Image Sensor Diffusion Barrier Structure for Dopant Control
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Solution Overview
Problem
The diffusion of dopants from the backside semiconductor layer into the sensor semiconductor layer in CMOS image sensors leads to unintended changes in dopant concentration, reducing the effective thickness of the sensor semiconductor layer, full well capacity, and increasing variability in breakdown voltage, thereby affecting the performance of the image sensor.
Innovation Solution
Incorporating a diffusion barrier structure between the sensor semiconductor layer and the backside semiconductor layer, doped with a third dopant different from the first and second dopants, to reduce the diffusion of dopants and trap interstitial defects, thereby maintaining the effective thickness and stability of the depletion region and breakdown voltage.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Illumination intensity
If a backside semiconductor layer is used in CMOS image sensors, then the sensor can achieve backside illumination and improved light sensitivity, but dopant diffusion from the backside layer into the sensor layer reduces effective thickness and full well capacity
Solution Approach 1:
An intermediate layer is introduced between the backside semiconductor layer and the sensor semiconductor layer. This intermediate layer acts as a mediator that prevents dopant diffusion from the backside layer into the sensor layer, thereby maintaining the effective thickness and full well capacity while allowing the backside illumination structure to function.
Solution Approach 2:
The semiconductor structure is segmented into distinct layers with different doping characteristics. By dividing the structure into a backside layer, an intermediate layer, and a sensor layer, the patent isolates the dopant sources and prevents unwanted diffusion while maintaining the functional benefits of backside illumination.
2Ease of manufacture
If dopant diffusion is allowed to occur, then the manufacturing process is simpler, but the breakdown voltage becomes highly variable and performance is reduced
Solution Approach 1:
The intermediate layer serves as a diffusion barrier that mediates between the backside semiconductor layer and the sensor semiconductor layer. This barrier prevents dopant migration while maintaining structural integrity, ensuring stable breakdown voltage without complicating the overall manufacturing process.
Solution Approach 2:
The intermediate layer is positioned specifically at the interface where dopant diffusion occurs. This localized structure provides the necessary diffusion prevention exactly where needed, without affecting other regions of the device and maintaining overall process simplicity.
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 diffusion barrier structure effectively reduces dopant diffusion, maintaining the sensor semiconductor layer's thickness and full well capacity, and stabilizing the breakdown voltage, thereby enhancing the overall performance of the image sensor.
Implementation Method 1
The diffusion barrier structure is arranged between the sensor semiconductor layer and the backside semiconductor layer to reduce a diffusion of a dopant from the backside semiconductor layer into the sensor semiconductor layer
Implementation Method 2
doped with a third dopant different from the first and second dopants, to reduce the diffusion of dopants and trap interstitial defects
Data Source
AI summary
The present disclosure relates to an integrated chip. The integrated chip includes a sensor semiconductor layer. The sensor semiconductor layer is doped with a first dopant. A photodetector is along a frontside of the sensor semiconductor layer. A backside semiconductor layer is along a backside of the sensor semiconductor layer, opposite the frontside. The backside semiconductor layer is doped with a second dopant. A diffusion barrier structure is between the sensor semiconductor layer and the backside semiconductor layer. The diffusion barrier structure includes a third dopant different from the first dopant and the second dopant.