CMOS Gate Electrode Stack for Precise MOSFET Threshold Control
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Solution Overview
Problem
Existing semiconductor devices face challenges in accurately controlling the threshold voltages of n-channel and p-channel MOSFETs to desired values due to variations in work function and atomic movement during manufacturing.
Innovation Solution
The semiconductor device incorporates a specific gate electrode structure for both n-channel and p-channel MOSFETs, utilizing titanium nitride, tantalum nitride, and hafnium nitride layers to stabilize the threshold voltages, with titanium-aluminum alloy regions to adjust the effective work function and reduce gate resistance.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If a conventional gate electrode structure is used, then the manufacturing process is simple, but the threshold voltage cannot be accurately controlled to desired values
Solution Approach 1:
The gate electrode is divided into multiple distinct layers (titanium nitride layer, tantalum nitride layer, and titanium-aluminum alloy layer), each performing a specific function. This segmentation allows independent optimization of each layer's properties to achieve precise threshold voltage control while managing complexity through functional specialization.
Solution Approach 2:
The gate electrode employs a composite structure combining different nitride materials (titanium nitride, tantalum nitride) and a titanium-aluminum alloy. This composite approach leverages the unique properties of each material - titanium nitride for work function control, tantalum nitride for stability, and titanium-aluminum alloy for resistance reduction - to simultaneously achieve accurate threshold voltage control and low gate resistance.
2Stability of the object's composition
If the gate electrode structure is simplified, then the manufacturing is easier, but atomic movement during manufacturing causes work function variations
Solution Approach 1:
The titanium nitride layer is positioned as the bottom-most gate electrode layer in direct contact with the gate insulating film, serving as a protective buffer that prevents atomic diffusion from subsequent layers during manufacturing processes. This beforehand cushioning approach anticipates and prevents work function variations caused by atomic movement, ensuring composition stability without complicating the manufacturing sequence.
Solution Approach 2:
The patent specifies precise thickness ranges for each gate electrode layer (titanium nitride: 1-5 nm, tantalum nitride: 1-3 nm, titanium-aluminum alloy: 2-10 nm) to optimize the balance between preventing atomic diffusion and maintaining manufacturability. By controlling these dimensional parameters, the invention achieves work function stability while keeping the manufacturing process feasible.
3Manufacturing precision
If titanium-aluminum alloy regions are added to adjust work function, then threshold voltage control improves, but gate resistance increases
Solution Approach 1:
The titanium-aluminum alloy layer is strategically positioned as the top-most gate electrode layer, creating a local quality distribution where the bottom layers (titanium nitride, tantalum nitride) provide low resistance and work function stability, while the top layer (titanium-aluminum alloy) provides work function adjustability for precise threshold voltage control. This spatial differentiation of material properties resolves the contradiction between threshold voltage precision and resistance management.
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 structure effectively controls the threshold voltages of both MOSFET types to desired levels, enhancing the stability and performance of the CMOS semiconductor device by minimizing atomic movement and resistance.
Implementation Method 1
it is desirable to control the threshold voltage of the n-channel MOSFET and the threshold voltage of the p-channel MOSFET to desired threshold voltages
Implementation Method 2
titanium-aluminum alloy regions to adjust the effective work function and reduce gate resistance
Data Source
AI summary
A semiconductor device of embodiments includes: an n-channel MOSFET including a first gate insulating film and a first gate electrode, the first gate electrode including a first region containing Ti and Al and a second region provided between the first gate insulating film and the first region, in contact with the first gate insulating film, and containing a first metal element and nitrogen (N); and a p-channel MOSFET including a second gate insulating film and a second gate electrode, the second gate electrode including a third region containing Ti and Al, a fourth region provided between the second gate insulating film and the third region, in contact with the second gate insulating film, and containing the first metal element and nitrogen (N), and a fifth region provided between the third region and the fourth region and containing nitrogen (N) and a second metal element of Hf or Zr.