Stacked Transistor Gate Spacers for Selective High-k Oxygenation
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Solution Overview
Problem
Challenges in forming stacked transistors with a common work function metal and selective oxygenation through discontinuous high-k material on inner sidewalls are encountered due to process control issues in replacement metal gate formation, particularly in nanosheet technology, where etching affects both top and bottom transistors, requiring precise control of dielectric isolation layers.
Innovation Solution
The use of vertically stacked gate spacers with different materials, where one spacer has a high-k liner on its inner sidewall, allows for selective oxygenation through top-down oxygenation in one transistor while maintaining the same work function metal for both, achieved by controlling oxygen vacancy levels in the high-k material using gate spacer recess processes.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If replacement metal gate formation is performed in stacked transistors, then work function control is improved, but etching affects both top and bottom transistors equally, making selective oxygenation difficult
Solution Approach 1:
The gate spacer structure is segmented into two distinct parts: a first gate spacer for the bottom transistor and a second gate spacer for the top transistor. This segmentation allows independent modification of each spacer, enabling selective oxygenation of the top transistor while maintaining the bottom transistor's original characteristics. The discontinuous high-k material on the second gate spacer's inner sidewall provides the necessary segmentation for selective processing.
Solution Approach 2:
The high-k material is applied discontinuously only on the inner sidewall of the second gate spacer, creating a localized region with different properties. This local quality change enables selective oxygenation to occur only in the top transistor region during thermal processing, while the bottom transistor remains unaffected. The discontinuous nature of the high-k material provides spatial selectivity for the oxygenation process.
2Adaptability or versatility
If vertical gate spacer stacking with different materials is used, then selective oxygenation is achieved, but process complexity increases
Solution Approach 1:
The first and second gate spacers are formed with different materials and structures in advance, before the oxygenation process. The second gate spacer is prepared with a discontinuous high-k material layer on its inner sidewall, which serves as a mask for selective oxygenation. This preliminary preparation enables subsequent selective oxygenation without requiring complex real-time process control.
Solution Approach 2:
The discontinuous high-k material on the second gate spacer acts as an intermediary layer that mediates the oxygenation process. During thermal processing, this high-k material selectively allows oxygen diffusion into the top transistor region while preventing oxygen diffusion into the bottom transistor region. The high-k material serves as a controlled interface that enables selective modification without direct contact between the oxygen source and the transistor channels.
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 enables precise control of work function and threshold voltage in stacked transistors, ensuring consistent performance across both top and bottom transistors by selectively adjusting oxygen levels in the high-k dielectric material, thereby improving process control and device reliability.
Implementation Method 1
selective oxygenation through top-down oxygenation in one transistor while maintaining the same work function metal for both, achieved by controlling oxygen vacancy levels in the high-k material
Data Source
AI summary
Embodiments of the present disclosure include stacked complementary transistors having a high-k material, a common work function metal, and a gate conductor metal. A vertically stacked sidewall is adjacent to the gate conductor metal, the vertically stacked sidewall including a first spacer and a second spacer, the second spacer being stacked on the first spacer. The high-k material is on an inner sidewall of the second spacer.