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CHARACTERIZATION AND PREPARATION OF ANTI- REFLECTION COATINGS IN THE
RANGE OF 3-5 µm FOR Si OPTICAL WINDOW
ABSTRACT
Thin film multilayer anti-reflection coatings (SiO2/Si/SiO2)having thicknesses 286/571/143nm were deposited byRF magnetron sputtering deposition technique on 0.5mmthick Si(100)-substrates. Post-deposition annealing isalso carried out in the temperature range 150-6500C for4hr at the rate of 100C/min. Si Optical window wasdesigned at 4.2µm wavelengths and correlated withmodeling software TFCAL. The films are transparent inthe 3‐5µm band of the electromagnetic spectrum, firmlyadhered to the substrate. The prepared multilayer thinfilms are characterized optically and structurally usingUV/VIS/IR spectrophotometer, Atomic Force Microscopy(AFM), X-Ray Diffraction (XRD), Scanning ElectronMicroscopy (SEM) and Energy Dispersive Microscopy(EDS)..
Antireflection (AR) coating has significant role on opticaland electro-optical applications[1]. This work wasdesigned at 4.2µm wavelength, prepared and
DESIGN OF Si/SiO2 THIN FILMS
■ The hybrid antireflective coating model was designed using thin film design TFCALC software.
■ SiO2 was used as the low index material, while high index material was Si
■ Refractive indices were calculated by Sellmeiers dispersion equation.
n2 - 1 = A1λ2 / (λ2-C1
2) + A2λ2/ (λ2-C2
2) + A3λ2/ (λ2-C3
2), [C1, C2, C3 and λ] = [µm] (3)
S.No. Material A1 A2 A3 C1
(µm)
C2
(µm)
C3
(µm)1 SiO2 0.696166 0.407943 0.897480 0.068404 0.116241 9.896162 Si 10.668429 0.00304347 1.5413341 0.30151648 1.1347511 1104.0
Before Annealing 1µmBefore Annealing
K. Iqbal*, A. Maqsood, M. Mujahid and M. H. AsgharSchool of Chemical and Materials Engineering (SCME), National University of Sciences and Technology (NUST), Sector H-12,
Islamabad, PakistanE-mail Address: [email protected]
INTRODUCTION
1.05
FC= 0.39
Parametric values of Sellmeier equation
Si (100)6500C
5500C
4500C
3500C
2500C
1500C
As-deposited
MATERIALS AND METHODS RESULTS
1. Structural identification
■ Atomic compositions were computed withthe help of ZAF method.
designed at 4.2µm wavelength, prepared andcharacterized for non-quarter-wave thick multilayer ARcoatings based on low-high refractive indexes in the3–5µm bands and total thickness was determined byFresnel equations. At 4.2µm wavelength, mainly carbondioxide takes part in reducing the %transmittance [2].
n2AR = ns×nair (1)
d = λ0 / (4 nAR ) (2)
S.No Material Deposition rate (Å/sec)
Argon flow rate (sccm)
Oxygen flow rate (sccm)
1 SiO2 1.1 190 212 Si 1.5 130 -
■ The crystal structure was determined andlattice parameters a = 5.44 Å of the sampleswere calculated by using Bragg’s equation.
■ Satellite peaks (or doublet or rocking curves)near at 690 degree shows unstrained from toplayer to Si substrate.
Sin 2θ / (h2 + k2 + l2) = λ2 / 4a2 (4)As- deposited
200X
200X
Before Annealing
Annealing at 650 0C
0.00 1.00 2.00 3.00 4.00 5.00 6.00 7.00 8.00 9.00 10.00
keV
0
100
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700
800
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1000
Cou
nts
OK
a
SiK
a
Sample : As-deposited
Acc. Voltage : 10.0 kV
Probe Current : 1.0 nA
0.00 1.00 2.00 3.00 4.00 5.00 6.00 7.00 8.00 9.00 10.00
keV
0
100
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OK
a
SiK
a
Sample : 650 0C
Acc. Voltage : 10.0kV
Probe Current : 1.0 nA
Sputtering system
Sputtering System RF magnetron Sputtering
Target Materials Si / SiO2
Target Size 4 inch
Forward Power 2.74 kW
Reflected Power 0.16 kW
Chamber Pressure 5.0 × 10-4 Pa
Characterization Techniques
Structural and Optical Analysis by following techniques:
Physical thickness SiO 2/Si/SiO2
Layer Material Physical thickness (nm)
1 SiO2 143
2 Si 571
3 SiO2 286
Deposition rate, Argon flow rate and Oxygen flow ra te for the individual layers
Refractive indices of SiO 2 & Si in the 3-5µm wave band Transmittance (%) vs Wavelength (µm) profile of Si/S iO2 layers
Si/O ratio of the surface of Multi-layer Thin Films
EDS analysis of As-deposited and 650 0C sample
1 µm
0.5µm1 µm
SiO2
Si
SiO2
Si substrate
CONCLUSIONS
2. Film surfaces and roughness
■ Films have columnar structure and the surface ofthe film is smooth and featureless.
3. Spectral distribution of Si/SiO2 coatings transmittance
■An Average transmission of Si/SiO2 coatings isachieved 75% in the 3-5µm wave bands.
0
5
10
15
20
25
RM
S R
ough
ness
(nm
)
Sample
As-deposited
T1 = 150 C
T2 = 250 C
T3 = 350 C
T4 = 450 C
T5 = 550 C
T6 = 650 C
Multilayer thin‐films of Si and SiO2 are successfully prepared by RF magnetronsputtering. Annealed at 6500C generates smooth films as well as enhanced opticalproperties. The resulting models were helpful for determining the errors in depositionprocesses of each of the utilized deposition techniques, and this was the main goal.
REFERENCES
[1] M. H. Asghar, M. Shoaib, F. Placido and S.Naseem, Cent. Eur. J. Phys., Vol. 6, No. 4,2008, pp. 853 - 863.[2] M. H. Asghar, M. B. Khan, and S. Naseem,Semiconductor Phys: Quan. Elect. & Optoelect.,Vol. 6, No. 4, 2003, pp. 508- 513.
This project was funded by NUST and the assistanceoffered by greatly acknowledged:■ A. A. Khan ■ M. Islam
ACKNOWLEDGEMENTS
Annealing of Samples
Temperatures 1 50 - 650 0C
Time 4 hr
Rate 10 0C
Technique ModelScanning Electron Microscope
(SEM) /Energy Dispersive Microscopy
(EDS)
JSM-6490A, Joel
X- Ray Diffraction(XRD)
Siemens / Bruker D 8
ConditionsTube Voltage 40 kV
Tube Current 40 mA
Wavelength CuKα 0.154178 nm
Step 0.04
Scan Speed 1°/ min
AFM JSPM5200, Jeol
ConditionsCantilever tip Si3N4
Operation Mode AC
Cantilever Frequency 174.161 kHz
Force Constant 1.00 N / m
Scan Speed 1°/ min
UV/VIS/IR Spectrometer U-3501, Hitachi
NANOPAPRIKA POSTER 2011
XRD analysis of As-deposited and annealed samples b etween intensity and angle 2 θ
RMS roughness of the as-deposited and annealed samp les
Three-dimensional AFM image of the as-deposited an d 650 0C sample
Typical SEM image of cross-sectional morphologies o f the as-deposited sample and surface of the as-deposited and 650 0C sample
Measured transmission spectra for the as-deposited and annealed samples
Si substrate
CO2
