Epitaxial Source/Drain Structure for Low-Leakage p-FET Strain Retention
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Solution Overview
Problem
Conventional epitaxial features in multi-gate transistors, particularly in p-type FETs, suffer from deteriorated DC performance due to increased resistance and loss of compressive strain caused by a dielectric film positioned above the source/drain features, which confines their volume and reduces their effectiveness in suppressing leakage current.
Innovation Solution
Positioning the dielectric film below the top surface of the substrate allows the source/drain features to extend into the substrate, expanding their volume and maintaining compressive strain, while an undoped base epitaxial layer is optionally formed between the substrate and the dielectric film to further suppress leakage current by providing a high resistance path.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Object-affected harmful factors
If a dielectric film is positioned above the source/drain features to suppress leakage current, then leakage current suppression is improved, but the source/drain feature volume is confined and compressive strain is lost, deteriorating DC performance
Solution Approach 1:
The dielectric film is repositioned from above the source/drain features to below them (between the substrate and source/drain features). This inversion of the dielectric film position allows the source/drain features to extend into the substrate, maintaining both leakage current suppression and compressive strain.
Solution Approach 2:
The source/drain features are extended vertically into the substrate by repositioning the dielectric film below them. This dimensional change allows the source/drain features to achieve greater volume and maintain compressive strain while the dielectric film continues to provide leakage current suppression through its high resistance path.
2Object-affected harmful factors
If source/drain feature volume is confined by a dielectric film above them, then leakage current suppression is improved, but compressive strain is lost and resistance increases
Solution Approach 1:
The dielectric film position is inverted from above to below the source/drain features, removing the volume confinement while maintaining leakage current suppression through the high resistance path provided by the dielectric film in its new position.
Solution Approach 2:
The structure is segmented into distinct regions: the dielectric film is separated below the source/drain features rather than above them. This segmentation allows the source/drain features to extend freely into the substrate for increased volume while the dielectric film maintains its leakage suppression function in the lower region.
3Object-affected harmful factors
If an undoped base epitaxial layer is formed between the substrate and dielectric film, then leakage current suppression is enhanced, but manufacturing complexity increases
Solution Approach 1:
The undoped base epitaxial layer is merged with the dielectric film structure, creating a combined high resistance path system. The undoped epitaxial layer works together with the dielectric film to provide enhanced leakage current suppression, with the epitaxial layer serving as an additional barrier in the same functional region.
Solution Approach 2:
The undoped base epitaxial layer acts as an intermediary between the substrate and the dielectric film, providing an additional high resistance path. This intermediary layer enhances leakage current suppression by creating a multi-layer barrier structure that impedes leakage current more effectively than a single layer alone.
Data Source
AI summary
The present disclosure provides a semiconductor device and a method of forming the same. A method according one embodiment of the present disclosure include forming a stack over a substrate, forming a fin-shape structure from patterning the stack and the substrate, recessing the fin-shape structure to form a source/drain trench, depositing a dielectric film in the source/drain trench with a top surface below a top surface of the substrate in the fin-shape structure, and forming an epitaxial feature over the dielectric film. A bottom surface of the epitaxial feature is below the top surface of the substrate in the fin-shape structure.