Selective MOCVD of titanium oxide and zirconium oxide thin films using single molecular precursors on Si(1 0 0) substrates

Article abstract of DOI:10.1016/j.jpcs.2007.08.008

Titanium oxide (TiO₂) and zirconium oxide (ZrO₂) thin films have been deposited on modified Si(1 0 0) substrates selectively by metal-organic chemical vapor deposition (MOCVD) method using new single molecular precursor of [M(OⁱPr)₂(tbaoac)₂] (M=Ti, Zr; tbaoac=tertiarybutyl-acetoacetate). For changing the characteristic of the Si(1 0 0) surface, micro-contact printing (μCP) method was adapted to make self-assembled monolayers (SAMs) using an octadecyltrichlorosilane (OTS) organic molecule which has -CH₃ terminal group. The single molecular precursors were prepared using metal (Ti, Zr) isopropoxide and tert-butylacetoacetate (tbaoacH) by modifying standard synthetic procedures. Selective depositions of TiO₂ and ZrO₂ were achieved in a home-built horizontal MOCVD reactor in the temperature range of 300-500 °C and deposition pressure of 1×10^-3-3×10^-2 Torr. N₂ gas (5 sccm) was used as a carrier gas during film depositions. TiO₂ and ZrO₂ thin films were able to deposit on the hydrophilic area selectively. The difference in surface characteristics (hydrophobic/hydrophilic) between the OTS SAMs area and the SiO₂ or Si-OH layer on the Si(1 0 0) substrate led to the site-selectivity of oxide thin film growth.

Full text of DOI:10.1016/j.jpcs.2007.08.008

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Journal of Physics and Chemistry of Solids 69 (2008) 128–132
www.elsevier.com/locate/jpcs
Selective MOCVD of titanium oxide and zirconium oxide thin films
using single molecular precursors on Si(1 0 0) substrates
Ã
B.-C. Kanga, , D.-Y. Junga, R.A. Fischerb, J.-H. Booa
aDepartment of Chemistry, Institute of Basic Science, Sungkyunkwan University, Suwon 440-746, Republic of Korea
bOrganometallics and Materials Chemistry, Ruhr-University Bochum, Universita¨sstr. 150, Bochum 44780, Germany
Received 23 September 2006; received in revised form 23 June 2007; accepted 10 August 2007
Abstract
Titanium oxide (TiO2) and zirconium oxide (ZrO2) thin films have been deposited on modified Si(1 0 0) substrates selectively by metal-
organic chemical vapor deposition (MOCVD) method using new single molecular precursor of [M(OiPr)2(tbaoac)2] (M ¼ Ti, Zr;
tbaoac ¼ tertiarybutyl-acetoacetate). For changing the characteristic of the Si(1 0 0) surface, micro-contact printing (mCP) method was
adapted to make self-assembled monolayers (SAMs) using an octadecyltrichlorosilane (OTS) organic molecule which has –CH3 terminal
group. The single molecular precursors were prepared using metal (Ti, Zr) isopropoxide and tert-butylacetoacetate (tbaoacH) by
modifying standard synthetic procedures. Selective depositions of TiO2 and ZrO2 were achieved in a home-built horizontal MOCVD
reactor in the temperature range of 300–500 1C and deposition pressure of 1 ꢀ 10ꢁ3–3 ꢀ 10ꢁ2 Torr. N2 gas (5 sccm) was used as a carrier
gas during film depositions. TiO2 and ZrO2 thin films were able to deposit on the hydrophilic area selectively. The difference in surface
characteristics (hydrophobic/hydrophilic) between the OTS SAMs area and the SiO2 or Si–OH layer on the Si(1 0 0) substrate led to the
site-selectivity of oxide thin film growth.
r 2007 Elsevier Ltd. All rights reserved.
Keywords: A. Oxides; A. Thin film; B. Vapor deposition; D. Surface properties
1. Introduction
and electrochemical properties [3–6]. Based upon these
properties, a variety of technological applications of TiO2
thin film are possible. Also, zirconium oxide (ZrO2)
has been extensively studied for use as a silicon dioxide
replacement in the gate-oxide insulating layer in comple-
mentary metal oxide semiconductor (CMOS) devices.
ZrO2 has high dielectric constants and a high-energy
band gap [7].
As these good properties and applications, metal oxide
thin films have been deposited by several physical and
chemical deposition techniques [8–11]. Among them,
chemical vapor deposition (CVD) technique using metal-
organic compound as a precursor (MOCVD) has many
advantages, such as good conformal coverage, the possi-
bility of epitaxial growth and selective deposition and the
application to large-area deposition, etc. Also this method
is low cost and is easy to control the deposition/growth
parameters. Thus, the MOCVD method is well known as
the one of the most powerful techniques and is suitable for
Oxide materials have a wealth of interesting physical
properties that can be used for various technological
applications. Many oxide materials have been used
extensively in the form of thin films because the applica-
tions involve micro-devices that require materials fabri-
cated on micron or submicron scales [1,2]. Titanium
dioxide (TiO2) films have found widespread application
as materials for optical coatings and protective layers for
very large-scale integrated circuits because of their wide
energy band gap, high refractive index, and good insulating
properties. Moreover, it is useful in fabricating dielectric
capacitors in microelectronic devices because of its high
dielectric constant. Up to now, TiO2 has been extensively
studied for its interesting electric, magnetic, catalytic,
Ã
Corresponding author. Tel.: +82 31 290 5972; fax: +82 31 290 7075.
E-mail address: bchkang@empal.com (B.-C. Kang).
0022-3697/$ - see front matter r 2007 Elsevier Ltd. All rights reserved.
doi:10.1016/j.jpcs.2007.08.008

