Pixel Isolation Doping Profile for Low-Dark-Current Image Sensors
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Solution Overview
Problem
Image sensors face challenges in reducing dark current and maintaining adequate full well capacity as pixel size decreases, leading to deterioration in dynamic range and signal-to-noise ratio due to high p-type impurity concentrations from general plasma doping processes.
Innovation Solution
A method of manufacturing image sensors involving the formation of a pixel isolation trench with a sacrificial layer, where a p-type impurity is doped using a plasma doping process to create a p-type neutral region with a concentration profile that decreases from the surface to the inside of the substrate, allowing for a low impurity concentration and increased photoelectric conversion region volume.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Object-affected harmful factors
If general plasma doping process is used to dope p-type impurity, then dark current suppression is improved, but full well capacity deteriorates due to high impurity concentration
Solution Approach 1:
The patent applies local quality by creating a non-uniform p-type impurity concentration distribution through the sacrificial layer method. The impurity concentration is highest at the pixel isolation trench interface (where dark current suppression is needed) and gradually decreases toward the center of the photoelectric conversion region (where full well capacity is needed). This gradient distribution allows simultaneous optimization of both dark current suppression and full well capacity by tailoring the impurity concentration to the specific functional requirements of different regions.
Solution Approach 2:
The sacrificial layer is formed on the pixel isolation trench before the plasma doping process. This preliminary action serves as a temporary mask that controls the doping profile, allowing p-type impurities to be introduced only in specific regions with desired concentration gradients. After doping, the sacrificial layer is removed, leaving the optimized impurity distribution. This preliminary structuring enables precise control over the final impurity concentration profile without requiring complex post-processing.
2Productivity
If pixel size is reduced to increase integration, then integration level is improved, but dark current suppression and full well capacity deteriorate
Solution Approach 1:
By implementing a gradient p-type impurity concentration distribution through the sacrificial layer doping method, the patent enables effective dark current suppression even in reduced-size pixels. The high impurity concentration at the pixel isolation interface maintains dark current suppression performance, while the gradual concentration reduction toward the center preserves adequate full well capacity. This local optimization allows pixels to be scaled down without proportionally degrading dark current characteristics.
3Object-affected harmful factors
If p-type impurity concentration is increased to suppress dark current, then dark current suppression is improved, but photoelectric conversion region volume decreases
Solution Approach 1:
The patent resolves this contradiction by creating a spatially varying impurity concentration profile. High p-type impurity concentration is localized at the pixel isolation trench interface where dark current suppression is critical, while the impurity concentration gradually decreases toward the center of the photoelectric conversion region. This ensures that the photoelectric conversion region maintains sufficient volume and low impurity content for efficient light detection, while the high impurity concentration zone at the interface provides effective dark current suppression. The sacrificial layer enables this precise spatial control of impurity distribution.
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 approach effectively suppresses dark current and improves full well capacity, enhancing the dynamic range and signal-to-noise ratio by maintaining a larger photoelectric conversion region volume while controlling impurity concentrations.
Implementation Method 1
doping a p-type impurity into the semiconductor substrate via an interface between the sacrificial layer and the side surface of the pixel isolation trench using a plasma doping process performed on a first surface of the sacrificial layer
Implementation Method 2
doping a p-type impurity into the semiconductor substrate via an interface between the sacrificial layer and the side surface of the pixel isolation trench using a plasma doping process
Data Source
AI summary
Provided are an image sensor and a method of manufacturing the image sensor. The method includes forming a pixel isolation trench in a semiconductor substrate to extend from a first surface of the semiconductor substrate to the inside of the semiconductor substrate, forming a sacrificial layer on an inner wall of the pixel isolation trench, implanting a p-type impurity from a surface of the sacrificial layer into the sacrificial layer and the semiconductor substrate by a plasma doping process, a first concentration of the p-type impurity at the surface of the sacrificial layer being greater than a second concentration of the p-type impurity at a sidewall of the pixel isolation trench, removing the sacrificial layer, and forming a pixel isolation structure by forming an insulating liner and a conductive layer sequentially on the inner wall of the pixel isolation trench.