Thin-Junction Image Sensor Structure for Dark Current Inhibition
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Solution Overview
Problem
CMOS image sensors experience increased dark current due to excess charge carriers generated at trench surfaces during the formation of deep trench isolation structures, leading to 'white pixel' defects and degraded image quality, particularly in backside illuminated sensors.
Innovation Solution
A dark-current-inhibiting image sensor design featuring a thin junction extending from a concave surface into the semiconductor substrate, electrically connected to a bias voltage, with a passivation layer and dielectric layer to reduce charge carrier diffusion, and an isolation well surrounding the photodiode to minimize defects.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If deep trench isolation structures are formed to optically and electrically isolate pixels, then pixel isolation is improved, but dark current increases due to excess charge carriers generated at trench surfaces
Solution Approach 1:
A thin junction layer is introduced as an intermediary between the photodiode and the trench surface. This thin junction acts as a mediator that prevents excess charge carriers generated at the trench surface from reaching the photodiode, thereby reducing dark current while maintaining effective pixel isolation.
Solution Approach 2:
The thin junction is formed in advance during the manufacturing process, before the trench is fully completed. This preliminary action ensures that the protective layer is already in place to prevent charge carrier generation and diffusion from the trench surface, addressing the dark current issue before it can manifest.
2Productivity
If plasma etching is used to form DTI trenches, then trench formation efficiency is improved, but semiconductor lattice damage increases causing white pixel defects
Solution Approach 1:
The thin junction structure converts the harmful effect of plasma etching damage into a beneficial outcome. By introducing this additional layer, the damage caused by plasma etching is localized and prevented from reaching the photodiode, thereby maintaining high trench formation efficiency while eliminating white pixel defects.
3Reliability
If measures are taken to reduce electrical and optical cross-talk between adjacent pixels, then pixel isolation is improved, but other image artifacts are introduced
Solution Approach 1:
The thin junction is applied locally at the trench region where cross-talk occurs, rather than throughout the entire pixel structure. This localized approach effectively reduces electrical and optical cross-talk between adjacent pixels without introducing artifacts in other regions of the image sensor.
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 solution effectively reduces dark current and white pixel defects, enhancing image quality by minimizing charge carrier diffusion and preventing junction depletion, thereby improving the overall performance of CMOS image sensors.
Implementation Method 1
reduce charge carrier diffusion
Implementation Method 2
electrically connected to a bias voltage
Data Source
AI summary
A dark-current-inhibiting image sensor includes a semiconductor substrate, a thin and a thin junction. The semiconductor substrate includes a front surface, a back surface opposite the front surface, a photodiode, and a concave surface between the front surface and the back surface. The concave surface extends from the back surface toward the front surface, and defines a trench that surrounds the photodiode in a cross-sectional plane parallel to the back surface. The thin junction extends from the concave surface into the semiconductor substrate, and is a region of the semiconductor substrate. The semiconductor substrate includes a first substrate region, located between the thin junction and the photodiode, that has a first conductive type. The photodiode and the thin junction have a second conductive type opposite the first conductive type.