Multi-Layer Metal Gate Structure for Low-EOT Oxide Control
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Solution Overview
Problem
As technology nodes decrease, the minimization of equivalent oxide thickness (EOT) becomes critical in semiconductor fabrication, particularly with the use of high-k dielectrics and metal gate structures, requiring an interfacial layer that contributes to EOT and necessitates the control of oxygen vacancies in gate dielectric layers.
Innovation Solution
A multi-layer metal gate structure is introduced, comprising a first metal layer with an oxygen-gettering composition, a second metal layer that gets oxygen from the interfacial layer, and a third metal layer that provides a compatible interface with polysilicon, allowing for controlled oxidation and reduction of the interfacial layer thickness, thereby enhancing the dielectric constant and reducing oxygen vacancies.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If an interfacial layer is introduced between the gate dielectric layer and silicon substrate, then the reliability is improved by providing a compatible interface, but the equivalent oxide thickness increases due to the additional layer contribution
Solution Approach 1:
The patent changes the chemical composition parameters of the interfacial layer by introducing a metal layer with specific oxygen-gettering properties. This metal layer has a higher affinity for oxygen than silicon, which modifies the interfacial layer's oxygen concentration and chemical state, thereby improving interface quality while controlling EOT
Solution Approach 2:
The patent creates a composite structure by combining the metal layer with the interfacial layer. The metal layer serves as an oxygen-gettering component that chemically interacts with the interfacial layer, forming a composite system that simultaneously improves interface compatibility and controls the effective oxide thickness
2Length of stationary object
If the thickness of the interfacial layer is reduced to minimize EOT, then the equivalent oxide thickness is improved, but oxygen vacancies increase in the gate dielectric layer
Solution Approach 1:
The metal layer acts as an intermediary between the interfacial layer and the gate dielectric layer. It provides oxygen to the gate dielectric layer through diffusion, compensating for oxygen vacancies that would otherwise occur when the interfacial layer is thinned. This mediator function allows EOT reduction without compromising dielectric quality
Solution Approach 2:
The metal layer is deposited beforehand to perform oxygen-gettering from the interfacial layer and subsequent oxygen diffusion to the gate dielectric layer. This preliminary oxygen redistribution ensures that when the interfacial layer is thinned, the gate dielectric layer remains adequately oxygenated, preventing vacancy formation
3Length of stationary object
If high-k dielectric materials are used to increase dielectric constant, then the equivalent oxide thickness is reduced for better control, but the fabrication process complexity increases
Solution Approach 1:
The patent changes the dielectric constant parameter by introducing high-k dielectric materials (such as hafnium oxide, tantalum oxide, or zirconium oxide) with k-values significantly higher than silicon dioxide. This allows achieving lower EOT with thicker physical layers, providing better control over threshold voltage and reducing leakage while managing fabrication complexity through controlled deposition processes
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
The multi-layer metal gate structure effectively reduces equivalent oxide thickness and controls oxygen vacancies, improving the performance and reliability of semiconductor devices by stabilizing threshold voltage and reducing positive bias temperature instability.
Implementation Method 1
The first metal layer includes an oxygen-gettering composition
Implementation Method 2
The second metal layer includes oxygen
Data Source
AI summary
A semiconductor device includes a gate dielectric layer and a gate electrode formed on the gate dielectric layer. The gate electrode includes a first metal layer, a second metal layer, and a third metal layer. The first metal layer includes an oxygen-gettering composition. The second metal layer includes oxygen. The third metal layer includes an interface with a polysilicon layer.