17Development of Novel Silicon Precursors for
Low − Temperature CVD ／ ALD Processes
岩山摩多永本庭田宏俊賢平＊ 1樹＊ 2
篤＊ 3一＊ 4

Development of Novel Silicon Precursors for
Low − Temperature CVD ／ ALD Processes
Kohei IWANAGA
Toshiki YAMAMOTO
Atsushi MANIWA
Ken-ichi TADA

Si-TBES (2) and Si-TBAS (4), novel CVD/ALD precursors bearing a diazasilacyclopentene framework, weresynthesized. Thermal analyses revealed that both of them are highly volatile, and their decomposition temperatures
were lower than those of comparable silicon precursors, Si(OEt)4 (TEOS) and SiH(NMe2)3 (TDMAS). Deposition
properties of SiO2 thin films were investigated by a thermal CVD apparatus. The deposition rates of SiO 2 thinfilms using these new precursors were higher than that of TDMAS. Deposition rate dependency on oxygen partialpressure indicates the high reactivity of the diazasilacyclopentene framework towards oxygen contributes to thehigh growth rates. Details of the SiO2 thin films were evaluated by XPS, AFM, and SIMS. While Si-TBAS can form
conformal SiO2 thin films efficiently, Si-TBES can provide a film with low carbon and nitrogen contamination.

1．Introduction

for the damage-free processes to form a thin film on
patterned film structures or heat labile substrate such

Silicon is the most commonly-used element inas glasses or plastics. Although SiH4 or Si(OEt)4 (TEOS)

semiconductor industry, and silicon containing

are well-known precursors for CVD/ALD processes [1],materials are used in various parts of semiconductor

they require high deposition temperature [2], plasmadevices. For these manufacturing processes, chemicalassistance [3-4], or highly reactive coreactant such asvapor deposition (CVD) and atomic layer depositionozone gas [5] to produce thin films.

(ALD) processes have been extensively investigatedWe have been designing state-of-art precursors

to form thin films on a three-dimensional surface withwhich have high reactivity with coreactant, and recently

a uniform thickness and conformality. As the recent

succeeded in developing a new titanium precursor,

improvement of device integrations and flexible devices,

Ti-DOT (1), which enables to form TiO2 thin films at

low-temperature deposition processes are required

high deposition rate by the CVD with oxygen [6]. This

＊ 1 東京研究所（兼）（公財）相模中央化学研究所＊ 2 （公財）相模中央化学研究所（兼）東京研究所＊ 3 東京研究所＊ 4 （公財）相模中央化学研究所

compound was also found to react readily with oxygengas concerted with the dissociation of the bidentate
vinylenediamide ligand as the neutral diimine. ThisTOSOH Research & Technology Review Vol.56（2012）18

result indicates that this reaction contributes to thewas filtered and the solvent was removed by distillation.

efficient rate of thin film formation. We herein report

The residue was purified by vacuum distillation (80℃/the syntheses, properties and film depositions of novel

3.8x102 Pa) to obtain 35.58 g of Si[N(t Bu)CH=CHN(t Bu)]silicon precursors bearing the diazasilacyclopentene

Cl (83% yield) as a colorless oil. 1H NMR (500 MHz,framework.

C6D6, 20 ℃ , δ/ppm): 6.40 (s, 1 H, SiH ), 5.77 (s, 2 H,
NCH =CH N), 1.21 (s, 18 H, NC(CH 3)3). 13C NMR (125MHz, C6D6, 20℃ , δ/ppm): 113.1, 51.9, 30.8.

2．Experiment
2.1

Synthesis of Si[N(t Bu)CH=CHN(t Bu)] (H)NH2 (4; Si-Preparations

TBAS).

