BSI Image Sensor Pixel Isolation for Crosstalk and Dark Current
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Solution Overview
Problem
Existing image sensors face challenges in achieving improved light-receiving efficiency and preventing crosstalk between pixels, particularly in backside illumination (BSI) configurations, where isolation films formed on the rear side of the substrate may not be sufficiently deep, leading to dark current issues and blooming phenomena.
Innovation Solution
The image sensor design incorporates isolation films with a lower refractive index, formed on the front side of the substrate, which taper from the light-receiving surface to the rear, effectively defining pixels and reducing crosstalk, while also simplifying the fabrication process by forming these films at the same level as other isolation films.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Use of energy by moving object
If isolation films are formed on the rear side of the substrate in BSI configuration, then light-receiving efficiency is improved, but isolation films may not be sufficiently deep leading to dark current issues and blooming phenomena
Solution Approach 1:
The patent transitions from forming isolation films only on the rear side (single dimension) to forming isolation films on both the front side and rear side of the substrate (multiple dimensions). The front side isolation films extend from the light-receiving surface toward the rear side, creating a multi-dimensional isolation structure that effectively blocks dark current and prevents blooming while maintaining the BSI light-receiving efficiency
Solution Approach 2:
The isolation structure is segmented into front side isolation films and rear side isolation films that work together. The front side isolation films are formed separately from rear side isolation films, with each serving specific functions: front side films provide deep isolation from the light-receiving surface, while rear side films provide additional isolation depth, collectively solving the dark current and blooming problems
2Use of energy by moving object
If isolation films are formed on the rear side of the substrate, then light sensitivity is improved, but crosstalk between pixels occurs due to insufficient isolation depth
Solution Approach 1:
The patent adds front side isolation films as a new dimensional element to the isolation structure. These films extend downward from the light-receiving surface, creating overlapping isolation zones with rear side films, thereby effectively blocking optical crosstalk between adjacent pixels while preserving light sensitivity
3Reliability
If multiple isolation films are formed at different levels, then pixel isolation is improved, but fabrication process complexity increases
Solution Approach 1:
The patent merges the formation of front side isolation films and rear side isolation films into a coordinated fabrication process. By establishing a systematic approach where front side films are formed first, followed by rear side films with proper alignment and depth control, the process achieves effective pixel isolation without excessive complexity
Solution Approach 2:
The front side isolation films are formed as a preliminary action before forming the rear side isolation films. This sequential approach with proper planning ensures that subsequent rear side film formation aligns correctly, simplifying the overall fabrication process while achieving the desired multi-level isolation structure
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 design enhances light-receiving efficiency, reduces dark current, and minimizes crosstalk, resulting in improved image sensor performance and productivity.
Implementation Method 1
isolation films with a lower refractive index, formed on the front side of the substrate
Data Source
AI summary
An image sensor with improved performance, and a method of fabricating the same are provided. The image sensor includes a sensor array region and a pad region, which is disposed outside the sensor array region, the image sensor comprising a first substrate including a first surface, upon which light is incident, and a second surface, which is opposite to the first surface, a first isolation film in the first substrate at the sensor array region, the first isolation film defining a plurality of unit pixels, a second substrate including a third surface, which faces the second surface of the first substrate, and a fourth surface, which is opposite to the third surface, a wiring structure between the second and third surfaces, the wiring structure including an interlayer insulating film and a wiring in the interlayer insulating film, a pad trench in the pad region, the pad trench exposing the wiring through the first substrate, a bonding terminal in the pad trench, the bonding terminal being connected to the wiring, and a second isolation film in the first substrate at the pad region, the second isolation film being adjacent to the pad trench, wherein widths of each of the first and second isolation films decrease in a direction from the second surface to the first surface.