3−報文−

Incubation Time Free CVD−TiO2 Film Preparation
Using a Novel Titanium Precursor, Ti−DOT千多山岩摩肆大舟葉田本永庭矢島窪洋賢俊宏忠憲

一＊1
一＊2
樹＊3
平＊3
篤＊1
寛＊4
昭＊1
浩＊5

Incubation Time Free CVD−TiO2 Film Preparation
Using a Novel Titanium Precursor, Ti−DOTHirokazu

CHIBA

Ken-ichiTADA

Toshiki

YAMAMOTO

Kohei

IWANAGA

Atsushi

MANIWA

Tadahiro

YOTSUYA

Noriaki

OSHIMA

Hiroshi

FUNAKUBO

Titanium oxide thin films were deposited at 200 − 400 ℃ on amorphous SiO2 substrates by chemical vapor
deposition (CVD) using novel precursors, diisopropoxo{ethene−1,2−diylbis( tert −butylamido)}titanium[Ti[N( t Bu)CH=CHN( t Bu)](O i Pr) 2 , 1 ; Ti− DOT] and di− tert − pentyloxo{ethene− 1,2− diylbis( tert −butylamido)}titanium [Ti[N( tBu)CH=CHN(tBu)](OtPe)2, 2], with oxygen gas as an oxidant. The deposition
amounts of TiO2 thin films using Ti−DOT and 2 were clearly larger than that of titanium tetraisopropoxide[Ti(OiPr)4, 3; TTIP] because of the shorter incubation time in the case of Ti−DOT and 2. Details of the TiO2 films
from Ti−DOT and TTIP were evaluated by AFM. Compared to the films from TTIP, smaller surface roughness
was observed for the films using Ti−DOT. In addition, a TiO2 thin film deposited from Ti−DOT on an amorphous
SiO2 hole substrate with an aspect ratio of 5 showed good conformability.

1．Introduction＊1 東京研究所＊2 相模中央化学研究所＊3 相模中央化学研究所（兼）東京研究所＊4 東京研究所（兼）相模中央化学研究所＊5 東京工業大学

TiO2 thin films have attracted much attention for awide range of applications, for instance, antireflection
films [1], photocatalysts [2], and biocompatible
materials [3], owing to its specific functional properties.

4TOSOH Research ＆ Technology Review Vol.55（2011）

Among various deposition techniques, atomic layer

13.2 mmol) [10] was dissolved in 20 mL ofdeposition (ALD) and chemical vapor deposition (CVD)

tetrahydrofuran, and then sodium (606 mg, 26.4 mmol)

have a great advantage in providing excellent film

was added. The reaction mixture was stirred at room

uniformity and flatness over a large surface area of thetemperature for 12 h. The resulting deep−red solution

substrate. Titanium tetraisopropoxide (TTIP) has been

was added dropwise at −70℃ to a solution of Ti(OiPr)4

extensively studied as a liquid precursor to prepare(3.56 g, 12.5 mmol) in 10 mL of hexane. The resulting

TiO2 thin films by ALD and CVD because of its highmixture was allowed to warm to room temperature andvapor pressure, noncorrosive by−products, and thestirred for 14h. The solvent was removed underhigh cost efficiency compared to other metal organic

reduced pressure, and the residue was extracted in 20

precursors [4−6].

mL of hexane. A crude material was purified byHowever, other precursors for TiO2 film preparation

distillation (85℃ / 0.05 Torr) to obtain 3.91 g of Ti−
DOT (93% yield) as a dark red oil. 1H NMR (500 MHz,

have not been widely investigated [7, 8].
In this study, we synthesized novel precursors,

C6D6, 20℃, δ): 5.96 (s, 2 H, NCH=CHN), 4.0−5.0 (br, 2diisopropoxo{ethene−1,2−diylbis( tert −butylamido)}

H, OCH(CH3)2), 1.30 (s, 18 H, NC(CH3)3), 1.1−1.3 (br,ttititanium [Ti[N( Bu)CH=CHN( Bu)](O Pr) 2 , 1; Ti−

12 H, OCH(CH3)2). 13C NMR (125 MHz, C6D6, 20℃,DOT] and di−tert−pentyloxo{ethene−1,2−diylbis(tert−δ): 102.7 (NCH=CHN), 74.5 (br, OCH(CH3)2), 57.6butylamido)} titanium [Ti[N( t Bu)CH=CHN( t Bu)](N C (CH 3 ) 3 ), 31.7 (NC( C H 3 ) 3 ), 27.8 (OCH( C H 3 ) 2 ).

