Compact Power Supplies Based on Heterojunction Switching in Wide Band Gap Semiconductors
NC STATE UNIVERSITY UCSB
Effects of surface oxide on wafer bonding of GaN and SiC
Jaeseob Lee, Robert F. Davis, and Robert J. NemanichNorth Carolina State University
Raleigh, NC 27695-8202 USA
February 12, 2002
Compact Power Supplies Based on Heterojunction Switching in Wide Band Gap Semiconductors
NC STATE UNIVERSITY UCSB
Outline
Motivation
- GaN/SiC HBT
Introduction
- Wafer Bonding of GaN/SiC
Experiment
Results
- AES of GaN,SiC- AFM of GaN/SiC- I-V of GaN/SiC
Discussion
Compact Power Supplies Based on Heterojunction Switching in Wide Band Gap Semiconductors
NC STATE UNIVERSITY UCSB
Advantage of GaN-SiC Device; high temperature, high power, high frequency operation
Larger bandgap emitter-restrict the diffusion of hole from base to emitter → high electron injection efficiency-heavily doped base → low base resistanceIndirect bandgap base-longer carrier lifetime(longer diffusion length)→ high base transportShort base width
higher Emitter efficiency Larger current gain
Al Emitter Contact
n-GaN Emitter Al/Cr Base Contact
p-SiC Base
n-SiC Collector
Al/Cr Collector Contact
GaN/SiC HBT proposed by J. Pankove, S.S. Chang, H.C. Lee, R.J. Moustakas, B. Van Zeghbroeck (Int. Electron Devices Meet Tech. Dig. ’94)
GaN/SiC HBT
Compact Power Supplies Based on Heterojunction Switching in Wide Band Gap Semiconductors
NC STATE UNIVERSITY UCSB
Direct GrowthNucleation ProblemDefect due to large mismatch
Buffer Layer(AlN) GrowthBuffer Layer acts as a insulator
Waferbonding Reduce defect formation at interface No insulating buffer layer between GaN and SiC
SiC
GaN
SiC
GaNAlN
SiC
GaN
GaN/SiC WB
Compact Power Supplies Based on Heterojunction Switching in Wide Band Gap Semiconductors
NC STATE UNIVERSITY UCSB
Electronegativity valuesElement Electronegativity
N 3.0C 2.5Si 1.8Ga 1.6
Bond and ionic characterBond Difference in
ElectronegativityIonic
CharacterN-Ga 1.4 39%N-Si 1.2 30%C-Ga 0.9 19%C-Si 0.7 12%N-C 0.5 7%
Si-Ga 0.2 1%
Si
C
Ga
N
Si–N
Si–GaC–N
C–Ga
Schematic [1120] projection of the GaN/SiC interface
GaN/SiC WB
Compact Power Supplies Based on Heterojunction Switching in Wide Band Gap Semiconductors
NC STATE UNIVERSITY UCSB
Dicing into 12.8×6.5 mm2 piecesDegreasing, HF(SiC)/HCl(GaN) dipN2 blow dry
Processing Flow Chart
Characterization(I-V)
Ex situ Cleaning
Ex situ Bonding
In situ Annealing
Characterization(AFM,AES)
600, 800, 1000oC, 1hr
Compact Power Supplies Based on Heterojunction Switching in Wide Band Gap Semiconductors
NC STATE UNIVERSITY UCSB
GaN
SiC
AFM of GaN/SiC
RMS roughness 20 ± 5 Å in 20×20 µm2 area of GaN and SiC
Compact Power Supplies Based on Heterojunction Switching in Wide Band Gap Semiconductors
NC STATE UNIVERSITY UCSB
0 200 400 600 800 1000 1200-200
0
200
HCl dip 10min(0001)Ga
GaN
dN(E
)/dE
electron energy, eV
Surface atomic concentration: Cl 0%, C 71%, N 33 8%, O 2 1%, Ga 57 9%
AES of GaN
Compact Power Supplies Based on Heterojunction Switching in Wide Band Gap Semiconductors
NC STATE UNIVERSITY UCSB
0
50
100
HF(10:1) 10min
HF(100:1) 1min
O
Si
C
Sur
face
ato
mic
co
