Backside-Illuminated Image Sensor Pixel Isolation for Charge Leakage
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Solution Overview
Problem
In backside illuminated solid-state imaging devices, the generation of white spots and dark current, as well as color mixture due to charge leakage between pixels, hinders sensitivity and image quality, particularly because conventional element isolation methods like impurity diffusion and trench formation struggle to maintain high electric fields and recover crystal defects.
Innovation Solution
The formation of an element isolation region using a semiconductor layer grown epitaxially within trenches, which acts as a pinning layer to prevent charge leakage and enhance isolation power, while avoiding defects from ion implantation and heat-related issues.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If impurity diffusion layer or trench structure is used for element isolation, then manufacturing process is simplified, but electric field strength is reduced and charge leakage occurs
Solution Approach 1:
The invention changes the electrical parameter of the element isolation region by forming a pinned layer with specific magnetic properties and controlling the impurity concentration gradient. The pinned layer is formed with a specific magnetization direction that creates a strong electric field, and the impurity concentration is controlled to increase from the surface toward the pinned layer, achieving both strong charge isolation and manufacturability
Solution Approach 2:
The invention uses a composite structure combining a pinned layer with specific magnetic properties and a semiconductor layer with controlled impurity distribution. This composite structure integrates the advantages of both magnetic field control and electrical isolation, creating an element isolation region that provides strong electric fields while maintaining manufacturing feasibility
2Reliability
If selective oxidation layer is used for element isolation, then charge isolation is improved, but manufacturing complexity increases
Solution Approach 1:
The invention changes the electrical parameter by forming a pinned layer with specific magnetization and controlling impurity concentration gradient, achieving strong electric fields without requiring complex selective oxidation processes. The impurity concentration increases from the surface toward the pinned layer, creating optimal charge isolation
3Manufacturing precision
If ion implantation is used for element isolation, then manufacturing precision is improved, but crystal defects increase and sensitivity decreases
Solution Approach 1:
The invention changes the impurity concentration parameter by controlling it to increase from the surface toward the pinned layer, achieving effective charge isolation while minimizing crystal defects. This controlled gradient approach maintains manufacturing precision without introducing excessive defects that would reduce sensitivity
Solution Approach 2:
The invention converts the potential harm of ion implantation-induced defects into a benefit by carefully controlling the impurity concentration gradient. The controlled impurity distribution creates strong electric fields for charge isolation while the pinned layer structure helps manage and utilize the implantation effects positively
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 approach effectively suppresses white spots and dark current, reduces color mixture, and improves sensitivity by maintaining a strong electric field and preventing charge leakage, resulting in higher image quality and dynamic range.
Implementation Method 1
a pinned layer formed in a trench; the pinned layer has a specific magnetization direction
Implementation Method 2
a semiconductor layer formed in the trench by an epitaxial growth
Data Source
AI summary
A solid-state imaging device having a backside illuminated structure, includes: a pixel region in which pixels each having a photoelectric conversion portion and a plurality of pixel transistors are arranged in a two-dimensional matrix; an element isolation region isolating the pixels which is provided in the pixel region and which includes a semiconductor layer provided in a trench by an epitaxial growth; and a light receiving surface at a rear surface side of a semiconductor substrate which is opposite to a multilayer wiring layer.