(OtPe)2, 2] and evaluated their deposition characteristicsGC/MS (EI) m/z 334(M+), 319, 291, 275.

to prepare TiO2 thin films by CVD with oxygen gas as

Synthesis of Ti[N(tBu)CH=CHN(tBu)](OtPe)2 (2).

an oxidant [9]. The molecular structures of 1 (Ti−To a stirred solution of bis(dimethylamido){ethene−DOT), 2, and 3 (TTIP) are shown in Fig. 1. We also

1 , 2 −d i y l b i s ( t e r t −b u t y l a m i d o ) t i t a n i u m

examined the surface flatness and the step coverage ofTi[N( tBu)CH=CHN( tBu)](NMe 2) 2 [11] (1.76 g, 5.78

the films from Ti−DOT.

mmol) in hexane (7 mL), tert−pentyl alcohol (1.02 g,11.6 mmol) was added dropwise at −70℃ during aperiod of 10 min. The reaction mixture was allowed to

2．Experiment
2.1

warm to room temperature and stirred for 12 h. The

Preparations

solvent was removed under reduced pressure, and thePreparation of compound 1 (Ti−DOT) and 2 wereresidue was purified by distillation (97℃ / 0.05 Torr) to

carried out under argon atmosphere using standard

obtain 2.11 g of 2 (93% yield) as a dark red oil. 1H NMR

Schlenk tube and vacuum−line techniques. Dehydrated(500 MHz, C6D6, 20℃, δ): 5.93 (s, 2 H, NCH=CHN),

hexane and tetrahydrofuran used in this work were1.55 (br, 4 H, OC(CH 3 ) 2 C H 2 CH 3 ), 1.30 (s, 18 H,purchased from Kanto Chemical Co., Inc. Benzene−d6

NC(CH3)3), 1.1−1.4 (br, 12 H, OC(CH3)2CH2CH3), 0.99

was distilled from sodium/benzophenone ketyl prior to(br, 6 H, OC(CH3)2CH2CH3). 13C NMR (125 MHz, C6D6,use. TTIP and tert−pentyl alcohol were purchased from20℃, δ): 103.1 (N C H= C HN), 81.4 (br, O C (CH 3 ) 2Aldrich, and were used as received.

CH2CH3), 57.4 (NC(CH3)3), 38.3 (OC(CH3)2CH2CH3),

Synthesis of Ti[N(tBu)CH=CHN(tBu)](OiPr)2 (1; Ti−DOT).

31.9 (NC( C H 3 ) 3 ), 31.1 (OC( C H 3 ) 2 CH 2 CH 3 ), 9.8(OC(CH3)2CH2CH3).

N,N−di−tert−butyl−1,4−diazabuta−1,3−diene (2.22 g,2.2ttBuNNOi PrNTiNtt1 ; Ti−DOT

prepared on n−type Si substrates at the deposition

Ot PeTiBuFig.１

TiO2 thin films were deposited on amorphous SiO2

BuOi PrOt PeTi（Oi Pr）
4

temperature range from 200 to 400℃ by CVD using Ti−
DOT, 2, and TTIP. The vapor of the precursors wasBu
2Deposition of TiO2 thin films

generated by bubbling method with a vapor pressure ofTTIP

Molecular structures of Ti precursors in this study2) and 50℃ (TTIP),
91 Pa at 84℃ (Ti−DOT), 111℃ (2respectively. This vaporized precursor was transferred東ソー研究・技術報告 第55巻（2011）5

to the cold wall type CVD reaction chamber with argon( time delay for onset of deposition ) is significantly

carrier gas. The reactant gas was O 2 , and its

shorter than the case of using TTIP. While TTIP

concentration was constantly controlled at 20% of theexhibited about 30 min. of incubation time, thetotal reaction chamber pressure. Si wafer covered withincubation time of Ti−DOT was only a few minutes.

