● Development of a Novel Ru Precursor
for Non-Oxidative MOCVD
Advanced Materials Research Laboratory, TOSOH Corporation
Sagami Chemical Research Institute

Hiroyuki OikeKen-ichi Tada

In this study, We developed a novel Ru precursor,

1．Introduction(η5 - 2 , 4 - d i m e t h y l - 1 - o x a - 2 , 4 - p e n t a d i e n y l ) (η5 -Ruthenium thin films have attracted much attention

ethylcyclopentadienyl)ruthenium [Rudense®], to form

for a wide variety of technological applications, such

pure Ru thin films under non-oxidative conditions andas metal capping layers , liners of Cu interconnects inevaluated the deposition characteristics of Rudense®

integrated circuits,2 and electrodes in dynamic random

by CVD with ammonia (NH3) as non-oxidative gas. 13

1access memory.

3-5

We also examined the surface flatness and the stepIn the cases of metal capping layers

coverage of the films from Rudense®.

and liners of Cu interconnects, Ru thin films have to bedeposited under non-oxidative conditions to prevent theOur development will contribute to improvement inoxidation of barrier layers or substrates.

energy efficiency.

However, many of the known Ru precursors, suchas bis(η5-ethylcyclopentadienyl) ruthenium, 6 (η5-2,4-2．Experimentdimethylpentadienyl) (η5 -ethylcyclopentadienyl)
ruthenium, 6 (η5-ethylcyclopentadienyl)(η5- pyrrolyl)

2.1

7Preparations

All manipulations were carried out under argon

ruthenium, and tris(2,2,6,6-tetramethyl-3,58

h ep t a n ed i o n a to ) r u the n i u m , r e q u i r e o x i d a t i v e(Ar) atmosphere with standard Schlenk techniques.

conditions for thin film deposition.

Acetonitrile, dichloromethane, diethylether, andSeveral precursors have been studied for non-hexane were purchased from Kanto Chemical Co. Inc.

oxidative MOCVD (metal organic chemical vapor

as dehydrated grade. Bis(η5-ethylcyclopentadienyl)

deposition). However, they have some weakruthenium (1), lithium carbonate, mesityl oxide, andpoints. Carbonyl coordinated precursors, such as

tetrafluoroboric acid diethyl ether complex were

49

purchased from Sigma-Aldrich Co. LLC and used

10without further purification. 1H- and 13C-NMR spectralack thermal stability and can not provide pure Ru thin

were recorded on a Varian VXR-500S instrument atfilms. Amidinate precursor, such as bis(N , N ’-di-tert-

293 K.

tricarbonyl(η -cycloocta-1,3,5,7-tetraene) ruthenium
4

and tricarbonyl(η -1,3-cyclohexadiene)ruthenium,butylacetamidinato)dicarbonylruthenium,

11

is a solid

at room temperature that means it has difficulties inSynthesis of [Ru(η5-C5H4Et )(NCMe)3][BF4] (2)handling for MOCVD processes. Recently, RuO4 12 has

Tetrafluoroboric acid diethyl ether complex (2.55 g,been investigated as a precursor for thin film deposition

15.7 mmol) was slowly added to a solution of bis(η5-with H2 as reaction gas, however, it is too heat-labile toethylcyclopentadienyl)ruthenium (1) (4.31 g, 15.0

feed into the CVD reactor.

mmol) in 40 mL of acetonitrile at 0 ℃ . The reaction

Ru

BF4

HBF4・Et2O0℃

MeCN
rt，20 h1

MeCN
MeCNRuNCMeOrt

2Fig.１，Li2CO380 ℃，8 hRuO
Rudense®

Synthetic route of Rudense®

67

TOSOH Research & Technology Review Vol.63（2019）℃ by CVD using Rudense ®. The Rudense®

mixture was stirred at this temperature for 0.5 h, andto 500

then warmed to room temperature and additionallywas supplied by a bubbling method with the vapor

stirred for 20 h. After the removal of solvent underpressure of 5.3 Pa at 64 ℃ . This vapor was transferred

reduced pressure, the residue was washed with CH2Cl2

to a cold wall type CVD reactor chamber using Ar as(5 mL)/Et2O (50 mL) to give complex 2 as a yellowisha carrier gas. NH 3 was used as a reaction gas. The

brown solid (5.93 g, 98%). 1H-NMR (500 MHz, CDCl3,concentration of NH3 was kept at 70% in the total reactor

δ/ppm): 4.10-4.15 (m, 2 H), 3.89-3.94 (m, 2 H), 2.40 (s,chamber pressure. The typical deposition conditions are

9 H), 2.03 (q, J = 7.0 Hz, 2 H), 1.07 (t, J = 7.0 Hz, 3 H).

summarized in Table 1.