All reactions were performed under argon

Si[N(t Bu)CH=CHN(t Bu)]Cl (6.44 g, 27.7 mmol)

atmosphere using standard Schlenk tube and vacuum-

was dissolved in 20 mL of hexane. The solution wasline techniques. The products were characterized on thedegassed by freeze-pump-thaw cycles, and NH 3 was

113

basis of H and C nuclear magnetic resonance spectra.

introduced from 5 L baloon. After starring at room

Dehydrated hexane and tetrahydrofuran used in thistemperature for 3 h, precipitate was filtered out and thework were purchased from Kanto Chemical Co., Inc.

solvent was removed by distillation. The residue w a sBenzene-d 6 was distilled from sodium/benzophenone

p u r i f i e d b y v a c u u m d i s t i l l a t i o n (78℃/3.7x102 Pa)

ketyl prior to use. Si(OEt) 4, SiHCl 3, and NH 3 wereto obtain 5.45 g of Si-TBAS (92%) as a pale-yellow oil.

purchased from Aldrich, TCI, Japan Fine Products,1

respectively, and were used as received.

NCH =CH N), 5.68 (s, 1H, SiH ), 1.29 (s, 18 H, NC(CH 3)3),

H NMR (500 MHz, C6D6, 20 ℃ , δ/ppm): 5.81 (s, 2 H,Synthesis of Si[N( Bu)CH=CHN( Bu)](OEt)2 (2; Si-0.83 (br, 2 H, NH 2). 13C NMR (125 MHz, C6D6, 20℃ , δTBES).

/ppm): 111.9, 51.4, 31.4.

tt

N,N '-di-tert -butyl-1,4-diazabuta-1,3-diene (8.15 g, 48.4mmol) [7] was dissolved in 80 mL of tetrahydrofuran,2.2

Measurement of physical properties

and then sodium (2.28 g, 99.2 mmol) was added. The

Thermal gravimetric analysis (TG) was performed

reaction mixture was stirred at room temperature

under an argon flow (400 ml/min) at a heating rate offor 16 h. To the resulting deep-red solution, Si(OEt)4

10℃/min. Differential scanning calorimetry (DSC) was(9.79 g, 47.0 mmol) was added dropwise at roommeasured at the same heating rate in a stainless steel

temperature and stirred for 24 h at 50℃. The resulting

closed container sealed under an argon atmosphere.

mixture was filtered and the solvent was removed underVapor pressures were measured with a diaphragm

reduced pressure. The residue was purified by vacuum

gauge (Baratron®) placed in a thermostatic oven.

distillation (76 ℃/2.0x10 2 Pa) to obtain 11.33 g of
Si-TBES (84% yield) as a colorless oil. 1H NMR (5002.3Deposition of SiO2 thin films

MHz, C6D6, 20 ℃ , δ/ppm): 5.78 (s, 2 H, NCH =CH N),

SiO2 thin films were deposited on sapphire (C-plane)

3.76 (q, J = 7 Hz, 4 H, OCH 2CH3), 1.29 (s, 18 H, NC

substrates at the deposition temperature range from 350

13(CH 3)3), 1.18 (t, J = 7 Hz, 6 H, OCH2CH 3). C NMR (125to 500℃ by CVD using Si-TBES, Si-TBAS, and TDMAS.

MHz, C6D6, 20℃ , δ/ppm): 110.7, 58.9, 50.9, 30.9, 18.4.

The vapor of the precursors was generated by bubblingttSynthesis of Si[N( Bu)CH=CHN( Bu)]Cl (3).

method. This vaporized precursor was transferred to theN,N '-di-tert -butyl-1,4-diazabuta-1,3-diene (32.00 g,

cold wall type CVD reaction chamber with argon carrier

190.2 mmol) was dissolved in the mixture of 50 mL ofgas. The reactant gas was O2, and its concentration wastetrahydrofuran and 150 mL of hexane, and then lithium

constantly controlled at 0 to 50% of the total reaction(2.66 g, 383 mmol) was added. The reaction mixture

chamber pressure. The typical deposition conditions ofwas stirred at room temperature for 16 h. The resulting

SiO2 thin films are summarized in Table 1.

deep-red solution was added dropwise to a solution ofSiHCl3 (25.20 g, 186 mmol) in 50 mL of hexane at 0℃.

