Nanosheet MOSFET Partial Release Strain Preservation
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Solution Overview
Problem
Current semiconductor technologies face challenges in preserving compressive strain in nanosheet MOSFETs during the fabrication process, which affects the electrical performance and current transport in nanosheet devices.
Innovation Solution
The method involves forming a heteroepitaxial film stack with sacrificial and channel layers, growing epitaxial source/drain material, and partially removing sacrificial layers to maintain strain, allowing for a replacement gate stack while avoiding source/drain recess etches, which helps in preserving compressive strain and enhancing current transport.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If conventional fabrication processes are used, then manufacturing simplicity is maintained, but compressive strain is lost during fabrication
Solution Approach 1:
The heteroepitaxial film stack is formed with sacrificial layers and channel layers in a specific configuration before the actual transistor fabrication begins. This preliminary structuring allows strain to be built into the system early, where it can be preserved through subsequent processing steps that would otherwise relax or remove the strain in conventional approaches.
Solution Approach 2:
Silicon germanium sacrificial layers are introduced as intermediary materials between the source/drain regions and the silicon channel. These sacrificial layers serve a dual purpose: they enable the epitaxial growth of strained silicon channel layers, and they are later selectively removed to create the final device structure while preserving the compressive strain in the channel.
2Reliability
If source/drain recess etches are performed, then source/drain contact is improved, but compressive strain in channel layers is relaxed
Solution Approach 1:
The silicon germanium sacrificial layers are selectively extracted from the heteroepitaxial film stack through selective etching processes. This extraction creates the necessary source/drain contact regions while leaving the silicon channel layers intact and strained, thereby achieving both good electrical contact and strain preservation without requiring traditional recess etches.
Solution Approach 2:
The material composition parameter is changed from silicon germanium (sacrificial) to silicon (channel) in a controlled manner through selective removal. This parameter change enables the transition from a strained heteroepitaxial structure to a functional transistor with preserved compressive strain in the channel, while establishing proper source/drain contacts.
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 preserves compressive strain in silicon germanium channel layers, increasing current transport and electrical channel width, thereby improving the performance of nanosheet MOSFETs.
Implementation Method 1
forming a heteroepitaxial film stack including at least one sacrificial layer and at least one channel layer
Implementation Method 2
forming an epitaxial source/drain material along the patterned heteroepitaxial film stack sidewalls
Implementation Method 3
The structure can be subjected to an additional thermal budget allowing the silicon-germanium (SiGe) and silicon sacrificial layers to completely relax
Data Source
AI summary
A method is presented for forming a nanosheet metal oxide semiconductor field effect transistor (MOSFET) structure. The method includes forming a heteroepitaxial film stack including at least one sacrificial layer and at least one channel layer, patterning the heteroepitaxial film stack, forming a dummy gate stack with sidewall spacers, and forming a cladded or embedded epitaxial source/drain material along the patterned heteroepitaxial film stack sidewalls. The method further includes removing the dummy gate stack, partially removing the at least one sacrificial layer, and forming a replacement gate stack.