Curved FinFETs With Undercut Ends For Carrier Mobility
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Solution Overview
Problem
Existing FINFET technologies face limitations in enhancing carrier mobility and device performance due to the lack of effective methods to strain the silicon active layer, which restricts the improvement of in-plane carrier mobility beyond a certain percentage.
Innovation Solution
The method involves forming a semiconductor fin with undercut end portions that are disconnected from the substrate, allowing straining layers to impart physical pressure and curve the fin into a bowed shape, thereby increasing stress within the crystalline lattice and enhancing carrier mobility.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If the fin is kept straight and connected to the substrate along its entire length, then the structural stability is maintained, but the carrier mobility cannot be enhanced beyond a certain percentage
Solution Approach 1:
The fin is segmented into two distinct regions: a central portion that remains connected to the substrate for structural stability, and end portions that are undercut and disconnected to enable curvature. This segmentation allows different parts of the fin to serve different functions - the connected central portion provides stability while the disconnected end portions can be curved by straining layers to enhance carrier mobility.
Solution Approach 2:
The fin is transformed from a straight configuration to a curved/bowed configuration by applying straining layers to the disconnected end portions. This curvature increases the stress within the crystalline lattice of the fin, which enhances carrier mobility by 10 to 25 percent. The curved shape is achieved while maintaining the central portion's connection to the substrate.
2Productivity
If the end portions of the fin are undercut to allow curvature, then carrier mobility is enhanced, but the manufacturing complexity increases
Solution Approach 1:
The undercutting of the end portions is performed as a preliminary action before applying the straining layers. By pre-disconnecting the end portions from the substrate, the fin structure is prepared in advance to accept the curvature-inducing straining layers without requiring complex simultaneous processing steps. This sequential approach simplifies the overall manufacturing process while achieving the desired curved configuration.
3Productivity
If straining layers are applied to curve the fin, then in-plane carrier mobility increases by 10 to 25 percent, but the device structure becomes more complex
Solution Approach 1:
Straining layers are applied locally to specific regions of the fin - particularly to the end portions that have been undercut and disconnected. This localized application of straining material creates the necessary curvature and stress in the critical regions where it most impacts carrier mobility, while avoiding unnecessary structural complexity in other parts of the device. The central portion remains relatively simple and connected to the substrate.
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 increases carrier mobility by 10 to 25% and improves device performance by creating a bowed fin structure with increased stress, leading to enhanced output current and switching performance.
Implementation Method 1
the straining layer imparts physical pressure on the fin such that the end portions are permanently moved away from a straight-line orientation with the central portion
Implementation Method 2
increasing stress within the crystalline lattice and enhancing carrier mobility
Data Source
AI summary
A method of forming a transistor patterns a semiconductor fin on a substrate, such that the fin extends from the substrate. Then, the method forms a gate conductor over a central portion of the fin, leaving end portions of the fin exposed. Next, the end portions of the fin are doped with at least one impurity to leave the central portion of the fin as a semiconductor and form the end portions of the fin as conductors. The end portions of the fin are undercut to disconnect the end portions of the fin from the substrate, such that the fin is connected to the substrate along a central portion and is disconnected from the substrate along the end portions and that the end portions are free to move and the central portion is not free to move. A straining layer is formed on a first side of the fin and the straining layer imparts physical pressure on the fin such that the end portions are permanently moved away from a straight-line orientation with the central portion after the forming of the straining layer. Thus, the undercutting in combination with the forming of the straining layer curves the fin such that, when viewed from a top of the substrate, the fin is bowed and has a curved shape.