Thermochemical reaction of ZrOx(Ny) interfaces on Ge and Si substrates

Article abstract of DOI:10.1063/1.2219347

We have studied the thermochemical characteristics of ZrO _x(N_y)/Ge and Si interfaces by employing postdeposition annealing. We found that Ge oxide species severely desorbed from the inherent interfacial layer, which was speculated to retard the formation of Zr germanate during high-temperature processing. These unique features enable ZrO _x(N_y)/Ge gate stack to show a better equivalent-oxide-thickness scalability as compared to ZrO_x(N _y)/Si gate stack. However, the volatilization of GeO _x-contained interfacial layer also caused the formation of small pits and/or holes in the overlying ZrO_x(N_y) gate dielectrics, which was expected to cause deterioration in the electrical properties of fabricated high-k/Ge devices.

Full text of DOI:10.1063/1.2219347

Thermochemical reaction of Zr O x ( N y ) interfaces on Ge and Si substrates
Chao-Ching Cheng, Chao-Hsin Chien, Je-Hung Lin, Chun-Yen Chang, Guang-Li Luo, Chun-Hui Yang, and Shih-
Lu Hsu
Citation: Applied Physics Letters 89, 012905 (2006); doi: 10.1063/1.2219347
View online: http://dx.doi.org/10.1063/1.2219347
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APPLIED PHYSICS LETTERS 89, 012905 ͑2006͒
Thermochemical reaction of ZrOx„Ny… interfaces on Ge and Si substrates
Chao-Ching Cheng
Institute of Electronics, National Chiao-Tung University, Hsinchu, Taiwan 300, Republic of China
Chao-Hsin Chiena͒
Institute of Electronics, National Chiao-Tung University, Hsinchu, Taiwan 300, Republic of China and
National Nano Device Laboratory, National Chiao-Tung University, Hsinchu, Taiwan 300, Republic of China
Je-Hung Lin and Chun-Yen Chang
Institute of Electronics, National Chiao-Tung University, Hsinchu, Taiwan 300, Republic of China
Guang-Li Luo, Chun-Hui Yang, and Shih-Lu Hsu
Nano Device Laboratory, National Chiao-Tung University, Hsinchu, Taiwan 300, Republic of China
͑Received 11 December 2005; accepted 2 June 2006; published online 6 July 2006͒
We have studied the thermochemical characteristics of ZrOx͑Ny͒/Ge and Si interfaces by employing
postdeposition annealing. We found that Ge oxide species severely desorbed from the inherent
interfacial layer, which was speculated to retard the formation of Zr germanate during
high-temperature processing. These unique features enable ZrOx͑Ny͒/Ge gate stack to show a better
equivalent-oxide-thickness scalability as compared to ZrOx͑Ny͒/Si gate stack. However, the
volatilization of GeOx-contained interfacial layer also caused the formation of small pits and/or
holes in the overlying ZrOx͑Ny͒ gate dielectrics, which was expected to cause deterioration in the
electrical properties of fabricated high-k/Ge devices. © 2006 American Institute of Physics.
͓DOI: 10.1063/1.2219347͔
There have been extensive studies on several promising
high-permittivity ͑high-k͒ candidates—including HfO2,1,2
ZrO2,3 and Al2O3 ͑Ref. 4͒—deposited on Ge because of the
application of its higher low-field carrier mobility; the admi-
rable capacitance properties and transistor performances
were continually demonstrated in recent years.5,6 However, it
seems essential to clarify what other advantages and/or dis-
advantages of Ge as a replacement of Si. For instance, the
thinner lower-permittivity interfacial layer ͑IL͒ was observed
in high-k/Ge system,7 which is beneficial in further scaling
the equivalent oxide thickness ͑EOT͒ below 1 nm. This find-
ing also implies that fundamental dissimilarities exist be-
tween the thermochemical properties of the Ge and Si; dis-
tinct thermal decomposition pathway of their oxides was
ever reported.8 To date, detailed material analysis of high-
k/Ge interfaces using x-ray photoelectron spectroscopy
͑XPS͒, however, remains quite rare. In the former studies,9,10
the authors confirmed that a substoichiometric Ge oxide
layer, in which the amount of Ge oxide was dependent upon
the ZrO2 overlayer thickness, did form at the ZrO2/Ge inter-
face. But, the influences of thermal instability of
GeOx-contained IL on the properties of the overlying high-k
dielectrics seem to be still insufficient. The purpose of this
work is to study thermal stability of high-k/Ge interface with
respect to high-k/Si interface through a comprehensive com-
parison of the photoemission spectra.
