Microwave ECR Plasma Assisted MOCVD of Y2O3 Thin Films Using Y(tod)3 Precursor and Their Characterization

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Microwave ECR Plasma Assisted MOCVD ofY2O3 Thin Films Using Y(tod)3 Precursor andTheir Characterization

Shruti Barve, Mukul Deo, Rajib Kar, Nimisha Sreenivasan,Ramaswamy Kishore, Arup Biswas, Bhalchandra Bhanage, Mohan Rao,Lalit Mohan Gantayet, Dinkar Patil*

Yttrium oxide (Y2O3) thin films were deposited by microwave electron cyclotron resonance(ECR) plasma assisted metal organic chemical vapour deposition (MOCVD) process usingindigenously developed metal organic precursors Yttrium 2,7,7-trimethyl-3,5-octanedionates,commonly known as Y(tod)3whichwere synthesized by an ultrasoundmethod. A series of thinfilms were deposited by varying the oxygen flow rate from 1–9 sccm, keeping all otherparameters constant. The deposited coatings were characterized by X-ray photoelectronspectroscopy, glancing angle X-ray diffraction and infrared spectroscopy. Thickness androughness for the films were measured by stylus profilometry. Optical properties of thecoatings were studied by the spectroscopic ellip-sometry. Hardness and elastic modulus of thefilms were measured by nanoindentation tech-nique. Being that microwave ECR CVD process isoperating-pressure-sensitive, optimum oxygenactivity is very essential for a fixed flow rate ofprecursor, in order to get a single phase cubicyttrium oxide in the films. To the best of ourknowledge, this is the first effort that describesthe use of Y(tod)3 precursor for deposition of Y2O3

films using plasma assisted CVD process.20 25 30 35 40 45 50 55 60 65 70 75 80

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S. Barve, R. Kar, L. M. Gantayet, D. PatilLaser and Plasma Technology Division, Bhabha Atomic ResearchCenter Trombay, Mumbai 400 085, IndiaE-mail: [email protected]. DeoHigh Pressure and Synchrotron Radiation Physics Division, BhabhaAtomic Research Center Trombay, Mumbai 400 085, IndiaN. Sreenivasan, M. RaoDepartment of Instrumentation and Applied Physics, IndianInstitute of Science, Bangalore 560 012, India

R. KishoreMaterials Science Division, Bhabha Atomic Research CenterTrombay, Mumbai 400 085, IndiaA. BiswasApplied Spectroscopy Division, Bhabha Atomic Research CenterTrombay, Mumbai 400 085, IndiaB. BhanageInstitute of Chemical Technology, Matunga, Mumbai 400 019,India

Plasma Process. Polym. 2011, 8, 740–749

� 2011 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim wileyonlinelibrary.com DOI: 10.1002/ppap.201000147

Microwave ECR Plasma Assisted MOCVD of Y2O3 Thin Films . . .

Introduction

Yttrium oxide thin films have been a topic of current

research interest due to their potential applications in

varied fields. Their high refractive index (1.8–2.4),

large dielectric constant (10–17), high breakdown strength

(1–5 MV � cm�1), high melting point (�2 400 8C), thermal

stability and hosting abilities for the lanthanide elements

make them highly important ceramics from technological

point of view. Y2O3 films are finding applications in many

areas, such as development of filters, optical coatings,

sensors, display devices, refractory materials, replacement

and replenishment of semiconductor films and dielectric

materials. Other structural forms of Y2O3 as nanotubes,

nanowires and nanorods are also being investigated for

their potential applications. Thermal stability of the cubic

yttria and its highmelting pointmakes it very useful in the

thermal barrier, reaction barrier/protective coatings. A

large variety of techniques like electron beam evaporation,

laser ablation, sputtering, thermal oxidation, plasma

assisted chemical vapor deposition (PACVD),metal-organic

chemical vapor deposition (MOCVD), molecular beam

epitaxy, hydrothermal deposition and atomic layer deposi-

tion etc. have been used for the deposition of yttriumoxide.

