Binyamin Rubin1, Jason George1, Sandeep Kohli1,Kyle Godin1, Riju Singhal1, David Deakins2
1Veeco Instruments, 2Meliora Scientific
Monochromatic and broadband optical monitoring methods for deposition of band pass filters
OCLA 2019 Symposium, RhySearch
▪ Introduction▪ OMS background▪ Bandpass filters
▪ Monochromatic monitoring▪ Laser source▪ White light source
▪ Broadband OMS▪ Non-quarter-wave designs▪ Quarter-wave designs▪ Effect of finite spectral resolution
▪ Conclusions
2
Overview
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Visual control by color variation Banning, 1947
1940s
Photo-electric detectors, chip changers
1950s
Broadband OMS Vidal et al., 1978
1970s
Fully automated OMSLaser OMS for DWDM
1990s
Multiple OMS commercially available from OEM and coating equipment vendors
Today
3
OMS History
Veeco Instruments Inc. – OCLA 2019
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OMS Classification
Optical MonitoringDirectMonitoring actual productThickness error accumulation
IndirectNo error accumulationThickness different from product - calibration required
Monochromatic:Strong error self-compensation for QW designsMore complex strategies for non-QW deigns
Broadband:Lower noise sensitivityError self compensationComplex data analysis
Transmittance Reflectance
Active Passive
Thin film physics model Level/spectrum matching
Veeco Instruments Inc. – OCLA 2019
Veeco Instruments Inc. – OCLA 20195
Ion Beam Deposition
▪ Smooth, fully densified films▪ Environmental stability▪ Low surface roughness▪ Stable deposition rate
Spector 1.5 with Load Lock
Spector HT
▪ Source side▪ Tunable laser, ~0.1 pm spectral width
▪ Detector side▪ Monochromator: Resolution <0.5 nm,
wavelength precision~0.1nm▪ CCD based spectrometer ≥1 nm,
wavelength precision ~1nm
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Spectral Selectivity and Resolution
Detector Light source
Monitoring substrate
Optics
Optical fiber
Optical Monitoring System
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▪ Spectral resolution is ability to resolve spectral features▪ Spectral resolution of any spectrometer is finite
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Finite Spectral Resolution
Light input
Grating
SlitDetector
Mirror Mirror
Grating spectrometer architecture
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Effect of Finite Spectral Resolution
M. Vignaux et al., "Trinary mappings: a tool for the determination of potential spectral paths for optical monitoring of optical interference filters," Appl. Opt. 57, 7012-7020 (2018)
▪ Spectral resolution needs to be taken into account when monitoring sharp spectral features
Spectral line of calibration light source measured with different spectrometer slit sizes
▪ Applications▪ Fluorescence microscopy▪ Clinical chemistry▪ Astronomy▪ Telecommunications
▪ Specifications▪ Pass band: fraction of nm - tens of nm▪ Blocking band: tens to hundreds of nm▪ Full width at half-maximum▪ Transmittance at center wavelength
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Bandpass Filters
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Wavelength, nm
T, %
BlockingBlocking
Pass Band
Center
Wavelength
Half Width
▪ DWDM filters: ultra-narrow pass band▪ Pass band for 100 GHz filter: >0.4 nm @ -0.5 db
▪ Tunable laser source▪ spectral line width ~0.1 pm
▪ Turning Point Monitoring
Veeco Instruments Inc. – OCLA 201910
Monochromatic Laser OMS
0 5 10 15 20 25 30 35 40 45 500
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Time
T,
%
1548 1548.5 1549 1549.5 1550 1550.5 1551 1551.5 1552-45
-40
-35
-30
-25
-20
-15
-10
-5
0
Wavelength, nm
Inse
rtio
n L
oss, d
b
200 GHz filter
100 GHz filter
50 GHz filter
▪ Bandpass filters with narrow pass band ▪ Broad spectral range: UV - NIR
Veeco Instruments Inc. – OCLA 201911
Monochromatic OMS with Broadband Light Source
1050 1055 10600
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Wavelength, nm
T, %
1545 1546 1547 1548 1549 1550 1551 1552 15530
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Wavelength, nm
T, %
▪ Comparison of two Bandpass Filter designs▪ Both designs are 80 layer /~8 µm total thickness
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Comparison of Broadband vs. Turning Point Performance
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Wavelength, nm
