CMOS Image Sensor MDTI Structure for NIR Crosstalk Isolation
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Solution Overview
Problem
CMOS image sensors face challenges in enhancing near-infrared (NIR) sensitivity while maintaining low lateral crosstalk and cost-effectiveness, as increasing the thickness of the photo absorption layer to improve NIR sensitivity leads to increased lateral crosstalk and higher fabrication costs.
Innovation Solution
The implementation of a CMOS image sensor with a multiple deep trench isolation (MDTI) structure, which includes a boundary deep trench isolation (BDTI) between adjacent pixel regions and a multiple deep trench isolation within individual pixel regions, using dielectric layers with a lower dielectric constant to redirect incoming radiation and improve NIR quantum efficiency.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If the thickness of the photo absorption layer is increased to improve NIR sensitivity, then NIR sensitivity is improved, but lateral crosstalk increases and fabrication cost increases
Solution Approach 1:
The photo absorption layer is divided into multiple segments or regions with different thicknesses. Thinner regions are positioned in areas where lateral crosstalk is problematic, while thicker regions are positioned where enhanced NIR sensitivity is needed. This segmentation allows simultaneous optimization of both NIR sensitivity and crosstalk suppression.
Solution Approach 2:
Different regions of the photo absorption layer are assigned different local properties, specifically varying thickness. Regions adjacent to pixel boundaries are made thinner to reduce lateral crosstalk, while central regions are made thicker to enhance NIR sensitivity. This local quality variation resolves the contradiction between sensitivity and crosstalk.
2Measurement precision
If the thickness of the photo absorption layer is increased to improve NIR sensitivity, then NIR sensitivity is improved, but fabrication cost increases
Solution Approach 1:
The photo absorption layer is segmented into multiple thickness regions, allowing the use of thinner layers in most areas while maintaining selective thicker regions for NIR sensitivity. This reduces the average material consumption and fabrication complexity compared to a uniformly thick layer, thereby lowering costs while preserving NIR performance.
Solution Approach 2:
The thickness parameter of the photo absorption layer is varied spatially rather than maintained uniformly. By optimizing the thickness distribution pattern, the invention achieves high NIR sensitivity in critical regions while reducing overall material usage and fabrication complexity, thus lowering manufacturing costs.
3Object-affected harmful factors
If deep trench isolation structures are added to reduce lateral crosstalk, then lateral crosstalk is reduced, but device complexity increases
Solution Approach 1:
The isolation structure is segmented into multiple deep trenches arranged in specific patterns within the photo absorption layer. These trenches are strategically positioned to provide effective crosstalk suppression only where needed, rather than implementing a continuous isolation structure throughout, thereby reducing overall structural complexity.
Solution Approach 2:
The deep trench isolation structures act as intermediary elements between adjacent pixel regions. By placing these trenches at specific locations within the photo absorption layer, they serve as localized barriers that reduce lateral crosstalk without requiring comprehensive isolation structures, thus balancing effectiveness with simplicity.
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 reduces lateral photon crosstalk and enhances NIR sensitivity, maintaining sensing quality and cost-effectiveness by effectively confining incident radiation to the photodiode region.
Implementation Method 1
using dielectric layers with a lower dielectric constant to redirect incoming radiation and improve NIR quantum efficiency
Implementation Method 2
a photodiode configured to convert radiation that enters the substrate from the back-side into an electrical signal
Data Source
AI summary
The present disclosure relates to a CMOS image sensor having a multiple deep trench isolation (MDTI) structure, and an associated method of formation. In some embodiments, the image sensor comprises a boundary deep trench isolation (BDTI) structure disposed at boundary regions of a pixel region surrounding a photodiode. The BDTI structure has a ring shape from a top view and two columns surrounding the photodiode with the first depth from a cross-sectional view. A multiple deep trench isolation (MDTI) structure is disposed at inner regions of the pixel region overlying the photodiode, the MDTI structure extending from the back-side of the substrate to a second depth within the substrate smaller than the first depth. The MDTI structure has three columns with the second depth between the two columns of the BDTI structure from the cross-sectional view. The MDTI structure is a continuous integral unit having a ring shape.