Multi-Gate Source/Drain Structure With Undoped Base for Mesa Leakage
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Solution Overview
Problem
Multi-gate devices, such as MBC transistors, suffer from current leakage near the mesa structure due to the gate structure engaging the substrate, which affects device performance.
Innovation Solution
A method is introduced to modify the mesa structure's profile by recessing the source/drain regions and enlarging the bottom portion of the source/drain openings, forming a source/drain feature with a modified profile to reduce leakage current, involving a two-step etching process and subsequent formation of undoped and doped semiconductor layers.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If the gate structure engages the mesa structure to provide control, then device functionality is improved, but leakage current through the mesa structure increases
Solution Approach 1:
The source/drain region is divided into multiple segments with different doping concentrations. The first source/drain region has a first doping concentration while the second source/drain region has a second doping concentration, allowing each segment to serve different electrical functions and reducing overall leakage current while maintaining device functionality
Solution Approach 2:
Different portions of the source/drain region are given different doping concentrations to create local quality variations. The first and second source/drain regions have different doping levels optimized for their specific locations, reducing leakage current in the mesa structure while preserving necessary electrical characteristics for device operation
2Ease of manufacture
If standard source/drain regions are used, then manufacturing simplicity is maintained, but leakage current through the mesa structure increases
Solution Approach 1:
The source/drain region is segmented into multiple regions with different doping concentrations, which can be achieved through standard semiconductor manufacturing techniques such as selective epitaxial growth or ion implantation, maintaining ease of manufacture while reducing leakage current
Solution Approach 2:
The doping concentration parameter is changed across different portions of the source/drain region. By varying the doping concentration from the first region to the second region, leakage current is reduced while maintaining compatibility with existing manufacturing processes
Data Source
AI summary
A semiconductor device and a method of forming the same are provided. In an embodiment, an exemplary semiconductor device includes a vertical stack of channel members disposed over a substrate, a gate structure wrapping around each channel member of the vertical stack of channel members, and a source/drain feature disposed over the substrate and coupled to the vertical stack of channel members, the source/drain feature comprising an undoped bottom layer and a doped upper layer, where a part of the undoped bottom layer of the source/drain feature is disposed directly under the gate structure.