Deep Trench Guard Ring Biasing for Pixel Leakage Isolation
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Solution Overview
Problem
Deep trench isolation structures in image sensing integrated circuits can suffer from defects and leakage currents due to etching processes, leading to dark current and white pixel issues, and the deep N-well formed by blanket implantation can interfere with guard ring structures, causing further leakage.
Innovation Solution
The implementation of a second deep trench isolation structure in the guard ring area, with conductive cores biased to enhance isolation, and the use of high-k dielectric materials to passivate defects, along with a conductive core within the trenches to generate an electric field that accumulates holes and prevent leakage.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If deep trench isolation structures are formed using etching processes, then isolation between light sensing elements is improved, but defects and leakage currents occur leading to dark current and white pixel issues
Solution Approach 1:
The patent changes the physical and chemical parameters of the trench by filling it with conductive material (such as doped polysilicon or metal) instead of leaving it empty or filling with insulator only. This parameter change transforms the trench from a passive isolation structure to an active guard ring structure that can generate electric fields to repel minority carriers, thereby preventing leakage currents and dark current while maintaining isolation between light sensing elements.
Solution Approach 2:
The conductive material in the trench acts as an intermediary structure between the isolation function and the guard ring function. It mediates between the need for electrical isolation and the need to prevent leakage currents by creating a potential barrier that actively repels minority carriers, thus resolving the contradiction between isolation quality and defect-induced leakage.
2Ease of manufacture
If blanket implantation is used to form deep N-well, then light sensing element formation is simplified, but guard ring structures are interfered with causing further leakage
Solution Approach 1:
The patent segments the trench structure into distinct regions: some trenches are filled with conductive material to form guard rings in specific areas, while other trenches may remain as simple isolation structures. This segmentation allows the deep N-well to be formed by blanket implantation for simplified manufacturing, while the conductive trench fills selectively restore guard ring functionality in critical leakage-prone areas without requiring complex selective implantation processes.
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 improves the isolation between light sensing elements, enhances the guard ring functionality, and reduces leakage currents, thereby improving the modulation transfer function and quantum efficiency of the image sensing IC.
Implementation Method 1
the conductive core may be electrically coupled to a biasing source configured to apply a bias voltage to the conductive core. By applying a bias voltage to the conductive core, the conductive core is able to generate an electric field that accumulates holes along sidewalls of the substrate defining the trench
Implementation Method 2
the deep trench isolation structures may be provided with a conductive core that is separated from the semiconductor substrate by the dielectric material that lines the trenches
Data Source
AI summary
A process used to form a first deep trench isolation (DTI) structure in a pixel region of a semiconductor substrate is also used to form a second DTI structure in a guard ring area that isolates the pixel region from a peripheral region. The guard ring area may have a PNP guard ring structure. The second DTI structure may include trenches in each of an inner ring, a middle, and an outer ring of the PNP guard ring structure. The first and second DTI structures may have conductive cores. The conductive cores of the inner and outer ring may be biased to a first voltage while the conductive cores of the middle ring may be biased to an opposite polarity second voltage. When the second DTI structure have conductive cores with these biases, the second DTI structure may be used as the guard ring without the PNP structure.