Self-Aligned Contact Trenches for Vertical Strain in VTFETs
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Solution Overview
Problem
Conventional techniques face challenges in introducing strain into vertical transport field-effect transistors (VTFETs) due to the free top surface, which relaxes the initial strain in vertically standing semiconductor fins, limiting carrier mobility and device performance.
Innovation Solution
The method involves forming fins over a substrate with self-aligned contact trenches and inner spacers, filling the trenches with highly stressed contact material that acts as both a metal conductor and stressor to induce vertical strain in the fin channels, enhancing carrier mobility by maintaining strain throughout the fabrication process.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If conventional techniques are used to form vertical FETs, then device structure is simple, but strain cannot be maintained in the fin channel due to free top surface
Solution Approach 1:
The method performs preliminary actions by forming strained semiconductor material layers and contact trenches with inner spacers before final contact formation. The inner spacers are formed in advance to define precise contact locations that will maintain strain in the fin channel throughout subsequent fabrication steps.
Solution Approach 2:
The contact material serves as an intermediary that transfers stress into the fin channel. By selecting contact materials with specific stress properties, the invention mediates between the electrical connection function and the strain induction function, allowing both metal conduction and stress transfer to the channel.
2Reliability
If strain is introduced into vertical FETs, then carrier mobility improves, but the free top surface causes strain relaxation
Solution Approach 1:
The invention applies local quality by forming inner spacers at specific locations (sidewalls of contact trenches) and using strained semiconductor material layers at particular positions in the fin structure. This localized approach maintains strain in the channel region while allowing other areas to have different properties.
Solution Approach 2:
The fin structure uses composite materials including strained semiconductor material layers formed over the fin. These layered composite structures maintain strain by combining materials with different properties, where the strained layers preserve stress in the channel despite the free top surface.
3Productivity
If device size is reduced for scaling, then integration density increases, but maintaining strain becomes more difficult
Solution Approach 1:
The invention transitions to vertical transport FETs with fins extending in the vertical dimension. By moving from planar to vertical architecture, the method achieves scaling and increased integration density while maintaining strain through the vertical fin channel using the contact material and inner spacer configuration.
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 effectively transfers stress into the fin channels, improving carrier mobility and drive current in VTFETs, enabling high-performance devices at smaller scales without increasing device size or capacitance.
Implementation Method 1
The contact material comprises a stressor material that induces vertical strain in the at least one fin
Data Source
AI summary
A method of forming a semiconductor structure includes forming at least one fin disposed over a top surface of a substrate, the fin providing a vertical transport channel for a vertical transport field-effect transistor. The method also includes forming a top source/drain region disposed over a top surface of the fin, and forming a first contact trench at a first end of the fin and a second contact trench at a second end of the fin, the first and second contact trenches being self-aligned to the top source/drain region. The method further includes forming inner spacers on sidewalls of the first contact trench and the second contact trench, and forming contact material in the first contact trench and the second contact trench between the inner spacers. The contact material comprises a stressor material that induces vertical strain in the fin.