Highly Reliable SiC MOS Transistors Operated at

Highly Reliable SiC MOS Transistors Operated at High Temperatures
X.W. Wang, W.J. Zhu, X. Guo, and T.P. MA
Department of Electrical Engineering, Yale University
A Major Problem of State-of-the-art
SiC MOSFETs at High Temperatures:
Very Short Operating Lifetimes.
C-V and Ig – Vg
Fabrication of SiC MOSFET
Source
Drain
Gate
100
3
10
2
10
1
10
0
10
-1
10
-2
10
-3
10
-4
10
-5
10
-6
10
-7
10
-8
10
-9
10
90
LPCVD SiO2
Conventional ONO
5
7
45 min
9
7
75 hour
11.4
6.4
Our Approach Has Resulted in
Extrapolated Lifetime of 280 Years
Lifetime (sec)
10
n+
n+
60
50
40
30
P
10
Meas. Freq: 10KHz
0
Temp: 450 C
10
-2
NOT: 5 X 10 cm
0
-12
-10
-8
-6
-4
-2
0
2
4
P+ 6H-SiC
JVD
O
N
O
12
10
9
6H-SiC, RCA Cleaning
100
10
6
In-situ, Sequential Deposition
of O-N-O Layers, Room Temp.
3
10
0
Anneal: 900 C, N2, 30 min
o
+ 950 C, WV, 30min
o
Stressed at 450 C
E ox=(Vg-Vth)/dox
0
1
16
NA-ND=3x10 /cm
2
3
4
5
6
7
Dielectric Field (MV/cm)
Key to success: Dielectric and Interface Engineering
5
Source of O
N2
SiH4
He
S. of N
S. of Si
Carrier
80
8
9
10
11
12
13
Low gate current and high
breakdown field contribute
to the excellent reliability.
VG-VT=8V
6V
40
4V
20
2V
20
4V
0
2V
0V
0V
0
0
2
4
6
8
10
14
(a)
60
6V
40
Vd (V)
Research done in collaboration with
Jesse Tucker and Mulpuri Rao of George Mason University
Research supported by ONR
7
NA-ND=3x1016/cm3
@ Room T
o
0
(b)
Id-Vd Characteeristics at 450 C
Key considerations:
1. N2O Treated SiC Surface
2. Room-temp Deposition of SiO2.
3. High-Quality Si3N4 Layer
6
nMISFET on 6H-SiC
W/L=250µm/200µm
VG -VT=8V
3
Id (µA)
N2O
Load to Furnace
10 years
o
10
4
100
nMISFET on 6H-SiC
W/L=250µm/200µm
80
60
SiC Surface Pre-cleaned
by N2O / He Plasma
280 years
o
450 C
Dielectric Field E(MV/cm)
@ 450 C
dox(equi.)=28nm
W/L=200µ/50µ
o
400 C
SiC MOSFET Id – Vd Curves
Load to Deposition Chamber
Gate Dielectric: JVD ONO
o
450 C
o
400 C
3
6
C-V characteristics indicate excellent
Gate dielectric and interface properties.
Formation of O-N-O Stack Gate Dielectric
18
15
JVD-ONO/6H-SiC (n-type)
Substrate Injection
Gate Voltage (V)
Id (µA)
10
70
20
10 nm
20 nm
10 nm
Source: Lipkin, IEEE Trans. on ED, Vol. 46, 1999
10
Ni
2
< 4.8 min
Al
Ni
Current Density J(A/cm )
Dry-Wet SiO2
Dielectric
80
Capacitance (pF)
SOA SiO2
Lifetime Breakdown Field (MV/cm))
o
o
(@ 350 C)
RT
350 C
JVD Field
Oxide
3.2-3.6
4.5-5
< 1.2 min
Al/JVD ONO/6H-SiC
2
4
6
Vd (V)
8
10
(a)
Id-Vd Characteeristics at R.T.
Conclusion:
By use of a novel gate dielectric, we have
demonstrated highly reliable & highly durable
SiC nMOSFETs operating at 450oC with over 4
orders of magnitude longer operating lifetimes
than the state-of-the-art.