T, %
Theoretical transmittance
Measured transmitance
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Wavelength, nm
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Theoretical transmittance
Measured transmitance
Non-Quarter Wave Design,Broadband Monitoring
Quarter Wave Design,Broadband OMS with Turning
Point Monitoring
▪ Broadband OMS enables monitoring non-QW layers▪ Design: 59-layer 5-cavity bandpass filter and 139 layers for additional
blocking and medium matching. Physical thickness is close to 20 microns▪ Better blocking performance achieved with broadband OMS
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Broadband OMS for Composite Design (QW + non-QW)
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Wavelength, nm
T, %
Broadband OMS
Monochromatic OMS
400 500 600 700 800 900 10000
0.2
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Wavelength, nmT
, %
Broadband OMS
Monochromatic OMS
▪ All QW designs ▪ Broadband monitoring used in single
wavelength mode + turning point control▪ Spectral resolution limits performance
for narrow pass band < 5 nm
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Quarter Wave Designs with Broadband OMS
▪ Spectral resolution of broad band monitoring is >1 nm ▪ We have developed a method for control of bandpass filters with narrower
width than the spectral resolution ▪ Example is a 3 cavity design: ▪ (HL)6H 2L (H L)6 H L - (HL)6H 4L (H L)6 H L - (HL)6H 2L (H L)6 H - 0.33H
0.34L 1.14H 1.02L▪ Ta2O5/SiO2 referenced at 532nm▪ ~0.6nm FWHM
Resolution Limited Turning Point Monitoring
O.Lyngnes, U.Brauneck, J.Wang, R.Erz, S.Kohli, B.Rubin, J.Kraus, D.Deakins"Optical monitoring of high throughput ion beam sputtering deposition", Proc. SPIE 9627, Optical Systems Design 2015: Advances in Optical Thin Films V, 962715
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OMS Monitoring Curve
Resolution-limited signal
Resolution-limited signal:- Shifted turning points.- Distorted curve shape.
Theoretical signal
O.Lyngnes, U.Brauneck, J.Wang, R.Erz, S.Kohli, B.Rubin, J.Kraus, D.Deakins"Optical monitoring of high throughput ion beam sputtering deposition", Proc. SPIE 9627, Optical Systems Design 2015: Advances in Optical Thin Films V, 962715
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Spectrum After First Cavity Deposited and Spectral Integration
525 526 527 528 529 530 531 532 533 534 535 536 537 538 539 5400
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Wavelength, nm
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Spectrum after first cavity deposited Signal at 532 nm integrated over 10 nm
O.Lyngnes, U.Brauneck, J.Wang, R.Erz, S.Kohli, B.Rubin, J.Kraus, D.Deakins"Optical monitoring of high throughput ion beam sputtering deposition", Proc. SPIE 9627, Optical Systems Design 2015: Advances in Optical Thin Films V, 962715
Veeco Instruments Inc. – OCLA 201917
▪ Generalized form of equation for non-absorbing single layer transmission on a substrate from Swanepoel’s paper*:
𝑇 =2𝑇𝑀𝑎𝑥𝑇𝑀𝑖𝑛
𝑇𝑀𝑎𝑥 + 𝑇𝑀𝑖𝑛 − (𝑇𝑀𝑎𝑥 − 𝑇𝑀𝑖𝑛) cos𝜑
𝜑 = 𝜋𝑅(𝑡 + 𝑡0)
*Swanepoel, R., “Determination of the thickness and optical constants of amorphous silicon”, J. Phys. E: Sci. Instrum., 16, 1214-1222 (1983).
Monitoring Curve Shape
O.Lyngnes, U.Brauneck, J.Wang, R.Erz, S.Kohli, B.Rubin, J.Kraus, D.Deakins"Optical monitoring of high throughput ion beam sputtering deposition", Proc. SPIE 9627, Optical Systems Design 2015: Advances in Optical Thin Films V, 962715
Veeco Instruments Inc. – OCLA 201918
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Sub-Resolution Narrow Bandpass with Broadband OMS
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T,
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Wavelength, nm
TheoryActual
▪ Monochromatic OMS with broadband light source is effective for bandpass filters with pass band ~0.1% CWL ▪ Laser OMS is best for ultra-narrow telecom filters <0.1% CWL
▪ Broadband OMS can be used to control QW and non-QW layers but has limited spectral resolution▪ Sub-resolution monitoring possible
▪ Multiple OMS are needed for broad range of applications▪ There is OMS for almost every application
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Conclusions
Ver:01012019
Thank You
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