Photothermal CVD of Carbon Thin Films using CH2I2 as the Precursor

DOI: 10.1002/cvde.200806666

Full Paper

Photothermal CVD of Carbon Thin Films usingCH2I2 as the Precursor**

By Abdul Rashid, Lars Landstrom,* Mikael Ottosson, and Klaus Piglmayer

Thin carbon films are deposited via CVD from the precursor methylene iodide (CH2I2) using two different activation sources; a

broadband IR lamp and a thermal plate. Large differences in deposition rates are observed when comparing the two sources of

activation. The characteristics of the deposition kinetics of the highly sensitive system are also investigated by employing a split,

symmetric reactor, and by using a qualitative model. Raman spectroscopy (RS) is used for microstructural characterization of

the films. The lamp technique allows a simple and low-cost experimental setup, for deposition of disordered carbon thin films at

relatively low temperatures and high rates.

Keywords: Carbon, Methylene iodide, IR lamp, Raman spectroscopy

1. Introduction

Carbon materials are suitable for a wide range of

applications and they also enable low cost and flexible

components for integration within complex systems, such as

electronic and photonic devices, to be developed. Intense

research is ongoing in developing patterning techniques,

e.g., for magnetic discs,[1–3] environmental sensors,[4] solar

cells,[5] hip joints,[6] semiconductors,[7] and plastics,[8–10] and

in creating new device structures and configurations for

X-ray optics,[11] electrochemical detectors,[12] and clinical

bioelectric measurements.[13] Opportunities can also be

found in combinations of hard and soft materials, and

layered structures, to combine various materials proper-

ties.[14,15] Currently, carbon nanomaterials show a very high

potential with respect to applications, for instance, in

nanoelectronics and field emission display technology.[16–18]

The intensive research in the field of carbon materials

shows the need for further developments to meet the

demands of future technologies. Here, some of the

important features to approach are; decrease in processing

[*] Dr. L. Landstrom, Dr. M. OttossonThe Angstrom Laboratory, Department of Materials ChemistryUppsala UniversityBox 538, SE-751 21 Uppsala (Sweden)E-mail: [email protected]

Dr. L. Landstrom, Dr. A. Rashid, Dr. K. PiglmayerInstitut fur Angewandte Physik, Johannes-Kepler-Universitat LinzA-4040, Linz (Austria)

Dr. A. RashidDepartment of PhysicsCOMSATS Institute of Information TechnologyDefence Road, Off Raiwind RoadLahore (Pakistan)

[**] We thank Prof. D. Bauerle for valuable discussions. One of us (L. L.)would like to thank the ‘‘Knut and Alice Wallenberg Foundation’’ forfinancial support.

Chem. Vap. Deposition 2008, 14, 279–285 � 2008 WILEY-VCH Verlag Gm

temperatures, further miniaturization, modification of

materials, increased flexibility, and cost effectiveness.

As presently employed standard precursors usually

require high apparent activation energies (i.e., high

temperatures for thermal processes), and the techniques

employed are often cost and/or effort intensive, and limited

in versatility. We take use of the easily handled and

dissociated methylene iodide (CH2I2) in combination with

various activation sources (for example, a broadband IR

lamp) resulting in low costs, high versatility, and flexibility,

allowing further tuning of processing parameters.

Recently, deposition of thin carbon films by IR lamp-

induced dissociation of CH2I2 under reduced pressures was

investigated.[19,20] In these preliminary reports, the large

increase in deposition rate compared to standard cold-wall

CVD methods (reactors of completely different geometry

were used) was observed and attributed to an additional

influence of photolysis effects. This idea was supported by

the successful high-rate deposition experiments performed

by purely photolytic dissociation of the precursor employing

various UV laser systems.[21–25]

At present, the methylene iodide system was investigated

in further detail to try to reveal the peculiarities of the

sensitive deposition processes. To allow for better control

and direct comparison between lamp-induced photophysical

(photon-irradiated substrate surface) and photothermal

(non-irradiated surface) processes, an integrated system

was used. Furthermore, standard thermal CVD processing

(induced by a thermal plate) was also directly compared to

lamp-activated deposition in a single cold-wall reactor. The

microstructure of the thin carbon films was characterized

by means of RS, and the density and hydrogen content of

the deposits were estimated by X-ray reflection (XRR)

and nuclear reaction analysis (NRA) measurements,

respectively.

