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X-ray photoelectron spectroscopic studies of the O ls state on the surface of dual ion beam deposited ZrOx films
~)
Solid State Communications, Vol. 77, No. 5, pp. 341-343, 1991. Printed in Great Britain.
0038-1098/9153.00+ .00 Pergamon Press plc
X-RAY PHOTOELECTRON SPECTROSCOPIC STUDIES OF THE O Is STATE ON THE SURFACE OF DUAL ION BEAM DEPOSITED ZrOx FILMS Y.S.Tang• and N.K.Huangb a
Department of Electronics and Electrical Engineering, University of Glasgow, Glasgow G12 8QQ, Scotland
b
Institute of Nuclear Science and Technology, Sichuan University, Chengdu, People's Republic of China (Received by D. Van Dyck - October 15, 1990)
The 0 Is state on the surface of dual ion beam deposited ZrOx films were studied by using x-ray photoelectron spectroscopy. Different from the bulk of the films, it was found that a new O Is peak exists on the surface, which is assigned to be due to the existence of carbon contamination.
X-ray photoelectron spectroscopy (XPS) has
composition of the ZrOx films, depending on the
widely been used in analyzing the bonding and
deposition parameters, is 0 _< x _< 2. The XPS
composition properties of materials including pre-
measurements were carried out on a VG ESCAL-
cision optical films, such as TiO v SiO v Ta20 ~,
AB MkII system using monochromatic AI Kcz
ZrO 2 films etc., especially on surface and interface
radiation (hv = 1486.6 eV) as the x-ray source,
studies. As one of the most important optical films,
which has a pass energy of 20 eV and a typical
ZrO 2 has been studied by several groups.tl-~l The
sampling depth of about 3 nm. During the experi-
deposition methods applied were vacuum evapora-
ments, an ultrahigh vacuum (better than 0.4x10 -'°
tion, ion beam assisted evaporation and dual ion
Torr) was maintained in the analyzer chamber. The
beam deposition techniques. For the characteriza-
sputtering beam was from a cold cathode A r ion
tion, various techniques, such as x-ray diffraction,
gun run at 4 kV, which gives an estimated etching
electron transmission spectroscopy, ellipsometry,
rate of about 3 nm/min.
Rutherford backscattering, XPS etc. have been
Figure la shows a wide scan spectrum in the
employed. In the previous studies,t3.4~ we reported
0-1000 eV kinetic energy range of a sample on the
the dual ion beam deposition process dependent
natural surface. The major components are Zr 3s,
refractive index, atomic composition and Zr bond-
Zr 3p, Zr 3d, Zr 4s, Zr 4p, 0 Is, 0 2s, C Is, C
ing properties of the ZrOx (0 < x _<2) films. Here
(KLL), Ar 2,o and Si 2p lines. After 10 min of ion
we concentrate on the O Is state on the natural
etching, the approximate composition becomes
surface of the dual ion beam deposited ZrOx films.
stoichiometric ZrOvm which is considered as the
Except for the state same as in the bulk of the
bulk of the films. It can be seen in figure lb that no
films, a new O Is state was observed, which will
apparent carbon related lines appear again. De-
be discussed in detail in this communication.
tailed depth profile studies were reported elsewhere.m
As reported before,m the samples were prepared
What is interesting is that the O l s line on the
by a dual ion beam deposition technique. The 341
342
X-RAY PHOTOELECTRON
SPECTROSCOPIC
STUDIES
Vol. 77, No. 5
due to the -Si-O-Si- bridging (high energy peak) and -=Si-O non-bridging (low energy peak) oxygen Io
J
~ N
I
configurations.[5-?l In our case, the situation is
~
slightly different from the above. Comparing figures 2a and 2b, it is obvious that the lower energy peak A locating at 531.2 eV is resulting from the D 0
(a)
Zr-O-Z~ bridging oxygen configuration (shown in figure 3a), but is the higher energy peak B locating at 533.3 eV due to the -~Zr-O- oxygen configuration? As we know, usually, the more ionic the
200
400
600
800
1000
oxygen ions, the lower kinetic energy the XPS peak locates at. So that the new O l s peak B
BINDING ENERGY (eV)
(533.3 eV) is more likely to be resolving a --Fig.1 XPS surveys of a sample both on the surface and in the bulk.
