75●A Novel MO Precursor for Tantalum Containing Film
Tokyo Research Center, TOSOH Corporation

１．Introduction

Kenichi Sekimoto
Noriaki Oshima

２．Synthesis of precursor

Tantalum nitride (TaN) is used for a diffusion barrier

Ta(EtCp) 2 (CO)H was synthesized from bis

film in copper (Cu) interconnects. Since TaN has poor

(ethylcyclopentadienyl)trihydridotantalum

adhesion to Cu, an adhesive layer is put between TaN(Ta(EtCp)2H3) and CO. The former trihydride complexand Cu film. A metal tantalum (Ta) film is one of thewas prepared following the literature method [5].

candidates for the adhesive layer. In the current

Ta(EtCp)2(CO)H was purified by distillation under aprocess, the Ta/TaN laminated film is deposited byreduced pressure. This precursor was purple liquid at

physical vapor deposition (PVD). Whereas the barrierroom temperature (mp = 15 ℃). The molecular

film is required to be thinner and more conformal withstructure was confirmed by nuclear magnetic

shrinkage of the interconnect dimensions. Thus,

resonance spectroscopy (NMR), infra red spectroscopy

chemical vapor deposition (CVD) and atomic layer(IR), inductively coupled plasma - atomic emission

deposition (ALD) processes have been investigated as aspectrometry (ICP-AES) and elemental analysis. The

new deposition method.

structure estimated by 1H-NMR reasonably explained

Several tantalum compounds have been investigatedthe 13C-NMR spectrum. These spectroscopic data andfor the precursors of CVD and ALD processes.

the result of the elemental analysis conclude theTantalum amide complexes such as pentakis

molecular structure in Fig. 1.

(dimethylamido)tantalum (PDMAT) [1] and tert-

１H-NMR (Benzene-d6, δppm)

butylimido tris(diethylamido)tantalum (TBTDET) [2,3]4.53(m, 2H, C5H4Et), 4.46(m, 2H, C5H4Et), 4.42(m,contain nitrogen atoms in the molecules. Therefore, it

2H, C 5 H 4 Et), 4.35(m, 2H, C 5 H 4 Et), 2.26(m, 4H,is difficult to make a metal tantalum film. Halogen

CH 3 CH 2 C 5 H 4 ), 1.00(t, J=7.5Hz, 6H, CH 3 CH 2 C 5 H 4 ),atoms in tantalum halides (TaCl5 and TaBr5) [4] are-6.16(s, 1H, Ta-H)

cause of corrosion or poor adhesion.

13

We developed the novel tantalum compound,

C-NMR (Benzene-d6, δppm)
264.26(CO), 112.38(C 5 H 4 Et), 83.71(C 5 H 4 Et),bis(ethylcyclopentadienyl)hydridocarbonyltantalum

83.40(C 5 H 4 Et),

(Ta(EtCp)2(CO)H, Fig. 1), for CVD and ALD process

23.26(CH3CH2C5H4), 15.92(CH3CH2C5H4)

which have neither nitrogen nor halogen atom.

IR(Nujol, νcm-1)

In thispaper, we introduce physical properties and film
deposition results of this precursor.

82.08(C 5 H 4 Et),

79.61(C 5 H 4 Et),1896(CO), 1721(Ta-H)
Elemental analysis and ACP-AES
Found (calculated) C: 46.2％(45.5％) H: 5.1％(4.8％)
Ta: 46.4％(45.7％)(Tantalum content was measured by ICP-AES.)

Et

CO

３．Physical properties of precursor

TaH［1］ Vaporizing and decomposition characteristics
The vaporizing and decomposition characteristics

Et

were investigated with thermo gravimetric (TG) andFig. １

Molecular structure of Ta（EtCp）（CO）
H2

differential scanning calorimetric (DSC) curves（ 75 ）76TOSOH Research ＆ Technology Review Vol.51（2007）changes after 24 hours at 170 ℃ and 96 hours at 140 ℃.

obtained under an argon atmosphere.
Fig. 2 illustrates the TG and DSC curves ofTa(EtCp)2(CO)H, and revealed that the vaporizing and［4］Viscosity

decomposition temperature of the precursor is 130 ℃

The viscosity was measured by B type Viscometer.

(TG) and 240 ℃ (DSC), respectively. Thus, theFig. 4 shows the viscosity diagram of Ta(EtCp)2(CO)H.

precursor vaporizes without any decomposition.

This diagram indicates that this precursor can be usedin direct liquid injection by heating. In addition, thisTG［％］

0−20−40−60−80−100−12025Fig.２

75125

175 225 275 325
Temperature［℃］375

precursor dissolves in hydrocarbon solvents. So it also
can be used in liquid injection as solution.

Temperature［℃］
7060

50

4030

2.933.1

3.2

3.3

100
Viscosity［cP］

65432
10−1−2−3−4DSC［mW］

20425

The TG and DSC curves of Ta（EtCp）2（CO）H
under an argon atmosphere at a heating rateof 10℃／min.

