silicon carbide department of electronics prof. dr. toomas rang [email protected] ehitajate...

Silicon CarbideSilicon Carbide

Department of ElectronicsDepartment of Electronicshttp://www.ttu.ee/elektronhttp://www.ttu.ee/elektron

Prof. Dr. Toomas RangProf. Dr. Toomas [email protected]@edu.ttu.ee

AddressAddressEhitajate tee 5Ehitajate tee 5

19086 Tallinn19086 TallinnESTONIAESTONIAPhone:Phone: +372 6 202 150+372 6 202 150Fax:Fax: +372 6 202 151+372 6 202 151

Silicon Carbide – trend to top?Silicon Carbide – trend to top?


The crystal growth quality road mapThe crystal growth quality road map

In 2005In 2005 3” wafers available3” wafers available with 0.2 micropipes/cmwith 0.2 micropipes/cm22

less than 50 dislocations/cmless than 50 dislocations/cm22


Electronic Energy processing has many parallels Electronic Energy processing has many parallels with information processingwith information processing

Both technologies have electromagnetics as a Both technologies have electromagnetics as a fundamental limitfundamental limit

Both technologies are eventually thermo-Both technologies are eventually thermo-mechanically limited (i.e. in terms of interface mechanically limited (i.e. in terms of interface reliability and loss density)reliability and loss density)

Both technologies are materials limitedBoth technologies are materials limited New applications for both are driven by a New applications for both are driven by a

relentless downward cost spiralrelentless downward cost spiral


6.5x106.5x1033 cm cm22 in hour in hour

World Wide is minimum profitable World Wide is minimum profitable production volume for semiconductor production volume for semiconductor

waferswafers

Reality today isReality today is SiSi 6.5x106.5x1066 cm cm22 in hour in hour SiCSiC 6.5x106.5x1022 cm cm22 in hour (military) in hour (military) SiCSiC 6.5x106.5x1011 cm cm22 in hour (others) in hour (others)


Must we Must we nevertheless nevertheless continue with continue with Silicon?Silicon?


PropertyProperty SiSi GaAsGaAs 3C-SiC3C-SiC 6H-SiC6H-SiC 4H-SiC4H-SiC DiamondDiamond

Melting point [C]Melting point [C] 14201420 12381238 28302830 28302830 28302830 40004000

Thermal conductivity Thermal conductivity [W/cmK][W/cmK]

1.51.5 0.460.46 55 4.94.9 4.94.9 2020

Bandgap [eV]Bandgap [eV] 1.11.1 1.431.43 2.392.39 3.023.02 3.263.26 5.455.45

Electron mobility Electron mobility [cm[cm22/Vs]/Vs]

15001500 85008500 10001000 370370 10001000 22002200

Hole mobility [cmHole mobility [cm22/Vs]/Vs] 600600 400400 5050 9090 5050 16001600

Saturation electron Saturation electron drift velocity [x10drift velocity [x1077cm/s]cm/s]

11 11 2.22.2 22 22 2.72.7

Breakdown field [x10Breakdown field [x1055 V/cm]V/cm]

33 66 -- 2020 3030 100100

Dielectric constantDielectric constant 11.811.8 12.512.5 9.79.7 9.79.7 9.79.7 5.55.5


Figures of meritFigures of merit

KFMKFM – Key’s – Key’s Figure of Merit (IC Figure of Merit (IC Applications)Applications)

KFJKFJ – Johnson’s – Johnson’s Figure of Merit Figure of Merit (High Power (High Power Applications)Applications)

KFMKFM KFJKFJ

SiSi 11 11

SiCSiC 6.56.5 281281


The major demands for metal layers areThe major demands for metal layers are Low resistivity for Ohmic, or low leakage currents for Schottky Low resistivity for Ohmic, or low leakage currents for Schottky

contactscontacts Easy to formEasy to form Easy to etch for pattern generation (e.g. microelectronics Easy to etch for pattern generation (e.g. microelectronics

approach)approach) Stable in oxidizing ambient; (e.g. microelectronics approach)Stable in oxidizing ambient; (e.g. microelectronics approach) Mechanical stability - good adherence, low stress;Mechanical stability - good adherence, low stress; Surface smoothnessSurface smoothness Stability throughout processingStability throughout processing Generally no reaction with other metalsGenerally no reaction with other metals Should not contaminate devices, wafers, or working apparatus;Should not contaminate devices, wafers, or working apparatus; Long lifetimesLong lifetimes Low electromigrationLow electromigration


BondingBonding process has the following important advantageous process has the following important advantageous one-step high temperature process for one-step high temperature process for

manufacturing multi-layer contacts (manufacturing multi-layer contacts (low energy low energy processprocess););

extra high adhesion between layers to be joined;extra high adhesion between layers to be joined; minimum number of inhomogeneities on large minimum number of inhomogeneities on large

area (area (near defect free contactsnear defect free contacts);); improves significantly the certain electrical improves significantly the certain electrical

characteristics of manufactured semiconductor characteristics of manufactured semiconductor devices compared to other technologies devices compared to other technologies


Cline’s initial proposal of two-stage mechanism Cline’s initial proposal of two-stage mechanism describes the Diffusion Welding (DW)describes the Diffusion Welding (DW)

The applied load causes The applied load causes plastic deformationplastic deformation of of the surface asperities thereby reducing the surface asperities thereby reducing interfacial voids.interfacial voids.

