Multi-Channel FET Contact Plug Geometry for Lower Contact Resistance
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Solution Overview
Problem
As the integration degree of semiconductor devices increases, the process for forming openings in vertically stacked channels becomes more challenging due to reduced opening diameters, making it difficult to effectively form contact plugs that can contact the epitaxial layers in a large area.
Innovation Solution
The semiconductor device incorporates a contact plug with a lower and middle portion sequentially stacked in the vertical direction, where the middle portion's width increases from the bottom to the top, allowing for a larger contact area with the first epitaxial layer, and a second epitaxial layer is disposed on the middle portion to contact the sidewall of the upper portion of the contact plug, facilitating improved contact resistance reduction.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If the integration degree of semiconductor devices is increased, then the device density and functionality are improved, but the opening diameter is reduced making the contact plug formation process more challenging
Solution Approach 1:
The contact plug transitions from a conventional cylindrical shape to a truncated cone shape with an inclined sidewall. This dimensional change in the plug geometry allows the contact area to be expanded in the horizontal dimension while maintaining the vertical stacking architecture, thereby resolving the contradiction between high integration and difficult opening formation.
Solution Approach 2:
The sidewall angle of the contact plug is changed from vertical (90 degrees) to an inclined angle between 60-80 degrees. This parameter change in the geometric configuration enables larger contact area without increasing the opening diameter, thus maintaining high device integration while improving manufacturability.
2Quantity of substance
If the opening diameter is reduced to increase device integration, then more channels can be stacked vertically, but the process for forming the opening becomes more challenging
Solution Approach 1:
By changing the contact plug shape to a truncated cone with inclined sidewalls, the contact area is expanded horizontally without requiring a larger opening diameter. This allows multiple channels to be stacked vertically while maintaining ease of manufacture through standard opening formation processes.
Solution Approach 2:
The contact plug exhibits non-uniform cross-sectional area along its height, with a larger area at the bottom (contacting the epitaxial layer) and a smaller area at the top. This local quality variation maximizes the contact area for electrical connection while keeping the opening size manageable for fabrication.
3Device complexity
If a conventional cylindrical contact plug is used, then the structure is simple, but the contact area with the epitaxial layer is limited
Solution Approach 1:
The contact plug is transformed from a cylindrical shape with vertical sidewalls to a truncated cone shape with inclined sidewalls. This dimensional change in geometry increases the base area that contacts the epitaxial layer, thereby improving electrical contact without significantly increasing overall structural complexity.
Solution Approach 2:
The inclined sidewall creates a curved surface profile rather than a straight vertical profile. This curvature allows the contact plug to achieve a larger contact footprint with the epitaxial layer while maintaining a compact vertical structure, balancing simplicity and contact area.
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 configuration enables the contact plug to effectively contact the first epitaxial layer over a larger area, reducing contact resistance and enhancing the semiconductor device's performance by allowing minor adjustments in process conditions without significant changes.
Implementation Method 1
the middle portion has a width that increases from a bottom to a top thereof along the vertical direction
Implementation Method 2
The second epitaxial layer contacts a portion of a sidewall of the upper portion of the contact plug
Data Source
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AI summary
A semiconductor device includes an active pattern (105) disposed on a substrate (100); a gate structure (350) disposed on the active pattern; nanowire channels (124) disposed on the substrate and that are spaced apart from each other in a vertical direction substantially perpendicular to an upper surface of the substrate; a first epitaxial layer (210) disposed on a portion of the active pattern adjacent to the gate structure; and a contact plug (330) disposed on the first epitaxial layer. The contact plug includes a straight and narrower lower portion (330a), a middle portion (330b) disposed on the lower portion, where the middle portion has a width that increases from a bottom to a top thereof along the vertical direction, and an upper portion (330c) disposed on and narrower than the middle portion. The device furthermore comprises an oppositely-doped second epitaxial layer (220) disposed on the middle portion (330b) of the contact plug (330)