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B.-C. Kang et al. / Journal of Physics and Chemistry of Solids 69 (2008) 128–132
129
stoichiometric and micro-structured thin film deposition.
The patterning of thin film is of considerable scientific and
technological interest. Soft lithography is a method to
make micro/nano size patterns and structures simply using
organic materials without involving high energy. In
particular, micro-contact printing (mCP) is a very con-
venient and nonphotolithographic technique that can
generate patterned features of self-assembled monolayers
(SAMs) on various surfaces [12]. The ability to control the
wettability of a solid surface is important and useful in a
range of technological applications [13–15]. In addition,
the mCP technique shows that hydrophobic patterns with
micron dimensions can be formed on hydrophilic surfaces
avoiding the use of photolithographic-type procedures. Xia
and Whitesides [13] and Folch and Schmidt [16] presented
the current state of development of soft lithographic
techniques and areas in which these techniques find
applications. The authors suggested the mCP technique
could apply to micro-electro-mechanical system (MEMS),
sensors, and microelectronics with large patterning features
over 100 mm scale, because small-area wafer and large
linewidths are perfectly suited for most those applications.
Earlier, we reported deposition of patterned TiO2 thin
films using titanium(IV) isopropoxide [Ti(OiPr)4] by
MOCVD on Si(1 0 0) substrates where the surface was first
modified by an octadecyltrichlorosilane (OTS) [17]. The
aim of the work presented here is to fabricate thin films and
micro/nano patterning of TiO2 and ZrO2 thin films by
using of new single molecular precursors. Herein, we report
that site-selective MOCVD of TiO2 and ZrO2 thin films
using bis-isopropoxy-bis-tertiarybutyl-acetoacetate tita-
nium [Ti(OiPr)2(tbaoac)2] as precursors on OTS patterned
Si(1 0 0) substrates.
ultrasonic cleaner without acid treatment to protect the
OTS patterning from being destroyed. The CVD experi-
ments were performed in a homebuilt MOCVD system.
Nitrogen was used as the carrier gas (5 sccm). The base
pressure of the MOCVD apparatus was 1 ꢀ 10ꢁ3 Torr, and
the working pressure was kept in the range of 30–50 mTorr.
The precursor bottle was heated at 80 1C. The deposition of
TiO2 thin films was carried out at 300–400 1C for 0.5–1 h.
And the depositions of ZrO2 thin films were performed at
450–500 1C for a period of 2–4 h. The as-grown films were
characterized by optical microscopy (OM), scanning
electron microscopy (SEM), energy dispersive X-ray
(EDX), atomic force microscopy (AFM) and micro-
Raman spectroscopy.
3. Results and discussion
Selectively deposited TiO2 thin films can be identified by
optical microscopy (OM). Fig. 1 shows an OM image of
the deposited TiO2 thin film that was selectively grown on
the OTS patterned Si(1 0 0) substrate at 400 1C for 1 h. The
relatively dark area corresponds to the TiO2 deposited area
and the bright area is OTS SAMs area.
SEM and AFM analyses were performed to see the
surface morphologies of the selectively deposited TiO2 thin
films. Fig. 2 shows the SEM image and EDX data
(see inset) of the selectively grown TiO2 thin film on the
OTS patterned Si(1 0 0) substrate. It was observed that the
images (which consist of two different contrasts shown in
Fig. 2) match well with the OM data. Moreover, it is seen
that boundary shape between the OTS SAMs area and the
TiO2 deposited area is also very sharp and clear. In order to
identify the composition of both dark (TiO2 film) and
bright areas (OTS SAMs), we utilized the EDX analysis
shown in the inset in Fig. 2. In the case of bright area, the
atomic ratio (%) of Ti and O was nearly 1:2, while in
the dark area there was no evidence of Ti and O elements.
2. Experimental
The polydimethylsiloxane [–Si(CH3)2O–]n (PDMS)
stamps were used for mCP and OTS [CH3(CH2)17SiCl3)]
SAMs were fabricated according to a previously reported
procedure [13]. A solution of OTS in dry hexane was used
as the ‘‘ink.’’ The OTS solution was applied to the PDMS
stamp using a spin coater. Then, the stamp was brought
into contact with the Si(1 0 0) substrate whose surface
contains a native oxide layer. The thermal stability of the
OTS SAMs on the Si(1 0 0) substrate is so strong that it
can endure around 450 1C in a vacuum condition. After
printing, thin films were deposited on these OTS patterned
Si(1 0 0) substrates by MOCVD using new metal-organic
precursors, [M(OiPr)2(tbaoac)2] (M ¼ Ti, Zr; tbaoac ¼
tertiarybutyl-acetoacetate) as a single molecular precursor.
Ti(OiPr)2(tbaoac)2 exists as pale-yellow crystalline solids at
room temperature, having a melting point 58 1C and
Zr(OiPr)2(tbaoac)2 is a white crystalline solid with 45 1C
melting point. The details of the synthesis and characteri-
zation of the compounds is reported in the literature
[18,19]. The OTS patterned Si(1 0 0) substrate was pre-
treated with ethanol and de-ionized (DI) water in an
Fig. 1. Optical microscope image of a TiO2 thin film deposited on the
OTS patterned Si(1 0 0) substrate. The dark image is TiO2 deposited area
and the bright image is OTS SAMs area.

