Multigate Device External Resistance Mitigation via Selective Epitaxy
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Solution Overview
Problem
Multigate devices, such as finFET and tri-gate transistors, face limitations due to high external resistance (Rext) and interface state density (Dit) in III-V types, primarily due to challenges in forming high-quality contacts and a high concentration of interface states at the oxide/semiconductor interface.
Innovation Solution
A method involving the growth of two highly doped conformal epitaxial layers on the fins of multigate devices, followed by selective removal to form a trench, allowing for the formation of a gate within the trench, which reduces external resistance by maintaining doped epitaxial layers in source and drain regions while minimizing processing complexity.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If conventional fabrication processes are used for III-V multigate devices, then device structure can be formed, but external resistance remains high due to difficulty in forming high-quality contacts
Solution Approach 1:
The patent applies preliminary action by growing highly doped epitaxial layers in the source and drain regions before final contact formation. This pre-doping creates low-resistance regions that facilitate subsequent contact formation, addressing the contact quality issue while maintaining reasonable processing complexity
Solution Approach 2:
The patent implements local quality by creating highly doped regions specifically in the source and drain areas through selective epitaxial growth. This localized doping improves contact quality where needed without requiring global process changes, balancing reliability improvement with manufacturing ease
2Reliability
If conventional fabrication processes are used for III-V multigate devices, then device structure can be formed, but interface state density remains high at the oxide/semiconductor interface
Solution Approach 1:
The patent applies parameter changes by modifying the doping concentration and distribution in the epitaxial layers. By creating highly doped regions adjacent to the oxide/semiconductor interface, the electrical properties are changed to reduce interface state effects without requiring high thermal budget processing
Solution Approach 2:
The patent uses the highly doped epitaxial layer as an intermediary between the metal contact and the oxide/semiconductor interface. This intermediate layer mediates the interaction, reducing the impact of interface states on device performance while avoiding the need for high-temperature processing
3Reliability
If highly doped epitaxial layers are grown and selectively removed to form trenches, then external resistance is reduced, but manufacturing process complexity increases
Solution Approach 1:
The patent applies segmentation by dividing the epitaxial layer formation into multiple highly doped layers with different doping concentrations and profiles. This segmented approach allows selective removal to form trenches while maintaining low external resistance, managing process complexity through structured segmentation
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 approach effectively lowers external resistance and interface state density, enhancing the performance of multigate devices by reducing contact resistance and improving high-speed device performance.
Implementation Method 1
growing a first conformal epitaxial layer directly on the fin and substrate, wherein the first conformal epitaxial layer is highly doped, growing a second conformal epitaxial layer directly on the first conformal epitaxial layer, wherein the second conformal epitaxial layer is highly doped
Data Source
AI summary
A method for fabricating a multigate device includes forming a fin on a substrate of the multigate device, the fin being formed of a semiconductor material, growing a first conformal epitaxial layer directly on the fin and substrate, wherein the first conformal epitaxial layer is highly doped, growing a second conformal epitaxial layer directly on the first conformal epitaxial layer, wherein the second conformal epitaxial layer is highly doped, selectively removing a portion of second epitaxial layer to expose a portion of the first conformal epitaxial layer, selectively removing a portion of the first conformal epitaxial layer to expose a portion of the fin and thereby form a trench, and forming a gate within the trench.