Transistor Gate Stack with Aluminum-Fluorine Threshold Control
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Solution Overview
Problem
As semiconductor devices continue to shrink in feature size, challenges arise in maintaining device performance due to issues with fluorine retention in work function metal layers, leading to instability in gate dielectrics and threshold voltages.
Innovation Solution
The implementation of an aluminum treatment followed by a fluorine treatment in the gate dielectric and work function metal layers, respectively, enhances fluorine retention and diffusion, improving flatband voltage and threshold voltage control.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If fluorine treatment is applied to work function metal layers, then threshold voltage control is improved, but fluorine retention becomes problematic leading to gate dielectric instability
Solution Approach 1:
An aluminum layer is introduced as an intermediary between the gate dielectric and the fluorine-containing work function metal layer. The aluminum layer absorbs excess fluorine through fluorine soak treatment, preventing fluorine from reaching and destabilizing the gate dielectric while still allowing the work function metal layer to provide threshold voltage control.
Solution Approach 2:
The aluminum layer is deposited and undergoes fluorine soak treatment before the final work function metal layer is formed. This preliminary fluorine absorption by aluminum prepares the structure to handle subsequent fluorine treatments of the work function metal layer without compromising gate dielectric stability.
2Productivity
If feature size is reduced to increase integration density, then more components can be integrated, but device performance maintenance becomes more difficult
Solution Approach 1:
The invention modifies the chemical composition and structure of the gate stack by introducing aluminum and fluorine treatments, changing the electrical parameters (work function, flatband voltage) to maintain device performance at reduced feature sizes. This allows continued scaling while preserving transistor characteristics.
3Reliability
If aluminum treatment is performed on gate dielectric, then fluorine retention in work function metal layer is improved, but additional process steps are required
Solution Approach 1:
The aluminum deposition and fluorine soak treatment are combined into a integrated process sequence that is incorporated into the existing gate stack formation workflow. The aluminum layer is deposited as part of the gate electrode structure, and the fluorine soak is performed as a single treatment step that benefits multiple layers simultaneously.
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
This approach results in improved device performance by increasing flatband voltage towards the band edge of the metal and decreasing threshold voltage, enhancing overall transistor performance.
Implementation Method 1
the aluminum deposited during the aluminum treatment attracts the fluorine from the fluorine treatment to improve retention of fluorine in the WFM layer
Implementation Method 2
the fluorine in the WFM layer would have a tendency to dissociate from the WFM layer before subsequent layers are formed... some of that fluorine then bypasses the aluminum residue to fill voids in the high-k gate dielectric
Data Source
AI summary
In some embodiments, a method includes forming a plurality of nanostructures over a substrate; etching the plurality of nanostructures to form first recesses; forming source/drain regions in the first recesses; removing first nanostructures of the plurality of nanostructures leaving second nanostructures of the plurality of nanostructures; depositing a gate dielectric over and around the second nanostructures; performing an aluminum treatment on the gate dielectric; depositing a first conductive material over and around the gate dielectric; performing a fluorine treatment on the first conductive material; and depositing a second conductive material over and around the first conductive material.