SiGe MOSFET Interfacial Layer Treatment for Higher Electron Mobility
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Solution Overview
Problem
The formation of an interfacial layer with silicon germanium channel regions in MOSFETs often results in dangling bonds, which decrease electron mobility, and the addition of a cap layer to mitigate this increases device thickness, compromising dimensions.
Innovation Solution
A method involving thermal annealing and trimethyl aluminum (TMA) pretreatment is used to remove germanium oxide from the interfacial layer, followed by nitridation to form a silicon oxynitride layer, which prevents germanium out-diffusion and maintains a low interface state density, allowing higher electron mobility without the need for an epitaxial cap layer.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If an interfacial layer is formed on silicon germanium channel region, then the interface between channel region and gate insulator is improved, but dangling bonds are created on the surface of interfacial layer which decreases electron mobility
Solution Approach 1:
The patent extracts and removes germanium oxide and dangling bonds from the interfacial layer surface through thermal annealing and TMA pretreatment processes, eliminating the harmful factor while preserving the beneficial interface quality
Solution Approach 2:
The patent applies preliminary thermal annealing and TMA pretreatment to the interfacial layer before depositing the gate insulator, proactively removing germanium oxide and passivating dangling bonds in advance to prevent mobility degradation
2Object-generated harmful factors
If a cap layer is epitaxially grown on the channel region to remove dangling bonds, then electron mobility is improved, but the thickness of the channel region increases which compromises device dimensions
Solution Approach 1:
The patent removes germanium oxide from the interfacial layer through thermal annealing and TMA pretreatment, eliminating the source of dangling bonds without adding any cap layer, thus maintaining the original channel thickness
Solution Approach 2:
The patent uses TMA (trimethyl aluminum) as an intermediary substance that reacts with germanium oxide to form removable byproducts, enabling removal of harmful germanium oxide without requiring an epitaxial cap layer
3Ease of manufacture
If germanium oxide is present in the interfacial layer, then the interfacial layer formation is simplified, but electron mobility decreases due to dangling bonds
Solution Approach 1:
The patent incorporates preliminary thermal annealing and TMA pretreatment steps into the manufacturing process that efficiently remove germanium oxide and passivate dangling bonds, maintaining ease of manufacture while eliminating harmful effects
Solution Approach 2:
The patent changes the thermal and chemical parameters of the interfacial layer through controlled annealing temperature and TMA exposure, transforming the layer from containing harmful germanium oxide to having removed germanium oxide and passivated surface
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 effectively removes germanium oxide, maintains a low interface state density, and enhances electron mobility while allowing for device scaling without increasing device thickness, thus addressing the mobility degradation and dimensional compromise issues.
Implementation Method 1
The interfacial layer is treated with trimethyl aluminum (TMA)
Implementation Method 2
The interfacial layer is treated with trimethyl aluminum (TMA)
Implementation Method 3
followed by nitridation to form a silicon oxynitride layer
Data Source
AI summary
A semiconductor device includes a silicon germanium channel, a germanium-free interfacial layer, a high-k dielectric layer, and a metal gate electrode. The silicon germanium channel is over a substrate. The germanium-free interfacial layer is over the silicon germanium channel. The germanium-free interfacial layer is nitridated. The high-k dielectric layer is over the germanium-free interfacial layer. The metal gate electrode is over the high-k dielectric layer.