Strained FET Raised Source Drain Epitaxy
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Solution Overview
Problem
Field effect transistors with short channel lengths experience a significant reduction in strain-induced enhancement of charge carrier mobility, leading to lower drive current and conductivity, as the biaxial stress in the channel region relaxes due to amorphization during the formation of source and drain extensions.
Innovation Solution
Forming raised source and drain regions adjacent to the gate electrode with biaxial strain, and using selective epitaxial growth to maintain strain around the channel region, while avoiding ion implantation-induced amorphization and strain relaxation, and incorporating dopant diffusion without altering the strain.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Quantity of substance
If ion implantation is used to form source and drain extensions, then dopant concentration is increased, but biaxial strain relaxes due to amorphization
Solution Approach 1:
The patent changes the physical state parameter of the semiconductor material by using selective epitaxial growth to maintain crystalline structure in channel contact regions while allowing amorphization in source/drain regions. This parameter change enables dopant diffusion without strain relaxation in the channel contact regions, resolving the contradiction between increasing dopant concentration and maintaining biaxial strain.
Solution Approach 2:
The patent applies different treatments to different regions: ion implantation and amorphization are applied locally to source and drain extensions, while channel contact regions are protected through selective epitaxial growth to maintain crystalline structure and biaxial strain. This local differentiation resolves the contradiction by allowing dopant concentration increase where needed without compromising strain where critical.
2Productivity
If channel length is reduced to increase transistor density, then device integration is improved, but strain-induced mobility enhancement is reduced
Solution Approach 1:
The patent ensures that channel contact regions adjacent to the channel maintain biaxial strain through selective epitaxial growth, while source and drain extensions can be heavily doped. This local strain preservation in critical regions maintains charge carrier mobility even when overall channel length is reduced for higher transistor density.
Solution Approach 2:
The patent performs selective epitaxial growth before final dopant diffusion to pre-establish the crystalline structure and biaxial strain in channel contact regions. This preliminary action ensures that subsequent doping processes do not relax the strain, maintaining high charge carrier mobility in shortened channel devices.
3Reliability
If dopant concentration in channel region is reduced to increase charge carrier mobility, then conductivity is improved, but threshold voltage control is affected
Solution Approach 1:
The patent creates a dopant concentration gradient where channel contact regions have high dopant concentration for good contact, while the channel region maintains lower dopant concentration for high mobility and proper threshold voltage. This local differentiation of dopant concentration resolves the contradiction between mobility enhancement and threshold voltage control.
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 maintains biaxial strain in the channel contact regions, enhancing charge carrier mobility and conductivity, particularly in transistors with channel lengths of 50 nm or less, thereby improving the performance of field effect transistors.
Implementation Method 1
providing a substrate comprising a biaxially strained layer of a semiconductor material
Implementation Method 2
Ions of a dopant material are implanted into the raised source region and the raised drain region
Implementation Method 3
using selective epitaxial growth to maintain strain around the channel region
Implementation Method 4
incorporating dopant diffusion without altering the strain
Data Source
AI summary
A method of forming a field effect transistor comprises providing a substrate comprising a biaxially strained layer of a semiconductor material. A gate electrode is formed on the biaxially strained layer of semiconductor material. A raised source region and a raised drain region are formed adjacent the gate electrode. Ions of a dopant material are implanted into the raised source region and the raised drain region to form an extended source region and an extended drain region. Moreover, in methods of forming a field effect transistor according to embodiments of the present invention, a gate electrode can be formed in a recess of a layer of semiconductor material. Thus, a field effect transistor wherein a source side channel contact region and a drain side channel contact region located adjacent a channel region are subject to biaxial strain can be obtained.