Stacked Image Sensor Wiring Layout for Stronger Cu Bonding
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Solution Overview
Problem
In solid-state imaging devices, a high coverage ratio of copper electrodes can lead to bonding voids and weak bonding strength between semiconductor substrates, hindering the miniaturization and performance of the devices due to increased wiring resistance.
Innovation Solution
The implementation of a conductive film with a lower coverage ratio as a wiring layer, featuring a trench-like shape with a planar aspect ratio greater than 1, reduces wiring resistance by increasing the area ratio of insulation films and preventing void formation during substrate bonding.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Loss of energy
If a high coverage ratio of copper electrodes is used, then wiring resistance is reduced, but bonding voids and weak bonding strength occur between semiconductor substrates
Solution Approach 1:
The patent applies local quality by making the copper electrode coverage ratio position-dependent: higher coverage ratio at the bonding surface to prevent voids, and lower coverage ratio in the wiring layer to reduce resistance. This spatial variation in electrode coverage resolves the contradiction between bonding strength and wiring resistance.
Solution Approach 2:
The patent resolves the contradiction by transitioning from a two-dimensional coverage ratio parameter to a three-dimensional structured approach with multiple layers (bonding surface layer and wiring layer) at different depths. Each layer has optimized coverage ratio suited to its function, eliminating the need to compromise between conflicting requirements.
2Loss of energy
If a high coverage ratio of copper electrodes is used, then wiring resistance is reduced, but miniaturization of solid-state imaging devices is hindered
Solution Approach 1:
The patent enables miniaturization while maintaining low wiring resistance by applying local quality differently at different locations: the bonding surface has high coverage for reliable connection, while the wiring layer has optimized coverage for low resistance, allowing compact device design without sacrificing electrical performance.
3Reliability
If a low coverage ratio of copper electrodes is used, then bonding strength is improved, but wiring resistance increases
Solution Approach 1:
The patent segments the copper electrode structure into functionally distinct parts: a bonding surface layer with high coverage ratio optimized for bonding strength, and a wiring layer with lower coverage ratio optimized for electrical conductivity. This segmentation allows each part to independently optimize its function without compromising the other.
Solution Approach 2:
The patent resolves the contradiction by adding a vertical dimension to the electrode structure, creating multiple layers at different depths. The bonding surface layer addresses bonding strength requirements, while the wiring layer addresses resistance requirements, allowing both to be optimized simultaneously through vertical stratification.
Data Source
AI summary
An imaging device includes a first substrate including a pixel array and a first multilayer wiring layer. The first multilayer wiring layer includes a first wiring that receives electrical signals based on electric charge generated by at least one photoelectric conversion unit, and a plurality of second wirings. The imaging device includes a second substrate including a second multilayer wiring layer and a logic circuit that processes the electrical signals. The second multilayer wiring layer includes a third wiring bonded to the first wiring, and a plurality of fourth wirings. At least one of the plurality of fourth wirings being bonded to at least one of the plurality of second wirings. The second multilayer wiring layer includes at least one fifth wiring that is connected to the plurality of fourth wirings and that receives a power supply signal.