Embedded SiGe Source-Drain Structure for Silicide Encroachment Control
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Solution Overview
Problem
Semiconductor devices with 20% eSiGe source/drain regions face low boron solubility and high silicide-to-eSiGe contact resistance, while 30% eSiGe regions suffer from silicide encroachment and strain relaxation, leading to channel mobility and junction leakage issues.
Innovation Solution
The method involves forming alternating thin layers of 20% and 30% eSiGe on a thick 30% eSiGe layer, allowing for controlled silicide depth and width, increasing active boron concentration, and reducing contact resistance through epitaxial growth and low-temperature rapid thermal annealing.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Quantity of substance
If 30% eSiGe is used for source/drain regions, then boron solubility and active B concentration are increased, but silicide encroachment occurs and channel strain is reduced
Solution Approach 1:
The eSiGe source/drain region is segmented into multiple layers with different Ge concentrations (e.g., 30% Ge at the interface, 20% Ge in the middle, 10% Ge at the top). This segmentation allows the silicide to be confined to the lower Ge concentration layer, preventing encroachment into the channel, while the overall structure maintains high B solubility and channel strain.
Solution Approach 2:
Different regions of the eSiGe source/drain structure are assigned different Ge concentrations tailored to their specific functions: higher Ge concentration (30%) near the silicide interface for B solubility, lower Ge concentration (10-20%) in the channel-proximal region for strain maintenance and silicide confinement. This local quality differentiation resolves the contradiction between B solubility and silicide control.
2Speed
If 30% eSiGe is used for source/drain regions, then channel strain is enhanced, but silicide encroachment causes junction leakage
Solution Approach 1:
The eSiGe structure is segmented into layers with varying Ge content, placing lower Ge concentration (10-20%) layers adjacent to the channel to maintain strain and prevent leakage, while higher Ge concentration (30%) layers are positioned away from the channel to provide B solubility without causing encroachment-related leakage.
Solution Approach 2:
The Ge concentration is locally optimized: regions near the channel have lower Ge (10-20%) for strain and leakage prevention, while regions farther from the channel have higher Ge (30%) for B solubility. This local quality approach simultaneously achieves high mobility and low leakage.
3Manufacturing precision
If 20% eSiGe is used for source/drain regions, then silicide is well-contained, but boron solubility and channel strain are reduced
Solution Approach 1:
The eSiGe structure is segmented into multiple layers with different Ge concentrations, allowing the silicide to be formed in a lower Ge concentration layer (ensuring containment) while higher Ge concentration layers are present in the overall structure to provide high B solubility and strain.
Solution Approach 2:
The eSiGe source/drain region is formed as a composite structure with multiple layers of different Ge concentrations (e.g., 30% Ge, 20% Ge, 10% Ge layers). This composite structure combines the advantages of different Ge concentrations: good silicide containment in lower Ge regions and high B solubility in higher Ge regions.
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 enhances channel strain, reduces silicide-to-eSiGe contact resistance, and minimizes junction leakage, achieving improved channel mobility and device performance while maintaining well-contained silicide layers.
Implementation Method 1
Silicon germanium (SiGe) is then epitaxially grown in the cavities 101 and doped with B
Implementation Method 2
Boron (B) is typically introduced as a dopant to reduce contact resistance
Implementation Method 3
implantation of B causes undesirable strain relaxation. Further, implanted B requires high temperature rapid thermal anneal (RTA), e.g., about 900° C. to about 1300° C., for activation
Data Source
AI summary
Semiconductor devices with embedded silicon germanium source/drain regions are formed with enhanced channel mobility, reduced contact resistance, and reduced silicide encroachment. Embodiments include embedded silicon germanium source/drain regions with a first portion having a relatively high germanium concentration, e.g., about 25 to about 35 at. %, an overlying second portion having a first layer with a relatively low germanium concentration, e.g., about 10 to about 20 at. %, and a second layer having a germanium concentration greater than that of the first layer. Embodiments include forming additional layers on the second layer, each odd numbered layer having relatively low germanium concentration, at. % germanium, and each even numbered layer having a relatively high germanium concentration. Embodiments include forming the first region at a thickness of about 400 Å to 28 about 800 Å, and the first and second layers at a thickness of about 30 Å to about 70 Å.