Solid-State Image Pickup Device Copper Diffusion Control
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Solution Overview
Problem
Copper interconnects in solid-state image pickup devices can diffuse into photoelectric conversion elements, leading to dark current or leakage current, causing white defects in image data due to their high diffusion coefficient.
Innovation Solution
A solid-state image pickup device is designed with a multilayer interconnect structure, where aluminum interconnects are used on the first substrate with photoelectric conversion elements and copper interconnects on the second substrate, with antidiffusion films to prevent copper diffusion, thereby reducing noise and dark current.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If copper interconnects are used in solid-state image pickup devices, then finer interconnection and pattern designing are achieved, but copper diffuses into photoelectric conversion elements causing dark current or leakage current
Solution Approach 1:
The device is divided into two separate substrates: a first substrate containing photoelectric conversion elements and an aluminum interconnect, and a second substrate containing peripheral circuits and a copper interconnect. This segmentation physically separates the copper interconnect from the photoelectric conversion elements, preventing copper diffusion while maintaining fine interconnection capabilities in the peripheral circuit area.
Solution Approach 2:
A bonding interface is introduced as an intermediary between the first substrate (aluminum interconnect) and the second substrate (copper interconnect). This bonding interface allows the two different interconnect materials to coexist in the same device without direct contact, enabling copper to be used for fine interconnection in the peripheral circuits while preventing its diffusion into the photoelectric conversion elements on the first substrate.
2Device complexity
If copper interconnects are used on the same substrate as photoelectric conversion elements, then device integration is improved, but copper incorporation causes white defects in image data
Solution Approach 1:
The device is segmented into two substrates bonded together: the first substrate with photoelectric conversion elements and aluminum interconnect, and the second substrate with peripheral circuits and copper interconnect. This segmentation maintains high device integration by combining both substrates into a single functional unit while preventing copper diffusion into the photoelectric conversion elements, thereby avoiding white defects in image data.
Solution Approach 2:
Different interconnect materials are assigned to different functional areas: aluminum is used in the region containing photoelectric conversion elements where copper diffusion would be harmful, while copper is used in the peripheral circuit region where fine interconnection is needed and copper diffusion would not affect image quality. This local differentiation resolves the contradiction between integration and image quality.
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
The configuration effectively prevents copper incorporation into photoelectric conversion elements, reducing noise and enhancing image quality by minimizing dark current and leakage current occurrences.
Implementation Method 1
antidiffusion films for the copper interconnects are not arranged above each photoelectric conversion element... copper may diffuse into the photoelectric conversion element because the diffusion coefficient of copper is extremely high
Data Source
AI summary
The present invention relates to a solid-state image pickup device. The device includes a first substrate including a photoelectric conversion element and a transfer gate electrode configured to transfer charge from the photoelectric conversion element, a second substrate having a peripheral circuit portion including a circuit configured to read a signal based charge generated in the photoelectric conversion element, the first and second substrates being laminated. The device further includes a multilayer interconnect structure, disposed on the first substrate, including an aluminum interconnect and a multilayer interconnect structure, disposed on the second substrate, including a copper interconnect.