Backside Source/Drain Epitaxy for Reliable Nanosheet FET Contacts
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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 neighboring source drain, and insufficient contact area for reliable connections.
Innovation Solution
A source drain epitaxy structure with a backside portion having a larger critical dimension than the frontside portion, along with a dielectric encapsulation liner and airgap in the inter-layer dielectric, to enhance contact reliability and capacitance reduction.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Area of moving object
If direct backside contact patterning is used in nanosheet FETs, then contact area is reduced, but contact reliability deteriorates and shorting risk increases
Solution Approach 1:
The patent transitions from planar contact patterning to three-dimensional epitaxial growth. By growing source/drain epitaxy structures that extend vertically and laterally in multiple dimensions, the contact area is significantly increased without compromising alignment precision. The epitaxial regions grow to encompass the nanosheet channels from multiple sides, providing robust electrical contact while maintaining manufacturing feasibility.
Solution Approach 2:
The patent performs preliminary epitaxial growth of source/drain regions before final contact patterning. This preliminary action establishes well-defined, enlarged contact regions that simplify subsequent alignment steps. The epitaxial structures are grown with controlled dimensions and positions that pre-establish reliable contact areas, eliminating the need for precise direct patterning alignment.
2Manufacturing precision
If critical dimension is reduced for better alignment, then manufacturing precision improves, but contact area becomes insufficient
Solution Approach 1:
The patent compensates for reduced critical dimensions by utilizing three-dimensional epitaxial growth. The source/drain epitaxy structures extend in multiple spatial dimensions, providing large contact areas even when the planar footprint is constrained by tight alignment requirements. This dimensional expansion allows sufficient contact area without compromising manufacturing precision.
Solution Approach 2:
The patent changes the growth parameters of the epitaxial structures to optimize contact area. By controlling temperature, pressure, and composition during epitaxial growth, the source/drain regions develop optimal dimensions and shapes that maximize contact area while maintaining precise alignment with nanosheet channels.
Data Source
AI summary
An upper portion of a source/drain epitaxy adjacent to channel layers of a nanosheet stack on a substrate, a lower portion of the source/drain epitaxy below the upper portion of the source/drain epitaxy, a second width of the lower portion of the source/drain epitaxy is greater than a first width of the upper portion of the source/drain epitaxy, a dielectric fill layer below the nanosheet stack, and a dielectric encapsulation liner between the dielectric fill layer and the lower portion of the source/drain epitaxy. Forming an upper portion of a source/drain epitaxy adjacent to semiconductor channel layers of a nanosheet stack, and forming a lower portion of the source/drain epitaxy below the upper portion of the source/drain epitaxy, a second width of the lower portion of the source/drain epitaxy is greater than a first width of the upper portion of the source/drain epitaxy.