Pixel Isolation Structure With Air Gap for Low-Dark-Current Image Sensors
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Solution Overview
Problem
Current image sensors face challenges in improving photosensitivity and minimizing dark current, while also requiring enhanced manufacturing yield and durability.
Innovation Solution
The image sensor design incorporates a pixel isolation portion with a filling insulation pattern, conductive structure, and insulating liner, featuring an air gap region and a fixed charge layer to reduce crosstalk and dark current, and includes a method of manufacturing that stabilizes these features without process defects.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a conventional pixel isolation structure is used, then manufacturing is simpler, but photosensitivity is reduced and dark current increases
Solution Approach 1:
The pixel isolation structure is segmented into multiple functional layers: filling insulation pattern, air gap region, conductive structure, and insulating liner. Each layer performs a specific function to collectively improve photosensitivity by reducing crosstalk and minimizing dark current through systematic division of isolation functions.
Solution Approach 2:
The pixel isolation structure uses composite materials including filling insulation material, air gap (vacuum), conductive material, and insulating liner material. This composite approach creates a multi-functional isolation structure that simultaneously achieves electrical isolation, mechanical support, and optical performance enhancement.
2Object-generated harmful factors
If pixel isolation is enhanced to reduce dark current, then dark current decreases, but manufacturing precision requirements increase
Solution Approach 1:
The insulating liner is formed beforehand on the substrate before creating the air gap region. This pre-formed protective layer cushions the substrate during subsequent manufacturing steps, preventing damage and reducing the precision requirements for later processes while ensuring effective isolation to minimize dark current.
Solution Approach 2:
The air gap region acts as an intermediary between the filling insulation pattern and the substrate, providing a buffer zone that reduces stress transmission and facilitates manufacturing. This intermediate structure enables effective pixel isolation with relaxed precision requirements compared to direct contact isolation methods.
3Reliability
If deep trenches are formed for pixel isolation, then isolation effectiveness improves, but substrate cracks may occur reducing yield
Solution Approach 1:
The insulating liner is deposited on the substrate before forming deep trenches for pixel isolation. This pre-formed cushioning layer prevents substrate cracks during trench formation and filling processes, maintaining high manufacturing yield while achieving effective pixel isolation.
Solution Approach 2:
The filling insulation pattern is formed with controlled density parameters to create an air gap region with specific void fraction. By optimizing the density and composition of the filling material, the structure achieves effective isolation while reducing stress concentration that could cause substrate cracks.
4Measurement precision
If air gap region is introduced to improve MTF, then modulation transfer function improves, but device complexity increases
Solution Approach 1:
The air gap region serves multiple functions simultaneously: it acts as an optical element to improve modulation transfer function, provides mechanical support to prevent substrate deformation, and contributes to electrical isolation. This multi-functionality achieves MTF enhancement without proportionally increasing device complexity.
Solution Approach 2:
The air gap region is nested within the filling insulation pattern, creating a hierarchical structure where the air gap is contained within the larger insulation framework. This nested arrangement achieves optical performance improvement while maintaining a compact overall structure that doesn't excessively increase device complexity.
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 design enhances photosensitivity, minimizes dark current, and improves manufacturing yield by preventing substrate cracks and maintaining modulation transfer function (MTF) characteristics, thereby increasing the durability and performance of the image sensor.
Implementation Method 1
The photodiode may convert incident light into an electrical signal
Implementation Method 2
having an air gap region... configured to reduce crosstalk
Implementation Method 3
a fixed charge layer contacting the second surface
Data Source
AI summary
An image sensor includes a substrate including a first surface and a second surface which is opposite to the first portion, and a pixel isolation portion provided in the substrate and configured to isolate unit pixels from each other. The pixel isolation portion includes a first filling insulation pattern extending from the first surface toward the second surface and having an air gap region, the first filling insulation pattern including a first sidewall and a second sidewall which is opposite to the first sidewall, a conductive structure including a first portion on the first sidewall, a second portion on the second sidewall, and a connection portion connecting the first portion and the second portion, and an insulating liner provided between the first portion and the substrate and between the second portion and the substrate.