Backside-Illuminated Global Shutter Sensor With Reflective Storage Shield
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Solution Overview
Problem
Front-side illuminated global shutter (FSIGS) image sensors face challenges in improving quantum efficiency (QE) and angular response (AR) due to a long optical path and radiation reflection from interconnect structures, which negatively impact shutter efficiency (SE).
Innovation Solution
A backside illuminated global shutter (BSIGS) image sensor configuration, where incident radiation passes through the backside of the semiconductor substrate, incorporating a photodetector, storage node, and a reflective structure that shields the storage node from radiation, reducing reflection and optimizing QE and AR while maintaining high SE.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If front-side illuminated global shutter configuration is used, then manufacturing process is simpler, but quantum efficiency and angular response are degraded due to long optical path and interconnect structure reflection
Solution Approach 1:
The patent inverts the traditional front-side illumination approach by implementing backside illumination. Incident radiation enters through the backside of the semiconductor substrate, passes through the substrate thickness, and reaches the photodetector. This inversion eliminates the long optical path through interconnect structures and reduces radiation reflection, thereby improving quantum efficiency and angular response while maintaining global shutter functionality.
2Reliability
If backside illuminated configuration is used, then quantum efficiency and angular response are improved by reducing optical path, but additional reflective structure is needed to maintain shutter efficiency
Solution Approach 1:
The patent converts the potentially harmful backside reflection into a beneficial element by implementing a reflective structure that redirects reflected radiation toward the photodetector. The reflective structure, positioned at the backside of the substrate, captures radiation that would otherwise be lost and redirects it to enhance signal detection, thereby improving quantum efficiency without compromising shutter efficiency.
3Area of stationary object
If storage node is closer to photodetector, then device area is reduced, but radiation reflection from storage node increases
Solution Approach 1:
The patent introduces a reflective structure as an intermediary element between the incident radiation and the storage node. This reflective structure is positioned to intercept radiation that would otherwise reflect off the storage node, and redirects it in a controlled manner. This allows the storage node to be positioned closer to the photodetector for area efficiency while preventing harmful radiation reflection.
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 BSIGS image sensor achieves improved QE and AR compared to FSIGS by reducing the optical path and eliminating radiation reflection, while maintaining high shutter efficiency through the use of a reflective structure and isolation structures.
Implementation Method 1
The image sensors comprise one or more photodetectors (e.g., photodiodes, phototransistors, photoresistors, etc.) configured to absorb incident radiation and output electrical signals corresponding to the incident radiation.
Implementation Method 2
A reflective structure is disposed on the backside of the semiconductor substrate opposite the front side. The reflective structure is disposed such that the reflective structure at least partially shields the storage node from incident radiation passing through the backside of the semiconductor substrate.
Data Source
AI summary
Various embodiments of the present disclosure are directed towards an image sensor. The image sensor includes a photodetector disposed in a semiconductor substrate. An interlayer dielectric (ILD) structure is disposed on a first side of the semiconductor substrate. A storage node is disposed in the semiconductor substrate and spaced from the photodetector, where the storage node is spaced from the first side by a first distance. A first isolation structure is disposed in the semiconductor substrate and between the photodetector and the storage node, where the first isolation structure extends into the semiconductor substrate from a second side of the semiconductor substrate that is opposite the first side, and where the first isolation structure is spaced from the first side by a second distance that is less than the first distance.