TiAl Bilayer Gate Stack for FinFET Threshold Voltage Control
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
The challenge in scaling transistor gate structures for smaller devices is the limited adjustment of threshold voltage due to decreased spacing, which affects the thickness and Al concentration of titanium-aluminum (TiAl) layers, leading to poor gap-fill and reliability issues in n-type finFETs, particularly with high Al concentration impairing TDDB and PBTI performance.
Innovation Solution
A method for forming gate stacks with TiAl layers having different Al concentrations, including a bilayer or trilayer structure where a Ti-rich layer with a low Al/Ti ratio functions as an oxygen getter, trapping oxygen atoms and reducing threshold voltage while maintaining transistor reliability.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If the thickness of TiAl work function layer is increased to reduce threshold voltage, then threshold voltage is reduced, but gap-fill quality deteriorates and reliability issues occur
Solution Approach 1:
The TiAl work function layer is divided into multiple sub-layers with different Al concentrations. The first TiAl layer has a first Al concentration and the second TiAl layer has a second Al concentration that is higher than the first. This segmentation allows each layer to contribute differently to threshold voltage control while maintaining overall reliability.
Solution Approach 2:
Different regions of the TiAl work function layer are assigned different Al concentrations to achieve different local functions. The first TiAl layer with lower Al concentration provides one set of properties while the second TiAl layer with higher Al concentration provides another set, enabling optimized threshold voltage control without compromising gap-fill quality.
2Reliability
If Al concentration in TiAl layer is increased to adjust threshold voltage, then threshold voltage is reduced, but TDDB and PBTI performance deteriorate
Solution Approach 1:
The work function layer is segmented into multiple TiAl layers with progressively increasing Al concentrations. This allows the threshold voltage tuning function to be distributed across layers, preventing any single high-Al layer from causing excessive TDDB and PBTI degradation while still achieving the desired threshold voltage reduction.
Solution Approach 2:
The Al concentration parameter is varied across different TiAl layers rather than being uniform. The first TiAl layer has a first Al concentration and the second TiAl layer has a second Al concentration that is higher, creating a gradient that balances threshold voltage control with reliability maintenance.
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 achieves a threshold voltage reduction of about 57% and a saturation current increase of 16% in n-type finFETs without adversely impacting p-type transistors, improving the reliability and performance of n-type finFETs.
Implementation Method 1
a Ti-rich layer with a low Al/Ti ratio functions as an oxygen getter, trapping oxygen atoms
Data Source
AI summary
The present disclosure describes a method for the formation of gate stacks having two or more titanium-aluminum (TiAl) layers with different Al concentrations (e.g., different Al/Ti ratios). For example, a gate structure can include a first TiAl layer with a first Al/Ti ratio and a second TiAl layer with a second Al/Ti ratio greater than the first Al/Ti ratio of the first TiAl layer.