Back-Side Illuminated Image Sensor Embedded Color Filters
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Solution Overview
Problem
Traditional back-side illuminated (BSI) image sensor devices face issues with light cross-talk and optical path length due to the disposition of the color filter array above a light-blocking metal grid, requiring accurate alignment and resulting in suboptimal performance, especially under low light conditions.
Innovation Solution
A unique fabrication process where a conductive bonding pad is formed before the light-blocking structures, allowing color filters to be embedded within the openings defined by the metal grid, reducing cross-talk and aligning them self-aligned with the pixels, thus shortening the optical path and enhancing quantum efficiency.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If the color filter array is disposed above the light-blocking metal grid, then the alignment between color filters and pixels can be achieved, but the optical path length increases and cross-talk between adjacent pixels occurs
Solution Approach 1:
The patent inverts the conventional fabrication sequence by forming the light-blocking metal grid structures first, then creating openings in these grids, and finally forming the color filter arrays within these openings. This reversal of the traditional process allows color filters to be positioned at the same level as the metal grid rather than above it, thereby shortening the optical path length while maintaining precise alignment through the self-aligned fabrication process
2Ease of manufacture
If the color filter array is disposed above the light-blocking metal grid, then the color filters can be formed, but cross-talk between adjacent pixels increases
Solution Approach 1:
The patent implements nesting by forming the color filter arrays within the openings defined by the light-blocking metal grid structures. The color filters are nested inside the metal grid framework, which provides inherent lateral confinement and isolation between adjacent pixels. This nested configuration prevents light from adjacent pixels from reaching unintended photodetectors, thereby reducing cross-talk while maintaining ease of manufacture through integrated fabrication steps
3Ease of manufacture
If the color filter array is disposed above the light-blocking metal grid, then the structure can be fabricated, but the optical sensitivity and quantum efficiency decrease
Solution Approach 1:
The patent inverts the conventional fabrication sequence by forming the light-blocking metal grid structures first, then creating openings in these grids, and finally forming the color filter arrays within these openings. This reversal of the traditional process allows color filters to be positioned at the same level as the metal grid rather than above it, thereby shortening the optical path length while maintaining precise alignment through the self-aligned fabrication process
Solution Approach 2:
The patent transitions from a vertical stacking arrangement (color filters above metal grid) to a co-planar arrangement (color filters at the same level as metal grid). This dimensional change in the spatial configuration eliminates the vertical offset between color filters and metal grid, reducing the optical path length and improving light collection efficiency, thereby enhancing optical sensitivity and quantum efficiency
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 cross-talk, improves optical sensitivity, and enhances quantum efficiency by embedding color filters within the metal grid openings, eliminating alignment constraints and minimizing optical losses.
Implementation Method 1
These devices utilize an array of pixels (which may include photodiodes and transistors) in a substrate to absorb (i.e., sense) radiation that is projected toward the substrate and convert the sensed radiation into electrical signals
Data Source
AI summary
Disclosed is a method of fabricating a semiconductor image sensor device. The method includes providing a substrate having a pixel region, a periphery region, and a bonding pad region. The substrate further has a first side and a second side opposite the first side. The pixel region contains radiation-sensing regions. The method further includes forming a bonding pad in the bonding pad region; and forming light-blocking structures over the second side of the substrate, at least in the pixel region, after the bonding pad has been formed.