tween the IL and Zr high-k dielectrics on Ge and Si sub-
strates, we analyzed the effect of N2 postdeposition anneal-
ing ͑PDA͒ on the chemical configuration by ex situ XPS
using an Al K␣ source ͑1486.6 eV͒. We also employed sec-
ondary ion mass spectroscopy ͑SIMS͒, high-resolution trans-
mission electron microscopy ͑HRTEM͒, and atomic force
microscopy ͑AFM͒ to characterize the entire structures and
surface morphology, respectively.
Figure 1 shows the SIMS depth profiles of elements in
the ultrathin ZrOxNy film on the Si and Ge substrates. The
overall thicknesses of the as-deposited films were estimated
to be ca. 30 Å and ca. 35 Å, respectively. We found that the
nitrogen, which mainly accumulated at the interface, exhib-
ited peak concentrations of ca. 2.3ϫ1021 at./cc and ca. 5.3
ϫ1020 at./cc, corresponding to the maximum atomic per-
centages of ca. 3.8% and ca. 0.85% in the as-deposited
ZrOxNy film on Si and Ge substrates, respectively. Lower
nitrogen level in ZrOxNy /Ge system can be reasonably at-
tributed to the fact that Ge is more easily oxidized than
nitrided.11 With 600 °C annealing, most of the nitrogen con-
tent was lost in Ge case, which may be perhaps due to the
lower thermal stability of Ge–N bonds.12 Also, it can be ob-
served that such a high temperature can significantly push
the Ge into the ZrOxNy film bulk; the outdiffusion mecha-
nism and the chemical states of incorporated Ge atoms will
be discussed in further detail below.
Two different high-k thin films were deposited on the
bare Ge and Si wafers by reactive sputtering chamber, which
are precleaned by cyclic rinse of diluted HF dip and de-
ionized water; ZrO2 was deposited in an Ar+O2 ambient
͓O2/Ar+O2=0.2͔ with a high-purity Zr target, while ZrOxNy
was deposited in an Ar+N2 ambient ͓N2/Ar+N2=0.33͔ with
residual oxygen. For studying the interfacial reaction be-
Figure 2͑a͒ displays the XPS core-level spectra for the
ZrO2 and ZrOxNy ultrathin films on Si substrates before and
after 600 °C PDA, respectively. As seen from Zr 3d spectra,
a Zr–O–Si intermediate layer inclined to emerge in the as-
deposited film prepared in an Ar/O2 ambient; while ZrOxNy
was the main composition in the film deposited in an Ar/N2
ambient. Interestingly, we observed that the spectra both
shifted to higher binding energy and became almost identical
after 600 °C PDA; this finding indicates that high-
a͒
Electronic mail: chchien@mail.ndl.org.tw
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0003-6951/2006/89͑1͒/012905/3/$23.00 89, 012905-1 © 2006 American Institute of Physics
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012905-2
Cheng et al.
Appl. Phys. Lett. 89, 012905 ͑2006͒
FIG. 1. SIMS profiles of the ZrOxNy on ͑a͒ Si and ͑b͒ Ge substrates before
͑solid lines͒ and after ͑dash lines͒ 600 °C PDA. The PDA time is 1 min.
