GAA Gate Stack Isolation Structure for Lower Leakage and Capacitance
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Solution Overview
Problem
The integration of gate-all-around (GAA) transistors in semiconductor manufacturing is challenging due to complexity in fabricating the gate structure around nanowires, leading to issues like increased OFF-state current and parasitic capacitance.
Innovation Solution
A semiconductor structure is developed with dielectric isolation features between source/drain and lower fin elements, using multi-patterning processes to form GAA devices, which include a gate dielectric layer and work function metal materials, and spacers to enhance gate control and reduce parasitic capacitance.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If gate-all-around (GAA) transistor structure is implemented to improve gate control, then gate-channel coupling is increased, but fabrication complexity increases
Solution Approach 1:
The fabrication process is segmented into multiple discrete steps: forming sacrificial nanowire structures, depositing gate dielectric material, depositing gate electrode material, and selective removal of sacrificial material. This segmentation allows complex GAA structures to be built through manageable sequential operations rather than attempting to form the complete structure in one step.
Solution Approach 2:
Sacrificial nanowire structures are formed in advance before the gate structure is built. These preliminary structures serve as templates that guide the subsequent deposition and formation steps, enabling precise positioning of the gate around the channel without requiring complex direct patterning of the final structure.
2Ease of manufacture
If conventional GAA fabrication methods are used, then gate structure can be formed, but OFF-state current increases
Solution Approach 1:
Dielectric isolation features are selectively placed at specific locations where source/drain regions interface with lower fin elements. This localized dielectric insertion creates electrical isolation precisely where needed to block leakage paths, without requiring comprehensive restructuring of the entire device. The isolation is applied locally at critical interfaces rather than uniformly throughout the structure.
3Reliability
If gate structure is integrated around nanowires, then multi-gate control is achieved, but parasitic capacitance increases
Solution Approach 1:
Parasitic capacitance pathways are extracted or removed by inserting dielectric isolation features between conductive elements. The dielectric material physically separates source/drain regions from lower fin elements, extracting the harmful capacitive coupling that would otherwise exist between these closely-spaced structures. This removes the parasitic effect rather than attempting to manage it through circuit design.
4Manufacturing precision
If multi-patterning processes are used to form GAA devices, then manufacturing precision is improved, but device complexity increases
Solution Approach 1:
Multiple patterning operations are nested within a unified process framework where each patterning step builds upon the previous one. Sacrificial structures are formed first, then gate dielectric and electrode materials are deposited conformally around them, and finally sacrificial material is removed. This nesting of operations within a single integrated flow achieves multi-patterning precision without requiring separate, standalone processing modules.
Data Source
AI summary
A method for forming a semiconductor structure is provided. The method includes forming an active region over a substrate. The active region includes a fin element and a plurality of first semiconductor layers and a plurality of second semiconductor layers which are alternately stacked over the fin element. The plurality of first semiconductor layers includes a lowermost first semiconductor layer, and the lowermost first semiconductor layer is thicker than other first semiconductor layers. The method further includes etching the active region to form a first source/drain recess, forming a dielectric isolation feature in the first source/drain recess, forming a first source/drain feature over the dielectric isolation feature in the first source/drain recess, removing the plurality of first semiconductor layers, and forming a gate stack surrounding the second semiconductor layers.