Pixel Sensor Layer Stack for Plasma Etch UV Protection
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Solution Overview
Problem
Plasma processing and etching in semiconductor manufacturing can damage photodiodes in image sensors by forming electron-hole pairs in dielectric layers, leading to increased dark current and decreased performance.
Innovation Solution
A layer stack comprising a first oxide layer, a layer with a band gap less than 8.8 eV, and a second oxide layer is used to absorb ultraviolet photons and prevent electron-hole pairs from migrating to photodiodes, thereby protecting them from damage.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If plasma processing and etching are used in semiconductor manufacturing, then manufacturing productivity is improved, but photodiodes are damaged by formation of electron-hole pairs leading to increased dark current
Solution Approach 1:
A dielectric layer is introduced as an intermediary between the plasma processing environment and the photodiode. This layer absorbs ultraviolet photons generated during plasma processing, preventing them from creating electron-hole pairs in the photodiode. The dielectric layer thus mediates the interaction between the manufacturing process and the sensitive photodiode structure, allowing plasma processing to proceed while protecting the photodiode from damage.
Solution Approach 2:
The harmful ultraviolet photons generated during plasma processing are converted into a beneficial effect by having them absorbed by the dielectric layer. Instead of allowing these photons to damage the photodiode by creating electron-hole pairs, the dielectric layer absorbs their energy, converting the potentially harmful radiation into harmless absorbed energy within the protective layer.
2Ease of manufacture
If conventional semiconductor processes are used for BSI image sensor fabrication, then manufacturing cost and integration are improved, but plasma processing damages photodiodes increasing dark current
Solution Approach 1:
The dielectric layer serves as a protective intermediary that allows conventional plasma processing to be used while preventing damage to the photodiode. It mediates between the plasma environment and the sensitive photodiode structure, enabling the use of standard manufacturing processes without compromising photodiode integrity.
Solution Approach 2:
The dielectric layer is formed on the photodiode surface before plasma processing occurs. This preliminary protective action ensures that when plasma processing and etching are subsequently performed, the photodiode is already protected from ultraviolet photon damage, preventing electron-hole pair formation before it can occur.
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 layer stack effectively reduces and blocks the effects of plasma processing and etching, maintaining dark current, white pixel, quantum efficiency, and cross-talk performance of pixel sensors.
Implementation Method 1
A layer stack comprising a first oxide layer, a layer with a band gap less than 8.8 eV, and a second oxide layer is used to absorb ultraviolet photons and prevent electron-hole pairs from migrating to photodiodes
Data Source
AI summary
A pixel sensor may include a layer stack to reduce and/or block the effects of plasma and etching on a photodiode and/or other lower-level layers. The layer stack may include a first oxide layer, a layer having a band gap that is approximately less than 8.8 electron-Volts (eV), and a second oxide layer. The layer stack may reduce and/or prevent the penetration and absorption of ultraviolet photons resulting from the plasma and etching processes, which may otherwise cause the formation of electron-hole pairs in the substrate in which the photodiode is included.