SiGe Stressor Segmentation for Dopant Out-Diffusion Control
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Solution Overview
Problem
High-mobility stressor materials used in semiconductor devices tend to out-diffuse dopant impurities at high temperatures, leading to adverse effects on device performance or functionality during subsequent fabrication operations.
Innovation Solution
The semiconductor structures are doped with a varying concentration of dopant impurities, with a lower portion free of dopants and upper portions having increasing dopant concentrations, formed using SiGe and boron, to prevent out-diffusion during high-temperature processing.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Speed
If doped high-mobility stressor materials are used to increase device speed, then electron and hole mobility is improved, but dopant impurities out-diffuse at high temperatures causing device failure
Solution Approach 1:
The stressor material layer is segmented into multiple sub-layers with different dopant concentrations. The lower portion has reduced or no dopant concentration while upper portions have higher dopant concentrations. This segmentation prevents dopant out-diffusion during high-temperature processing while maintaining high mobility in the channel region.
Solution Approach 2:
Different regions of the stressor material are assigned different dopant concentrations based on their functional requirements. The lower portion near the interface has low or zero dopant to prevent diffusion, while upper portions have higher dopant concentrations to provide local mobility enhancement without causing harmful diffusion effects.
2Reliability
If dopant impurities are added to stressor materials to reduce resistivity, then device speed increases, but dopant out-diffusion occurs during high-temperature fabrication operations
Solution Approach 1:
The stressor material structure is prepared in advance with a graded or stepped dopant concentration profile before high-temperature processing. The lower portion is intentionally designed with reduced or zero dopant concentration to create a diffusion barrier, preventing dopant migration during subsequent fabrication steps.
Solution Approach 2:
The stressor material is formed as a composite structure with multiple layers having different dopant concentrations. This composite architecture combines regions of high dopant concentration (for mobility enhancement) with regions of low or zero dopant concentration (for diffusion prevention), achieving both performance and stability.
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 solution effectively prevents boron out-diffusion, ensuring stable device performance and functionality even during high-temperature semiconductor manufacturing operations.
Implementation Method 1
Each source/drain region is formed of a lower portion of SiGe free of boron dopant impurities and an upper portion of SiGe including boron dopant impurities therein
Data Source
AI summary
A semiconductor structure and method for forming the same provide a high mobility stressor material suitable for use as source/drain regions or other active devices. The structure is formed in a substrate opening and is doped with an impurity such as boron in upper portions but is void of the impurity in regions that contact the surfaces of the opening. The structure is therefore resistant to out-diffusion of the dopant impurity during high temperature operations and may be formed through selective deposition using reduced pressure chemical vapor deposition or reduced pressure epitaxial deposition.