Image Sensor Isolation Structures for Crosstalk Reduction
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Solution Overview
Problem
Crosstalk phenomenon occurs in CMOS image sensors due to reflected light missing the target photoelectric conversion element and hitting neighboring elements, leading to reduced operation characteristics and production yield.
Innovation Solution
The formation of isolation structures that penetrate through the inter-layer dielectric layer and extend into the substrate between photoelectric conversion regions, along with metal lines acting as reflectors, to redirect incident light back to the target elements and prevent crosstalk, while also improving device characteristics through specific trench and isolation structure designs.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Use of energy by moving object
If a reflector is used to redirect incident light back to the target photoelectric conversion element, then light utilization efficiency is improved, but crosstalk phenomenon occurs when reflected light hits neighboring photoelectric conversion elements
Solution Approach 1:
The patent segments the reflection function by introducing separate reflector structures positioned adjacent to each photoelectric conversion element rather than using a single common reflector. This segmentation allows each element to have its dedicated reflected light path, preventing reflected light from neighboring elements from causing crosstalk while maintaining high light utilization efficiency.
Solution Approach 2:
The patent introduces isolation structures as intermediary elements between adjacent photoelectric conversion elements. These isolation structures act as mediators that block or absorb stray reflected light before it can reach neighboring photoelectric conversion elements, thereby eliminating crosstalk while allowing the reflectors to continue redirecting light effectively to their target elements.
2Object-generated harmful factors
If isolation structures are introduced to prevent crosstalk, then crosstalk phenomenon is reduced, but device complexity and fabrication difficulty increase
Solution Approach 1:
The patent merges the isolation structures with the existing inter-layer dielectric layers and substrate structures. The isolation structures are formed as continuous extensions that integrate with the dielectric layers, eliminating the need for separate isolation components and reducing overall device complexity while still effectively preventing crosstalk.
Solution Approach 2:
The isolation structures serve multiple functions simultaneously: they act as barriers to prevent crosstalk between adjacent photoelectric conversion elements, provide mechanical support, and serve as part of the dielectric layer system. This multi-functionality reduces the need for additional dedicated isolation components, thereby simplifying the overall device structure.
3Manufacturing precision
If multiple masking steps are used to form precise isolation structures, then manufacturing precision is improved, but fabrication time and productivity are reduced
Solution Approach 1:
The patent performs preliminary formation of the isolation structures during the same masking and etching steps used to define the photoelectric conversion element patterns. By establishing the isolation structure footprints early in the fabrication process through preliminary masking, subsequent processing steps can proceed without requiring additional masking operations, thereby maintaining precision while improving productivity.
Solution Approach 2:
The patent combines the isolation structure formation process with the existing photoelectric conversion element fabrication steps. The same mask patterns and etching processes used to define the active elements also define the isolation structures, merging multiple fabrication operations into a single integrated process flow that maintains precision without sacrificing productivity.
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 solution effectively reduces or eliminates crosstalk, enhances device performance, and simplifies the fabrication process by allowing for a single masking step and thermal treatment of isolation structures, thereby improving production yield and device characteristics.
Implementation Method 1
an isolation structure which penetrates through the first inter-layer dielectric layer between the photoelectric conversion regions and further extends into the substrate
Implementation Method 2
first metal lines formed over the first inter-layer dielectric layer and each aligned with the photoelectric conversion regions
Implementation Method 3
an optical filter and a light condenser formed over a back side of the substrate
Implementation Method 4
an optical filter and a light condenser formed over a back side of the substrate
Data Source
AI summary
An image sensor includes: a first inter-layer dielectric layer formed over a front side of a substrate including photoelectric conversion regions; isolation structures each of which penetrates through the first inter-layer dielectric layer and has a portion buried in the substrate; first metal lines formed over the first inter-layer dielectric layer to correspond to the photoelectric conversion regions; and an optical filter and a light condenser formed over a back side of the substrate.