Conductive Trench Isolation for Image Sensors
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Solution Overview
Problem
Pixel crosstalk and dark current in semiconductor-based image sensors degrade image resolution and sensitivity, with existing solutions either failing to eliminate these issues or exacerbating dark current.
Innovation Solution
The implementation of conductive deep trench isolation regions with a conductive fill and a fixed charge layer in image sensors, which induces a positive charge in the semiconductor layer to block charge transport between pixels, reducing electrical crosstalk and dark current.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Object-affected harmful factors
If heavily doped regions are used to isolate individual pixels, then pixel crosstalk is reduced, but dark current increases
Solution Approach 1:
The semiconductor substrate is divided into discrete pixel regions separated by deep trench isolation structures. These trenches physically segment the continuous semiconductor material into isolated pixel cells, preventing electrical coupling between adjacent pixels while maintaining low dark current through proper trench design and filling.
Solution Approach 2:
An intermediary material (such as oxide or nitride) is deposited within the deep trench isolation structures to provide electrical isolation between pixels. This intermediary layer blocks charge carrier transport between adjacent pixels without requiring heavy doping, thereby reducing crosstalk while minimizing dark current generation.
2Object-affected harmful factors
If pixel isolation structures are implemented, then crosstalk is reduced, but manufacturing complexity increases
Solution Approach 1:
The deep trench isolation structures are formed early in the fabrication process, before pixel electrode deposition and device assembly. By establishing the isolation architecture preliminarily, subsequent manufacturing steps can proceed without additional complexity, as the trench structures serve as pre-defined boundaries for all subsequent processing.
Solution Approach 2:
The deep trench isolation structures serve multiple functions simultaneously: they provide electrical isolation between pixels, define pixel boundaries, support subsequent electrode deposition, and contribute to mechanical stability. This multi-functionality reduces the need for separate dedicated isolation structures, thereby simplifying overall manufacturing.
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 mitigates charge transfer between pixels, significantly reducing undesirable electrical effects such as crosstalk and dark current, thereby enhancing image sensor performance and resolution.
Implementation Method 1
a fixed charge layer in image sensors, which induces a positive charge in the semiconductor layer to block charge transport between pixels
Implementation Method 2
block charge transport between pixels, reducing electrical crosstalk and dark current
Data Source
AI summary
An image sensor including a plurality of photodiodes disposed in a semiconductor layer and a plurality of deep trench isolation regions disposed in the semiconductor layer. The plurality of deep trench isolation regions include: (1) an oxide layer disposed on an inner surface of the plurality of deep trench isolation regions and (2) a conductive fill disposed in the plurality of deep trench isolation regions where the oxide layer is disposed between the semiconductor layer and the conductive fill. A plurality of pinning wells is also disposed in the semiconductor layer, and the plurality of pinning wells in combination with the plurality of deep trench isolation regions separate individual photodiodes in the plurality of photodiodes. A fixed charge layer is disposed on the semiconductor layer, and the plurality of deep trench isolation regions are disposed between the plurality of pinning wells and the fixed charge layer.