Stacked Transistor Frontside Contact Replacement After Top Anneal
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Solution Overview
Problem
The sequential fabrication stages of stacked transistors in semiconductor integrated circuits (ICs) adversely affect the components of the bottom transistor, particularly due to the high-temperature reliability anneal of the top source/drain region, which alters the properties of the yet-to-be-formed bottom source/drain contact.
Innovation Solution
The fabrication sequence involves forming a bottom source/drain contact placeholder, which is removed and replaced after the top transistor is formed, integrating a monolithic region and deep via region in the same stage, ensuring no interfacial impedance and maintaining the stability of the bottom source/drain contact properties.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If a bottom source/drain contact placeholder is formed during sequential fabrication, then the top transistor can be formed first, but the bottom source/drain contact properties are altered by high-temperature annealing
Solution Approach 1:
The patent applies preliminary action by forming the bottom source/drain contact placeholder before the top transistor fabrication, allowing the placeholder to be in place during high-temperature annealing. This preliminary placement enables the placeholder to withstand the annealing process without being altered, while the actual bottom source/drain contact is formed later without exposure to high-temperature annealing that would alter its properties.
2Reliability
If the bottom source/drain contact is formed before top transistor annealing, then contact properties remain stable, but fabrication time increases
Solution Approach 1:
The patent applies segmentation by dividing the bottom source/drain contact formation into two distinct stages: first forming a placeholder structure, then replacing it with the actual contact after top transistor annealing. This segmentation allows the placeholder to endure high-temperature processing while the final contact is formed in a separate, lower-temperature step, thereby maintaining contact property stability without significantly extending the overall fabrication cycle.
3Reliability
If a replacement contact structure is implemented, then contact resistance is reduced, but device complexity increases
Solution Approach 1:
The patent applies the intermediary principle by introducing a bottom source/drain contact placeholder as a temporary mediator structure. This placeholder serves as an intermediate element that occupies the contact position during top transistor fabrication and annealing, then is removed and replaced by the final bottom source/drain contact. The intermediary placeholder enables the sequential fabrication process while the final replacement contact achieves low contact resistance through direct integration with the bottom source/drain region.
Data Source
AI summary
A semiconductor IC structure includes a stacked transistor that has a top transistor stacked upon a bottom transistor. The bottom transistor includes at least a bottom source/drain region. The semiconductor IC structure further includes a replacement bottom source/drain region contact that includes a deep via region through at least the top semiconductor IC device and a monolithic region within the bottom semiconductor IC device directly coupled against a top surface of the bottom source/drain region. There is no interfacial impedance between the deep via region and the monolithic region. For example, there is no liner (e.g., such as a diffusion barrier, adhesion liner, or the like) between the deep via region and the monolithic region.