Lanthanide Implant Work Function Adjustment
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Solution Overview
Problem
Conventional CMOS transistor fabrication faces challenges in achieving predictable and stable threshold voltages due to limitations in gate dielectric thickness and dopant diffusion, particularly in scaling down semiconductor devices while maintaining performance.
Innovation Solution
Incorporating a lanthanide series material into the gate dielectric and silicon-based gate electrode, with subsequent annealing to drive the lanthanide series material into the gate dielectric, effectively reducing the work function of NMOS transistors and tuning the threshold voltage without affecting PMOS transistors.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If gate dielectric thickness is reduced to enable device scaling, then device density and integration are improved, but threshold voltage control and electrical performance deteriorate
Solution Approach 1:
The patent introduces lanthanide series materials to modify the work function of the gate electrode, thereby changing the electrical parameters of the transistor. By adjusting the work function through material composition control, the threshold voltage can be precisely tuned even with thin gate dielectrics, resolving the contradiction between device scaling and threshold voltage control.
Solution Approach 2:
The patent employs composite gate electrode structures incorporating lanthanide series materials combined with other materials (such as tungsten, molybdenum, or polysilicon). These composite materials provide both the low work function needed for NMOS devices and the mechanical stability required for thin-gate structures, enabling both high device density and reliable threshold voltage control.
2Manufacturing precision
If dopant implantation is used to adjust threshold voltage, then threshold voltage tuning is achieved, but dopant diffusion causes variability and manufacturing precision deteriorates
Solution Approach 1:
The patent extracts the threshold voltage control mechanism from dopant implantation and relocates it to the gate electrode work function adjustment. By using lanthanide series materials in the gate electrode, threshold voltage is controlled through material selection rather than dopant diffusion, eliminating the variability introduced by dopant spreading and improving both manufacturing precision and device reliability.
Solution Approach 2:
The lanthanide series material acts as an intermediary between the gate electrode structure and the channel, mediating the electrical characteristics without requiring dopant implantation into the channel. This intermediary approach allows precise threshold voltage control through material properties rather than chemical doping, reducing manufacturing variability.
3Ease of manufacture
If polysilicon gate is doped to adjust work function, then gate work function is tuned, but gate conductivity and process complexity increase
Solution Approach 1:
Instead of changing the doping level of polysilicon to adjust work function, the patent changes the material composition by incorporating lanthanide series elements. This parameter change in material composition provides a more direct and controllable method for adjusting work function without the need for complex doping processes, thereby reducing overall device complexity while maintaining ease of manufacture.
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 reduces the work function of NMOS transistors, enhancing the stability and predictability of threshold voltages, enabling improved device performance and scalability while maintaining equivalent electrical performance.
Implementation Method 1
with subsequent annealing to drive the lanthanide series material into the gate dielectric
Implementation Method 2
effectively reducing the work function of NMOS transistors and tuning the threshold voltage
Data Source
AI summary
Semiconductor devices and fabrication methods are provided, in which fully silicided gates are provided. A lanthanide series metal is implanted into the gate electrode layer prior to silicidation and diffuses into the gate dielectric during an activation anneal. This process and resultant structure provides adjustment of the gate electrode work function, thereby tuning the threshold voltage of the resulting transistor.