Molybdenum Carbon Gate Stack for CMOS Workfunction Tuning
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Solution Overview
Problem
Existing conducting materials in CMOS devices below the 0.1 micron region are not compatible with existing IC technology, making them difficult to manufacture and integrate with the gate stack, dielectric, and spacers.
Innovation Solution
Using compounds containing molybdenum or tungsten as the metal and carbon, oxygen, or chalcogenides as the further element, which allows for a wide workfunction range and simplifies manufacturing by using gaseous compounds like CH4 and O2 to form the conducting materials, ensuring compatibility with IC technology.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If conventional conducting materials (Ru, Zr, Nb, Ta, MoSi, TaSi, Ni, RuO2, MoN, TaN) are used for metal gates, then the workfunction requirements for NMOST and PMOST can be met, but compatibility with existing IC technology and gate stack materials deteriorates
Solution Approach 1:
The patent changes the chemical composition parameters of the conducting material by using compounds of molybdenum or tungsten with carbon, oxygen, or chalcogenides. This allows tuning of the workfunction while maintaining compatibility with existing IC technology, as these compounds can be formed using standard deposition and annealing processes already present in IC manufacturing
Solution Approach 2:
The patent employs composite materials consisting of metal compounds (molybdenum or tungsten combined with carbon, oxygen, or chalcogenides) rather than pure metals. These composite materials provide both the required workfunction characteristics and compatibility with gate stack materials including silicon oxide, silicon nitride, and tungsten silicide spacers
2Reliability
If different conducting materials are used for NMOST and PMOST gates, then the specific workfunction requirements (4.2 eV for NMOST, 5.2 eV for PMOST) are satisfied, but manufacturing complexity increases
Solution Approach 1:
The patent applies local quality by forming different compounds (e.g., molybdenum carbide vs. molybdenum oxide) in different regions (NMOST vs. PMOST) of the same metal layer. This is achieved through selective exposure to gaseous compounds during annealing, where masks control which areas react with carbon, oxygen, or chalcogenide gases, thereby creating locally differentiated workfunctions from a single deposited metal layer
Solution Approach 2:
The patent makes the single metal layer (molybdenum or tungsten) multi-functional by enabling it to serve as both NMOST gate material and PMOST gate material through subsequent compound formation. The same metal layer can be selectively converted to different compounds with different workfunctions, eliminating the need for separate metal deposition processes for n-type and p-type transistors
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 solution provides a semiconductor device with improved compatibility with IC technology, enabling easy manufacturing and achieving the desired workfunction range from 4.1 eV to 5.2 eV for both n-type and p-type transistors using a single metal layer, reducing complexity and enhancing manufacturing efficiency.
Implementation Method 1
the conducting material may be formed using gaseous compounds of the further elements mentioned, e.g. CH4, O2 and H2Se
Data Source
AI summary
The invention relates to a CMOS device (10) with an NMOST I and PMOST 2 having gate regions (1D,2D) comprising a compound containing both a metal and a further element. According to the invention the first and second conducting material both comprise a compound containing as the metal a metal selected from the group comprising molybdenum and tungsten and both comprise as the further element an element selected from the group comprising carbon, oxygen and the chalcogenides. Preferably both the first and second conducting material comprise a compound of molybdenum and carbon or oxygen. The invention also provides an attractive method of manufacturing such a device.