FIG. 2. Zr 3d, Si 2p, Ge 2p3, Ge 3d, N 1s, and O 1s core-level spectra of
ZrOxNy and ZrO2 thin films on ͑a͒ Si and ͑b͒ Ge substrates before ͑solid
lines͒ and after ͑dash lines͒ 600 °C PDA.
temperature annealing tends to convert both the Zr–N and
Zr–O bonds into the configuration of Zr–O–Si bond.13,14
From the O 1s broad spectra, we confirm this tendency by
observing the shifting toward higher binding energy and the
increased peak intensity, which is also consistent with the
findings of the Si 2p spectra. A N2 ambient instead of an O2
ambient facilitates to minimize the thickness of the IL during
sputtering and suppress the further growth due to a few SiNx
bond ͑the N 1s spectra͒ against the overoxidation.
can readily oxidize the entire Ge substrate and incur the for-
mation of volatile GeO as well. Therefore, after 600 °C ther-
mal annealing, the GeOx-contained IL certainly revealed
acute volatilization, which was also evidenced by the re-
duced intensities of the corresponding O 1s spectra. In our
previous study, such an IL shrinking tendency after N2 an-
nealing has also been observed from the TEM images of the
HfOxNy /Ge gate stacks.17 We also noticed that the Ge–N
and/or Zr–N bonds were undetected in the N 1s spectra ͑not
Pronouncedly, the resultant high-k films on Ge substrate
depicted several noteworthy distinct features with respect to
their counterparts, as presented in Fig. 2͑b͒. First, from the
Zr 3d spectra, there is no evidence of the emergence of in-
terfacial Zr–O–Ge bonding albeit the films deposited in an
Ar/O2 ambient. The subsequent 600 °C annealing still can-
not prompt the occurrence of Zr germanate, i.e., ZrGeOx;
indeed, the spectrum profiles even slightly move backward to
lower binding energy, implying poor intermixing and alloy-
ing in Ge and Zr systems. Next, a broad band consisting of
Ge dioxides and suboxides was observed both in Ge 2p3 and
Ge 3d spectra. Through the curve fitting for these two Ge
core levels with mixed Gaussian-Lorentzian line shapes, the
amounts of three components—including element Ge, GeO,
and GeO2—were extracted. The reduced intensity ratio of
GeOx ͑xϹ2͒ to Ge substrate is illustrated in Fig. 3; the inset
displays the HRTEM image of as-deposited ZrO2/Ge gate
stack, in which an IL of ca. 22 Å can be equivocally seen,
showing agreement with the estimated thickness of ca. 20 Å
by XPS calculation.15,16 Upon the increasing PDA tempera-
ture, thermally induced transformation of GeOx into GeO
gaseous species led to severe IL desorption through the top
FIG. 3. The ratio of GeOx to Ge substrate vs annealing conditions for
ZrOxNy /Ge and ZrO2 /Ge gate stacks. Inset: Cross-sectional TEM image of
ZrO2 /Ge before the PDA.
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high-k films. In addition, residual oxygen in a N2 ambient
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Cheng et al.
Appl. Phys. Lett. 89, 012905 ͑2006͒
shown͒, which may be owing to the detection limit for lower
nitrogen concentration in ZrOxNy /Ge structure.
This study was mainly sponsored by Taiwan Semicon-
ductor Manufacturing Company, Ltd. and partly supported
by the National Science Council of Taiwan under Contract
No. NSC94-2215-E009-066. One of the authors ͑C.-C.C.͒ is
grateful to Dr. Fu-Liang Yang and Dr. Chien-Chao Huang for
fruitful discussions and to Dr. Ming-Yi Yang for technical
assistance.
From the viewpoint of aggressive EOT scaling, it is de-
lighted to see an IL contraction on the Ge system. From the
AFM images ͑not shown͒, the smooth surface morphology of
as-deposited ZrO2 overlayer on Ge was found ͑Rrmsϳ1 Å͒,
but, the outdiffused species led to small pits and/or holes on
the top surface of Zr high-k dielectrics after 600 °C anneal-
ing for 1 min ͑Rrmsϳ3 Å͒; this in turn possibly created a
considerably high defect density and then severely jeopar-
dized the insulating properties of high-k/Ge capacitors.17 Ex-
tending the annealing time to 5 min even resulted in the
tremendous surface roughness ͑Rrmsϳ26 Å͒ and the distor-
tion of Zr 3d spectra ͑not shown͒, indicative of the destruc-
tion of overlying high-k dielectrics. With above examina-
tions, we speculate that the desorption of GeOx-contained IL
is the possible origin of why we did not observe the forma-
tion of Zr germanate after high-temperature annealing on Ge.