bH & Co. KGaA, Weinheim 279

Full Paper

2. Results and Discussion

2.1. Process Characteristics

First, a comparison of carbon thin films deposited by

standard thermal activation (T-CVD), here activated by a

thermal plate, and photothermal activation (PT-CVD) by

means of an IR lamp was performed in the same reactor

chamber with otherwise the same experimental parameters

(see Sec. 4). Reactor I has been built to verify CVD rates

already published (see the literature[26]), and to allow direct

comparison, in the same geometry, between IR lamp-

induced deposition and thermal-plate activation. That is, the

activation source was either a resistively heated BN-coated

graphite plate or an IR lamp. Reactor II was utilized to

separate possible photon–induced effects from pure thermal

ones. In the latter case, the ‘‘thermal CVD’’ process is

induced on the back side of the sample, with identical

transport and gas flow conditions. Both the reactors were

cold-wall set-ups. The Arrhenius plots in Figure 1 obtained

for the two activation sources show a surprisingly large

difference in rates of growth, i.e., PT-CVD rates being

almost one order of magnitude higher than the T-CVD

rates at elevated temperatures. The apparent activation

energy (Ea) is approximately 140 kJmole�1 for the PT-CVD

process. This observed value of Ea is quite low compared to

other, more common carbon precursors (�620 kJmole�1

for CH4 and �250 kJmole�1 for C2H4). The low activation

energy is most likely related to the dissociation energies of

the precursor molecule. For example, the dissociation of the

first C-H bond in a methane molecule requires about 4.5 eV,

whereas the C-I bond strength in methylene iodide is

�2.5 eV. The T-CVD process shows quite low deposition

rates within the entire examined temperature region, and

seems to already reach saturation (mass transport limita-

tion) at moderate temperatures; below the saturation

temperature, similar activation energy can be observed.

Fig. 1. Arrhenius plot for carbon films deposited from the CH2I2 precursor.

Open circles correspond to rates from IR lamp- (PT-CVD) and triangles to

thermal plate-activated CVD (T-CVD). The full circles are from PT-CVD

but with the UV part of the broadband spectrum filtered out. The dashed line

is the best linear fit for the values in the kinetically controlled region

(apparent activation energy, Ea� 140 kJmole�1) and the solid line is drawn

parallel to fitted dashed line as a guide for the eye. Total pressure 10mbar;

reactant partial pressure 0.47mbar; flow rate 10 sccm.

280 www.cvd-journal.de � 2008 WILEY-VCH Verlag GmbH &

With this reactor, photolysis effects were also investigated,

i.e., the influence of near-UV and deep-UV radiation on the

deposition rates, by employing a red cut-off filter in the light

path of the lamp. No significant differences in growth

rates were observed with this modification, see Figure 1

(full circles).

Additionally, to provide fully identical operating condi-

tions, a symmetric reactor with two separate chambers

(see Sec. 4) was employed for simultaneous comparison of

the two means of activation. Results are depicted in

Figure 2a, where circles correspond to the lamp-irradiated

side of the substrate (PT-CVD) and squares to the opposite

(T-CVD) side. Furthermore, the influence of any convective

flow differences was investigated by mounting the lamp

either from above or below the reactor. For this case, the

notes ‘above’ and ‘below’, placed in parenthesis in Figure 2a,

indicate the position of the lamp with respect to the reactor.

The observed rates coincide in the kinetic region but a slight

difference can be observed at elevated temperatures (in the

mass transport-controlled temperature region), and the

results were independent of the position of the lamp (above

or below). The Ea for the process (in the kinetic region)

was again found to be around 140 kJmole�1, confirming

the value from Figure 1.