13

C-NMR (125 MHz, CDCl3, δ/ppm): 124.9, 96.7, 70.0,63.4, 20.3, 13.6, 3.7.

2.4

Evaluation of Ru thin films

Deposition amount of the films was measured
55by the X-ray fluorescence (XRF) calibrated by

Synthesis of Ru(η -C5H4Et)(η -CH2C(Me)CHC(Me)®

standard samples. The crystallinity, depth profiles

O) (Rudense )Lithium carbonate (1.36 g, 18.4 mmol) was added toof contaminations, and surface roughness werea solution of complex 2 (1.49 g, 3.68 mmol) in 15 mL ofdetermined by X-ray diffraction (XRD), secondary

mesityl oxide at room temperature. After the stirring

ion mass spectroscopy (SIMS), and atomic force

for 0.5 h at room temperature, the reaction mixture

microscopy (AFM), respectively. The resistivity of thewas stirred at 80 ℃ for 8 h. After the removal of solvent

films was measured by a four-point probe method atunder reduced pressure, the residue was extracted withroom temperature. Transmission electron microscopy

hexane (60 mL) and filtered through a Celite-padded(TEM) was used to characterize film morphology andG4 glass filter. The filtrate was concentrated, and theconformality.

residual oil was purified by distillation under reducedpressure (88℃ , 5 Pa) to give Rudense® as a deep redliquid (0.93 g, 86%). 1H-NMR (500 MHz, CDCl3,δ/ppm):
5.44 (s, 1 H), 4.59-4.63 (m, 1 H), 4.51-4.55 (m, 1 H), 4.48-

3．Results and discussion
3.1

Physical properties of Rudense®

4.51 (m, 1 H), 4.37-4.40 (m, 1 H), 3.80 (s, 1 H), 2.24 (s, 3Rudense® is a deep red liquid around roomH), 2.13 (q, J = 7.5 Hz, 2 H), 1.70 (s, 3 H), 1.53 (s, 1 H),

temperature. The vaporization property and the self-13

1.12 (t, J = 7.5 Hz, 3 H). C-NMR (125 MHz, CDCl3, δdecomposition temperature of Rudense® were measured/ppm): 134.2, 101.1, 100.3, 84.2, 75.7, 74.5, 74.4, 73.9,

with the help of TG and DSC, respectively (Fig. 2). As

52.3, 26.7, 24.1, 21.2, 14.8.

shown in the TG curve, Rudense® exhibited single-stepweight loss and had almost no residues. The exothermic

2.2

peak due to thermal decomposition was observed

Measurement of physical properties

Thermogravimetric analysis (TG) was carried out

around 230 ℃ by DSC. The Clausius-Clapeyron plots ofunder an argon flow (400 mL/min) at a heating rate

Rudense ® are presented in Fig. 3, and the vaporof 2 ℃ /min with an instrument that was containedpressure was determined to be 13 Pa at 76℃ . Thesein a high-purity nitrogen-filled glovebox to prevent

results indicate that Rudense ® has sufficient vapor

decomposition arising from exposure to air. Differential
scanning calorimetry analysis (DSC) was performed ata heating rate of 10 ℃ /min with a sealed container ina high-purity argon gas atmosphere. Vapor pressures®

were estimated with a diaphragm gauge (Baratron )placed in a thermostatic oven.
2.3

Deposition of Ru thin films

Ru thin films were deposited on Pt, Ru, Si, and SiO2
substrates at the deposition temperature range from 300
68

Table１

Typical deposition conditions of Ru thinfilms by CVD

Depo. pressure
Precursor feed
Carrier gas
Reaction gas
Total gas flow
Substrate

1.3 kPa
0.024 sccm
30 sccm (Ar)
70 sccm (NH3)100 sccm
Pt (150 nm)/Ta2O5/SiO2/Si
Ru (100 nm)/Ti/SiSiSiO2(100 nm)/Si東ソー研究・技術報告

exhibits much higher resistivity.

