Metal Gate Work Function Control for Threshold Voltage Optimization
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Solution Overview
Problem
Current semiconductor devices face limitations in optimizing threshold voltages of N-channel and P-channel transistors due to depletion of polysilicon doping, which affects drive current and requires complex processes to adjust work functions, thereby reducing productivity.
Innovation Solution
A semiconductor device with distinct gate stack structures for N-channel and P-channel transistors, incorporating nitrogen-rich titanium nitride and titanium-rich titanium nitride metal-containing gate electrodes, along with a dipole formation layer and threshold voltage adjust regions, allows for independent optimization of threshold voltages by varying effective work functions and using germanium to reduce energy band gap.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If polysilicon is used as gate electrode material, then the device can be manufactured with conventional processes, but the doping concentration decreases due to depletion and diffusion, limiting threshold voltage optimization
Solution Approach 1:
The patent changes the material parameter from polysilicon to metal (such as tungsten, titanium nitride, or other metal compounds) for the gate electrode. This material substitution fundamentally alters the electrical properties, providing stable work functions that enable precise threshold voltage control without the depletion and diffusion issues affecting polysilicon-based devices.
Solution Approach 2:
The patent employs composite gate electrode structures combining multiple materials, such as metal layers with adjacent doped regions or multi-layer metal compounds. These composite structures integrate the advantages of different materials to achieve both manufacturability and precise threshold voltage optimization through controlled work function values.
2Manufacturing precision
If metal gate electrodes with adjusted work functions are used, then threshold voltage optimization is improved, but the process complexity increases and productivity decreases
Solution Approach 1:
The patent performs preliminary work function adjustment during the gate electrode formation process itself, rather than requiring separate post-processing steps. By selecting metals with appropriate work functions or forming metal compounds with specific stoichiometries during deposition, the desired threshold voltage characteristics are achieved directly, streamlining the manufacturing process.
Solution Approach 2:
The patent applies different metal materials or metal compound compositions to different gate electrodes (N-channel vs. P-channel) based on their specific threshold voltage requirements. This localized material optimization allows each transistor type to achieve optimal performance with tailored gate electrode properties without requiring complex universal processing steps.
3Area of moving object
If transistor size is decreased for miniaturization, then device integration density is improved, but drive current degrades due to polysilicon depletion
Solution Approach 1:
The patent changes the gate electrode material parameter from polysilicon to metal, which fundamentally alters the electrical characteristics at the gate-dielectric interface. This material substitution eliminates the polysilicon depletion effect that limits drive current in miniaturized devices, enabling maintained or enhanced drive current despite reduced transistor dimensions.
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 independent control of threshold voltages for N-channel and P-channel transistors, enhancing their performance and simplifying the integration process by reducing threshold voltages and preventing effective work function degradation.
Implementation Method 1
a dipole formation layer formed between the second gate dielectric layer and the second metal-containing gate electrode
Implementation Method 2
an effective work function promotion layer formed over the first metal-containing gate electrode
Implementation Method 3
a channel region formed under the first gate stack structure and containing a threshold voltage adjust species
Data Source
AI summary
A semiconductor device includes a substrate including first and second regions. A first gate stack structure containing a first effective work function adjust species is formed over the first region and a second gate stack structure containing a second effective work function adjust species is formed over the second region. A channel region is formed under the first gate stack structure and contains a threshold voltage adjust species.