Epitaxial Source/Drain Doping for Low-Resistance GAA Transistors
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Solution Overview
Problem
Conventional epitaxial features in multi-gate transistors, such as GAA transistors, do not adequately balance dopant concentration in source/drain regions, leading to issues like metal gate extrusion and reduced device performance due to excessive dopant diffusion during gate replacement processes.
Innovation Solution
Perform an additional dopant implantation, specifically using phosphorus ion implantation after the gate replacement process to increase dopant concentration in the source/drain features, particularly in n-type transistors, to enhance resistance while preventing metal gate extrusion.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If conventional epitaxial features are used in multi-gate transistors, then the device structure is simple and manufacturing is easier, but dopant concentration is not adequately balanced leading to metal gate extrusion and reduced device performance
Solution Approach 1:
The epitaxial feature is divided into multiple segments with different dopant concentrations. A first dopant (e.g., boron) is implanted at a first concentration in a first region, and a second dopant (e.g., phosphorus) is implanted at a second concentration in a second region. This segmentation allows independent optimization of dopant profiles to prevent metal gate extrusion while maintaining device performance.
Solution Approach 2:
Different regions of the epitaxial feature are given different local dopant concentrations and types. The first region receives a first dopant at a first concentration, while the second region receives a second dopant at a second concentration. This local quality variation addresses the specific need to balance dopant concentrations in different areas to prevent gate extrusion.
2Reliability
If dopant concentration in source/drain regions is increased to reduce resistance, then resistance is lowered, but metal gate extrusion occurs during gate replacement processes
Solution Approach 1:
The dopant concentration parameter is changed across different regions of the epitaxial feature. By implanting a first dopant at a first concentration in a first region and a second dopant at a second concentration in a second region, the parameter optimization prevents metal gate extrusion while achieving the desired resistance reduction.
Solution Approach 2:
The epitaxial feature is created as a composite structure with different dopant types and concentrations in different regions. This composite approach combines the benefits of low resistance with the prevention of metal gate extrusion by carefully managing dopant distribution.
3Reliability
If additional dopant implantation is performed after gate replacement to increase dopant concentration, then resistance is reduced and device performance is improved, but the process complexity and manufacturing steps increase
Solution Approach 1:
The dopant implantation is performed as a preliminary action during the epitaxial feature formation, before the gate replacement process. This timing allows the dopant concentration to be established in advance, preventing metal gate extrusion while achieving the desired resistance reduction without requiring additional post-gate-replacement steps.
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
The additional dopant implantation method effectively lowers resistance in the source/drain regions without causing metal gate extrusion, improving device performance and yield rates in multi-gate transistors.
Implementation Method 1
performing an ion implantation to increase a dopant concentration of a dopant in the epitaxial feature
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 includes forming a stack of channel layers interleaved by sacrificial layers, patterning the stack to form a fin-shape structure, forming a dummy gate stack over a channel region of the fin-shape structure, recessing a source/drain region to form a source/drain trench, forming an epitaxial feature in the source/drain trench, after the forming of the epitaxial feature removing the dummy gate stack, releasing the channel layers in the channel region as channel members, forming a gate structure wrapping around each of the channel members, and after the forming of the gate structure performing an ion implantation to increase a dopant concentration of a dopant in the epitaxial feature.