching the first side of the first structure to the first side of the second structure, the first bonding pad contacts the second bonding pad;
• and then
• forming a power rail on a second side of the second structure that is opposite the first side thereof, wherein the second substrate extends between the first bonding pad and the power rail, and the second contact plug electrically connects the second bonding pad to the power rail.