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130
Fig. 2. SEM image of a TiO2 thin film deposited on the OTS patterned
Si(1 0 0) substrate. Inset shows EDX spectra obtained from the selectively
grown TiO2 film (A) and OTS SAMs surface (B).
Fig. 4. Micro-Raman spectra of (a) Si(1 0 0) substrate, (b) OTS SAMs
area, and (c) TiO2 deposited area (Raman laser radiation: 514.5 nm,
20 mW).
From the images of Fig. 3(a) and (b), also we can see two
different contrasts similar to SEM images, indicating good
selectivity. With the height profile (see inset) of the 2D
AFM image, we can reconfirm the selective growth of TiO2
thin film and the TiO2 thin film was able to selectively
deposit on 10 mm area with thickness of about 120 nm.
The clear and convincing evidence of selective growth
was obtained by micro-Raman analysis with a 514 nm laser
and 20 mW power. Fig. 4 shows the micro-Raman spectra
of the Si(1 0 0) substrate (a), OTS SAMs printed area
(b) and TiO2 deposited area (c), respectively. In the case of
(a) and (b), there were no characteristic bands except for
the peaks originated from the Si(1 0 0) substrate. However,
in Fig. 4(c), we clearly found that the three bands
corresponding to the anatase TiO2 Raman active funda-
mental modes, are recorded at 144 cmꢁ1 (Eg), 399 cmꢁ1
(B1g), and 639 cmꢁ1 (Eg). The band positions were in very a
good agreement with published data on either polycrystal-
line powders or monocrystals [21,22]. Moreover, the bands
due to rutile and brookite phase of TiO2 were not observed.
With these data, we were able to conclude that the anatase
phase TiO2 thin film was able to mainly grow on the
Si(1 0 0) substrate on which OTS SAMs were not covered,
strictly speaking, a native oxide layer on Si(1 0 0) surface.
This result proved the selectivity of TiO2 thin film on the
OTS patterned Si(1 0 0) substrate.
Fig. 3. (a) 3D AFM image of selective growth of TiO2 thin film on
Si(1 0 0) surface. (b) 2D AFM image of the same film as (a), and height
profile obtained from the direction of black line area.
Selectivity of deposited ZrO2 film can be identified by
optical microscopy (OM) images. Fig. 5 shows an OM
image of the deposited ZrO2 films on OTS patterned
Si(1 0 0) substrate at 450 1C for 2 h. It shows contrast
between OTS SAMs area and ZrO2 thin films deposited
region. The relatively dark area corresponds to the ZrO2
deposited area and the bright area is OTS SAMs area.
Fig. 6 shows the SEM images of selectivity grown on
OTS patterned Si(1 0 0) substrate. In the case of (a), grown
at 450 1C for 2 h, it shows that boundary shape between the
This is a good agreement with reported data of selective
growth of TiO2 thin film with Ti(OiPr)2(tbaoac)2 [18] and
of the CVD grown TiO2 thin films with Ti(OiPr)4 [20].
Fig. 3(a) shows the 3D AFM image of the selectively
grown TiO2 thin film on OTS SAMs patterned Si(1 0 0)
substrate at 400 1C. The selective deposition of thin film
and the sharp boundary between TiO2 thin film area and
OTS SAMs area was clearly seen. Fig. 3(b) also shows the
2D AFM image obtained from the same film as Fig. 3(a).

