Interconnect structure for stacked device

A stacked integrated circuit device comprising:

• a first semiconductor element having a first substrate, a dielectric block disposed in the first substrate, and first conductive features over the first substrate, wherein each of the first conductive features has a first segment having a first thickness and a second segment having a second thickness that is different from the first thickness, wherein a sidewall of the first segment is not aligned with a sidewall of the second segment, and wherein the first segment and the second segment jointly define a partial recess;
• a second semiconductor element bonded to the first semiconductor element, wherein the second semiconductor element comprises a second substrate and second conductive features over the second substrate;
• and a conductive deep-interconnection-plug coupled between the first and second conductive features and filling the partial recess, wherein the conductive deep- interconnection-plug comprises:
• an upper portion with a first width, wherein a portion of the upper portion isolated by the dielectric block;
• and a lower portion with a second width.

A device comprising:

• a first substrate;
• a dielectric element disposed in the first substrate;
• a first interconnect structure disposed over the first substrate, wherein the first interconnect structure contains a first inter-metal-dielectric (IMD) and a first conductive element embedded in the first IMD, wherein the first conductive element has a first segment having a first thickness and a second segment having a second thickness that is different from the first thickness, and wherein a side surface of the first segment in combination with an upper surface of the second segment define a partial recess;
• a second substrate;
• a second interconnect structure disposed over the second substrate, wherein the second interconnect structure is attached to the first interconnect structure, and wherein the second interconnect structure contains a second IMD and a second conductive element embedded in the second IMD;
• and an elongated interconnection plug that extends through the first substrate, through the first interconnect structure and filling the partial recess, and through a portion of the second interconnect structure, wherein the elongated interconnection plug is electrically coupled to both the first conductive element and the second conductive element;
• and a barrier layer surrounding the elongated interconnection plug, wherein the barrier layer is in physical contact with a sidewall of the first conductive element.