FinFET Gate Stack Concaves to Prevent Sub-Fin Leakage
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Solution Overview
Problem
The increasing depth of recesses in FinFETs can lead to sub-fin leakage paths, compromising the electrical control and performance of the devices.
Innovation Solution
The fabrication process involves forming semiconductor fins with specific concave structures that accommodate the source and drain regions, ensuring they are embedded within the gate stack to prevent leakage and enhance control over the conducting channel.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If the depth of recesses is increased to accommodate source and drain regions, then the electrical control over the channel is improved, but sub-fin leakage paths occur compromising device reliability
Solution Approach 1:
The patent applies curvature by forming rounded concaves at the bottom of the recesses instead of sharp V-shaped corners. This rounding of the recess geometry prevents sub-fin leakage paths by eliminating sharp corners where leakage can occur, while still maintaining adequate recess depth for source and drain accommodation. The curved bottom surface of the recesses provides both the needed depth for electrical control and prevents the leakage issue through geometric modification.
2Reliability
If the lateral dimension of recesses is increased to embed source and drain regions, then the device boost is enhanced, but the manufacturing precision becomes more difficult to control
Solution Approach 1:
The patent employs preliminary action by forming a mandrel structure before creating the final recesses. The mandrel serves as a pre-formed template that defines the recess geometry, including the rounded bottom shape. This preliminary structure enables subsequent etching processes to replicate the desired geometry with high precision, avoiding the difficulty of directly forming complex rounded concaves and ensuring consistent lateral dimensions across all recesses.
3Ease of manufacture
If V-shaped concaves are formed in fins, then the source and drain embedding is facilitated, but the fin structure strength is reduced
Solution Approach 1:
The patent replaces the V-shaped concave geometry with rounded concaves at the recess bottoms. This curvature modification maintains the embedding capability for source and drain regions while significantly improving fin structure strength. The rounded geometry distributes mechanical stress more evenly compared to sharp V-shaped corners, preventing stress concentration and potential fin breakage during subsequent processing steps.
Data Source
AI summary
A FinFET including a gate stack, a semiconductor fin embedded in the gate stack, a source and a drain disposed is provided. The semiconductor fin extends along a widthwise direction of the gate stack and has a first concave and a second concave exposed at sidewalls of the gate stack respectively. The source and drain are disposed at two opposite sides of the gate stack. The source includes a first portion in contact with and embedded in the first concave. The drain includes a second portion in contact with and embedded in the second concave. The first portion and the second portion are covered by the gate stack.