Zr-O-Si= or a =Zr-O-C= bonding oxygen configuration. From the composition and depth profile analyses2) it seems likely to be the -Zr-O-C-
natural surface of the samples has a shoulder on
bonding oxygen configuration (see figure 3b) due
the higher energy side, as shown in figure 2a. A
to the carbon contamination on the sample surface.
number of experiments indicate that the double
To confirm the above idea, we first clean a
peaks always exist despite the different values of x
sample surface by using the Ar* ion beam to etch
in the films, but the energy separation of this two
the sample for 5 min until XPS showing the
peaks varies with x and is typically within a range
existence of only one O Is peak, and then intro-
of 1.8-2.3 eV. This is similar to the previous
duce it into a carbon contaminated chamber for
observed results on the real surface of glasses,
one hour. Further XPS measurements on the
such as alkali silicate glasses, where two O ls
surface of this sample indicate the reappearance of
peaks were observed, which were assigned to be
the double O l s peaks, similar to that shown in figure 2a, which gives a strong evidence of the above discussion.
0 Is
A
B
(b)
In conclusion, we have studied the O Is state on the surface of the dual ion beam deposited ZrOx films. Two O l s peaks were observed, which are
.4 [.., z
Zr N
o L)
Zr \
0
N Zr--O --Zr--O--Zr / O / Zr 527
529
531
533
535
537
Zr--O /
0 N -- Zr--O--C / O
Zr
539
BINDING ENERGY (eV)
Fig.2 Comparison of the O I s states on the surface and in the bulk of a sample.
(a)
(b)
Fig.3 Bonding models of oxygen on the natural surface of the samples.
Vol. 77, No. 5
X-RAY PHOTOELECTRON SPECTROSCOPIC STUDIES
343
common for all the samples with different values
Acknowledgement - The authors are grateful to
of x, and are respectively assigned to -=Zr-O-Z~
Mr.H.Liu of the University of Surrey for his help
and ----Zr-O-C--bonding oxygen configurations,
with the XPS experiments. REFERENCES
[1] P.J.Martin, J. Mater. Sci. 21, 1(1986) and references therein.
[5] O.Puglisi, A.Torrisi and G.Marletta, Non-Cryst. Solids 68, 219(1984).
[2] K-H.Muller, J. Vac. Sci. & Technol. A4, 184(1986).
[6] J.G.Clabes, R.E.Fem and G.H.Frischat, J. Vac.
[3] Y.S.Tang, B.J.Sealy and N.K.Huang, 7th Int.
[7] J.S.Jen and M.R.Kalinowski, J. Non-Cryst.
Conf. on Ion Beam Modification of Materials, Knoxville, USA, Sept. 1990. [4] Y.S.Tang, J.E.Castle, H.Liu, J.F.Watts and N.K.Huang, Phys. St. Sol. (a) 121, K61(1990).
J.
Sci. & Technol. A4, 1580(1986).
Solids 38 & 39, 21(1989).
Solid State Communications, Vol. 77, No. 5, pp. 341-343, 1991. Printed in Great Britain.
0038-1098/9153.00+ .00 Pergamon Press plc
X-RAY PHOTOELECTRON SPECTROSCOPIC STUDIES OF THE O Is STATE ON THE SURFACE OF DUAL ION BEAM DEPOSITED ZrOx FILMS Y.S.Tang• and N.K.Huangb a
Department of Electronics and Electrical Engineering, University of Glasgow, Glasgow G12 8QQ, Scotland
b
Institute of Nuclear Science and Technology, Sichuan University, Chengdu, People's Republic of China (Received by D. Van Dyck - October 15, 1990)
The 0 Is state on the surface of dual ion beam deposited ZrOx films were studied by using x-ray photoelectron spectroscopy. Different from the bulk of the films, it was found that a new O Is peak exists on the surface, which is assigned to be due to the existence of carbon contamination.
X-ray photoelectron spectroscopy (XPS) has
composition of the ZrOx films, depending on the
widely been used in analyzing the bonding and
deposition parameters, is 0 _< x _< 2. The XPS
composition properties of materials including pre-
measurements were carried out on a VG ESCAL-
cision optical films, such as TiO v SiO v Ta20 ~,
AB MkII system using monochromatic AI Kcz
ZrO 2 films etc., especially on surface and interface
radiation (hv = 1486.6 eV) as the x-ray source,
studies. As one of the most important optical films,
which has a pass energy of 20 eV and a typical
ZrO 2 has been studied by several groups.tl-~l The
sampling depth of about 3 nm. During the experi-
deposition methods applied were vacuum evapora-
ments, an ultrahigh vacuum (better than 0.4x10 -'°
tion, ion beam assisted evaporation and dual ion
Torr) was maintained in the analyzer chamber. The
beam deposition techniques. For the characteriza-
sputtering beam was from a cold cathode A r ion
tion, various techniques, such as x-ray diffraction,
gun run at 4 kV, which gives an estimated etching
electron transmission spectroscopy, ellipsometry,
rate of about 3 nm/min.
