Solid-State 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, as disclosed in PTL 1, does not adequately address the issue of thermal expansion mismatch between copper bonding pads and insulating films, leading to potential gaps at the bonding plane and copper diffusion, which can result in white spots and other defects.
Innovation Solution
The method involves forming a first substrate with photoelectric converters and a first wiring structure, and a second substrate with peripheral circuits and a second wiring structure. The substrates are bonded such that the first and second wiring structures are in contact, with at least one of the wiring structures having a concave portion where the conductive material forms the bottom face, ensuring a flat bonding plane without gaps.
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 at the bonding plane
Solution Approach 1:
The patent applies local quality by creating a recessed region specifically at the bonding pad area where the insulating film is removed to expose the conductive material. This localized modification allows the bonding pad surface to be at a different level than the surrounding insulating film, compensating for thermal expansion differences and preventing gap formation during bonding while maintaining the overall structure integrity.
2Manufacturing precision
If copper bonding pads are recessed to prevent gaps, then bonding plane flatness is improved, but copper diffusion may occur causing white spots
Solution Approach 1:
The patent introduces a barrier metal layer as an intermediary between the copper bonding pad and the surrounding environment. This barrier layer prevents copper diffusion into the insulating film or adjacent structures that would cause white spots, while still allowing the recessed bonding pad structure to maintain bonding plane flatness. The barrier metal acts as a mediator that enables both benefits simultaneously.
3Measurement precision
If pixel size is reduced to achieve high definition images, then image quality is improved, but light receiving area of photoelectric converter is decreased
Solution Approach 1:
The patent applies segmentation by dividing the substrate into multiple layers with different functions. The photoelectric converter layer is optimized for light reception with adequate pixel size, while the bonding structure is segmented into recessed regions and barrier metal layers that prevent interference with light reception. This layered segmentation allows high definition imaging with reduced overall device thickness without compromising light receiving area.
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 and prevents copper diffusion, thereby reducing the occurrence of defects like white spots and enhancing the reliability and performance of the solid-state image pickup device.
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.