Variable Work Function Metal Gate Transistor
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Solution Overview
Problem
Traditional semiconductor manufacturing techniques face challenges in achieving adjustable threshold voltages due to polysilicon depletion and Fermi level pinning effects, especially as feature sizes shrink, leading to issues like short-channel effects and gate leakage currents, which are not adequately addressed by existing technologies.
Innovation Solution
A method for manufacturing a transistor with a gate having a variable work function using atomic layer deposition (ALD) to grow a tunable work function metal layer, specifically using titanium or tantalum alloys like TiAlC(N) or TaAlC(N), by controlling environmental factors such as precursor source reactant ratios, pulse sequences, growth temperature, and thickness to achieve adjustable threshold voltages.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If a traditional polysilicon gate is used to simplify the manufacturing process and save production costs, then the manufacturing complexity is reduced, but polysilicon depletion effect and Fermi level pinning effect occur which seriously affect device performance
Solution Approach 1:
The patent changes the material parameter of the gate electrode from polysilicon to metal materials with different work functions. By selecting metals such as titanium nitride, tantalum nitride, or tungsten with specific work function values, the gate can achieve desired threshold voltages without suffering from polysilicon depletion or Fermi level pinning effects, thus improving device performance while maintaining manufacturing feasibility
Solution Approach 2:
The patent employs composite gate structures combining metal layers with high-k dielectric materials. The metal gate electrode is paired with high-k dielectric gate insulators to form a composite structure that eliminates polysilicon-related issues while enabling better electrical characteristics and threshold voltage control through the combination of different material properties
2Device complexity
If a single work function metal layer is used to simplify the gate structure, then the device structure is simplified, but the threshold voltage cannot be adjusted for different functional circuit modules
Solution Approach 1:
The patent introduces dynamic adjustability into the gate structure by enabling post-deposition tuning of the work function metal layer. Through controlled diffusion of aluminum or nitrogen during annealing processes, or by adjusting atomic layer deposition parameters, the work function can be dynamically adjusted after fabrication to match different circuit requirements, making the same physical structure adaptable to multiple functional needs
Solution Approach 2:
The patent utilizes parameter changes in the metal gate material composition and structure to achieve different work function values. By controlling the concentration of alloying elements like aluminum in titanium-aluminum-nitride or by adjusting nitrogen content in metal nitrides, the work function can be tuned across a range of values to satisfy different threshold voltage requirements for various circuit modules
3Ease of manufacture
If traditional PVD technique is used for metal gate deposition to maintain process simplicity, then the manufacturing process remains simple, but the filling of metal gate in gate-last process meets significant challenges during miniaturization
Solution Approach 1:
The patent replaces the physical vapor deposition (PVD) mechanical deposition process with chemical vapor deposition (CVD) or atomic layer deposition (ALD) chemical deposition processes. These chemical deposition methods provide better step coverage, conformal filling, and control over thin film formation in high-aspect-ratio structures, overcoming the limitations of PVD in gate-last processes while enabling precise metal gate formation in miniaturized devices
4Reliability
If atomic layer deposition is used to achieve precise work function control and eliminate polysilicon effects, then device performance is improved, but the manufacturing process complexity increases
Solution Approach 1:
The patent segments the gate electrode formation into distinct functional layers: a base metal layer providing structural foundation and a work function control layer deposited by ALD that provides electrical characteristics. This segmentation allows each layer to be optimized independently - the base layer for mechanical stability and the ALD layer for precise work function control - thereby achieving high performance while managing process complexity through functional decomposition
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 allows for precise modulation of the work function, enabling adjustable threshold voltages and improved device performance by eliminating polysilicon depletion and Fermi level pinning effects, thus enhancing the semiconductor device's functionality and reliability.
Implementation Method 1
providing an atomic layer deposition reaction device; introducing a precursor source reactant into the atomic layer deposition reaction device; and controlling an environmental factor for the atomic layer deposition device to grow a work function metal layer
Implementation Method 2
performing ion implantation on an exposed area of the semiconductor substrate at both sides of the dummy gate stack to form source/drain regions
Implementation Method 3
annealing the source/drain regions
Data Source
AI summary
The present disclosure provides a method for manufacturing a transistor having a gate with a variable work function, comprising: providing a semiconductor substrate; forming a dummy gate stack on the semiconductor substrate and performing ion implantation on an exposed area of the semiconductor substrate at both sides of the dummy gate stack to form source/drain regions; removing the dummy gate and annealing the source/drain regions; providing an atomic layer deposition reaction device; introducing a precursor source reactant into the atomic layer deposition reaction device; and controlling an environmental factor for the atomic layer deposition device to grow a work function metal layer. The present disclosure also provides a transistor having a gate with a variable work function. The present disclosure may adjust a variable work function, and may use the same material system to obtain an adjustable threshold voltage within an adjustable range.