Doped Pixel Isolation Structure for Dark Current Control in Image Sensors
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Solution Overview
Problem
Current image sensors face challenges in achieving improved electrical and optical performance characteristics, particularly in reducing power consumption and dark current issues, which affect their efficiency and resolution in portable devices.
Innovation Solution
The design incorporates a semiconductor substrate with a pixel isolation structure that includes a semiconductor pattern vertically penetrating the substrate, a sidewall insulating pattern, and a dopant region with varying dopant concentrations, along with a contact plug connected to the dopant region, to enhance photoelectric conversion and reduce dark current.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If conventional pixel isolation structures are used, then manufacturing is simpler, but dark current increases and electrical performance deteriorates
Solution Approach 1:
The pixel isolation structure is segmented into multiple functional regions: a first pixel isolation layer for basic isolation, a semiconductor pattern with dopant regions for electrical control, and a second pixel isolation layer for additional isolation. This segmentation allows each layer to perform its specific function optimally, reducing dark current while maintaining manufacturability.
Solution Approach 2:
Dopant regions are selectively formed in specific areas of the semiconductor pattern, creating local variations in electrical properties. The dopant concentration varies spatially to optimize charge carrier control at critical interfaces, thereby reducing dark current without requiring complete restructuring of the entire pixel isolation system.
2Reliability
If higher dopant concentration is used throughout, then electrical conductivity improves, but dark current increases due to thermal generation
Solution Approach 1:
The dopant concentration is optimized locally rather than uniformly. High dopant concentration is applied in regions requiring good electrical conductivity (such as contact regions and charge transfer paths), while lower concentration is maintained in regions where thermal generation would produce excessive dark current. This spatially varying dopant profile achieves both electrical performance and dark current reduction.
Solution Approach 2:
The dopant concentration parameter is changed across different regions of the semiconductor pattern. By controlling the doping level as a variable parameter rather than a fixed value, the structure achieves optimal electrical conductivity where needed while minimizing thermal generation and dark current in other regions.
3Reliability
If pixel isolation structure is added, then dark current reduces, but manufacturing complexity and process steps increase
Solution Approach 1:
The pixel isolation structure is merged with the semiconductor pattern formation process. The semiconductor pattern that would otherwise be a separate component is integrated with the pixel isolation layers, allowing simultaneous formation of both structures through coordinated processing steps. This reduces the total number of discrete manufacturing operations.
Solution Approach 2:
The first pixel isolation layer and semiconductor pattern are formed preliminarily before final device assembly. By preparing these structures in advance with pre-configured dopant regions, subsequent processing steps are simplified, and the overall manufacturing complexity is reduced despite the enhanced functional capability.
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 improves the electrical and optical performance of image sensors by reducing dark current and power consumption, leading to better signal transfer speed and reduced differences in dark current characteristics between central and edge regions, thus enhancing overall sensor performance.
Implementation Method 1
a dopant region in at least a portion of the semiconductor pattern... a dopant concentration in the upper region may be greater than a dopant concentration in the lower region
Implementation Method 2
photoelectric conversion regions of second conductivity type respectively provided in the pixel regions
Data Source
AI summary
An image sensor includes a semiconductor substrate of first conductivity type having first and second surfaces and including pixel regions, photoelectric conversion regions of second conductivity type respectively provided in the pixel regions, and a pixel isolation structure disposed in the semiconductor substrate to define the pixel regions and surrounding each of the photoelectric conversion regions. The pixel isolation structure includes a semiconductor pattern extending from the first surface to the second surface of the semiconductor substrate, a sidewall insulating pattern between a sidewall of the semiconductor pattern and the semiconductor substrate, and a dopant region in at least a portion of the semiconductor pattern.