Stacked Image Sensor Bonding Structure for Dark Current Suppression
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Solution Overview
Problem
The bonding method in existing solid-state image pickup devices using copper can lead to metal impurity diffusion, causing dark current and leakage current, which results in image defects and operational failures, especially in devices with a large number of pixels.
Innovation Solution
Surrounding conductive materials with diffusion preventing films during bonding to prevent metal impurity diffusion, using a dual or single damascene structure with barrier metals to ensure electrical connection while minimizing contamination.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If copper bonding pads are used for bonding substrates, then electrical connection is achieved, but metal impurity diffusion occurs causing dark current and leakage current
Solution Approach 1:
A barrier metal layer is introduced as an intermediary between the copper bonding pads and the semiconductor substrates. This barrier metal prevents direct contact between copper and the substrate, thereby blocking metal impurity diffusion while maintaining electrical connectivity. The barrier metal acts as a mediator that resolves the contradiction between achieving reliable electrical connection and preventing harmful copper diffusion.
Solution Approach 2:
The bonding structure is transformed from a simple copper bonding pad to a composite structure consisting of multiple layers: copper bonding pad, barrier metal layer, and optionally other intermediate layers. This composite material approach allows the system to simultaneously achieve good electrical conductivity (from copper) and prevent diffusion (from barrier metal), resolving the technical contradiction.
2Measurement precision
If pixel size is reduced to increase definition, then image resolution is improved, but light receiving area decreases reducing sensitivity
Solution Approach 1:
The patent transitions from a planar single-substrate structure to a three-dimensional stacked multi-substrate structure. By stacking the first substrate (with photoelectric converters) and second substrate (with other circuits) vertically, the patent achieves higher integration density without reducing pixel size, thereby maintaining both image definition and detection sensitivity simultaneously.
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 effectively suppresses the generation of dark current and leakage current, enhancing the reliability and performance of solid-state image pickup devices by preventing metal impurity diffusion at bonding portions.
Implementation Method 1
a diffusion preventing film having a capability of preventing diffusion of copper
Data Source
Figure 1
Figure 2A~2B
Figure 3
AI summary
A solid-state image pickup device capable of suppressing the generation of dark current and/or leakage current is provided. The solid-state image pickup device has a first substrate provided with a photoelectric converter on its primary face, a first wiring structure having a first bonding portion which contains a conductive material, a second substrate provided with a part of a peripheral circuit on its primary face, and a second wiring structure having a second bonding portion which contains a conductive material. In addition, the first bonding portion and the second bonding portion are bonded so that the first substrate, the first wiring structure, the second wiring structure, and the second substrate are disposed in this order. Furthermore, the conductive material of the first bonding portion and the conductive material of the second bonding portion are surrounded with diffusion preventing films.