J. Plasma Fusion Res. SERIES, Vol. 8 (2009)

Substrate temperature dependence of deposition profile of plasma CVD
carbon films in trenches
Jun Umetsu,1 Kazuhiko Inoue,1 Takuya Nomura,1 Hidefumi Matsuzaki,1 Kazunori Koga,1, 4Masaharu Shiratani,1, 4 Yuichi Setsuhara,2, 4 Makoto Sekine,3, 4 and Masaru Hori,3, 4
123Department of Electronics, Kyushu University, 744 Motooka, Fukuoka 819-0395, Japan

Joining and Welding Research Institute, Osaka University, 11-1 Mihogaoka, Ibaraki 567-0047, Japan

Department of Electrical Engineering and Computer Science, Nagoya University, Furo-cho, Nagoya 464-8603, Japan
4JST, CREST(Received: 8 September 2008 / Accepted: 27 February 2009)

To control deposition profile of carbon films in trenches, we have studied substrate temperature and aspect ratio
dependence of deposition rate of carbon films, deposited by CVD plasma of toluene diluted H2, in trenches. The
deposition rates increases with decreasing the aspect ratio, because the incident radical flux per surface area in atrench increases with decreasing the aspect ratio. The deposition rate increases with decreasing the substratetemperature, because of the lower etching rate by H atoms at the lower temperature.

Keywords: plasma CVD, carbon film, deposition profile, aspect ratio, trench

ICP H atom source

Diamond-like carbon (DLC) films first reported in the1970s were deposited by ion beam deposition. [1, 2], andhydrogenated amorphous carbon (a-C:H) films introducedin the beginning of 1980s were deposited by rf plasma
chemical vapor deposition (CVD) [3]. Since then a-C:Hfilms deposited by rf plasma CVD have been studied
intensively by several authors [4]. Moreover, the mostwidely used technique for DLC films deposition is rf
plasma CVD. DLC is a term used to describe a variety ofcarbon based materials with attractive properties, such as ahigh mechanical hardness, chemical inertness, opticaltransparency and wide band gap [5-8]. DLC films havewidespread applications as protective coatings in several
areas such as car parts, biomedical coatings andmicro-electromechanical systems (MEMS). Deposition
profile of the DLC and a-C:H films in trenches is one of
the concerns to realize coatings on patterned substrates.
We have studied deposition profile of plasma CVD
Cu films in trenches for nano-fabrications [9-16]. We havesucceeded in controlling deposition profile of Cu intrenches, and have realized sub-conformal, conformal andanisotropic deposition, for which Cu is filled preferentiallyfrom the bottom of trenches without being deposited on thesidewall of trenches, using a H-assisted plasma CVD
method [9-16].

13.56MHz~
H2

CCP Main discharge
28MHz

~

1. Introduction

Substrate

H2
Vaporizer

RF biasLiquid delivery system
C7H8400kHz~Fig. 1. Experimental setup.

We are applying the deposition profile control method
to carbon films in trenches. Here, we report dependence ofdeposition rate of plasma CVD carbon films in trenches onsubstrate temperature and on aspect ratio.

author’s e-mail: j.umetsu@plasma.ed.kyushu-u.ac.jp1443©2009 by The Japan Society of Plasma
Science and Nuclear Fusion Research

J. Umetsu et al., Substrate Temperature Dependence of Deposition Profile of Plasma CVD Carbon Films in Trenches

Deposition rate (nm/min)20(a)Bottom
1510SiO2
50C
Sidewall0123

Aspect ratio

4WN

1�m5

trench depth
trench widthFig. 2. Dependence of deposition rate on aspect ratio.
Substrate temperature 220 oC, Pm 45W, bias voltage-100 V, C7H8 4.5sccm. Trench width 2.0-2.2 �m.
Aspect ratio �Si(b)SiO2

2. Experimental

Experiments were performed using the H-assisted
plasma CVD reactor, in which a capacitively-coupled maindischarge and an inductive-coupled discharge for an H
atom source were sustained as shown in Fig. 1. Thisreactor provided independent control of generation rates ofdeposition radicals and H atoms. For the main discharge, amesh powered electrode of 85 mm in diameter and a planesubstrate electrode of 85 mm in diameter were placed at adistance of 33 mm. The discharge of H atom source wassustained with an rf induction coil of 100 mm in diameter
placed at 65 mm above the substrate electrode of the maindischarge. Deposition was carried out without employing
the H atom source. The excitation frequency of the maindischarge was 28 MHz and the supplied power Pm wasbelow 45 W. An rf bias voltage of 400 kHz was applied tothe substrate for controlling kinetic energy of ions incident
on it. The supplied power Pbias was 0-5 W. Toluene (C7H8)
was vaporized at 150 oC, and supplied with H2. The flowrate of toluene and that of H2 were 4.5 sccm and 90 sccm.
The total pressure was 13 Pa and the partial pressure oftoluene was 0.62 Pa. Si substrates with trenches coveredwith WN were treated by ultrasonic cleaning using
trichloroethylene, acetone, and ultra pure water, then they
were dried before deposition experiments.
Thickness and deposition profile of carbon films intrenches were obtained with a scanning electron microscope (SEM:JEOL, JSM-6320FZ). Chemical compositions
were analyzed with an energy dispersive X-ray
spectrometer (EDS:OXFORD, ISIS-L200). Information on
structure of carbon films was obtained with a laser Raman
spectrometer (JASCO, NRS-3100).

