Back-Illuminated Image Sensor Incident Light Attenuation Unit
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Solution Overview
Problem
Back-illuminated image sensors face challenges with reflected light causing optical noise and crosstalk due to the presence of a wiring layer on the front surface, which affects image quality, and existing solutions like global shutters still experience issues with parasitic light sensitivity.
Innovation Solution
An image sensor design incorporating an incident light attenuation unit with a lid portion, wall portion, and bottom portion to attenuate light transmitted through the photoelectric conversion unit, formed simultaneously with the wiring layer, and strategically positioned to reduce stray light incidence on adjacent pixels.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Area of moving object
If a wiring layer is formed on the front surface of the semiconductor substrate in a back-illuminated image sensor, then the aperture ratio of the pixel can be improved, but reflected light from the wiring layer causes optical noise and crosstalk
Solution Approach 1:
The light-shielding film is divided into multiple regions: a first light-shielding film region covering the charge holding unit, a second light-shielding film region covering adjacent pixels, and a third light-shielding film region extending toward the center. This segmentation allows different parts of the shielding structure to address different sources of reflected light, effectively reducing both optical noise and crosstalk while maintaining the aperture ratio benefit of the front-side wiring layer
Solution Approach 2:
The light-shielding film is strategically positioned with varying coverage areas: it fully covers the charge holding unit to prevent reflected light incidence, partially covers adjacent pixels to reduce crosstalk, and extends toward the center of the pixel to address reflected light from the photoelectric conversion unit. This local quality approach optimizes the shielding effect in different regions without unnecessarily reducing the overall aperture ratio
2Object-affected harmful factors
If a light-shielding portion is arranged within the substrate to block reflected light, then crosstalk and optical noise are reduced, but the structure complexity and manufacturing difficulty increase
Solution Approach 1:
The light-shielding film is integrated with the color filter layer, combining two functional elements into a single structure. This merging approach reduces the overall device complexity by eliminating the need for separate light-shielding portions within the substrate, while still achieving effective reduction of crosstalk and optical noise through the combined structure
3Object-affected harmful factors
If a light-shielding portion is arranged within the substrate, then reflected light is blocked, but manufacturing precision requirements increase due to alignment constraints
Solution Approach 1:
By integrating the light-shielding film with the color filter layer that is already precisely aligned with the pixel structure, the invention eliminates the need for separate alignment processes. This merging approach maintains effective light shielding while significantly reducing manufacturing precision requirements compared to implementing separate light-shielding portions within the substrate
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 reduces the incidence of stray light on charge holding units, preventing image quality deterioration and crosstalk, thereby improving the overall image signal quality.
Implementation Method 1
a photoelectric conversion unit that is formed in a semiconductor substrate and performs photoelectric conversion based on incident light
Implementation Method 2
an incident light attenuation unit that attenuates the incident light transmitted through the photoelectric conversion unit
Data Source
AI summary
The incidence of incident light transmitted through a photoelectric conversion unit onto a charge holding unit, a pixel in the adjacency, and the like can be blocked in a pixel. An image sensor includes a pixel, a wiring layer, and an incident light attenuation unit. The pixel includes a photoelectric conversion unit that is formed in a semiconductor substrate and performs photoelectric conversion based on incident light, and a pixel circuit that generates an image signal according to a charge generated by the photoelectric conversion. The wiring layer is arranged on a surface of the semiconductor substrate different from a surface onto which the incident light is incident, and transports either the image signal or a signal applied to the pixel circuit. The incident light attenuation unit attenuates the incident light transmitted through the photoelectric conversion unit.