Simultaneously measured temperatures on both sides of

the substrate/thin films revealed only small differences

(about 15K at most), see Figure 2b. In addition, a very small

broadening of the surface temperature profile will also occur

on the non-irradiated side of the sample. As all the

Fig. 2. a) Deposition rates from the fully symmetrical reactor. Circles corre-

spond to the lamp incident (PT-CVD) side of the substrate and squares to the

opposite (T-CVD) side. Above/below in parenthesis denotes the position of

the lamp. Total pressure 10mbar; reactant partial pressure 0.47mbar; flow

rate 10 sccm. b) Simultaneously measured temperatures on the two substrate

surfaces. ‘‘Up’’ refers to the side facing the lamp and ‘‘down’’ the opposite

side.

Co. KGaA, Weinheim Chem. Vap. Deposition 2008, 14, 279–285

Full Paper

experimental parameters are identical for both sides, we can

deduce the existence of mass transport characteristics which

are highly sensitive to changes in the substrate temperature

conditions, i.e., that even slightest modifications of the

temperature profile will significantly alter the transport

properties.

The large differences in rates between PT- and T-CVD,

depicted in Figure 1, could then also be partially related to a

more homogeneous temperature profile in the case of the

thermal plate as compared to the lamp. The parallel shift

of curves (of the kinetic regimes of PT- and T-CVD

dependencies in Fig. 1) might also be due to the differences

in surface temperature profiles. An additional effect might

be the efficient heating of the gas phase. This heating induces

a subsequent thermodiffusion which could also be related to

the observed shift. As the Knudsen number Kn ¼ l=L � 1,

(l is the mean free path of gas molecules and L is the

characteristic length� substrate length), temperature will

be continuous across the substrate/gas interface and the

heating of the gas zone might further be increased due to

small H2 product molecules effectively transferring heat

away from the hot surface. Because of the big differences in

molecular mass of reactant and product species, e.g., CH2I2and H2, a pronounced Soret effect can be expected to occur.

Such an effect may induce a shift of the linear (kinetic)

regions in the Arrhenius curves,[27] as observed in Figure 1.

(The additional presence of heavy products such as I2 will

not influence the effect in a first order approach).

As we have to consider that the large differences in rates

originate from transport properties, an important factor

must be dimensionality, but in both cases thin and

homogeneous deposits over large areas (15mm� 15mm

in the lamp case, and 25mm� 35mmwith the thermal plate)

are obtained, indicating the typical characteristics for one-

dimensional (1D) transport. The way out of this dilemma is

the fact that a flow system is present. In this case the key

quantity determining and characterizing the transport

properties is the boundary layer formed between the

substrate surface and the undisturbed gas stream, and is

inevitably linked to chemically active flow systems.[28] Its

characteristic thickness (d) is derived for laminar flow, and

with the assumption of constant pressure from the equations

of conservation of mass and of energy (Navier-Stokes

equations), as Equation 1.[28]

d

L¼

ffiffiffiffiffiffiffiffin

UL

r(1)

n is the kinematic viscosity and U the flow velocity. For 1D-

transport, which represents the standard condition in large

area CVD, the condition d/L� 1 must be satisfied. In the

present case,L is on the same length scale for both lamp and

thermal plate zones, and with the parameters used in our

experiments we find d/L� 1. This indicates that although we

observe clear 1D-growth characteristics, i.e., thin homo-

Chem. Vap. Deposition 2008, 14, 279–285 � 2008 WILEY-VCH Verlag G

geneous film over the whole substrate, the rates are

determined largely on a 3D-scale, involving the whole

reactor volume. As a consequence, for the lamp case, this

implies 3D-transport characteristics similar to pyrolytic

CVD induced by focused laser beams, leading to a huge

increase in total rate.[29]

Of importance here is which gas-phase constituent

determines the rates. As the amount of reactive species

entering the reactor volume per unit time is more than

30 times larger than what is actually deposited, it appears

unlikely that the transport limitations are set by a depletion

of reactants.

Our observations, listed below, have led to the conclusion

that the key species is most likely H2.

1. S

mb

mall amounts of hydrogen were detected throughout the

whole thickness of the T-CVD thin films and our results,

as confirmed by NRA measurements and also reported

earlier,[19] coincide well with H concentrations reported

in the literature,[26] whereas no hydrogen was found in

the PT-CVD films. That is, the different hydrogen

contents are most likely related to the modifications in

transport of H2.

