Stacked Image Sensor Bonding With Conductive Polymer Pads
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Solution Overview
Problem
In the bonding of semiconductor substrates, finer Cu electrode pitches are desired, but the polishing process often results in recessed Cu electrodes, leading to connection failures and potential short circuits due to silicidation beyond the electrode boundaries.
Innovation Solution
A solid-state imaging device is developed with conductive polymers interposed between metal pads on bonded semiconductor bases, ensuring electrical connection and preventing short circuits by compensating for recessed electrode dimensions and providing flexible conductivity.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Area of moving object
If Cu electrodes are made finer to achieve smaller pitch, then electrode density increases, but Cu electrodes become recessed during polishing making connection difficult
Solution Approach 1:
A conductive polymer layer is introduced as an intermediary material between the recessed Cu electrode and the bonding interface. This polymer layer fills the recessed portion of the Cu electrode, providing a planarized conductive surface that enables reliable bonding while maintaining the fine pitch design. The polymer serves as a mediator that compensates for the topography issue without requiring change to the Cu electrode itself.
Solution Approach 2:
The invention changes the physical and chemical parameters of the bonding interface by applying a conductive polymer coating. This polymer layer modifies the surface topology from recessed to planar, and changes the material composition from pure Cu to Cu-polymer composite, enabling successful bonding at finer pitches where traditional Cu-Cu bonding would fail due to recess issues.
2Shape
If Cu electrodes are polished to flatten surface, then surface uniformity improves, but Cu electrodes become recessed leading to connection failure
Solution Approach 1:
The conductive polymer acts as an intermediary that restores the Cu electrode surface to a planar state after polishing-induced recession. By filling the recessed areas, the polymer creates a uniform bonding surface while maintaining electrical continuity, thus preserving both surface uniformity and connection reliability simultaneously.
Solution Approach 2:
The invention creates a composite structure at the bonding interface consisting of Cu electrode + conductive polymer. This composite material combines the electrical conductivity of Cu with the planarizing and protective properties of the polymer, achieving both surface uniformity and reliable connection that neither material could achieve alone.
3Reliability
If silicidation is extended beyond Cu electrode boundaries, then electrical connection improves, but short circuit occurs between adjacent electrodes
Solution Approach 1:
The conductive polymer layer serves as a protective intermediary that prevents silicidation from extending beyond the Cu electrode boundaries. By covering the electrode surface, the polymer acts as a barrier that allows controlled silicidation within the electrode area while preventing lateral diffusion of silicon that would cause short circuits between adjacent electrodes.
Solution Approach 2:
The invention replaces the traditional direct Cu-Si bonding interface with a polymer-mediated interface. This substitution allows the silicidation process to proceed with improved electrical connection while the polymer layer provides precise spatial control, preventing the harmful lateral spread of silicide that causes short circuits.
Data Source
AI summary
Electrical connection between mutually facing electrodes is provided. A solid-state imaging device includes: a first semiconductor base; a second semiconductor base bonded to the first semiconductor base; and a conductive polymer, the first semiconductor base including a first semiconductor layer in which a photoelectric conversion unit is provided, a first multilayer wiring layer stacked on the first semiconductor layer, and a first metal pad formed on a surface of the first multilayer wiring layer on a side opposite to the first semiconductor layer, the second semiconductor base including a second semiconductor layer in which an active element is provided, a second multilayer wiring layer stacked on the second semiconductor layer, and a second metal pad on a surface of the second multilayer wiring layer on a side opposite to the second semiconductor layer, the conductive polymer electrically connecting the first metal pad and to the second metal pad.