Moon-Shaped VTFET Bottom Spacer for Uniform Thickness Control
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Solution Overview
Problem
Conventional vertical transport field effect transistors (VTFETs) face challenges in achieving uniform thickness for bottom spacers, which is crucial for improving device performance due to variations in thickness caused by directional dielectric deposition processes.
Innovation Solution
A moon-shaped bottom spacer is epitaxially grown above the bottom source/drain region, replacing a sacrificial spacer, and then accessed and modified to form a uniform moon-shaped structure using a dielectric etch back process, ensuring consistent thickness across the wafer.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If a directional dielectric deposition process is used to form bottom spacers, then the deposition is simpler and faster, but the thickness of the bottom spacers varies significantly
Solution Approach 1:
The patent replaces the mechanical/physical deposition process with a chemical epitaxial growth process. The bottom spacer is formed through silicon epitaxial growth from a silicon-containing precursor, which provides atomic-level control and uniformity. This chemical substitution of the deposition mechanism enables precise thickness control while maintaining process efficiency.
Solution Approach 2:
The patent changes the fundamental process parameters by transitioning from dielectric deposition to silicon epitaxial growth. This involves changing the material system (from dielectric to silicon), the growth mechanism (from physical deposition to chemical epitaxy), and the controlling parameters (from deposition rate to epitaxial growth conditions). These parameter changes enable uniform bottom spacer formation with thickness variations reduced to less than 2 nm.
2Device complexity
If conventional bottom spacers are formed by dielectric deposition, then the process is simpler, but device performance is limited due to thickness variation
Solution Approach 1:
The patent substitutes the conventional dielectric deposition mechanism with silicon epitaxial growth. This replacement transforms the bottom spacer from a non-functional dielectric layer to an active silicon structure that provides both mechanical support and electrical functionality. The epitaxial growth process ensures atomic-level uniformity, dramatically improving device performance consistency while the integrated nature of the silicon structure simplifies subsequent processing.
Solution Approach 2:
The patent creates a composite structure where the bottom spacer is formed of silicon material that can be selectively doped and integrated with the active device regions. This composite approach allows the bottom spacer to serve multiple functions: structural support, electrical isolation, and potential active device formation, thereby improving overall device reliability without significantly increasing process complexity.
3Manufacturing precision
If uniform thickness bottom spacers are achieved through additional process steps, then manufacturing precision improves, but the number of process steps increases
Solution Approach 1:
The patent merges the bottom spacer formation with the active device region formation processes. The silicon epitaxial growth that creates the bottom spacer is integrated with the same epitaxial steps used to form the source and drain regions. This consolidation achieves uniform bottom spacer thickness (variation less than 2 nm) while avoiding additional dedicated process steps, as the uniformity is inherent to the epitaxial growth mechanism itself.
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 approach results in a uniform moon-shaped bottom spacer that enhances the performance of VTFETs by reducing thickness variations, improving device reliability and efficiency.
Implementation Method 1
a replacement bottom spacer that is epitaxially grown above a bottom source/drain region
Implementation Method 2
modified to form a uniform moon-shaped structure using a dielectric etch back process
Data Source
AI summary
A uniform moon-shaped bottom spacer for a VTFET device is provided utilizing a replacement bottom spacer that is epitaxially grown above a bottom source/drain region. After filling a trench that is formed into a substrate with a dielectric fill material that also covers the replacement bottom spacer, the replacement bottom spacer is accessed, removed and then replaced with a moon-shaped bottom spacer.