24G12
Infrared Spectroscopic Study on Effects of Substrate Temperatures
on Oxidation of Amorphous Carbon Films
酸素プラズマによるアモルファス炭素薄膜の酸化過程における基板温度依存性
Yuya TAKAKI1, Kojiro HARA2, Yoshiki TAKAMI1
Masanori SHINOHARA1, Yoshinobu MATSUDA1 and Hiroshi FUJIYAMA1
高木雄也1，原 幸治郎2，高見佳生1，篠原正典1，松田良信1，藤山 寛1
Graduate School of Engineering, Nagasaki Univ.1, Graduate School of Sci. and Technol., Nagasaki Univ. 2
1-14, Bunkyo-machi, Nagasaki 852-8521, Japan1,2
長崎大院工1，長崎大院生産2〒852-8521 長崎市文教町1-14

Oxidation process of the amorphous carbon film deposition has been investigated, using infraredabsorption spectroscopy in multiple internal reflection geometry (MIR-IRAS). Amorphous carbon film wasoxidized by the exposure to oxygen molecules and oxygen plasma. We observed the decreases of thedensity of CHX species, and the increases of those of OH species, with longer exposure to oxygenmolecules. It means that the CH bonds were decomposed to form OH species. We also observed thetemporal evolution of the OH peak due to oxygen plasma exposure. The results indicated that the carbon
film was oxidized, and moreover the film was also evaporated with the longer exposure.

1. Introduction

An amorphous carbon film has frequently
used in various fields because the films have a
lot of useful properties: chemical inertness,mechanical hardness, smooth surface, andbio-compatibility. Moreover, the addition ofother kinds of atoms induces the different film
property. The film shows hydrophilic property
if the oxygen atoms were inserted into the film,
as a result, the films show hydrophilic property.
Plasma oxidation is one of the effective
oxidation methods. But there were not many
reports on oxidation of amorphous carbon thatrelationship of substrate temperature relatedoxidation process and hydrophilic property.
Furthermore, the detailed oxidation process ofamorphous carbon was not sufficiently
understood. We have investigated the oxidation
process of amorphous carbon films due tooxygen plasma, with “in-situ” and “real time”
infrared absorption spectroscopy in multiple
internal reflection geometry (MIR-IRAS). In
this paper, we report the effect of the substratetemperature on the plasma oxidation of theamorphous carbon films.
2. ExperimentsFigure 1 shows the experiment system. ThePECVD chamber was equipped with anMIR-IRAS monitoring system. The substrate
was heated with resistive heater. The Si prisms
were made of n-type Si (100) wafers. Theprisms had a dimension of 0.5×10×40mm, withmirror-polished 45° bevels on each of the shortedges. Amorphous film was deposited withmethane plasma. Oxidation of the film wasperformed with oxygen plasma. All spectra
were recorded at 4cm-1 resolution. The
reflection spectrum of the as-deposited film
was used as the reference spectrum of all
spectra, in order to recognize the changed
portion due to the oxygen plasma exposure.

Fig. 1 Experiment System3. Results and Discussions

Figure 2 shows the initial oxidation processof the amorphous carbon film due to theexposure to oxygen plasma. The carbon film
was polymer-like structure, because the film
was deposited using acetylene plasma without
substrate bias. The flow rate of oxygen
molecules was 2sccm, and the gas pressure was6.7 Pa.
In this graph, each spectrum was deduced byusing the spectrum of the as-deposited
amorphous carbon film as a reference spectrum.
Thereby, the changed portions due to oxidation canbe deduced from the as-deposited amorphous
carbon film. The infrared spectra have several

broad peaks. In this research, we pay attention
to two peaks: one is located between 2,800 and
3,000cm-1, the other is located between 3,000
and 3,400cm-1. The former is assigned to C-H
mode, and the latter is assigned to O-H mode.
The results showed that the quantity ofOH-group in the amorphous carbon film wasdecreased, on the contrary to the increases ofthe substrate temperatures.
Moreover, Table 1 shows the contact angleof the substrate which was measured using astylus step height meter. From the result, it isfound that the substrate at room temperature ismaintained hydrophilic property. The contact
angle was increased with the substratetemperature. These results indicate that changes
in OH-group have a close relationship withhydrophilic functionality.
4. Conclusion
We investigated the effects of substratetemperature on the oxidation of an amorphous
carbon film, with the infrared spectroscopy inmultiple
internalreflection
geometry(MIR-IRAS). The infrared spectra indicate thatthe quantity of OH group in the film wasdecreased, on the contrary to the increases insubstrate temperatures.

Fig.2 IRAS spectra of oxidation of an amorphous
carbon film at different temperatures.

Table.1.Contact angle of the substrate

Acknowledgments
This research was partially supported by aGrant-in-Aid for Young Scientists (A), no.
22110511 (2010-2012) from the Ministry of
Education, Culture, Sports, Science andTechnology (MEXT) of Japan.