Backside Illumination Image Sensor Dielectric Reflector
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Solution Overview
Problem
Conventional backside illumination image sensors face challenges with reduced quantum efficiency due to light passing through dielectric layers, leading to over-etching issues during manufacturing, which can cause leakage current, cross-talk, and potential short circuits.
Innovation Solution
The implementation of a dielectric reflector structure with a contact etch stop layer over the logic region and a protective layer over the pixel region, enhancing reflectivity and reducing over-etching risks by controlling the etching process.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If the thickness and reflectivity of the overlying dielectric layer are increased to reduce light passing through the sensor, then quantum efficiency is improved, but manufacturing defects arise due to over-etching during contact formation
Solution Approach 1:
The dielectric layer is segmented into two distinct layers: a first dielectric layer (thinner, over pixel region) and a second dielectric layer (thicker, over logic region). This segmentation allows each layer to be optimized for its specific function - the first layer maintains etching controllability while the second layer provides enhanced reflectivity and light blocking, thereby resolving the contradiction between quantum efficiency and manufacturing precision.
Solution Approach 2:
Different dielectric layer thicknesses are applied to different regions of the substrate: the pixel region receives a thinner first dielectric layer to facilitate precise etching and contact formation, while the logic region receives a thicker second dielectric layer to maximize light reflection and blocking. This local differentiation resolves the contradiction by allowing each region to have the optimal dielectric thickness for its specific requirements.
2Ease of manufacture
If conventional backside illumination design is used without differentiated dielectric layers, then manufacturing process is simpler, but light passes through dielectric layers reducing quantum efficiency and causing cross-talk
Solution Approach 1:
The dielectric structure is segmented into region-specific layers that can be formed using standard semiconductor fabrication techniques. The first dielectric layer is formed over the pixel region and the second dielectric layer is formed over the logic region, allowing each to be optimized independently while maintaining compatibility with conventional manufacturing processes.
Solution Approach 2:
The patent applies different dielectric layer configurations to different regions: a thinner first dielectric layer over pixel regions for optimal light reflection and a thicker second dielectric layer over logic regions for enhanced light blocking. This local quality approach improves quantum efficiency and reduces cross-talk while remaining manufacturable with standard processes.
3Productivity
If pixel size is reduced to increase sensor resolution, then more pixels fit on the sensor, but pixel sensitivity decreases and cross-talk between pixels increases
Solution Approach 1:
The differentiated dielectric layer structure provides localized optical optimization for each pixel region. The first dielectric layer's specific thickness and material properties are tailored to maximize light reflection back to the photodiode in pixel regions, thereby maintaining high sensitivity even as pixel sizes are reduced to increase density.
Solution Approach 2:
The patent converts the potentially harmful effect of light passing through the dielectric layer into a beneficial reflection by carefully controlling the dielectric layer thickness and material properties. This causes light that would otherwise be lost to be reflected back to the photodiode, maintaining sensitivity in smaller pixels while reducing cross-talk to adjacent pixels.
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 configuration increases quantum efficiency while minimizing damage from over-etching, ensuring improved performance and reliability of the image sensor.
Implementation Method 1
A backside illuminated image sensor is disclosed having enhanced quantum efficiency. The image sensor utilizes a dielectric reflector structure which serves to reflect a portion of the incident light back into a pixel region of the image sensor.
Data Source
AI summary
A system and method for image sensing is disclosed. An embodiment comprises a substrate with a pixel region and a logic region. A first resist protect oxide (RPO) is formed over the pixel region, but not over the logic region. Silicide contacts are formed on the top of active devices formed in the pixel region, but not on the surface of the substrate in the pixel region, and silicide contacts are formed both on the top of active devices and on the surface of the substrate in the logic region. A second RPO is formed over the pixel region and the logic region, and a contact etch stop layer is formed over the second RPO. These layers help to reflect light back to the image sensor when light impinges the sensor from the backside of the substrate, and also helps prevent damage that occurs from overetching.