Each process is having its own advantages and limita-

tions.[1] Uniformity and purity of the deposited coatings,

plus ability to deposit on the large and complex substrates,

precision and repeatability are important commercial

aspects of the thin film deposition processes. Obviously

minimum contaminations in the deposition process,

plasma uniformity over the substrate, precise control of

the deposition parameters, repeatability and low deposi-

tion temperature are certain important requirementsof the

thin film deposition process. It has been known that,

microwave ECRMOCVDprocess is a highly efficient process

of plasma generation giving large area plasma uniformity

at the substrate location.[2] The system works at low

operating pressures,[3] and hence atom-by-atom deposi-

tions are possible, which leads to precision in the

deposition. Electrodelessnatureand lowpressureoperation

helps keep very low contamination level during the

deposition process.[1] And finally, energetic and ionization

processes involved in this plasma deposition method

makes it suitable for low temperature operation, which

helps in depositing very complex films as multiple oxide

coatings. Unlike conventional CVD processes, ECR MOCVD

can deposit films on varied types of substrates which may

get damage at higher temperature, e.g. one cannot afford to

have higher temperature while depositing on semiconduc-

tors. For the MOCVD of Y2O3 coatings, the most promising

and highly used precursors are b-diketones. These pre-

cursors have beenused inmetal-organic CVDprocesses due

to their high volatility at very low evaporation tempera-

tures, thermodynamic stability, atmospheric stability, non-


� 2011 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim

corrosive nature (unlike fluorinated precursors) and ease of

handling.[4] In the tris type, non-halide b-diketone pre-

cursors Y(tod)3 (2,7,7-trimethyl-3,5-octanedionate of

yttrium) precursor is found to be much better in terms of

volatilityandstability thancommonlyusedY(thd)3 (2,2,6,6-

tetramethyl-3,5-heptanedionate of yttrium) and Y(acac)3(Yttrium Acetyl acetonate) precursors.[5,6] Due to the

presence of asymmetric isobutyl group in the structure,

flexibility of the Y(tod)3 molecule increases and better

shieldingof the centralmetal cation ispossible,which leads

to increase in the volatility.[6]

Here,we report on themicrowaveECRplasmadeposition

of the Y2O3 coatings using a Y(tod)3 precursor that is

developed in our laboratory. The precursor synthesis

process is discussed elsewhere.[7] The precursor tempera-

ture was fixed at 180 8C during all deposition experiments

and generated precursor vapors are introduced into the

deposition chamber. A series of thin film depositions were

carried out by varying the oxygen flow rate from 1–9 sccm.

All other parameters are kept constant throughout the

deposition experiments.

The deposited films were characterized by various

characterization techniques like: X-ray photoelectron

spectroscopy (XPS), glancing angle X-ray diffraction

(GAXRD), infrared spectroscopy (110–4 000 cm�1) and

spectroscopic ellipsometry. Thickness of the deposited

filmswasmeasured by stylus profilometer andmechanical

properties of the films were studied by using load depth

sensing nano indentation technique. Efforts were made

here to explain the role of oxygenactivityduringdeposition

on the properties of the deposited Y2O3 coatings.

Experimental Section

Microwave ECR plasma-assisted MOCVD setup that is used for the

depositions is described in detail elsewhere.[8] Initially substrates

were thoroughly cleaned in RCA-I solution and then in 10% HF

solution for 2min to remove the native oxide on the surface of the

substrates. Substrates were then ultrasonically cleaned in metha-

nol for 20min, driedunder the infrared light and then immediately

transferred to the substrate holder in the deposition chamber. The

whole system including precursor delivery lines was pumped

down to �1�10�5 mbar pressure by using a diffusion pump in

combination with a rotary pump. The substrate temperature was

kept constant at 350 8Cbyusingaproportionate integral derivative(PID) controller. Initially, argon gas flow (5 sccm) was started and

microwave ECR plasma was generated. Plasma was tuned for

minimum reflected power and for plasma uniformity over the

substrate area, by using tuning elements in the microwave

transmission line. After the sputter-cleaning of the substrates in

the argon plasma for 20min, argon gas flow rate was adjusted to

1 sccm and oxygen gas flow rate was adjusted to 1–9 sccm (in

different depositions). Precursor evaporator including delivery

lines was heated to a constant value of 180 8C simultaneously.

Keeping all other parameters constant, a set of five films were

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Figure 1. TGA plots for Y(tod)3 precursor measured in i) argon gasat atmospheric pressure (Ar gas), and ii) under vacuum at10�6 mbar pressure.

