CMOS Light Pipe Structure for Uniform QE and Low Dark Current
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
Current methods for forming light pipe structures in CMOS image sensors result in high dark current and non-uniformity due to plasma etching, which damages the semiconductor substrate and causes variations in light pipe heights, affecting quantum efficiency.
Innovation Solution
A method involving a low power etch process to form openings with U-shaped etch stop layers, followed by a wet etch process to create light pipe structures with a bottom surface extending below the bottommost wiring layer, reducing damage and achieving uniformity.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If plasma etching is used to form light pipe structures, then the etching process can be performed, but dark current increases and manufacturing precision deteriorates due to substrate damage and height variations
Solution Approach 1:
The patent divides the light pipe structure into multiple segments at different heights, with each segment having a specific function. The first light pipe segment extends to a first height and the second light pipe segment extends to a second height, allowing differential etching and reducing the harmful effects of plasma damage on the substrate while maintaining manufacturing capability.
Solution Approach 2:
The patent applies different properties to different parts of the light pipe structure. The first light pipe segment has different characteristics than the second light pipe segment, with each segment optimized for its specific location and function. This local differentiation allows the structure to achieve both manufacturability through plasma etching and precision in critical areas.
2Ease of manufacture
If plasma etching is used to form light pipe structures, then the etching process can be completed, but the semiconductor substrate is damaged causing increased dark current
Solution Approach 1:
By segmenting the light pipe structure into multiple height levels, the patent reduces the extent of plasma exposure to the underlying semiconductor substrate. The first light pipe segment at a lower height protects critical substrate areas from excessive plasma damage, thereby reducing dark current generation while still allowing the etching process to complete.
Solution Approach 2:
The patent employs a multi-segment design that acts as a protective buffer between the plasma etching process and the semiconductor substrate. The light pipe segments provide a physical barrier that cushions the substrate from direct plasma exposure, preventing damage before it can occur to the sensitive photodetector regions.
3Ease of manufacture
If plasma etching is used to form light pipe structures, then the etching can be performed, but quantum efficiency decreases due to substrate damage
Solution Approach 1:
The segmented light pipe structure with multiple height levels reduces plasma damage to the semiconductor substrate, thereby preserving the quantum efficiency of the photodetectors. The first light pipe segment at a lower height provides protection to the substrate while the second segment maintains the necessary optical functionality, achieving both manufacturability and high quantum efficiency.
4Ease of manufacture
If light pipe heights vary, then manufacturing variations occur, but uniform light distribution to photodetectors is compromised
Solution Approach 1:
By dividing the light pipe into segments at different heights with specific functions, the patent achieves a balance between manufacturing flexibility and light distribution uniformity. Each segment can be optimized for its specific role, with the lower segment providing structural stability and protection, while the upper segment ensures uniform light delivery to photodetectors.
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 decreases dark current, reduces the number of white pixels, and enhances quantum efficiency by mitigating plasma damage and ensuring uniform light distribution across photodetectors.
Implementation Method 1
The light pipe structures are configured to guide incident radiation to underlying photodetector by total internal reflection (TIR), thereby increasing a quantum efficiency (QE) of the image sensor.
Data Source
AI summary
Various embodiments of the present disclosure are directed towards a method for forming an image sensor. The method includes forming a photodetector in a substrate. A lower interconnect portion of an interconnect structure is formed over the photodetector. A removal process is performed to define a first opening overlying the photodetector in the lower interconnect portion. A lower etch stop layer is formed lining the first opening. The lower etch stop layer has a U-shape in the first opening. An upper interconnect portion of the interconnect structure is formed over the lower etch stop layer. A light pipe structure is formed overlying the photodetector. The U-shape of the lower etch stop layer extends continuously along sidewalls and a bottom surface of the light pipe structure.