Transcript Silicon Carbide

Silicon Carbide
Department of Electronics
http://www.ttu.ee/elektron
Prof. Dr. Toomas Rang
[email protected]
Address
Ehitajate tee 5
19086 Tallinn
ESTONIA
Phone:
+372 6 202 150
Fax:
+372 6 202 151
Silicon Carbide – trend to top?
Silicon Carbide
The crystal growth quality road map
In 2005
 3” wafers available
 with 0.2 micropipes/cm2
 less than 50 dislocations/cm2
Silicon Carbide
Electronic Energy processing has many parallels
with information processing
 Both technologies have electromagnetics as a
fundamental limit
 Both technologies are eventually thermomechanically limited (i.e. in terms of interface
reliability and loss density)
 Both technologies are materials limited
 New applications for both are driven by a
relentless downward cost spiral
Silicon Carbide
Silicon Carbide
6.5x103 cm2 in hour
World Wide is minimum profitable production
volume for semiconductor wafers
Reality today is
 Si
6.5x106 cm2 in hour
 SiC
6.5x102 cm2 in hour (military)
 SiC
6.5x101 cm2 in hour (others)
Silicon Carbide
 Must
we
nevertheless
continue with
Silicon?
Silicon Carbide
Property
Si
GaAs
3C-SiC
6H-SiC
1420
1238
2830
2830
2830
4000
Thermal conductivity
[W/cmK]
1.5
0.46
5
4.9
4.9
20
Bandgap [eV]
1.1
1.43
2.39
3.02
3.26
5.45
1500
8500
1000
370
1000
2200
Hole mobility [cm2/Vs]
600
400
50
90
50
1600
Saturation electron drift
velocity [x107cm/s]
1
1
2.2
2
2
2.7
Breakdown field [x105
V/cm]
3
6
-
20
30
100
11.8
12.5
9.7
9.7
9.7
5.5
Melting point [C]
Electron mobility
[cm2/Vs]
Dielectric constant
4H-SiC Diamond
Silicon Carbide
Silicon Carbide

Figures of merit

KFM – Key’s
Figure of Merit (IC
Applications)

KFJ – Johnson’s
Figure of Merit
(High Power
Applications)
KFM
KFJ
Si
1
1
SiC
6.5
281
Silicon Carbide
The major demands for metal layers are











Low resistivity for Ohmic, or low leakage currents for Schottky
contacts
Easy to form
Easy to etch for pattern generation (e.g. microelectronics
approach)
Stable in oxidizing ambient; (e.g. microelectronics approach)
Mechanical stability - good adherence, low stress;
Surface smoothness
Stability throughout processing
Generally no reaction with other metals
Should not contaminate devices, wafers, or working apparatus;
Long lifetimes
Low electromigration
Silicon Carbide
Bonding process has the following important advantageous




one-step high temperature process for
manufacturing multi-layer contacts (low energy
process);
extra high adhesion between layers to be joined;
minimum number of inhomogeneities on large
area (near defect free contacts);
improves significantly the certain electrical
characteristics of manufactured semiconductor
devices compared to other technologies
Silicon Carbide
Cline’s initial proposal of two-stage mechanism
describes the Diffusion Welding (DW)
 The applied load causes plastic deformation of
the surface asperities thereby reducing
interfacial voids.
 Bond development continues by diffusion
controlled mechanism including grain boundary
diffusion and power law creep
Generally the surface should be prepared better
than 0.4 m
Silicon Carbide
Materials to be
bonded



Direct Bonding
Interlayer
needed
Not examined
Silicon Carbide
Interlayers

Generally these layers are needed to join the
incompatible materials, for example aluminum and
steel.

Another use of compliant interlayer is to accommodate
mismatch strains generated when bonding materials
have widely different thermal expansion coefficient.
This is important in joining ceramics to metals where a
five to ten fold difference in thermal expansion
coefficients is not usual.

A reason to reduce bonding temperature and time.
Silicon Carbide
Silicon Carbide

Adhesion test
Temp [0C]
Pressure
[MPa]
Bond
quality
500
20-50
None
550
20-50
Bad
600
20
Bad
600
30
Very Good
600
50
Excellent
Silicon Carbide

Cristal Defects (comet tails, micropipes)
Silicon Carbide
Screw and Edge Defects at the SiC Si-face surface
Silicon Carbide
4H-SiC wafer upper surface
Silicon Carbide

Structure and examples
4H-SiC
Al
Al
(ND - NA) 21017 cm-3 4H-SiC
(ND - NA) 8.51018 cm-3 4H-SiC
50 m
5 m
350 m
Al
50 m
W
1.2 mm
W
Silicon Carbide

U-I characteristics
VA characteristics 4H-SiC Schottky
Temperature influence Al-4H-SiC Schottky forward
10
3
2,5
1
20C
2
50C
50C
100C
200C
1
300C
400C
0,5
100C
0,1
200C
I [A]
1,5
I[A]
20C
300C
0,01
400C
500C
0
600C
500C
0,001
600C
-0,5
0,0001
-1
-32
-22
-12
U[V]
-2
0
1
2
U [V]
3
4
Silicon Carbide

(Na ~ 5x1015
cm–3)
10
0,33
(A/cm2)
20
0,44
(A/cm2)
9
0,66
(A/cm2)
18
0,88
(A/cm2)
16
1,33
(A/cm2)
1 (A/cm2)
8
7
1,33
(A/cm2)
14
1,77
(A/cm2)
6
1,66
(A/cm2)
12
2,22
(A/cm2)
5
3,33
(A/cm2)
10
4,44
(A/cm2)
4
6,66
(A/cm2)
8
8,88
(A/cm2)
3
16,6
(A/cm2)
6
22,2
(A/cm2)
2
33,3
(A/cm2)
4
44,4
(A/cm2)
1
50
(A/cm2)
66,6
(A/cm2)
0
0
200 400 600
t(C)
83,3
(A/cm2)
100
(A/cm2)
U(V)

Forward voltage
drop:
(a) n0-n-– 4H-SiC
(Nd ~ 1x1015 cm–3)
(b) p0-6H-SiC
U(V)

66,6
(A/cm2)
2
88,8
(A/cm2)
0
0
200
400
t(C)
600
111,1
(A/cm2)
133,3
(A/cm2)
Silicon Carbide
SEM Picture (made in Furtwangen)
Silicon Carbide
Bn2
Bn1
Bn3
Bn4
Inhomogeneities at the SIC surface
Silicon Carbide
Schematic barrier height picture
Silicon Carbide
1.80E+03
1.60E+03
Current density [A/cm^2]
1.40E+03
1.20E+03
1.00E+03
8.00E+02
6.00E+02
4.00E+02
1
2.00E+02
vertical slices
0.00E+00
1
12
5
9
13
17
21
25
29
horizontal slices
Current distribution at Pt-Au-Pt 6H-SiC interface
Silicon Carbide
161.5
161.4
T [°K]
161.3
161.2
161.1
161
6 vertical slices
29
27
25
23
12
21
19
17
15
13
11
9
7
5
3
1
160.9
horizontal slices
Temperature distribution in Pt-Au-Pt 6H-SiC interface
Silicon Carbide
2 
q
p  n  N

2
 0
x
J p  q D p
p

 q p p
x
x
J n  q Dn
n

 q n n
x
x
Jp

 p


 q  R  G 
x
t 


 Jn
n

 q R  G 
x
t 

2 
J  Jn  J p   0
 x t
Schottky interface:
J = q(nm - n0) vR
n0 = NC exp[-(q Bn/k T)]
nm = NC exp[-{q (xm) + q Bn}/k T]
Silicon Carbide

What will come next?