BSI CMOS Image Sensor Backside Pits for Higher Quantum Efficiency
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Solution Overview
Problem
Conventional Back Side Illuminated (BSI) CMOS image sensors face limitations in light absorption efficiency and quantum efficiency due to reflection and non-uniform photo response, which affect image quality and sensitivity.
Innovation Solution
A semiconductor device with a semiconductor layer having a tilted lattice plane, featuring pyramid or prism pit portions on its surface to scatter and refract light, enhancing absorption efficiency and quantum efficiency by reducing reflection.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If conventional BSI CMOS image sensors are used, then the structure is simple and manufacturing is easier, but light absorption efficiency and quantum efficiency are insufficient due to reflection and non-uniform photo response
Solution Approach 1:
The patent applies curvature by forming spherical or dome-shaped microlens structures on the semiconductor substrate surface. These curved microlens structures refract and focus incident light onto the photodiode active regions, improving light absorption efficiency and quantum efficiency while maintaining manufacturing feasibility through standard photolithography and reflow processes
Solution Approach 2:
The patent changes the physical and optical parameters of the semiconductor device by introducing microlens structures with specific refractive indices, curvature radii, and heights. These parameter changes optimize light refraction and focusing characteristics, enhancing photo response uniformity and absorption efficiency across different incident angles
2Ease of manufacture
If the semiconductor surface is flat, then manufacturing is easier, but light reflection reduces absorption efficiency and quantum efficiency
Solution Approach 1:
The patent replaces the flat semiconductor surface with curved microlens structures that have spherical or dome-shaped profiles. These curved surfaces reduce light reflection by minimizing abrupt refractive index changes and instead guide light through gradual refraction into the photodiode regions, thereby reducing energy loss
Solution Approach 2:
The patent converts the harmful reflection effect into a beneficial refraction effect by designing microlens structures that utilize the refractive index difference between air and semiconductor material. Instead of light being reflected away, the curved surfaces refract incident light at controlled angles, focusing it onto the photodiode active regions and converting reflection loss into useful light absorption
3Device complexity
If conventional planar structures are used, then device complexity is low, but photo response non-uniformity affects image quality
Solution Approach 1:
The patent introduces curved microlens structures that systematically control light refraction paths. The spherical or dome-shaped profiles ensure uniform light distribution across the photodiode array by compensating for angular variations in incident light, thereby improving photo response uniformity without requiring complex heterogeneous structures
Solution Approach 2:
The microlens structures serve multiple functions simultaneously: they act as light refraction elements, focus light onto photodiode regions, and provide angular compensation for incident light. This multi-functionality achieves improved photo response uniformity while maintaining relatively simple device architecture and manufacturing processes
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 significantly enhances the quantum efficiency and absorption rate of the semiconductor device, leading to improved image quality and sensitivity by effectively scattering and refracting incident light into the semiconductor layer.
Implementation Method 1
pyramid or prism pit portions on its surface to scatter and refract light
Implementation Method 2
pyramid or prism pit portions on its surface to scatter and refract light
Implementation Method 3
enhancing absorption efficiency and quantum efficiency by reducing reflection
Data Source
AI summary
A method of forming a semiconductor device includes forming photodiodes extending from a front-side surface of a semiconductor layer into the semiconductor layer; forming transistors on the front-side surface of the semiconductor layer; forming an interconnect structure over the transistors, the interconnect structure comprising an inter-metal dielectric and metal lines in the inter-metal dielectric; etching first regions of a backside surface of the semiconductor layer to form trenches in the semiconductor layer and non-overlapping the photodiodes; after forming the trenches, etching second regions of the backside surface of the semiconductor layer to form pits in the semiconductor layer and overlapping the photodiodes; and depositing a dielectric material in the trenches and the pits.