Germanium Photodiode Silicon Cap Protection
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Solution Overview
Problem
Germanium-based photodiodes are susceptible to damage during semiconductor processing due to its low melting point and sensitivity to chemicals like hydrogen peroxide, leading to performance limitations such as high dark current.
Innovation Solution
A silicon cap is formed over the germanium structure to protect it from thermal damage and chemical exposure, allowing for annealing at higher temperatures and reducing dark current, while also enabling self-aligned silicided contacts.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If germanium is exposed to high temperatures for annealing, then dark current is reduced, but germanium structure deteriorates due to low melting point
Solution Approach 1:
A silicon cap layer is deposited over the germanium structure to serve as a protective intermediary. This cap has high melting point and thermal stability, allowing the germanium underneath to undergo annealing at elevated temperatures without direct exposure to thermal damage. The silicon cap absorbs the thermal stress and protects the germanium from deterioration while still permitting the beneficial reduction of dark current through the annealing process.
Solution Approach 2:
The silicon cap is formed over the germanium structure before the annealing process is applied. This preliminary protective action ensures that when high-temperature annealing is subsequently performed to reduce dark current, the germanium is already shielded and can withstand the thermal treatment without structural deterioration.
2Ease of manufacture
If germanium is exposed to chemicals like hydrogen peroxide during processing, then cleaning is achieved, but germanium dissolves
Solution Approach 1:
The silicon cap acts as a chemical barrier between the germanium structure and harsh chemicals used in processing. During cleaning steps involving hydrogen peroxide or other aggressive chemistries, the silicon cap protects the germanium from direct contact and dissolution, while still allowing the cleaning process to proceed effectively on exposed surfaces.
3Reliability
If silicon cap is added to protect germanium, then thermal and chemical protection is provided, but device complexity increases
Solution Approach 1:
The silicon cap serves multiple functions simultaneously: it provides thermal protection during annealing, chemical protection during processing, and enables self-aligned silicided contact formation. By consolidating these multiple protective and functional roles into a single structural element, the overall device complexity is minimized while achieving comprehensive protection.
Solution Approach 2:
The protection function and the contact formation function are merged into the same silicon cap structure. The cap not only protects the germanium but also serves as the basis for forming self-aligned silicided contacts, eliminating the need for separate protective layers and contact structures.
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 silicon cap significantly reduces dark current in germanium photodiodes by protecting them from thermal damage and chemical exposure, improving performance and enabling efficient contact formation.
Implementation Method 1
A silicon cap is formed over the germanium structure to protect it from thermal damage
Implementation Method 2
A silicon cap is formed over the germanium structure to protect it from thermal damage and chemical exposure
Implementation Method 3
allowing for annealing at higher temperatures and reducing dark current
Data Source
AI summary
There are disclosed herein various implementations of a photodiode including a silicon substrate, and an N type germanium region situated over the silicon substrate, the N type germanium region being a cathode of the photodiode. In addition, the photodiode includes a P type germanium region situated over the N type germanium region, the P type germanium region being an anode of the photodiode. The photodiode also includes a P type silicon cap over the P type germanium region, an anode contact of the photodiode situated on the P type silicon cap, and one or more cathode contacts of the photodiode electrically connected to the N type germanium region.