2.4

Evaluation of the thin films

The resulting mixture was allowed to warm to room

Deposition amount of the films was measured bytemperature and stirred for 3 h. The resulting mixture

the X-ray fluorescence (XRF) calibrated by standard

東ソー研究・技術報告

Si−TBES（2）51℃
31.4 Pa
20 sccm
220 sccm
13.3 kPa
1.2×10−4 mol ／hPrecursors
Bath temperature
Vapor pressure＊
Carrier gas（Ar）flow rate
Diluent gas（Ar）flow rate
Internal pressure of bubbler
Feeding rate＊＊

Si−TBAS（4）40℃
31.4 Pa
20 sccm
220 sccm
13.3 kPa
1.2×10−4 mol ／ hTDMAS
1℃
126 Pa10 sccm
230 sccm
26.7 kPa1.2×10−4 mol ／h

60 sccm（20％）
300 sccm
350−500℃
60 min
1.3 kPa

Reaction gas（O2）flow rate
Total gas flow rate
Deposition temperature
Deposition timeChamber pressure＊＊

19

Typical film deposition conditions for SiO2 thin films by CVD

Table１＊

第 56 巻（2012）

Vapor pressures of the precursors were estimated on Clausius−Clapeyron plots in Fig.3
The feeding rates of precursors were calculated assuming that the precursors werevaporizing as monomer

samples. The film composition and surface roughness

plots of these precursors, and the vapor pressureswere measured by X-ray photoelectron spectroscopy

estimated from the plot were summarized in Table 2.

(XPS) and atomic force microscopy (AFM), respectively.

Their volatilities are sufficient to apply to CVD and ALD

The depth profiles of the thin film were measured byprocesses.
Their thermal stabilities were compared with well-secondary ion mass spectroscopy (SIMS).

known precursors, TEOS and TDMAS [8] by DSC (Fig.
4). Exothermic peaks due to thermal decomposition

3．Results and discussions
3.1

were observed for Si-TBES (2) and Si-TBAS (4) at

Syntheses and properties of Si-TBES (2) and378℃ and 320℃, respectively. In contrast, TEOS andTDMAS were not decomposed below 450℃ . Although

Si-TBAS (4)Si-TBES (2) was readily synthesized by the reaction

these precursors showed slight exothermic baselineof TEOS with disodium vinylenediaminide (5) (Fig.

shifts around 320℃, the same behavior was observed1). By the reaction of lithium vinylenediaminide 6 withby cooling and reheating the samples. It means thesetrichlorosilane, corresponding chlorohydrosilane 3 wasexotherms do not come from decompositions, but fromobtained in good yield. Si-TBAS (4) was obtained by thethe reversible change of heat capacity, possibly by phasereaction of excess NH3 with 3 in high yield (Fig. 2).
Both of Si-TBES (2) and Si-TBAS (4) are liquid att

But

NNa
NNattthexane／THF

OEt

But

SiHCl3NNLi

hexane／THF

Ntt

Bu
Si

Bu3ClH

NH3

Temperature［℃］
7060

50

Fig.３

NSiBu
4

Synthetic route of Si−TBAS（4）

NH2
H

40100

2.80

2.90
3.00
1000／T［K−1］

3.10

3.20

Clausius−Clapeyron plots of Si−TBES（2）and
Si−TBAS（4）

BuNt

80

Si−TBES（2）Si−TBAS（4）102.70Synthetic route of Si−TBES（2）

NLi

Fig.２OEt

2BuBu
6SiNt

Bu
5Fig.１

BuNSi(OEt)41000
Vapor pressure［Pa］

room temperature. Fig. 3 shows the Clausius-Clapeyron

90

Table２

Vapor pressures of 2 and 4 calculated
from Clausius−Clapeyron plotsPrecursors
0.1 Torr
Si−TBES（2）37℃
28℃
Si−TBAS（4）1.0 Torr
69℃
62℃

TOSOH Research & Technology Review Vol.56（2012）

thin films at lower temperature than comparableprecursors. Although Si-TBES (2) and Si-TBAS (4) have
low decomposition temperature, TG curves revealed
that they still have the sufficient volatilities to vaporize
without any undesirable residue (Fig. 5).
3.2

Deposition rate［mol cm−2 h−1］

Si-TBAS (4) will be suitable to form silicon containing

SiO2 thin film deposition by a CVD apparatus

Fig.６

Deposition rate［mol cm−2 h−1］

as the reaction gas. Fig. 6 shows the deposition rate of
SiO2 plotted against the deposition temperature ranging
from 350℃ to 500℃ . The deposition rates using thesenew precursors were higher than that using TDMAS.
Especially, Si-TBAS (4) enables to form the thin filmwith about twice to 20 times higher deposition rate thanTDMAS at the deposition temperature of 350 to 500℃ .
the concentration of oxygen. The total flow rate was

