Self-Aligned Backside Contacts Without Deep Placeholders
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Solution Overview
Problem
Conventional methods for forming backside contacts in nanosheet transistor structures face challenges such as damage to the gate hard mask, spacer loss, and high aspect ratio patterning, which can lead to gate bending or collapse, necessitating a solution that avoids deep placeholders under source drain regions.
Innovation Solution
The semiconductor structure employs self-aligned backside contacts by using a buffer layer to separate source drain regions from the backside dielectric layer, allowing for contact formation without deep placeholders, and includes a bottom dielectric isolation layer to separate nanosheet stacks from the backside dielectric layer, enabling direct contact of source drain regions with the backside dielectric layer.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If deep placeholders are used under source drain regions for backside contact formation, then contact alignment is improved, but gate damage and spacer loss occur
Solution Approach 1:
The buffer layer is formed in advance before source drain region formation, creating a protective structure that prevents gate damage and spacer loss during subsequent processing steps. This preliminary protective measure eliminates the need for deep placeholders while maintaining contact alignment precision.
Solution Approach 2:
The buffer layer acts as an intermediary between the source drain regions and the underlying structure, providing mechanical support and protection during contact formation. This intermediary layer enables precise contact alignment without requiring deep placeholders that would cause gate damage.
2Reliability
If self-aligned backside contacts are formed without deep placeholders, then gate integrity is improved, but contact formation complexity increases
Solution Approach 1:
The buffer layer is formed to self-align with the source drain regions through conformal deposition, automatically providing the necessary structural support and alignment without requiring additional complex processing steps. This self-aligning mechanism maintains gate integrity while simplifying the overall contact formation process.
3Reliability
If buffer layer is introduced to separate source drain regions from backside dielectric, then contact reliability is improved, but device structure complexity increases
Solution Approach 1:
The buffer layer serves multiple functions simultaneously: it provides mechanical support during contact formation, enables self-alignment of backside contacts, protects the gate structure, and facilitates reliable electrical contact. This multi-functionality improves contact reliability without proportionally increasing device structure complexity.
Data Source
AI summary
A semiconductor structure including first source drain regions and second source drain regions arranged above a backside dielectric layer, and a buffer layer physically separating at least one of the second source drain regions from the backside dielectric layer, where at least one of the first source drain regions is in direct contact with the backside dielectric layer.