Metal Gate Structure with TiAl3 Work Function Layer
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Solution Overview
Problem
Conventional semiconductor devices face issues with leakage current due to tunneling effects and inferior performance caused by boron penetration and depletion effects, especially when using silicon dioxide or silicon oxynitride gate dielectric layers and polysilicon gates, which hinder the progression to next-generation semiconductor technology.
Innovation Solution
A metal gate structure is developed with a high-K gate dielectric layer, a titanium tri-aluminide (TiAl3) work function metal layer formed through an in-situ anneal treatment, and a top barrier layer, which improves Al diffusion and tunes the work function to an ideal value of 3.9-4.3 eV, enhancing the reliability and performance of the semiconductor device.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Volume of moving object
If the thickness of silicon dioxide gate dielectric layer is reduced to achieve scaling down, then the device size is reduced, but leakage current due to tunneling effect increases
Solution Approach 1:
The patent changes the material parameter of the gate dielectric layer from silicon dioxide to high-K material (such as hafnium oxide), which has a higher dielectric constant. This allows achieving the same equivalent oxide thickness (EOT) with a thicker physical layer, thereby reducing tunneling current while maintaining device scaling.
Solution Approach 2:
The patent employs a composite gate structure consisting of multiple layers including high-K gate dielectric layer, metal gate electrode, and barrier layers. This composite structure combines materials with different properties to simultaneously achieve low leakage current and appropriate work function for device operation.
2Ease of manufacture
If conventional polysilicon gate is used, then the manufacturing process is simple, but boron penetration and depletion effect occur which increases equivalent thickness of gate dielectric layer and reduces gate capacitance
Solution Approach 1:
The patent extracts the doping function from the gate electrode material itself by using undoped or lightly-doped metal, eliminating the need for heavy doping that causes boron penetration and depletion effects in polysilicon gates.
Solution Approach 2:
The patent introduces barrier layers (such as titanium nitride or tantalum nitride) as intermediary layers between the metal gate electrode and the gate dielectric layer. These intermediary layers prevent unwanted diffusion and interface reactions while maintaining electrical functionality.
3Reliability
If work function metals are used to replace polysilicon gate, then gate capacitance is improved, but the work function may not be precisely controlled to ideal value
Solution Approach 1:
The patent applies different materials with different work functions to different regions or layers of the gate electrode structure. By stacking multiple metal layers with complementary work function characteristics, the composite structure achieves a precise effective work function that matches device requirements.
Solution Approach 2:
The patent controls the work function by adjusting the composition ratio, thickness, and stacking sequence of multiple metal layers. Post-deposition annealing is also used to modify the work function parameter through controlled diffusion and phase transformation.
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 metal gate structure achieves superior reliability and performance by reducing leakage current and improving the driving force of semiconductor devices, addressing the limitations of conventional materials and processes.
Implementation Method 1
the anneal treatment is in-situ performed to induce a phase transformation of the work function metal layer to form a TiAl3 work function metal layer
Implementation Method 2
simultaneously to improve Al diffusion and thus the work function of the metal gate structure is tuned to an ideal value: 3.9-4.3 eV
Implementation Method 3
performing an anneal treatment to the work function metal layer in-situ
Implementation Method 4
conventional methods, which are used to achieve optimization, such as reducing thickness of the gate dielectric layer, for example the thickness of silicon dioxide layer, have faced problems such as leakage current due to tunneling effect
Data Source
AI summary
A method for manufacturing a metal gate structure includes providing a substrate having a high-K gate dielectric layer and a bottom barrier layer sequentially formed thereon, forming a work function metal layer on the substrate, and performing an anneal treatment to the work function metal layer in-situ.