2. A
bottleneck to H-free deposits is the final breaking of C-
H bonds and the removal of H from the surface. Such a

desorption process is highly sensitive towards surface

temperature.

3. S
tudies on hydrogen desorption from diamond surfaces
show that the rate becomes pronounced at around 900K

and exhibits a maximum at about 1200K. Molecular and

atomic hydrogen were supplied to the surface, and as

desorption products only H2-molecules were detected.[30]

In our experiments, deposition rates also accelerate

significantly at around 900K (see Fig. 2a).

Based on the above statements, we formulate the diffusive

transport of hydrogen (concentration N and diffusivity D)

out from the reaction zone by assuming a quasi steady-state

and linear concentration decay DN¼N�N0 through the

boundary layer of thickness d in the gas phase, where we set

N0 � 0. Although a more complete picture of the kinetics

would include temperature dependent adsorption and

desorption between the surface and the concentration N

close to it, we restrict our picture to the final limiting step for

the rate W, expressed as Equation 2.

W � DDN

d(2)

To relate the quantity N to the accessible reactant

concentration NR we use the fact that deposition rates

depend linearly on NR,[26], as shown in Equation 3.

W � kðTÞNR; (3)

H & Co. KGaA, Weinheim www.cvd-journal.de 281

Full Paper

Fig. 4. Observed rates of deposition as functions of total pressure for two

different temperatures of the CH2I2 precursor before reaching the refluxer.

Best fits by Eq. 7 are included as dashed and solid lines. The growth rates were

obtained at a substrate temperature of 1130K.

Fig. 3. The deposition rate as a function of mass flow rate. The observed rates

follow square root dependence (as expected from Eqs. 1 and 4) and the best

curve fit is inserted as a dashed line. The growth rates were obtained at a

substrate temperature of 1130K.

k(T) includes the thermal activation of the rate. Ideally, for

each precursor molecule involved in the deposition reaction,

one H2 molecule leaves, and thus we assume NR�N. The

latter relations allow a validity confirmation of the boundary

layer theory based on Equation 1. In our case, the deposition

rate should follow a square-root dependence on the mass

flow rate, at otherwise constant parameters, as shown in

Equation 4.

W � DDN

d� D

N

d/

ffiffiffiffiffiU

p(4)

This dependence is verified with experimental data shown

in Figure 3. The boundary layer approach also explains the

difference of about 1.4 in the maximum rate of deposition

observed in the two different reactor set-ups, Figures 1 and

2. As the flow doubles for the symmetric reactor (its height is

half of the lamp/thermal plate reactor, see Sec. 4), d will be

decreased by the square root of the relative increase in flow

rate. That is, the deposition rate will beffiffiffi2

ptimes less than in

the symmetric reactor. Finally, it should be noted that the

present description, as it is based solely on boundary layer

transport, is principally also valid for, e.g., NR.

A variation of total pressure is easily performed in the

experiments, and allows for an optimization of the growth

rate, see Figure 4. The rate dependence on total pressure in

the saturation regime can also be described in the frame of

boundary layer theory. Assuming that the precursor source

and the condensation unit within the refluxer can be treated

as stationary interfaces, the balances of fluxes at the

corresponding boundary layers can phenomenological be

expressed as Equations 5 and 6.

a1 Ne �Nið ÞD1

d1� b1UNi ¼ 0 (5)

a2 Ni �Ncð ÞD2 � b2U NR �Nið Þ ¼ 0 (6)
d2
Here,Ne,Ni, andNc are the concentrations of the reactant

at the source interface, in the intermediate transport


channel, and at the condensation unit, respectively.

Neglecting Nc and solving for NR, and taking into account

the particular dependences of Di, di and U on total pressure

p,[28,29], we arrive at the characteristic expression,

Equation 7.

