Asymmetric Source/Drain Epitaxy for Stacked FET Contact Spacing
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Solution Overview
Problem
Existing stacked field-effect transistor (FET) fabrication methods do not effectively provide sufficient spacing between top and bottom source/drain contacts, leading to potential short circuits due to confined epitaxial regions and limited tip-to-tip distance.
Innovation Solution
The method involves forming an asymmetric source/drain epitaxial structure with a horizontal protrusion on one side, allowing for wider tip-to-tip spacing by forming contacts on the protrusion, which is unconfined by fang spacers, thereby preventing short circuits and allowing for wider contact placement.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If conventional symmetric source/drain epitaxial structures are used in stacked FETs, then fabrication is simplified, but the tip-to-tip distance between top and bottom source/drain contacts is insufficient leading to potential short circuits
Solution Approach 1:
The patent applies asymmetry by creating an asymmetric source/drain epitaxial structure where the bottom source/drain region has a horizontal protrusion on one side that extends beyond the channel region. This asymmetric design provides extended contact area and increased tip-to-tip distance between top and bottom contacts, preventing short circuits while maintaining fabrication feasibility through selective spacer formation and epitaxial growth processes
2Manufacturing precision
If fang spacers are used to confine source/drain epitaxial regions, then lateral growth is controlled, but the tip-to-tip distance between contacts is reduced increasing short circuit risk
Solution Approach 1:
The patent applies local quality by selectively removing fang spacers from specific regions to create asymmetric confinement. The fang spacers are removed from the bottom source/drain region on one side to allow horizontal protrusion growth, while remaining on other sides to maintain confinement where needed. This localized modification provides both precise epitaxial control and adequate contact spacing
3Ease of manufacture
If symmetric source/drain contacts are formed, then layout is simplified, but adequate spacing between top and bottom contacts cannot be achieved
Solution Approach 1:
The patent applies preliminary action by forming the asymmetric horizontal protrusion in the bottom source/drain epitaxial region before forming the contacts. This pre-formed protrusion creates the necessary spacing and contact area in advance, allowing subsequent contact formation to proceed with simplified alignment while ensuring adequate separation between top and bottom contacts
Data Source
AI summary
Embodiments of the invention include a stacked device having a first epitaxial region and a second epitaxial region vertically displaced from the first epitaxial region. The first epitaxial region comprising an asymmetric profile with a horizontal protrusion. A contact is formed on the horizontal protrusion of the first epitaxial region