Image Sensor Air Gap and Reflection Pattern for Crosstalk Reduction
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Solution Overview
Problem
Image sensors face issues with optical crosstalk due to light reflection and refraction, leading to image distortion and reduced sensitivity, especially as pixel density increases, causing crosstalk and blooming between adjacent pixels.
Innovation Solution
A method for manufacturing a back-illuminated image sensor with a reflection pattern and air gap to redirect light back to the photodiode, reducing crosstalk by forming a trench in the dielectric layer and filling it with oxide to create a light guide, which prevents light from being incident on adjacent pixels.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If the integration density of image sensors is increased to reduce pixel size, then the pixel density and resolution are improved, but optical crosstalk between adjacent pixels increases due to light reflection and refraction
Solution Approach 1:
The patent converts the harmful reflected light that causes crosstalk into a beneficial element by introducing a reflection pattern that deliberately reflects light back to the photodiode. The air gap is designed to reflect tilted light back to the corresponding pixel, transforming what would be crosstalk-inducing reflected light into useful light that enhances the photoelectric conversion efficiency
Solution Approach 2:
The air gap acts as an intermediary structure between the photodiode and the external environment. It serves as both a light guide for incident light and a reflection surface for tilted light, mediating the light path to prevent crosstalk while improving light utilization. The air gap's refractive index difference creates total internal reflection for tilted light, guiding it back to the correct pixel
2Use of energy by moving object
If a reflection pattern is added to improve light utilization, then optical sensitivity is improved, but device complexity increases due to additional manufacturing steps
Solution Approach 1:
The patent merges the formation of the air gap with existing manufacturing processes. The air gap is created by removing dielectric material during standard photolithography and etching steps that are already part of the image sensor fabrication process. The reflection pattern is formed using the same metal deposition and patterning steps used for creating interconnection structures, combining multiple functions into a single integrated structure
Solution Approach 2:
The air gap structure serves multiple functions simultaneously: it acts as a light guide for incident light, a reflection surface for tilted light, and an isolation structure between pixels. The reflection pattern also serves dual purposes by both improving light utilization and defining pixel boundaries, reducing the need for separate structures
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
Improves optical sensitivity and reduces crosstalk by ensuring light is reabsorbed in the photodiode, enhancing image resolution and preventing data mixing between pixels.
Implementation Method 1
the air gap may totally reflect the light and guide the light to a corresponding pixel
Implementation Method 2
a reflection pattern, which may reflect light transmitted through a dielectric layer of an interconnection layer and condense light on a photodiode (PD)
Implementation Method 3
Each of the pixels may include a photodiode (PD) and transistors. A semiconductor layer and the PD disposed on the semiconductor substrate may sense external light and generate photocharges
Data Source
AI summary
In an example embodiment, the method of manufacturing an image sensor includes forming an interlayer dielectric (ILD) on a substrate. The substrate may have a plurality of pixels arranged thereon and each of the pixels includes a photoelectric conversion device configured to sense external light and generate photo charges. Furthermore, the method may include forming a metal on the ILD and removing portions of the metal to form a reflection pattern. Additionally, the method may include removing the ILD to a depth to form a trench adjacent to the reflection pattern and forming an air gap in the trench by forming oxide over the substrate such that the reflection pattern and the upper portion of the trench are covered.