Heat flux［a.u.］

1.3

1.4

1.5

1.6

11.8

1.7

Temperature dependency of the deposition rate of theSiO2 films from 2,4 and TDMAS

2.0×106

Fig.７

Si−TBES（2）Si−TBAS（4）TDMAS

1.5×106

140100

1.0×10660
0.5×106
200Fig. 7 illustrates the deposition rates plotted against

01020304050Concentration of O2［vol％］Oxygen concentration dependency of the deposition
rates of the SiO2 films from 2,4 and TDMAS at 500℃

varied from 0 to 150 sccm, corresponding to from 0%

Tdec＝378℃

to 50% of the oxygen concentration. Interestingly, thegrowth rates using Si-TBES (2) and Si-TBAS (4) are

Tdec＝320℃

less influenced by the concentration of oxygen, whileTDMAS

TDMAS requires higher concentration of oxygen toTEOS

produce thin films. These results indicate that Si-TBES
200300400500Temperature［℃］Fig.４

100101×10−81.2on sapphire (C-plane) substrates and oxygen was used

100Si−TBES（2）Si−TBAS（4）TDMAS

1×10−7thermal CVD apparatus. SiO2 thin films were produced

Si−TBAS（4）300

1000／T［K−1］(2), Si-TBAS (4) and TDMAS were investigated by aSi−TBES（2）Deposition temperature［℃］
400

1×10−6

Deposition properties of SiO2 thin films using Si-TBES

fixed at 300 sccm, and the oxygen flow rate was500

1×10−5Calcd. growth rate［nm h−1］transitions. These results indicate that Si-TBES (2) andCalcd. growth rate［nm h−1］20(2) and Si-TBAS (4) react readily with oxygen to form
SiO2 thin film. Although the whole reaction mechanism
is unclear, it presumably starts with the dissociation

DSC curves of silicon precursorsof the bidentate vinylenediamide ligand in the samemanner as Ti-DOT (1), followed by the decomposition

Weight Loss［％］

0of the reactive silicon containing species to form SiO2(Fig. 8).

−20−40Si−TBES（2）

3.3

−60
−80

The atomic compositions of the films deposited atSi−TBAS（4）500℃ were observed by XPS (Table 3). All of the films
contain oxygen and silicon at the ratio of approximately−100100200300400500

Temperature［℃］

Fig.５

Characterization of the deposited thin films

TG curves of Si−TBES（2）and Si−TBAS（4）2:1, concluding the formation of SiO2 thin films. Carbon
and nitrogen concentrations were below the detection
limit for Si-TBES (2) and TDMAS, while Si-TBAS (4)東ソー研究・技術報告

t

SiNtt

BuN

SiO2 thin film

［O2SiR1R2］

Nt

BuBuPlausible decomposition pathway of the silicon precursors

Fig.８

Table３＋R221BuNO2R1

第 56 巻（2012）

concentration of carbon and nitrogen than Si-TBES (2)Atom concentration of the films
estimated by XPSand TDMAS. This tendency possibly come from therapid film growth using Si-TBAS (4), which prevents

Concentration［atom％］
OSiCN
Si−TBES（2） ＜1 ＜167
31
Si−TBAS（4） ＜16929
2TDMAS6931＜1 ＜1＊Deposition Temperature：500℃Precursors

carbon and nitrogen from the desorption.
Root-mean-square (Rms) surface roughness values
were evaluated with AFM images (Fig. 10 and Table5). SiO2 thin films were deposited on amorphous SiO2/Si substrates using oxygen as the reaction gas. Since Si-produced SiO2 film containing 2% of nitrogen, which

TBAS (4) can produce SiO2 thin films more efficiently

may derived from SiNH2 moiety.

than TDMAS, the deposition time using Si-TBAS (4) isSIMS was performed in order to investigate the depth

1/15 of that using TDMAS. Nevertheless, the film using

profiles of the carbon and nitrogen contamination (Fig.