101［2］Vapor pressure3.4−11000／T［K ］

The vapor pressure was determined by a staticmethod. Fig. 3 depicts the vapor pressures ofFig.４Ta(EtCp)2(CO)H at various temperatures. The formulaof vapor pressure = 1.68 x 1011 x exp (-8.87 x 1000/T)
was obtained from the curve of 1000/T vs. vapor

Viscosity diagram of Ta（EtCp）2（CO）H

４．Film depositionpressure. The vapor pressure calculated from thisFilm depositions on Si/SiO2 or Si substrates were

formula is 1 Pa at 70 ℃ and 8 Pa at 100 ℃. These values

performed using cold wall type thermal CVD andsuggest that this precursor is volatile enough to beelectron cyclotron resonance (ECR) plasma CVD

used in the CVD and ALD process.

equipments. The vapor of the precursor was generated
by bubbling method. The film thicknesses weredetermined from TEM images. The resistivities of theTemperature［℃］

Vapor pressure［Pa］

130

120

110films were measured using a standard four-probe

100method. The compositions of the films were analyzed

100

by auger electron spectroscopy (AES).
10［1］Film deposition by thermal CVD
The metal tantalum film deposition was attempted by
the thermal CVD. The deposition condition is1

summarized in Table 1.
2.45 2.50 2.55 2.60 2.65 2.70

The resistivity of the film deposited below 500 ℃ was

1000／T［K−1］Fig.３

too high to measure it with the standard method. The
resistivity of the film deposited at 600 ℃ could be

Vapor pressure diagram of Ta（EtCp）2（CO）H

determined to be 1.78 x 105 μΩcm (film thickness was［3］Thermal stability250nm); it is still high for the adhesive layer of Cu
1

Thermal stability was confirmed by changes of H-interconnects. The high resistivity will be due to theNMR before and after heating. This precursor had nocontamination of carbon. Actually, the AES depth（ 76 ）

東ソー研究・技術報告 第51巻（2007）

77

Tabel１ Experimental condition by thermal CVD
Bubbler Temperature
Bubbler Pressure
Carrier gas（Ar）flow rate
Dilute gas（Ar）flow rate
Total flow rate

90℃
13.3kPa
100sccm
100sccm
200sccm

Deposition Pressure
Deposition Time
Substrate
Substrate Temperature

Concentration［atom％］profiles of deposited film at 600 ℃ revealed 55atom％
carbon and 10atom％ oxygen in the film as shown inFig. 5. The high carbon concentration may be derived
from incomplete thermal decomposition of theprecursor.

100
Si80
Ta60

C40
20

N0O

0Concentration［atom％］

1.33kPa
120minSi／SiO2600℃

1234

5Sputter Time［min］

10080

Fig.６

C60
Ta

40
20

N

005

The composition of film deposited by ECR
plasma CVD.

SiO
10presence of hydrogen gas was examined in order to15

202530reduce the carbon concentration in the film. The

35

deposition condition is summarized in Table 3.

Sputter Time［min］

Argon gas, which added 4％ of hydrogen gas, wasFig.５

The composition of film deposited by thermal CVD.

used as a source of plasma. The film thickness of theobtained film was 14.3nm. Fig. 7 shows the AES depth［2］Film deposition by ECR plasma CVD

profile of the film. Although carbon concentration

In order to decompose the precursor completely, theincreased slightly, the resistivity decreased to 109 μΩ

ECR plasma CVD technique was investigated. Thecm. This result is assumed to be due to decrease ofdeposition condition is summarized in Table 2.

oxygen concentration in the film.

The film thickness of the obtained film was 7.2nm
Concentration［atom％］and its resistivity was 143 μΩcm. Fig. 6 shows theAES depth profiles of the deposited film. The carbon
concentration decreased to about 50％ of that in thefilm deposited by thermal CVD, indicating that the ECRplasma CVD decomposes the precursor more than thethermal CVD.

100
Si80

Ta60
C

4020O

N

0012

345Sputter Time［min］［3］Film deposition by ECR plasma CVD with 4％
Fig.７hydrogen gas

The composition of film deposited by ECR plasmaCVD with 4％ hydrogen gas

Furthermore, ECR plasma CVD deposition in theTabel２

Experimental condition by ECR plasma CVD

Bubbler Temperature
Bubbler Pressure
Carrier gas（Ar）flow rate
Plasma Source gas（Ar）
flow rate
Total flow rate

90℃
6.67kPa
28sccm10sccm38sccmDeposition Pressure
Deposition Time
Substrate
Substrate Temperature

0.2kPa30min
Si400℃

Plasma Power600W（ 77 ）78

TOSOH Research ＆ Technology Review Vol.51（2007）

Tabel３

Experimental condition by ECR plasma CVD with 4％ hydrogen gas

Bubbler Temperature
90℃
Deposition Pressure
Bubbler Pressure
9.33kPaDeposition Time
Carrier gas（Ar）flow rate
55sccmSubstrate
Plasma Source gas（Ar／H2） 40sccm
Substrate Temperature
flow rate （H2:1.6sccm）
Total flow rate
95sccmPlasma Power

５．Conclusions
A novel tantalum precursor for CVD and ALD,
Ta(EtCp)2(CO)H, which is nitrogen and halogen freeand liquid phase at room temperature, was developed.
The vapor pressure and decomposition temperature
indicates that this precursor is suitable for CVD and
ALD process.
The film deposited by the thermal CVD at 600 ℃
contained the large amount of carbon and have highresitivity. On the other hand, the carbon concentrationin the film deposited by the ECR plasma CVD at 400 ℃
was about half of that in the film deposited by thethermal CVD, resulting in the low resistivity.
Furthermore the film deposited by the ECR plasma
CVD in the presence of 4％ hydrogen gas had lower
resistivity.

６．References
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1.0kPa300minSi300℃
600W