Rutherford backscattering, XPS etc. have been
Figure la shows a wide scan spectrum in the
employed. In the previous studies,t3.4~ we reported
0-1000 eV kinetic energy range of a sample on the
the dual ion beam deposition process dependent
natural surface. The major components are Zr 3s,
refractive index, atomic composition and Zr bond-
Zr 3p, Zr 3d, Zr 4s, Zr 4p, 0 Is, 0 2s, C Is, C
ing properties of the ZrOx (0 < x _<2) films. Here
(KLL), Ar 2,o and Si 2p lines. After 10 min of ion
we concentrate on the O Is state on the natural
etching, the approximate composition becomes
surface of the dual ion beam deposited ZrOx films.
stoichiometric ZrOvm which is considered as the
Except for the state same as in the bulk of the
bulk of the films. It can be seen in figure lb that no
films, a new O Is state was observed, which will
apparent carbon related lines appear again. De-
be discussed in detail in this communication.
tailed depth profile studies were reported elsewhere.m
As reported before,m the samples were prepared
What is interesting is that the O l s line on the
by a dual ion beam deposition technique. The 341
342
X-RAY PHOTOELECTRON
SPECTROSCOPIC
STUDIES
Vol. 77, No. 5
due to the -Si-O-Si- bridging (high energy peak) and -=Si-O non-bridging (low energy peak) oxygen Io
J
~ N
I
configurations.[5-?l In our case, the situation is
~
slightly different from the above. Comparing figures 2a and 2b, it is obvious that the lower energy peak A locating at 531.2 eV is resulting from the D 0
(a)
Zr-O-Z~ bridging oxygen configuration (shown in figure 3a), but is the higher energy peak B locating at 533.3 eV due to the -~Zr-O- oxygen configuration? As we know, usually, the more ionic the
200
400
600
800
1000
oxygen ions, the lower kinetic energy the XPS peak locates at. So that the new O l s peak B
BINDING ENERGY (eV)
(533.3 eV) is more likely to be resolving a --Fig.1 XPS surveys of a sample both on the surface and in the bulk.
Zr-O-Si= or a =Zr-O-C= bonding oxygen configuration. From the composition and depth profile analyses2) it seems likely to be the -Zr-O-C-
natural surface of the samples has a shoulder on
bonding oxygen configuration (see figure 3b) due
the higher energy side, as shown in figure 2a. A
to the carbon contamination on the sample surface.
number of experiments indicate that the double
To confirm the above idea, we first clean a
peaks always exist despite the different values of x
sample surface by using the Ar* ion beam to etch
in the films, but the energy separation of this two
the sample for 5 min until XPS showing the
peaks varies with x and is typically within a range
existence of only one O Is peak, and then intro-
of 1.8-2.3 eV. This is similar to the previous
duce it into a carbon contaminated chamber for
observed results on the real surface of glasses,
one hour. Further XPS measurements on the
such as alkali silicate glasses, where two O ls
surface of this sample indicate the reappearance of
peaks were observed, which were assigned to be
the double O l s peaks, similar to that shown in figure 2a, which gives a strong evidence of the above discussion.
0 Is
A
B
(b)
In conclusion, we have studied the O Is state on the surface of the dual ion beam deposited ZrOx films. Two O l s peaks were observed, which are
.4 [.., z
Zr N
o L)
Zr \
0
N Zr--O --Zr--O--Zr / O / Zr 527
529
531
533
535
537
Zr--O /
0 N -- Zr--O--C / O
Zr
539
BINDING ENERGY (eV)
Fig.2 Comparison of the O I s states on the surface and in the bulk of a sample.
(a)
(b)
Fig.3 Bonding models of oxygen on the natural surface of the samples.
Vol. 77, No. 5
X-RAY PHOTOELECTRON SPECTROSCOPIC STUDIES
343
common for all the samples with different values
Acknowledgement - The authors are grateful to
of x, and are respectively assigned to -=Zr-O-Z~
Mr.H.Liu of the University of Surrey for his help
and ----Zr-O-C--bonding oxygen configurations,
with the XPS experiments. REFERENCES
[1] P.J.Martin, J. Mater. Sci. 21, 1(1986) and references therein.
[5] O.Puglisi, A.Torrisi and G.Marletta, Non-Cryst. Solids 68, 219(1984).
[2] K-H.Muller, J. Vac. Sci. & Technol. A4, 184(1986).
[6] J.G.Clabes, R.E.Fem and G.H.Frischat, J. Vac.
[3] Y.S.Tang, B.J.Sealy and N.K.Huang, 7th Int.
[7] J.S.Jen and M.R.Kalinowski, J. Non-Cryst.
Conf. on Ion Beam Modification of Materials, Knoxville, USA, Sept. 1990. [4] Y.S.Tang, J.E.Castle, H.Liu, J.F.Watts and N.K.Huang, Phys. St. Sol. (a) 121, K61(1990).
J.
Sci. & Technol. A4, 1580(1986).
Solids 38 & 39, 21(1989).