Image Sensor Metal Grid Layout for Higher Quantum Efficiency
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Solution Overview
Problem
The existing metal grid structures in image sensors reflect incident light away from photodetectors due to remnants of the metal grid layer at intersection points, reducing the quantum efficiency (QE) of photodetectors and overall image sensor performance.
Innovation Solution
A method is developed to form a metal grid structure with elongated grid segments intersecting at right angles, preventing remnants of the metal grid layer from extending between adjacent segments, thereby minimizing light reflection and enhancing QE. This is achieved by etching the metal grid structure using a masking layer and elongated masking segments to define rectangular grid openings that directly overlay photodetectors.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a metal grid structure is formed over photodetectors, then electrical connectivity and signal transmission are improved, but light reflection increases and quantum efficiency decreases
Solution Approach 1:
The metal grid structure is divided into discrete grid segments that are separated by grid openings. Each grid segment is independently positioned over photodetector regions, allowing light to pass through the openings to the photodetectors while the segments provide electrical connectivity. This segmentation reduces continuous metal coverage that would otherwise reflect light, thereby improving quantum efficiency while maintaining electrical functionality.
Solution Approach 2:
The metal grid structure implements different properties in different regions: grid segments provide electrical connectivity where needed, while grid openings allow light transmission where photodetectors are located. The structure transitions from a uniform metal layer to a patterned configuration with varying metal density, creating local quality variations that simultaneously satisfy electrical and optical requirements.
2Ease of manufacture
If metal grid layer remnants are present at intersection points, then manufacturing simplicity is maintained, but light reflection increases and quantum efficiency decreases
Solution Approach 1:
Metal grid layer remnants at intersection points are completely removed through selective etching processes. The intersection regions are specifically targeted to eliminate metal material that would otherwise reflect light, while the remaining grid segments maintain their electrical connectivity function. This extraction of harmful metal remnants resolves the contradiction by prioritizing optical performance in critical light-path regions.
Solution Approach 2:
Instead of accepting metal remnants as an inevitable byproduct of grid formation, the approach inverts the logic by deliberately designing the grid structure to prevent remnant formation. The grid segments are formed with spacing and geometry that prevents metal layer continuity at intersections, and etching processes are optimized to completely remove any potential remnants, transforming the problem from acceptance to prevention.
3Loss of energy
If grid openings are made larger to improve light transmission, then quantum efficiency increases, but electrical connectivity between grid segments deteriorates
Solution Approach 1:
The dimensions of grid openings and grid segments are optimized to specific parameter ranges that balance optical and electrical requirements. Grid opening size, segment width, segment spacing, and segment length are all controlled within defined parameters to ensure sufficient light transmission while maintaining adequate electrical conductivity. These parameter changes allow the structure to operate in an optimal performance window.
Solution Approach 2:
The metal grid structure functions as a composite system combining conductive metal segments with transparent or low-reflection regions (grid openings). This composite configuration allows different portions of the structure to serve different functions: metal segments provide electrical connectivity while openings provide optical transmission paths, achieving a synergistic effect that neither component could accomplish alone.
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
The improved metal grid structure increases the quantum efficiency of photodetectors by reducing light reflection, thereby enhancing the performance of image sensors.
Implementation Method 1
existing metal grid structures in image sensors reflect incident light away from photodetectors
Implementation Method 2
pixel sensors, which are unit devices for the conversion of an optical image into digital data
Data Source
AI summary
Various embodiments of the present disclosure are directed towards an image sensor. The image sensor comprises a plurality of photodetectors disposed within a substrate. A metal grid layer is disposed over the substrate. The metal grid layer comprises a metal grid structure overlying a central pixel region of the substrate. The metal grid layer continuously extends from the central pixel region to a peripheral pixel region of the substrate that laterally encloses the central pixel region. An upper metal structure is disposed over the metal grid layer. The upper metal structure overlies the peripheral pixel region. The upper metal structure is laterally offset from the metal grid structure. A lower surface of the upper metal structure is disposed vertically over an upper surface of the metal grid structure.