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depositedwith variationof oxygengas flow rate in the plasmafilm

A (1 sccm), B (3 sccm), C (4 sccm),D (7 sccm)andE (9 sccm). Precursor

vaporswere showered in the plasma (on the substrates) by using a

gas distribution ring. The final operating pressures in the

deposition chamber were 1.2� 10�4 mbar, 3.7�10�4 mbar,

5.9�10�4 mbar, 7.2�10�4 mbar and 7.8�10�4 mbar for films

A, B, C, D and E, respectively. Depositionswere carried out typically

at microwave power of 480W for 2h. Precursor temperature was

fixed to an appropriate value by studying the evaporation

characteristics of the precursor in vacuum. Thickness and rough-

ness of the filmsweremeasured by the stylus profilometer (Dektak

150, Veeko). XPS analysis was performed with SPECS GmbH

spectrometer (Phoibos 100 MCD Energy Analyzer) using MgKa

radiation (1 253.6 eV). The residual pressure inside the analysis

chamberwas in10�10mbar range.Thespectrometerwascalibrated

by using photoemission lines of Ag (Ag 3d3/2¼ 367 eV with

reference to the Fermi level). Peaks were recorded with constant

pass energy of 40 eV and counts per second are optimized to

minimize thenoise level in the spectrum.Becauseof surface charge

inducedpeakshifts,C1sat284.6 eVwastakenasa referenceenergy

position to correct the shift. An X’Pert PRO X-ray Diffractometer

(PANalytical) with 40 kV, 30mA power CuKa source was used for

getting the glancing angle X-ray diffraction patterns on the

deposited films. Incident angle of the source beamwas fixed to 1.88andX-ray diffractionpatterns are obtained in the 2u range of 208 to808 with the scan step of 0.058 per 3 s for all the films. IR

spectrometer (Bruker Vertex 80V) was configured with potassium

bromide (KBr), Mylar multilayer beam splitters, liquid nitrogen

cooledHgCdTe (MID-IR) andDeuteratedTriglycinSulphate (FAR-IR)

detectors. A 118 reflection accessory was used for taking the IR

spectra. Infrared spectra were recorded in the FAR-IR region (100–

600 cm�1), as well as in the MID-IR region (600–4000 cm�1) at a

spectral resolution of 2 cm�1. Spectroscopic Ellipsometry unit

(model SE800,makeSENTECH InstrumentsGmbH)wasused tofind

out the variation of optical properties of the films in 300nm to

1 200nmwavelength range. The experimentallymeasured ellipso-

metric parameters C and D have been fitted with theoretically

generated spectra. The theoretical values have been generated by

using Tauc-Lorentz model. Using the best fitted parameters the

refractive indices of the films were measured. Nanoindentation

was carried out using ultra-nano hardness tester (CSM, Switzer-

land) under load control mode up to amaximum load of 250mN. A

Berkovich three-sided pyramidal diamond nanoindenter with a

nominal angle of 65.38 was used for measuring the hardness and

elastic modulus of the films.

Results and Discussion

Thermo-gravimetric Analysis

Precursor evaporation characteristicswere studied inargon

gas at one atmospheric pressure and also in vacuum of

�10�6 mbar as shown in the Figure 1. From these

characteristics, it is seen that in argon gas at one

atmospheric pressure, approximately 76% mass of the

precursor is lost in the 190 8C to 350 8C temperature range,

small kinks in between are showing the preferential



evaporationof somegroups fromthe largeY(tod)3precursor

molecule (Figure 1i). At 10�6 mbar pressure, a single step

evaporation of the precursor starting at�162 8C is observed

giving �81% mass loss till 200 8C. Vacuum TGA (Figure 1ii)

indicates that there are no features that shows precursor

decomposition below162 8C. It is evident fromFigure 1 that

low pressure helps in increasing vaporization of the solids

precursor. Toget reasonableflowrateof theprecursor at the

experimental operating pressures, precursor evaporator

temperature was fixed to 180 8C throughout the deposi-

tions.

Thickness and Roughness

Thickness and roughness values are high for film A,

decrease and pass through minima for film C and again

increase forfilmEas shown in the Figure 2.Deposition rates

calculated from the thickness values give the same trend. It

ismaximum for the filmA (�100 A �min�1), it decreases for

the film B (�65 A �min�1) with a further decrease for film C

(�18 A �min�1). Finally it increases for film D

(�75 A �min�1) and further for film E (�116 A �min�1),

giving minima for film C.

X-ray Photoelectron Spectroscopy

Survey scans taken on the deposited films show threemain

peaks corresponding to the energy levels of Y 3d, O 1s and

C 1s peaks. All the three peaks are further scanned in detail

with 0.05 eV step. Detailed scans are analyzed by using XPS

Peak fit 4.1. FWHM values for the fitted peaks are fixed

within the range 1 to 1.2 eV for Y 3d andO 1s peaks, while it

DOI: 10.1002/ppap.201000147

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Figure 2. Variations in the thickness and roughness of the depos-ited films.