Bond development continues by Bond development continues by diffusion diffusion controlledcontrolled mechanism including grain boundary mechanism including grain boundary diffusion and power law creep diffusion and power law creep

Generally the surface should be prepared better Generally the surface should be prepared better than 0.4 than 0.4 mm


Materials to be Materials to be bondedbonded

Direct BondingDirect Bonding Interlayer Interlayer

neededneeded Not examinedNot examined


InterlayersInterlayers Generally these layers are needed to join the Generally these layers are needed to join the

incompatible materialsincompatible materials, for example aluminum and , for example aluminum and steel.steel.

Another use of compliant interlayer is to accommodate Another use of compliant interlayer is to accommodate mismatch strainsmismatch strains generated when bonding materials generated when bonding materials have widely different thermal expansion coefficient. have widely different thermal expansion coefficient. This is important in This is important in joining ceramics to metalsjoining ceramics to metals where a where a five to ten fold difference in thermal expansion five to ten fold difference in thermal expansion coefficients is not usual.coefficients is not usual.

A reason to A reason to reduce bonding temperaturereduce bonding temperature and time. and time.


Adhesion testAdhesion test

Temp Temp [[00C]C]

Pressure Pressure [MPa][MPa]

Bond Bond qualityquality

500500 20-5020-50 NoneNone

550550 20-5020-50 BadBad

600600 2020 BadBad

600600 3030 Very GoodVery Good

600600 5050 ExcellentExcellent


Cristal Defects (comet tails, micropipes)Cristal Defects (comet tails, micropipes)


Screw and Edge Defects at the SiC Si-face surfaceScrew and Edge Defects at the SiC Si-face surface


4H-SiC wafer upper surface4H-SiC wafer upper surface


Structure and examplesStructure and examples

Al

(ND - NA) 8.51018 cm-3 4H-SiC

Al

(ND - NA) 21017 cm-3 4H-SiC

W

4H-SiC

W Al

5 m 50 m

1.2 mm

350 m

50 m


U-I characteristicsU-I characteristics

VA characteristics 4H-SiC Schottky

-1

-0,5

0

0,5

1

1,5

2

2,5

3

-32 -22 -12 -2

U[V]

I[A

]

20C

50C

100C

200C

300C

400C

500C

600C

Temperature influence Al-4H-SiC Schottky forward

0,0001

0,001

0,01

0,1

1

10

0 1 2 3 4

U [V]

I [A

]

20C

50C

100C

200C

300C

400C

500C

600C

Silicon CarbideSilicon Carbide Forward voltage Forward voltage

drop:drop: (a) (a) nn00-n-n--– 4H-SiC– 4H-SiC

((NNdd ~ 1x1015 cm ~ 1x1015 cm–3–3))

(b) p(b) p00-6H-SiC-6H-SiC

((NNaa ~ 5x1015 ~ 5x1015 cmcm–3–3))

0

1

2

3

4

5

6

7

8

9

10

0 200 400 600

t(C)

U(V

)

0,33(A/cm2)

0,66(A/cm2)

1 (A/cm2)

1,33(A/cm2)

1,66(A/cm2)

3,33(A/cm2)

6,66(A/cm2)

16,6(A/cm2)

33,3(A/cm2)

50(A/cm2)

66,6(A/cm2)

83,3(A/cm2)

100(A/cm2)

0

2

4

6

8

10

12

14

16

18

20

0 200 400 600

t(C)

U(V

)

0,44(A/cm2)

0,88(A/cm2)

1,33(A/cm2)

1,77(A/cm2)

2,22(A/cm2)

4,44(A/cm2)

8,88(A/cm2)

22,2(A/cm2)

44,4(A/cm2)

66,6(A/cm2)

88,8(A/cm2)

111,1(A/cm2)

133,3(A/cm2)


SEM Picture (made in Furtwangen)SEM Picture (made in Furtwangen)


Inhomogeneities at the SIC surfaceInhomogeneities at the SIC surface

Bn2

Bn1

Bn3

Bn4


Schematic barrier height pictureSchematic barrier height picture


Current distribution at Pt-Au-Pt 6H-SiC interfaceCurrent distribution at Pt-Au-Pt 6H-SiC interface

1 5 9 13 17 21 25 2912

1

0.00E+00

2.00E+02

4.00E+02

6.00E+02

8.00E+02

1.00E+03

1.20E+03

1.40E+03

1.60E+03

1.80E+03

Cu

rren

t d

ensi

ty [

A/c

m^

2]

horizontal slices

vertical slices


Temperature distribution in Pt-Au-Pt 6H-SiC interfaceTemperature distribution in Pt-Au-Pt 6H-SiC interface

1 3 5 7 9

11 13

15

17

19

21

23

25

27

29

12

6

160.9

161

161.1

161.2

161.3

161.4

161.5

T[°K]

horizontal slices

vertical slices


Schottky interface:Schottky interface:

J = q(nJ = q(nmm - n - n00)) vvRR

nn00 = = NNCC exp[-( exp[-(q q BnBn//k Tk T)])]

nnmm = = NNCC exp[-{ exp[-{q q ((xxmm) + ) + q q BnBn}/}/k Tk T]]

Nnpq

x

02

2

xpq

x

pDqJ ppp

xnq

x

nDqJ nnn

t

pGRq

x

J p

t

nGRq

x

Jn

txJJJ pn

2

0


What will come next?What will come next?

silicon carbide department of electronics prof. dr. toomas rang [email protected] ehitajate...

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