Wrap-around Contact for Vertical FETs
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Solution Overview
Problem
Conventional top source/drain contacts in vertical field effect transistors (VFETs) face issues with shrinking landing surface area, leading to contact misalignments, dead or partially dead devices, and lower yields due to increased source/drain heights and shrinking widths, which affect device performance and manufacturing efficiency.
Innovation Solution
A method for forming a wrap-around contact (WAC) on the top source/drain of VFETs involves recessing the gate to expose sidewalls, forming a top spacer, and using sacrificial spacers that are selectively etched to create a cavity for a conductive material, ensuring improved contact alignment and area.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If conventional top source/drain contacts are used in VFETs, then the fabrication process is simple, but the contact area shrinks leading to misalignments and lower yields
Solution Approach 1:
The contact structure is segmented into multiple components: a bottom contact layer formed first, followed by spacer formation, and then a top contact layer. This segmentation allows each layer to be precisely controlled and aligned independently, improving overall contact alignment precision while managing fabrication complexity through systematic process breakdown
Solution Approach 2:
The bottom contact layer and spacers are formed in advance before the top contact layer is deposited. This preliminary action establishes precise alignment references that guide subsequent processing steps, ensuring accurate contact alignment while the complexity is managed through pre-planned process sequencing
2Productivity
If source/drain heights increase and widths shrink, then device density improves, but contact reliability deteriorates due to smaller landing area
Solution Approach 1:
The contact structure transitions from a single-planar contact to a multi-layered vertical structure with bottom and top contact layers connected through spacers. This dimensional change allows the contact to maintain reliability by distributing the electrical connection across multiple surfaces and depths, compensating for the reduced landing area caused by shrunk source/drain dimensions
Solution Approach 2:
The contact structure is nested with multiple layers: the bottom contact layer is positioned first, then spacers are formed around it, and finally the top contact layer is deposited. This nested arrangement creates a robust contact pathway that maintains electrical reliability even when the overall contact footprint is reduced for higher device density
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
The WAC method enhances contact reliability and device yield by increasing the contact area and reducing misalignments, thereby improving the performance and manufacturing efficiency of VFETs.
Implementation Method 1
The source/drain region can include a first material, the sacrificial spacer can include a second material, and the second material can be selected such that the second material can be etched selective to the first material
Data Source
AI summary
Embodiments of the present invention are directed to forming a wrap-around contact (WAC) for a vertical field effect transistor (VFET). In a non-limiting embodiment of the invention, a top spacer is formed on a surface of a gate. A sacrificial spacer is formed on the top spacer. A source/drain region is formed over the top spacer and between sidewalls of the sacrificial spacer. The sacrificial spacer can be replaced with a wrap-around contact. The source/drain region can include a first material, the sacrificial spacer can include a second material, and the second material can be selected such that the second material can be etched selective to the first material.