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Figure 3. Comparison of Y 3d XPS high resolution scans.


is fixed in the range of 1 to 1.3 eV for C 1s sub-peaks. L:G

ratios are fixed to 20%, 35% and 60% for Y 3d, O 1s and C 1s

peaks respectively. Minimum numbers of sub-peaks are

fitted in each peak to get the least value of x2 as <1.3,<0.4

and <0.3 for Y 3d, O 1s and C 1s peaks respectively.

Y 3d detailed scan peaks obtained for the films are

deconvoluted and compared in the Figure 3. It is observed

that, three different chemical environments are found for

the yttrium atoms, in the form of reduced yttrium oxide,

pure yttrium oxide and yttrium hydroxide. Peak pairs with

binding energies at �156.6 eV and at �158.7 eV for Y 3d5/2and Y 3d3/2 respectively, confirm the presence of stoichio-

metric yttrium oxide.[9] Second type of bonding in the Y 3d

peak, present at lower binding energies (�155.7 eV,

�158 eV) is characteristic of reduced yttrium oxide.[10,11]

Peak pairs shifted to higher binding energies (�157.5 eV,

�159.6 eV) can be attributed to Y�O�H or Y�O�C

bonding.[9,12] Yttrium oxide is known to be hygroscopic

in nature, and hence there is a possibility that, combining

with the atmosphericmoisture and carbon dioxide it forms

hydroxides, carbonates and hydro-carbonates of yttrium.

Hence the higher binding energy peak pair (�157.5 eV,

�159.6 eV) is possibly due to the surface adsorption of

hydrogen and carbon by the deposited films. O 1s peak is

also deconvoluted into its subcomponents as indicated in

the Figure 4. O 1s peak basically consists of two sub-peak

groupsoneat�529.5 eVcharacteristic ofY�Obondingsand

other at�531.5 eV representing C�O bonds. Each sub-peak

group is formed by three sub-peaks. In the subpeak group

corresponding to Y�O bond, largest peak is found at

�529.3 eV which is characteristic of stoichiometric Y2O3

formation in the film.[9,11] High binding energy sub-peak

present at �530 eV are indicative of non-stoichiometric

yttrium oxide.[11] Binding energy sub-peak components



around 528.5 eV indicates the presence of Y�O�H or

Y�O�C bonding in the films as found in the deconvoluted

Y3dpeak. In thesub-peakgrouprepresentingC�Obonding,

sub-peaks at very high binding energies above 532 eV and

533 eV are representative of C¼O groups and C�O�C/

C�O�Hgroups respectively as shown in Figure 4,while the

lowest subpeak at �531 eV indicates the presence of

O�C¼O bonding in the film.[9] These peaks are found due

to the adsorption of moisture on the surface of the films,

which possibly is just a surface phenomenon and does not

represent the bulk. Qualitatively, it can be seen from

Figure 4 that, sub-peak group corresponding to C�O

bonding is decreasing in amplitude, as the flow rate of

oxygen in increased in thedepositionof filmAtofilmC. C 1s

peak is deconvoluted into subpeaks as shown in Figure 5. It

can be seen that, main subpeak in the C 1s peaks of all the

films, is at�284.6 eV and can be identified as free carbon.[8]

Subpeaks at binding energies at around 285.5 eV, �289 eV,


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Raw data Peak sum Y-O-H / Y-O-C Y2O3 Y2O3-x O-C=O C=O C-O-H / C-O-C

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Figure 4. Comparison of O 1s XPS high resolution scans.

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Figure 5. Comparison of C 1s XPS high resolution scans.

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290.2 eV and �291.5 eV represent C�O�H/C�O�C, C¼O,

O�C¼O and (O)2�C¼O bonding respectively.[9] It can be

seen that, as oxygen flow increases in the deposition of film

A to film E, carbon peaks on the higher binding energies

diminish. This indicates that, more the oxygen flow during

the deposition, less is the carbon contamination that is

found in the film. XPS being the surface analysis technique

and analysis is done ex situ, it is possible that presence of

carbon bonding in thefilm is just a surface phenomenon, as

discussed above. A small peak on lower binding energywas

found in the film A which possibly indicates some carbide

formation on the filmsurface. But no such subpeak is found

in the Y 3d peak of film A, as seen from the Figure 3.

