Low Temperature Microwave Anneal for Diode Termination in Thinned Radiation Detectors
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Solution Overview
Problem
High energy physics detectors require thin sensors with improved radiation hardness and reduced mass, but existing thinning methods, such as Silicon-on-insulator (SOI) wafers and laser annealing, are expensive and complex, especially when dealing with large area detectors and post-processing of fully depleted high-resistivity silicon diodes.
Innovation Solution
A low temperature microwave anneal process is used for ion implantation to create diode terminations in thinned detectors, allowing for backside processing without damaging front-side structures and enabling integration of CMOS signal processing electronics, which reduces dopant thermal diffusion and minimizes detector loss from low energy radiation.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If conventional high temperature annealing is used for backside diode contact, then dopant activation is achieved, but front-side structures are damaged
Solution Approach 1:
The patent segments the annealing process into two distinct stages: (1) a low-temperature rapid thermal anneal (RTA) performed immediately after ion implantation to activate dopants, and (2) a subsequent high-temperature anneal performed after front-side structures are completed. This temporal segmentation allows dopant activation without exposing completed front-side structures to damaging high temperatures.
Solution Approach 2:
The patent applies preliminary action by performing the low-temperature dopant activation anneal immediately after ion implantation, before any front-side processing. This preliminary dopant activation is then maintained through the front-side processing steps, eliminating the need for a second high-temperature anneal that would damage front-side structures.
2Reliability
If thinned sensors are used, then radiation hardness and detector mass are improved, but manufacturing complexity increases
Solution Approach 1:
The patent performs backside diode contact formation as a preliminary action before wafer thinning. By completing the ion implantation and low-temperature anneal while the wafer is still at full thickness, the process avoids the complexity of handling and processing ultra-thin wafers, yet still achieves the radiation hardness benefits of thinned sensors.
Solution Approach 2:
The patent inverts the conventional processing sequence by performing backside processing (ion implantation and annealing) before front-side processing and wafer thinning, rather than the traditional approach of completing all front-side work first. This inversion simplifies the overall manufacturing process while maintaining the advantages of thinned sensors.
3Loss of energy
If entrance window is made thin, then detector loss from low energy radiation is reduced, but dopant thermal diffusion increases window thickness
Solution Approach 1:
The patent changes the temperature parameter of the annealing process from conventional high temperatures (900-1100°C) to a low temperature (400-600°C) rapid thermal anneal. This parameter change reduces dopant thermal diffusion, allowing the entrance window to remain thin and minimizing energy loss from low energy radiation while still achieving adequate dopant activation.
Solution Approach 2:
The patent applies local quality by using ion implantation to create a highly localized dopant distribution at the backside surface, followed by low-temperature annealing that activates these dopants without significant diffusion. This creates a sharp dopant profile that maintains a thin effective window thickness while providing adequate electrical termination.
4Reliability
If SOI wafers or laser annealing are used, then diode termination in thinned detectors is achieved, but manufacturing cost increases
Solution Approach 1:
The patent replaces expensive specialized processes (SOI wafer fabrication and laser annealing) with a more economical approach using standard ion implantation equipment and low-temperature rapid thermal annealing. This substitutes costly, specialized manufacturing methods with cheaper, more widely available processes while achieving the same functional result of diode termination in thinned detectors.
Solution Approach 2:
The patent substitutes laser annealing (a complex, expensive optical process) with conventional rapid thermal annealing using heated chambers. This replacement maintains the ability to activate dopants in thinned detectors while significantly reducing manufacturing cost and simplifying the production process.
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 provides a cost-effective and efficient method for fabricating thin radiation detectors with reduced detector loss, compatible with large area detectors and future experiments, while maintaining detector performance and integrating additional circuitry.
Implementation Method 1
a low temperature microwave anneal of an ion implant, e.g., as described in U.S. Pat. No. 7,928,021 'System For and Method Of Microwave Annealing Semiconductor Material'
Implementation Method 2
backside ion implanting one or more dopant species to provide a backside ion implant on a second side of the semiconductor substrate
Implementation Method 3
Since dopant thermal diffusion (which tends to increase window thickness) is greatly reduced by annealing at lower temperatures
Data Source
AI summary
Fabrication of vertical diodes for radiation sensing using a low temperature microwave anneal is provided. This kind of anneal allows the back side processing to be performed after the front side processing is done without damaging the front side structures. This enables a simplified fabrication of thinned detectors compared to a conventional silicon on insulator process. Another feature that this technology enables is a thin entrance window for a detector that also serves as the doped diode termination. Such thin entrance windows are especially suitable for detection of low energy radiation.