Backside Illuminated Image Sensor Storage Gate Optical Shield
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Solution Overview
Problem
Image sensors with global shutters face issues such as image distortion and quality degradation due to light pollution in storage structures, which affect shutter efficiency, dark current, and image lag, particularly in fast-moving object capture.
Innovation Solution
The use of an optical shield, such as silicon oxide or germanium, is implemented in the storage gate to prevent light from reaching the storage node, thereby isolating it optically and reducing image charge pollution, and the shield is formed without etching steps through impurity atom implantation and annealing, ensuring effective light reflection or absorption.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If storage structures are used to temporarily store image charge in global shutter image sensors, then simultaneous image capture capability is improved, but light pollution in storage structures causes image charge degradation and reduces image quality
Solution Approach 1:
An optical shield structure is introduced as an intermediary element between the storage node and the incident light path. The shield comprises a first portion and a second portion that together block light from reaching the storage node, preventing light-induced charge generation while allowing the storage function to operate normally.
Solution Approach 2:
The optical shield is divided into multiple segments (first portion and second portion) that can be independently formed through separate implantation and annealing processes. This segmentation allows for precise positioning and optimization of light blocking while minimizing impact on other device characteristics.
2Object-affected harmful factors
If conventional etching steps are used to form optical shields, then light blocking capability is achieved, but manufacturing complexity and process steps increase
Solution Approach 1:
The conventional mechanical etching process is replaced with a field-based approach using ion implantation followed by thermal annealing. The implantation of impurity atoms creates a modified region that forms the optical shield through diffusion during annealing, eliminating the need for complex etching machinery and multiple patterning steps.
Solution Approach 2:
The formation process transitions from removing material (etching) to adding and diffusing impurity atoms (implantation and annealing). By controlling implantation dose, energy, and annealing temperature, the optical shield properties are tuned without requiring additional process steps.
3Device complexity
If impurity atom implantation and annealing are used to form optical shields, then manufacturing steps are reduced, but precise control of shield properties becomes critical
Solution Approach 1:
The implantation and annealing process parameters are optimized based on measured outcomes from previous runs. By monitoring the optical and electrical characteristics of formed shields, the implantation dose, energy, and annealing conditions are adjusted to achieve consistent results, creating a controlled feedback loop that ensures precision.
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 enhances image quality by minimizing light-induced distortion and charge pollution, improving shutter efficiency and reducing dark current, thereby enabling better capture of fast-moving objects without image lag.
Implementation Method 1
the shield is formed without etching steps through impurity atom implantation and annealing, ensuring effective light reflection or absorption
Implementation Method 2
the shield is formed without etching steps through impurity atom implantation and annealing
Implementation Method 3
the shield is formed without etching steps through impurity atom implantation and annealing
Data Source
AI summary
A method of backside illuminated image sensor fabrication includes forming a plurality of photodiodes in a semiconductor material, where the plurality of photodiodes are disposed to receive image light through a backside of the backside illuminated image sensor. The method further includes forming a transfer gate coupled to extract image charge from a photodiode in the plurality of photodiodes, and forming a storage gate coupled to the transfer gate to receive the image charge. Forming the storage gate includes forming an optical shield in the semiconductor material; depositing a gate electrode proximate to a frontside of the semiconductor material; and implanting a storage node in the semiconductor material, where the storage node is disposed in the semiconductor material between the optical shield and the gate electrode.