NR ¼ Ne1� ap�0:5

1þ bp0:5(7)

a and b are combinations of constants from Equations 5 and

6. In Figure 4, best fits of Equation 7 to the measured

deposition rates are included. A reasonable correlation is

obtained, so Equation 7 allows a rough optimization of the

deposition rate. The level of accuracy obviously increases

with the temperature difference of the precursor source and

the condensation unit in the refluxer.

2.2. Characterization of Deposited Thin Films

The densities of the different films were estimated by

means of XRR measurements via the critical angle of total

reflection. The films investigated were deposited at temp-

eratures of �1100K (saturation region) with both PT- and

T-CVD. Interestingly, the films deposited by T-CVD had a

lower density (1.7 g cm�3) as compared to the PT-CVD ones

with densities of 1.8 g cm�3. Considering that thin carbon

films deposited by T-CVD always have a slight hydrogen

incorporation through the whole thickness of the films

(ranging from�15 at.-% at 850K to�4 at.-% at 1150K, with

a quasi-linear characteristics of the decay), and the PT-CVD

films have less than 1 at.-% hydrogen (which is mostly

because of surface contaminants), this is a very plausible

explanation of the density difference. Furthermore, this

observation again supports the assumption that the T-CVD

kinetics involve a slower hydrogen outward flux (as

discussed earlier), resulting in hydrogen incorporation

within the film and a lower growth rate (at the same

temperature) as compared to PT-CVD.


Full Paper

Fig. 5. Raman spectra measured from a) T-CVD thin carbon films and b) thin

films obtained with PT-CVD. In b) both the deposit on the upper side (facing

the lamp) and lower side of the same substrate were measured. (Excitation

wavelength used in the measurements was 514 nm.)

Fig. 6. Measured spectrum (dotted line) from carbon film deposited by

T-CVD at 940K and the four necessary peaks for a reasonable fit.

The microstructure of the deposited films was character-

ized by means of RS. Different spectra from both T- and

PT-CVD films can be seen in Figure 5. For both the

activation sources, the Raman spectra contains two distinct

peaks, the ‘graphitic’ (G) peak at around 1600 cm�1 and a

broader ‘disordered’ (D) peak centered around 1355 cm�1

related to the G point phonons of E2g symmetry and zone

boundary phonons of A1g symmetry, respectively.[31,32]

Some differences can be observed when comparing the

two excitation sources. The T-CVD deposits show slightly

broader features and consequently more overlap of the

G and D peaks. The overall spectra for all the films suggest

that the films exhibit a disordered/nanocrystalline graphitic

structure and can be denoted as disordered carbon (DC)

with mainly sp2 character.

To deconvolute the measured spectra, four Voigt peaks

were necessary to obtain a reasonable fit (see Fig. 6). The

small peaks at 1180 and 1510 cm�1 were kept locked in

position to obtain a stable fit procedure. These two shifts

were chosen because a free fit (without strongly overlapping

peaks) resulted in positions around these shifts and features

around these values are often reported in the literature;[33–36]

their possible origin will be briefly discussed later. Some of

the data obtained from the fits and their temperature

dependence for both T- and PT-CVD deposits are depicted

in Figure 7.

First, we consider the T-CVD thin carbon films. The

positions of the G and D peaks as well as the peak height


ratio (ID/IG) are depicted in Figure 7 (circles). The G peak

position is roughly constant at a value of 1597 cm�1 and the

ID/IG ratio shifts to higher values at higher deposition

temperature. From the ID/IG ratios, the characteristic size of

the in-plane graphitic grains (La) can be estimated via the

empiric relation ID=IG ¼ CðlÞ=La, where CðlÞ is a wave-

length dependent constant (found to be 4.4 nm for 514 nm

excitation wavelength).[31] La was found to slightly decrease

from about 5.5 nm to 5 nm in the temperature range studied.

The ratio of full width at half maximum values for the main

bands (FWHMG/FWHMD) follows the same trend as the ID/

IG ratio, that is a roughly linear increase was found and the

ratio increase from about 0.43 to 0.49 in the temperature

range studied.