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131
OTS SAMs area and ZrO2 deposited area is clear.
However, as the deposition time was increased up to 4 h,
the boundary became very unclear. It means the ZrO2 was
able to deposit both hydrophilic area and hydrophobic
area. We can suggest that the terminal group of OTS was
oxidized and changed its character from hydrophobic to
hydrophilic or removed from the substrate surface because
the high deposition temperature and long deposition time
[25]. The morphology of ZrO2 thin film grown on Si(1 0 0)
substrate was denser and smoother than that of ZrO2 thin
film grown on OTS SAMs surface.
XPS survey spectrum analysis was carried out of the as-
deposited ZrO2 film grown on Si(1 0 0) substrate at 450 1C
(not shown here). The strong Zr3d and O1s peaks were
clearly indicated. However, C1s peak clearly appeared
around 300 eV binding energy, we can guess that the
carbon comes from the precursor during depositions and/
or surface contamination from the air. Also, the O1s and
Zr3d high-resolution XPS spectra were performed
(not shown here). In the case of O1s, there are two
oxidation states attributed to O2ꢁ and OHꢁ species at the
binding energy of about 532 and 530 eV. We can ensure
that the OHꢁ peak is just a surface contamination peak
probably originated from H2O in the air. The Zr3d5/2 peak
observed as a single peak at binding energy of 182.2 eV,
which is a good agreement to Zr4+
.
Fig. 7 shows the 3D AFM image of selectively grown
ZrO2 thin film on OTS SAMs patterned Si(1 0 0) substrate
at 450 1C for 2 h. The selectivity of thin film and the sharp
boundary between ZrO2 thin film area and OTS SAMs are
clearly distinguished. The thickness of deposited ZrO2 thin
film was approximately 30–40 nm. The growth rate of ZrO2
thin films using Zr(OiPr)2(tbaoac)2 was much slower than
that of TiO2 thin films.
OTS SAMs have been demonstrated as a promising
candidate for a MOCVD resist layer which can block the
surface functional groups that are necessary for nucleation
Fig. 5. OM images of a ZrO2 thin film deposited on the OTS patterned
Si(1 0 0) substrate.
Fig. 7. 3D and 2D AFM images of selective growth of a ZrO2 thin film on
Si(1 0 0) substrate.
Fig. 6. SEM image of a ZrO2 thin film deposited on the OTS patterned Si(1 0 0) substrate at (a) 450 1C for 2 h and (b) 450 1C for 4 h.

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and growth during the deposition [23]. In this experiment,
OTS can prevent nucleation for TiO2 and ZrO2 thin film on
the SAMs surfaces because it has hydrophobic terminal
group (–CH3), i.e., there are no reaction factors for
chemisorption between the metal-organic (MO) precursors
and –CH3 groups. But the MO precursors can obtain
electrons from the ‘‘base’’ originated from native oxide
layers on the Si(1 0 0) surface and they can make
chemisorptions with substrate very strongly. After all, thin
film is able to be formed on it. However, OTS SAMs are
weak in respect of thermal stability over 450 1C [25], they
should change their identities or make some defects on the
OTS SAMs area. Therefore, it is difficult to make thin films
selectively on substrates by combination of mCP and
MOCVD methods at high temperatures. Thomas et al.
showed that Ti(OiPr)2(tbaoac)2 precursor showed slightly
superior properties in terms of evaporation behavior,
deposition temperature, and smaller amount of residue
material than those of Zr(OiPr)2(tbaoac)2 precursor [24].
And Zr(OiPr)2(tbaoac)2 precursor could induce high van
der Waals force with OTS SAMs surface and low
molecular mobility on the OTS SAMs area owing to its
high molecular weight compared to Ti(OiPr)2(tbaoac)2.
These disadvantage factors should require a long nuclea-
tion time on the Si(1 0 0) substrate and cause less site-
selective deposition than that of TiO2 in our experiment.
However, it is expected that the combination of mCP
of SAMs and MOCVD is a better method for fabri-
cating micro-size, various functional thin films at low
temperatures.
Acknowledgments
The authors gratefully acknowledge the support by the
BK21 project of Ministry of Education, Korea.
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[M(OiPr)2(tbaoac)2, M ¼ Ti, Zr] were used as precursors
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