Self-Aligned Wrap-Around Contacts for Nanosheet Transistors
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Solution Overview
Problem
The scaling of nanosheet transistors is limited by the large contact area required for wrap-around contacts, which leads to increased resistance and reduced device density due to the need for a wide contact area to ensure alignment, even in worst-case scenarios.
Innovation Solution
A method is developed to form self-aligned wrap-around contacts using a smaller contact area by employing an etch-stop layer and sacrificial layers, allowing for the formation of a wrap-around contact and a second contact without limiting device scaling, while ensuring alignment in worst-case scenarios.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a large contact area is used for wrap-around contacts to ensure alignment in worst-case scenarios, then alignment reliability is improved, but device scaling is limited due to increased space between nanosheet stacks
Solution Approach 1:
The patent applies preliminary action by forming the etch-stop layer on the continuous outer surface of the raised source/drain region before forming the wrap-around contact. This pre-positioned layer serves as a self-aligned reference that guides subsequent contact formation, ensuring proper alignment without requiring excessive contact area. The etch-stop layer is formed at a specific location that anticipates the need for alignment in worst-case scenarios, thereby resolving the contradiction between reliability and scaling.
Solution Approach 2:
The etch-stop layer acts as an intermediary element between the raised source/drain region and the wrap-around contact. This intermediate layer provides a self-aligned reference surface that enables precise contact formation without requiring a large contact area. The intermediary etch-stop layer mediates the alignment relationship, allowing the contact to be properly positioned while maintaining compact dimensions for device scaling.
2Reliability
If a large contact area is used for wrap-around contacts, then alignment is ensured in worst-case scenarios, but contact resistance increases due to the wider contact area
Solution Approach 1:
The etch-stop layer is formed in advance on the continuous outer surface of the raised source/drain region, creating a self-aligned reference before the wrap-around contact is formed. This preliminary positioning ensures that the contact achieves proper alignment without requiring a large contact area, thereby reducing contact resistance while maintaining alignment reliability in worst-case scenarios.
Solution Approach 2:
The etch-stop layer serves as an intermediary that enables precise alignment between the wrap-around contact and the raised source/drain region. By providing a self-aligned reference surface, this intermediate layer allows the contact to be narrowly dimensioned, which reduces contact resistance while ensuring proper alignment through the mediating etch-stop layer.
3Reliability
If the contact area is made significantly wider than the nanosheets, then wrap-around contact formation is ensured, but device density is reduced due to limited space between individual nanosheet stacks
Solution Approach 1:
The etch-stop layer is pre-formed on the continuous outer surface of the raised source/drain region, establishing a self-aligned reference that guides wrap-around contact formation. This preliminary action ensures reliable contact formation without requiring the contact area to be significantly wider than the nanosheets, thereby maintaining high device density while ensuring proper contact formation.
Solution Approach 2:
The etch-stop layer acts as an intermediary that enables reliable wrap-around contact formation with compact dimensions. By providing a self-aligned reference surface, this intermediate layer allows the contact to be narrowly dimensioned, which increases device density by reducing the space required between individual nanosheet stacks while ensuring reliable contact formation.
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 reduces contact resistance and enables more densely packed nanosheet transistors, allowing for smaller integrated circuits while maintaining manufacturing reliability.
Implementation Method 1
removing the second sacrificial layer selective to the etch-stop layer
Implementation Method 2
removing an upper portion of the dielectric layer to expose a portion of the second sacrificial layer
Data Source
AI summary
This disclosure relates to forming a wrap-around contact on a nanosheet transistor, the method including: forming an etch-stop layer over a continuous outer surface of a raised source/drain (S/D) region of the nanosheet transistor; forming a sacrificial layer over the etch-stop layer, the etch-stop layer including a different material than the sacrificial layer; depositing a dielectric layer over the sacrificial layer; removing an upper portion of the dielectric layer to expose a portion of the sacrificial layer; removing the sacrificial layer selective to the etch-stop layer; and depositing a conductor in the removed upper portion of the dielectric layer to form a wrap-around contact and a second contact.