124 lines
4.5 KiB
Markdown
124 lines
4.5 KiB
Markdown
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# Review of Silicon Carbide Processing for Power MOSFET
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# Abstract
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inverter 逆变器
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# Introduction
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Over the last 50 years,
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the advancements of power devices have been primarily due to Si-based power devices.
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However, due to limitations of the intrinsic physical properties of Si,
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devices based on Si cannot be used for future power devices.
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Hence, SiC-based power components have been a topic for extensive research
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for high voltage/power applications for more than a decade.
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The material cost of SiC is much lesser than that of GaN,
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and the processing lines of SiC-based devices have great compatibility with that of Si-based devices.
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## SiC Materials Properties
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![image-20231228180742974](assets/image-20231228180742974.png)
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![image-20231228180819011](assets/image-20231228180819011.png)
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6H-SiC and 4H-SiC are the most preferred polytypes, especially for device production,
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as they can make a large wafer and are also commercially available.
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For high power, high temperature, and high-frequency device applications,
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4H-SiC is the most used and established-material due to its high electron mobility,
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higher bandgap, higher critical electric field,
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and shallower ionization energy of dopant, along with the availability of the single crystalline wafer.
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In addition, 4H-SiC does not exhibit anisotropy electron mobility.
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The intrinsic carrier concentration of the polytypes is much lower than that of the Si,
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which makes SiC a suitable candidate for high-temperature applications.
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## SiC Power Devices
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A semiconductor device is said to be a power device if it is used as a rectifier or a switch in power electronics.
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Most of the SiC-based power rectifiers and power switches for high voltage applications
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are designed as vertical devices based on semi-conducting substrates.
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The main advantages of SiC power devices over Si power devices are as follows:
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* improved voltage capability
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* outstanding switching performance
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* positive temperature coefficient
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On comparing theoretical limits of SiC and GaN,
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GaN limits show a better trade-off between the breakdown voltage and on-resistance.
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However, GaN-based devices are mainly employed for high-speed lower voltage applications,
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and, due to lower thermal conductivity than SiC, SiC-based devices are preferred for high-temperature applications.
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![image-20231228180854148](assets/image-20231228180854148.png)
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## SiC Applications
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Si devices are used for lower power and lower frequency applications,
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while GaN-based devices are used for lower voltage and lower power high-frequency applications
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such as data centers and consumer systems;
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SiC devices are used for higher power, higher voltage switching power applications
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such as trains, electric vehicles and their battery chargers, and industrial automation.
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![image-20231228180910058](assets/image-20231228180910058.png)
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# SiC Critical Step
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SiC power devices tend to show better performance when it is used as n-channels rather than p-channels;
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to achieve even more enhanced performance,
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the device needs to be grown epitaxially on low-resistivity p-type substrates.
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The total defects of SiC wafers are mainly intrinsic material defects and structural defects
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caused by epitaxial growth.
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These defects act as recombination centers and reduce the carrier lifetime of the thick drift region significantly.
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... reduce these defects to a very low level of about $10^{11} \mathrm{cm^{-2}}$.
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The supply of large-size and high-quality materials and the epitaxial growth process with low defect density
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are the keys to the commercialization of SiC devices.
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## SiC Substrate
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The in-situ visualization of the PVT growth process is available.
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## SiC Epitaxy
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$\mathrm{H_2}$ etching
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## Ion Implant
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Most of the diffused impurities during implantation can be ignored.
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High temperature (~500 ℃) implantation is usually used.
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## Oxidation
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# SiC MOSFETs
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## Planar and Trench MOSFETs
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## Superjunction MOSFETs
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# Device Reliability
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The oxide trap charging and its activation are the two main reasons behind the instability of threshold voltage.
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## Threshold Voltage Degradation
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## Gate Oxide Degradation
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## Body Diode Degradation
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The root cause of stacking faults at forward voltage is due to the expansion of base-plane dislocations (BPD)
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during forward conduction.
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The coincident electrons and holes provide energy for the BPD
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to expand into a triangular stacking fault in the drift region.
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The extended BPD penetrates through the epitaxial layer, creating a barrier for the conduction of multiple carriers,
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resulting in reduced carrier mobility.
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# Conclusions
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