Stacked Multi-Gate Contact Structure for Selective Epitaxial Growth
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Solution Overview
Problem
The challenge in fabricating stacked multi-gate devices, such as complementary field effect transistors (C-FETs), lies in creating contacts that selectively access the source/drain features of both the upper and lower devices while avoiding unwanted epitaxial growth on the top source/drain features.
Innovation Solution
A method is developed to selectively deposit epitaxial material on the bottom source/drain feature of a C-FET device, using a plasma treatment to condition the upper source/drain feature, followed by an additional epitaxial growth process to form low-resistance contacts, while minimizing impact on the upper feature.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If conventional contact formation methods are used in stacked multi-gate devices, then contacts can be formed to access source/drain features, but unwanted epitaxial growth occurs on the top source/drain features
Solution Approach 1:
The patent applies preliminary action by performing plasma treatment on the top source/drain feature before the epitaxial growth process. This preliminary plasma exposure conditions the surface to prevent unwanted epitaxial growth, while the bottom source/drain feature remains untreated and ready for controlled epitaxial growth. The plasma treatment modifies the surface properties in advance to achieve selective growth behavior in subsequent processing steps.
Solution Approach 2:
The patent implements local quality by creating different surface conditions on different parts of the device. The top source/drain feature receives plasma treatment to create a non-growing surface condition, while the bottom source/drain feature maintains its natural surface condition that allows epitaxial growth. This spatial differentiation of surface properties enables selective epitaxial growth only where desired.
2Reliability
If contacts are formed to access both upper and lower device source/drain features, then device connectivity is achieved, but contact resistance and aspect ratio increase
Solution Approach 1:
The patent applies self-service by allowing the bottom source/drain feature to undergo in-situ epitaxial growth that forms low-resistance contact regions automatically during the manufacturing process. The epitaxial material grows conformally on the exposed bottom source/drain surface, creating self-aligned, low-resistance contact regions without requiring additional processing steps or complex contact hole formation procedures.
3Productivity
If stacked device structure is used to increase device density, then functional density increases, but fabrication complexity increases
Solution Approach 1:
The patent merges multiple functions into a single epitaxial growth process step. The same in-situ epitaxial growth process simultaneously forms source/drain regions for the bottom device and low-resistance contact regions for contacts accessing the bottom device. This consolidation of functions reduces the total number of processing steps required for stacked device fabrication, thereby reducing overall fabrication complexity despite the increased device density.
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 allows for efficient formation of contacts with low resistance and reduced aspect ratio, enhancing the performance of the C-FET device by ensuring selective epitaxial growth on the bottom source/drain feature without affecting the upper feature.
Implementation Method 1
using a plasma treatment to condition the upper source/drain feature
Implementation Method 2
an additional epitaxial growth process to form low-resistance contacts
Data Source
AI summary
Methods and devices that include forming a first epitaxial region and a second epitaxial region above the first epitaxial region. An opening may be formed extending from the first region to the second region. And a liner layer is deposited on a sidewall and a bottom of the opening. A plasma treatment is performed on the liner layer, which can form a conditioned or passivated region of the first epitaxial region that may be maintained during the growth of additional epitaxial material on the second epitaxial region.