Strained Semiconductor Structure With Tapered Epitaxial Profile
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Solution Overview
Problem
Current techniques for forming strained structures in semiconductor devices, such as MOSFETs, do not adequately produce sufficient stress in the channel region to enhance carrier mobility and improve saturation drain current.
Innovation Solution
The semiconductor device incorporates strained source and drain regions with a specific cross-sectional profile, featuring a vertical section and a tapered section that tapers away from the surface at an angle of 50° to 70°, formed using epitaxial silicon germanium (SiGe) to enhance carrier mobility and stress in the channel region.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If strained structures are formed using conventional techniques, then the device structure is simplified, but sufficient stress is not produced in the channel region to improve saturation drain current
Solution Approach 1:
The strained structure is formed with a specific cross-sectional profile where the first portion extends from the surface and the second portion tapers at an angle of 50°-70° with respect to an axis parallel to the surface. This localized geometric modification concentrates stress in the channel region, producing sufficient stress to improve saturation drain current by 10-20% while maintaining manufacturing feasibility through standard epitaxial growth processes.
2Reliability
If the strained feature is placed closer to the channel region, then carrier mobility is enhanced, but short channel effects like drain-induced barrier lowering increase
Solution Approach 1:
The strained structure employs a three-dimensional cross-sectional profile with a tapered second portion at an angle of 50°-70° with respect to an axis parallel to the surface. This dimensional approach allows the structure to extend closer to the channel region to enhance carrier mobility while the tapered geometry controls the stress distribution to mitigate short channel effects such as drain-induced barrier lowering, achieving a balance between mobility enhancement and device stability.
3Ease of manufacture
If a vertical strained structure is used, then manufacturing is simplified, but the stress distribution is insufficient to improve device performance
Solution Approach 1:
The strained structure features an asymmetric cross-sectional profile where the second portion tapers at an angle of 50°-70° with respect to an axis parallel to the surface, rather than being purely vertical. This asymmetric geometry optimizes stress distribution in the channel region, improving device performance through enhanced carrier mobility while remaining compatible with standard epitaxial growth and fabrication processes.
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
This approach improves the saturation drain current by 10 to 20% compared to existing methods, while maintaining control over the proximity of the strained feature to the channel region, reducing short channel effects like drain-induced barrier lowering (DIBL), even in advanced technology processes below 32 nm.
Implementation Method 1
strained structures utilizing epitaxy silicon germanium (SiGe) may be used to enhance carrier mobility
Data Source
AI summary
The present disclosure provides a semiconductor device that includes a semiconductor substrate, a gate structure disposed on a surface of the substrate, and strained structures disposed in the substrate at either side of the gate structure and formed of a semiconductor material different from the semiconductor substrate. Each strained structure has a cross-sectional profile that includes a first portion that extends from the surface of substrate and a second portion that tapers from the first portion at an angle ranging from about 50° to about 70°. The angle is measured with respect to an axis parallel to the surface of the substrate.