.

1. Effect of Cu thickness and temperature on growth of graphene on 8-inch
Cu/SiO2/Si wafer using cold-wall CVD reactor
Nurhidaya Soriadi ⇑
, Mohd Faizol Abdullah, Firzalaila Syarina Md Yakin, Siti Aishah Mohamad Badaruddin,
Mohd Ismahadi Syono
Advanced Devices Lab, MIMOS Berhad, Technology Park Malaysia, Kuala Lumpur 57000, Malaysia
a r t i c l e i n f o
Article history:
Available online 11 February 2021
Keywords:
Cold-wall CVD
Copper thin film
Dewetting
Graphene growth
Grain size
a b s t r a c t
The growth of graphene by chemical vapor deposition (CVD) method on Cu thin film using a cold-wall
CVD reactor is desirable for developing a compatible graphene transfer process on large SiO2/Si wafer.
We reported the growth of graphene on the evaporated Cu on an 8-inch SiO2/Si wafer for the varied thick-
ness of 100–600 nm. We found the temperature for the cold-wall CVD reactor needs to be 825 °C or
higher for methane decomposition and graphene growth. The high-temperature process results in the
formation of isolated and interconnected Cu islands due to the dewetting mechanism. The evaporated
Cu film on SiO2/Si wafer needs to be sufficiently thick minimum of 600 nm to mitigate the dewetting dur-
ing the 825 °C process. Successfully grown graphene on 8-inch Cu/SiO2/Si wafer using a cold-wall reactor
was monolayer without crystal defect. The grain size of graphene was at an average of 2.5 mm, correlated
to the grain size of Cu film which is slightly smaller at an average of 2 mm. We anticipate further enlarge-
ment of Cu grain size along with graphene grain size by the thickening of Cu film and by using higher
process temperature.
Ó 2021 Elsevier Ltd. All rights reserved.
Selection and peer-review under responsibility of the scientific committee of the 3rd International Con-
ference on Materials Engineering & Science.
1. Introduction
Chemical vapor deposition (CVD) growth of graphene on Cu
thin film is one step closer towards the development of a compat-
ible graphene transfer method onto a large-area Si wafer. At pre-
sent, graphene is commonly grown on 25 mm-thick Cu foil or
thicker with an acceptably good crystal quality [1]. However, the
transfer of graphene from Cu foil onto target substrate e.g. Si and
SiO2/Si wafer for device fabrication was proven challenging with-
out inducing breakages, wrinkles, and residual impurities [1]. On
the other hand, an alternative approach of growing graphene on
Cu thin film evaporated on SiO2/Si wafer may offer a solution for
developing a more robust graphene transfer methodology. This is
very promising considering the technological compatibility of Cu/
SiO2/Si wafer with a cold-wall CVD reactor, which is slowly replac-
ing the use of conventional hot-wall CVD for growing graphene [2].
Such a home-made hot-wall CVD furnace consumes more power
but requires longer process time due to poor temperature control,
thus not desirable for the industrial-scale synthesis of graphene.
Tao et al. demonstrated the growth of monolayer graphene on
the evaporated Cu on SiO2/Si substrate using a cold-wall CVD reac-
tor [3]. They managed to grow graphene at 875 °C and found grain
size of graphene is correlated to the grain of Cu(1 1 1). Their aver-
age Cu grain size on 1 mm-thick film was within 10–20 mm. In
recently, Huet et al. reported on the growth of monolayer graphene
on evaporated Cu on a 3-inch SiO2/Si wafer using a hot-wall CVD
furnace [4]. Their grown graphene on 1 mm-thick Cu film at
1050 °C was reported with a large grain size up to 1 mm, far larger
than the Cu grain size that approximately within 100 mm. In terms
of thin film, 1 mm-thick Cu film can be considered as thick and not
desirable for the graphene transfer process which involves Cu etch-
ing/removal. Thinning of Cu film however invites another problem
which is dewetting of Cu, especially at high-temperature pro-
cess 1000 °C [5]. In this work, we investigated the use of a signif-
icantly thin Cu film from 100 to 600 nm to grow the monolayer
graphene using the cold-wall CVD reactor at a lower temperature,
just above the effective decomposition of methane to reduce the
dewetting. We discussed the quality and grain size of the grown
https://doi.org/10.1016/j.matpr.2020.12.800
2214-7853/Ó 2021 Elsevier Ltd. All rights reserved.
Selection and peer-review under responsibility of the scientific committee of the 3rd International Conference on Materials Engineering Science.
⇑ Corresponding author.
E-mail address: nurhidaya.soriadi@mimos.my (N. Soriadi).
Materials Today: Proceedings 42 (2021) 2948–2952
Contents lists available at ScienceDirect
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2. graphene according to the dewetting and grain size of the evapo-
rated Cu thin film.