0DSC［a.u.］

－20
TG［％］

第 63 巻（2019）

－40
－60

3.3

Deposition time dependency

The deposition time dependency of Ru film thickness
on Pt, Ru, Si, and SiO2 substrates at 400 ℃ is presentedin Fig. 5. The incubation time on Pt and Ru substrates－80

was shorter than that on Si and SiO 2 substrates.

－100

100200Although the deposition rates on Si and SiO2 substrates

300

Temperature［℃］Fig.２

were much smaller than Pt and Ru at the initial stage,®

TG and DSC curves of Rudense

the deposition rate gradually became almost the sameas that on Pt and Ru substrates, because the surfaces ofSi and SiO2 substrates were covered with Ru thin films.

Temperature［℃］120

Vapor pressure［Pa］

103

100

80

From these results, it is suggested that the nucleation

60

rate on Si and SiO2 substrates is lower than the rate onPt and Ru substrates.

102

3.4

101

Deposition temperature dependency

The deposition temperature dependency of Ru film

100
2.5

deposition rate on Pt, Ru, Si, and SiO2 substrates is2.7

2.9

3.1

1000/T［K－1］100

Clausius-Clapeyron plots of Rudense®

pressure and thermal stability for CVD processes.
3.2

Reactivity with ammonia

NH3 concentration dependency of deposition rate ofFilm thickness［nm］

Fig.３

Ru thin films on SiO2 substrate at 450 ℃ is shown in

80
604020Fig. 4. The deposition rate is increased with increase

0in the concentration of NH 3, which emphasizes thatRudense® has favorable reactivity with NH3. In addition,
the resistivity of the films prepared in the presence◇ Pt. sub.
□ Ru sub.
△ Si sub.
〇 SiO2 sub.

060120180240Depo. time［min］

Deposition time dependency of Ru film thickness
on Pt, Ru, Si, and SiO2 substrates at 400℃Fig. ５of 20% or more of NH3 concentration is as low as 10
to 20 μΩ cm, while the films deposited with lower NH31030

10420103

10102

01Fig.４0102030
40
Concentration of NH3［vol％］50

Depo. rate［nm/h］

40◇ Pt. sub.
□ Ru sub.
△ Si sub.
〇 SiO2 sub.

50

5Resistivity［μΩ・cm］

Depo. rate［nm/h］

604030201010NH3 concentration dependency of deposition
rate and electric resistivity of Ru thin films
on SiO2 substrate at 450 ℃

0300

350

400

Depo. temp.［℃］Fig. ６

Deposition temperature dependency of Ru film
deposition rate on Pt, Ru, Si, and SiO2 substrates

69

TOSOH Research & Technology Review Vol.63（2019）shown in Fig. 6. Ru thin films were not deposited on

3.6

Depth profile

Si and SiO2 substrates at 350 ℃ or lower. In contrast,

SIMS was performed to investigate the depth profiles

smooth film growth were observed on Pt and Ruof the carbon, nitrogen, and oxygen concentration in Ru

substrates. Since the substrate selective deposition wasthin films deposited on Pt, Ru, Si, and SiO2 substrates®

observed at 350 ℃ , Rudense has a possibility to achieve

at 400 ℃ (Fig. 8). Each impurity on the surfaces of Ru

area-selective CVD under non-oxidative conditions.

films on Pt, Ru, Si, and SiO2 substrates was higher than
1022 atoms/cc. In contrast, each impurity inside of Ru

3.5

film was less than 1021 atoms/cc. Hence, the high-purity

Crystallinity

Ru film can be formed from Rudense®.

The Ru thin films deposited on Pt, Si, and SiO 2
substrates at 400℃ were analyzed by XRD to ascertain
their crystallographic orientation (Fig. 7). All deposited

3.7

Resistivity

Ru thin films were crystallized and showed the mostFor a 50 nm-thick Ru film on Si substrate and a 51 nm-intense (002) reflection, corresponding to c-axis

thick Ru film on SiO2 substrate deposited in the 70% NH3

oriented Ru metal. In addition, low intense (100) andconcentration at 400 ℃ , the resistivity measurements(101) reflections were observed from the deposited

gave values of 16 and 17 μΩ cm, respectively. Thesefilms on Si and SiO2 substrates. The other reflections

values were close to that of bulk Ru (7 μΩ cm).14

were associated with the substrates.

