Gate-All-Around Nanosheet Junctions with Channel Pull Back
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Solution Overview
Problem
Current nanosheet device designs have high defect density at source and drain ends, limiting the induction of compressive strain in channel layers, which hampers device performance.
Innovation Solution
The technique involves forming an alternating stack of nanosheets, creating pockets by selectively pulling back certain nanosheets, filling these pockets with a strain-inducing material, and forming source and drains on either side of the fin stack, followed by burying dummy gates and replacing them with gates in a gate-all-around configuration to induce compressive strain effectively.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If source and drain are formed at the ends of channels using current nanosheet device designs, then device structure is completed, but high defect density is introduced at source and drain ends, limiting compressive strain induction in channel layers
Solution Approach 1:
The channel stack is segmented into alternating first and second nanosheets, allowing selective removal of second nanosheets to create pockets. This segmentation enables the channel to be divided into strained and unstrained regions, with strain-inducing material placed only in specific segments (pockets) rather than throughout the entire channel structure.
Solution Approach 2:
Compressive strain is applied locally to specific regions of the channel rather than uniformly across the entire channel. By filling only certain pockets with strain-inducing material, the invention creates localized strain zones that improve hole mobility in critical regions while maintaining overall channel functionality and reducing defect density at source and drain interfaces.
2Ease of operation
If channel layers are suspended between source and drain to enable gate-all-around design, then gate control is improved, but ability to induce compressive strain in channel layers is reduced
Solution Approach 1:
The invention introduces a vertical dimension to strain induction by creating pockets within the stacked nanosheet structure. Rather than attempting to strain the entire channel horizontally between source and drain, the solution uses vertical pocket formation and fills them with strain-inducing material, adding a z-dimensional approach to strain management that complements the gate-all-around configuration.
Solution Approach 2:
Strain-inducing material acts as an intermediary element inserted into pockets within the channel stack. This intermediary material mediates between the suspended channel structure and the desired compressive strain, allowing the channel to remain suspended for gate-all-around access while still achieving effective strain through the intermediary strain-inducing material in the pockets.
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 method enhances the compressive strain in nanosheet channels, reducing defect density and improving overall device performance by allowing for a more effective gate-all-around configuration.
Implementation Method 1
A compressively-strained channel for p-channel field-effect transistors (p-FETs) serves to increase the hole mobility and thus enhance device performance
Data Source
AI summary
Techniques for optimizing junctions of a gate-all-around nanosheet device are provided. In one aspect, a method of forming a nanosheet device includes: forming an alternating series of first/second nanosheets including a first/second material as a stack on a wafer; forming a dummy gate(s) on the stack; patterning the stack into a fin stack(s) beneath the dummy gate(s); etching the fin stack(s) to selectively pull back the second nanosheets in the fin stack(s) forming pockets in the fin stack(s); filling the pockets with a strain-inducing material; burying the dummy gate(s) in a dielectric material; selectively removing the dummy gate(s) forming a gate trench(es) in the dielectric material; selectively removing either the first nanosheets or the second nanosheets from the fin stack(s); and forming a replacement gate(s) in the gate trench(es). A nanosheet device is also provided.