Recessed Inner Gate Spacers for Strain-Induced Carrier Mobility in GAA Transistors
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Solution Overview
Problem
Gate-all-around (GAA) transistors, such as nanowire or nanoribbon transistors, face performance mismatches due to reduced hole mobility, particularly in PMOS transistors, attributed to lack of strain in the channel body, which affects carrier mobility and performance uniformity between PMOS and NMOS devices.
Innovation Solution
The technique involves recessing inner gate spacers to expose tip regions of the channel body, allowing the source and drain regions to clad the tip regions on multiple sides, thereby inducing uniaxial strain and enhancing carrier mobility. Additionally, integrating high channel mobility materials in the channel body and forming a core and peripheral structure with different materials to improve transistor performance.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If inner gate spacers are recessed to expose tip regions of the channel body, then carrier mobility is improved through uniaxial strain induction, but manufacturing complexity increases due to additional recessing steps
Solution Approach 1:
The inner gate spacers are recessed in advance before source and drain region formation, preparing the structure to receive cladding material that will induce uniaxial strain. This preliminary action enables the subsequent strain induction mechanism to work effectively on the exposed tip regions of the channel body.
Solution Approach 2:
The recessing is applied selectively to specific regions of the inner gate spacers, exposing only the tip regions of the channel body where strain induction is most beneficial. This localized approach ensures that uniaxial strain is concentrated where it most effectively improves carrier mobility, rather than applying strain uniformly throughout the entire channel.
2Reliability
If source and drain regions are formed to clad tip regions of the channel body on multiple sides, then uniaxial strain is induced to enhance carrier mobility, but device structure becomes more complex
Solution Approach 1:
The source and drain regions are formed to clad or wrap around the tip regions of the channel body on multiple sides, creating a nested structure where the cladding regions envelop the channel tips. This nested configuration maximizes the strain induction effect by surrounding the channel body with strain-inducing material from multiple directions.
3Reliability
If high channel mobility materials are integrated in the channel body with different compositional structures, then performance matching between PMOS and NMOS transistors is improved, but manufacturing precision requirements increase
Solution Approach 1:
The channel body is constructed with different materials or compositional structures in different regions - specifically, high channel mobility materials are integrated into the channel body to create compositionally distinct core and peripheral structures. This local differentiation allows optimization of carrier mobility in specific regions while maintaining overall device performance matching.
Solution Approach 2:
The channel body employs composite material structures combining different semiconductor materials with distinct compositional characteristics. This composite approach enables simultaneous optimization of hole mobility in PMOS and electron mobility in NMOS devices, achieving performance matching through material composition rather than geometric scaling alone.
Data Source
Figure 1A~1B
Figure 1C~1D
Figure 2
AI summary
A semiconductor structure includes a body including semiconductor material, and a gate structure at least in part wrapped around the body. The semiconductor structure further includes a source region and a drain region, the body laterally extending between the source and drain regions. The body has a middle region between first and second tip regions. In an example, the source region at least in part wraps around the first tip region of the body, and/or the drain region at least in part wraps around the second tip region of the body. In another example, the body includes a core structure and a peripheral structure (e.g., cladding or layer that wraps around the core structure in the middle region of the body) that is compositionally different from the core structure. The body can be, for instance, a nanoribbon, nanosheet, or nanowire or a gate-all-around device or a forksheet device.