2019 Tech Briefs webinar presentation: How Reactive Magnetron Sputter Coating Enables Complex Filter Design and Precision Manufacturing

C H R O M A T E C H N O L O G Y C O R P ® www.chroma.com/FISH
SPUTTERING OF OPTICAL COATINGS
How Reactive Magnetron Sputter Coating Enables
Complex Filter Design and Precision Manufacturing

+1-802-428-2500 | 800-824-7662 | sales@chroma.com | www.chroma.com
C H R O M A T E C H N O L O G Y C O R P ®
Sputtering Basics
Features
Sputter coating, like electron beam or thermal
evaporative (“soft”) coating, is a form of physical vapor
deposition (PVD) that occurs under high vacuum.
Material is ejected from a “target” via ionized gas
bombardment (ex. argon+) due to an electric field that
creates a plasma.
Magnetron Sputtering is one type of sputtering
technique where magnetic fields help contain the
plasma, thereby increasing efficiency.
A negative high voltage is applied to the
metal target and ionized argon gas is
accelerated toward the target thereby
dislodging metal material.

Sputtering Basics
Features
With reactive sputtering, oxide coatings can be made
by introducing oxygen gas which reacts with the metal
during deposition.
Ion-assist is used to deliver energy to the growing
film in order to promote void-free growth and enhance
film durability.
The high energy of the sputtered material
produces a much denser coating than what
could be achieved using electron beam or
thermal evaporation processes.

Sputtering of Optical Coatings: Features & Benefits
Benefit to
Application
Coating
Properties
Sputtering
Characteristics
close matching to CIE color functions
Raman edge/notch filter spectral acuity
multi band designs optimized to application
enables narrow-bands for multi-spectral imaging
repeatability of execution
complex designs, needle layers
tight spectral tolerances
high-precision layer thickness control
thickness proportional to sputter power
optical monitoring
reactive sputtering w/ ionized oxygen
Process characteristics
flat/image quality dichroic for structured illumination
environmental durability for remote sensing
high laser damage threshold for laser mirror
high throughput for telecom bandpass filter
deep blocking for multi-photon microscopy
reasonable coating stress
low inclusion of sputter gas
high density
hardness and adhesion
high transmission, low absorption
low scatter
high purity
increased throw/ large mean-free path
dense plasma, high energy
high vacuum, low pressure
Physical characteristics
high temperature
low ripple

Vacuum chamber
Metal target
Silicon or metal target
Glass substrate
Optical monitoring system
(measures transmission of
light through coating
during deposition)
Vacuum
pump
low-index
sputter
cathode
high-index
sputter
cathode
Atmospheric
pressure
Sputtering
Characteristics
Physical
high temperature
optical monitoring
Process

Vacuum chamber
Metal target
Glass substrate
during deposition)
Vacuum
pump
low-index
sputter
cathode
high-index
sputter
cathode
High vacuum
Sputtering
Characteristics
Physical
high temperature
optical monitoring
Process

Sputtering
Characteristics
Physical
high temperature
optical monitoring
Process
Vacuum chamber
Metal target
Glass substrate
during deposition)
Vacuum
pump
low-index
sputter
cathode
high-index
sputter
cathode
high-index
deposition
cloud
O2+
Ar+
Ar+
High vacuum
high-index
deposition
cloud

Vacuum chamber
Metal target
Glass substrate
during deposition)
Vacuum
pump
low-index
sputter
cathode
high-index
sputter
cathode
low-index
deposition
cloud
O2+
Ar+
High vacuum
Sputtering
Characteristics
Physical
high temperature
optical monitoring
Process

R1 R2
Incident Wave
Glass
Air
Reflected Waves
Multi-layer stacks use
constructive interference
of the reflected waves (at
and off of the multiple
interfaces) in order to
“block” unwanted light.
Thin Film Stack – alternating
high and low index layers
(not to scale)
Transmission
Interference

