Wraparound Source/Drain Contacts for Lower Contact Resistance
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Solution Overview
Problem
Providing good ohmic contacts to the source or drain regions of semiconductor devices is challenging as the devices scale downward, as existing contacts do not effectively utilize the total surface area, particularly the sidewalls of epitaxial regions, leading to high contact resistance.
Innovation Solution
Forming conductive contacts that wrap around the source or drain regions, including a highly conductive outer layer such as a silicide, to enhance ohmic contact by contacting the sidewalls and potentially forming backside contacts, thereby increasing the contact area and reducing resistance.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If conventional contacts are used on source or drain regions, then the device structure is simple, but the contact resistance is high due to insufficient contact area
Solution Approach 1:
The contact structure transitions from a conventional planar contact to a wraparound contact that extends onto the sidewalls of the epitaxial region. This adds a vertical dimension to the contact area, utilizing the sidewall surface to create additional contact pathways and reduce contact resistance.
Solution Approach 2:
The conductive contact is formed as a wraparound structure that nests around the epitaxial source or drain region, with the contact material conformally covering the sidewalls and extending onto the top surface, creating a nested configuration that maximizes contact area.
2Reliability
If the contact area is increased by wrapping around the epitaxial region, then the ohmic contact is improved, but the manufacturing process becomes more complex
Solution Approach 1:
The epitaxial region is grown with exposed sidewalls in advance, creating a pre-formed structure that is ready to receive the wraparound contact. This preliminary preparation of the sidewall surface enables subsequent conformal contact deposition without requiring complex restructuring operations.
Solution Approach 2:
The sidewall surface of the epitaxial region serves as an intermediary surface that facilitates the transition from planar to three-dimensional contact. By utilizing the sidewall as an intermediate contact area, the structure enables progressive contact formation and reduces manufacturing complexity.
Data Source
AI summary
Techniques are provided herein to form semiconductor devices having epitaxial diffusion regions (e.g., source and/or drain regions) wrapped by a conductive contact. In an example, a semiconductor device includes a source or drain region and a conductive layer that extends around the source or drain region such that the conductive layer at least contacts the sidewalls of the source or drain region or wraps completely around the source or drain region. In some examples, a conducive contact extends upward through a thickness of an adjacent dielectric layer and contacts the conductive layer from below, thus forming a backside contact. By forming a conductive layer around multiple sides of the source or drain region (rather than just contacting a top or bottom surface) more surface area of the source or drain region is contacted thus providing an improved ohmic contact and a lower overall contact resistance.