2. Experimental
The substrate for growth in this work was an 8-inch SiO2/Si
(100 nm-thick SiO2) wafer. The Cu film catalyst was deposited on
SiO2/Si wafer by electron beam evaporation system (Evatec BAK-
641) for the varied thickness of 100–600 nm. The source for evap-
oration was 99.99% purity Cu pellets from Kurt J. Lesker Co. Next,
graphene was grown on the Cu/SiO2/Si wafer using the cold-wall
CVD system (Aixtron Black Magic). Before the growth, the evapo-
rated Cu film was annealed in H2/Ar (750/250 sccm) ambient at
either 725 °C or 825 °C for 5 min to remove the native oxide and
to enlarge its grain size. In the following, CH4/H2/Ar (5/40/960
sccm) flowed into the reaction chamber for 4 min to grow the gra-
phene. The sample was then slowly cooled to 130 °C in continuous
Ar flow before vented to be taken out from the reaction chamber.
The surface morphology of Cu film and graphene was investigated
using the field emission scanning electron microscopy (FESEM)
system (JEOL JSM-7500F) at a magnification of 10 k. The crystal
quality of graphene was inspected using the Raman spectroscopy
system (NTEGRA Spectra II) using 473 nm laser excitation at room
temperature.
3. Results and discussion
3.1. Thickness and temperature dependence on dewetting of Cu film
Fig. 1(a)–(f) respectively show the FESEM image of Cu film with
varied thickness of 100–600 nm after the 725 °C process. We found
solid-state dewetting was obvious for the thin Cu with a thickness
of 100–300 nm, where the Cu particles form the isolated and inter-
connected islands instead of forming a continuous film. Dewetting
of Cu was driven by the high interfacial energy between Cu and
SiO2/Si. Consequently, Cu rearranges itself as the islands to mini-
mize the area in contact with the substrate [5]. The dewetting of
Cu was gradually suppressed after the thickening of the evaporated
Cu layer from 400 to 600 nm. The enlargement of grain size during
the heat treatment formed a continuous film on 600 nm-thick Cu.
The average grain size for this sample was around 2 mm.
The mechanism and suppression of Cu dewetting can be
explained by considering the Young-Laplace equation with h as
the equilibrium contact angle:
cs ¼ ci þ cf cosh ð1Þ
where cs, ci, and cf is the isotropic energy surface per unit area for
SiO2/Si substrate, the interface of Cu-SiO2/Si, and the Cu thin film,
respectively [6]. For the Cu thickness of 400–600 nm, many areas
did not satisfy the condition of cs ci + cf, therefore did not dewet-
ted. During the high-temperature process of 725 °C, grain bound-
aries of Cu were enlarged and ruptures of Cu film started at the
grain boundary when:
R
t
3sin
3
u
2 3cosu þ cos3u
ð Þ
ð2Þ
where R is the radius of the Cu grain, t is the thickness of Cu film,
and u = sin–1
(cgb/2cf) is the pitch angle for groove separation at
grain boundaries with cgb is the energies of the Cu grain boundaries
[6]. Therefore, decreasing t results in the accelerated formation of
the void and eventually ruptures of the Cu film.
Fig. 2(a)–(f) respectively show the FESEM image of Cu film with
varied thickness of 100–600 nm after the 825 °C process. We
observed higher temperature heat treatment on 100 nm-thick Cu
caused the film to agglomerated into microparticles. It is known
that the dewetting of metal including Cu dominated by the surface
diffusion kinetic rather than evaporation–condensation kinetic [7].
The increase in temperature exponentially increase the surface dif-
fusion of Cu, therefore undesirably results in a severe dewetting
condition. For the film thickness of 200–400 nm, the dewetting
of Cu results in isolated and interconnected islands. The dewetting
was reduced when the thickness of the Cu film was increased to
500 nm. The average grain size for the 600 nm-thick Cu was
around 2 mm and comparable to the previous CVD process at
725 °C.
3.2. Graphene growth on the Cu film
Fig. 3(a) and (b) show the Raman spectra from the Cu film with
a thickness of 100–600 nm from the CVD process of 725 and
825 °C, respectively. From the plots, there was no response from
the sample of 100 nm-thick Cu due to the sparse distribution of
Cu microparticles and islands. We observed a sharp peak at
Fig. 1. Surface condition of Cu film after 725 °C process for the varied thickness of the evaporated Cu: (a) 100 nm. (b) 200 nm. (c) 300 nm. (d) 400 nm. (e) 500 nm. (f) 600 nm.
N. Soriadi, Mohd Faizol Abdullah, Firzalaila Syarina Md Yakin et al. Materials Today: Proceedings 42 (2021) 2948–2952
2949

3. 1285 cm1
appeared on every sample of 200–600 nm-thick Cu.
This peak corresponds to the CO2 molecules on the Cu surface.
No graphene peak found from the 725 °C process, indicating this
temperature was infective to decompose the methane for the
growth of graphene. When the temperature increased to 825 °C,
prominent G-peak intensity (IG) at 1580 cm1
and 2D-peak
intensity (I2D) at 2700 cm1
were observed from the sample of
200–600 nm-thick Cu. It is known that IG originated from the
first-order phonons scattering at the C-point, while I2D is the
second-order of zone-boundary phonons of the graphitic materials
[8]. The ratio of I2D/IG 2 obtained in the plot of Fig. 4(b) indicates
the process managed to grow monolayer graphene on all the 200–
600 nm-thick Cu films. The absence of defect-related inten-
sity 1350 cm1
suggests the high quality of CVD grown graphene
on the Cu films [9–11].
