Plasma Shielding for SPAD Dark Count Reduction
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Solution Overview
Problem
Existing semiconductor structures for single photon avalanche diodes (SPADs) face high dark count rates due to surface damage from plasma processes during manufacturing, particularly affecting the depletion region and multiplication region around the pn-junction, which limits the lowest light intensity that can be reliably detected.
Innovation Solution
A light sensitive semiconductor structure is developed with a plasma shielding structure comprising polysilicon and metal layers to protect the depletion region near the silicon surface, with shallow trench isolation (STI) burying the edge of the pn-junction beneath the STI to minimize plasma damage, thereby reducing dark count rates.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If plasma processes are used during manufacturing, then device fabrication is enabled, but surface damage occurs in the depletion region increasing dark count rate
Solution Approach 1:
A plasma shielding structure comprising polysilicon and metal layers is introduced as an intermediary between the plasma environment and the silicon surface. This shielding structure absorbs plasma damage, protecting the depletion region and multiplication region from surface damage that would otherwise increase dark count rate.
Solution Approach 2:
The plasma shielding structure is formed before final device completion, preemptively protecting vulnerable regions from plasma damage during subsequent manufacturing steps. The shielding is in place before plasma processes occur, preventing surface damage before it can affect the depletion region.
2Device complexity
If the pn-junction edge is exposed at the silicon surface, then device structure is simplified, but plasma damage to the depletion region increases dark count rate
Solution Approach 1:
The plasma shielding structure acts as a protective intermediary layer positioned directly over the pn-junction edge and depletion region. This shielding comprises polysilicon and metal layers that absorb plasma bombardment, preventing direct damage to the junction edge while maintaining the simplified exposed structure.
Solution Approach 2:
The plasma shielding is applied locally at critical regions where the pn-junction edge meets the silicon surface and where the depletion region is most vulnerable to plasma damage. This localized protection targets specific high-risk areas without requiring complete structural modification of the entire device.
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 proposed structure significantly reduces dark count rates by one to two orders of magnitude, enhancing the ability to detect low light intensities by shielding the depletion region from plasma damage, improving the overall performance of SPADs in low light settings.
Implementation Method 1
a plasma shielding structure comprising polysilicon and metal layers to protect the depletion region near the silicon surface
Implementation Method 2
single photon detectors such as single photon avalanche diodes (SPADs) and avalanche photodiodes (APDs)
Implementation Method 3
multiplication region and the depletion region around the pn-junction
Data Source
AI summary
A light sensitive semiconductor structure including a pn-junction in a silicon substrate. The pn-junction includes a central part and an edge part around surrounding the central part, the edge part being in contact with a surface of the silicon substrate. The structure further includes a plasma shielding structure covering at least a depletion width of the pn-junction over at least a part of the edge part where the edge part contacts the surface of the silicon substrate.