Pixel Semiconductor Layout for Charge Transfer and Leakage Control
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Solution Overview
Problem
In photoelectric conversion apparatuses with a depletion layer stopping layer and image plane phase difference autofocus function, signal electric charge leakage between pixels occurs due to potential barriers, leading to image quality deterioration.
Innovation Solution
The apparatus includes a pixel structure with a semiconductor region having a lower impurity concentration in the in-pixel separation portion compared to the depletion layer stopping region, facilitating electric charge transfer and reducing potential barriers between the semiconductor region and charge accumulation region.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Quantity of substance
If a depletion layer stopping layer is introduced to suppress depletion layer expansion and increase saturation charge amount, then saturation charge amount is improved, but potential barrier formation disrupts electric charge transfer and causes signal leakage into adjacent pixels
Solution Approach 1:
The patent applies local quality by creating a fourth semiconductor region with specifically controlled impurity concentration between the in-pixel separation portion and charge accumulation region. This region has a lower concentration of second conductivity type impurities compared to the in-pixel separation portion, locally modifying the electrical properties to reduce potential barriers and facilitate charge transfer while maintaining pixel isolation where needed.
Solution Approach 2:
The patent changes the impurity concentration parameter in the fourth semiconductor region to resolve the contradiction. By setting the concentration of second conductivity type impurities in the fourth semiconductor region to be lower than in the in-pixel separation portion, the potential barrier is reduced, enabling proper electric charge transfer from the photoelectric conversion region to the charge accumulation region while preventing signal leakage.
2Reliability
If in-pixel separation portion with high impurity concentration is used to isolate pixels, then pixel isolation is improved, but electric charge transfer from photoelectric conversion region is disrupted
Solution Approach 1:
The patent creates different local regions with different impurity concentrations: the in-pixel separation portion maintains high impurity concentration for pixel isolation, while the fourth semiconductor region between it and the charge accumulation region has lower impurity concentration to facilitate charge transfer. This spatial variation in material properties resolves the contradiction between isolation and transfer efficiency.
Solution Approach 2:
The patent segments the semiconductor structure into distinct regions with different impurity concentrations. The fourth semiconductor region is specifically positioned between the in-pixel separation portion and charge accumulation region, creating a gradient structure that allows different functions (isolation vs. transfer) to coexist in adjacent zones.
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 enhances image quality by minimizing signal leakage and maintaining the image plane phase difference autofocus function, particularly in back surface incident type photoelectric conversion systems.
Implementation Method 1
a semiconductor region, which is located below the depletion layer stopping layer and in which photoelectric conversion is performed
Implementation Method 2
electric charge transfer from a semiconductor region, which is located below the depletion layer stopping layer and in which photoelectric conversion is performed, to the charge accumulation region
Implementation Method 3
there is a potential barrier between the depletion layer stopping layer and the charge accumulation region
Data Source
AI summary
An apparatus includes pixels each including a conversion unit. The conversion unit includes a first semiconductor region of a first conductivity type, a second semiconductor region of a second conductivity type, and a third semiconductor region of the first conductivity type in order from a light incident surface side, and includes an in-pixel separation portion of the second conductivity type. The second semiconductor region includes a first end and a second end opposing the first end. The conversion unit further includes a fourth semiconductor region between the first and second ends. The in-pixel separation portion separates the first semiconductor region into a first region overlapping the first end and a second region overlapping the second end in a top view from the light incident surface side. A concentration of a second conductivity type impurity is lower in the fourth semiconductor region than in the in-pixel separation portion.