Backside Image Sensor Metal Layout for Low Capacitance and Stray Light
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Solution Overview
Problem
Back-illuminated imaging apparatuses face challenges in reducing long-wavelength light transmission through semiconductor substrates, leading to increased capacitance and stray light mixing, which affects sensitivity and image quality.
Innovation Solution
A photoelectric conversion apparatus is designed with a metal portion that includes openings over the wire and floating diffusion, reducing parasitic capacitance and stray light mixing by strategically placing the metal portion to minimize its impact on the photoelectric conversion elements, thereby enhancing sensitivity and image quality.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If a metal reflection film is provided closer to the semiconductor substrate than to a wiring layer, then long-wavelength light transmission is reduced and sensitivity is improved, but capacitance increases due to the metal portion covering the photoelectric conversion element
Solution Approach 1:
The metal portion is divided into multiple segments: a first metal portion that covers the photoelectric conversion element to reflect long-wavelength light and improve sensitivity, and a second metal portion that is positioned to minimize capacitance increase. The segmentation allows the metal structure to perform both functions - light reflection and low capacitance - by spatially separating its roles.
Solution Approach 2:
The metal portion is strategically positioned to have different properties in different regions: over the photoelectric conversion element it provides high reflectivity for long-wavelength light, while in other regions it is configured to minimize capacitive coupling. This local differentiation of metal placement and structure allows simultaneous achievement of sensitivity improvement and capacitance control.
2Object-affected harmful factors
If a metal reflection film is provided closer to the semiconductor substrate than to a wiring layer, then long-wavelength light transmission is reduced, but stray light mixing increases affecting image quality
Solution Approach 1:
The metal portion is segmented into specific regions: a first region that reflects long-wavelength light to prevent color mixture, and a second region configured to manage stray light. This segmentation allows different portions of the metal structure to address different harmful effects independently.
Solution Approach 2:
The metal portion, which could potentially cause stray light reflections, is strategically configured so that its reflective property becomes beneficial. By positioning the metal to reflect long-wavelength light specifically toward the photoelectric conversion element rather than allowing random stray light mixing, the harmful reflection is converted into a beneficial light-guiding function that improves image quality.
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 the increase in capacitance and reduces stray light mixing, improving the sensitivity and image quality of the back-illuminated imaging apparatus by optimizing the placement and structure of the metal portion.
Implementation Method 1
a metal reflection film is provided closer to the semiconductor substrate than to a wiring layer. The transmitted light is reduced by the reflection film
Implementation Method 2
The semiconductor substrate includes a photoelectric conversion element. The floating diffusion is configured to hold a charge generated by the photoelectric conversion element
Data Source
AI summary
A photoelectric conversion apparatus includes a semiconductor substrate, a floating diffusion, an amplifying transistor, first and second contact plugs, a wire, and a metal portion. The semiconductor substrate has a first plane and a second plane to be entered by light, and includes a photoelectric conversion element. The amplifying transistor includes a first gate electrode. The first contact plug is connected to the floating diffusion. The second contact plug is connected to the first gate electrode. The wire is configured to electrically connect the first gate electrode and the floating diffusion to each other. The metal portion, which is arranged between the first plane and a third plane, covers at least a part of the photoelectric conversion element in a planar view, and has an opening over which at least a part of the wire is superimposed in a planar view.