Avalanche Photodiode Segmented Terminal Manufacturing
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Solution Overview
Problem
Avalanche photodiodes, particularly silicon photomultipliers, suffer from spurious 'dark counts' due to minority carrier currents in the absence of light, which are undesirable and affect their sensitivity and accuracy in applications like Positron Emission Tomography and Laser Ranging.
Innovation Solution
The manufacturing process involves forming an insulating layer over a semiconductor substrate, defining and implanting dopants through patterned masks to create shallow and deep terminals with spatially separated regions, thereby reducing noise by forcing minority carriers to non-active regions, and using a quench resistor to limit avalanche current.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a continuous dopant implantation structure is used in avalanche photodiodes, then the device can achieve high current handling capability, but minority carrier currents cause spurious dark counts that reduce detection accuracy
Solution Approach 1:
The dopant implantation structure is segmented into spatially separated regions rather than being continuous. The first dopant forms a shallow terminal with first and second spatially separated regions, and the second dopant forms a deep terminal with similarly separated regions. This segmentation interrupts the continuous path for minority carrier current while maintaining electrical functionality, thereby reducing dark count noise by up to 83%.
2Measurement precision
If higher reverse bias voltage is applied to increase avalanche gain, then photon detection sensitivity is improved, but dark count rate increases due to enhanced impact ionization
Solution Approach 1:
The segmented dopant structure creates interrupted field regions that allow the device to operate at higher reverse bias voltages for improved photon detection sensitivity without proportionally increasing dark count rate. The spatial separation of dopant regions (e.g., 1-10 micrometer gaps) interrupts the avalanche multiplication path for thermally generated carriers while maintaining efficient photon detection in the active regions.
3Object-generated harmful factors
If the dopant implantation regions are spatially separated, then dark current is reduced by forcing minority carriers to non-active regions, but the manufacturing process complexity increases
Solution Approach 1:
The segmentation is achieved through standard semiconductor manufacturing techniques including multiple ion implantation steps with photolithographic patterning. While the process involves multiple steps (first dopant implantation, mask removal, second dopant implantation), these are conventional techniques that can be integrated into existing fabrication workflows, making the increased complexity manageable and scalable.
Solution Approach 2:
The insulating layer is formed over the semiconductor substrate before dopant implantation to define the active regions and prevent dopant diffusion into unwanted areas. This preliminary structuring simplifies subsequent dopant implantation steps by providing built-in masks and defined implantation zones, reducing the overall manufacturing complexity despite the segmented structure.
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 significantly reduces dark current noise by up to 83% and allows for higher voltage operation with minimal impact on detection efficiency, enhancing the sensitivity and reliability of avalanche photodiodes in photon detection applications.
Implementation Method 1
A first dopant is implanted through the first patterned mask and the insulating layer to form the shallow terminal. A second dopant is implanted through the second patterned mask and insulating layer to form the deep terminal
Implementation Method 2
In existing avalanche diodes light interacts with a silicon lattice to generate electron hole pairs which cause breakdown at a junction where there is a peak electric field
Implementation Method 3
APDs exhibit internal current gain effect of about 100-1000 due to impact ionization, or avalanche effect, when a high reverse bias voltage is applied
Implementation Method 4
The current generated by an avalanche event must be quenched by an appropriate current limited scheme so that the device can recover and reset after an avalanche event
Data Source
AI summary
In one form, a process of manufacturing an avalanche photodiode includes forming an insulating layer over an active region of a semiconductor substrate. A shallow terminal of the avalanche photodiode is defined using a first patterned mask. A first dopant is implanted through the first patterned mask and the insulating layer to form the shallow terminal. The first patterned mask is removed. A deep terminal of the avalanche photodiode is defined using second patterned mask. A second dopant is implanted through the second patterned mask and insulating layer to form the deep terminal of the avalanche photodiode. A respective terminal of at least one of the shallow terminal and the deep terminal is defined using a respective patterned mask that forms at least two regions that are spatially separated from each other with no implanted structure located in a space therebetween.