FinFET Fabrication via Segmented STI for Threshold Control
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Solution Overview
Problem
Current processes for fabricating FinFETs are insufficient in producing devices with satisfactory performance, particularly in controlling the channel region and threshold voltage.
Innovation Solution
A method involving the formation of a fin-shaped structure on a substrate, followed by the creation of shallow trench isolation and gate structures, with a portion of the STI removed to expose the sidewalls underneath the gate structures, allowing for epitaxial growth and metal gate formation.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If conventional FinFET fabrication process is used, then manufacturing simplicity is maintained, but device performance is insufficient
Solution Approach 1:
The patent segments the STI structure into two distinct levels: a first STI portion at a higher elevation and a second STI portion at a lower elevation. This segmentation allows different regions of the device to have optimized characteristics, with the first STI providing isolation and the second STI enabling improved gate-to-fin control, thereby enhancing overall device performance without requiring a complete overhaul of the fabrication process
Solution Approach 2:
The patent introduces a vertical dimensionality change by creating a stepped STI structure with two different elevation levels. This dimensional variation allows the gate structure to be positioned at different heights relative to the fin, improving the overlapping area between gate and fin while maintaining manufacturing feasibility through standard etching and deposition techniques
2Reliability
If gate structure is formed directly on STI and fin structure, then manufacturing simplicity is maintained, but channel control and threshold voltage control are insufficient
Solution Approach 1:
The patent applies local quality by creating a non-uniform STI structure where different portions have different elevations. The first STI portion maintains higher elevation for isolation, while the second STI portion is removed to create a lower elevation region. This local variation enables the gate to achieve better control over the channel region directly beneath it, improving both channel control and threshold voltage control without complicating the overall manufacturing process
3Reliability
If STI is removed to expose sidewalls, then epitaxial layer size and shape are improved, but manufacturing complexity increases
Solution Approach 1:
The patent employs preliminary action by selectively removing the second STI portion before the epitaxial growth step. This pre-removal creates the desired stepped structure and exposes the necessary sidewalls in advance, allowing the subsequent epitaxial growth to proceed more effectively with improved layer size and shape control. The selective removal is performed using standard etching techniques with appropriate masking, maintaining manufacturing feasibility
Data Source
AI summary
A method for fabricating fin-shaped field-effect transistor (FinFET) is disclosed. The method includes the steps of: providing a substrate; forming a fin-shaped structure in the substrate; forming a shallow trench isolation (STI) on the substrate and around the bottom portion of the fin-shaped structure; forming a first gate structure on the STI and the fin-shaped structure; and removing a portion of the STI for exposing the sidewalls of the STI underneath the first gate structure.