Metal Source/Drain Structure With Epitaxial Sidewall Contact
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Solution Overview
Problem
Conventional epitaxial source/drain features in multi-gate transistors exhibit less-than-desirable conductivity due to shrinking dimensions, leading to increased contact resistance in semiconductor devices.
Innovation Solution
A method is introduced where a thin epitaxial layer is formed on exposed channel member surfaces in source/drain openings, allowing a metal source/drain feature to be filled, thereby replacing a substantial portion of the epitaxial source/drain feature and reducing contact resistance. This involves forming a dummy epitaxial feature, removing it to expose the channel surfaces, growing a thin epitaxial layer, and depositing a metal silicide and source/drain feature.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If conventional epitaxial source/drain features are used in multi-gate transistors, then the device structure is simpler to manufacture, but the conductivity is insufficient and contact resistance increases due to shrinking dimensions
Solution Approach 1:
The patent employs a composite source/drain structure consisting of three distinct layers: a doped epitaxial semiconductor layer (first material), an undoped or lightly-doped epitaxial semiconductor layer (second material), and a metal layer (third material). This composite structure combines the advantages of each material to achieve both low contact resistance and high conductivity, resolving the technical contradiction between reliability and device complexity.
Solution Approach 2:
The patent applies different doping concentrations and material properties to different regions of the source/drain structure. The first epitaxial layer has a first doping concentration optimized for one region, while the second epitaxial layer has a second doping concentration optimized for another region. This local quality differentiation allows each layer to perform its specific function optimally, improving overall conductivity without excessive complexity.
2Productivity
If the dimensions are shrunk to increase functional density, then production efficiency improves and costs decrease, but contact resistance to epitaxial source/drain features increases
Solution Approach 1:
By introducing a metal layer in combination with doped and undoped epitaxial semiconductor layers, the patent creates a composite source/drain structure that maintains low contact resistance even as dimensions are shrunk. The metal component provides excellent electrical conductivity that compensates for the increased contact resistance inherent in scaled-down epitaxial features.
Solution Approach 2:
The patent changes the electrical parameters of the source/drain structure by introducing layers with different doping concentrations and material properties. The metal layer provides high conductivity, while the differently-doped epitaxial layers provide graded transitions, collectively maintaining low contact resistance despite dimension reduction.
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
The approach results in reduced contact resistance and improved current conduction through the metal source/drain feature, enhancing the conductivity and performance of multi-gate transistors.
Implementation Method 1
improved current conduction through the metal source/drain feature, enhancing the conductivity and performance of multi-gate transistors
Data Source
AI summary
A method according to the present disclosure includes providing a workpiece. The workpiece includes a fin-shaped structure including a channel region and a source/drain region, a metal gate structure disposed over the channel region, a dummy source/drain feature disposed over the source/drain region, and a dielectric structure disposed over the dummy source/drain feature. The method further includes forming a trench through the dielectric structure and the dummy source/drain feature to expose a sidewall of the channel region, forming an epitaxial layer over the sidewall of the channel region, and forming a metal feature over a sidewall of the epitaxial layer and in the trench.