Back-Illuminated Photoelectric Conversion Layout for Flare Reduction
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Solution Overview
Problem
Conventional back-illuminated imaging devices suffer from significant reflected light due to the thin silicon layer used for photodiodes, leading to flare and degraded image quality as incident light not absorbed by the semiconductor substrate is reflected into the device.
Innovation Solution
Incorporating an on-chip lens to condense incident light, a front-surface-side reflective film to reflect transmitted light, and a back-surface-side reflective film with an opening matching the condensed light's size to reflect and redirect reflected light, along with scattering portions to manage and scatter light effectively.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a thin silicon layer is used as the semiconductor substrate to enable back-illuminated imaging, then sensitivity is improved and manufacturing yield increases, but reflected light increases causing flare and degraded image quality
Solution Approach 1:
The patent converts the harmful reflected light into a beneficial effect by introducing a reflective film on the back surface that redirects the reflected light back into the semiconductor substrate. This causes the light to undergo multiple reflections between the front and back surfaces, increasing the probability of photoelectric conversion and improving sensitivity while eliminating the harmful flare effect.
Solution Approach 2:
The patent implements a nested structure where the reflective film is positioned within the back surface region of the semiconductor substrate, and the light path is nested with multiple reflections between front and back surfaces. This nested arrangement allows the reflected light to be trapped and reused within the substrate volume, converting waste light into useful photoelectric conversion opportunities.
2Reliability
If incident light is emitted onto the back surface without passing through front surface wiring, then sensitivity is improved, but reflected light from the thin substrate increases causing flare
Solution Approach 1:
The patent converts the harmful reflected light that causes flare into a beneficial effect by using the reflective film to redirect it back into the substrate. This transforms the flare-causing reflected light into additional photoelectric conversion opportunities, simultaneously maintaining high sensitivity and eliminating flare.
Solution Approach 2:
The reflective film acts as an intermediary element between the back surface and the photoelectric conversion units. It mediates the light path by reflecting transmitted light back into the substrate, preventing direct escape of reflected light that would cause flare, while still allowing useful light to reach the photoelectric conversion units.
3Ease of manufacture
If the semiconductor substrate is thinned to reduce reflected light, then manufacturing complexity is reduced, but image quality degrades due to increased flare
Solution Approach 1:
The patent converts the harmful effect of substrate thinning (increased reflected light and flare) into a benefit by introducing the reflective film. The thin substrate continues to provide manufacturing advantages while the reflective film captures and redirects the previously harmful reflected light, maintaining or even improving image quality despite the reduced substrate thickness.
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 effectively reduces reflected light within the imaging device, enhancing image quality by confining incident light and minimizing flare, thereby improving sensitivity and image clarity.
Implementation Method 1
an on-chip lens that condenses incident light
Implementation Method 2
a front-surface-side reflective film that is disposed on the front surface side of the substrate and reflects transmitted light
Implementation Method 3
a back-surface-side reflective film that is disposed on the back surface side of the substrate... and further reflects the condensed incident light
Implementation Method 4
a photoelectric conversion unit that performs photoelectric conversion on the condensed incident light
Implementation Method 5
a substrate-back-surface scattering portion that is formed in the back surface of the substrate and scatters the condensed incident light
Data Source
AI summary
Reflected light from a back-illuminated photoelectric conversion element is to be reduced. The photoelectric conversion element includes an on-chip lens, a substrate, a front-surface-side reflective film, and a back-surface-side reflective film. The on-chip lens condenses incident light. A photoelectric conversion unit that performs photoelectric conversion on the condensed incident light is disposed in the substrate, and the back surface side of the substrate is irradiated with the condensed incident light. The front-surface-side reflective film is disposed on the front surface side that is a different side from the back surface side of the substrate, and reflects transmitted light that is the incident light having passed through the photoelectric conversion unit. The back-surface-side reflective film is disposed on the back surface side of the substrate, has an opening of substantially the same size as the condensing size of the condensed incident light, and further reflects the reflected transmitted light.