Image Sensor Reflection Component for Dense Pixel Quantum Efficiency
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Solution Overview
Problem
As semiconductor image sensors shrink and pixels become more densely spaced, the amount of light incident on each pixel decreases, leading to reduced quantum efficiency (QE) and image quality, necessitating a solution to enhance photon detection without compromising image quality.
Innovation Solution
Incorporating a reflection component with a low refractive index material, such as an air gap or alternating layers of silicon nitride, on the opposite side of the light sensing element to redirect incident light back towards the pixel, increasing the quantum efficiency by leveraging the refractive index difference between materials.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If pixels are densely spaced to increase resolution, then device integration is improved, but quantum efficiency deteriorates due to reduced incident light
Solution Approach 1:
The patent converts the harmful effect of light loss at the substrate interface into a beneficial reflection by introducing a reflection component. The low refractive index material (air gap or low-k dielectric) creates total internal reflection, turning the previously wasted light into useful photons that re-enter the photodiode and contribute to electron generation, thereby maintaining quantum efficiency despite dense pixel spacing
Solution Approach 2:
The patent adds a vertical dimension to light management by placing a reflection component at the bottom interface of the substrate. Instead of only considering horizontal light paths, the solution utilizes the vertical interface between substrate and low-k material to reflect light back upward into the photodiode, effectively adding a third dimension (depth) to the optical path and increasing light utilization without increasing pixel area
2Reliability
If a reflection component is added to increase quantum efficiency, then light detection is improved, but device complexity increases
Solution Approach 1:
The patent changes the refractive index parameter at the substrate interface by introducing a low-k dielectric material or air gap. This parameter change (from high refractive index substrate to low refractive index material) automatically creates the reflection effect through physics principles, eliminating the need for complex reflective coatings or additional optical components while achieving the desired light reflection and quantum efficiency improvement
3Area of stationary object
If incident light area is reduced to increase pixel density, then device integration is improved, but light detection capability deteriorates
Solution Approach 1:
The patent creates a continuous light utilization path by reflecting light that would otherwise be lost at the substrate interface back into the photodiode. This continuous action ensures that photons which initially passed through the pixel are given a second chance to be detected, effectively extending the useful action of incident light and compensating for the reduced pixel area without requiring larger pixels
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 reflection component effectively increases the quantum efficiency of the semiconductor image sensor, improving image quality by enhancing electron generation and offsetting the reduction in light incidence, particularly in pixels detecting green light, which is most visible to the human eye.
Implementation Method 1
Incorporating a reflection component with a low refractive index material, such as an air gap or alternating layers of silicon nitride, on the opposite side of the light sensing element to redirect incident light back towards the pixel, increasing the quantum efficiency by leveraging the refractive index difference between materials.
Implementation Method 2
The reflection component effectively increases the quantum efficiency of the semiconductor image sensor, improving image quality by enhancing electron generation
Data Source
AI summary
A method of making a semiconductor image sensor includes forming a photodiode in a substrate. The method further includes forming a recess in the substrate. The method further includes depositing a sacrificial material in the recess. The method further includes forming an interconnect structure over the sacrificial material. The method further includes etching a plurality of trenches in the interconnect structure. The method further includes removing the sacrificial material by passing an etchant through the plurality of trenches.