CMOS Image Sensor Plug Relocation for Low Dark Current
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Solution Overview
Problem
Conventional CMOS image sensors experience current leakage due to the placement of plugs at the interface of shallow trench isolation regions, which hinders the achievement of low dark current performance.
Innovation Solution
The plug connecting the photodiode and transfer transistor is relocated to be spaced apart from the shallow trench isolation region, with n+ ions implanted at a depth sufficient to contact the photodiode but isolated from the high-energy ion interface, allowing for a low dark current by eliminating leakage current.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If the plug is placed at the interface of the shallow trench isolation region to connect the photodiode and transfer transistor, then the connection is achieved, but current leakage occurs leading to high dark current
Solution Approach 1:
The plug is extracted from the shallow trench isolation region interface and relocated to the active region. This separation removes the source of current leakage (the harmful interaction at the STI interface) while maintaining the essential function of connecting the photodiode to the transfer transistor through the active region.
Solution Approach 2:
The active region serves as an intermediary medium between the photodiode and transfer transistor. By forming the plug within the active region rather than at the STI interface, the active region mediates the connection while preventing the harmful electrical interaction that causes dark current leakage.
2Ease of manufacture
If n+ ions are implanted with high energy to form the plug connection, then the plug formation is achieved, but current leakage is generated at the interface
Solution Approach 1:
The plug formation process applies local quality by concentrating the n+ ion implantation specifically within the active region boundaries. This localized approach ensures sufficient dopant concentration for reliable plug formation while avoiding the shallow trench isolation region interface where high-energy implantation would generate leakage current.
Solution Approach 2:
The implantation parameters (energy, dose, location) are optimized to achieve effective plug formation within the active region. By adjusting these parameters, the plug achieves adequate electrical connection without introducing the high-energy ion damage at the STI interface that causes leakage current.
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 configuration effectively reduces current leakage, enhancing the performance of CMOS image sensors by ensuring low dark current levels, critical for optimal image sensor operation.
Implementation Method 1
a plug injected with n+ ions is formed within the substrate 10
Data Source
AI summary
Disclosed herein are a CMOS image sensor and a method of manufacturing the same, which can reduce current leakage through a plug connecting a photodiode and a transfer transistor to each other, and thereby provide low dark current levels. The CMOS image sensor includes a first epitaxial layer on or in a substrate. A photodiode PD is in the first epitaxial layer. A second epitaxial layer is on or in the substrate (e.g., on the first epitaxial layer). A shallow trench isolation region is in an area of the substrate. A plug is in the substrate (e.g., the second epitaxial layer) connected with the photodiode and spaced apart from the shallow trench isolation region. A transfer transistor having a gate electrode and source/drain regions is connected with the plug.