Micro-lens Structure for Image Sensor Quantum Efficiency
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Solution Overview
Problem
CMOS image sensors face reduced quantum efficiency due to reflection of incident radiation off the flat top surface of passivation layers, leading to cross-talk between photodetectors and decreased absorption of light.
Innovation Solution
Incorporating micro-lenses with convex upper surfaces between protrusions on the substrate, which are etched at a higher rate than the passivation layer, to focus incident radiation towards the photodetectors, thereby reducing reflection and increasing absorption.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If a flat top surface passivation layer is used, then manufacturing is simplified, but quantum efficiency is reduced due to reflection of incident radiation
Solution Approach 1:
The patent applies curvature by forming micro-lenses with convex upper surfaces over the protrusions. These curved micro-lens surfaces refract and focus incident radiation onto the photodetectors, reducing reflection losses while maintaining the simplicity of the flat passivation layer manufacturing process.
2Reliability
If micro-lenses are added to focus radiation, then quantum efficiency increases, but device complexity increases
Solution Approach 1:
The patent merges the micro-lens structure with the existing protrusion formation process. The micro-lenses are formed as part of the same fabrication sequence that creates the protrusions, combining multiple functions into a unified structure that reduces overall device complexity despite adding optical focusing capability.
Solution Approach 2:
The micro-lenses serve multiple functions: they focus incident radiation onto photodetectors, reduce reflection losses, and maintain compatibility with the existing protrusion structure. This multi-functionality increases quantum efficiency without requiring separate additional components.
3Productivity
If etching rate of protrusions is increased, then micro-lens formation is improved, but manufacturing precision may be affected
Solution Approach 1:
The patent applies local quality by using selective etching processes that target specific regions. The protrusions are etched at higher rates in localized areas where micro-lenses are formed, while maintaining precise control over the overall etching process to ensure manufacturing precision is not compromised.
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 enhances quantum efficiency by directing more incident radiation towards the photodetectors, improving the overall performance of the image sensor.
Implementation Method 1
micro-lenses with convex upper surfaces... to focus incident radiation towards the photodetectors
Implementation Method 2
micro-lenses... to focus incident radiation towards the photodetectors, thereby reducing reflection and increasing absorption
Data Source
AI summary
Various embodiments of the present disclosure are directed towards a method for forming an image sensor, the method includes forming a photodetector within a substrate. The substrate is etched to define a plurality of first protrusions over the photodetector. A first dielectric layer is deposited on the substrate. A second dielectric layer is deposited on the first dielectric layer. An etching process is performed on the first and second dielectric layers such that the first dielectric layer comprises a plurality of second protrusions different from the plurality of first protrusions. The first dielectric layer is etched more quickly than the second dielectric layer during the etching process.