Photoelectric Conversion Pixel Isolation Using Heavy Ion Implantation
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Solution Overview
Problem
Photoelectric conversion apparatuses face challenges in miniaturization and multifunctionality due to carrier isolation issues, leading to reduced sensitivity, saturation, and resolution, as existing isolation structures can cause charge movement beyond acceptable limits between photodiodes.
Innovation Solution
A photoelectric conversion apparatus with a semiconductor layer structure that includes a first and second photoelectric conversion region, separated by an intra-pixel isolation region containing an impurity element with a mass number twice that of the main constituent element, which helps maintain isolation performance while allowing for miniaturization by forming a narrow and deep impurity profile using ion implantation and local thermal treatment.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Volume of moving object
If an isolation region higher in impurity concentration than a well is formed for carrier isolation into photodiodes, then pixel miniaturization is enabled, but sensitivity and saturation deteriorate due to charge movement beyond allowable values
Solution Approach 1:
The patent applies local quality by creating distinct impurity concentration zones within the pixel structure. Specifically, it forms a first impurity region with a first impurity concentration and a second impurity region with a second impurity concentration, where the impurity concentrations are differentiated locally to achieve both miniaturization and proper charge isolation. This local differentiation allows the isolation structure to serve multiple functions without compromising sensitivity or saturation.
2Area of moving object
If the isolation structure between photodiodes is made narrower for miniaturization, then pixel density increases, but charge movement between photodiodes increases causing resolution loss
Solution Approach 1:
The patent employs parameter changes by varying the impurity concentration parameter across different regions. It establishes a first impurity concentration for the first impurity region and a second impurity concentration for the second impurity region, where these concentration parameters are specifically tuned to maintain charge confinement accuracy even when the isolation structure dimensions are reduced for miniaturization.
3Reliability
If impurity concentration is increased for better carrier isolation, then charge isolation performance improves, but dark current increases due to saturation charge management issues
Solution Approach 1:
The patent applies local quality by creating differentiated impurity regions where the first impurity region and second impurity region have different impurity concentrations. This local differentiation allows effective carrier isolation in specific areas while managing saturation charge in other areas, thereby preventing excessive dark current generation that would result from uniformly high impurity concentration throughout the structure.
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 enables effective charge isolation and saturation charge management, enhancing the apparatus's miniaturization capabilities while reducing dark current and maintaining high isolation performance, even with reduced pixel size.
Implementation Method 1
forming a narrow and deep impurity profile using ion implantation and local thermal treatment
Implementation Method 2
a first photoelectric conversion region and a second photoelectric conversion region
Data Source
AI summary
A photoelectric conversion apparatus includes a plurality of pixels. Each of the plurality of pixels includes a first photoelectric conversion region and a second photoelectric conversion region. A first semiconductor region is disposed between the first photoelectric conversion region and the second photoelectric conversion region. The first photoelectric conversion region and the second photoelectric conversion region contain a first element mainly forming the first photoelectric conversion region and the second photoelectric conversion region, and the first photoelectric conversion region and the second photoelectric conversion region contain a second element. The first semiconductor region contains the first element and a third element. A mass number of the third element is twice or more a mass number of the first element.