Punch-through stopper formation in finFET devices
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Solution Overview
Problem
The formation of punch-through stopper regions in finFET devices on bulk semiconductor substrates is hindered by non-uniform dopant profiles due to Gaussian implant depth profiles, leading to undesirable threshold voltage variations and sub-threshold punch-through leakage.
Innovation Solution
A process involving the etching of trenches to form a fin structure, followed by selective ion implantation through the bottom walls of these trenches to create dopant regions that extend partially under the channel region, allowing for an abrupt concentration interface and reducing the need for additional anneal processes, thereby minimizing dopant diffusion and threshold voltage variations.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If dopant ions are implanted at a target depth coinciding with the base of the fin using a conventional ion implant process, then punch-through leakage is reduced, but a non-uniform dopant profile is created across the active channel region due to Gaussian implant depth distribution
Solution Approach 1:
The patent segments the ion implantation process into two distinct stages: (1) implanting dopant ions through the bottom wall of the trench to form dopant regions in the substrate, and (2) selectively removing portions of these dopant regions by etching the substrate at the trench bottom wall. This segmentation allows independent control of dopant placement and profile shaping, resolving the contradiction between achieving sufficient dopant concentration for leakage reduction and maintaining uniformity across the channel region.
Solution Approach 2:
The patent extracts excess dopant from regions where it would cause non-uniformity by etching the substrate at the bottom wall of the trench to remove portions of the implanted dopant regions. This extraction process eliminates the harmful tail end of the Gaussian distribution while preserving the beneficial high-concentration region needed for punch-through leakage reduction, thereby achieving both reliability improvement and profile uniformity.
2Reliability
If a high concentration of dopant ions is implanted into the substrate prior to forming the fin to create a punch-through stopper region, then sub-threshold punch-through leakage is reduced, but threshold voltage variations occur across the height of the fin channel due to concentration gradient
Solution Approach 1:
The patent performs preliminary ion implantation through the trench bottom wall before fin formation, placing dopant ions at the desired depth with high precision. This preliminary action ensures that the punch-through stopper region is formed at the correct location with appropriate concentration, while the subsequent selective removal step prevents threshold voltage variations by eliminating excess dopant that would otherwise cause concentration gradients across the fin channel height.
Solution Approach 2:
The patent applies local quality by creating a highly localized dopant region precisely at the trench bottom wall through targeted ion implantation, then selectively removing dopant from specific areas to achieve the desired profile. This local control allows the dopant concentration to be high where needed for leakage reduction while maintaining uniformity across the active channel region, thereby resolving the threshold voltage uniformity issue.
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 results in desirable electrical characteristics by forming an abrupt dopant interface and reducing sub-threshold punch-through leakage, enabling further scaling of channel lengths while maintaining uniform dopant profiles across the fin channel.
Implementation Method 1
a first dose of ions may be implanted such that a portion of the first dose of ions is implanted through a bottom wall of each trench to form a pair of first dopant regions in the substrate
Implementation Method 2
The substrate at the bottom wall of each trench may be etched to increase a depth of each trench. Etching the substrate at the bottom wall of each trench may remove a portion of each first dopant region under each trench
Data Source
AI summary
In forming a punch-through stopper region in a fin field effect transistor (finFET) device, a substrate may be etched to form a pair of trenches that define a fin structure. A portion of a first dose of ions may be implanted into the substrate through a bottom wall of each trench to form a pair of first dopant regions that at least partially extend under a channel region of the fin structure. The substrate at the bottom wall of each trench may be etched to increase a depth of each trench. Etching the substrate at the bottom wall of each trench may remove a portion of each first dopant region under each trench. A remaining portion of the pair of first dopant regions under the fin structure may at least partially define the punch-through stopper region of the finFET device.