# Review of Silicon Carbide Processing for Power MOSFET

# Abstract

inverter 逆变器

# Introduction

Over the last 50 years,
  the advancements of power devices have been primarily due to Si-based power devices.
However, due to limitations of the intrinsic physical properties of Si,
  devices based on Si cannot be used for future power devices.

Hence, SiC-based power components have been a topic for extensive research
  for high voltage/power applications for more than a decade.

The material cost of SiC is much lesser than that of GaN,
  and the processing lines of SiC-based devices have great compatibility with that of Si-based devices.

## SiC Materials Properties

![image-20231228180742974](assets/image-20231228180742974.png)

![image-20231228180819011](assets/image-20231228180819011.png)

6H-SiC and 4H-SiC are the most preferred polytypes, especially for device production,
  as they can make a large wafer and are also commercially available.
For high power, high temperature, and high-frequency device applications,
  4H-SiC is the most used and established-material due to its high electron mobility,
  higher bandgap, higher critical electric field,
  and shallower ionization energy of dopant, along with the availability of the single crystalline wafer.
In addition, 4H-SiC does not exhibit anisotropy electron mobility.

The intrinsic carrier concentration of the polytypes is much lower than that of the Si,
  which makes SiC a suitable candidate for high-temperature applications. 

## SiC Power Devices

A semiconductor device is said to be a power device if it is used as a rectifier or a switch in power electronics.

Most of the SiC-based power rectifiers and power switches for high voltage applications
  are designed as vertical devices based on semi-conducting substrates.

The main advantages of SiC power devices over Si power devices are as follows:

* improved voltage capability
* outstanding switching performance
* positive temperature coefficient
  

On comparing theoretical limits of SiC and GaN,
  GaN limits show a better trade-off between the breakdown voltage and on-resistance.
However, GaN-based devices are mainly employed for high-speed lower voltage applications,
  and, due to lower thermal conductivity than SiC, SiC-based devices are preferred for high-temperature applications.

![image-20231228180854148](assets/image-20231228180854148.png)

## SiC Applications

Si devices are used for lower power and lower frequency applications,
  while GaN-based devices are used for lower voltage and lower power high-frequency applications
  such as data centers and consumer systems;
SiC devices are used for higher power, higher voltage switching power applications
  such as trains, electric vehicles and their battery chargers, and industrial automation.

![image-20231228180910058](assets/image-20231228180910058.png)

# SiC Critical Step

SiC power devices tend to show better performance when it is used as n-channels rather than p-channels;
  to achieve even more enhanced performance,
  the device needs to be grown epitaxially on low-resistivity p-type substrates.

The total defects of SiC wafers are mainly intrinsic material defects and structural defects
  caused by epitaxial growth.
These defects act as recombination centers and reduce the carrier lifetime of the thick drift region significantly.

... reduce these defects to a very low level of about $10^{11} \mathrm{cm^{-2}}$.

The supply of large-size and high-quality materials and the epitaxial growth process with low defect density
  are the keys to the commercialization of SiC devices.

## SiC Substrate

The in-situ visualization of the PVT growth process is available.

## SiC Epitaxy

$\mathrm{H_2}$ etching

## Ion Implant

Most of the diffused impurities during implantation can be ignored.

High temperature (~500 ℃) implantation is usually used.

## Oxidation

# SiC MOSFETs

## Planar and Trench MOSFETs

## Superjunction MOSFETs

# Device Reliability

The oxide trap charging and its activation are the two main reasons behind the instability of threshold voltage.

## Threshold Voltage Degradation

## Gate Oxide Degradation

## Body Diode Degradation

The root cause of stacking faults at forward voltage is due to the expansion of base-plane dislocations (BPD)
  during forward conduction.
The coincident electrons and holes provide energy for the BPD
  to expand into a triangular stacking fault in the drift region.
The extended BPD penetrates through the epitaxial layer, creating a barrier for the conduction of multiple carriers,
  resulting in reduced carrier mobility.

# Conclusions

