Non-Conformal FinFET Work Function Layers for Gate Leakage Control
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Solution Overview
Problem
As semiconductor devices continue to shrink, conformally formed films in FinFETs can lead to gate leakage and defects due to thinning or damage of top portions of the films during processing.
Innovation Solution
The implementation of non-conformal work function metal layers with varying thickness, composition, and phases, where the layers are thicker on the top surface of the semiconductor fin and thinner on the sidewalls, reducing leakage and improving device performance.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If conformal films are deposited as gate dielectric layers and gate electrode layers, then the films provide uniform coverage, but the top portions of the conformal film become thinner or incur damages during processing leading to gate leakage
Solution Approach 1:
The work function metal layer is formed with non-uniform thickness where the thickness varies across different regions of the fin structure. Specifically, the layer has greater thickness at the top surface of the fin compared to the sidewalls, creating local quality variations that provide better leakage control at critical areas while maintaining appropriate coverage elsewhere.
Solution Approach 2:
The invention introduces asymmetric thickness distribution in the work function metal layer, breaking the symmetry of conformal deposition. The layer thickness is intentionally made asymmetric with respect to the fin structure, being thicker at the top and thinner at the sidewalls, which addresses the gate leakage issue that arises from symmetric conformal films.
2Ease of manufacture
If conformal films are used, then complete coverage is achieved, but top portions become thinner or damaged during processing
Solution Approach 1:
The work function metal layer exhibits local quality variations in thickness, being thicker at the top surface and thinner at the sidewalls. This non-uniform thickness distribution provides enhanced protection and integrity at the top portions where damage is most likely to occur during processing, while still achieving adequate coverage across the entire structure.
3Reliability
If non-conformal work function metal layers with varying thickness are implemented, then leakage control is improved, but device complexity increases
Solution Approach 1:
The non-conformal work function metal layer with spatially varying thickness provides improved leakage control through local quality optimization. The thicker regions at the top surface enhance leakage control where it is most critical, while the overall structure remains relatively simple with a single layer type, avoiding the need for multiple complex layers.
Data Source
AI summary
Embodiments of the present disclosure provide a FinFET transistor having a gate structure including one or more non-conformal work function metal layers. In some embodiments, work function metal layers may be non-conformal in at least one of thickness, composition, and/or phases. The non-conformality in the work function metal layer lowers leakage, improve device performance, and increase device reliability.