Tensile Strained Planar Photodiode Fabrication via Thermal Mismatch
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Solution Overview
Problem
Existing methods for fabricating planar photodiodes with tensile mechanical strain are complex and difficult to control, making it challenging to produce devices with precise and simplified processes suitable for near-infrared light detection.
Innovation Solution
A process involving the production of a semiconductor stack with an antireflection layer and a peripheral trench filled with a crystalline semiconductor, where the epitaxy temperature is used to induce tensile strain in the detecting section, allowing for the creation of planar photodiodes with improved spectral absorption range and reduced fabrication complexity.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If a stack of thin layers (silicon nitride, silicon oxide, amorphous silicon) is deposited to induce mechanical strain, then tensile strain is achieved in the germanium layer, but the fabricating process becomes complex
Solution Approach 1:
The patent uses the difference in thermal expansion coefficients between silicon (lower) and germanium (higher) to induce tensile strain. By growing silicon peripheral sections on a silicon substrate and bonding a germanium detecting section to them, the strain is generated through thermal mismatch during cooling from the epitaxy temperature, eliminating the need for complex multi-layer deposition stacks.
2Manufacturing precision
If localized structuring and suspension techniques are used to strain the semiconductor layer, then tensile strain is achieved, but the fabricating process becomes complex and strain control becomes difficult
Solution Approach 1:
The device is segmented into a detecting section (germanium) and peripheral sections (silicon). The peripheral sections are grown directly on the substrate and serve as both structural support and strain-inducing elements. This segmentation simplifies the process by eliminating the need for localized structuring and suspension techniques, as the strain is uniformly applied through the bonded interface.
3Reliability
If direct bonding of structured layers is used, then the strained layer is attached to the substrate, but the mechanical strength requires additional consolidating anneal steps
Solution Approach 1:
The patent performs preliminary actions by growing the peripheral sections with sufficient thickness during the epitaxy process to ensure adequate mechanical strength before bonding. The peripheral sections are designed to be thick enough to provide structural support and maintain strain without requiring additional consolidating anneal steps, as the strain is locked in during the cooling phase of epitaxy.
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 process enables the production of planar photodiodes with tensile strain, enhancing their spectral absorption range and maintaining strain through an epitaxial link, resulting in improved optical and electrical properties, such as a direct electronic band structure, suitable for near-infrared detection with high spatial resolution and simplified fabrication.
Implementation Method 1
decreasing the temperature to a value lower than the epitaxy temperature, the detecting section then being tensilely strained by the peripheral section
Data Source
AI summary
The invention relates to a process for fabricating at least tensilely strained planar photodiode 1, comprising producing a stack formed from a semiconductor layer 53, 55 made of a first material and from an antireflection layer 20; producing a peripheral trench 30 that opens onto a seed sublayer 22 made of a second material of the antireflection layer 20; epitaxy of a peripheral section 31 made of the second material in the peripheral trench 30; and returning to room temperature, a detecting section 10 then being tensilely strained because of the difference in coefficients of thermal expansion between the two materials.