In our case, three dominant effects can be assumed to

affect the graphitization of the films: i) the rate of deposition –

where a higher rate may decrease the graphitization;

ii) deposition temperature – where a higher temperature

is expected to increase the graphitization (annealing effect);

and iii) hydrogen incorporation in the films may also inhibit

the graphitization.

As can be seen in Figure 7c, the ID/IG ratio increases

slightly as the temperature increases, which suggests a slight

decrease in the coherence length according to the above

mentioned empiric relation. The values of the characteristic

size is around 5 nm, i.e., we are still in the nanocrystalline

carbon region where the expression is usually accepted.[37]

However, other reports on similar spectra suggest that the

empirical formula may not be applicable due to a lack of 2D

ordering of six-fold rings, and that the increase is indicative

of a decrease in the disorder of the threefold network and

subsequent increase of six-fold ring areas.[35,36]

Interesting behavior is observed for the position of the D

peak. The peak shifts to higher energies up to a deposition

temperature of about 940K, then a decrease in the position

is observed at temperatures higher than �1040K. It is also

noted that the FWHM of both theG andD peaks follow the

same trend as the D peak position. We suggest that this

behavior is mainly due to the growth rate dependence on

temperature in the various temperature regions (see Fig. 1).

That is, at deposition temperatures below �950K, the

mbH & Co. KGaA, Weinheim www.cvd-journal.de 283

Full Paper

Fig. 7. a) and b) Positions of theG andD peaks as functions of the deposition

temperature and c) peak height ratios (ID/IG) of the D and G peaks from

Fig. 5.

increase in growth rate is relatively high (steeper slope) as

compared to above 1000K (where similar deposition rates

are observed, resulting in a higher degree of annealing).

It is likely that the steeper slope of rate of deposition/

temperature in the lower temperature range results in a

relatively fast increase of the number and distribution of

clusters of different dimensions and bond orders, which

can be assigned to the D band,[37] and thus up-shifts and

broadens the same. At higher temperatures (but with similar

rate of deposition) the annealing effect is dominant resulting

in more uniform grains and less disorder as the deposition

temperature increases, thus decreasing the FWHMs and

may also downshift the D position. Of the two other peaks

(fixed at 1180 and 1510 cm�1, respectively), the 1510 cm�1

intensity normalized to theG peak drops from�0.4 to 0.3 as

the temperature is increased from 865 to 940K. At higher

temperatures the ratio is roughly constant at 0.3. According

to the literature, the origin of this band is likely from a

network of amorphous carbon with both sp2 and sp3 bonding

and the change in ratio can be attributed to an annealing

effect where weak tetrahedral bonds are converted to

threefold coordinated.[36] The origin of the band at

�1180 cm�1 is still under discussion, but we find it likely

that the band can be related to graphitic-like bond character,

as seen in the literature.[35]

For the PT-CVDfilms one can see that the Raman spectra

obtained from both sides of the thin substrate are very

similar, which again suggests that any photolytic contribu-

tion can be neglected. Overall, the G and D peaks are

narrower as compared to those in the T-CVD films,


indicating a better graphitic crystallinity in these films.

Otherwise, the trends are very similar to what was observed

for the T-CVD carbon films. The small up-shift of the G

band may be due to the better ordering and increase of the

sp2 bonding fraction.[37] The fact that the films are hydrogen

free may also influence this shift. Even though the rates of

deposition in most of the studied temperature range are

much higher, the overall crystallinity is better for the films

deposited by lamp activation. We attribute this better

ordering to the absence of hydrogen throughout the films,

resulting in less bond order distortion.

3. Summary

In a cold-wall, CVD flow-system operating under low

total pressures, employing the precursor molecule CH2I2,

we found that large-area processing utilizing a focused IR

halogen lamp still induces strong 3D transport effects as

compared to the similar size classic CVD technique. These

3D effects results in an increase of the deposition rate of

almost one order of magnitude. The reason for this effect is

found in an unusually large thickness of the boundary layer

which induces a transport regime of similar size to the

surface area and chamber dimensions, and, in transport-

related kinetics, included the heating of the gas phase and

accompanied effects of thermodiffusion. The influence of

the deposition rate due to photolysis effects seems to be

negligible.

