Amorphous Boron Interfacial Layer for PFET Source Drain Contact Resistance
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Solution Overview
Problem
The existing methods for increasing dopant concentration in PFET source/drain contacts are limited to about 5×10^20 atoms/cm^2, which restricts the improvement of transistor performance due to limited boron concentration in silicon or silicon germanium.
Innovation Solution
A method involving epitaxial growth, trench contact formation, and deposition of a conformal layer of amorphous boron with a concentration of 5×10^21 to 5×10^22 atoms/cm^2 within the trench contact patterns, followed by filling with high-k dielectric material and conductive metal to achieve high boron concentration in PFET source/drain contacts.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Quantity of substance
If conventional epitaxial growth is used to form source/drain contacts, then the manufacturing process is simple, but the boron concentration is limited to about 5×10^20 atoms/cm^2
Solution Approach 1:
The source/drain contact structure is segmented into multiple functional layers: an interfacial layer containing high boron concentration (5×10^21 to 5×10^22 atoms/cm^2), a semiconductor layer, and a silicide layer. This segmentation allows each layer to be optimized independently, with the interfacial layer specifically engineered to achieve the required high boron concentration while maintaining overall structural integrity and electrical performance
Solution Approach 2:
High boron concentration is applied locally only in the interfacial layer region where it is most needed for reducing contact resistance, rather than uniformly throughout the entire source/drain structure. The boron concentration gradient is carefully controlled to be highest at the silicon-silicide interface and decrease toward the surface, optimizing electrical performance while controlling dopant diffusion into adjacent regions
2Quantity of substance
If ion implantation is used to increase boron concentration, then boron activity can be improved, but the maximum concentration is still limited to about 5×10^20 atoms/cm^2
Solution Approach 1:
The invention changes the fundamental parameter of boron concentration from the conventional limit of 5×10^20 atoms/cm^2 to a new regime of 5×10^21 to 5×10^22 atoms/cm^2 in the interfacial layer. This parameter change is achieved through modified epitaxial growth conditions that enable supersaturated boron incorporation, fundamentally altering the dopant concentration capability beyond what conventional ion implantation can achieve
Solution Approach 2:
The source/drain contact is structured as a composite material system consisting of silicon, silicon germanium, and boron-doped interfacial layers with varying compositions and concentrations. This composite structure allows optimization of each component's properties, with the high-boron interfacial layer providing excellent electrical contact while the silicon germanium portions provide mechanical stress control and lattice matching
3Reliability
If higher boron concentration is achieved, then contact resistance is reduced, but dopant diffusion may affect adjacent regions
Solution Approach 1:
The interfacial layer with high boron concentration is formed preliminarily before final silicide deposition and annealing steps. This preliminary formation of the boron-rich layer ensures that the high concentration is established in the correct location before subsequent processing, allowing controlled diffusion during annealing to occur only after the interfacial layer structure is already in place to guide the diffusion pattern
Solution Approach 2:
The interfacial layer acts as an intermediary between the silicon substrate and the silicide contact layer, containing the high boron concentration in a controlled manner. This intermediary layer mediates the interaction between silicon and silicide, providing a transition zone that reduces contact resistance while preventing uncontrolled boron diffusion into the silicide and adjacent channel regions through its specific thickness and concentration profile
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 enables a PFET source/drain contact with a boron concentration up to 3×10^22 atoms/cm^2, reducing resistance and enhancing transistor performance by increasing boron activity in the contact region.
Implementation Method 1
performing an epitaxial growth process to form epitaxial contacts on opposing sides of a gate positioned over a substrate
Implementation Method 2
performing a deposition process to deposit a conformal layer including substantially pure amorphous boron within the trench contact patterns
Data Source
AI summary
A semiconductor device includes a gate disposed over a substrate; a source region and a drain region on opposing sides of the gate; and a pair of trench contacts over and abutting an interfacial layer portion of at least one of the source region and the drain region; wherein the interfacial layer includes boron in an amount in a range from about 5×1021 to about 5×1022 atoms/cm2.