SiC MOSFET Channel Mobility via Cesium Ion Diffusion
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Solution Overview
Problem
The development of high voltage SiC MOSFET devices is limited by interface traps at the SiC/SiO2 interface, which reduce mobility and are difficult to address due to issues with sodium mobility and implantation damage from cesium ion implantation.
Innovation Solution
Diffusing cesium ions into the oxide layer after its formation, using a CsCl solution and high-temperature annealing to reduce interface trap density and enhance channel mobility without inducing implantation damage.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If cesium ion implantation is used to reduce interface trap density, then channel mobility is improved, but implantation damage occurs
Solution Approach 1:
The patent uses an intermediary approach by first depositing cesium ions onto the oxide surface, then using thermal diffusion as a mediator to gradually transfer cesium ions into the oxide bulk. This indirect method avoids the direct implantation damage while achieving the desired interface trap reduction through controlled thermal diffusion processes.
Solution Approach 2:
The patent replaces the mechanical/physical impact of ion implantation with a thermal diffusion process. Instead of using high-energy ion beams that cause implantation damage, the invention uses thermal energy to drive cesium ion diffusion into the oxide, substituting a gentle thermal process for a harsh mechanical implantation process.
2Manufacturing precision
If sodium is used to treat the oxide interface, then channel mobility increases, but sodium mobility causes instability at operating temperatures
Solution Approach 1:
The patent changes the key parameter from using sodium ions to using cesium ions. This parameter change is effective because cesium has lower mobility in oxides compared to sodium, while still providing the beneficial interface trap reduction effect. This substitution maintains channel mobility improvement while achieving the required gate voltage stability at operating temperatures.
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 increases channel mobility from 20 cm^2/V-s to 100 cm^2/V-s, providing stable gate voltage at operating temperatures and avoiding implant damage, making it suitable for power MOSFET fabrication.
Implementation Method 1
diffusing cesium ions into the oxide layer after its formation, using a CsCl solution and high-temperature annealing
Implementation Method 2
high-temperature annealing to reduce interface trap density and enhance channel mobility
Implementation Method 3
high-temperature annealing
Data Source
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Figure 3A~3B
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AI summary
Methods of forming a semiconductor structure include providing an insulation layer on a semiconductor layer and diffusing cesium ions into the insulation layer from a cesium ion source outside the insulation layer. A MOSFET including an insulation layer treated with cesium ions may exhibit increased inversion layer mobility.