Light Pipe Structure Etching for Uniform Quantum Efficiency
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Solution Overview
Problem
Existing methods for forming light pipe structures in CMOS image sensors cause damage to the semiconductor substrate, leading to increased dark current and non-uniformity of quantum efficiency due to high power etching processes, which result in varying heights of the light pipe structures and plasma damage.
Innovation Solution
A method involving a low power etch process to form an opening over photodetectors, using U-shaped lower and upper etch stop layers, followed by a wet etch process to create a light pipe structure with its bottom surface below the bottommost wiring layer, mitigating substrate damage and ensuring uniformity.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If a high power etching process is used to form the light pipe structure, then the etching speed and productivity are improved, but the semiconductor substrate is damaged causing increased dark current and non-uniform quantum efficiency
Solution Approach 1:
The patent changes the etching parameters from high power to low power to reduce substrate damage. Specifically, the method uses a low power etching process that minimizes plasma damage to the substrate while still achieving the necessary light pipe structure formation, thereby reducing dark current and improving quantum efficiency uniformity.
Solution Approach 2:
The patent introduces U-shaped etch stop layers as intermediary structures that protect the substrate during the etching process. These etch stop layers act as a mediator between the etching process and the substrate, preventing direct plasma damage to the substrate while allowing the light pipe structure to be formed.
2Productivity
If a high power etching process is used to form the light pipe structure, then the etching speed is improved, but the quantum efficiency uniformity deteriorates due to varying heights of light pipe structures
Solution Approach 1:
The patent changes the etching power parameter from high to low, which results in more uniform light pipe structure heights and improved quantum efficiency uniformity. The low power etching process prevents the variations in height that occur with high power etching.
Solution Approach 2:
The U-shaped etch stop layers serve as intermediary structures that ensure uniform depth and height of the light pipe structures. These etch stop layers mediate the etching process to achieve consistent dimensions across all light pipe structures, thereby improving quantum efficiency uniformity.
3Object-affected harmful factors
If a low power etching process is used to minimize substrate damage, then dark current is reduced and quantum efficiency is improved, but the etching speed and productivity decrease
Solution Approach 1:
The patent segments the etching process into multiple stages: first forming openings through the interconnect dielectric structure, then forming the light pipe structures. This segmentation allows the use of low power etching for precision work while maintaining overall process efficiency.
Solution Approach 2:
The patent performs preliminary actions by first forming the U-shaped etch stop layers and then using wet etching to expand the openings. This preliminary preparation allows the subsequent low power etching to be more efficient and less time-consuming.
4Ease of manufacture
If plasma damage occurs during etching, then the light pipe structure can be formed, but the semiconductor substrate is damaged leading to increased dark current
Solution Approach 1:
The U-shaped etch stop layers act as intermediary protective structures during the plasma etching process. These etch stop layers mediate between the plasma etching process and the substrate, allowing light pipe structure formation while preventing direct plasma damage to the substrate.
Solution Approach 2:
The patent converts the potentially harmful plasma etching process into a beneficial process by using U-shaped etch stop layers that protect the substrate. The plasma etching is still used for its effectiveness in forming the light pipe structure, but the harmful effects are mitigated by the protective etch stop layers.
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 reduces dark current and increases quantum efficiency by minimizing substrate damage and ensuring uniform radiation distribution across photodetectors, enhancing the overall performance of the image sensor.
Implementation Method 1
The light pipe structures are configured to guide incident radiation to underlying photodetector by total internal reflection (TIR)
Implementation Method 2
performing a low power etch process to form an opening overlying the photodetector
Implementation Method 3
A wet etch process is performed to expand the light pipe opening and to remove excess material of the upper interconnect portion
Data Source
AI summary
Various embodiments of the present disclosure are directed towards an integrated chip including a photonic element in or on a substrate. A dielectric structure is over the substrate. The dielectric structure comprises opposing sidewalls and a lower surface over the photonic element. A conductive structure is in the dielectric structure. An etch stop structure is in the dielectric structure. The etch stop structure comprises a pair of vertical segments along the opposing sidewalls of the dielectric structure and a lateral segment extending between the pair of vertical segments. A bottom surface of the lateral segment is vertically offset from a bottom surface of the conductive structure in a direction towards the substrate by a first distance. The bottom surface of the lateral segment is vertically offset from a top surface of the substrate by a second distance greater than the first distance.