Polycrystalline Merged Source-Drain FinFET
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Solution Overview
Problem
FinFET devices face challenges in reducing source-drain resistance while maintaining device performance and reliability, particularly due to extended deposition time and selectivity loss during epitaxial deposition processes.
Innovation Solution
A method is developed to form a polycrystalline layer surrounding single-crystal epitaxial layers on FinFETs, merging the source-drain regions, which reduces deposition time and prevents selectivity loss, and limits dopant diffusion, thereby enhancing device performance and reliability.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If single-crystal epitaxial deposition is used to form source-drain regions, then device performance is improved, but deposition time is extended and selectivity is lost
Solution Approach 1:
The source-drain region formation is segmented into two distinct materials: single-crystal epitaxial regions for performance-critical areas and polycrystalline regions for speed-critical areas. This segmentation allows each material to be optimized for its specific function, resolving the contradiction between device performance and deposition time by placing the right material in the right location.
Solution Approach 2:
Different crystal structures are applied to different locations within the source-drain region. Single-crystal epitaxial material is used where high carrier mobility is needed (under the gate), while polycrystalline material is used where fast deposition and dopant confinement are priorities (outer regions). This local differentiation resolves the contradiction by optimizing each location for its specific requirement.
2Reliability
If single-crystal epitaxial deposition is used to form source-drain regions, then device performance is improved, but selectivity is lost during deposition
Solution Approach 1:
The deposition process is segmented into two sequential steps with different selectivity characteristics. First, single-crystal epitaxial deposition is performed with high selectivity to the fin surface. Second, polycrystalline deposition is performed to fill remaining spaces. This segmentation restores selectivity control by using two different deposition modes rather than relying on a single prolonged epitaxial process.
Solution Approach 2:
The single-crystal epitaxial deposition is performed partially, only to the extent needed to form the core source-drain regions under the gate. The remaining volume is filled by polycrystalline deposition. This partial action approach maintains selectivity by limiting the epitaxial process to where it is most needed, avoiding the selectivity loss that would occur with extended deposition.
3Productivity
If polycrystalline material is used to merge source-drain regions, then deposition time is reduced, but dopant diffusion may increase
Solution Approach 1:
Dopant diffusion control is optimized locally by placing polycrystalline material (with lower dopant diffusion) in the outer source-drain regions where contacts are formed, while single-crystal epitaxial material is used in the central region under the gate where precise dopant placement is critical. This local optimization resolves the contradiction by matching material properties to functional requirements.
Solution Approach 2:
The source-drain region is segmented into multiple material zones with different dopant diffusion characteristics. The polycrystalline segments are used where fast deposition is needed and dopant diffusion is less critical, while single-crystal segments are used where precise dopant control is needed. This segmentation allows the system to achieve both fast overall deposition and localized dopant precision.
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 faster deposition rates, improved selectivity, and reduced dopant diffusion, leading to enhanced device performance and increased reliability by forming a merged source-drain region with a smooth surface for contact metal landing.
Implementation Method 1
Single-crystal epitaxial layers may be deposited surrounding the second portion of the first fin and the second fin such that the single-crystal epitaxial layer on the first fin does not contact the single-crystal epitaxial layer on the second fin
Implementation Method 2
A polycrystalline layer may be deposited surrounding the single-crystal epitaxial layers, so that the polycrystalline layer contacts the single-crystal epitaxial layer on the first fin and the single-crystal epitaxial layer on the second fin thereby forming a merged source-drain region
Data Source
AI summary
A method of forming a semiconductor structure includes forming a first fin and a second fin on a substrate. A gate structure is formed over a first portion of the first fin and the second fin without covering a second portion of the first fin and the second fin. Single-crystal epitaxial layers are deposited surrounding the second portion of the first fin and the second fin such that the single-crystal epitaxial layer on the first fin does not contact the single-crystal epitaxial layer on the second fin. A polycrystalline layer is then deposited surrounding the single-crystal epitaxial layers, so that the polycrystalline layer contacts the single-crystal epitaxial layer on the first fin and the single-crystal epitaxial layer on the second fin. The single-crystal epitaxial layers and the polycrystalline layer form a merged source-drain region.