CMOS Image Sensor Crosstalk Reduction via Composite Grid Structure
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Solution Overview
Problem
Conventional BSI CMOS image sensors face issues with optical crosstalk and increased thickness due to the presence of a passivation layer, which affects light confinement and quantum efficiency, and the buried color filter array structure does not effectively prevent crosstalk between adjacent color filters.
Innovation Solution
A semiconductor device with a composite grid structure where a dielectric grid layer is directly disposed on a metal grid layer, and color filters fill cavities within this structure, reducing optical paths and enhancing quantum efficiency, while reflective structures through the device layer block light diffusion to adjacent photoelectric devices, thereby minimizing crosstalk.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a passivation layer is added to protect the metal grid layer, then the metal grid layer is protected from corrosion, but the device thickness increases and optical crosstalk worsens due to light diffusion
Solution Approach 1:
The patent removes the passivation layer entirely and replaces it with a composite grid structure where the metal grid layer is directly exposed. The metal grid layer itself serves as the protective barrier, and the dielectric grid layer provides the necessary insulation and structural support without adding excessive thickness.
Solution Approach 2:
The patent employs a composite grid structure combining metal grid layer and dielectric grid layer in direct contact. This composite structure achieves both protection and optical performance without requiring a separate passivation layer, thereby reducing overall device thickness while maintaining reliability.
2Reliability
If a passivation layer is added to protect the metal grid layer, then the metal grid layer is protected from corrosion, but optical crosstalk increases due to light diffusion through the passivation layer
Solution Approach 1:
The patent removes the passivation layer that was causing light diffusion and optical crosstalk. By eliminating this layer, light propagation is improved and crosstalk between adjacent pixels is reduced, while the metal grid layer remains protected through the composite structure design.
Solution Approach 2:
The composite grid structure with direct contact between metal and dielectric layers creates a configuration that prevents light diffusion while maintaining protection. The dielectric layer provides optical isolation without the harmful light-diffusing properties of traditional passivation layers.
3Adaptability or versatility
If additional layers are added between metal and dielectric grid layers, then manufacturing flexibility is increased, but the process window is reduced and manufacturing difficulty increases
Solution Approach 1:
The patent merges the metal grid layer and dielectric grid layer into direct contact, eliminating intermediate layers. This simplification increases the process window for manufacturing while maintaining the necessary functional flexibility through the composite structure design.
4Object-affected harmful factors
If the color filter array is buried deeper in the structure, then light confinement is improved, but optical paths are lengthened and quantum efficiency decreases
Solution Approach 1:
The patent removes the passivation layer that was forcing the color filters to be positioned deeper in the structure. By eliminating this layer, the color filters can be positioned closer to the surface, shortening optical paths while maintaining effective light confinement through the composite grid structure.
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 solution reduces optical paths, enhances quantum efficiency, and improves imaging performance by eliminating additional layers between the metal and dielectric grid layers and using reflective structures to block light diffusion, thus reducing crosstalk and increasing the process window for manufacturing.
Implementation Method 1
reflective structures through the device layer block light diffusion to adjacent photoelectric devices, thereby minimizing crosstalk
Implementation Method 2
color filters respectively fill the cavities
Data Source
AI summary
A semiconductor device includes a substrate, a device layer, an anti-reflective coating layer, reflective structures, a composite grid structure, a passivation layer and color filters. The device layer is disposed on the substrate, in which trenches are formed in the device layer and the substrate. The anti-reflective coating layer conformally covers the device layer, the substrate and the trenches. The reflective structures are disposed on the anti-reflective coating layer in the trenches respectively. The composite grid structure overlies the anti-reflective coating layer and the reflective structures. The composite grid structure includes cavities passing through the composite grid structure, and the composite grid structure includes a metal grid layer and a dielectric grid layer sequentially stacked on the reflective structures. The passivation layer conformally covers the composite grid structure. The color filters respectively fill the cavities.