CWN
1�m SiFig. 3.

Cross section SEM images of carbon films

deposited in a trench. Pm 45W, bias voltage -100 V, C7H8
4.5sccm. Substrate temperature 220 oC.
(a) Aspect ratio =1.18, and (b)aspect ratio = 4.46.

3. Results and Discussion

First, we have studied aspect ratio dependence ofdeposition rates at the bottom and sidewall of trenches.
Figures 2 and 3 show the results. The deposition rate at thebottom increases from 7.39 nm/min to 16.7 nm/min and at
the sidewall increases from 1.53 nm/min to 6.78 nm/minwith decreasing the aspect ratio from 4.23 to 1.18. The
maximum deposition rate of 16.7 nm/min at the bottom
and 6.78 nm/min at the sidewall are obtained for the aspectratio of 1.18. The deposition rates at the bottom andsidewall increases with decreasing the aspect ratio. We
speculate that the incident radical flux per surface area in a
trench increases with decreasing the aspect ratio and hence
the aspect ratio dependence in Fig.2 is realized.
Next, we have studied dependence of the deposition
rates at the bottom, sidewall and top of trenches on thesubstrate temperature. Figures 4 and 5 show the results.

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J. Umetsu et al., Substrate Temperature Dependence of Deposition Profile of Plasma CVD Carbon Films in Trenches

Deposition rate (nm/min)

60

Deposition rate (nm/min)(a)

TopSidewall
Bottom50403020SiO2100C(b)

WN

501�m

4030Si(b)20100Deposition rate (nm/min)(a)(c)

50

SiO240C3020100100WN1�m150200o

Substrate temperature ( C)

250SiFig. 5. Cross section SEM image of carbon films
deposited in a trench. Pm 45W, bias voltage -100 V, C7H8Fig. 4. Dependence of deposition rate on substratetemperature for aspect ratio of (a)1.18-1.42,(b)1.43-1.78, (c)2.29-2.49, Pm 45W, bias voltage -100V, C7H8 4.5sccm. Trench width 2.0-2.2 �m.

4.5sccm.
(a) nearby conformal profile at substrate temperature of
100oC, and (b) anisotropic profile at substrate temperatureof 220oC.

The maximum deposition rate of 38.1 nm/min at thebottom and 20.9 nm/min at sidewall are obtained for
100oC. The deposition rates at the bottom and sidewall
increase with decreasing the temperature from 220oC to100oC. The experimsntal deposition rate DR is expressedas, DR=DRneutral + DRion - ER, where DRneutral and DRion
are the deposition rate due to neutral radicals and ions, andER is the chemical etching rate due to H atoms. The first
two terms is the right hand side of the above equation havelittle temperature dependence [17]. The etching rate by H
atoms increases with temperature, and hence theexperimental deposition rate decreases with temperature asshown in Fig. 4. Moreover, we have deduced the apparent
activation energy from the results above 140oC. Table lshows the activation energies of deposition rates at theTable l. Activation energy of deposition rate.

Aspectratio

1.18-1.42

1.43-1.78

2.29-2.49

Sidewall-0.17 [eV]㩷

-0.20 [eV]㩷

-0.22 [eV]㩷

Bottom-0.14 [eV]㩷

-0.097 [eV]㩷

-0.12 [eV]㩷

sidewall and bottom for trenches of aspect ratio of
1.18-1.42, 1.43-1.78 and 2.29-2.49. All activation energies
are minus, which corresponds to the lower deposition rates
at the higher temperature.
We have analyzed chemical compositions of the films

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5 104350

4340

4 10

Intensity (arb. units)

Intensity (arb. units)

J. Umetsu et al., Substrate Temperature Dependence of Deposition Profile of Plasma CVD Carbon Films in Trenches

SiW

43 1042 1041 100CO0W
24keV

68320
3100400800

1200 -1 1600

wavenumber (cm )2000

Fig. 7. Raman spectrum of carbon film. Pm=45W,
Substrate temperature 153oC, C7H8 4.5sccm, H290sccm, total pressure 0.1 Torr.
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[5]
[6]
[7]
[8]

4. Conclusions

We have realized sub-conformal and conformal
deposition of plasma CVD carbon films in trenches. We
have studied substrate temperature and aspect ratio
dependence of deposition rate of carbon films in trenches.
The deposition rates increases with decreasing the aspectratio, because the incident radical flux per surface area in a
trench increases with decreasing the aspect ratio. The
deposition rate increases with decreasing the substratetemperature, because of the lower etching rate by H atoms
at the lower temperature.

Acknowledgement

This work was partly supported by JST, CREST.

References[4]-1(1380cm )

330

300

10with EDS. Figure 6 shows the chemical compositions ofcross section of a trench with film. The main chemicalcomposition of films is carbon.
Finally, we have measured Raman spectrum of carbon
films. Figure 7 shows the result. There exist a small
graphite-peak (1580cm-1) and a disorder-peak (1380cm-1) .

[3]-1D-peak (1580cm )WFig. 6. Chemical compositions of cross section of atrench of film. Pm=45W, Substrate temperature 153oC,
C7H8 4.5sccm, H2 90sccm, total pressure 0.1 Torr.

[1][2]G-peak

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