Gate-All-Around Metal Gate Stacks for Dual Threshold Voltage Control
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Solution Overview
Problem
Semiconductor devices face challenges in achieving high integration, reliability, and multi-functionality due to limitations in manufacturing techniques for gate-all-around type transistors, particularly in controlling threshold voltages across different transistors.
Innovation Solution
The semiconductor device incorporates gate-all-around type transistors with varying threshold voltages by using a combination of work function metal layers and gate dielectric patterns, where the first transistor has a single work function metal layer and the second transistor includes an additional work function metal layer, allowing for different threshold voltages through precise control of work function patterns and gate dielectric layers.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Adaptability or versatility
If a single work function metal layer is used in all transistors, then the manufacturing process is simple, but all transistors have the same threshold voltage which limits device functionality
Solution Approach 1:
The patent applies local quality by providing different work function metal layer configurations to different transistors based on their specific threshold voltage requirements. The first transistor receives a single work function metal layer while the second transistor receives multiple work function metal layers, allowing each transistor to have locally optimized electrical properties tailored to its functional role in the circuit.
Solution Approach 2:
The work function pattern is segmented into multiple metal layers with different work functions, where each layer can be independently controlled and optimized. This segmentation allows the second transistor to have multiple work function metal layers that can be selectively formed or removed to achieve the desired threshold voltage, while the first transistor maintains a simpler single-layer structure.
2Adaptability or versatility
If different work function patterns are formed in different trenches, then transistors have different threshold voltages, but the manufacturing process becomes more complex
Solution Approach 1:
The patent applies preliminary action by forming a common work function metal layer across all trenches before selective removal or additional layer formation. This preliminary uniform layer is deposited over the entire substrate, and then subsequent selective etching or additional layer deposition is performed only in specific trenches where different threshold voltages are required, simplifying the overall manufacturing process.
Solution Approach 2:
Different work function patterns are applied locally to different trenches based on the specific transistor requirements. The first trench receives a single work function metal layer configuration while the second trench receives multiple work function metal layers, allowing local optimization of threshold voltage without requiring completely different manufacturing processes for each transistor type.
3Reliability
If gate-all-around transistors are manufactured with precise threshold voltage control, then device reliability improves, but manufacturing precision requirements increase
Solution Approach 1:
The work function pattern uses composite material structures with multiple metal layers having different work functions. By combining metals with different work function characteristics (e.g., tungsten with high work function and molybdenum with lower work function), the patent achieves precise threshold voltage control through material composition rather than relying solely on dimensional precision, thereby improving reliability while managing manufacturing precision requirements.
Solution Approach 2:
The patent controls threshold voltage by changing the work function parameter through selective combination of metal layers with different work functions. Instead of relying entirely on precise control of layer thickness or area, the invention adjusts the electrical parameter (work function) itself by selecting appropriate metal materials and their combinations, making the manufacturing process more robust against dimensional variations.
Data Source
AI summary
Disclosed are semiconductor devices and methods of manufacturing the same. The semiconductor device comprises a first transistor on a substrate, and a second transistor on the substrate. Each of the first and second transistors includes a plurality of semiconductor patterns vertically stacked on the substrate and vertically spaced apart from each other, and a gate dielectric pattern and a work function pattern filling a space between the semiconductor patterns. The work function pattern of the first transistor includes a first work function metal layer, the work function pattern of the second transistor includes the first work function metal layer and a second work function metal layer, the first work function metal layer of each of the first and second transistors has a work function greater than that of the second work function metal layer, and the first transistor has a threshold voltage less than that of the second transistor.