Fig. 4(a) shows the FESEM image of graphene on 600 nm-thick
Cu film after the 825 °C process. We noticed there were several
white dots on graphene, especially at the grain boundaries. The
dots were most probably the location where monolayer-limited
growth of graphene occurred. This condition was explained in
the previous report in ref. [12], where high hydrogen concentration
in the cold-wall reaction chamber deactivated the nucleation sites
for the bi-layer graphene. The formation of an adlayer is prohibited
by the desorption of the hydrogenation species [13]. Fig. 4(b) com-
pares the grain sizes between monolayer graphene to the 600 nm-
thick Cu film (substrate) after the 825 °C process. The average grain
size of monolayer graphene was around 2.5 mm and can reach up to
6 mm, while the average grain size of Cu was around 2 mm. The
grain size of graphene was certainly influenced by the grain size
of the catalytic metal substrate. Typical growth on Cu foil with rel-
atively large grain size compared to the Cu thin film has a great
advantage in terms of obtaining graphene with large grain size,
for example up to 5.9 mm as reported in ref. [14]. We are expecting
further grain size enlargement of Cu film without dewetting issues,
potentially up to 100 mm by increasing the thickness of Cu and
applying higher temperature heat treatment.
Fig. 5(a)–(f) shows the optical microscopy image for the gra-
phene/Cu/SiO2/Si for the varied thickness of the evaporated Cu of
100–600 nm. Large-area imaging enables the evaluation of pores
distribution. Note that the definition of pore does not apply for
Fig. 2. Surface condition of Cu film after 825 °C process for the varied thickness of the evaporated Cu: (a) 100 nm. (b) 200 nm. (c) 300 nm. (d) 400 nm. (e) 500 nm. (f) 600 nm.
Fig. 3. Raman spectra from the sample with varied Cu thickness after the CVD growth: (a) 725 °C process. (b) 825 °C process.
N. Soriadi, Mohd Faizol Abdullah, Firzalaila Syarina Md Yakin et al. Materials Today: Proceedings 42 (2021) 2948–2952
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4. 100 and 200 nm-thick Cu due to the completely disconnected Cu
islands. The average distance between neighboring pores for the
300–600 nm-thick Cu was 4.70 mm, 7.51 mm, 10.16 mm, and
23.74 mm, respectively. The standard deviation for each data was
2.07 mm, 2.54 mm, 3.95 mm, and 14.80 mm, respectively. A signifi-
cant increase in pore distance (more than double) was observed
between 500 nm and 600 nm-thick Cu. This suggests that the
thickness of Cu needs to be 600 nm and above to effectively reduce
the effect of dewetting during the 825 °C process for obtaining a
long-order continuous layer of graphene. Those pores, fortunately,
did not induce defects on the monolayer graphene as no defect
peak was detected in the previous Raman spectra.
4. Conclusion
The growth temperature of graphene using a cold-wall CVD
reactor need not lower than 825 °C. Even though the lower temper-
ature of 725 °C helps reduced the dewetting of Cu film, no gra-
phene was obtained after the CVD process due to the ineffective
Fig. 4. Monolayer graphene grown after the 825 °C process on 600 nm-thick Cu film: (a) Surface condition. (b) Grain size distribution of graphene and Cu film.
Fig. 5. Large-area pore distribution on graphene/Cu/SiO2/Si after 825 °C process on the varied Cu thickness: (a) 100 nm. (b) 200 nm. (c) 300 nm. (d) 400 nm. (e) 500 nm. (f)
600 nm.
N. Soriadi, Mohd Faizol Abdullah, Firzalaila Syarina Md Yakin et al. Materials Today: Proceedings 42 (2021) 2948–2952
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5. decomposition of methane. The thickness of Cu film needs to be
sufficiently thick more than 600 nm to enable continuous Cu film
after the high-temperature process. Isolated and interconnected
Cu islands result in a non-continuous graphene layer. Successfully
grown graphene at 825 °C on 8-inch Cu/SiO2/Si wafer using a cold-
wall CVD reactor was monolayer without crystal defect. The grain
size of graphene was at an average of 2.5 mm. It was associated
with the grain size of the Cu film, which was at an average of 2 mm.
CRediT authorship contribution statement
Nurhidaya Soriadi: Formal analysis, Investigation, Methodol-
ogy, Writing - original draft. Mohd Faizol Abdullah: Conceptual-
ization, Methodology, Writing - review editing. Firzalaila
Syarina Md Yakin: Investigation, Methodology. Siti Aishah Moha-
mad Badaruddin: Project administration, Resources, Validation.
Mohd Ismahadi Syono: Validation, Funding acquisition,
Supervision.
Declaration of Competing Interest
The authors declare that they have no known competing finan-
cial interests or personal relationships that could have appeared
to influence the work reported in this paper.
Acknowledgments
This project is internally funded by MIMOS Berhad.
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