Back-illuminated Sensor Boron Doping for High Flux UV Detection
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Solution Overview
Problem
Current image sensors face challenges in efficiently detecting high-energy DUV and VUV photons due to absorption issues and surface defects, leading to low quantum efficiency and sensitivity, especially when exposed to high radiation flux densities, which requires higher intensity light sources and can cause damage or degradation.
Innovation Solution
The development of back-thinned image sensors with a boron layer on the back surface, where boron diffuses into the silicon to create a p-type doped layer, combined with refractory metal interconnects and anti-reflection coatings, allowing for finer design rules and reduced surface defects, enhancing quantum efficiency and sensitivity.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If silicon dioxide is used as the insulating layer in DUV and VUV sensors, then the bandgap provides theoretical protection against photon absorption, but dangling bonds and defects in the oxide absorb photons and reduce quantum efficiency
Solution Approach 1:
The patent removes the silicon dioxide insulating layer entirely from the sensor structure. By eliminating this layer, the source of photon absorption through dangling bonds and defects is removed, directly improving quantum efficiency in the DUV and VUV ranges without requiring defect mitigation strategies
Solution Approach 2:
The patent employs a composite structure combining silicon-on-sapphire (SOS) or silicon-on-insulator (SOI) substrates with metal interconnect layers. This composite approach allows the silicon layer to be optimized for photon detection while the sapphire or insulator layer provides mechanical support and electrical isolation without interfering with UV/VUV photon transmission
2Reliability
If higher intensity light sources are used to maintain signal-to-noise ratio under high radiation flux, then detection sensitivity is maintained, but the optics and sample are exposed to higher intensities causing damage or degradation
Solution Approach 1:
The patent changes the fundamental parameter of photon detection efficiency by eliminating the silicon dioxide layer. This parameter change in the sensor structure itself allows for high quantum efficiency without requiring increased light source intensity, thereby maintaining signal-to-noise ratio while avoiding optics and sample damage
Solution Approach 2:
The patent converts the harmful effect of high radiation flux density into a benefit by designing a sensor structure that is specifically optimized for high-flux operation. The eliminated oxide layer prevents radiation-induced absorption, allowing the sensor to thrive in high-radiation environments rather than being damaged by them
3Ease of manufacture
If conventional metal interconnects are used in back-thinned sensors, then manufacturing is simpler, but the metal layers cause stress and delamination at high temperatures during boron deposition
Solution Approach 1:
The patent changes the material parameter of the interconnect layer from conventional metals to refractory metals. This material substitution allows the interconnect structure to withstand the high temperatures required for boron deposition without delamination, enabling the formation of the p-type doped layer at temperatures above 450°C
Solution Approach 2:
The patent creates a composite interconnect structure using refractory metals that can be deposited at high temperatures. This composite approach combines the mechanical properties needed for interconnection with the thermal stability required for subsequent high-temperature processing steps
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 approach results in image sensors with high quantum efficiency and long-life operation under high fluxes of DUV and VUV radiation, enabling more efficient detection and reduced risk of damage from high light intensities, while allowing for finer design rules and more flexible interconnects.
Implementation Method 1
boron diffuses into the silicon to create a p-type doped layer
Implementation Method 2
anti-reflection coatings, allowing for finer design rules and reduced surface defects, enhancing quantum efficiency and sensitivity
Implementation Method 3
image sensors suitable for sensing radiation in deep UV (DUV) and vacuum UV (VUV) wavelengths
Data Source
AI summary
An image sensor for electrons or 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. The circuit elements are connected by metal interconnects comprising a refractory metal. An anti-reflection or protective layer may be 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.