Etch Stop Layer for BSI Image Sensor Cross-Talk Reduction
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Solution Overview
Problem
As semiconductor image sensors, particularly backside-illuminated (BSI) image-sensor devices, face challenges with optical cross-talk, electrical cross-talk, and dark current issues due to shrinking pixel sizes and spacing, which degrade light-sensing reliability and accuracy.
Innovation Solution
The implementation of an etch stop layer and a buffer layer with high etch selectivity, along with reflective pieces and a color filter, reduces dark current and optical cross-talk by creating a depletion region and optimizing the optical path, thereby enhancing quantum efficiency and phase detection auto focus (PDAF) performance.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If pixel size and spacing are reduced to increase pixel density, then productivity and device resolution are improved, but optical cross-talk, electrical cross-talk, and dark current increase causing degradation of light-sensing reliability
Solution Approach 1:
The patent divides the semiconductor substrate into isolated pixel regions using deep trench isolation structures. These trenches physically segment the continuous substrate into discrete pixel units, preventing optical and electrical cross-talk between adjacent pixels while maintaining high pixel density. The isolation structures create individual optical paths for each pixel, ensuring that light from one pixel does not interfere with neighboring pixels.
Solution Approach 2:
The patent introduces an etch stop layer as an intermediary between the deep trench isolation structure and the photodiode. This etch stop layer acts as a mediator that defines the precise depth of the photodiode during etching, ensuring that the photodiode terminates at the correct position above the isolation structure. This intermediary layer enables precise control of photodiode depth, which is critical for maintaining quantum efficiency while preventing cross-talk in high-density pixel arrays.
2Reliability
If substrate thickness is reduced to improve light transmission in BSI devices, then quantum efficiency is improved, but structural integrity and manufacturing precision become more difficult to maintain
Solution Approach 1:
The patent applies the etch stop layer before forming the photodiode structure. This preliminary action establishes a predetermined termination point for the photodiode etching process, ensuring that the photodiode will terminate at the correct depth relative to the isolation structure. By pre-positioning the etch stop layer, the manufacturing process achieves precise thickness control without requiring complex real-time monitoring during photodiode formation.
Solution Approach 2:
The patent utilizes the etch selectivity parameter between different materials (etch stop layer versus surrounding materials) to achieve precise depth control. By selecting materials with significantly different etch rates, the etch stop layer can be used to define the photodiode depth with high precision. This parameter change approach allows the photodiode to be etched to the correct depth while automatically stopping at the etch stop layer, ensuring consistent quantum efficiency across manufacturing batches.
3Reliability
If deep trench isolation structures are implemented to reduce cross-talk, then optical and electrical isolation are improved, but manufacturing complexity and process difficulty increase
Solution Approach 1:
The etch stop layer serves as an intermediary that simplifies the deep trench isolation manufacturing process. By introducing this intermediate layer, the patent enables precise photodiode depth definition without requiring complex multi-step etching processes. The etch stop layer acts as a self-aligned stop point that automatically defines the photodiode termination depth, reducing the need for additional alignment steps and process complexity while maintaining effective cross-talk isolation.
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 effectively minimizes dark current and optical cross-talk, improving the overall light-sensing accuracy and quantum efficiency of the image sensing device, particularly in BSI image-sensor devices.
Implementation Method 1
reduces dark current and optical cross-talk by creating a depletion region
Implementation Method 2
reflective pieces and a color filter, reduces dark current and optical cross-talk by creating a depletion region and optimizing the optical path
Implementation Method 3
reflective pieces and a color filter, reduces dark current and optical cross-talk
Data Source
AI summary
A method for manufacturing an image sensing device includes forming an interconnection layer over a front surface of a semiconductor substrate. A trench is formed to extend from a back surface of the semiconductor substrate. An etch stop layer is formed along the trench. A buffer layer is formed over the etch stop layer. An etch process is performed for etching the buffer layer. The buffer layer and the etch stop layer include different materials.