FinFET Source/Drain Epitaxy for Lateral Expansion Confinement
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Solution Overview
Problem
Silicon phosphate source/drain regions in finFETs expand laterally during epitaxy growth, causing damage to adjacent structures due to their isotropic nature, which complicates the formation of silicon germanium source/drain regions and can lead to recessing issues in pMOS fin structures.
Innovation Solution
A method involving the formation of first and second epitaxy structures with specific lattice constants and dopant concentrations, where the first epitaxy structure includes a p-type stressor and the epitaxy coat includes an n-type stressor, is used to create slim, bar-like source/drain regions that apply stress to the channel region, preventing lateral expansion and ensuring precise placement without damaging adjacent structures.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If silicon phosphate is used to form nMOS source/drain regions, then the source/drain regions can be formed with appropriate doping characteristics, but the lateral expansion of silicon phosphate causes damage to neighboring structures
Solution Approach 1:
A mandrel structure is formed before the silicon phosphate deposition to define the lateral boundaries of the source/drain region. The mandrel acts as a preliminary structure that prevents lateral expansion during epitaxial growth, ensuring the silicon phosphate remains confined to the desired region while maintaining proper doping characteristics
Solution Approach 2:
The mandrel structure serves as an intermediary element between the deposition process and the final source/drain region. It mediates the lateral confinement of silicon phosphate during growth, allowing the material to be deposited with appropriate doping while preventing harmful lateral expansion into neighboring structures
2Reliability
If silicon germanium is used to form pMOS source/drain regions, then the source/drain regions can be formed with appropriate doping characteristics, but the recessing process may cause damage to laterally expanding nMOS source/drain regions
Solution Approach 1:
The mandrel structure is formed in advance to define the lateral boundaries of the nMOS source/drain region before the pMOS recessing process. This preliminary structure protects the nMOS region from damage during subsequent processing steps, allowing silicon germanium to be deposited with appropriate doping characteristics
Solution Approach 2:
The mandrel structure provides beforehand protection or cushioning to the nMOS source/drain region against the harmful effects of the recessing process. It acts as a protective barrier that prevents damage to the laterally expanding nMOS regions while allowing the pMOS source/drain regions to be formed with silicon germanium
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 confines the source/drain regions, preventing lateral expansion and ensuring accurate placement, thereby minimizing damage to adjacent structures and maintaining the integrity of both nMOS and pMOS regions during the fabrication of finFETs.
Implementation Method 1
epitaxial growth of p-type and n-type stressor structures
Data Source
AI summary
A method includes forming a fin in a substrate. The fin is etched to create a source/drain recess. A source/drain feature is formed in the source/drain recess, in which a lattice constant of the source/drain feature is greater than a lattice constant of the fin. An epitaxy coat is grown over the source/drain feature, in which a lattice constant of the epitaxy coat is smaller than a lattice constant of the fin.