Aluminum-Oxygen Work Function Layer for Threshold Voltage Tuning
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Solution Overview
Problem
As semiconductor devices become smaller, it is challenging to adjust the threshold voltage effectively due to limited space for the work function layer, leading to degraded device performance, as increasing the layer's thickness reduces the process window and hampers high device integration.
Innovation Solution
A semiconductor structure with a work function layer containing aluminum and oxygen, where the molar percentage concentration of aluminum atoms decreases from the substrate surface to the top, allowing for improved threshold voltage adjustment without thickness changes, and a barrier layer is added to protect the work function layer from environmental effects.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If the thickness of the work function layer is increased to adjust the threshold voltage, then the threshold voltage adjustment capability is improved, but the device integration density deteriorates due to limited space
Solution Approach 1:
The work function layer employs a non-uniform aluminum concentration distribution, with higher aluminum content near the substrate interface and lower aluminum content toward the top surface. This local variation in composition allows different regions of the layer to serve different functions: the bottom region provides strong threshold voltage control, while the top region maintains compatibility with subsequent processing steps and allows for higher integration density.
Solution Approach 2:
The invention changes the compositional parameter of the work function layer by creating a gradient in aluminum concentration rather than using a uniform composition. This parameter change enables the layer to achieve both adequate thickness for threshold voltage control and compatibility with high-density integration requirements.
2Volume of moving object
If the work function layer thickness is reduced to improve device integration, then the device integration density is improved, but the threshold voltage adjustment capability deteriorates
Solution Approach 1:
By concentrating the aluminum content in specific regions of the work function layer (particularly near the substrate interface), the invention maximizes the threshold voltage control effectiveness within a reduced overall layer thickness, enabling both high integration density and adequate voltage control.
Solution Approach 2:
The compositional gradient in the work function layer allows the layer to be thinner overall while maintaining sufficient threshold voltage adjustment capability through the localized high-aluminum region that provides the necessary electrical control.
3Manufacturing precision
If the aluminum concentration in the work function layer is increased to improve threshold voltage control, then the threshold voltage adjustment capability is improved, but aluminum aggregation increases leading to performance degradation
Solution Approach 1:
The work function layer uses a spatially varying aluminum concentration, with the highest aluminum content localized near the substrate interface where it is most effective for threshold voltage control. The aluminum concentration then decreases toward the top surface, which prevents aluminum aggregation and maintains device reliability while preserving threshold voltage control capability.
Solution Approach 2:
The invention performs preliminary action by pre-distributing aluminum atoms in a controlled gradient pattern during layer formation, preventing aluminum aggregation before it can occur. This pre-established concentration gradient ensures both effective threshold voltage control and prevention of performance-degrading aggregation.
Data Source
AI summary
A semiconductor structure and a fabrication method thereof. The semiconductor structure, includes a substrate; and a work function layer on the substrate, that the work function layer contains aluminum and oxygen elements, the work function layer includes a first surface and a second surface opposite to the first surface, a distance between the first surface and a surface of the substrate is less than a distance between the second surface and the surface of the substrate, and along a direction from the first surface to the second surface, a molar percentage concentration of aluminum atoms in the work function layer decreases, and a molar percentage concentration of oxygen atoms in the work function layer decreases. The semiconductor structure can improve the ability to adjust the threshold voltage of a device, thereby improving the performance of the formed semiconductor structure.