Wrapped Source/Drain Contact Structure for Lower Ohmic Resistance
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Solution Overview
Problem
Forming effective ohmic contacts to epitaxial source or drain regions in integrated circuits is challenging due to the difficulty in leveraging the total surface area, particularly the sidewalls, of these regions, leading to high contact resistance.
Innovation Solution
A conductive contact is formed that wraps around the source or drain regions, including their sidewalls, with a dielectric layer between the conductive contact and the subfin region, and a highly conductive outer layer such as a silicide layer extending around all outside edges to enhance the ohmic contact.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a conventional contact structure is used to contact the source or drain regions, then the device structure remains simple, but the contact resistance is high due to insufficient surface area contact
Solution Approach 1:
The contact structure transitions from a conventional planar contact to a wrapped contact that extends around the sidewalls of the source/drain regions. This adds a vertical/dimensional component to the contact, increasing the contact surface area from merely top/bottom surfaces to including sidewall surfaces, thereby reducing contact resistance without excessive complexity increase
Solution Approach 2:
The conductive contact material is positioned to wrap around and enclose portions of the source/drain regions, creating a nested configuration where the contact surrounds the semiconductor region. This nested arrangement maximizes the interfacial contact area between the conductive material and the doped semiconductor, improving ohmic contact while maintaining a compact structure
2Reliability
If the contact surface area is increased to reduce contact resistance, then the ohmic contact improves, but the manufacturing process becomes more difficult
Solution Approach 1:
The source/drain regions are doped with high concentration dopants before the contact formation process. This preliminary doping action creates highly conductive regions that facilitate better ohmic contact. By preparing the semiconductor regions in advance with appropriate doping, the subsequent contact formation becomes easier and more effective, as the doped regions naturally attract and conduct electrons more readily
Solution Approach 2:
The dopant concentration in the source/drain regions is significantly increased to create highly conductive regions. This parameter change (increasing dopant concentration) transforms the electrical properties of the semiconductor regions, making them more conductive and easier to form low-resistance contacts with. The high dopant concentration reduces the contact resistance by providing more charge carriers at the contact interface
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 provides a better ohmic contact with lower overall contact resistance by increasing the surface area contacted and using a highly conductive material to improve conductivity.
Implementation Method 1
a highly conductive outer layer such as a silicide layer extending around all outside edges to enhance the ohmic contact
Data Source
Figure 1A~1B
Figure 2A~2B
Figure 3A~3B
AI summary
Techniques are provided herein to form semiconductor devices having one or more epitaxial source or drain regions wrapped by a conductive contact to form an improved ohmic contact. A first semiconductor device includes a first semiconductor region extending between a first source or drain region and a second source or drain region, and a second semiconductor device includes a second semiconductor region extending between the first source or drain region and a third source or drain region. The first and second semiconductor devices include a subfin region adjacent to a dielectric layer. A conductive layer extends around the first source or drain region such that the conductive layer at least contacts the sidewalls of the first source or drain region and both upper and lower surfaces of the source or drain region. A dielectric layer is also present between the conductive contact and the subfin region.