Backside Illuminated Sensor Pixel Opaque Isolation Layer
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Solution Overview
Problem
High-resolution image sensors are susceptible to optical noise due to stray light, particularly in backside illuminated photodiodes, which limits their accuracy and applicability, as the closely packed photodiodes are more exposed to reflections from neighboring diodes and metallization layers.
Innovation Solution
The implementation of an opaque isolation layer or light shields with metal components coated in dielectric layers over the photodiodes to absorb or reflect stray light, reducing noise by limiting its impact on the semiconductor diffusion regions, and the use of vertically extending electrodes to further minimize stray light interference.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If the spacing between photodiodes is decreased to increase resolution, then the image sensor resolution is improved, but the susceptibility to optical noise from stray light increases
Solution Approach 1:
The patent introduces an opaque isolation layer as an intermediary element positioned between adjacent photodiodes. This isolation layer acts as a mediator that blocks stray light from reaching neighboring photodiodes, thereby reducing optical noise while allowing the photodiodes to maintain close spacing for high resolution imaging.
Solution Approach 2:
The patent divides the semiconductor substrate into isolated regions by introducing opaque isolation layers between adjacent photodiodes. This segmentation creates separate optical zones that prevent cross-contamination of light between neighboring pixels, enabling high-density packing without compromising signal purity.
2Measurement precision
If photodiodes are made narrower and deeper to increase resolution, then the image sensor resolution is improved, but the susceptibility to stray light reflections increases
Solution Approach 1:
The opaque isolation layer serves as a protective intermediary that surrounds the narrow, deep photodiode structures. This isolation layer blocks stray light reflections from metallization layers and neighboring structures from reaching the photodiode active regions, thereby protecting the high-resolution photodiode design from optical interference.
3Use of energy by moving object
If backside illumination is used to improve light sensitivity, then the photodiode light sensitivity is improved, but the exposure to stray light from metallization layers increases
Solution Approach 1:
The opaque isolation layer acts as a protective intermediary positioned between the backside-illuminated photodiodes and the metallization layers. This isolation layer blocks stray light reflections from the metallization layers from reaching the photodiodes, thereby enabling backside illumination to maintain high light sensitivity without suffering from increased stray light interference.
4Object-affected harmful factors
If opaque isolation layers are added to reduce stray light, then optical noise is reduced, but the device complexity increases
Solution Approach 1:
The patent merges the opaque isolation layer formation with existing semiconductor manufacturing processes. The isolation layer is integrated into the photodiode fabrication sequence, combining multiple functions (isolation, structural support, optical blocking) into a single integrated structure, thereby reducing overall device complexity despite adding optical isolation functionality.
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 significantly reduces optical noise and inter-channel cross-talk, enhancing the immunity of photodiodes to stray light and improving the overall accuracy and reliability of image sensors.
Implementation Method 1
opaque isolation layer or light shields with metal components coated in dielectric layers over the photodiodes to absorb or reflect stray light
Implementation Method 2
opaque isolation layer or light shields with metal components coated in dielectric layers over the photodiodes to absorb or reflect stray light
Data Source
AI summary
Backside illuminated sensor pixel structure. In one embodiment, an image sensor includes a plurality of photodiodes arranged in rows and columns of a pixel array that are disposed in a semiconductor substrate. Individual photodiodes of the pixel array are configured to receive incoming light through a backside of the semiconductor substrate. The individual photodiodes have a diffusion region formed in an epitaxial region and a plurality of storage nodes (SGs) that are disposed on the front side of the semiconductor substrate and formed in the epitaxial region. An opaque isolation layer having a plurality of opaque isolation elements is disposed proximate to the front side of the semiconductor substrate and proximate to the diffusion region of the plurality of photodiodes. The opaque isolation elements are configured to block a path of incoming light from the backside of the semiconductor substrate toward the storage nodes.