GAA Nanosheet Channel Thickness Tuning for Threshold Voltage Control
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
Conventional nanosheet devices, such as gate-all-around (GAA) transistors, face challenges in controlling threshold voltage due to smaller depletion regions, smaller channel volumes, and mobility degradation from heavy doping, making it difficult to achieve different threshold voltages in various regions.
Innovation Solution
The method involves forming nanosheet transistors on multiple fins, implanting a threshold modifying impurity, such as germanium, into the p-type GAA transistor channel, and trimming critical dimensions to adjust the threshold voltage, allowing for a wider tuning range without the need for complex metal work function schemes.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If conventional nanosheet devices are used, then gate control is improved, but threshold voltage control becomes difficult
Solution Approach 1:
The patent introduces selective doping regions with different dopant concentrations and types in the channel region, creating local variations in electrical properties. This allows different threshold voltages to be achieved in different regions of the same device while maintaining overall gate control through the gate-all-around structure.
Solution Approach 2:
The patent modifies the threshold voltage by changing physical parameters such as dopant concentration, dopant type, and channel thickness in specific regions. These parameter changes enable precise control of threshold voltage without compromising the gate control provided by the nanosheet structure.
2Manufacturing precision
If heavy doping is applied to adjust threshold voltage, then threshold voltage control is improved, but mobility degradation occurs
Solution Approach 1:
The patent applies doping selectively in specific regions of the channel rather than uniform heavy doping throughout. This localized approach allows threshold voltage adjustment in regions where it is needed while preserving high mobility in other regions, thus avoiding the trade-off between threshold voltage control and carrier mobility.
3Ease of manufacture
If conventional fabrication processes are used, then manufacturing simplicity is maintained, but threshold voltage tuning range is limited
Solution Approach 1:
The patent incorporates doping steps and critical dimension trimming operations at specific stages during the fabrication process, before final device assembly. These preliminary actions enable wide threshold voltage tuning while maintaining compatibility with conventional CMOS fabrication workflows, as the modifications are integrated into existing process steps.
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 enables simplified fabrication of nanosheet transistors with improved threshold voltage tuning, allowing for the creation of low, standard, and high threshold voltage regions, enhancing device performance and process efficiency.
Implementation Method 1
implanting a threshold modifying impurity, such as germanium, into the p-type GAA transistor channel
Data Source
AI summary
Embodiments of the present disclosure includes a semiconductor device. The semiconductor device includes first suspended nanostructures vertically stacked over one another and disposed on a substrate, a first gate stack engaging the first suspended nanostructures, a first gate spacer disposed on sidewalls of the first gate stack, second suspended nanostructures vertically stacked over one another and disposed on the substrate, a second gate stack engaging the second suspended nanostructures, and a second gate spacer disposed on sidewalls of the second gate stack. A middle portion of the first suspended nanostructures has a first thickness measured in a direction perpendicular to a top surface of the substrate. A middle portion of the second suspended nanostructures has a second thickness measured in the direction. The second thickness is smaller than the first thickness.