Strained Channel FinFET Stress Management via Epitaxial Layering
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Solution Overview
Problem
As fin length scales increase in metal-oxide-semiconductor field-effect transistors (MOSFETs), axial stress components in silicon germanium (SiGe) fins become relaxed, leading to suboptimal finFET performance due to strain relaxation.
Innovation Solution
The semiconductor device incorporates a substrate with isolation features, a fin substrate disposed between and above these features, and an epitaxial layer deposited over exposed portions, including the top surface and sidewalls of the fin substrate, to counterbalance the relaxation of longitudinal stress components.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Device complexity
If fin length is increased to improve device manufacturability and reduce complexity, then axial stress components become relaxed, but finFET performance deteriorates due to strain relaxation
Solution Approach 1:
The patent changes the material composition parameter by incorporating SiGe alloy with varying germanium concentrations in the fin structure. This material parameter change enables maintenance of compressive stress in longer fins without requiring excessive strain that would cause dislocation, thus resolving the contradiction between fin length and performance
Solution Approach 2:
The patent uses composite SiGe material structure with different germanium concentrations in different regions (higher Ge concentration in channel region, lower in source/drain regions). This composite approach allows optimized stress distribution throughout the fin structure, maintaining performance while enabling longer fin lengths
2Reliability
If SiGe fin material is used to increase carrier mobility and improve performance, then compressive stress is enhanced, but strain relaxation occurs at longer fin lengths causing performance degradation
Solution Approach 1:
The patent applies local quality by varying the germanium concentration locally within the fin structure - higher Ge content (e.g., 30-50%) in the channel region to maximize stress and mobility, and lower Ge content (e.g., 0-20%) in source/drain regions to prevent excessive strain. This localized material optimization maintains compressive stress stability throughout the fin length
Solution Approach 2:
The fin structure is segmented into different material regions with optimized Ge concentrations for specific functions: channel region for high mobility, source/drain regions for stress management. This segmentation allows each region to contribute optimally to overall stress stability without causing relaxation
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 configuration enhances transistor performance by maintaining high uni-axial compressive stress levels, optimizing the channel region's performance and improving overall device efficiency.
Implementation Method 1
an epitaxial layer disposed over exposed portions of the fin substrate
Data Source
AI summary
Various strained channel transistors are disclosed herein. An exemplary semiconductor device includes a substrate and a fin structure disposed over the substrate. The fin structure includes a first epitaxial layer disposed on the substrate, a second epitaxial layer disposed on the first epitaxial layer, and a third epitaxial layer disposed on the second epitaxial layer. The second epitaxial layer includes a relaxed transversal stress component and a longitudinal compressive stress component, and the third epitaxial layer has uni-axial strain. A gate structure is disposed on a channel region of the fin structure, such that the gate structure interposes a source region and a drain region of the fin structure.