NSFET Gate Liner Structure for Work Function Thickness Control
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Solution Overview
Problem
As semiconductor devices undergo miniaturization, the reduction in minimum feature size leads to issues such as non-uniform work function material thickness, causing threshold voltage variations in nanosheet field-effect transistors (NSFETs), and the diffusion of aluminum from the work function material into other layers, which affects device performance.
Innovation Solution
A liner material is formed around the work function material in NSFETs to prevent merging of work function material between adjacent nanosheets and reduce aluminum diffusion, ensuring uniform thickness and improving device performance by forming a gate layer stack that includes an interfacial dielectric material, gate dielectric material, work function material, and a liner material.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If the minimum feature size is reduced to improve integration density, then more components can be integrated into a given area, but non-uniform work function material thickness and aluminum diffusion occur, causing threshold voltage variations
Solution Approach 1:
A liner material layer is introduced as an intermediary between the work function material and adjacent nanosheets. This liner material prevents direct contact and interaction, thereby stopping aluminum diffusion from the work function material while maintaining the desired thin feature dimensions for high integration density
Solution Approach 2:
The gate structure is segmented into multiple functional layers: gate dielectric material, work function material, and liner material. This segmentation allows each layer to perform its specific function independently, with the liner material specifically addressing the diffusion problem without affecting the overall device scaling
2Productivity
If the minimum feature size is reduced to improve integration density, then more components can be integrated into a given area, but threshold voltage variations occur due to non-uniform work function material thickness
Solution Approach 1:
The liner material acts as a mediator that ensures uniform spacing and prevents merging of work function material between adjacent nanosheets, thereby maintaining consistent threshold voltage across all devices in the integrated circuit
Solution Approach 2:
The liner material is selectively placed in specific locations where work function material diffusion and merging would occur, providing localized protection without affecting the overall device performance or requiring changes to the entire structure
3Adaptability or versatility
If work function material is used to adjust threshold voltage, then device electrical characteristics can be optimized, but aluminum diffusion into other layers occurs, affecting device performance
Solution Approach 1:
The liner material serves as a diffusion barrier that prevents aluminum atoms from the work function material from migrating into adjacent layers, while allowing the work function material to retain its threshold voltage tuning capability
Solution Approach 2:
The harmful diffusion property of aluminum is extracted and blocked by the liner material, separating the beneficial electrical characteristics of the work function material from its harmful diffusion behavior
Data Source
AI summary
A semiconductor device includes: a fin protruding above a substrate; source/drain regions over the fin; nanosheets between the source/drain regions; and a gate structure over the fin and between the source/drain regions, the gate structure including: a gate dielectric material around each of the nanosheets; a work function material around the gate dielectric material; a liner material around the work function material, where the liner material has a non-uniform thickness and is thicker at a first location between the nanosheets than at a second location along sidewalls of the nanosheets; and a gate electrode material around at least portions of the liner material.