NbMC Gate Electrodes for Work Function Tuning
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Solution Overview
Problem
As MOSFET devices are scaled down, replacing polysilicon with metal as a gate electrode material makes it difficult to tune the work function difference between the gate and channel, leading to challenges in modifying the threshold voltage, and existing work-function layers are less conductive, affecting device performance.
Innovation Solution
The use of niobium metal or metalloid carbide (NbMC) layers with a cyclic deposition process to form thin-film structures, allowing for the creation of tunable work function layers with low resistivity and high oxidation resistance, enabling easy tuning of work functions over a wide range.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Adaptability or versatility
If polysilicon is used as gate electrode material, then work function tuning is easy and threshold voltage control is simple, but device performance and scalability are limited
Solution Approach 1:
The patent uses composite gate electrode structures combining metal layers with work function tuning layers (such as TiN, TaN, or other metal nitrides/carbides) to achieve both high performance and tunable work function. The metal layer provides high conductivity while the tuning layer enables work function adjustment, resolving the contradiction between performance and adaptability.
Solution Approach 2:
The patent adjusts work function by changing the composition, thickness, and material parameters of the gate electrode layers. By varying the metal layer composition (e.g., tungsten, cobalt, titanium) and the work function tuning layer properties, the gate work function can be precisely controlled to achieve desired threshold voltages while maintaining high device performance.
2Reliability
If metal replaces polysilicon as gate electrode material, then device performance improves, but work function tuning becomes difficult
Solution Approach 1:
The gate electrode is segmented into multiple functional layers: a bottom metal layer providing high conductivity and performance, and an upper work function tuning layer enabling adjustable work function. This segmentation allows each layer to optimize its specific function, resolving the contradiction between performance and tunability.
Solution Approach 2:
A work function tuning layer (intermediary material such as TiN, TaN, or metal carbides) is introduced between the metal gate electrode and the channel. This intermediary layer mediates between the high-performance metal and the need for work function adjustment, enabling threshold voltage control without sacrificing device performance.
3Adaptability or versatility
If work function layers are added to tune work function, then threshold voltage control improves, but conductivity decreases
Solution Approach 1:
The work function tuning layer is applied locally at the gate electrode interface where work function adjustment is needed, while the bulk metal layer maintains high conductivity. This local application ensures threshold voltage control is achieved without significantly impacting overall gate conductivity.
Solution Approach 2:
The composite gate structure combines a highly conductive metal layer (tungsten, cobalt, or titanium) with a thinner work function tuning layer (metal nitride or carbide). The metal layer dominates the conductivity while the tuning layer controls the work function, resolving the contradiction between these two properties.
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
The NbMC layers provide low resistivity and high oxidation resistance, facilitating the tuning of work functions and improving device performance by allowing for a wide range of work function adjustments while maintaining desired conductivity.
Implementation Method 1
using a first cyclic deposition process, forming a layer comprising NbMC, wherein M represents a metal, such as aluminum and/or metalloid (sometimes referred to as a semimetal), such as boron, on the surface of the substrate, and wherein the first cyclic deposition process comprises at least one deposition cycle comprising alternately providing to the reaction space a first precursor comprising Nb and a second precursor comprising a metal (and/or metalloid) and carbon
Data Source
AI summary
Methods of forming thin-film structures including one or more NbMC layers, and structures and devices including the one or more NbMC layers are disclosed. The NbMC layers enable tuning of various structure and device properties, including resistivity, current leakage, and work function.