Stacked Transistor Bottom Contact With Wider Silicide Isolation
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Solution Overview
Problem
Fabricating a bottom contact for stacked transistors at smaller technology nodes is challenging due to difficulties in forming adequate isolation from the top source drain region without decreasing the effective contact area with the bottom source drain region, leading to increased contact resistance.
Innovation Solution
A semiconductor structure with a bottom contact structure having a larger silicide area, utilizing a replacement spacer to prevent shorting to the gate or top source drain region, while decreasing contact resistance with the bottom source drain region, by forming a metal silicide with a wider lateral width than the contact structure and using a replacement spacer made from a different material than the top gate spacer.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a bottom contact structure is formed with adequate isolation from the top source drain region, then shorting is prevented, but the effective contact area with the bottom source drain region decreases, leading to increased contact resistance
Solution Approach 1:
The patent introduces a lateral dimension expansion by forming a metal silicide layer that extends beyond the bottom contact structure footprint. This creates a larger effective contact area in the lateral direction without compromising vertical isolation, thus reducing contact resistance while maintaining reliability
Solution Approach 2:
The metal silicide acts as an intermediary between the bottom contact structure and the bottom source drain region. It provides a larger contact interface that reduces contact resistance while the replacement spacer maintains the necessary isolation, effectively mediating between conflicting requirements
2Manufacturing precision
If the bottom contact structure is enlarged to increase contact area, then contact resistance decreases, but isolation from the gate and top source drain region becomes difficult, leading to potential shorting
Solution Approach 1:
The patent segments the contact system into distinct functional components: the bottom contact structure for electrical connection, the metal silicide for enhanced contact area, and the replacement spacer for isolation. This segmentation allows each component to optimize its function without compromising others
Solution Approach 2:
The replacement spacer serves as an intermediary isolation structure that separates the enlarged metal silicide contact area from the gate and top source drain region. This enables the contact area to be enlarged for lower resistance while the spacer maintains necessary electrical isolation
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 solution effectively provides electrical contact to the bottom source drain region with reduced contact resistance and prevents shorting, enabling successful fabrication of stacked transistors at smaller technology nodes.
Implementation Method 1
a metal silicide between the bottom source drain region and the bottom contact structure, the metal silicide having a width larger than a width of the bottom contact structure
Data Source
AI summary
A stacked transistor structure including a top source drain region above a bottom source drain region, where a width of the bottom source drain region is greater than a width of the top source drain region, a bottom contact structure directly above and in electrical contact with the bottom source drain region, a metal silicide between the bottom source drain region and the bottom contact structure, the metal silicide having a width larger than a width of the bottom contact structure; a replacement spacer surrounding the bottom contact structure; and a top gate spacer separating the replacement spacer from a gate conductor.