CMOS Image Sensor Bonding Structure for Gap-Free Copper Pads
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Solution Overview
Problem
The existing bonding method for solid-state image pickup devices, particularly in CMOS type devices, fails to account for the thermal expansion mismatch between copper bonding pads and insulating films, leading to potential gaps and copper diffusion, which can result in white spots and reduced image quality.
Innovation Solution
A method involving a first substrate with photoelectric converters and a second substrate with peripheral circuits, where both substrates have wiring structures with concave portions containing conductive materials, ensuring a flat bonding plane by aligning the substrates such that the conductive material forms the bottom face of the concave portions, thereby mitigating thermal expansion issues.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If copper bonding pads are used for bonding substrates, then electrical connection is achieved, but thermal expansion mismatch with insulating films causes gaps to form at the bonding plane
Solution Approach 1:
The patent applies local quality by creating a recessed structure specifically at the bonding pad area where the concave portion is formed in the insulating film. This localized structural modification allows the copper bonding pad to be positioned at a lower level, compensating for its higher thermal expansion coefficient and preventing gap formation during thermal cycles, while leaving the rest of the bonding plane flat.
Solution Approach 2:
The patent changes the geometric parameter of the bonding structure by forming a concave portion in the insulating film. This parameter change (creating a recessed area) allows the copper bonding pad to be embedded at a lower level, compensating for thermal expansion differences and maintaining bonding plane flatness under thermal stress.
2Reliability
If copper bonding pads have a convex shape to ensure contact, then electrical connection is improved, but copper diffusion occurs into surrounding materials causing white spots
Solution Approach 1:
The patent applies local quality by creating a recessed structure specifically at the bonding pad area where the concave portion is formed in the insulating film. This localized structural modification allows the copper bonding pad to be positioned at a lower level, compensating for its higher thermal expansion coefficient and preventing gap formation during thermal cycles, while leaving the rest of the bonding plane flat.
Solution Approach 2:
The patent applies preliminary anti-action by pre-forming a recessed structure in the insulating film before bonding. This preliminary action creates a containment structure that prevents copper diffusion into surrounding materials, addressing the copper diffusion problem before it can occur during operation or thermal cycling.
3Productivity
If pixel size is reduced to increase pixel density, then image definition is improved, but light receiving area decreases reducing sensitivity
Solution Approach 1:
The patent applies segmentation by dividing the device into two separate substrates: a first substrate containing photoelectric converters and a second substrate containing peripheral circuits. This segmentation allows independent optimization of each substrate, enabling smaller pixel sizes for higher density on the first substrate while maintaining adequate light receiving areas through precise control of the photoelectric converter structure and bonding interface.
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
This approach eliminates gaps at the bonding plane, preventing copper diffusion and enhancing image sensitivity and pixel density by maintaining a flat bonding interface.
Implementation Method 1
the relationship between the coefficient of thermal expansion of the copper bonding pad and that of the insulating film has not been studied, and a gap may be generated at a bonding plane after the bonding
Data Source
AI summary
A member for a solid-state image pickup device having a bonding plane with no gaps and a method for manufacturing the same are provided. The manufacturing method includes the steps of providing a first substrate provided with a photoelectric converter on its primary face and a first wiring structure, providing a second substrate provided with a part of a peripheral circuit on its primary face and a second wiring structure, and performing bonding so that the first substrate, the first wiring structure, the second wiring structure, and the second substrate are disposed in this order. In addition, at least one of an upper face of the first wiring structure and an upper face of the second wiring structure has a concave portion, and a conductive material forms a bottom face of the concave portion.