Backside Illumination Image Sensor Grids with High-Reflective Layers
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Solution Overview
Problem
Backside Illumination (BSI) image sensor chips face challenges in minimizing light loss and optical cross-talk to maximize quantum efficiency, as existing technologies struggle to effectively isolate light between image sensors.
Innovation Solution
A grid structure is formed on the backside of the image sensor chip with a chromium adhesion layer, chromium oxide layer, and a high-refractive index layer on top surfaces and sidewalls of metal grid lines, which acts as a high light-reflective layer to reduce light penetration to neighboring grids and enhance light reflection to the active image sensors.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Object-affected harmful factors
If metal grids are formed to isolate light between image sensors, then optical cross-talk is reduced, but light loss increases and quantum efficiency decreases
Solution Approach 1:
The patent applies composite materials by forming a multi-layer structure on the metal grid including a chromium adhesion layer, a chromium oxide layer, and a high-refractive index layer. This composite structure combines materials with different optical properties to achieve both light reflection and minimal absorption, thereby reducing optical cross-talk while minimizing light loss and improving quantum efficiency
Solution Approach 2:
The patent changes the optical parameters by introducing layers with specific refractive indices. The high-refractive index layer (with refractive index greater than 2.0) is specifically designed to reflect light back to the image sensor, changing the light propagation parameters to reduce both cross-talk and light loss simultaneously
2Object-affected harmful factors
If light isolation structures are added to reduce cross-talk, then image sensor isolation improves, but manufacturing complexity increases
Solution Approach 1:
The patent segments the light isolation function into multiple functional layers: a chromium adhesion layer for structural integrity, a chromium oxide layer for intermediate optical properties, and a high-refractive index layer for light reflection. This segmentation allows each layer to perform its specific function efficiently, improving isolation while keeping the overall structure manageable through clear functional division
Solution Approach 2:
The chromium oxide layer acts as an intermediary between the chromium adhesion layer and the high-refractive index layer. This intermediate layer provides a transition in optical properties and ensures proper adhesion between layers, simplifying the overall manufacturing process by providing a systematic approach to layer integration
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 significantly reduces optical cross-talk, increases the signal-to-noise ratio, and improves quantum efficiency by reflecting a great portion of incident light back to the image sensors while minimizing light loss to neighboring grids.
Implementation Method 1
acts as a high light-reflective layer to reduce light penetration to neighboring grids and enhance light reflection to the active image sensors
Implementation Method 2
a high-refractive index layer over the high light-reflective layer, wherein the high light-reflective layer and the high-refractive index layer extend on top surfaces and sidewalls of the grid
Data Source
AI summary
A device includes a semiconductor substrate having a front side and a backside, a photo-sensitive device disposed on the front side of the semiconductor substrate, and a first and a second grid line parallel to each other. The first and the second grid lines are on the backside of, and overlying, the semiconductor substrate. The device further includes an adhesion layer, a metal oxide layer over the adhesion layer, and a high-refractive index layer over the metal layer. The adhesion layer, the metal oxide layer, and the high-refractive index layer are substantially conformal, and extend on top surfaces and sidewalls of the first and the second grid lines.