ISDRS 2007, December 12-14, 2007, College Park, MD, USA
Zhi Chen, Pangleen Ong, and Chandan B. Samantaray
Department of Electrical & Computer Engineering, University of Kentucky, Lexington, KY, USA, Email: zhichen@engr.uky.edu.
Since discovery of RTP-induced phonon-energy-coupling enhancement (PECE) effect for reducing leakage current of SiO
2
and HfSiON [1-4], many people have been suspecting its authenticity. This is because there are many puzzling issues regarding the PECE effect. For example, in our early publications [1-4] we did not present both the I-V and C-V curves of the same sample. Also, the mechanism for generation of the PECE effect was not clear at that time.
In this abstract, we will present, for the first time, a TEM image of a RTP-processed SiO
2
sample to confirm the authenticity of the PECE effect. We will show the key factor that generates the
PECE effect and study the leakage current reduction of HfSiON.
Fig. 1a shows I-V curves of SiO
2
samples before and after RTP, where there are 3 orders of magnitude leakage current reduction. The TEM image in Fig. 1b demonstrates that the leakage current reduction is not due to the oxide thickness increase. All these results suggest that the observed leakage current reduction is true and reproducible. Fig. 2 shows that a little amount of oxygen is the key factor for leakage reduction. Thin oxide processed in RTP in pure N
2
or He exhibits very high leakage current. After introducing a little amount of O
2
, leakage current is reduced by 100 times. RTP not only creates necessary structure change for the PECE effect but also meanwhile generates defects for high leakage current. The O
2
is necessary for repairing the defects.
This repairing also causes slight regrowth of oxide (1-
2Å). Once this thin repairing layer (1-2Å) is lost, the
PECE effect disappears.
Any chemicals attacking oxide may cause losing of the PECE effect. Therefore, even if one accidentally generates this effect, it may be lost in the followed fabrication processes.
The PECE effect is caused by phonon energy
10
-2
10
-3
10
-4
10
-5
10
-6
10
-7
10
-8
(a)
Control T ox
=2.4nm
RTP T ox
=2.5nm
10
-9 ~1100 C 45s
0 0.2
0.4
0.6
0.8
1 1.2
Voltage (V)
10
3
X
(b)
Si
2.5 nm
Oxide
Figure 1 (a) Gate leakage current of control SiO
2
on n-type Si without
RTP treatment and that with RTP-induced PECE effect. The V
FB
is 0 V for the Al/SiO
2
/n-Si MOS capacitors. (b) Cross sectional TEM of the same RTP-processed sample shown in (a). TEM was carried out by M. J.
Kim and R. M. Wallace of Univ. of Texas at Dallas. coupling from Si-O bonds to Si-Si bonds. Therefore, as long as there are Si-O bonds in an insulator on a Si substrate, the PECE effect should occur. For Hf/(Hf+Si)=50%, the leakage current reduction is 1.5 orders of magnitude (See Fig. 3). When Hf/(Hf+Si) is increased to 65%, the leakage current reduction is reduced to 1 order of magnitude (See Fig. 4). The results in Fig. 1 can be considered as Hf/(Hf+Si)=0%. Using these results, we can construct a curve, orders of magnitude reduction vs. Si/(Si+Hf) or concentration of Si-O bonds, as shown in Fig. 5. It is amazing that we obtained a linear relation. The straight line also passes the origin, which represents HfO
2
. This clearly suggests that the leakage reduction correlates with concentration of
Si-O bonds. Fig. 6 shows the leakage current of HfSiON with EOT of 1nm after the PECE effect is added. The optimum Hf concentration is ~50-60%. Fig. 7 shows the scalability of HfSiON and
SiON with the PECE effect applied. HfSiON’s EOT can be scaled down to below 3Å .
This work was supported by National Science Foundation (EPS- 0447479).
References
[1] Z. Chen et al., Proc. ISDRS 2005, pp. 240-241.
[2] Z. Chen et al., Appl. Phys. Lett. 88, 082905 (2006).