A slightly lower density (1.7 g cm�3) was observed in the

T-CVD films as compared to the PT-CVDfilms (1.8 g cm�3).

This difference is most likely due to hydrogen incorporation

within the films deposited by T-CVD. The lower rate of

hydrogen transport away from the surface possibly explains

the hydrogen content throughout these carbon films. RS on

the carbon films shows that the microstructure can be

described as disordered/nanocrystalline carbon ofmostly sp2

character. A slightly better crystallinity was obtained by PT-

CVD.

The broadband IR lamp assisted technique allows the

efficient formation of disordered/nanocrystalline thin car-

bon films with easy handling and low costs.

4. Experimental

Two different flow-through reactors were used for the experiments (seeFig. 8). The first used was a reactor (5 cm� 5 cm in cross-section) with a BN-covered graphite thermal plate mounted inside and with an optional(maximum power of 150W) infrared lamp (slightly focused with waistdiameter of approximately 6mm) from above normal to the thermal plate, seeFigure 8a. The second reactor (see Fig. 8b) was a fully symmetric constructionwith respect to the transport properties on both the lamp (photophysical) sideand the opposite (photothermal) side, and had a total cross-section of about5 cm� 2.5 cm in the gas-flow direction. The IR lamp was the only excitationsource in the symmetric set-up, and the lamp could be mounted either fromabove or below, normal to the substrate. The thin substrate was placed inbetween two quartz plates (with a d¼ 1 cm hole in the center) which coveredthe whole flow direction, creating two separate deposition regions.


Full Paper

Fig. 8. Schematic figures of the different cold-wall CVD reactors used. a) For

the combined lamp- and/or thermal plate-activated processes and b) the fully

symmetrical set-up for direct comparison between photophysical and thermal

processes.

The methylene iodide (CH2I2) precursor was introduced into the reactorvia a refluxer at 19 8C and a carrier flow of Ar at 10 sccm). Experiments werecarried out under a total pressure in the range of 1.5–25mbar, and thesubstrates used were double polished, 300mm thick, single crystal Si(100) cutto 15mm� 15mm. Temperatures have been measured on both sides of thesubstrate by thin Ni/NiCr thermocouples attached to the surface of interest,although the thickness of 300mm is approximately thermally thin with respectto the lamp spot of about 6mm in diameter.Typical deposition time was 20min, and scanning electron microscopy

(SEM) of cross-sections of the samples was used for determining the thicknessof the films. RS was used for microstructural information of the carbondeposits, and XRR measurements were used to determine the density of thefilms. In addition, the hydrogen concentration throughout the carbon layerswas probed via nuclear reaction analysis.

Received: March 10, 2008

Revised: June 30, 2008

[1] G. Vurens, D. Klein, Proc. SPIE 1999, 27, 3619.

[2] N. Gopinathan, C. Robinson, F. Ryan, Thin Solid Films 1999, 355/356,401.

[3] S. Yongjian, C. Xing, M. M. Yang, IEEE Trans. Magn. 2003, 39, 594.


[4] C. A. Taylor, W. K. S. Chiu, Proc. SPIE 2002, 4639, 152.

[5] T. Soga, T. Jimbo, K. M. Krishna, M. Umeno, Int. J. Mod. Phys. B 2000,14, 206.

[6] A. S. Loir, F. Garrelie, C. Donnet, M. Belin, B. Forest, F. Rogemond, P.Laporte, Thin Solid Films 2004, 453, 531.

[7] A. Fissore, M. A. R. Alves, E. da Silva Braga, L. Cescato, J. Micro-electron. 1999, 30, 833.

[8] M. Yoshida, T. Tanaka, S. Watanabe, M. Shinohara, J. W. Lee, T.Takagi, Surf. Coat. Technol. 2003, 174, 1033.

[9] N. K. Cuong, M. Tahara, N. Yamauchi, T. Sone, Surf. Coat. Technol.2003, 174, 1024.

[10] T. Noguchi, K. Suizu, K. Nagayama, Appl. Surf. Sci. 2002, 197, 357.

[11] A. M. Baranov, Surf. Coat. Technol. 2001, 148, 149.