Glancing Angle X-ray Diffraction

GAXRD patterns for all films are shown in the Figure 6. It is

seen that, there is a clear variation in the observed crystal

structure from film A to film E. Film A deposited under a



relatively reduced environment (low oxygen flow rate)

shows the presence of hexagonal (hex) yttrium hydroxide

(JCPDS no. 83-2042). Peaks visible in the pattern like (110),

(200), (210) and (220) are coincidingwith the lines from the

said JCPDS card. A small peak at�298 indicates that, there isa possibility of the presence of BCCyttriumoxide in thefilm

A. As the oxygen partial pressure is further increased by

increasing the flow rate to 3 sccm (film B), mixed crystal

structures (cubic Y2O3 and hexagonal Y(OH)3) are seen from

the GAXRD pattern as seen in the Figure 6. Lines from the

JCPDS card numbered 41-1105matchedwell with the lines

from the GIXRD pattern of film B. Multiphase structure of

the film B is confirmed due to the presence of clearly

resolved lines of both the phases at �588. Due to the

existence of nearly located peaks of BCC Y2O3 and hex

DOI: 10.1002/ppap.201000147

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Figure 7. FAR-IR reflectance spectra for the deposited films.

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Figure 6. GAXRD patterns for the deposited films.


Y(OH)3 structures, all other peaks in the GAXRD pattern for

thefilmB, are unresolved. As the oxygenflowrate is further

increased,GAXRDpattern forfilmCshowssinglephaseBCC

yttrium oxide structure with all lines matching with the

lines from JCPDS card no. 41-1105. Decrease in FWHM and

increase in intensity of the peaks in the GAXRD pattern for

film C indicates that, grain size of cubic yttrium oxide is

increasing for film C as compared to film B. When oxygen

flow rate is increased further to 7 sccm, film D again shows

dual phasemixture of BCC Y2O3 and hex yttriumhydroxide

structures. Though other peaks are not well resolved, peak

positioned at �588 confirms the presence of two phases in

the filmD. Peak intensities and FWHMvalues fromGAXRD

pattern indicate that grain sizes are decreasing from film C

to film D again. Finally, as oxygen input during the

deposition is increased to 9 sccm, crystal structure for filmE

is again a multiphase (BCC oxideþhex hydroxide) of

yttrium with broad and less intense peaks indicating

unresolved lines of both the phases.

Infrared Spectroscopy

Reflectance spectra in the FAR-IR (100–600 cm�1) andMID-

IR region (600–4 000 cm�1) taken on the deposited films are



shown in the Figure 7 and Figure 8, respectively. Presence of

cubic yttriumoxide in all films is confirmed by the triplet at

around 300 cm�1 in the FAR-IR region.[13] This confirms the

presence of BCC Y2O3 even in the film A as indicated from

the GAXRD results. All bands including band at 156 cm�1,

lower phonon vibrations in 180–190 cm�1 range, band at

241 cm�1, triplet at 305, 330 and 374 cm�1 and bands at

448 cm�1, 498 cm�1, 560 cm�1 are seen in theFAR IRspectra

of film C. Out of these, only few peaks including triplet

around 300 cm�1 and low lying phonon frequencies are

seen in other films.While peaks at the positions of 156, 420,

498 and 560 cm�1 are seen to be shifted on higher

wavenumber side for all other films except film C. For film

C, characteristic bands for yttrium oxide (�305 cm�1,

330 cm�1 and 376 cm�1) are well resolved and sharp as

reported previously.[13] Triplet intensity is decreasing for

film A (low oxygen flow), as well as for film E (high oxygen

flow), as seen from the Figure 7. This decrease in the

intensity and increase in thewidth of the IR bands towards

filmAandfilmEare basically indicative of a decrease in the

particle size of the yttrium oxide in the film.[14] These

observations support the XRD results as discussed in the

previous section. MID-IR bands for the films are shown in

theFigure8. It is observed that, thesebandsarevery intense

incaseof thefilmsA,DandE. SmallpeaksofO�Hstretching

mode of free hydroxyl groups,[15] in the range of 3 500–


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Figure 8. MID-IR reflectance spectra for the deposited films.

746

S. Barve et al.

3 700 cm�1 are seen in all films which support the

observations from Y 3d peak in the XPS analysis

(Figure 3). At 1 772 cm�1, a strong and wide peak is seen

for film D, which indicates that some carbonyl groups are

present in the film.[15] A significant peak corresponding to

�C¼C� stretchmode[16] isalso found forfilmsAandE in the

range of 1 640–1 680 cm�1. C�H bending modes (1 450–

1 470 cm�1) are found for all films, but are very strong for

filmsA, D and E.[15] Films A andD also show the presence of

some C�O groups represented by the band at 1 300 cm�1,

but this band for filmD ismore intense than that for filmA.

