Strained Si and SiGe Transistor Channels for Mobility
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Solution Overview
Problem
Conventional CMOS structures struggle to significantly enhance the mobility of both nMOSFET and pMOSFET transistors due to limitations in strain application methods, particularly with high Ge concentration channels causing crystal defects and compatibility issues with existing Si-LSI processes.
Innovation Solution
A semiconductor device comprising strained Si and SiGe layers with specific biaxial and uniaxial strain configurations, where n-channel MIS transistors are formed on biaxial tensile strained Si layers and p-channel MIS transistors on uniaxial compression strained SiGe layers, optimizing strain modes independently for each type of transistor.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Speed
If high Ge concentration channel is used to increase pMOSFET mobility, then mobility increases, but crystal defects and separation formation problems occur
Solution Approach 1:
The patent applies different strain configurations to different transistor types: biaxial tensile strain for nMOSFET channels and uniaxial compressive strain for pMOSFET channels. This local differentiation allows each transistor type to achieve optimal mobility enhancement without requiring high Ge concentration that would cause crystal defects across the entire device.
Solution Approach 2:
The patent segments the channel material composition and strain application by transistor type. nMOSFETs use strained Si channels with biaxial tensile strain, while pMOSFETs use strained SiGe channels with uniaxial compressive strain. This segmentation enables targeted mobility optimization for each transistor type without the adverse effects of high Ge concentration in all channels.
2Speed
If biaxial compression-strained SiGe is used for pMOSFET channel, then mobility can be increased, but separation formation and interfacial characteristics deteriorate
Solution Approach 1:
The patent applies uniaxial compressive strain specifically in the channel length direction for pMOSFETs rather than biaxial compression. This localized strain application achieves mobility enhancement while maintaining better interface characteristics and reducing separation formation issues associated with biaxial compression in high Ge concentration materials.
3Speed
If large strain is applied to achieve sufficient mobility increase, then mobility improves, but compatibility with existing Si-LSI process deteriorates
Solution Approach 1:
The patent optimizes the strain parameters by applying biaxial tensile strain to nMOSFETs and uniaxial compressive strain to pMOSFETs at moderate levels. This parameter optimization achieves sufficient mobility enhancement for both transistor types while maintaining compatibility with existing Si-LSI fabrication processes, avoiding the need for extreme strain conditions that would require process retooling.
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 effectively increases the mobility of both n and p MOS transistors without high Ge concentration, improving separation, reducing crystal defects, and enhancing compatibility with existing processes, while maintaining low leakage current and reliable interfacial characteristics.
Implementation Method 1
a strained Si layer formed on the insulating film and having a biaxial tensile strain; a strained SiGe layer formed on the insulating film and having a uniaxial compression strain
Data Source
AI summary
A semiconductor device includes an n-channel MIS transistor and a p-channel MIS transistor on a semiconductor layer formed on an insulating layer, in which the channel of the n-channel MIS transistor is formed of a strained Si layer having biaxial tensile strain and the channel of the p-channel MIS transistor is formed of a strained SiGe layer having uniaxial compression strain in the channel length direction.