ncen
trat
ion(
%)
0 100 200 300 400 500 600
HF(10:1) 10min
HF(100:1) 1min
SC1, SC2,6H(0001)Si
n-SiC
dN(E
)/dE
electron energy, eV
Surface atomic concentration: Si 26 4%, C 20 4%, O 54 4% after HF(100:1) 1min dip Si 21 3%, C 73 13%, O 7 1% after HF( 10:1) 10min dip
AES of (0001)Si SiC
Compact Power Supplies Based on Heterojunction Switching in Wide Band Gap Semiconductors
NC STATE UNIVERSITY UCSB
-5.0 -2.5 0.0 2.5 5.0-100
-50
0
50
100
HF(100:1) 1min
HF(10:1) 10min
I(m
A)
V(V)HF( 10:1) 10min dipped SiC to GaN pair shows more ohmic behavior
IV of GaN/SiC(n-type to n-type)
Ti
Ti
n-SiCn-SiC
Compact Power Supplies Based on Heterojunction Switching in Wide Band Gap Semiconductors
NC STATE UNIVERSITY UCSB
Bonding process to 2H (0001)Ga GaN
6H SiC surface
HF HF dip
(min)
Annealing Temp(oC)
Annealing Time(min)
Heating rate(oC/min)
Bonding
Results
Trials
(0001)Si 100:1 1 1000,800 240,60 10 No(1 partial bonding)
11
10 1000,800 240,60 5 No 2
60 1000,800 60 5 Yes 2
10:1 10 1000,800 60 5 Yes 2
600 60 5 No 1
(000-1)C 100:1 1 1000 240,30 5 Yes 5
10:1 10 1000 240,60 5 Yes 2
800 60 5 Yes 1
600 60 5 No 1
Bonding result
Compact Power Supplies Based on Heterojunction Switching in Wide Band Gap Semiconductors
NC STATE UNIVERSITY UCSB
0 20 40 60 80 100 120 140 1600
10
20
30
40
50
60
70
80
90
100
C
Si
O
6H(0001)Si n-SiC
Sur
face
ato
mic
con
cent
ratio
n(%
)
HF(100:1) dip time(min)
0 20 40 60 80 100 120 140 1600
10
20
30
40
50
60
70
80
90
100
C
Si
O
6H(000-1)C n-SiC
Sur
face
ato
mic
con
cent
ratio
n(%
)
HF(100:1) dip time(min)
Surface Conc. of SiC
Surface atomic concentration: SiC (0001)Si ; Si 274%, C 15 3%, O 575% after 1min dip Si 214%, C 7614%, O 31% after 60min dipSiC (000-1)C ; Si 234%, C 7313%, O 41% after 1min dip
Si 214%, C 7614%, O 31% after 60min dip
HF(100:1) dip of (0001)Si/(000-1)C 6HSiC
Compact Power Supplies Based on Heterojunction Switching in Wide Band Gap Semiconductors
NC STATE UNIVERSITY UCSB
6.5 mm
12.8 mm
406 µm pSiC 3.5E18
1 µm GaN <1E170.1 µm AlN Conductive260 µm nSiC 4~6E18
Ti
Pt or Ti
1 mm
1 mm
p-6H SiC(0001)Si ;Degreasing, HF(10:1) 10min dip
2H GaN(0001)Ga ;Degreasing, HCl 1min dip
600oC, 800oC, 1000oC 1hr annealing for WB
WB of GaN/SiC
Compact Power Supplies Based on Heterojunction Switching in Wide Band Gap Semiconductors
NC STATE UNIVERSITY UCSB
-5.0 -2.5 0.0 2.5 5.0-100
-50
0
50
100
Ti/p-SiC
Pt/p-SiC
Ti/n-SiC
I(m
A)
V(V)
IV of metal/SiC
Ohmic behavior of Metal/SiC
800oC,20min
Tin-SiC
Tin-SiC
Ptp-SiC
800oC 20min
MetalSiC
Metal/polished side
Metal/unpolished side Ohmic contact
Compact Power Supplies Based on Heterojunction Switching in Wide Band Gap Semiconductors
NC STATE UNIVERSITY UCSB
(0001)C SiC/(0001)Ga GaN pair shows low resistance than(000-1)Si SiC/(0001)Ga GaN pair
IV of GaN/SiC(n-type to n-type)
-5.0 -2.5 0.0 2.5 5.0-100
-50
0
50
100
Si-Ga
C-Ga
I(m
A)
V(V)
(0001)Si, (000-1)C SiC; HF(10:1) 10min dip(0001)Ga GAN; HCl 1min dip
Ti
Ti
n-SiCn-SiC
Compact Power Supplies Based on Heterojunction Switching in Wide Band Gap Semiconductors
NC STATE UNIVERSITY UCSB
IV of GaN/SiC(n-type to p-type)
-5.0 -2.5 0.0 2.5 5.0-100
-50
0
50
100
Si-Ga
C-Ga
I(m