MID-IR results thus support theXPSanalysis confirming the

existence of hydroxide and carbonate bonding in the films,

which are due to the adsorbed contaminations of the film

surfaces. Though quantitative analysis from IR spectra is

notaccurate, it canbeseenthat,hydrogenandcarbonbands

are very significant for films A, D and E as compared to that

for film C and film B.

Ellipsometry

Optical properties of the films are studied by spectroscopic

ellipsometry. Variations of refractive index (n) for the films

with wavelength are shown in the Figure 9. Variation in n

for film A are drastic over the wavelength range. Film B is

having higher n values (2.05 to 1.985) and better trend over

the range of wavelength. Variation in the n values (2.35 to



2.21) for the film C is matching the reported values for the

cubic yttrium oxide.[17,18] Again for film D, n values vary in

the range of 1.62 to 1.89 over thewavelength range. Finally

for film E, refractive index is low as compared to the other

films. Figure 10 gives the variation in the extinction

coefficient (k) of the films in the spectral region of 300–

1 200nm. k values for the films give a similar trends as

found for that of n over the wavelength. From Figure 9 and

Figure 10, it is observed that, film C is giving minimum

valueof absorption (near to zero)with thevalues increasing

towards film A as well as film E.

Nanoindentation

Using a Berkovich diamond indenter nine indents were

made on each filmand the values of elasticmodulus (E) and

hardness (H) are calculated as the average. Variations in the

E andH values for the films are shown in the Figure 11 and

Figure 12, respectively. Considering the error bars shown in

the graph it is seen that, E is higher for film C, while it

decreases towardsfilmAandfilmE. Similar trend is seen for

H values for the films (Figure 12). Some inconsistency in the

hardness value of film C is observed possibly because the

hardness of the film is an intrinsic property of thematerial,

which depends on the interplay between the sliding planes

present and residual porosity in the crystal structure.

DOI: 10.1002/ppap.201000147

200 400 600 800 1000 12000.000.060.120.18

200 400 600 800 1000 12000.000.080.160.24

200 400 600 800 1000 1200

0.00.61.2

200 400 600 800 1000 12000.00.10.20.3

200 400 600 800 1000 12000.100.150.200.25

E

Wavelength (nm)

D

C

Extin

ctio

n C

oeff.

(k)

B

A

Figure 10. Variation of extinction coefficient with the wavelengthfor the deposited films.

1 3 4 7 9

40

60

80

100

120

140

160

Elas

tic M

odul

us (G

Pa)

Oxygen flow rate (sccm)

Figure 11. Elastic modulus variation for the deposited films.

1 3 4 7 9

3

4

5

6

7

8

Har

dnes

s (G

Pa)

Oxygen flow rate (sccm)

Figure 12. Hardness variation for the deposited films.


Discussion

GAXRDresults showthestructural changes in thedeposited

films with the variation in oxygen flow rates during the

depositions. From the observations, it is clear that a single

phase cubic yttrium oxide structure is formed only at an

optimum oxygen gas flow rate (oxygen partial pressure)



during deposition. Decreasing or increasing oxygen flow

rate changes the nature of the deposited phase in the film

from BCC Y2O3 to hex Y(OH)3. FAR-IR results confirm the

presence of BCC Y2O3 phase in all films. Decrease in the

intensity of bandswith theassociated increase in thewidth

of the bands is seen in the FAR-IR spectra and support the

GAXRD observations in respect to decrease in the grain size

of BCC yttrium oxide towards film A and E. Replacement of

‘O’ atoms in Y2O3 by ‘OH’ groups possibly increases the

bindingenergyofY�Obond,which isvisible fromtheslight

shift of some of the FAR-IR bands towards higher wave

number side (Figure 7) for films A, B, D and E as discussed

earlier. It has been known that, hex Y(OH)3 structure has an

intrinsic tendency to grow in the rod/tube like structure

where hexagonal columns are developed in the ‘c’ direction

of the crystal structure.[19] Deposition ofmixture of phases,

as well as columnar growth of hex Y(OH)3 increases the

voids in the films[20] towards films A and E. Yttrium oxide

being hygroscopic in nature, voids generated in the films

are susceptible to the adsorption and absorption of

moisture and atmospheric carbon dioxide into the film

leading to the formation of hydroxides and carbonates in

the films. This effect adds up to the effect of structural

change fromBCC Y2O3 (filmC) to hex Y(OH)3 towards filmA

and E, showing the maximum presence of hydroxide and

carbonate groups in the MID-IR spectra of these films. XPS

results support the observations from MID-IR spectra,

thoughquantitative estimationof different phaseswasnot

possiblewith the technique. Increase in thevoids andhence

increase in thewater susceptible sites in thefilmsdecreases

the refractive indices, as well as make them thermodyna-

mically unstable.[18,21] These effects are seen with the

decrease in thenand increase in thekvalues towardsfilmA

andEasseen fromtheellipsometry results (Figure9and10).


