Deep Trench Isolation Liner Doping to Reduce Photodiode Dark Current
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Solution Overview
Problem
Dark current from photodiodes into trench isolation structures reduces the sensitivity and breakdown voltage of CMOS image sensors, leading to defective white pixels.
Innovation Solution
Doping a liner of the trench isolation structure with zinc (Zn) and/or gallium (Ga) to reduce dark current, increasing the sensitivity and breakdown voltage of photodiodes.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If trench isolation structures are used to separate photodiodes, then pixel isolation is achieved, but dark current flows into the trench structures reducing sensitivity and breakdown voltage
Solution Approach 1:
A liner layer is introduced as an intermediary between the photodiode and the trench isolation structure. This liner layer acts as a mediator that prevents direct interaction between the photodiode and the trench, thereby blocking dark current flow while maintaining the isolation function of the trench structure.
Solution Approach 2:
The electrical properties of the liner layer are optimized by controlling its thickness (5-50 nm) and material composition (metal oxide such as aluminum oxide, titanium oxide, or silicon oxide). These parameter changes create a potential barrier that blocks dark current while allowing the structure to maintain its isolation functionality.
2Reliability
If dark current is reduced through liner layer doping, then sensitivity and breakdown voltage increase, but additional processing steps are required
Solution Approach 1:
The liner layer is formed between the photodiode and the trench isolation structure before the trench is filled with isolation material. This preliminary action ensures that the liner layer is in direct contact with the photodiode surface, maximizing its effectiveness in blocking dark current while integrating seamlessly into the existing process flow.
Solution Approach 2:
The liner layer is applied locally only where needed - specifically on the surface of the photodiode and potentially on the trench walls - rather than throughout the entire device. This localized application reduces the overall complexity of the device while maintaining the dark current blocking function where it is most critical.
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 approach effectively reduces the number of white pixels and enhances the sensitivity and breakdown voltage of photodiodes in CMOS image sensors.
Implementation Method 1
driving zinc, gallium, or a combination thereof into the liner layer
Implementation Method 2
Dark current from the photodiodes into the trench isolation structures still persists and reduces the sensitivity and breakdown voltage of the photodiodes
Data Source
AI summary
Doping a liner of a trench isolation structure with zinc and/or gallium reduces dark current from a photodiode. For example, the zinc and/or gallium may be deposited on a temporary oxide layer and driven into a high-k layer surrounding a deep trench isolation structure and an interface between the high-k layer and surrounding silicon. In another example, the zinc and/or gallium may be deposited on an oxide layer between the high-k layer and surrounding silicon. As a result, sensitivity of the photodiode is increased. Additionally, breakdown voltage of the photodiode is increased, and a quantity of white pixels in a pixel array including the photodiode are reduced.