Back Side Illuminated Image Sensor Defect Reduction
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Solution Overview
Problem
Existing fabrication methods for back side illuminated (BSI) image sensor devices fail to adequately address defects near the back side of the substrate, leading to dark currents and white pixels, which degrade image quality and performance.
Innovation Solution
A method involving the formation of a recrystallized silicon layer on the back side of the substrate through annealing, with a portion of the substrate near the back side being melted, and a radiation-sensing region formed to sense radiation projected through the back side, utilizing a dopant implantation process to reduce defects and enhance melting depth without exceeding the thermal budget.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Shape
If a thinning process and polishing process are performed to reduce substrate thickness for BSI image sensor fabrication, then the back side of the substrate becomes smooth and flat, but defects are introduced near the back side of the substrate
Solution Approach 1:
The patent applies preliminary action by performing defect removal processes (chemical etching, plasma treatment, or ion implantation) on the back side of the substrate before the thinning and polishing operations. This preliminary defect removal prevents defects from being introduced or concentrated during subsequent thinning and polishing processes, thereby maintaining both smoothness and reliability.
Solution Approach 2:
The patent changes physical and chemical parameters of the substrate surface through various treatments including chemical etching with specific solutions, plasma treatment with controlled parameters, or ion implantation with adjusted energy and dosage. These parameter changes modify the surface properties to prevent defect formation during thinning and polishing while maintaining the required smoothness.
2Ease of manufacture
If existing fabrication methods are used for BSI image sensor devices, then the manufacturing process is simple, but defects near the back side cause dark currents and white pixels that degrade image quality
Solution Approach 1:
The patent applies local quality by targeting specific regions near the back side of the substrate for defect removal treatments. Chemical etching, plasma treatment, or ion implantation are applied locally to areas where defects are most likely to occur, rather than treating the entire substrate uniformly. This localized approach maintains manufacturing simplicity while significantly improving defect reduction capability in critical areas.
3Reliability
If dopant implantation is used to reduce defects and enhance melting depth, then image sensor performance improves, but thermal budget constraints must be maintained
Solution Approach 1:
The patent applies partial action by using dopant implantation with carefully controlled dosage and energy levels to achieve sufficient defect reduction and melting depth enhancement without excessive thermal input. The implantation parameters are optimized to provide just enough doping to improve performance while staying within the thermal budget constraints of the overall fabrication process.
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 significantly reduces dark current and white pixels by achieving a deeper melting depth and recrystallization, improving image sensor performance and maintaining thermal budget constraints.
Implementation Method 1
annealing the substrate in a manner so that a portion of the substrate near the back side is melted
Implementation Method 2
utilizing a dopant implantation process to reduce defects and enhance melting depth without exceeding the thermal budget
Implementation Method 3
photodiodes and transistors, that can absorb radiation projected toward the substrate and convert the sensed radiation into electrical signals
Data Source
AI summary
Provided is an image sensor device. The image sensor device includes a substrate having a front side and a back side. The image sensor also includes a radiation-detection device that is formed in the substrate. The radiation-detection device is operable to detect a radiation wave that enters the substrate through the back side. The image sensor further includes a recrystallized silicon layer. The recrystallized silicon layer is formed on the back side of the substrate. The recrystallized silicon layer has different photoluminescence intensity than the substrate.