748

S. Barve et al.

It has been found that, porosity andwater adsorption in the

film increases with the increase in the thickness of

the films.[21] Decrease in the density of the films with the

increase in thevoidspresent in thedepositedfilmshasbeen

correlated by some investigators.[22]Minimumthickness of

film C with n and k variations approximating to the bulk

value of BCC-Y2O3 is an evidence of these effects. Oxygen

flow variations during the deposition changes the rough-

ness of the films due to the columnar growth of the

film.[22,23] This also explains why hexagonal Y(OH)3structures are found to have high surface roughness.

Thin films generally grow in the columnar fashion, but

efficient plasma ion activity and heavy ion bombardment

can convert the tensile stresses in the films to compressive

stresses increasing the lateral mobility of the adatoms at

the substrate surface.[16,20] Structural change of theyttrium

oxide film to amost stable cubic structure (filmC) indicates

thepresenceofmostefficientoxygen ionactivityduring the

deposition. Efficient ion activity during deposition leads to

more dense coatings andmore sputtering of loosely bound

species from the substrate surface in the plasma. Effects of

this are seen in terms of the preferred growth of a single

phase as well as in the decrease of thickness and growth

rates of the film C.

MicrowaveECRplasmagenerationoperates efficiently in

the optimum conditions of operating pressure (10�3 to

10�5 mbar pressure range). Plasma is efficiently ionized in

this pressure range giving maximum ion activity in the

plasma.[24,25] When oxygen flow is increased during the

deposition, the plasma generation process deviates from

this optimum pressure range of efficient ionization. Hence,

ion density, as well as ion energy is changed, which further

affects the ionization of precursor gas in the deposition

chamber and chemistry at the surface of the substrate in

such away that, films D and E give amixture of cubic oxide

and hexagonal hydroxide phase of yttrium even in the

presence of high oxygen flow rate. This indicates that, not

only the high oxygen flow rate but also the efficient

ionization of the gases are important for getting the

required phase formation during the plasma depositions of

yttrium oxide films. When oxygen partial pressure

decreases in the system, hexagonal hydroxide phase (film

A) isdeveloped. This canbeexplainedasbelow.Oxygen ions

play a dual role during the deposition process. First, it helps

in the deposition of yttrium oxide film on the substrate by

oxidizing the yttrium containing species, and, secondly,

they are also utilized in removal of unwanted carbon and

hydrocarbon species that are generated in the plasma due

to precursor decomposition. When oxygen flow rate is

decreased to 1 sccm (film A), oxygen ion activity that is

generated in thedepositionsystemispossiblynotsufficient

to completely oxidize the yttrium containing species in the

plasma. This possibly leads to the incorporation of more

hydrogen and carbon containing species in the film A,



which help in the deposition of hydroxide phase. These

observations thus clearly indicate that optimization of

the oxygen flowwith the precursor flow rate, as well as the

optimization of the plasma ion activity during deposition,

are important factors for the deposition of a single phase

film.

Conclusion

Single phase cubic Y2O3 thin films are successfully

deposited on various substrates using microwave ECR

Plasma assisted CVD process and indigenously developed

precursor Y(tod)3 at a low substrate temperatures of 350 8C.The characterization results from various techniques are

supporting each other. The investigations reported here

clearly bring out the role of oxygen activity in the plasma

during the deposition of Y2O3 films using microwave ECR

plasma CVD process. The ECR CVD process being pressure

sensitive, increase in the oxygen flow rate during the

depositiondoesnotguarantee thesupplyof enoughoxygen

ions tohelp ingetting stoichiometric/singlephase coatings.

Properties of the deposited films are dependent on the

controlling parameters, and slight tuning of those para-

meters can bring the required changes in the film proper-

ties. The investigations reported here indicate that it is

essential tokeep theoptimumflowrateofoxygengas in the

system for depositing good quality C-Y2O3 film by ECR

plasma MOCVD process.

Acknowledgements: The authors are thankful to Prof. R. O.Dusane, IIT Mumbai, for his help during GAXRD work. Thanksare due to Dr. R. Mishra, Chemistry Division, BARC, Mumbai, forhis help during TGA work and Prof. R. Pintoo, IIT Mumbai, for hishelp during ellipsometry measurements. The authors are alsothankful to Mr. N. Chand, L&PTD, BARC, Mumbai, for his helpduring the deposition experiments.

