Back Side Illumination Image Sensor Reflective Element
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Solution Overview
Problem
Back side illumination (BSI) image sensors face performance issues due to long-wavelength light passing through the photodiode layer without absorption, leading to unsatisfactory image quality.
Innovation Solution
A reflective element with a U-shaped profile is integrated into the dielectric layer under the photodiode layer, utilizing a top-flat pyramid structure formed through multiple etching operations with photoresist trimming, to collect and reflect back light that is not absorbed by the photodiode layer, enhancing light absorption and electron signal conversion.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If a conventional BSI image sensor structure is used, then manufacturing cost and integration are improved, but light absorption efficiency deteriorates due to long-wavelength light passing through the photodiode layer
Solution Approach 1:
The patent converts the harmful effect of long-wavelength light passing through the photodiode layer (which causes energy loss) into a beneficial effect by introducing a reflective element that redirects this light back to the photodiode layer for absorption. The reflective element transforms the wasted light into useful photons that can generate additional electron-hole pairs, thereby improving quantum efficiency without changing the fundamental BSI structure
Solution Approach 2:
The patent introduces a vertical dimension to light management by adding a reflective element beneath the photodiode layer. This creates a light recycling path in the vertical direction, allowing light that would otherwise escape through the substrate to be reflected back upward, effectively increasing the optical path length and absorption probability without expanding the horizontal pixel area
2Manufacturing precision
If the photodiode layer is made thinner to reduce manufacturing complexity, then manufacturing precision is improved, but light absorption capability deteriorates
Solution Approach 1:
The reflective element captures light that would otherwise be lost due to the thin photodiode layer's limited absorption capacity, converting this potential loss into additional absorption opportunities by reflecting light back through the photodiode material
Solution Approach 2:
The reflective element enables continuous light absorption by creating a recycling mechanism where unabsorbed light is redirected back to the photodiode layer, allowing multiple passes of light through the thin photodiode material until absorption occurs, thereby maintaining high absorption efficiency despite reduced layer 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 improves light absorption and electron signal conversion, resulting in brighter and more vivid images by effectively recycling light, thereby enhancing the image sensor's sensitivity and performance.
Implementation Method 1
a reflective element is disposed in a dielectric layer under the photodiode layer, and the reflective element is configured to collect the light that cannot be absorbed by the photodiode layer in time and reflect the light back toward the photodiode layer
Implementation Method 2
a reflective element is disposed in a dielectric layer under the photodiode layer, and the reflective element is configured to collect the light that cannot be absorbed by the photodiode layer in time and reflect the light back toward the photodiode layer to improve the absorption of the light and further improve the conversion of an electron signal from the photon
Data Source
AI summary
A back side illumination (BSI) image sensor is provided. The BSI image sensor includes a semiconductor substrate, a first dielectric layer, a reflective element, a second dielectric layer and a color filter layer. The semiconductor substrate has a front side and a back side. The first dielectric layer is disposed on the front side of the semiconductor substrate. The reflective element is disposed on the first dielectric layer, in which the reflective element has an inner sidewall contacting the first dielectric layer, and the inner sidewall has a zigzag profile. The second dielectric layer is disposed on the first dielectric layer and the reflective element. The color filter layer is disposed on the backside of the semiconductor substrate.