Si-TBAS (4) was fairly smooth, and its Rms value was

9 and Table 4). Compared with the film deposited fromcomparable to the film from TDMAS of approximately

TDMAS, that from Si-TBES (2) obviously had lower

the same thickness. These results indicate that theconcentration of carbon and nitrogen. In contrast, Si-Si-TBAS (4) can provide SiO 2 thin films of the same

TBAS (4) tended to form thin films with slightly higher

roughness in shorter deposition time than TDMAS.

Table４

Carbon and nitrogen concentration
calculated from SIMS4．Conclusions

Concentration［atm％］
CN
0.03
0.03
Si−TBES（2）Si−TBAS（4）
1.5
1.0
TDMAS
0.06
0.30

Novel precursors Si-TBES (2) and Si-TBAS (4)bearing a diazasilacyclopentene framework weresynthesized, and their volatilities, thermal properties,
and deposition characteristics were evaluated. They1023（a）Carbon content

Concentration［atoms／cc］

Concentration［atoms／cc］

Precursors

1022
Si−TBAS（4）

1021

TDMAS

1020

Si−TBES（2）

1019
1018
1017

050

100

1502001023（b）Nitrogen content
1022
Si−TBAS（4）

1021

TDMAS

1020

Si−TBES（2）10191018
10170

Depth［nm］

Fig.９

50100150200

Depth［nm］

Depth profiles of (a) carbon and (b) nitrogen concentration in SiO2 thin films

Table５Precursors
Si−TBAS（4）TDMAS

Surface roughness of as−deposited films

Deposition
Temp.［℃］
500500

Deposition
Time［min］
10150

Film Thickness
［nm］
1815

Rms［nm］
0.260.30

TOSOH Research & Technology Review Vol.56（2012）

22（a）

６．(a) H. Chiba, K. Tada, T. Yamamoto, K. Iwanaga,（b）A. Maniwa, T. Yotsuya, N. Oshima, H. Funakubo,TOSOH Research & Technology Review 55, 3(2011). (b) T. Yamamoto, K. Tada, K. Iwanaga, H.
Chiba, A. Maniwa, T. Yotsuya, N. Oshima and H.
500 nm

500 nmFunakubo, Abstracts; Fall Meeting of the Materials

Research Society, Boston , G6.38 (2010).
Fig.10

AFM images of SiO2 thin films on amorphous SiO2／Si
substrates deposited from (a) Si−TBAS (4) and(b) TDMAS

７．M. Haaf, A. Schmiedl, T. A. Schmedake, D. R.
Powell, A. J. Millevolte, M. Denk, and R. West. J.

Am. Chem. Soc. , 120, 12714(1998).
８．L. Bartholomew, C. Barelli, J. Owyang, R. DiCarlo,

are volatile enough for CVD/ALD precursors, and their

D. Shenai, C. Marsman and Y. Senzaki, ECS Trans .

decomposition temperatures were significantly lower

3, 37 (2007).

than those of TEOS and TDMAS. CVD processes withthese precursors provided SiO2 thin films efficiently, andthe oxygen concentration dependency of the deposition
rates indicated the high reactivity of Si-TBES (2) andSi-TBAS (4) towards oxygen caused the efficient thinfilm formation. Characterizations of the deposited films
revealed that Si-TBAS (4) can produce smooth thin film
efficiently, while the film deposited from Si-TBES (2)contains less carbon and nitrogen contamination thanthat from Si-TBAS (4) and TDMAS. Syntheses of otherdiazasilacyclopentene derivatives and their deposition
properties are under investigation.

5．References
１．B. Lesse and A. R. Mills, in Chemical Vapour

Deposition: Precursors, Processes and Applications ,A. C. Jones and M. L. Hitchman, 2. Editors, p. 535,
RSC Publishing, UK (2009).
２．C. Adams and C. D. Capio, J. Electrochem. Soc .
126, 1042 (1979).
３．C. Adams, F. B. Alexander, C. D. Capio and T. E.
Smith, J. Electrochem. Soc . 128, 1545 (1981).
４．G. N. Parsons, J. H. Souk and J. Batey, J. Appl.

Phys . 70, 1553 (1991).
５．H.-U. Kim and S.-W. Rhee, J. Electrochem. Soc .
147, 1473 (2000).