Backside Bottom Contact Layout for Nanosheet FET Alignment
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Solution Overview
Problem
Proper alignment for direct backside contact patterning in nanosheet FETs is challenging due to critical dimension issues, leading to potential shorting between backside contact and gate or source drain, and inadequate contact resistivity.
Innovation Solution
A multi-layer dielectric structure is formed beneath the source drain region, allowing selective removal of insulators and spacers to create an enlarged contact opening, ensuring reliable backside contact formation by maintaining sufficient spacing from sacrificial placeholders.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If direct backside contact patterning is performed in nanosheet FETs, then contact alignment is achieved, but critical dimension issues cause shorting between backside contact and gate or source drain
Solution Approach 1:
The patent segments the contact formation process into multiple stages: first forming a sacrificial placeholder structure, then forming the bottom contact around it, and finally removing the placeholder. This segmentation allows precise control of contact dimensions and positioning, avoiding shorting while achieving proper alignment with source drain regions and gates.
Solution Approach 2:
The patent performs preliminary actions by forming the sacrificial placeholder structure before forming the bottom contact. This placeholder defines the exact contact footprint and positioning in advance, ensuring that when the contact is formed and placeholder removed, the contact achieves precise alignment without critical dimension issues that would cause shorting.
2Reliability
If backside contact is formed directly below source drain region, then contact resistivity is improved, but spacing from sacrificial placeholders becomes insufficient
Solution Approach 1:
The patent transitions from two-dimensional planar spacing considerations to three-dimensional vertical integration. The bottom contact is formed extending vertically below the source drain region while maintaining horizontal spacing from sacrificial placeholders. This dimensional change allows the contact to achieve low resistivity through direct vertical connection while the placeholder spacing prevents shorting in the horizontal plane.
Data Source
AI summary
A semiconductor structure including a source drain region directly adjacent to a nanosheet stack, a bottom contact directly below the source drain region, the bottom contact includes a top portion directly below the source drain region, a middle portion directly below the top portion, a first bottom portion directly below the middle portion, a second bottom portion directly below the first bottom portion, where the middle portion is more narrow than the top portion and more narrow than the first bottom portion. A semiconductor structure including a bottom contact directly below a source drain region, the bottom contact includes a top portion directly below the source drain region, a middle portion directly below the top portion, a first bottom portion directly below the middle portion, where the middle portion is more narrow than the top portion and more narrow than the first bottom portion.