Dual-Film Pixel Separation in Image Sensors for Crosstalk Control
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Solution Overview
Problem
Current image sensors face challenges in optimizing pixel separation patterns for improved reflectance and step coverage, which affect crosstalk and dark current characteristics.
Innovation Solution
The image sensor incorporates a substrate with first and second conductive films, where the first conductive film has higher reflectance than the second for a predetermined wavelength range, and the second conductive film has greater step coverage, with specific materials like aluminum and copper used for enhanced performance.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a single conductive film is used in pixel separation patterns, then the structure is simple, but both reflectance and step coverage cannot be optimized simultaneously
Solution Approach 1:
The pixel separation pattern is divided into two distinct conductive films: a first conductive film (Aluminum) providing high reflectance for crosstalk prevention, and a second conductive film (Copper) providing excellent step coverage for filling pixel separation trenches. This segmentation allows each film to be optimized for its specific function, resolving the contradiction between performance and complexity.
Solution Approach 2:
The pixel separation pattern uses a composite structure of two different conductive materials with complementary properties. Aluminum provides high reflectance (70-90% in visible range) for preventing crosstalk, while Copper provides superior electrical conductivity and step coverage. The composite design achieves both high reliability and functional optimization without excessive complexity.
2Object-affected harmful factors
If high reflectance material is used, then crosstalk is reduced, but step coverage in trenches may be insufficient
Solution Approach 1:
The function of pixel separation is segmented into two tasks: the first conductive film (Aluminum) is dedicated to optical reflection for crosstalk prevention, while the second conductive film (Copper) is dedicated to providing continuous electrical pathways and filling trenches with excellent step coverage. This functional segmentation resolves the contradiction between optical performance and manufacturing precision.
Solution Approach 2:
The first conductive film acts as an intermediary layer between the substrate and the second conductive film. It provides the reflective function while allowing the second conductive film to conformally coat the trench walls and bottom, achieving both high reflectance and excellent step coverage through the intermediary structure.
3Manufacturing precision
If high step coverage material is used, then trench filling is improved, but reflectance for wavelength-specific performance decreases
Solution Approach 1:
The conductive films are segmented by function: the second conductive film (Copper) is optimized for step coverage and electrical conductivity, while the first conductive film (Aluminum) is optimized for optical reflectance in the visible wavelength range (70-90%). This segmentation allows each material to excel at its primary function without compromise.
Solution Approach 2:
The composite structure combines Copper's superior step coverage and electrical conductivity with Aluminum's high optical reflectance. The first conductive film layer provides the reflective barrier for wavelength-specific performance, while the second conductive film ensures complete trench filling and continuous electrical pathways, achieving both manufacturing precision and optical performance.
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 configuration improves crosstalk prevention and dark current characteristics, leading to a more reliable image sensor with improved light reception and signal processing.
Implementation Method 1
the first conductive film has a greater reflectance than the second conductive film for a predetermined wavelength range
Implementation Method 2
An image sensor is a type of semiconductor device that converts optical information into electrical signals
Data Source
AI summary
An image sensor includes a substrate having a first surface and a second surface opposing to the first surface, first pixel separation patterns defining a plurality of unit pixels, which include photoelectric conversion regions in the substrate, each of the first pixel separation patterns including a first conductive film and a second conductive film on the first conductive film, and microlenses on the second surface of the substrate, wherein the first conductive film extends along sidewalls of the second conductive film to separate the second conductive film from the substrate, the first conductive film has a greater reflectance than the second conductive film for a predetermined wavelength range, and the second conductive film has a greater step coverage than the first conductive film.