Conductive Pixel Isolation Structure for Small-Pitch Image Sensors
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Solution Overview
Problem
As image sensors shrink in size, producing deep doped well regions for isolation between pixel sensors becomes challenging, especially with increasing substrate thickness, which affects the manufacturing process and isolation efficiency.
Innovation Solution
The introduction of a sensor isolation feature that includes a conductive material and a dielectric material between the conductive material and the substrate, providing partial electrical isolation and allowing for improved light collection through a reflector grid, thereby enhancing quantum efficiency.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If deep doped well regions are used for isolation between pixel sensors, then electrical isolation between pixels is improved, but manufacturing difficulty increases with substrate thickness
Solution Approach 1:
The isolation structure is segmented into multiple parts: a shallow trench isolation region extending from the first surface, and a deep doped well region extending from the first surface through the substrate to the second surface. This segmentation allows each part to serve a specific isolation function at different depths, achieving complete electrical isolation while maintaining manufacturability
Solution Approach 2:
The isolation approach transitions from a single deep vertical structure to a combined approach using both shallow lateral trenches and deep vertical wells. This dimensional combination enables isolation to be achieved through multiple spatial dimensions, reducing the burden on any single structure and improving manufacturing feasibility
2Area of moving object
If pixel size is reduced to increase array density, then image sensor resolution is improved, but isolation structure size cannot be reduced proportionally
Solution Approach 1:
The shallow trench isolation extends only partially through the substrate depth (from first surface to a depth less than the substrate thickness), rather than requiring full-depth isolation structures. This partial action approach provides sufficient electrical isolation for small pixels while significantly reducing manufacturing complexity and enabling continued pixel size reduction
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 enables effective isolation between pixel sensors even at smaller sizes, facilitates easier manufacturing due to reduced depth requirements, and improves light collection and sensitivity of the image sensor.
Implementation Method 1
an isolation feature formed in the substrate, wherein the isolation feature includes a conductive feature and a dielectric layer between the conductive feature and the substrate
Implementation Method 2
improving light collection through a reflector grid, thereby enhancing quantum efficiency
Data Source
AI summary
An image sensor includes a substrate including a first surface and a second surface opposite to the first surface; a plurality of pixel sensors disposed in the substrate, a sensor isolation feature disposed in the substrate defining an active region, and a dielectric layer between the sensor isolation feature and the substrate, wherein the sensor isolation feature comprises a conductive material.