[3] Z. Chen and J. Guo, Solid-State Electronics, vol. 50, 1004–1011 (2006).
ISDRS 2007 – http://www.ece.umd.edu/ISDRS

ISDRS 2007, December 12-14, 2007, College Park, MD, USA
[4] C. B. Samantaray and Z. Chen, Appl. Phys. Lett., vol. 89, 162903 (2006).
[5] E. P. Gusev et al., IEDM Tech. Dig., 451 (2001).
[6] K. Sekine et al., IEDM Tech. Dig.,103 (2003).
[7] M. Koike et al., IEDM Tech. Dig.,107 (2003).
[8] M. Koyama et al., IEDM Tech. Dig., 849 (2002).
[9] W. Tsai et al., IEDM Tech Dig., 311 (2003).
10
1 High Leakage
10
-1
10
-1
RTP 1040C in pure He
10
-2
HfSiON with Hf/(Hf+Si)=50%
T phys
=3nm; EOT=1nm
Control
10
-3
10
1.5
X
Control
10
-3
X100
10
-4
10
-5
10
-7
RTP 1040C 0.42%O
2 in He (Repairing in O
2
)
0 0.2
0.4
0.6
0.8
1 1.2
10
-5
RTP 1050C 60s
10
-6
-1.2
-1 -0.8 -0.6 -0.4 -0.2
0
Voltage (V)
Figure 2 RTP treatment of SiO
2
(2.2 nm) in pure
He leads to high leakage current while RTP treatment in He with 0.42% O
2
leads to reduced leakage current. T ox
is 2.3nm after RTP.
10
1
10
0
HfSiON with Hf/(Hf+Si)=65%
(a)
10X
(b)
10
-1
10
-2
(a) Control
(c)
(b) RTP 900C
10
-3 (c) RTP 1000C
(d)
(d) RTP 1100C
10
-4
T phys
=3.7nm; EOT=1.2nm
10
-5
-2.5
-2 -1.5
-1 -0.5
0
Fig. 3 Gate leakage current of HfSiON with
Hf/(Hf+Si)=50% which is reduced by 1.5 orders of magnitude, after RTP.
3.5
100
3
2.5
2
1.5
1
0.5
Vg (V)
Hf/(Hf+Si) Ratio (%)
80 60 40 20 0
0
0 20 40 60 80 100 120
Vg (V)
Fig. 4 Gate leakage current of HfSiON with
Si/(Hf+Si) Ratio (%)
Fig. 5 Orders of magnitude reduction vs Si concentration. It is amazing that it is linearly
Hf/(Hf+Si)=65% which is reduced by 1 orders of magnitude after RTP. related to concentration of Si-O bonds. This is an evidence of PECE effect.
1000
100
10
1
0.1
0.01
10
3
X
Jg@EOT=1nm w/o PECE
Jg@EOT=1nm w/ PECE
10
2
X
10X
0.001
-20 0 20 40 60 80 100 120
Hf/(Hf+Si) (%)
Fig. 6 Leakage current of HfSiON vs Hf concentration for EOT= 1nm. Data (w/o
PECE) are from Fig. 14 for 0%, Koyama et al.
[8] for 20%-40%, Seikine et al. [6] for 50%,
Koike et al. [7] for 60% & 80%, and Tsai et al
[9] for 100%..
10
3
10
1
10
-1
SiON (ITRS)
10
-3
10
-5
10
-7
10
-9
0
HfSiON (Sekine et al.)
HfO2 (Gusev et al.)
SiO2-RTP -This Work
SiON-RTP -This Work
HfSiON(Koike et al.)
HfSiON (Control)-This Work
HfSiON (RTP)-This Work
5 10 15
EOT(Angstrom)
20
Fig. 7 Gate leakage current vs EOT for various oxides and high-k oxides. With help of the
PECE effect, high-k oxides can be scaled down to <0.3 Å. Some data are from ITRS, Sekine et al. [6], Gusev et al. [5], and Koike et al. [7].
ISDRS 2007 – http://www.ece.umd.edu/ISDRS