CMOS Image Sensor Capacitor Layout Against Plasma Damage
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Solution Overview
Problem
CMOS image sensors suffer from performance degradation due to plasma damage during dry etching processes, particularly in high dynamic range (HDR) applications, which is not detectable by conventional inspection methods and affects photodetectors, leading to issues like dark currents and white pixels.
Innovation Solution
The design of CMOS image sensors with enlarged charge-collecting capacitors covering more than half of the pixel element footprint provides protection against plasma damage during fabrication, using materials like high-energy plasma etching to reduce substrate damage and enhance photodetector performance.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If dry etching processes are used to fabricate CMOS image sensors, then manufacturing precision and device complexity are improved, but plasma damage to photodetectors occurs causing performance degradation
Solution Approach 1:
The patent applies preliminary anti-action by forming a protective layer over the photodetector before the dry etching process. This protective layer prevents plasma damage from occurring in the first place, rather than attempting to repair damage after etching. The protective layer is strategically positioned to shield the photodetector while allowing the etching process to proceed with high precision for other structures.
Solution Approach 2:
The protective layer serves as an intermediary between the plasma environment and the photodetector. It mediates the interaction by absorbing or deflecting harmful plasma particles while permitting the necessary etching processes to occur elsewhere in the device structure. This intermediary approach allows both high manufacturing precision and photodetector reliability to be achieved.
2Ease of manufacture
If conventional inspection methods are used, then manufacturing cost is reduced, but plasma damage defects are not detected leading to reliability issues
Solution Approach 1:
The patent employs optical inspection methods that detect changes in light interaction with the device structure. Plasma damage creates subtle optical property changes that are visible through advanced optical microscopy or reflectometry, allowing defect detection without adding significant manufacturing complexity. The inspection technique leverages optical contrast differences to identify damaged regions.
3Reliability
If capacitor size is increased to cover more than half of pixel element footprint, then protection against plasma damage is improved, but pixel element area for light sensing is reduced
Solution Approach 1:
The patent applies local quality by providing non-uniform protection across the pixel element. The protective structures are strategically positioned to cover only the photodetector and critical regions that are most vulnerable to plasma damage, rather than uniformly protecting the entire pixel element. This allows the capacitor and other structures to occupy necessary areas while providing focused protection where needed.
Solution Approach 2:
The patent utilizes vertical dimensionality by forming three-dimensional protective structures such as trenches filled with protective material or vertically extending protective layers. This approach provides plasma damage protection in the vertical dimension without significantly increasing the horizontal footprint that would reduce light sensing area. The protective structures extend downward or upward rather than laterally.
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 enlarged capacitors effectively shield photodetectors from plasma damage, improving operational performance and reducing degradation in HDR applications by minimizing dark currents and white pixels.
Implementation Method 1
plasma damage during dry etching processes
Data Source
AI summary
Some embodiments relate to an integrated circuit (IC) image sensor having an array of pixel elements. Each pixel element of the array includes a semiconductor substrate having a first surface and an opposite second surface, a photodetector disposed within the substrate, and a portion of an interconnect structure disposed over the first surface of the semiconductor substrate. The interconnect structure includes conductive interconnects embedded in dielectric layers. The portion of the interconnect structure includes a photodetector gate electrode over the photodetector, and a capacitor. The pixel element has a footprint over the first surface. The capacitor has a footprint over the first surface. The footprint of the capacitor covers more than half of the footprint of the pixel element, which provides increased protection to the photodetector during manufacturing.