Back-Illuminated Image Sensor With Textured Boron Surface for DUV Detection
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Solution Overview
Problem
Existing image sensors struggle to efficiently detect high-energy photons in deep ultraviolet (DUV) and vacuum ultraviolet (VUV) wavelengths due to high reflectivity of silicon, leading to low efficiency and potential damage from high-intensity light sources, and are prone to electron recombination at the silicon surface.
Innovation Solution
A low-reflectivity back-illuminated image sensor with a textured silicon surface and a boron layer is developed, featuring a semiconductor membrane with circuit elements on one surface and a textured, boron-coated surface on the opposite, reducing reflectivity and enhancing photon absorption.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If a standard silicon surface is used for DUV/VUV detection, then the sensor structure is simple, but the reflectivity is high (65% at 193 nm) reducing detection efficiency
Solution Approach 1:
The patent applies surface texturing with pyramidal structures (curved/asymmetric geometry) on the back surface of the silicon sensor. This curvature approach reduces reflectivity by preventing specular reflection and increasing light trapping, achieving near-zero reflectivity at DUV wavelengths while maintaining structural feasibility through etching processes.
Solution Approach 2:
The patent creates a composite structure by combining silicon with a textured surface morphology and additional surface treatments. The pyramidal texture creates a composite interface that reduces reflectivity through multiple internal reflections and increased absorption paths, effectively combining geometric structure with material properties.
2Reliability
If a 21 nm oxide layer is grown on silicon to reduce reflectivity, then reflectivity decreases to 40%, but the sensor efficiency is still insufficient for high-speed inspection requiring 100,000+ photons per pixel
Solution Approach 1:
The patent replaces the planar oxide interface with a pyramidal textured surface, creating curved interfaces that trap light through multiple internal reflections. This geometric approach achieves superior light trapping compared to flat oxide layers, reducing reflectivity to near-zero levels without requiring precise oxide thickness control.
Solution Approach 2:
The patent changes the surface geometry parameter from flat to pyramidal texture, fundamentally altering the light-matter interaction. This parameter change transforms the reflectivity characteristic from 40% (with oxide) to near-zero, achieving the required detection efficiency for high-speed inspection applications.
3Productivity
If high radiation flux density is used to maintain signal-to-noise ratio at high inspection speeds, then inspection speed is maintained, but photon-induced damage accumulates causing sensor degradation over time
Solution Approach 1:
The patent converts the harmful high radiation flux into a beneficial signal by maximizing photon absorption efficiency. The textured surface ensures that even at high flux densities, photons are absorbed before causing damage, converting potential harm into useful signal while extending sensor operational life through improved quantum efficiency.
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 sensor achieves high quantum efficiency and long-life operation under high fluxes of DUV and VUV radiation by minimizing surface reflection and electron recombination, maintaining sensitivity and reducing the need for higher intensity light sources.
Implementation Method 1
a second textured surface opposite of the first surface... The second textured surface comprises a pseudo-random distribution of at least one of upright pyramids, inverted pyramids, or nanocones
Implementation Method 2
the textured surface... reduces reflection and enhances photon absorption by creating a pseudo-random or periodic distribution of pyramidal structures on the back surface
Implementation Method 3
a low-reflectivity back-illuminated image sensor is developed with a semiconductor membrane featuring an epitaxial layer and a textured surface, coated with a thin layer of high-purity amorphous boron, which reduces reflection and enhances photon absorption
Implementation Method 4
back-illuminated image sensor... allowing for effective detection of DUV and VUV radiation
Data Source
AI summary
An image sensor for short-wavelength light includes a semiconductor membrane, circuit elements formed on a first surface of the semiconductor membrane, and a boron-coated, textured surface on a second surface of the semiconductor membrane. The textured surface comprises pseudo-random, periodic, and/or random distribution of upright pyramids, inverted pyramids, and/or nanocones. The textured surface reduces the reflection of incident light across wide bands in the DUV and VUV regimes, thus increasing the amount of light absorbed and improving the efficiency of the image sensor. Reflectance may be further reduced by applying an antireflective coating on the textured surface. The image sensor may be a two-dimensional area sensor, or a one-dimensional array sensor. and incorporated in an inspection system.