Field Effect Device With Localized Dopant Diffusion Barrier
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Solution Overview
Problem
The continuous reduction in transistor dimensions makes it challenging to produce high-performance transistors with stable and well-defined gate lengths due to unpredictable fabrication method aspects, leading to variations in electric performance and increased leakage current.
Innovation Solution
A field effect transistor design with modified diffusion areas under lateral spacers, where a diffusion barrier element is implanted at a non-zero angle to create a region with reduced dopant diffusion, ensuring a more controlled and homogeneous channel length, and a method involving a sacrificial gate electrode and selective epitaxy to enhance source/drain electrode formation.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If the gate length is continuously reduced to improve transistor density, then the transistor size decreases and integration density increases, but the gate length becomes increasingly sensitive to fabrication variations leading to unpredictable effective lengths and performance degradation
Solution Approach 1:
A diffusion barrier is formed in advance in the channel region before source/drain doping occurs. This preliminary barrier prevents subsequent dopant diffusion into the channel, ensuring that the effective channel length remains stable and predictable even as the physical gate length is reduced for higher density integration.
Solution Approach 2:
The diffusion barrier acts as an intermediary element between the source/drain regions and the channel. It mediates the dopant distribution by blocking dopant atoms from entering the channel region, thereby decoupling the source/drain doping process from channel doping and maintaining precise gate length control.
2Reliability
If high doping concentration is incorporated in source/drain areas to minimize access resistance, then the transistor on-resistance decreases and performance improves, but dopant diffusion during thermal processing extends into the channel causing leakage current
Solution Approach 1:
The diffusion barrier creates a localized region with different doping characteristics. The channel region maintains low or zero doping concentration to prevent leakage, while the source/drain regions can be heavily doped to minimize access resistance. This local differentiation allows each region to be optimized for its specific function without compromising the other.
Solution Approach 2:
The channel region is segmented into zones with different doping concentrations. The central channel portion remains undoped or lightly doped to maintain low leakage, while regions adjacent to source/drain can have controlled doping. The diffusion barrier enables this segmentation by preventing uniform dopant distribution throughout the channel.
3Reliability
If thermal annealing is performed to activate dopants and cure implantation defects, then dopant activation increases and device performance improves, but excessive thermal budget causes unwanted dopant diffusion and junction rounding
Solution Approach 1:
The diffusion barrier is formed before thermal annealing and dopant activation steps. This preliminary barrier remains in place during subsequent high-temperature processing, allowing sufficient thermal budget to be applied for complete dopant activation and defect curing without causing unwanted diffusion into the channel, as the barrier physically blocks such diffusion.
4Ease of manufacture
If conventional ion implantation with gate electrode as mask is used for source/drain formation, then self-alignment is achieved, but the doping profile and extent are difficult to control precisely due to lateral diffusion and unpredictable fabrication variations
Solution Approach 1:
The diffusion barrier serves as an intermediary that provides precise control over dopant distribution. By placing the barrier at a defined location in the channel region before doping, it creates a sharp boundary that limits dopant penetration. This intermediary structure enables better control of the doping profile compared to relying solely on gate shadowing during implantation.
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 results in transistors with improved ruggedness against fabrication uncertainties, reduced leakage current, and enhanced electric performance by maintaining a non-doped channel and highly doped source/drain areas with controlled diffusion, thus achieving better consumption characteristics.
Implementation Method 1
a modified diffusion area arranged in the extension of the lateral spacers and separating the conduction channel and one of the source/drain electrodes, the modified diffusion area comprising a first doping impurity diffusion barrier element
Implementation Method 2
performing tilted ion implantation of a diffusion barrier element with a non-zero angle with respect to the surface of the semiconductor material film
Implementation Method 3
The implantation step is followed by activation/diffusion annealing which enables, a part of the defects created when implantation is performed to be cured and the greatest possible quantity of doping impurities to be placed in electrically active sites
Data Source
AI summary
The field effect device comprises a sacrificial gate electrode having side walls covered by lateral spacers formed on a semiconductor material film. The source/drain electrodes are formed in the semiconductor material film and are arranged on each side of the gate electrode. A diffusion barrier element is implanted through the void left by the sacrificial gate so as to form a modified diffusion area underneath the lateral spacers. The modified diffusion area is an area where the mobility of the doping impurities is reduced compared with the source/drain electrodes.