Received: October 19, 2010; Revised: March 9, 2011; Accepted:March 16, 2011; DOI: 10.1002/ppap.201000147

Keywords: electron cyclotron resonance (ECR); low-pressuredischarges; oxides; plasma-enhanced chemical vapor deposition(PECVD); thin films

[1] Chemical Vapor Deposition: Precursors, Processes and Appli-cations, A. C. Jones, M. L. Hitchman, Eds., RSC Publishing, UK2009.

[2] S. A. Barve, N. S. Nandurkar, N. Chand, S. B. Singh, N. Mithal,Jagannath, B. M. Bhanage, D. S. Patil, L. M. Gantayet, J. Phys.:Conf. Ser. 2008, 114, 012045.

DOI: 10.1002/ppap.201000147


[3] J. Asmussen, J. Vac. Sci. Technol. 1989, A7, 883.[4] H. Mols,B L. Niinisto, M. Utriainen, Adv. Mater. Opt. Electron.

1994, 4, 389.[5] W. C. Andersen, B. C. Noll, S. P. Sellers, L. L. Whildin, R. E.

Sievers, Inorg. Chim. Acta 2002, 336, 105.[6] W. S. Rees, Jr., A. R. Barron, Mater. Sci. Forum 1993, 137-139,

473.[7] India 236638 (2009), B. M. Bhanage, N. S. Nandurkar, D. S. Patil.[8] S. A. Barve, Jagannath, N. Mithal, M. N. Deo, N. Chand, B. M.

Bhanage, L. M. Gantayet, D. S. Patil, Surf. Coat. Technol. 2010,204, 3167.

[9] T. Gougousi, Z. Chen, Thin Solid Films 2008, 516, 6197.[10] M. B. Pomfret, C. Stoltz, B. Varughese, R. A. Walker, Anal.

Chem. 2005, 77, 1791.[11] V. Craciun, J. Howard, E. S. Lambers, R. K. Singh, D. Craciun,

J. Perriere, Appl. Phys. 1999, A 69 [Suppl.], S535.[12] C. Durand, C. Dubourdieu, C. Vallee, V. Loup, M. Bonvalot,

O. Joubert, H. Roussel, O. Renault, J. Appl. Phys. 2004, 96, 1719.[13] Y. Repelin, C. Proust, E. Husson, J. M. Beny, J. Solid State Chem.

1995, 118, 163.[14] R. Srinivasan, R. Yogamalar, A. Chandra Bose,Mater. Res. Bull.

2010, 45, 1165.



[15] W. Li, X. Wang, Y. Li, Chem. Commun. 2004, 2, 164.[16] S. A. Barve, Jagannath, M. N. Deo, R. Kishore, A. Biswas, L. M.

Gantayet, D. S. Patil, Appl. Surf. Sci. 2010, 257, 215.[17] Y. Nigara, Jpn. J. Appl. Phys. 1968, 7, 404.[18] X. J. Wang, L. D. Zhang, J. P. Zhang, G. He, M. Liu, L. Q. Zhu,

Mater. Lett. 2008, 62, 4235.[19] Y. Mao, J. Y. Huang, R. Ostroumov, K. L. Wang, J. P. Chang,

J. Phys. Chem. C 2008, 112, 2278.[20] J. J. Cuomo, J. M. E. Harper, C. R. Guarnieri, D. S. Yee, L. J.

Attanasio, J. Angilello, C. T. Wu, R. H. Hammond, J. Vac. Sci.Technol. 1982, 20, 349.

[21] D. F. Bezuidenhout, R. Pretorius, Thin Solid Films 1986, 139,121.

[22] G. Atanassov, R. Trielsch, D. Popov, Thin Solid Films 1993, 223,288.

[23] M. M. Giangregorio, M. Losurdo, A. Sacchetti, P. Capezzuto,G. Bruno, G. Malandrino, I. L. Fragala, R. L. Nigro, L. Armelao,D. Barreca, E. Tondello, Appl. Phys. Lett. 2007, 91, 061923.

[24] S. Geisler, A. Brockhaus, J. Engemann, J. Vac. Sci. Technol. 2001,A19, 539.

[25] W. J. Varhue, M. Massimo, J. M. Carrullis, V. Baranauskas,E. Adams, E. Broitman, J. Vac. Sci. Technol. 1993, A11, 1870.


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Microwave ECR Plasma Assisted MOCVD of Y2O3 Thin Films Using Y(tod)3 Precursor and Their Characterization