FinFET Dual Workfunction Gate Vth Tuning
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Solution Overview
Problem
Current semiconductor technologies face challenges in achieving a wide range of gate threshold voltages for FinFET devices without introducing process complexity, cost, or variability issues, such as those associated with polysilicon doping and metal gate layers.
Innovation Solution
The fabrication of FinFET devices with a gate structure comprising two overlying metal layers of different workfunctions, where the thickness of one metal layer is varied to control the effective workfunction and threshold voltage, allowing for a range of gate threshold voltages to be achieved without the drawbacks of existing methods.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of operation
If polysilicon doping is used to adjust work function and tune Vth, then threshold voltage can be controlled, but process complexity increases and device reliability deteriorates due to gate depletion and dopant penetration
Solution Approach 1:
The patent extracts the doping process entirely from the gate material system. Instead of using doped polysilicon, the invention uses undoped polysilicon combined with metal layers, removing the harmful doping step while maintaining Vth control capability through metal layer composition and thickness
Solution Approach 2:
The patent introduces metal layers as an intermediary between the polysilicon gate and the channel. These metal layers (such as tungsten, molybdenum, or titanium nitride) serve as the work function tuning mechanism without requiring dopant introduction, thus avoiding gate depletion and dopant penetration issues
2Ease of operation
If channel region doping is used to tune Vth, then threshold voltage can be adjusted, but manufacturing precision deteriorates due to random-doping fluctuations and mobility reduction
Solution Approach 1:
The patent applies different metal layer compositions or thicknesses in different regions to achieve local Vth control without introducing random fluctuations. The metal gate structure allows precise control of work function through layer thickness and material selection, providing uniform and predictable Vth across devices
Solution Approach 2:
The patent changes the work function parameter by selecting different metal materials or adjusting metal layer thickness rather than changing channel doping. This approach provides continuous and predictable Vth control through well-defined material properties, avoiding the statistical variations inherent in doping processes
3Adaptability or versatility
If different gate metal layers are used to achieve different Vth values, then a full palette of Vth can be obtained, but device complexity and manufacturing cost increase
Solution Approach 1:
The patent creates a universal gate structure where the same polysilicon-based process can be used for all devices, and Vth differentiation is achieved through metal layer variations rather than fundamentally different gate materials. This maintains process compatibility across the entire fabrication flow
Solution Approach 2:
The patent segments the gate structure into polysilicon and metal layers, where the polysilicon provides the base gate function and the metal layer provides the work function tuning. This segmentation allows independent optimization of each layer's function while maintaining overall process simplicity
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 the tuning of threshold voltages across a wide range, allowing for the coexistence of high-speed and low-power devices on the same chip, reducing process complexity and variability, while maintaining high current drive and low static power dissipation.
Implementation Method 1
a gate structure comprising two overlying metal layers of different workfunctions, the thickness of one metal layer being varied to control the effective workfunction and threshold voltage
Data Source
AI summary
Disclosed are a method to fabricate a semiconductor device having a two-layered gate structure, and so fabricated a semiconductor. The gate threshold voltage can be tuned by using two metal layers with different workfunctions, disposed over a fin structure on a substrate and extending in parallel to the current flow direction in the fin structure, and by varying individual thicknesses of the layer so as to change the relative coverage of the fin structure by the layers. The method may comprise providing a substrate having a fin structure, depositing first and second gate metals, and forming a gate dielectric layer. The method may further comprise determining the workfunctions of the first and second gate metals and their thicknesses to achieve a desired gate threshold voltage. Forming the first and second gate metal layers and the dielectric layer may use processes such as deposition, epitaxial growth, CMP, or selective etching.