Aluminum-Rich Interface for Low Thickness-Dependent nMOS Work Function
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Solution Overview
Problem
Existing n-metal TiAlC gate stacks have high resistivity and require thick films to achieve useful work function, leading to integration reliability and chamber defect challenges, especially in scaling down to 10 nm devices, where thinning the TiAl film results in significant work function increase and increased Al concentration is needed.
Innovation Solution
A film stack comprising a high-k dielectric layer, a high-k capping layer, and an n-metal layer with an aluminum-rich interface, where the n-metal layer includes a TaSiAl film with an aluminum-rich interfacial layer adjacent the high-k capping or dielectric layer, reducing work function dependence on thickness and improving resistivity.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Volume of moving object
If TiAlC film thickness is reduced to achieve smaller gate fill volumes, then device scaling is improved, but work function increases significantly and resistivity increases
Solution Approach 1:
The patent applies local quality by creating an aluminum-rich interfacial layer at the TiAlC/high-k interface, while the bulk TiAlC layer maintains its original composition. This localized aluminum enrichment at the interface specifically addresses the work function issue without requiring overall thickening of the TiAlC layer, thus resolving the contradiction between thin film requirements and work function stability.
Solution Approach 2:
The patent creates a composite structure consisting of the TiAlC layer combined with an aluminum-rich interfacial layer. This composite approach allows the system to achieve both low resistivity (from TiAlC) and stable work function (from aluminum-rich interface), resolving the contradiction between volume reduction and performance maintenance.
2Length of moving object
If TiAlC film thickness is reduced for 10 nm devices, then device scaling is achieved, but resistivity increases to >2000μΩ-cm
Solution Approach 1:
The aluminum-rich interfacial layer is localized at the critical interface region, allowing the bulk TiAlC layer to remain thin while still achieving low resistivity through the improved interface quality. This resolves the contradiction between thin film requirements and integration reliability.
3Reliability
If Al concentration is increased to reduce work function, then work function decreases, but chamber defects and integration reliability issues occur
Solution Approach 1:
The patent concentrates aluminum enrichment only at the interface region rather than throughout the entire TiAlC layer. This localized approach achieves the necessary work function control while avoiding the chamber defects and reliability issues associated with high bulk aluminum concentration.
Solution Approach 2:
The patent extracts the aluminum enrichment function to a separate interfacial layer, distinct from the bulk TiAlC layer. This separation allows the interface to have high aluminum concentration for work function control while the bulk material remains free of the harmful effects associated with high aluminum content.
4Volume of moving object
If TiAlC film is thinned below 20 Å, then gate fill volume is reduced, but effective work function increases significantly
Solution Approach 1:
The aluminum-rich interfacial layer provides localized work function control at the critical interface, enabling thin TiAlC films to maintain precise work function values. This resolves the contradiction between volume reduction and work function precision.
Data Source
AI summary
Film stacks and methods of forming film stacks including a high-k dielectric layer on a substrate, a high-k capping layer on the high-k dielectric layer, an n-metal layer on the high-k capping layer and an n-metal capping layer on the n-metal layer. The n-metal layer having an aluminum rich interface adjacent the high-k capping layer.