Solid-State Image Sensor Isolation Structure for Stable Phase Detection
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Solution Overview
Problem
Conventional solid-state imaging devices face issues with maintaining signal linearity and phase difference detection due to variations in sensitivity and light amount between photoelectric conversion elements, especially when pixel size is miniaturized, leading to potential barrier height changes and isolation region modulation.
Innovation Solution
A solid-state imaging device with a semiconductor layer containing photoelectric conversion units, isolation portions, and transfer transistors that form distinct potential barriers, using insulating materials and impurity-implanted semiconductor regions to control signal flow and maintain signal range for phase difference detection.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Area of moving object
If the pixel size is miniaturized, then the integration density is improved, but the isolation region distance to transfer gate decreases causing potential barrier height changes
Solution Approach 1:
The isolation portion is divided into two distinct regions: a first region extending from the element formation surface with insulating material, and a second region on the light incidence surface side with implanted impurities. This segmentation allows each region to contribute differently to the potential barrier, enabling stable barrier height control even in miniaturized pixels where the isolation region is close to the transfer gate.
Solution Approach 2:
Different regions of the isolation portion are given different properties: the first region uses insulating material to provide baseline isolation, while the second region uses impurity implantation to create a localized potential barrier. This local quality differentiation ensures that the potential barrier height remains stable and controllable despite the reduced distance to the transfer gate in miniaturized pixels.
2Manufacturing precision
If the potential barrier height between photodiodes is reduced to maintain signal linearity, then the signal range for addition is improved, but the signal range for phase difference detection is narrowed
Solution Approach 1:
The potential barrier height is precisely controlled by adjusting the impurity concentration and depth in the second region of the isolation portion. By optimizing these parameters, the barrier height is set to a level that simultaneously maintains signal linearity for addition operations and preserves sufficient signal range for phase difference detection, resolving the trade-off between these two requirements.
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
The solution effectively suppresses signal range narrowing, ensuring accurate phase difference detection and maintaining signal linearity by controlling potential barriers and isolating photoelectric conversion elements, even in miniaturized pixels.
Implementation Method 1
an isolation portion provided between the first photoelectric conversion portion and the second photoelectric conversion portion and capable of forming a first potential barrier
Implementation Method 2
a first transfer transistor capable of transferring a signal charge from the first photoelectric conversion portion to the charge accumulation region and forming a second potential barrier higher than the first potential barrier when the signal charge is not transferred
Implementation Method 3
the isolation portion includes a first region formed by an insulating material extending in a thickness direction of the semiconductor layer from the element formation surface side, and a second region provided on the light incidence surface side of the first region and formed by a semiconductor region into which impurities exhibiting a first conductivity type are implanted
Data Source
AI summary
A solid-state imaging device as disclosed includes a semiconductor layer having a light incidence surface and an element formation surface. The semiconductor layer includes a plurality of photoelectric conversion units including a first photoelectric conversion portion, a second photoelectric conversion portion, an isolation portion, a charge accumulation region, a first transfer transistor capable of transferring a signal charge from the first photoelectric conversion portion to the charge accumulation region, and a second transfer transistor capable of transferring a signal charge from the second photoelectric conversion portion to the charge accumulation region. The isolation portion includes a first region formed by an insulating material extending in a thickness direction of the semiconductor layer from the element formation surface side, and a second region provided on the light incidence surface side of the first region and formed by a semiconductor region into which impurities exhibiting a first conductivity type are implanted.