High-k Metal Gate Stack Diffusion Barrier for CMOS Threshold Voltage Control
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Solution Overview
Problem
The use of silicon germanium (SiGe) in semiconductor devices leads to inconsistent threshold voltage shifts in p-FET and undesirable shifts in n-FET devices, which cannot be fully explained by band-gap narrowing or valence band offset, particularly due to the presence of germanium near the high-k dielectric in the n-FET gate stack.
Innovation Solution
Incorporating a diffusion barrier layer between the germanium material layer and the high-k dielectric in the n-FET device to prevent the incorporation and subsequent shift in threshold voltage, while maintaining a germanium material layer in both n-FET and p-FET devices with a high-k dielectric and conductive electrode layer.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Speed
If germanium material layer is used in n-FET device to achieve higher electron mobility, then electron mobility is improved, but threshold voltage shifts undesirably due to germanium diffusion into the high-k dielectric
Solution Approach 1:
A diffusion barrier layer is introduced as an intermediary between the germanium material layer and the high-k dielectric layer. This barrier layer prevents germanium atoms from diffusing into the dielectric, thereby maintaining stable threshold voltage while allowing the germanium layer to remain in place for high electron mobility.
Solution Approach 2:
The gate stack is segmented into distinct functional layers: the germanium material layer for high mobility, the diffusion barrier layer for preventing contamination, and the high-k dielectric layer for gate control. This segmentation allows each layer to perform its specific function without interfering with the others.
2Manufacturing precision
If silicon germanium is used in p-FET device to reduce threshold voltage to band edge, then threshold voltage is improved, but flatband voltage shifts due to band-gap modulation
Solution Approach 1:
The band-gap properties of the channel material are modified by incorporating germanium, which changes the electrical parameters including threshold voltage and flatband voltage. The diffusion barrier layer enables these parameter changes to occur in a controlled manner, preventing unwanted voltage shifts.
3Adaptability or versatility
If germanium is incorporated near the high-k dielectric to achieve voltage shifts, then voltage tuning is achieved, but inconsistent threshold voltage shifts occur between devices
Solution Approach 1:
The diffusion barrier layer serves as a mediator that controls the interaction between germanium and the high-k dielectric. It allows voltage tuning through controlled germanium proximity while preventing the inconsistent threshold voltage shifts that occur when germanium directly contacts the dielectric.
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 stabilizes the threshold voltage of n-FET devices, allows for higher electron and hole mobility channels without compromising threshold voltage, and simplifies integration by preventing germanium diffusion into the high-k dielectric, thus addressing the inconsistencies in voltage shifts caused by SiGe.
Implementation Method 1
Incorporating a diffusion barrier layer between the germanium material layer and the high-k dielectric in the n-FET device to prevent the incorporation and subsequent shift in threshold voltage
Data Source
AI summary
A high-k metal gate stack and structures for CMOS devices and a method for forming the devices. The gate stack includes a germanium (Ge) material layer formed on the semiconductor substrate, a diffusion barrier layer formed on the Ge material layer, a high-k dielectric having a high dielectric constant greater than approximately 3.9 formed over the diffusion barrier layer, and a conductive electrode layer formed above the high-k dielectric layer.