Dual Work Function Metal Gate Electrodes via Interface Dipole Control
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Solution Overview
Problem
The integration of dual work function metal gate electrodes in semiconductor devices is challenging due to the difficulty in controlling the work function, especially after high temperature annealing, where dipoles form at the metal/dielectric interface, leading to shifts in work function values.
Innovation Solution
The solution involves forming interface dipoles by disposing electronegative and electropositive species at the metal/dielectric interface to control the work function of metal gate electrodes, increasing or decreasing the work function values as needed, by forming a first metal gate electrode with a plurality of electronegative species and a second metal gate electrode with a plurality of electropositive species.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If dual work function metal gate electrodes are integrated to achieve low threshold voltages, then device performance is improved, but control of work function becomes difficult due to dipole formation at high temperature annealing
Solution Approach 1:
The patent changes the chemical composition parameters of the metal gate electrode by incorporating specific metals (tungsten, molybdenum, tantalum) in controlled ratios, and adjusts the dipole layer characteristics (thickness, composition) to precisely control the work function value. This allows achieving desired work function values (4.0-4.8eV for PMOS, 3.8-4.2eV for NMOS) while maintaining stability during high temperature annealing.
Solution Approach 2:
The patent introduces an intermediary dipole layer between the metal gate electrode and the dielectric material. This intermediate layer acts as a mediator that controls the interface dipole formation, thereby stabilizing the work function value during thermal processing. The dipole layer composition and structure are engineered to prevent excessive dipole formation that would otherwise cause work function shifts.
2Ease of manufacture
If high temperature annealing is applied to metal gate electrodes, then device fabrication is completed, but work function shifts towards mid-gap due to dipole formation at metal/dielectric interface
Solution Approach 1:
The patent performs preliminary engineering of the metal gate electrode composition and interface structure before high temperature annealing. By pre-configuring the metal composition (mixing noble and non-noble metals) and preparing the interface structure with controlled dipole layers, the work function stability is ensured during subsequent thermal processing. This preliminary preparation prevents work function shifts rather than correcting them after annealing.
Solution Approach 2:
The patent creates a composite metal gate structure combining noble metals (iridium, platinum, palladium) with non-noble metals (tungsten, molybdenum, tantalum). This composite material approach leverages the oxidation resistance of noble metals and the electrical properties of non-noble metals, while the specific composition ratio controls dipole formation behavior during annealing, maintaining work function stability.
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 effectively controls the work function of metal gate electrodes, allowing for precise tuning of the values to meet the requirements for PMOS and NMOS transistors, enhancing device performance by stabilizing the work function values and preventing shifts during high temperature annealing.
Implementation Method 1
a first plurality of interface dipoles can be formed to provide the first metal gate electrode with an increased work function value
Implementation Method 2
A first portion of the metal layer can then be converted to a first gate material having a plurality of electronegative species disposed at a first interface between the first gate material and the dielectric material
Data Source
AI summary
Exemplary embodiments provide structures for dual work function metal gate electrodes. The work function value of a metal gate electrode can be increased and/or decreased by disposing various electronegative species and/or electropositive species at the metal/dielectric interface to control interface dipoles. In an exemplary embodiment, various electronegative species can be disposed at the metal/dielectric interface to increase the work function value of the metal, which can be used for a PMOS metal gate electrode in a dual work function gated device. Various electropositive species can be disposed at the metal/dielectric interface to decrease the work function value of the metal, which can be used for an NMOS metal gate electrode in the dual work function gated device.