Back-Illuminated Sensor Anti-Reflection Layer
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Solution Overview
Problem
Image sensors used for deep UV and vacuum UV wavelengths face challenges in efficiently detecting high-energy photons due to reflection issues and electrical defects at the silicon surface, leading to low efficiency and short lifespan under high radiation flux.
Innovation Solution
The development of image sensors with a thin high-purity amorphous boron layer and anti-reflection coatings deposited using atomic layer deposition (ALD) techniques on the back surface, enhancing photon transmission and reducing electrical defects, allowing for long-life operation under high flux conditions.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a silicon surface is used for back-illuminated sensors, then the sensor can detect photons, but electrical defects and dangling bonds at the silicon surface cause electron recombination and low quantum efficiency
Solution Approach 1:
A thin layer of amorphous boron is deposited on the silicon surface to act as an intermediary. This boron layer passivates the dangling bonds and electrical defects at the silicon surface, preventing electron recombination while allowing photons to transmit through to the silicon detector. The boron layer serves as a mediator that eliminates the harmful surface effects without blocking the detection function.
Solution Approach 2:
The sensor structure combines silicon with a thin amorphous boron layer to create a composite surface structure. This composite material approach leverages the photon-detecting capability of silicon while adding the surface-passivating properties of boron, resulting in improved quantum efficiency and reduced electron recombination at the interface.
2Reliability
If anti-reflection coatings are deposited on the sensor surface, then photon transmission is enhanced, but conventional deposition methods introduce contamination and defects that reduce sensor lifespan
Solution Approach 1:
The deposition process parameters are changed to achieve lower deposition temperatures and reduced contamination. By modifying the deposition conditions (such as using plasma-enhanced chemical vapor deposition or controlling substrate temperature), the anti-reflection coating can be deposited without introducing harmful contaminants or defects that would reduce sensor lifespan, while still achieving the desired optical performance.
3Productivity
If high photon flux density is used to achieve high signal-to-noise ratio, then inspection speed is improved, but radiation damage accumulates rapidly reducing sensor operational lifespan
Solution Approach 1:
The amorphous boron layer is deposited beforehand to cushion or protect the silicon surface from radiation damage. This protective layer absorbs some of the radiation stress and prevents direct damage to the silicon crystal structure, allowing the sensor to withstand higher photon flux densities for extended periods. The boron layer acts as a sacrificial protective barrier that extends the sensor's operational lifespan under high-radiation conditions.
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 solution results in high-quantum-efficiency image sensors that are highly sensitive to DUV and VUV radiation, maintaining efficiency and extending operational lifespan by minimizing recombination of electrons at the silicon surface.
Implementation Method 1
Anti-reflection layers for short wavelengths, such as deep UV (DUV) and vacuum UV (VUV), are desired for back-illuminated sensors used in inspection, metrology, and related applications
Implementation Method 2
Deposited directly on the back surface of the epitaxial layer is a thin (e.g., between about 2 nm and about 20 nm thick) layer high-purity amorphous boron
Implementation Method 3
allowing for long-life operation under high flux conditions
Data Source
AI summary
An image sensor for short-wavelength light includes a semiconductor membrane, circuit elements formed on one surface of the semiconductor membrane, and a pure boron layer on the other surface of the semiconductor membrane. An anti-reflection or protective layer is formed on top of the pure boron layer. This image sensor has high efficiency and good stability even under continuous use at high flux for multiple years. The image sensor may be fabricated using CCD (charge coupled device) or CMOS (complementary metal oxide semiconductor) technology. The image sensor may be a two-dimensional area sensor, or a one-dimensional array sensor.