Ultra-Thin Fin Structure With Tapered Base for Gate Control
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Solution Overview
Problem
Ultra-thin fin structures in fin field effect transistors (finFETs) are prone to bending or collapsing due to lack of structural integrity, compromising gate control and saturation current during fabrication processes.
Innovation Solution
Forming ultra-thin fins with a tapered bottom profile using silicon and silicon-germanium (SiGe) materials, with varying germanium concentration and controlled taper angles, to enhance structural rigidity and gate control.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If ultra-thin fin structures are used to improve gate control, then gate control is improved, but structural integrity deteriorates causing bending or collapsing
Solution Approach 1:
The fin structure employs a tapered profile where the width varies along the height: narrower at the top (5-15 nm) for optimal gate control and wider at the bottom (8-20 nm) for enhanced structural support. This local variation in dimensions allows the same structure to simultaneously achieve both improved gate control and maintained structural integrity.
Solution Approach 2:
The fin structure is formed as a composite of silicon and silicon-germanium (SiGe) materials with varying germanium concentrations. The SiGe portions provide enhanced mechanical strength and structural rigidity compared to pure silicon, while maintaining the ultra-thin profile needed for gate control. The composite material approach allows optimization of both electrical performance and mechanical stability.
2Manufacturing precision
If ultra-thin fin structures are used, then gate control is improved, but vulnerability to mechanical stress increases
Solution Approach 1:
The tapered profile concentrates the width variation strategically: the top portion maintains ultra-thin dimensions (5-15 nm) for optimal gate control, while the bottom portion widens (8-20 nm) to serve as a mechanical anchor that resists bending and collapsing during fabrication processes like isolation region formation.
Solution Approach 2:
The silicon-SiGe composite structure provides enhanced mechanical properties. The SiGe regions with higher germanium content offer superior structural rigidity and stress resistance, reducing the vulnerability of ultra-thin fins to mechanical stress during manufacturing while preserving the narrow top section for gate control.
3Manufacturing precision
If fin width is reduced for better gate control, then gate control is improved, but structural rigidity deteriorates
Solution Approach 1:
The fin structure implements spatially varying dimensions: the top width (5-15 nm) is optimized for gate control, while the bottom width (8-20 nm) is increased to provide structural rigidity. This local differentiation allows the structure to be thin where needed for electrical performance and thick where needed for mechanical stability.
Solution Approach 2:
The silicon-SiGe composite material system provides enhanced structural rigidity throughout the fin structure. The SiGe portions, particularly in the wider bottom section, offer superior mechanical properties that compensate for the reduced overall width, maintaining structural rigidity while enabling the ultra-thin profile required for gate control.
Data Source
AI summary
The present disclosure describes a method for forming ultra-thin fins with a tapered bottom profile for improved structural rigidity and gate control characteristics. The method includes forming a fin structure that includes an epitaxial layer portion and a doped region portion surrounded by an isolation region so that a top section of the epitaxial layer portion is above the isolation region. The method also includes depositing a silicon-based layer on the top portion of the epitaxial layer above the isolation region and annealing the silicon-based layer to reflow the silicon-based layer. The method further includes etching the silicon-based layer and the fin structure above the isolation region to form a first bottom tapered profile in the fin structure above the isolation region and annealing the fin structure to form a second bottom tapered profile below the first bottom tapered profile and above the isolation region.