In this study, we showed that the thermal stability of high-
k/substrate interface on Ge is not as good as that on Si due to
inherent poor quality of Ge native oxide. Seeking for the
means of restraining the Ge-mixed oxides at the interface
will be indispensable in pursuit of high-performance high-k
gate dielectrics on Ge substrates or epitaxial Ge films.
Thermal stability of ZrOx͑Ny͒/Si and Ge interfaces has
been studied through the physical characterization. We found
that the IL has distinct thermochemical properties on these
two substrates. High-temperature processing aids the IL
growth and the formation of Zr silicate in ZrOx͑Ny͒/Si gate
stack. On the contrary, severe IL volatilization and the inhi-
bition of Zr germanate were found in ZrOx͑Ny͒/Ge system;
these features are expected to possess a better EOT scalabil-
ity with respect to ZrOx͑Ny͒/Si system. However, the gener-
ated localized pits in deposited high-k films owing to the
desorption of the underlying IL may severely degrade the
electrical properties of fabricated high-k/Ge devices.
1A. Dimoulas, G. Mavrou, G. Vellianities, E. Evangelou, N. Boukos, M.
Houssa, and M. Caymax, Appl. Phys. Lett. 86, 032908 ͑2005͒.
2W. P. Bai, N. Lu, and D.-L. Kwong, IEEE Electron Device Lett. 26, 378
͑2005͒.
3H. Kim, C. O. Chui, K. C. Saraswat, and P. C. Mclntyre, Appl. Phys. Lett.
83, 2647 ͑2003͒.
4J. J.-H. Chen, N. A. Bojarczuk, Jr., H. Shang, M. Copel, J. B. Hannon, J.
Karasinski, E. Preisler, S. K. Banerjee, and S. Guha, IEEE Trans. Electron
Devices 51, 1441 ͑2004͒.
5C. C. Yeo, B. J. Cho, F. Gao, S. J. Lee, M. H. Lee, C.-Y. Yu, C. W. Liu, L.
J. Tang, and T. W. Lee, IEEE Electron Device Lett. 26, 761 ͑2005͒.
6N. Wu, Q. Zhang, C. Zhu, D. S. H. Chan, A. Du, N. Balasubramanian, M.
F. Li, A. Chin, and J. K. O. Sin, IEEE Electron Device Lett. 25, 631
͑2004͒.
7K. Kita, K. Kyuno, and A. Toriumi, Appl. Phys. Lett. 85, 52 ͑2004͒.
8K. Prabhakaran, F. Maeda, Y. Watanabe, and T. Ogino, Appl. Phys. Lett.
76, 2244 ͑2000͒.
9D. Chi, C. O. Chui, K. C. Saraswat, B. B. Triplett, and P. C. Mclntyre, J.
Appl. Phys. 96, 813 ͑2004͒.
10C. O. Chui, D.-I. Lee, A. A. Singh, P. A. Pianetta, and K. C. Saraswat, J.
Appl. Phys. 97, 113518 ͑2004͒.
11N. Wu, Q. Zhang, C. Zhu, C. C. Yeo, S. J. Whang, D. S. H. Chan, M. F.
Li, B. J. Cho, A. Chin, D.-L. Kwong, A. Y. Du, C. H. Tung, and N.
Balasubramanian, Appl. Phys. Lett. 84, 3741 ͑2004͒.
12K. Prabhakaran and T. Ogino, Surf. Sci. 387, L1068 ͑1997͒.
13H. Kato, T. Nango, T. Miyagawa, T. Katagiri, K. S. Seol, and Y. Ohki, J.
Appl. Phys. 92, 1106 ͑2002͒.
14M. J. Guittet, J. P. Crocombette, and M. Gautier-Soyer, Phys. Rev. B 63,
125117 ͑2001͒.
15V. Craciun, I. W. Boyd, B. Hutton, and D. Williams, Appl. Phys. Lett. 75,
1261 ͑1999͒.
16T. Deegan and G. Hughes, Appl. Surf. Sci. 123/124, 66 ͑1998͒.
17C.-C. Cheng, C.-H. Chien, C.-W. Chen, S.-L. Hsu, C.-H. Yang, and C.-Y.
Chang, J. Electrochem. Soc. 153, F160 ͑2006͒.
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