Double Epitaxial Layer Infrared Image Sensor
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
Current CMOS image sensors face limitations in infrared light sensitivity due to shallow photodiode implant depth and isolation structure depth, constrained by existing photolithography, implantation, and etching processing technologies, which restrict the absorption of infrared light and increase crosstalk between pixels.
Innovation Solution
The image sensor employs a double epitaxial layer structure with deeper photodiodes and isolation structures, formed by epitaxial growth and ion implantation, allowing for increased implant depth and reduced crosstalk, enhancing light sensitivity to infrared light without affecting visible light sensitivity.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If photodiode implant depth is increased to improve infrared light absorption, then infrared sensitivity is improved, but processing complexity and manufacturing difficulty increase due to limitations in existing photolithography, implantation, and etching technologies
Solution Approach 1:
The patent transitions from a single-layer epitaxial structure to a multi-layer epitaxial structure, adding vertical dimensionality to the photodiode implantation process. This allows achieving greater effective implant depth through multiple sequential implantation steps into different epitaxial layers, thereby improving infrared sensitivity while working within the constraints of existing processing technologies.
Solution Approach 2:
The patent divides the single photodiode implantation process into multiple segmented implantation steps across different epitaxial layers. Each layer receives a portion of the total implant dose, and the cumulative effect achieves the desired deep implant profile for infrared sensitivity without requiring a single excessively deep implantation that would exceed processing capabilities.
2Object-affected harmful factors
If isolation structure depth is increased to reduce crosstalk between pixels, then crosstalk is reduced, but manufacturing precision requirements increase due to constraints in existing etching and implantation technologies
Solution Approach 1:
The patent extends the isolation structure depth by utilizing multiple epitaxial layers, effectively increasing the vertical dimension of isolation. This allows achieving deeper isolation to prevent crosstalk while distributing the manufacturing precision requirements across multiple less stringent steps rather than requiring a single ultra-precise deep etching operation.
Solution Approach 2:
The isolation structure formation is segmented into multiple steps corresponding to different epitaxial layers. Each isolation implantation step targets a specific layer with moderate precision requirements, and the cumulative isolation effect across layers achieves the desired crosstalk reduction without demanding excessive precision from any single manufacturing step.
3Reliability
If deeper photodiodes are implemented to enhance infrared light absorption, then infrared sensitivity is improved, but device complexity increases due to the need for multiple epitaxial layers and corresponding isolation structures
Solution Approach 1:
The multi-layer epitaxial structure serves multiple functions simultaneously: it provides the necessary depth for infrared light absorption, enables segmented implantation to manage processing complexity, and allows for distributed isolation structures to reduce crosstalk. This universal structure addresses multiple requirements without requiring separate dedicated components for each function.
Solution Approach 2:
The patent merges the functions of light absorption, charge collection, and isolation into an integrated multi-layer epitaxial structure. The photodiodes and isolation structures are combined across multiple layers, creating a unified device architecture that achieves infrared sensitivity while managing complexity through functional integration rather than separate components.
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 improves the sensitivity to infrared light by doubling the implant depth of photodiodes and isolation structures, overcoming processing limitations and reducing crosstalk, thereby enhancing the overall performance of the image sensor.
Implementation Method 1
Each photosensitive element absorbs a portion of the incident image light. Each photosensitive element included in the image sensor, such as photodiodes, generates image charges upon absorption of the image light.
Implementation Method 2
The first epitaxial layer is formed on the first side of the semiconductor substrate. The second epitaxial layer is formed on the first epitaxial layer.
Data Source
AI summary
An image sensor include a semiconductor substrate, a first epitaxial layer, a second epitaxial layer, a plurality of photodiodes, and a plurality of pixel isolation structures. The first epitaxial layer is formed on the semiconductor substrate, and the second epitaxial layer is formed on the first epitaxial layer. Each photodiode includes a first diffusion region formed in the first epitaxial layer and a second diffusion region formed in the second epitaxial layer. The second diffusion region is extended through the second epitaxial layer and electrically coupled to the first diffusion region. Each pixel isolation structure include a first isolation structure formed between adjacent first diffusion regions in the first epitaxial layer and a second isolation structure formed between adjacent second diffusion regions in the second epitaxial layer. The second isolation structure is extended through the second epitaxial layer to connect to the first isolation structure.