Rear-Illuminated Sensor With Thinned Insulation Layer
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Solution Overview
Problem
In solid-state imaging devices, the presence of circuitry and wiring on the semiconductor substrate obstructs incident light, making it difficult to improve sensitivity, and the configuration of transistors in the logic circuit vertically oriented relative to pixels on the sensor chip leads to adverse effects from hot carrier light, causing noise and deteriorating image quality.
Innovation Solution
A rear-projection type solid-state imaging device is designed with wiring in the periphery region of the pixel area, where the insulation layer is selectively thinned to reduce the distance between the on-chip lens and the light-receiving face, improving light-receiving properties by minimizing the obstruction and noise from hot carrier light.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If the photoelectric converter receives incident light at the front face side with circuit and wiring, then the circuit and wiring can be provided on the semiconductor substrate, but the incident light is blocked by the circuit and wiring making it difficult to improve sensitivity
Solution Approach 1:
The patent inverts the conventional front-illuminated structure to a rear-illuminated structure. The photoelectric converter receives incident light from the rear face (opposite side) where no circuit or wiring is present, eliminating light blockage. The front face is used for providing circuit and wiring, thus resolving the contradiction between having functional circuitry and maintaining light sensitivity.
2Ease of manufacture
If transistors in the logic circuit are disposed in the vertical direction relative to pixels, then the logic circuit can be configured, but hot carrier light is emitted causing noise and deteriorating image quality
Solution Approach 1:
The patent extracts the logic circuit from the same substrate as the sensor and places it on a separate logic substrate. This separation removes the source of hot carrier light (the vertically-oriented transistors in the logic circuit) from proximity to the pixels, thereby eliminating the noise problem while still allowing the logic circuit to be configured and manufactured.
3Reliability
If the insulation layer is thinned to reduce distance between on-chip lens and light-receiving face, then light-receiving properties are improved, but the wiring structure becomes more complex
Solution Approach 1:
The patent moves the wiring from the light-receiving face (2D plane) to the periphery region and to the opposite face of the substrate (utilizing the third dimension/depth). By providing wiring in the periphery region rather than over the pixel area, and by using through-substrate vias to connect to the opposite face, the wiring structure achieves the necessary connectivity without interfering with light reception, thus improving light-receiving properties without excessive complexity.
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 the light-receiving capabilities of the photoelectric converters, reduces noise, and improves image quality by minimizing the distance between the on-chip lens and the light-receiving face, thereby increasing sensitivity and product yield.
Implementation Method 1
The photoelectric converter is a photodiode, for example, and generates signal load by receiving the incident light via an external optical system with a light-receiving face and performing photoelectric conversion.
Data Source
AI summary
A solid-state imaging device has a sensor substrate having a pixel region on which photoelectric converters are arrayed; a driving circuit provided on a front face side that is opposite from a light receiving face as to the photoelectric converters on the sensor substrate; an insulation layer, provided on the light receiving face, and having a stepped construction wherein the film thickness of the pixel region is thinner than the film thickness in a periphery region provided on the outside of the pixel region; a wiring provided to the periphery region on the light receiving face side; and on-chip lenses provided to positions corresponding to the photoelectric converters on the insulation layer.