Heterogeneous Gettering Layer Near Pixels to Reduce Dark Current
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Solution Overview
Problem
Conventional impurity gettering methods in semiconductor image sensors, such as CMOS image sensors, are inadequate in reducing dark current and white pixel performance due to the inefficiency of gettering centers in collecting metal ions and defects, often resulting in crystal defects and leakage near photodiodes.
Innovation Solution
A heterogeneous layer with a super defective structure is introduced near the pixel region, utilizing a semiconductor material with a lattice constant different from the substrate, which induces defects and strains to effectively collect impurities and defects, thereby improving gettering efficiency without damaging the silicon region.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If conventional gettering centers (silicon defects from carbon implantation) are generated close to photodiodes, then impurity collection capability is improved, but crystal defects and leakage are induced in nearby photodiodes, worsening dark current and white pixel performance
Solution Approach 1:
A heterogeneous layer is introduced as an intermediary between the photodiode and the gettering center. This layer acts as a mediator that provides a transition zone with different material properties, allowing impurity collection while protecting the photodiode from direct exposure to harmful crystal defects. The heterogeneous layer absorbs or confines the crystal defects generated during thermal processing, preventing them from reaching and damaging the photodiode structure.
Solution Approach 2:
The device structure is segmented into distinct functional regions: the photodiode region, the heterogeneous layer, and the gettering center region. This segmentation allows each region to perform its specific function independently - the photodiode for light detection, the heterogeneous layer for defect management, and the gettering center for impurity collection - while minimizing interference between them.
2Reliability
If a backside poly layer is used as a gettering center, then metal ions and defects can be collected during thermal process, but the layer is located far from photodiodes (hundreds of micrometers), degrading gettering capability as metal ions cannot travel that far
Solution Approach 1:
The heterogeneous layer is positioned locally adjacent to the photodiode structure, providing high-quality gettering functionality precisely where it is needed - close to the light-sensitive region. This local placement ensures that metal ions generated near the photodiode during thermal processing can be collected efficiently without having to travel long distances, while the layer's specific material properties are optimized for its local function of defect management and impurity collection.
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 heterogeneous layer effectively reduces dark currents and white pixels by confining defects within the layer, ensuring high gettering efficiency while preventing silicon damage and leakage, thus enhancing the overall performance of the image sensor.
Implementation Method 1
a heterogeneous layer with a super defective structure is introduced near the pixel region, utilizing a semiconductor material with a lattice constant different from the substrate, which induces defects and strains to effectively collect impurities and defects
Implementation Method 2
The heterogeneous layer effectively reduces dark currents and white pixels by confining defects within the layer, ensuring high gettering efficiency while preventing silicon damage and leakage
Data Source
AI summary
Apparatus and methods for effective impurity gettering are described herein. In some embodiments, a described device includes: a substrate; a pixel region disposed in the substrate; an isolation region disposed in the substrate and within a proximity of the pixel region; and a heterogeneous layer on the seed area. The isolation region comprises a seed area including a first semiconductor material. The heterogeneous layer comprises a second semiconductor material that has a lattice constant different from that of the first semiconductor material.