Ru(002)Pt(111)

Intensity［a. u.］Ru film on Pt

Si(200)Ru(101)Ru(100)Ru film on Si

Ru film on SiO2
2530

35

40

45

5055

θ－2θ［degree］

Fig.７1024

Concentration［atoms/cc］

1023

XRD patterns of Ru thin films deposited on Pt, Si, and SiO2
substrates at 400 ℃（b） N Profiles

C Profiles（a）interfaceinterfaceinterface

Ru/SiO21022Ru/SiO2
1021

Ru/Si
Ru/Ru

10

Ru/Si

Ru/SiO2

Ru/Si

20

Ru/Ru

Ru/Ru

1019
Ru/Pt

Ru/Pt
1018
0204060

Depth［nm］

Fig.８70（c） O Profiles

80

02040

Ru/Pt
60

Depth［nm］

80

020406080

Depth［nm］

Depth profiles of (a) carbon, (b) nitrogen, and (c) oxygen concentrationin Ru thin films deposited on Pt, Ru, Si, and SiO2 substrates at 400 ℃

東ソー研究・技術報告

3.8

Surface roughness

第 63 巻（2019）

Table３

AFM micrographs of Ru thin films deposited on SiO2
substrate at 350, 400, and 500 ℃ are shown in Fig. 9.

Detailed deposition conditions of Ru thinfilms by pulsed CVD

AFM analysis shows the film morphology and surface

Depo. temperatureDepo. pressure

roughness to be dependent on deposition temperature

Pulsing sequence(Table 2), and particle sizes were found to increase withincreasing deposition temperature. The film deposited
at 500 ℃ exhibits a high degree of crystallinity. Goodsurface flatness was demonstrated for the films
deposited at 350 and 400 ℃ .
3.9

Gas flow rate
Cycle number
Substrate
Hole diameterAspect ratio

Step coverage

TEM

Ru thin film was deposited on SiO2 holes prepared350 ℃
1.3 kPa
5.0-5.0-10.0-10.0 s(Rudense®-Ar-NH3-Ar)
20/30/15 sccm
(Carrier/purge/NH3)
600
SiO2/Si
200 nm
5.0

Ru/EDXTop

on Si substrate with an aspect ratio of 5.0 at 350 ℃ bypulsed CVD. The pulsing sequence was Rudense® (5.0s), Ar purge (5.0 s), NH3 (10.0 s), and Ar purge (10.0Middles) for 600 cycles. The detailed deposition conditions
are summarized in Table 3. Cross-sectional TEM-EDX
image of the film is presented in Fig. 10. The deposited

Bottomfilm was continuous, and film conformality was good
within the tested aspect ratio. The step coverage (the100 nmfilm thickness on groove wall divided by the film
Fig.10thickness on flat surface) was over 90%.

4．Conclusions

Cross-sectional TEM-EDX images of Ru thin filmon SiO2 holes prepared on Si substrate at 350 ℃

The characteristics of the film was low-impurity, low-A synthetic procedure was presented for a novel

resistivity and good surface flatness. In addition, the®

liquid precursor, Rudense . By using Rudense , Ru

film deposited at 350 ℃ by pulsed CVD showed a goodthin films were deposited on various substrates such

step coverage on a substrate with holes. Furthermore,as Pt, Ru, Si, and SiO2 under non-oxidative conditions.

the incubation time of the Ru thin film depositions on Pt®

and Ru substrates was shorter than that on Si and SiO2(b)(a)

substrates. Although Ru thin films were not deposited(c)on Si and SiO2 substrates at 350℃ , Ru thin films weredeposited on Pt and Ru substrates. Therefore, Rudense®
is a promising precursor for area-selective CVD

500nm

Fig.９

500nm

500nm

AFM ( 2 µm × 2 µm) micrographs for Ru thin films
deposited on SiO2 substrate at a deposition temperature(a) 500 ℃ (b) 400 ℃ (c) 350 ℃

processes under non-oxidative conditions.

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Table２

Surface roughness of deposited Ru thin films
on SiO2 substrate［nm］ Rms［nm］
Depo. temp.［℃］ Film thickness
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