FinFET Flat-Topped Epitaxial Source/Drain Contact Resistance
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Solution Overview
Problem
The semiconductor industry faces challenges in fabricating FinFETs due to complexities in achieving a flat-topped epitaxial source/drain structure, which affects contact resistance and integration with adjacent fins, particularly in maintaining a uniform top surface and reducing contact resistance.
Innovation Solution
A method involving a gate-first process to form a FinFET with a flat-topped epitaxial source/drain structure, where a first epitaxial layer is grown vertically and then a second epitaxial layer with higher doping is grown selectively over and between adjacent fins, merging them to form a continuous layer, and a silicide layer is formed farther from the fins to reduce contact resistance.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a gate-first process is used to form FinFET with epitaxial source/drain regions, then the gate control of the channel is improved, but the manufacturing complexity increases due to multiple epitaxial growth steps and process variations
Solution Approach 1:
The source/drain structure is segmented into multiple epitaxial layers with different doping concentrations and orientations. The first epitaxial layer has a first doping concentration and the second epitaxial layer has a second doping concentration, creating distinct functional zones that improve gate control while managing process complexity through systematic layering
Solution Approach 2:
Different regions of the source/drain structure are given different local properties through selective doping concentrations and crystal orientations. The first and second epitaxial layers have different doping concentrations tailored to specific functional requirements, allowing optimized performance in different areas of the same structure
2Ease of manufacture
If the epitaxial source/drain regions are formed with uniform doping, then the manufacturing process is simplified, but the contact resistance increases and performance deteriorates
Solution Approach 1:
The epitaxial source/drain structure employs non-uniform doping distribution with at least two different doping concentrations in different layers. This local variation in doping quality reduces contact resistance at critical interfaces while maintaining manufacturability through controlled epitaxial growth processes
Solution Approach 2:
The doping concentration parameter is changed between different epitaxial layers to optimize electrical performance. The first epitaxial layer has a first doping concentration and the second epitaxial layer has a second doping concentration, allowing parameter optimization for reduced contact resistance without overwhelming process complexity
3Productivity
If the source/drain regions are formed closer to the fins, then the device density is increased, but the sensitivity to process variations and defects increases
Solution Approach 1:
The epitaxial source/drain regions are formed with preliminary doping and structural preparation before final device assembly. The multi-layer epitaxial structure is prepared in advance with controlled doping concentrations, which reduces sensitivity to subsequent process variations and defects while maintaining high device density
Solution Approach 2:
The multi-layer epitaxial structure provides a cushioning effect against process variations. The different doping concentrations and layer structures create buffer zones that mitigate the impact of process variations and defects, allowing closer spacing of source/drain regions to fins without proportionally increasing sensitivity
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 enhances contact landing area, reduces contact resistance, and improves the uniformity and reproducibility of the source/drain regions, making the FinFET less sensitive to process variations and defects, while increasing the ION current efficiency.
Implementation Method 1
forming first epitaxial layers on the recessed portions of the fins
Implementation Method 2
forming a second epitaxial layer over the first epitaxial layers, wherein the second epitaxial layer merges with adjacent second epitaxial layers
Implementation Method 3
the second epitaxial layer with higher doping is grown selectively over and between adjacent fins
Implementation Method 4
a silicide layer is formed farther from the fins to reduce contact resistance
Data Source
AI summary
A method includes forming a first fin and a second fin over a substrate, depositing an isolation material surrounding the first and second fins, forming a gate structure along sidewalls and over upper surfaces of the first and second fins, recessing the first and second fins outside of the gate structure to form a first recess in the first fin and a second recess in the second fin, epitaxially growing a first source/drain material protruding from the first and second recesses, and epitaxially growing a second source/drain material on the first source/drain material, wherein the second source/drain material grows at a slower rate on outermost surfaces of opposite ends of the first source/drain material than on surfaces of the first source/drain material between the opposite ends of the first source/drain material, and wherein the second source/drain material has a higher doping concentration than the first source/drain material.