Backside Illuminated Image Sensor Waveguide Crosstalk Reduction
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Solution Overview
Problem
Backside illuminated (BSI) image sensor devices face challenges in maintaining high quantum efficiency as device scaling down continues, particularly due to light crosstalk and reduced light concentration caused by improper alignment of color filters and waveguides, leading to inefficiencies in light transmission to the corresponding light sensing regions.
Innovation Solution
Incorporating a waveguide structure within the dielectric layer over the back surface of the substrate, where the waveguide is aligned with color filters and light sensing regions, utilizing a refractive index difference to confine light and prevent crosstalk through total internal reflection, ensuring that filtered light is directed accurately to the appropriate sensing regions.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If device scaling down is implemented to achieve higher integration density, then device integration density is improved, but light crosstalk increases and quantum efficiency deteriorates
Solution Approach 1:
A waveguide structure is introduced as an intermediary component between the color filter layer and the light sensing region. The waveguide includes a core region with higher refractive index and cladding regions with lower refractive index, forming an optical conduit that mediates light transmission. This intermediary structure guides light from the color filter directly to the intended sensing region, preventing crosstalk to adjacent regions while maintaining high integration density achieved through device scaling.
2Device complexity
If color filters and waveguides are not properly aligned, then manufacturing complexity is reduced, but light crosstalk increases and color separation deteriorates
Solution Approach 1:
The waveguide structure implements local quality by creating a spatially varying refractive index distribution. The core region has a higher refractive index than the cladding regions, establishing localized optical properties that confine light within the core. This local refractive index differentiation enables precise light guidance to specific sensing regions, improving color separation and reducing crosstalk without requiring complex alignment procedures across the entire device.
3Object-generated harmful factors
If waveguide structure is implemented with refractive index difference, then light confinement is improved and crosstalk is reduced, but device complexity increases
Solution Approach 1:
The waveguide structure is segmented into distinct functional regions: a core region for light propagation and cladding regions for optical confinement. This segmentation is achieved by selectively removing portions of the dielectric layer to form trenches, then filling these trenches with materials having different refractive indices. The segmented structure provides effective light confinement and crosstalk reduction while maintaining a fabrication process that integrates with existing semiconductor manufacturing techniques.
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 waveguide structure enhances light confinement and reduces crosstalk, thereby improving quantum efficiency and color separation, leading to more efficient light detection and better performance in BSI image sensor devices.
Implementation Method 1
utilizing a refractive index difference to confine light and prevent crosstalk through total internal reflection
Implementation Method 2
The waveguide includes a core region and cladding regions. The refractive index of the core is greater than the refractive index of the cladding regions.
Data Source
AI summary
The present disclosure provides an integrated circuit device comprising a substrate having a back surface and a sensing region disposed in the substrate and being operable to sense radiation projected towards the back surface of the substrate. The device further includes a waveguide disposed over the back surface of the substrate. The waveguide is aligned with the sensing region such that the waveguide is operable to transmit the radiation towards the aligned sensing region. The waveguide includes a waveguide wall, and an inner region disposed adjacent to the waveguide wall. A diffractive index of the waveguide wall is less than a diffractive index of the inner region.