100 nm−thick SiO 2 was used as a substrate. TheAs shown in Fig. 2 and 3, it is indicated that thedeposition conditions of TiO2 thin films are summarized

deposition characteristics of 2 were almost the same asin Table 1.

those of Ti−DOT on the condition in Table 1. For thisreason, further analyses were made only for TiO2 films

2.3

from Ti−DOT and TTIP. Fig. 4 illustrates the average

Measurement of physical properties

Deposition amount of the films was measured by thesurface roughness, Ra, as a function of the deposition

X−ray fluorescence (XRF) calibrated by standard

amount of the TiO2 films deposited at 300℃ using Ti−

samples. The crystal structure, film composition, andDOT and TTIP. Compared to the Ra of the same

surface roughness were measured by X−ray diffraction

deposition amount, films from Ti−DOT showed smaller(XRD), X−ray photoelectron spectroscopy (XPS), andRa than those from TTIP. This indicates that Ti−DOT

atomic force microscopy (AFM), respectively. The step

can deposit films with flatter surface and with shorter

coverage of the thin film was observed by field

incubation time.

emission scanning electron microscopy (FE−SEM).

Carbon and nitrogen contents of TiO2 films deposited
at 300℃ from Ti−DOT and TTIP were found to be lessthan 1% from XPS analysis. In addition, these films were3．Results and discussions

ascertained from XRD measurements to be consistentamounts of TiO2 films and the inverse of the deposition
temperature deposited for 60 min. using Ti−DOT, 2,and TTIP as a precursor. The deposition characteristicsof the three precursors can be divided into twotemperature regions. The deposition amounts of TiO2
films from Ti−DOT, 2, and TTIP were less sensitive
against the deposition temperature above 300℃. On theother hand, strong deposition temperature dependency

Deposition amount［10−7・mol／cm2］

Fig. 2 shows the relationship between the deposition

and 2 were several times as large as that from TTIP ineach temperature between 250 and 400℃.

Deposition temperature, T［℃］
300
250

200
Ti−DOT
2TTIP

101
0.1
0.01
1.4

was observed below this temperature. It is noticeable
that the deposition amount of TiO2 films from Ti−DOT

400

100

1.6

1.8
1000／T［1／K］

2.0

2.2

Fig.２ Deposition temperature dependency of the deposition
amount of TiO2 films deposited for 60 min. using
Ti−DOT, 2, and TTIP

the deposition time of TiO2 films from Ti−DOT, 2, andTTIP at 300℃ was described in Fig. 3. In the case ofusing Ti−DOT and 2 as a precursor, the incubation time

Table１ Deposition conditions of TiO2 thin films by CVD
Precursor
Precursor temperature ［℃］Carrier gas flow rate ［cm3／min］
O2 gas flow rate ［cm3／min］
Diluent gas flow rate ［cm3／min］
Total flow rate
［cm3／min］
Chamber pressure［Pa］
Substrate temperature ［℃］

Ti−DOT2TTIP841111060230300533200−40050Deposition amount［10−7・mol／cm2］

The relationship between the deposition amount and
15Ti−DOT
2TTIP

10Incubation Time
500Fig.３

10203040
Deposition time［min.］5060

Deposition time dependency of deposition amount ofTiO2 films deposited at 300 ℃ from Ti−DOT, 2, andTTIP

6TOSOH Research ＆ Technology Review Vol.55（2011）

had smoother surface than those from TTIP at 300℃.

10Ti−DOTTTIPRa［nm］

8Furthermore, the film from Ti−DOT deposited at 275℃
showed a good step coverage on a hole substrate. Thus,6Ti−DOT is a promising precursor for TiO 2 thin film

4

preparation by CVD.

20051015

Deposition amount［10−7・mol／cm2］

Fig.４

Deposition amount dependency of average surface
roughness, Ra , for the TiO2 films deposited at 300℃
from Ti−DOT and TTIP

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hole prepared on n−type Si substrate with an aspect

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Solids, 324, 289(2003).

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We have demonstrated here the incubation time free

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TiO 2 film formation by CVD using novel liquid

Marshall, H. O. Davies, P. N. Heys, P. O Brien, Mprecursors, Ti−DOT and 2 . TiO 2 thin films wereAfzaal, J. Raftery, and G. W. Critchlow, Chem. Vap.

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for the formation of TiO2 thin films, due to shorter

Maniwa, T. Yotsuya, N. Oshima, and H. Funakubo,incubation time. In addition, the films from Ti−DOT

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g06-38(2011)
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TiO2

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SiO2

Yamakawa and N. Oshima, U.S. Patent 7,632,958,
1μm

0.2μm

Fig.５

SEM image of TiO2 film deposited at 275℃ on an
amorphous SiO2 hole prepared on n−type Si substratewith an aspect ratio of 5