Abstract
This paper describes the use of area-selective electroless Cu deposition for topography control of Cu-SiCN hybrid bonding pads. The electroless deposition of Cu allows one to obtain protrusions on hybrid bonding Cu pads without further polishing optimization. A recessed Cu pad after chemical mechanical polishing becomes a protrusion after electroless deposition. This indicates that the electroless Cu film was selectively deposited on Cu, without deposition on the SiCN surface. A void-free Cu-Cu bonding interface was observed after annealing at 350 °C with an electroless Cu layer at the interface. 100% electrical connection was obtained at 1.4-μm pitch where the deposition thickness was on target.
Highlights
HYBRID bonding is a promising direct wafer bonding approach which creates mechanical joints and electrical connections (Cu-Cu) simultaneously [1,2,3,4]
We demonstrated area-selective Cu deposition on hybrid bonding Cu pads by electroless deposition
Electroless deposition (ELD) Cu only deposited on the Cu pads, without deposition on the SiCN surface
Summary
HYBRID bonding is a promising direct wafer bonding approach which creates mechanical joints (dielectric-dielectric) and electrical connections (Cu-Cu) simultaneously [1,2,3,4]. Two wafers are finished by a Cu/dielectric damascene process with atomic-scale dielectric surface roughness and minimal Cu protrusion/recess [1,2]. The capabilities of this approach strongly depend on the quality of the chemical mechanical polishing (CMP) processes. The required range of the recess and protrusion of a Cu pad from the dielectric field is below 5 nm for fine-pitch connections [1,2]. The review of this letter was arranged by xxx. (Corresponding author: Fumihiro Inoue)
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