FinFET Gate Structure with TiAl and TiN Work Function Metals
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Solution Overview
Problem
Conventional FinFET devices with high-k metal gates face challenges in simultaneously fabricating n-type and p-type MOS devices with satisfactory performance, particularly due to differences in work function requirements and the impact of oxygen concentration on metal gate reliability.
Innovation Solution
The simultaneous formation of PMOS and NMOS FinFET devices with metal gate structures, utilizing n-type and p-type work function metal layers with specific TiAl and TiN compositions, and incorporating fluorine to improve the High-k/Metal Gate stack reliability by reducing BTI and SILC, while maintaining optimal oxygen and fluorine concentrations to prevent device drift.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If conventional FinFET devices with high-k metal gates are fabricated, then device density and performance are improved, but the ability to simultaneously fabricate n-type and p-type MOS devices with satisfactory performance deteriorates
Solution Approach 1:
The gate structure is segmented into distinct n-type and p-type work function metal layers (TiAl and TiN respectively) formed at different stages. The n-type work function metal layer is formed first, followed by the p-type work function metal layer, allowing each to be optimized independently for their respective device types while coexisting in the same fabrication process
Solution Approach 2:
Different work function metal layers are applied to different regions of the gate structure based on device type. NMOS devices receive n-type work function metal layers (TiAl) while PMOS devices receive p-type work function metal layers (TiN), with each material selected for its specific work function properties suitable for the corresponding device type
2Reliability
If oxygen concentration in metal gate layers is reduced to improve reliability, then BTI and SILC are reduced, but device drift may occur if fluorine concentration is not properly controlled
Solution Approach 1:
The invention optimizes the concentrations of oxygen and fluorine in the metal gate layers by changing processing parameters. Specifically, oxygen concentration is reduced to minimize BTI and SILC, while fluorine concentration is controlled within specific ranges to prevent device drift, achieving a balanced composition that satisfies both reliability and stability requirements
Solution Approach 2:
The fabrication process incorporates feedback control through sequential layer formation and composition adjustment. The n-type and p-type work function metal layers are formed in sequence with controlled compositions, and subsequent processing steps adjust oxygen and fluorine concentrations based on measured device characteristics, creating a feedback loop that optimizes both reliability and stability
Data Source
AI summary
A semiconductor device includes a n-type gate structure over a first semiconductor fin, in which the n-type gate structure is fluorine incorporated and includes a n-type work function metal layer overlying the first high-k dielectric layer. The n-type work function metal layer includes a TiAl (titanium aluminum) alloy, in which an atom ratio of Ti (titanium) to Al (aluminum) is in a range substantially from 1 to 3. The semiconductor device further includes a p-type gate structure over a second semiconductor fin, in which the p-type gate structure is fluorine incorporated includes a p-type work function metal layer overlying the second high-k dielectric layer. The p-type work function metal layer includes titanium nitride (TiN), in which an atom ratio of Ti to N (nitrogen) is in a range substantially from 1:0.9 to 1:1.1.