Resonance Solid-State Imaging Element Near-Infrared Sensitivity
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Solution Overview
Problem
Conventional silicon-based solid-state imaging elements have limited sensitivity to near-infrared light due to physical absorption limitations, and using Silicon on Insulator (SOI) substrates increases manufacturing costs.
Innovation Solution
A resonance type solid-state imaging element is developed using a silicon substrate with a P-type impurity layer of higher concentration, where a recess is formed on the reverse face to enhance light reflection and sensitivity, allowing light to be converted into charges without the need for expensive SOI substrates.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a Silicon on Insulator (SOI) substrate is used to form a recess on the reverse face, then sensitivity to near-infrared light is improved through enhanced light reflection, but manufacturing cost increases
Solution Approach 1:
The patent replaces the expensive SOI substrate with a cheaper silicon substrate. The high-concentration P-type impurity layer serves as a temporary etching stopper during recess formation, after which its original function is superseded by the recess structure itself for light reflection. This substitution achieves the same optical enhancement effect at lower manufacturing cost.
Solution Approach 2:
The patent changes the impurity concentration parameter of the P-type layer to be significantly higher than in conventional silicon substrates. This high concentration (1×10^19 to 1×10^21 atoms/cm³) provides two benefits: it acts as an effective etching stopper during recess formation and creates sufficient reflectivity difference at the interface to enhance light reflection, replacing the need for SOI substrate.
2Ease of manufacture
If silicon substrate is used instead of SOI substrate, then manufacturing cost is reduced, but sensitivity to near-infrared light deteriorates due to physical absorption limitations
Solution Approach 1:
The patent segments the silicon substrate by introducing a distinct high-concentration P-type impurity layer within the silicon matrix. This creates a localized region with different optical and etching properties, enabling the formation of a recess structure that enhances light reflection specifically in the near-infrared region while maintaining overall silicon substrate cost advantages.
Solution Approach 2:
The high-concentration P-type impurity layer serves as an intermediary element that mediates between the silicon substrate and the recess structure. During manufacturing, it acts as an etching stopper to define the recess depth. In operation, the interface between this layer and the surrounding silicon provides the reflectivity enhancement needed for near-infrared sensitivity, thus mediating both manufacturing and optical performance 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
This approach improves sensitivity to both visible and near-infrared light while reducing manufacturing costs by using a silicon substrate with a P-type impurity layer as an etching stopper to form a recess, increasing the quantum efficiency and light conversion.
Implementation Method 1
a resonance type light receiving device as a single light receiving element has been known which reflects light made incident from the obverse face of a substrate, on which the pixels are provided, on the reverse face thereof to increase the quantum efficiency
Implementation Method 2
the conventional resonance type single light receiving device utilizes the resonance effect that light made incident from the obverse face of the substrate is reflected on the reverse face thereof and the thus reflected light is further reflected on the obverse face thereof
Implementation Method 3
an imaging region in which a plurality of pixels each including a photoelectric converter and a transistor are provided
Data Source
AI summary
A solid-state imaging element includes a layered substrate made of silicon and composed of, for example, an N-type substrate, a P-type layer, and an N-type layer. In the layered substrate, an imaging region in which a plurality of pixels are arranged and a peripheral circuit region are formed. A recess reaching the reverse face of the P-type layer is formed in a reverse face portion of the layered substrate in the imaging region, and a reflective film is formed on at least the inner face of the recess. Light is reflected on the reverse face and the obverse face of the layered substrate.