Trapezoidal Light Pipe for FSI Image Sensor
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Solution Overview
Problem
Existing image sensor device structures have limitations in light collection efficiency and sensitivity, particularly in front-side illuminated (FSI) image sensors, due to the design of the trench and light pipe configuration which affects the amount of incident light reaching the pixel regions.
Innovation Solution
The FSI image sensor device structure incorporates a light pipe with a wide top portion and a narrow bottom portion, formed by a trench with a trapezoidal photoresist mask and filled with a transparent dielectric layer, enhancing light collection by optimizing the trench dimensions and materials to improve the refractive index and light transmission.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a conventional trench structure is used in FSI image sensors, then the device structure is simple and easy to manufacture, but the light collection efficiency is insufficient and sensitivity is reduced
Solution Approach 1:
The patent applies asymmetry by creating a trench structure with a wide top portion and a narrow bottom portion, rather than a uniform cross-section. This asymmetric geometry optimizes light collection at the top while maintaining structural integrity at the bottom, directly resolving the contradiction between light collection efficiency and structural simplicity.
Solution Approach 2:
The patent transitions from a two-dimensional uniform trench to a three-dimensional tapered structure by varying the trench width along its depth. This dimensional change allows the trench to collect more light at the surface while maintaining a manageable footprint at the pixel region, improving light collection efficiency without proportionally increasing overall device complexity.
2Reliability
If the trench top width is increased to collect more light, then light collection efficiency improves, but the manufacturing precision requirements increase due to the trapezoidal photoresist mask formation
Solution Approach 1:
The patent applies preliminary action by forming a trapezoidal photoresist mask before trench etching. This pre-formed mask with the desired trapezoidal profile ensures that the trench acquires the correct wide-top/narrow-bottom geometry during etching, achieving both wide light collection and controlled manufacturing precision through proactive pattern design.
Solution Approach 2:
The patent changes the geometric parameters of the photoresist mask from a conventional rectangular shape to a trapezoidal shape with specific angle and dimension ratios. This parameter change in the mask geometry directly translates to the desired trench geometry, optimizing light collection while maintaining manufacturability through controlled dimensional variations.
3Reliability
If a light pipe is added to enhance light transmission, then sensitivity improves, but the device complexity and number of manufacturing steps increase
Solution Approach 1:
The patent merges the light pipe function with the trench structure by forming the light pipe within the tapered trench itself. This integration combines what would traditionally be separate components (trench and light pipe) into a single unified structure, improving sensitivity through enhanced light transmission while avoiding the additional complexity of separate light pipe fabrication steps.
Solution Approach 2:
The tapered trench structure serves multiple functions simultaneously: it acts as both the structural feature for device fabrication and as the light pipe for optical transmission. This multi-functionality eliminates the need for dedicated light pipe components, improving sensitivity while maintaining manufacturing simplicity.
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 significantly increases the amount of incident light reaching the pixel regions, thereby enhancing the sensitivity and performance of the FSI image sensor device by improving light collection efficiency.
Implementation Method 1
filled with a transparent dielectric layer, enhancing light collection by optimizing the trench dimensions and materials to improve the refractive index and light transmission
Data Source
AI summary
A method for forming an FSI image sensor device structure is provided. The method includes forming a pixel region in a substrate and forming a dielectric layer over the substrate. The method includes forming a trench through the dielectric layer, and the trench includes a top portion and a bottom portion, and the trench is directly above the pixel region. The method includes forming a protection layer in the bottom portion of the trench and enlarging a top width of the top portion of the trench, and the trench has a wide top portion and a narrow bottom portion. The wide top portion has top sidewall surfaces, the narrow bottom portion has bottom sidewall surfaces, and the top sidewall surfaces taper gradually toward the bottom sidewall surfaces. The method includes filling a transparent dielectric layer in the trench to form a light pipe.