Overhanging Source/Drain Contact for Lower Parasitic Capacitance
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
Existing source/drain contacts in multi-gate devices, such as FinFETs and MBC transistors, suffer from increased parasitic capacitance due to elongated contacts overlapping adjacent gate structures, leading to undesirable performance in ring oscillator (RO) and cell height reduction challenges.
Innovation Solution
A source/drain contact design that spans over multiple active regions with a portion overhanging over an adjacent source/drain feature, separated by a dielectric, reducing areal overlap with adjacent gate structures and thus parasitic capacitance.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If source/drain contacts are elongated to span over multiple active regions, then connectivity efficiency is improved and number of metal lines is reduced, but parasitic capacitance increases due to overlap with adjacent gate structures
Solution Approach 1:
The source/drain contact is designed with an overhanging structure that extends in the vertical dimension above the adjacent source/drain feature. This three-dimensional configuration allows the contact to span multiple active regions horizontally while the overhanging portion rises vertically to clear adjacent gate structures, thereby maintaining connectivity efficiency while reducing parasitic capacitance through spatial separation.
2Area of stationary object
If source/drain contacts are elongated to reduce cell height, then area is reduced, but parasitic capacitance increases due to overlap with adjacent gate structures
Solution Approach 1:
The contact structure utilizes vertical stacking to achieve area reduction. By extending the contact vertically with an overhanging portion that clears adjacent gate structures, the design reduces the horizontal footprint and cell height while avoiding parasitic capacitance through the vertical separation created by the overhang configuration.
Solution Approach 2:
The source/drain contact is nested over the adjacent source/drain feature in a vertical arrangement. The overhanging portion of the contact is positioned above and separated from the adjacent source/drain feature by a dielectric material, creating a nested configuration that reduces horizontal area while maintaining electrical connectivity and minimizing parasitic effects.
3Reliability
If source/drain contacts are elongated to maintain connectivity, then electrical connection is improved, but parasitic capacitance increases due to overlap with adjacent gate structures
Solution Approach 1:
The contact structure achieves reliable electrical connection by spanning multiple active regions horizontally while simultaneously extending vertically with an overhanging portion. This vertical extension separates the contact from adjacent gate structures in the vertical dimension, maintaining low resistance electrical connectivity while reducing parasitic capacitance through increased spatial separation.
Solution Approach 2:
A dielectric feature is introduced as an intermediary material between the overhanging portion of the source/drain contact and the adjacent source/drain feature. This dielectric layer provides electrical isolation that prevents parasitic capacitance formation while allowing the contact to maintain its elongated configuration for reliable connectivity across multiple active regions.
Data Source
AI summary
Semiconductor structures and methods are provided. A semiconductor structure according to the present disclosure includes a first fin structure and a second fin structure over a substrate, a first source/drain feature disposed over the first fin structure and a second source/drain feature disposed over the second fin structure, a dielectric feature disposed over the first source/drain feature, and a contact structure formed over the first source/drain feature and the second source/drain feature. The contact structure is electrically coupled to the second source/drain feature and is separated from the first source/drain feature by the dielectric feature.