A)
V(V)
(0001)C SiC/(0001)Ga GaN pair and (000-1)Si SiC/(0001)Ga GaN pair show rectifying behavior
1000ºC 1hr in-situ annealing Ti
Pt
n-SiCp-SiC
Ti
Ti
n-SiCp-SiC
Compact Power Supplies Based on Heterojunction Switching in Wide Band Gap Semiconductors
NC STATE UNIVERSITY UCSB
IV of GaN/SiC(n-type to p-type)
-5.0 -2.5 0.0 2.5 5.0-100
-50
0
50
100
Si-Ga
C-Ga
I(m
A)
V(V)
(0001)C SiC/(0001)Ga GaN pair shows rectifying behavior But (000-1)Si SiC/(0001)Ga GaN pair shows ohmic behavior
800ºC 1hr in-situ annealing Ti
Pt
n-SiCp-SiC
Ti
Ti
n-SiCp-SiC
Compact Power Supplies Based on Heterojunction Switching in Wide Band Gap Semiconductors
NC STATE UNIVERSITY UCSB
IV of GaN/SiC(n-type to p-type)
(0001)C SiC/(0001)Ga GaN pair shows rectifying behavior But (000-1)Si SiC/(0001)Ga GaN pair shows ohmic behavior
800ºC 1hr in-situ annealing
-20 -10 0 10 20-100
-50
0
50
100
Si-Ga
C-Ga
I(m
A)
V(V)
Ti
Pt
n-SiCp-SiC
Ti
Ti
n-SiCp-SiC
Compact Power Supplies Based on Heterojunction Switching in Wide Band Gap Semiconductors
NC STATE UNIVERSITY UCSB
(0001)C SiC/(0001)Ga GaN pair and (000-1)Si SiC/(0001)Ga GaN pair do not bond at 600ºC 1hr in-situ annealing
600ºC 1hr in-situ annealing
5mm
(a) (0001)Si SiC/(0001)GaGaN (b) (000-1)C SiC/(0001)GaGaN
5mm
IR image of GaN/SiC
Compact Power Supplies Based on Heterojunction Switching in Wide Band Gap Semiconductors
NC STATE UNIVERSITY UCSB
Conclusion
Polarity is important factor in WB of SiC/GaN
(000-1)C n-SiC/(0001)Ga n-GaN pair has the low resistance (nearly Ohmic)
(000-1)C p-SiC/(0001)Ga n-GaN pair keep good rectifying behavior at lower bonding temperature(800oC)
No bonding happened at 600oC with wafer surface having RMS roughness 20Å in 20×20 µm2.
Compact Power Supplies Based on Heterojunction Switching in Wide Band Gap Semiconductors
NC STATE UNIVERSITY UCSB
Future Research
Characterize the bonded interface with FiB-TEM
Bond patterned GaN structures appropriate for HBT
Explore improved polishing of SiC and GaN surface to get low T bonding
Compact Power Supplies Based on Heterojunction Switching in Wide Band Gap Semiconductors
NC STATE UNIVERSITY UCSB
Fabrication of HBT
Substrate ; 300µm nSiC 4~6E18
Epi 1 ; 12.0µm nSiC 6.9E15
Epi 2 ; 0.2 µm pSiC 3.5E18
Substrate ; 260µm nSiC 4~6E18
0.1µm AlN cunductive1 µm nGaN 4~6E18
From Dr. Davis group
From Cree Research Inc.
2in
Compact Power Supplies Based on Heterojunction Switching in Wide Band Gap Semiconductors
NC STATE UNIVERSITY UCSB
After bonding & Polishing
6.5 mm
6.5 mm
0.2 μm pSiC 3.5E18
12 μm nSiC 6.9E15
substrate nSiC 4~6E18
1 μm nGaN 4~6E180.1 μm AlN Conductive1 μm nSiC 4~6E18
2 μm
300 μm
Polishing SiC substrate; 260µm to 50 µm BondingPolishing SiC substrate: 50 µm to 2 µm
by Diamond lapping film
GaN on Si wafer is easy for layer transfer
Compact Power Supplies Based on Heterojunction Switching in Wide Band Gap Semiconductors
NC STATE UNIVERSITY UCSB
0.2 μm pSiC 3.5E18
12 μm nSiC 6.9E15
substrate nSiC 4~6E18
0.5 μm nGaN 4~6E18
Al Al/Cr
Al/Cr
RIE/metallizing Plan
SF6 500Å/min SiC20min for 1μm
Cl2/Ar 4000Å/min GaN2.5min for 1μm
Al deposition Al/Cr deposition
RIE RIE
By Parallel-plate RIE