Deep Sunk Isolation Region for CMOS Image Sensor Leakage Reduction
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Solution Overview
Problem
CMOS image sensors experience high leakage current and limited radiation sensitivity due to defects in isolation regions, which affect the performance of the radiation-sensitive elements.
Innovation Solution
The further semiconductor region is sunk deeper into the semiconductor body and made wider than the isolation region, reducing leakage current and allowing for increased radiation sensitivity by eliminating the need for isolation regions in certain areas, thereby expanding the radiation-sensitive surface.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If isolation regions are used to separate neighboring picture elements, then picture element separation is achieved, but leakage current increases due to defects in isolation regions
Solution Approach 1:
The patent changes the physical parameters of the isolation region by sinking it deeper into the semiconductor body (increasing depth from conventional shallow trench isolation to a deeper configuration) and increasing its width. These parameter changes transform the isolation region from a potential source of leakage current to a leakage-reducing structure, as the deeper and wider configuration allows for better defect management and reduced electric field concentration at defect sites.
Solution Approach 2:
The patent extends the isolation region in the vertical dimension by sinking it deeper into the semiconductor body, rather than only relying on lateral separation. This vertical extension creates an additional dimension for isolation effectiveness, allowing the structure to block leakage current paths that would otherwise travel through or around shallow isolation regions.
2Area of stationary object
If isolation regions are used to separate neighboring picture elements, then picture element separation is achieved, but radiation-sensitive surface area is reduced
Solution Approach 1:
By extending the isolation function into the vertical dimension through deeper sinking of the isolation region, the patent reduces the need for lateral isolation width. This allows picture elements to be positioned closer together at the surface level, increasing the radiation-sensitive surface area while maintaining effective separation through the deeper vertical isolation structure.
Solution Approach 2:
The patent optimizes the depth parameter of the isolation region to achieve effective separation with reduced lateral footprint. By increasing the depth of the isolation region, the required lateral width for adequate separation is reduced, thereby freeing up surface area for radiation-sensitive elements.
3Ease of manufacture
If conventional shallow trench isolation is used, then manufacturing is simplified, but leakage current remains high due to surface defects
Solution Approach 1:
The patent modifies the geometric parameters of the isolation region by increasing both depth and width within the constraints of existing manufacturing processes. These parameter changes can be achieved using adapted masks and standard ion implantation or diffusion processes, maintaining ease of manufacture while significantly improving leakage current performance through the deeper and wider configuration.
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 reduces leakage current and enhances radiation sensitivity, allowing for a 20% larger radiation-sensitive surface area per pixel element while maintaining or reducing the total length of isolation structures, thus improving the overall performance of the CMOS image sensor.
Implementation Method 1
each radiation-sensitive element contains a semiconductor region of a first conductivity type in which charge carriers generated by incident radiation are accumulated
Implementation Method 2
in the part of the semiconductor body of the second conductivity type underneath the isolation region a further semiconductor region of the second conductivity type is formed, having an increased doping concentration. Because of this region the leakage current is reduced and the capacitance of the radiation-sensitive element is increased because it functions as a barrier for charge carriers
Data Source
AI summary
Disclosed are embodiments of a semiconductor device comprising a semiconductor body with a semiconductor image sensor comprising a two-dimensional matrix of picture elements, each picture element comprising a radiation-sensitive element coupled to MOS field effect transistors for reading the radiation-sensitive elements, wherein a semiconductor region is sunken in the surface of the body having the same conductivity type as the body and having an increased doping concentration, the semiconductor region being disposed between the radiation-sensitive elements of neighboring picture elements.