Composite Image Sensor Grid for Crosstalk and Peeling Control
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Solution Overview
Problem
As CMOS image sensors with smaller pixel regions are fabricated to increase resolution, optical crosstalk between neighboring pixels increases, and the adhesion strength between metal and oxide grids in the composite grid structure decreases, leading to peeling defects and degradation of quantum efficiency and signal-to-noise ratio.
Innovation Solution
An adhesion enhancement layer is interposed between the oxide and metal grids to improve adhesion strength, reducing peeling defects and maintaining robustness even with scaled-down gridlines, thereby enhancing the composite grid structure's robustness and optical isolation.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If pixel regions are made smaller to increase resolution, then image sensor resolution is improved, but optical crosstalk between neighboring pixels increases
Solution Approach 1:
A composite grid structure comprising metal gridlines and oxide gridlines is introduced as an intermediary element between neighboring pixel regions. The metal gridlines provide optical isolation to reduce crosstalk, while the oxide gridlines enhance adhesion and structural integrity. This intermediary structure enables smaller pixel dimensions without sacrificing optical isolation performance.
Solution Approach 2:
The patent employs a composite grid structure combining two different materials (metal and oxide) with complementary properties. The metal component (e.g., tungsten, aluminum) provides superior optical isolation due to its reflective properties, while the oxide component (e.g., silicon oxide) provides excellent adhesion to the substrate and planarization capabilities. This composite approach resolves the contradiction by leveraging the strengths of both materials.
2Strength
If gridlines are scaled down to maintain composite grid structure robustness, then structural integrity is improved, but adhesion strength between metal and oxide grids decreases
Solution Approach 1:
The patent applies different materials with optimized local properties at different positions within the grid structure. The metal gridlines are positioned where optical isolation is most critical, while the oxide gridlines are positioned where adhesion to the substrate and planarization are most needed. This local optimization of material placement maintains robustness even as overall grid dimensions are scaled down.
Solution Approach 2:
The composite grid structure combines metal and oxide materials that complement each other's properties. The oxide layer provides strong adhesion to the substrate and underlying layers, while the metal layer provides structural robustness and optical isolation. This composite material system maintains both adhesion strength and structural integrity even when scaled to smaller dimensions.
3Measurement precision
If grid dimensions are reduced to increase pixel density, then image sensor resolution is improved, but peeling defects increase due to decreased adhesion strength
Solution Approach 1:
The oxide gridlines serve as an intermediary adhesion layer between the metal gridlines and the substrate. This intermediary layer prevents direct contact between metal and substrate, reducing stress concentration and preventing peeling defects that would otherwise occur when grid dimensions are reduced. The oxide layer's excellent adhesion properties compensate for the reduced scale.
Solution Approach 2:
The composite metal-oxide grid structure addresses peeling defects by distributing mechanical stress across two materials with different mechanical properties. The oxide material, being more compliant and adherent, absorbs stress that would otherwise cause peeling at the metal-substrate interface. This enables manufacturing of smaller grids without increasing defect rates.
Data Source
AI summary
An image sensor includes a substrate, a grid, and a color filter. The grid is over the substrate. From a cross-sectional view, the grid includes a first grid and a second grid over the first grid, the first grid has lower portion that has a first sidewall and a second sidewall opposing the first sidewall, the second grid has a third sidewall and a fourth sidewall opposing the third sidewall, and a width between the third sidewall and the fourth sidewall is less than a width between the first sidewall and the second sidewall. The color filter extends through the grid structure.