Sputtering of Optical Coatings
Benefit to
Application
Coating
Properties
Sputtering
Process
Characteristics
close matching to CIE color functions
Raman edge/notch filter spectral acuity
enables narrow-bands for multi-spectral imaging
repeatability of execution
complex designs, needle layers
tight spectral tolerances
optical monitoring
Process characteristics
flat/image quality dichroic for structured illumination
environmental durability for remote sensing
high laser damage threshold for laser mirror
high throughput for telecom bandpass filter
deep blocking for multi-photon microscopy
reasonable coating stress
low inclusion of sputter gas
high density
hardness and adhesion
high transmission, low absorption
low ripple
high purity
Physical characteristics
high temperature
low scatter

From Process to Production
Spectral Plots
Visualizing performance
Sputtered Coatings
Enabling complex designs
Precision:
Control & Optimization
Transmittance:
Transmission & Optical Density

Reading Spectral Plots
Transmittance: fraction of incident light transmitted through sample: T = I ÷ I0
Transmission: transmittance expressed in percent: %T = (I ÷ I0) × 100
Transmission is typically used to describe transmittance of desired light
Optical Density (OD) = -log T = -log [(%T) / 100
Optical Density includes loss of transmittance due to absorbance, reflectance
and scattering
It’s a measure of the total impedance of light through a medium (filter)
Transmission
Transmittance expressed as: Transmittance expressed as:
Optical Density

Transmission & Optical Density, plotted together
Slope: steepness of transition from transmission to optical density
Steeper slopes require more thin film layers
Steep slopes are necessary for applications such as Raman spectroscopy and fluorescence microscopy

Transmission: theoretical & measured filter spectra
Accuracy and precision: good match of theoretical and actual %T data
5 independent production lots of each filter

Optical Density: theoretical & measured filter spectra
Accuracy and precision: good match of theoretical and actual OD data
5 independent production lots of each filter
OD measurement is noise-limited

Accuracy, precision, high %T, low ripple, steep slopes

Blocking: A fundamental optical challenge in fluorescence microscopy
Ratio between the light intensity of a fluorescence microscopy light source and fluorescence signal is typically in the
range of 1e6 – 1e10: 1, with extremes in cases such as single-molecule TIRF as high as 1e15 : 1

Classical Fabry-Perot type of optical coating design
Design approach: based on “quarter-wave stacks” composed of individual layers with thicknesses which are
factors of ¼ wavelength of light

%T spectra of one production lot
Sputtering enables computational optimization

%T spectra of two independent production lots, overlaid

%T spectra of three independent production lots, overlaid

%T spectra of four independent production lots, overlaid

%T spectra of five independent production lots, overlaid

%T spectra of six independent production lots, overlaid

%T spectra of seven independent production lots, overlaid

%T spectra of eight independent production lots, overlaid

%T spectra of nine independent production lots, overlaid

%T spectra of ten independent production lots, overlaid

Combined %T and OD spectra of ten independent production lots, overlaid

notch filters with narrow rejection band, deep & steep blocking, broad transmission
488nm narrow notch rejection filter with UV/VIS/SWIR transmission

notch filters with narrow rejection band, deep, steep blocking, broad transmission
488nm & 561nm narrow notch rejection filters with UV/VIS/SWIR transmission

488nm, 561nm, & 633nm narrow notch rejection filters with UV/VIS/SWIR transmission

488nm, 561nm 633nm & 785nm narrow notch rejection filters with UV/VIS/SWIR transmission

488nm, 561nm 633nm & 785nm narrow notch rejection filters with deep, steep & broad blocking (high OD over
range)

Examples of customized CIE- type Z, Y & X photometry filters
Extremely accurate, F1’ < 2%
Black trace = target Yellow trace = design theory Shaded traces = measured filter spectra
Z

Z Y

Z Y X

THANK YOU
Published in Bellows Falls, Vermont, US
Chroma optical filters and related products may be purchased online or
via phone. For more information, please e-mail sales@chroma.com,
visit www.chroma.com or call 800.824.7662.

2019 Tech Briefs webinar presentation: How Reactive Magnetron Sputter Coating Enables Complex Filter Design and Precision Manufacturing

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