Source/Drain Via Structure for Lower Contact Resistance
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Solution Overview
Problem
The high contact resistance between source/drain contact plugs and overlying vias in integrated circuits, primarily due to the small contact area, adversely affects the drive current of transistors.
Innovation Solution
The formation of vias is modified to laterally expand the bottom portion to increase the contact area with the source/drain contact plugs, while also expanding the top portion to enhance contact with overlying conductive features, thereby reducing overall contact resistance.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Volume of moving object
If the contact area between source/drain contact plugs and via is reduced due to miniaturization, then the integrated circuit dimensions are reduced, but the contact resistance increases
Solution Approach 1:
The patent transitions from a uniform cylindrical via structure to a via with varying cross-sectional dimensions along its length. The via features a larger cross-sectional area at the bottom contact region and a smaller cross-sectional area at the top, effectively using dimensional variation along the vertical axis to increase contact area without increasing the lateral footprint of the integrated circuit.
Solution Approach 2:
The via structure is designed with different geometric properties at different locations: the bottom portion has a larger cross-sectional area to maximize contact area with the source/drain contact plug and reduce contact resistance, while the top portion has a smaller cross-sectional area to maintain appropriate spacing and alignment with overlying conductive features. This local differentiation of geometric quality resolves the contradiction between minimizing overall dimensions and maximizing contact area.
2Reliability
If the via cross-sectional area is increased to reduce contact resistance, then the contact area increases, but the alignment precision with overlying conductive features deteriorates
Solution Approach 1:
The patent resolves the alignment precision issue by varying the via cross-sectional area along its length rather than using a uniform cross-section. The larger bottom area provides sufficient contact area for low contact resistance, while the smaller top area maintains the precise lateral dimensions needed for alignment with overlying conductive features. This dimensional variation along the vertical axis allows both large contact area and precise alignment to coexist.
Solution Approach 2:
Different portions of the via are assigned different geometric qualities: the bottom portion has a larger cross-sectional area optimized for contact resistance reduction, while the top portion has a smaller cross-sectional area optimized for alignment precision. This local differentiation allows each portion to fulfill its specific functional requirement without compromising the other.
Data Source
AI summary
A structure includes a transistor including a first source/drain region, a source/drain contact plug over and electrically coupling to the first source/drain region, and a via over and contacting the source/drain contact plug. The via has a bottom portion having a first length, and an upper portion having a second length. The first length is greater than the second length. Both of the first length and the second length are measured in a same direction parallel to a top surface of the source/drain contact plug.