FinFET Epitaxial Source/Drain Layers for Dopant Diffusion Control
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Solution Overview
Problem
The challenge of shortened channel lengths in FinFETs leading to increased diffusion of active dopant species and short-channel effects such as drain-induced barrier lowering (DIBL) compromises device performance.
Innovation Solution
A method for forming epitaxial source/drain features in FinFETs by etching trenches in the fins, depositing a dopant-containing film, and applying controlled annealing processes to form multiple epitaxial layers with specific dopant species, thereby controlling dopant diffusion and enhancing device performance.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If channel length is shortened to increase functional density, then productivity increases, but dopant diffusion increases and device performance deteriorates
Solution Approach 1:
The source/drain region is segmented into multiple epitaxial layers with different compositions and doping levels. The first epitaxial layer has a different semiconductor composition than the second epitaxial layer, creating distinct zones that control dopant distribution. This segmentation allows the channel length to be shortened while maintaining dopant confinement through the layered structure.
Solution Approach 2:
Different regions of the source/drain structure are given different local properties through selective doping. The first epitaxial layer is doped with a first dopant species while the second epitaxial layer is doped with a second dopant species, creating localized doping profiles that prevent excessive dopant diffusion into the channel region while maintaining electrical functionality.
2Productivity
If channel length is shortened to increase functional density, then productivity increases, but dopant diffusion control becomes more difficult
Solution Approach 1:
The epitaxial layers are formed with predetermined compositions and doping levels before the final doping process. The first and second epitaxial layers are grown with specific semiconductor compositions that prepare the structure to receive and confine dopant species in controlled manner, enabling precise dopant diffusion control even with shortened channel lengths.
Solution Approach 2:
The epitaxial layers act as intermediary structures between the source/drain contacts and the channel. These layers with different semiconductor compositions serve as buffer zones that mediate dopant transport, allowing controlled dopant diffusion while preventing excessive diffusion that would occur in a direct source/drain to channel configuration with shortened length.
3Ease of manufacture
If conventional doping methods are used in shortened channel FinFETs, then manufacturing is simpler, but short-channel effects increase
Solution Approach 1:
The source/drain structure uses composite semiconductor materials with different compositions in the first and second epitaxial layers. This composite structure enables effective dopant confinement and short-channel effect suppression while maintaining a manufacturing process that builds upon conventional epitaxial growth and doping techniques, balancing manufacturing ease with performance improvement.
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 method effectively reduces dopant diffusion, minimizing resistance and short-channel effects, thereby improving the performance of FinFET devices.
Implementation Method 1
a first annealing process is performed to cause the first dopant species to diffuse into the fin
Implementation Method 2
forming a source/drain feature including a first epitaxial layer, a second epitaxial layer, and a third epitaxial layer
Data Source
AI summary
A method of forming source/drain features in a FinFET device includes providing a fin formed over a substrate and a gate structure formed over a fin, forming a recess in the fin adjacent to the gate structure, forming a first epitaxial layer in the recess, forming a second epitaxial layer over the first epitaxial layer, and forming a third epitaxial layer over the second epitaxial layer. The second epitaxial layer may be doped with a first element, while one or both of the first and the third epitaxial layer includes a second element different from the first element. One or both of the first and the third epitaxial layer may be formed by a plasma deposition process.