SiC/SiO2の特性と膜生成法
東京工業大学 物質・情報卓越教育院

松下雄一郎
2021/7/15（Thu）押山先生PJ MTG

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Background: Why SiC?
ReducedPower loss

・SiC application is already started as a power-device semiconductor.
・SiC-power devices start to replace Si-power devices in many places.

Si-power

SiC-power

By replacing Si-powerdevices with SiC, the energy
loss can be reduced
substantially.

Application of SiC devices isnow expanding.

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Issue: High density of interface states in SiC-MOS devices
MOS devices are the most important element in power devices.
Cross section of MOSFETHigh density of interfce defects
appears at the SiC/SiO2.
~100 times higher than Si/SiO2
The interface defects trap
electron carriers leading tohigh resistivity at the interface.
Electron mobility is only a few
percent of theoretical values.
Actual devices : 20-30 cm2/Vs
Theoretical value: 1000 cm2/Vs

Reduction of the interface-state density is necessary.
However, identification of the interface states is NOT achieved yet.

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Contents
Based on DFT calculations, we have found an interface-state candidate
and proposed one process to reduce the interface-state density.
1, Interface-state candidate : Originated from carbon defects

2, Novel formation process of SiO2 film without thermal oxidazation
3, Summary
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Mystery in the thermal oxidation process of SiC
After the oxidation of SiC, the final products (under enoughoxygen and long oxidation time enough) are clear, but...

Problem: Halfway products of carbon species are unclear.
(Could be related to interface states.
Further, it is not clarified whether the halfway products ofcarbon species are distributed in the interface area or not.)Need to identify the halfway products of carbon species
5Theoretical preceding works related to carbon defects
Many DFT calculations performed for carbon related defects.
S. Wang, et al., PRL 98, 026101 (2007).

F. Devynck, et al., PRB 83,195319 (2011).

Knaup, et al., PRB 72,115323 (2005).

SiO2O

SiO2 side？

SiC

C2 defects distributed in
SiC bulk

C2 defects distributed
at just the interface

SiC

SiC side？

Justinterface？

C2 defects distributedin SiO2 film

However, still people don't know which carbon defects are more reasonable one.
This work

Following the energetics, we have clarified the stable carbon structures on the SiC side,
SiO2 side, and the just interface on the same footing by comprehensive DFT calculations.

6Calculation models (SiC-side・SiO2-side)
SiC-side (All possible C1, C2 defects)
Total 23 defect structures[1] Y.-I. Matsushita and A. Oshiyama,Jpn. J. Appl. Phys. 57, 125701 (2018).

SiO2-side (C1, C2 defects screened by CPMD calculations)

Total 24 defect structures7

Calculation models (Just interface)
Just interface (Comprehensive C1, C2 defects)

Total 79 defect structures8

We have performed comprehensive DFT calculations for the 126
carbon defects distributed in the three regions:
SiC・SiO2・SiC/SiO2 interfaces.
According to the results:
・Higher oxidation temperature
4is preferable.
This agrees with experimental
2fact [1].
Unstable

0-2-4interface

StableDefect formation energy (eV)DFT calculations for the 126 carbon defects[1] T. Hosoi, et al., Appl. Phys. Lett. 109, 182114(2016).

・Carbon defects distributed atjust interface are stable.

J. Appl. Phys. 126, 145302 (2019).

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Stable top 5 C-defects at 1600 K
Stableinterface#6 Si-C-C-Si

interface#7 Si-C-C-O-Si

interface#8 Si2-C-C-O

SiO2-side#9 Si2-C-C-Si2

OC CSiCCOSiCCinterface#10 Si3-C
PbcセンタCCC

μO = (E(SiO2) - E(Si))/2 , μSi = E (Si) , μC = E(SiC) - E(Si)・Of the top five C-defects, four defects are distributed at just interface and only one C-defect on
SiO2 side is ranked.
・C-dangling bond (#10 Si3-C) appears as a stable structure：Very recently ESR detected it (Agree with an experimental fact). [1][1] Appl. Phys. Lett. 116, 071604 (2020)

Carbon-related defects likely to be formed and mostly distributed at the interface. 10Contents
1, Interface-state candidate : Originated from carbon defects
Carbon-related defects are formed and mostly distributed at the interface.

2, Novel formation process of SiO2 film without thermal oxidazation

3, Summary
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Unstable

420-2-4interface

J. Appl. Phys. 126, 145302 (2019).

StableDefect formation energy (eV)More important message from the DFT results
Carbon related defects formed ininterfaces are energeticallystable.
Result1: As long as thermaloxidation is used, it means thatcarbon defects will inevitably
aggregate at the interface.
Implicit message: If you want to
reduce the interface C-defects,
we have to give up theconventional thermaloxidation to form the SiO2 film.

12Novel formation method of SiC/SiO2
Following the DFT results, we proposed a novel formation process of SiO2 film
without thermal oxidation.
Appl. Phys. Express 13 091003 (2020).
Candidate: Carbon defects

Conventional
approachHigh density ofinterface defects

Thermal oxy.

Still high density ofinterface statesremains.
NO-gas treatment

Point1: Not oxidize theSiC but only Si films.

Proposedapproach

Point2: N2 gas usedinstead of NO gas.
High quality interface

Si epi

Oxidization of Si.

N2-gas treatment

We checked the efficiencyof our proposed approach
experimentally.

13Great success of our proposed method
Found that 10 times high quality SiC/SiO2 interfaces realize.
Interface-state
densityDensity of interface defects at SiC/SiO2

Density of interface defects

Oxidation only
Conventional
methodOxidation+NO
treatmentThis work
High quality

Energy (eV)Appl. Phys. Express 13 091003 (2020).

This work

Density of interface states is reduced substantiallydown to 1/10.
This will make SiC-power devices cheaper down to~1/10.

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Contents
1, Interface-state candidate : Originated from carbon defects

Carbon-related defects are formed and mostly distributed at the interface.

2, Novel formation process of SiO2 film without thermal oxidazation
Achieved 10 times higher quality interface reducing the C-defects at the interface

3, Summary
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Summary Part 1
Interface-state candidate : Carbon defects near the SiC/SiO2
Performed DFT calculations for total 126 carbon defects distributed on SiO2-side, SiC-side,and just interface and clariﬁed the stability among them.
Carbon defects at just interface are energetically favorable.

Defect formation energy (eV)Found that the thermal oxidation inevitably induces interface defects

interface16

Summary Part 2
Novel formation process of SiO2 film without thermal oxidazation
10 times higher quality interface is achieved.
Point1: Not oxidize theSiC but only Si films.

Proposed
approach

Point2: N2 gas usedinstead of NO gas.
High quality interface

Si epi

Oxidization of Si.

N2-gas treatment

Appl. Phys. Express 13 091003 (2020).

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ご清聴ありがとうございました
Thank you for our attention

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