Self-Aligned S/D Metal Contact With Sidewall Wrap for Lower Resistance
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Solution Overview
Problem
The challenge of reducing contact resistance between source/drain features and metal contacts becomes more significant as device sizes decrease, particularly due to limited spacing and increased metal contact resistance, which deteriorates device integration and increases the risk of electric breakdown.
Innovation Solution
A method is introduced where a sacrificial dielectric layer is deposited and partially removed to form a contact trench, allowing the S/D contact to partially wrap around one sidewall of the epitaxial S/D feature, while the opposing sidewall remains free of contact, optimizing the contact area and spacing to reduce resistance and improve breakdown performance.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If the spacing between adjacent source/drain regions is reduced to increase device integration density, then device integration improves, but metal contact resistance increases and contact reliability deteriorates
Solution Approach 1:
The S/D contact structure transitions from a planar top-surface contact to a three-dimensional structure that wraps around the sidewall of the epitaxial S/D feature. This vertical/dimensional extension of the contact interface increases the effective contact area without requiring additional lateral spacing, thereby reducing contact resistance while maintaining high device integration density.
Solution Approach 2:
The S/D contact is formed to partially wrap around the sidewall of the epitaxial S/D feature, creating a nested configuration where the contact material surrounds a portion of the S/D feature sidewall. This nested structure maximizes the contact interface area within the limited lateral space, improving electrical connection without increasing the footprint.
2Reliability
If the metal contact landing area is increased to reduce contact resistance, then contact resistance decreases, but the spacing between adjacent source/drain regions must increase, reducing device integration
Solution Approach 1:
Instead of increasing the lateral landing area of the contact, the invention extends the contact interface vertically by wrapping around the sidewall of the epitaxial S/D feature. This dimensional transition allows the contact area to increase without consuming additional lateral space, thereby maintaining high device integration density while reducing contact resistance.
Solution Approach 2:
The contact structure is segmented into multiple contact interfaces: a top surface contact portion and a sidewall contact portion. This segmentation distributes the contact resistance reduction across multiple interfaces, achieving the desired electrical performance without requiring a single large landing area that would reduce integration density.
3Reliability
If the contact area with epitaxial S/D feature is increased to reduce contact resistance, then contact resistance decreases, but the risk of electric breakdown between adjacent contacts increases
Solution Approach 1:
The S/D contact structure exhibits local quality variation by partially wrapping around the epitaxial S/D feature sidewall rather than fully surrounding it. This selective wrapping increases contact area for electrical connection while deliberately leaving gaps or maintaining spacing in regions where electric breakdown risk would be elevated, thereby balancing contact resistance reduction with breakdown prevention.
Data Source
AI summary
The present disclosure provides a semiconductor device. The semiconductor device includes a semiconductor fin over a substrate, an epitaxial source/drain (S/D) feature disposed over the semiconductor fin, first and second dielectric layers over the substrate, and an S/D contact disposed on the epitaxial S/D feature. The first and second dielectric layers have different material compositions. A first sidewall of the epitaxial S/D feature is facing the first dielectric layer, a second sidewall of the epitaxial S/D feature is facing the second dielectric layer, and the S/D contact partially covers a top surface of the epitaxial S/D feature and extends continuously to cover the first sidewall of the epitaxial S/D feature.