FinFET Source/Drain Layer Structure to Prevent SRAM Fin Merging
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Solution Overview
Problem
In fin-based field effect transistors, the merging of source/drain layers grown from adjacent active fins can lead to electrical failures in static random access memory (SRAM) devices due to the vertical and horizontal growth of these layers.
Innovation Solution
The semiconductor device design includes distinct source/drain layer structures with varying germanium and carbon concentrations and angled sidewall surfaces to prevent layer merging, using selective epitaxial growth (SEG) processes to form these layers, and incorporates contact plugs with specific orientations and dimensions to ensure electrical isolation.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If selective epitaxial growth is used to form source/drain layers, then the layers grow vertically and horizontally to fill recesses, but this causes merging of source/drain layers from adjacent fins leading to electrical failure
Solution Approach 1:
The source/drain layer formation is segmented into multiple discrete layers (first source/drain layer, second source/drain layer, third source/drain layer) with different materials and functions. The first layer provides stress, the second layer provides doping, and the third layer prevents merging. This segmentation allows each layer to perform its specific function without causing electrical failure between adjacent transistors.
Solution Approach 2:
A third source/drain layer is introduced as an intermediary barrier layer between the second source/drain layers of adjacent fins. This intermediate layer physically prevents the merging of source/drain layers from neighboring fins while still allowing the beneficial stress and doping effects from the lower layers to be maintained.
2Strength
If source/drain layers are grown to apply stress to channel regions, then layer thickness and composition are increased, but this increases the risk of layer merging between adjacent fins
Solution Approach 1:
Different source/drain layers are formed with locally optimized properties: the first source/drain layer has specific composition for stress, the second layer has doping characteristics for electrical properties, and the third layer has barrier properties to prevent merging. Each layer's thickness and composition are locally tailored to its specific function rather than using a uniform structure.
Solution Approach 2:
The source/drain structure uses composite materials with different compositions and properties in each layer. The first source/drain layer may contain silicon-germanium for stress, the second layer contains doped silicon for electrical characteristics, and the third layer contains materials optimized for preventing merging. This composite approach allows simultaneous achievement of stress application and growth control.
3Reliability
If multiple source/drain layers are formed with different compositions, then electrical isolation is improved, but device structure and manufacturing process become more complex
Solution Approach 1:
The source/drain structure is segmented into three distinct layers with clear functional differentiation. The first layer provides stress, the second layer provides doping, and the third layer provides isolation. This segmentation achieves reliable electrical isolation while maintaining a systematic and manageable structure rather than a random complex structure.
Solution Approach 2:
Each source/drain layer performs multiple functions where possible. For example, the first source/drain layer provides both structural support and stress application, the second layer provides both doping and partial stress, and the third layer provides both merging prevention and electrical isolation. This multi-functionality reduces the need for additional separate components, thereby managing complexity.
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
Prevents electrical failures between adjacent transistors while applying proper stress to channel regions, enhancing the performance of SRAM devices by maintaining structural integrity and electrical isolation.
Implementation Method 1
a source/drain layer may be formed on an active fin by a selective epitaxial growth (SEG) process
Data Source
AI summary
A semiconductor device may include a first active fin, a plurality of second active fins, a first source/drain layer structure, and a second source/drain layer structure. The first active fin may be on a first region of a substrate. The second active fins may be on a second region of the substrate. The first and second gate structures may be on the first and second active fins, respectively. The first source/drain layer structure may be on a portion of the first active fin that is adjacent to the first gate structure. The second source/drain layer structure may commonly contact upper surfaces of the second active fins adjacent to the second gate structure. A top surface of the second source/drain layer structure may be further from the surface of the substrate than a top surface of the first source/drain layer structure is to the surface of the substrate.