GAA Nanosheet Transistor Threshold Voltage Tuning via Local Doping
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Solution Overview
Problem
Conventional nanosheet devices, such as gate-all-around (GAA) transistors, face challenges in controlling threshold voltage due to smaller depletion regions and mobility degradation from heavy doping, making it difficult to achieve different threshold voltages in various regions within integrated circuits.
Innovation Solution
The method involves forming nanosheet transistors on multiple fins, implanting a threshold modifying impurity like germanium into the p-type GAA transistors to create a distinctive distribution, and trimming critical dimensions to adjust threshold voltage, allowing for a wider tuning range without the complexity of complicated metal work function schemes.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If heavy doping is used to control threshold voltage in conventional nanosheet devices, then threshold voltage control is improved, but mobility degradation occurs
Solution Approach 1:
The patent applies local quality by differentiating the doping strategy between n-type and p-type nanosheet devices. p-type devices receive heavy doping to achieve proper threshold voltage control, while n-type devices are kept lightly doped or undoped to preserve carrier mobility. This selective doping approach allows each device type to have optimized electrical characteristics without compromising the other.
Solution Approach 2:
The patent segments the doping process into distinct stages and regions. Multiple doping steps are employed with different dopant types (boron, phosphorus, arsenic) applied at different times and to different device regions. This segmentation enables precise control over the spatial and temporal distribution of dopants, achieving the desired threshold voltage characteristics while minimizing mobility degradation.
2Ease of manufacture
If conventional nanosheet devices are used, then fabrication simplicity is improved, but threshold voltage tuning capability deteriorates
Solution Approach 1:
The patent introduces dynamic threshold voltage tuning capability by implementing multiple doping steps that can be selectively applied to different device regions. The doping process is made adjustable through controlled application of different dopant types and concentrations, allowing the threshold voltage to be dynamically tuned during fabrication without requiring complex post-processing or multiple device variants.
Solution Approach 2:
The patent utilizes parameter changes by varying dopant concentration, dopant type, and doping timing to achieve different threshold voltage characteristics. By changing these parameters across different fabrication steps and device regions, the patent enables wide threshold voltage tuning range while maintaining compatibility with conventional fabrication processes.
3Adaptability or versatility
If multiple metal work function schemes are used to achieve different threshold voltages, then threshold voltage diversity is improved, but device complexity increases
Solution Approach 1:
The patent extracts the threshold voltage control function from the gate metal work function and relocates it to the channel doping profile. By removing the need for multiple metal layers with different work functions, the patent simplifies the gate stack structure while maintaining the capability to achieve diverse threshold voltages through controlled doping of the channel region.
Solution Approach 2:
The patent makes the doping process multi-functional by using it not only for threshold voltage control but also for channel formation, carrier concentration adjustment, and device type differentiation. This universal approach to doping eliminates the need for separate processing steps for each function, reducing overall device complexity while achieving diverse threshold voltage characteristics.
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 adjustable threshold voltages, achieving multiple voltage levels (LVt, SVt, HVt) in different regions, improving transistor performance and manufacturing efficiency.
Implementation Method 1
implanting a threshold modifying impurity like germanium into the p-type GAA transistors
Data Source
AI summary
Embodiments of the present disclosure includes a method of forming a semiconductor device. The method includes providing a substrate having a plurality of first semiconductor layers and a plurality of second semiconductor layers disposed over the substrate. The method also includes patterning the first semiconductor layers and the second semiconductor layers to form a first fin and a second fin, removing the first semiconductor layers from the first and second fins such that a first portion of the patterned second semiconductor layers becomes first suspended nanostructures in the first fin and that a second portion of the patterned second semiconductor layers becomes second suspended nanostructures in the second fin, and doping a threshold modifying impurity into the first suspended nanostructures in the first fin.