[12] R. Kostecki, X. Song, K. Kinoshita, Electrochem. Solid-State Lett. 2002,5, E29.

[13] Y. Iriyama, Y. Hasegawa, T. Ihara, J. Photopolym. Sci. Technol. 2000,13, 39.

[14] M. Ishihara, M. Suzuki, T. Watanabe, O. Tsuda, T. Nakamura, A.Tanaka, Y. Koga, Diamond Relat. Mater. 2004, 13, 1449.

[15] G. Musa, I. Mustata, V. Ciupina, R. Vladoiu, G. Prodan, E. Vasile, H.Ehrich, Diamond Relat. Mater. 2004, 13, 1398.

[16] J. Y. Shim, E. J. Chi, H. K. Baik, K. M. Song, Thin Solid Films 1999, 355/356, 223.

[17] A. Weber, U. Hoffmann, C. P. Klages, J. Vac. Sci. Technol. A 1998, 16,919.

[18] P. Finnie, J. Bardwell, I. Tsandev, M. Tomlinson, M. Beaulieu, J. Fraser,J. Lefebre, J. Vac. Sci. Technol. A 2004, 22, 747.

[19] M. Lindstam, O. Wanstrand, M. Boman, K. Piglmayer, Surf. Coat.Technol. 2001, 138, 264.

[20] M. Lindstam, M. Boman, K. Piglmayer, Nucl. Instrum. Methods Phys.Res. B 2002, 192, 274.

[21] K. Piglmayer, M. Lindstam, M. Boman, Surf. Rev. Lett. 2001, 8, 609.

[22] M. Lindstam, M. Boman, K. Piglmayer, Thin Solid Films 2001, 394, 115.

[23] M. Lindstam, M. Boman, K. Piglmayer, Appl. Surf. Sci. 2001, 172, 200.

[24] K. Piglmayer, G. Stenberg, M. Boman, Appl. Surf. Sci. 1997, 109/110,449.

[25] G. Stenberg, K. Piglmayer, M. Boman, J.-O. Carlsson, Appl. Surf. Sci.1997, 109/110, 549.

[26] G. Stenberg, M. Boman, J.-O. Carlsson, Diamond Relat. Mater. 1997, 6,1143.

[27] D. Bauerle, B. Luk’yanchuk, K. Piglmayer, Appl. Phys. A 1990, 50, 385.

[28] R. F. Probstein, Physicochemical Hydrodynamics, Butterworth Publish-ers, Stoneham 1989.

[29] D. Bauerle, Laser Processing and Chemistry, 3rd Ed., Springer Verlag,Berlin 2000.

[30] R. E. Thomas, R. A. Rudder, R. J. Markunas, J. Vac. Sci. Technol. A1992, 10, 2451.

[31] F. Tunistra, J. L. Koenig, J. Chem. Phys. 1970, 53, 1126.

[32] R. J. Nemanich, S. A. Solin, Phys. Rev. B 1979, 20, 392.

[33] J. Schwan, S. Ulrich, V. Batori, H. Ehrhardt, S. R. P. Silva, J. Appl. Phys.1996, 80, 440.

[34] V. Paillard, P. Melinon, V. Dupuis, J. P. Perez, A. Perez, B. Champag-non, Phys. Rev. Lett. 1993, 71, 4170.

[35] P. Milani, M. Ferretti, P. Piseri, C. E. Bottani, A. Ferrari, A. L. Bassi, G.Guizzetti, M. Patrini, J. Appl. Phys. 1997, 82, 5793.

[36] S. Bhargava, H. D. Bist, A. V. Narlikar, S. B. Samanta, J. Narayan, H. B.Tripathi, J. Appl. Phys. 1996, 79, 1917.

[37] A. C. Ferrari, J. Robertson, Phys. Rev. B 2000, 61, 14095.

mbH & Co. KGaA, Weinheim www.cvd-journal.de 285

Photothermal CVD of Carbon Thin Films using CH2I2 as the Precursor

Documents

Transcript of Photothermal CVD of Carbon Thin Films using CH2I2 as the Precursor