Sub-fin Leakage Control in FinFET Transistors
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Solution Overview
Problem
FinFET transistors face challenges in minimizing off-state leakage, particularly in sub-fin regions, due to defects and doping issues, which degrade performance and increase external resistance, especially as transistor architectures shrink.
Innovation Solution
The implementation of a replacement fin in FinFET transistors, where source and drain regions are epitaxially grown in trenches extending into the sub-fin region, with a band offset from the substrate material, reducing sub-fin leakage and maintaining high transistor drive current.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If source and drain regions are formed in conventional FinFET structures, then transistor drive current is achieved, but off-state leakage increases due to defects and doping issues in sub-fin regions
Solution Approach 1:
The source and drain regions are segmented into two distinct parts: an upper portion formed in the fin structure and a lower portion extending into the sub-fin region. This segmentation allows the upper portion to provide drive current while the lower portion acts as a barrier to sub-fin leakage, resolving the contradiction between achieving drive current and preventing leakage.
Solution Approach 2:
Different regions of the source and drain structures are given different properties: the upper portions are doped to provide conductivity for drive current, while the lower portions extending into sub-fin regions are designed with specific doping profiles or material compositions to create potential barriers that block leakage currents. This local differentiation resolves the contradiction by optimizing each region for its specific function.
2Productivity
If transistor architectures are shrunk to improve integration density, then productivity increases, but off-state leakage worsens due to increased impact of sub-fin defects
Solution Approach 1:
The solution extends the source and drain regions vertically into the sub-fin region below the fin structure, utilizing the depth dimension to create leakage barriers. This vertical extension into the third dimension (depth below fin) allows leakage control without compromising the horizontal scaling needed for high integration density, thus resolving the contradiction between productivity and reliability.
3Reliability
If doped regions extend into sub-fin region to reduce leakage, then off-state leakage decreases, but manufacturing precision requirements increase
Solution Approach 1:
The lower portions of source and drain regions act as intermediary structures between the upper doped regions and the substrate. These intermediary regions provide a transition zone where doping profiles can be gradually modified, reducing the abruptness of doping transitions and thereby lowering manufacturing precision requirements while still achieving effective leakage blocking.
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 effectively reduces off-state leakage while maintaining high on-state drive current, improving the 'on/off' current ratio and minimizing the impact of defective regions on transistor performance.
Implementation Method 1
source and drain regions are epitaxially grown in trenches extending into the sub-fin region
Implementation Method 2
with a band offset from the substrate material, reducing sub-fin leakage
Data Source
AI summary
A replacement fin in a heterogeneous FinFET transistor in which source and drain regions are grown in corresponding trenches that extend into a sub-fin region. This depth of the epitaxial source/drain regions, in combination with the selected materials, can reduce off-state leakage while also keeping high defect density portions out of the active portions of the source and drain. In one embodiment, materials are selected for the source and drain regions that have an energy band offset from the material selected for the substrate. This band offset between the source/drain material can further reduce sub-fin leakage.