VTFET Backside Wraparound Contact for Higher Circuit Density
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Solution Overview
Problem
Existing VTFET technologies face challenges in achieving lower circuit density due to the need for sideways extensions of bottom source/drain epitaxy for frontside contact connections, which also result in high contact resistance, making it difficult to thermally anneal backside contacts effectively.
Innovation Solution
Implementing a wraparound backside contact that touches both the bottom and side surfaces of the source/drain structure, reducing contact resistance and enabling greater circuit density by increasing the contact surface area.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If frontside contact connection with sideways extension of bottom source/drain epitaxy is used, then contact connection is achieved, but circuit density decreases and contact resistance increases
Solution Approach 1:
The patent inverts the conventional frontside contact approach by implementing a backside contact that wraps around to touch both the bottom surface and side surface of the source/drain structure. This inversion eliminates the need for sideways extensions while achieving reliable electrical connection, thereby resolving the contradiction between contact reliability and circuit density.
Solution Approach 2:
The backside contact extends into the vertical dimension by wrapping around the source/drain structure, touching both the bottom surface and side surface. This dimensional approach provides multiple contact paths without requiring lateral expansion, thus maintaining high circuit density while ensuring reliable contact connection.
2Reliability
If frontside contact connection with sideways extension is used, then contact connection is achieved, but contact resistance increases
Solution Approach 1:
By inverting to a backside contact configuration that wraps around the source/drain structure, the patent achieves reliable contact connection without the high contact resistance associated with frontside contacts requiring sideways extensions.
Solution Approach 2:
The backside contact merges multiple contact functions by simultaneously touching both the bottom surface and side surface of the source/drain structure. This combined contact approach reduces contact resistance by providing multiple parallel conduction paths.
3Productivity
If backside contact is implemented, then circuit density increases, but thermal annealing effectiveness decreases
Solution Approach 1:
The backside contact's wraparound configuration extends into the vertical dimension, allowing it to touch both the bottom surface and side surface of the source/drain structure. This dimensional approach maintains high circuit density while providing sufficient thermal contact area for effective annealing.
Data Source
AI summary
A vertical transport field effect transistor (VTFET) apparatus includes a fin-shaped channel structure; a gate stack that surrounds the channel structure; a top source/drain structure at a top end of the channel structure; a top interconnect layer above the top source/drain structure; a top contact that electrically connects the top source/drain structure to the top interconnect layer; a bottom source/drain structure at a bottom end of the channel structure; a backside interconnect layer below the bottom source/drain structure; and a backside contact that touches a bottom surface of the bottom source/drain structure and also touches a side surface of the bottom source/drain structure and electrically connects the bottom source/drain structure to the backside interconnect layer.