Ultra-Thin Fin Profile With Tapered Bottom for Bend Resistance
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Solution Overview
Problem
Ultra-thin fin structures in finFETs lack structural integrity, leading to bending or collapsing during fabrication processes due to mechanical stress and limited saturation current compared to thicker fin structures.
Innovation Solution
The method involves forming ultra-thin fins with a tapered bottom profile using silicon and silicon-germanium materials, with a Ge concentration varying along the fin height, to enhance structural stiffness while maintaining gate control, by tailoring the dimensions and Ge concentration to achieve optimal mechanical and electrical performance.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If ultra-thin fin structures are used, then gate control over the channel region is improved, but structural integrity deteriorates leading to bending or collapsing during fabrication
Solution Approach 1:
The fin structure employs a tapered bottom profile where the width varies along the height, being narrower at the top and wider at the bottom. This local variation in geometry provides enhanced structural support at the base while maintaining the ultra-thin top section for gate control, thus resolving the contradiction between improved gate control and deteriorated structural integrity
Solution Approach 2:
The fin structure is formed as a composite of silicon and silicon-germanium materials with varying Ge concentration along the fin height. The silicon-germanium portion at the bottom provides enhanced mechanical strength and structural integrity, while the silicon portion at the top maintains electrical performance, thus resolving the contradiction between gate control and structural integrity
2Reliability
If ultra-thin fin structures are used, then gate control is improved, but susceptibility to bending during fabrication increases
Solution Approach 1:
The tapered bottom profile creates a local geometric reinforcement at the fin base where the width is increased relative to the top section. This local thickening provides resistance against bending forces during fabrication processes while preserving the ultra-thin dimension at the top for effective gate control
Solution Approach 2:
The silicon-germanium material with higher Ge concentration at the bottom portion of the fin structure provides enhanced mechanical stiffness and resistance to bending, while the silicon material at the top maintains the electrical characteristics needed for gate control, thus reducing bending susceptibility without compromising 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.