Source/Drain Epi Height Layout for Low-Resistance Contacts
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Solution Overview
Problem
In advanced semiconductor technology nodes, the formation of source/drain contact vias near metal compound features in single-fin EPI structures can lead to diffusion of chemical elements like fluorine, increasing the resistivity of these features, which affects the integrity and performance of transistors.
Innovation Solution
The implementation of epitaxially grown source/drain structures with varying heights and geometries for n-type and p-type features ensures sufficient clearance between the metal compound features and the contact vias, preventing chemical element diffusion and maintaining the integrity of the metal silicide features during the contact formation process.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If contact vias are formed near metal compound features in single-fin EPI structures, then contact features can be created for electrical connection, but chemical element diffusion (e.g., fluorine) increases resistivity of metal compound features
Solution Approach 1:
The patent introduces an intermediary barrier layer between the contact via and the metal compound feature. This barrier layer prevents direct interaction and chemical element diffusion from the contact via into the metal compound feature, thereby maintaining low resistivity and preserving contact quality without requiring increased spacing.
Solution Approach 2:
The patent transitions from a two-dimensional planar spacing approach to a three-dimensional solution by forming the metal compound feature with varying height (raised structure). This vertical dimensionality change allows the top surface of the metal compound feature to be positioned higher than the contact via bottom, creating natural clearance and preventing chemical diffusion without relying solely on lateral spacing.
2Object-affected harmful factors
If clearance is increased between metal compound features and contact vias, then chemical element diffusion is prevented, but series resistance increases
Solution Approach 1:
The patent resolves this contradiction by utilizing the vertical dimension to create clearance. The metal compound feature is formed with a raised top surface that extends higher than the contact via bottom, providing chemical diffusion prevention through vertical separation rather than lateral spacing. This maintains horizontal overlap and low series resistance while preventing harmful chemical element diffusion through the height difference.
Solution Approach 2:
The barrier layer serves as an intermediary that allows the contact via to be positioned closer to the metal compound feature without chemical element diffusion. The barrier layer blocks the diffusion path while maintaining electrical connectivity, thus reducing series resistance compared to designs requiring larger clearances.
3Ease of manufacture
If n-type and p-type source/drain features have the same geometry, then manufacturing is simplified, but sufficient clearance cannot be ensured for preventing chemical diffusion
Solution Approach 1:
The patent applies local quality by forming the metal compound feature with non-uniform height - the top surface is raised above the bottom surface. This local geometric variation in the metal compound feature creates sufficient vertical clearance with contact vias while maintaining a relatively simple overall structure. The raised portion is localized only where needed for diffusion prevention, balancing manufacturing simplicity with effective chemical diffusion barrier.
Solution Approach 2:
The patent introduces asymmetry in the metal compound feature geometry, where the top surface height differs from the bottom surface height. This asymmetric structure provides the necessary vertical clearance to prevent chemical element diffusion from contact vias into the metal compound feature, while the asymmetry is localized and does not significantly complicate the overall manufacturing process.
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 approach effectively reduces the series resistance and maintains the quality of metal compound features, enhancing the performance and reliability of transistors by preventing adverse chemical diffusion during the contact formation process.
Implementation Method 1
ensures sufficient clearance between the metal compound features and the contact vias, preventing chemical element diffusion
Data Source
AI summary
A semiconductor structure includes an n-type epitaxial source/drain feature (NEPI) and a p-type epitaxial source/drain feature (PEPI) over a substrate, wherein a top surface of the NEPI is lower than a top surface of the PEPI. The semiconductor structure further includes a metal compound feature disposed on the top surface of the NEPI and the top surface of the PEPI. The metal compound feature extends continuously from the top surface of the NEPI to the top surface of the PEPI. The semiconductor structure further includes a contact feature disposed on the metal compound feature and a via structure disposed over the contact feature.