Metal Gate Stack Barrier Layers for 3D FET Aluminum Diffusion
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Solution Overview
Problem
The challenge of metal diffusion, particularly aluminum diffusion, between closely spaced transistors in 3D FETs leads to threshold voltage shifts and degradation of FET properties, which is crucial for low power consumption and device performance.
Innovation Solution
Incorporation of an aluminum diffusion barrier layer at the upper and/or bottom surfaces of the work function adjustment material layer containing aluminum to protect underlying layers and nearby FET devices from aluminum diffusion.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If aluminum-containing work function adjustment material layer is used to adjust threshold voltage, then FET performance is improved, but aluminum diffusion to nearby FETs causes threshold voltage shifts and degradation
Solution Approach 1:
A diffusion barrier layer is introduced as an intermediary between the aluminum-containing work function adjustment material layer and the underlying layer or nearby FET structures. This barrier layer (comprised of materials such as titanium nitride, tantalum nitride, or silicon nitride) mediates the interaction by blocking aluminum diffusion while allowing the work function adjustment material to perform its intended function of threshold voltage control.
Solution Approach 2:
The gate structure is segmented into multiple functional layers: the work function adjustment material layer containing aluminum is separated from the underlying layer and nearby FET structures by the diffusion barrier layer. This segmentation isolates the aluminum source, preventing harmful diffusion while maintaining the threshold voltage adjustment capability.
2Productivity
If transistor dimensions are reduced for down-scaling, then integration density is improved, but metal diffusion between closely spaced transistors increases
Solution Approach 1:
The diffusion barrier layer serves as a mediator that enables closer spacing of transistors by preventing metal diffusion between adjacent structures. This allows the industry to achieve higher integration density through down-scaling while maintaining device reliability by blocking the harmful diffusion effect that would otherwise worsen with reduced spacing.
3Reliability
If diffusion barrier layer is added to prevent aluminum diffusion, then FET property stability is improved, but device structure complexity increases
Solution Approach 1:
The diffusion barrier layer is designed with optimized thickness parameters (typically 1-10 nm) and material composition to provide effective aluminum diffusion blocking while minimizing the increase in overall gate structure complexity. By carefully controlling the barrier layer parameters, the structure maintains simplicity relative to the performance improvement achieved.
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 aluminum diffusion barrier layer effectively prevents threshold voltage changes and maintains FET properties, ensuring reliable performance and low power consumption in integrated circuits.
Implementation Method 1
Incorporation of an aluminum diffusion barrier layer at the upper and/or bottom surfaces of the work function adjustment material layer containing aluminum to protect underlying layers and nearby FET devices from aluminum diffusion
Data Source
AI summary
A semiconductor device includes a gate structure disposed over a channel region and a source/drain region. The gate structure includes a gate dielectric layer over the channel region, one or more work function adjustment material layers over the gate dielectric layer, and a metal gate electrode layer over the one or more work function adjustment material layers. The one or more work function adjustment layers includes an aluminum containing layer, and a diffusion barrier layer is disposed at at least one of a bottom portion and a top portion of the aluminum containing layer. The diffusion barrier layer is one or more of a Ti-rich layer, a Ti-doped layer, a Ta-rich layer, a Ta-doped layer and a Si-doped layer.