Silicide Gate Electrode Threshold Control
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Solution Overview
Problem
The dual metal gate process for MOSFETs faces issues such as degradation of the gate insulating film during etching, difficulty in controlling the work function of gate electrodes with high dielectric constant insulating films, and fluctuations in work function due to non-uniformity in tungsten silicide composition, leading to reduced performance and reliability.
Innovation Solution
A semiconductor device with a gate insulating film of high dielectric constant, containing metal oxide or metal silicate with nitrogen, and a gate electrode composed of silicide with specific nickel silicide phases, allowing for controlled work function modulation and avoiding depletion, using metals like nickel, tantalum, or hafnium to form silicides at lower temperatures.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If a dual metal gate process is used to control threshold voltage, then the work function of gate electrodes can be modulated, but the gate insulating film is degraded during etching steps
Solution Approach 1:
The patent changes the material composition parameter of the gate electrode from pure metal to silicide compound, which fundamentally alters the fabrication process. The silicide material can be deposited as a complete layer without requiring selective etching, thereby eliminating the etching-induced degradation of the gate insulating film while still enabling threshold voltage control through composition adjustment.
Solution Approach 2:
The patent extracts the problematic etching step from the fabrication process by using silicide material that can be deposited uniformly across both n-type and p-type MOSFET gates. This removes the need for selective removal of metal gates, thereby protecting the gate insulating film from etching damage while maintaining the ability to control threshold voltage.
2Manufacturing precision
If tungsten silicide is used to form gate electrodes, then the work function can be controlled, but non-uniformity in composition causes fluctuations in work function
Solution Approach 1:
The patent changes from tungsten silicide to nickel silicide, which has different deposition and reaction characteristics. Nickel silicide can be formed by reacting nickel metal with silicon, and the composition can be more uniformly controlled through the reaction process, reducing work function fluctuations caused by composition non-uniformity.
Solution Approach 2:
The patent uses nickel silicide as a composite material system where the work function can be tuned by controlling the nickel-to-silicon ratio. This composite approach allows for more stable and uniform composition control compared to tungsten silicide, as the nickel silicide formation process better maintains compositional homogeneity across the gate electrode area.
3Stability of the object's composition
If high-temperature processes are used to form silicides, then complete silicide conversion is achieved, but source/drain diffusion regions become highly resistive
Solution Approach 1:
The patent changes the temperature parameter of the silicide formation process to a lower range that is sufficient to convert the gate electrode to silicide but not high enough to cause excessive resistivity in the source/drain diffusion regions. This temperature optimization allows complete silicide conversion at the gate while maintaining low resistance at the source/drain contacts.
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 precise control of threshold voltage in MOSFETs, suppresses fluctuations, and maintains high reliability by avoiding high-temperature processes and etching-related damage, ensuring stable and efficient transistor performance.
Implementation Method 1
composing a gate insulating film of a material having a high dielectric constant to thereby physically thicken a gate insulating film
Implementation Method 2
A gate electrode contains silicide of metal M as a primary constituent
Data Source
AI summary
There is provided a semiconductor device which is capable of solving a problem of threshold control in CMOS transistor, accompanied with combination of a gate insulating film having a high dielectric constant and a metal gate electrode, and significantly enhancing performances without deterioration in reliability of a device. The semiconductor device includes a gate insulating film composed of a material having a high dielectric constant, and a gate electrode. A portion of the gate electrode making contact with the gate insulating film has a composition including silicide of metal M expressed with MxSi1-X (0<X<1), as a primary constituent. X is greater than 0.5 (X>0.5) in a p-type MOSFET, and is equal to or smaller than 0.5 (X≦0.5) in a n-type MOSFET.