InGaAs MOSFET Source-Drain Resistivity via Epitaxial Doping
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Solution Overview
Problem
Current MOSFET technologies face challenges in reducing resistivity at the source-drain junction due to limitations in ion implantation, particularly in thin InGaAs layers, where diffusion is negligible and recrystallization is not possible, leading to minimal resistivity reduction.
Innovation Solution
The method involves epitaxially growing in-situ silicon-doped InGaAs adjacent to a selectively etched active channel layer, allowing for controlled and active silicon doping, which reduces resistivity effectively.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If silicon ion implantation is used to reduce resistivity in thin InGaAs layers, then the process is simple and widely applicable, but the resistivity reduction is minimal due to negligible diffusion and lack of recrystallization
Solution Approach 1:
The patent changes the fundamental parameter of dopant introduction from post-growth ion implantation to in-situ doping during epitaxial growth. This allows silicon to be incorporated actively into the InGaAs lattice during the growth process itself, achieving effective dopant activation and significant resistivity reduction (53 ohm/square vs. 500-1500 ohm/square with ion implantation) without relying on thermal diffusion or recrystallization
Solution Approach 2:
The patent replaces the mechanical/physical process of ion implantation with a chemical vapor deposition process (epitaxial growth) that incorporates dopants during material formation. This substitution enables active dopant incorporation through chemical reactions during growth rather than relying on physical ion bombardment and subsequent thermal activation
2Ease of manufacture
If ion implantation is performed on thin InGaAs layers, then the process is straightforward, but diffusion is negligible and recrystallization is not possible
Solution Approach 1:
The patent performs dopant incorporation during the epitaxial growth process itself, before any subsequent processing steps. By incorporating silicon during the formation of the InGaAs layer, the dopant is activated in-situ without requiring subsequent diffusion or recrystallization steps, ensuring reliable dopant activation while maintaining process simplicity
3Adaptability or versatility
If silicon is implanted into InGaAs, then the process is well-established, but the implanted silicon is not active until diffusion occurs
Solution Approach 1:
The epitaxial growth process itself performs the dopant activation function that would otherwise require separate diffusion and recrystallization steps. The growing crystal lattice automatically incorporates silicon atoms into active positions, making the growth process self-sufficient for achieving activated doping without additional processing
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 results in significantly lower sheet resistance (53 ohm/square) compared to silicon ion implantation (500-1500 ohm/square), with an abrupt dopant concentration profile, enhancing the performance of the MOSFET.
Implementation Method 1
The implanted Si is not active until it diffuses into the InGaAs and replaces host ions in the lattice
Implementation Method 2
epitaxially growing silicon doped active channel material adjacent to the remaining active channel layer
Data Source
AI summary
A metal-oxide-semiconductor field effect transistor (MOSFET) and a method of fabricating a MOSFET are described. The method includes depositing and patterning a dummy gate stack above an active channel layer formed on a base. The method also includes selectively etching the active channel layer leaving a remaining active channel layer, and epitaxially growing silicon doped active channel material adjacent to the remaining active channel layer.