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A truly disruptive coating technology
would deliver coated parts with higher performance, better
quality and lower prices through high-yield, large-scale
manufacturing. That is exactly the disruptive contribution
of the new, proprietary Dual Rotary Magnetron (DRM) Coating
Technology at the Precis Design Corporation (Patent No.:
US 6,365,010 B1).
Capabilities
of DRM Coating Technology:
The benefits of DRM coating --high performance,
quality and competitive pricing-- are made possible by its
powerful range of capabilities.
- HIGH PRODUCTION
YIELD FOR EVEN COMPLEX PARTS.
For example, when producing parts as complicated as 100
GHz band pass filters for telecommunication applications,
DRM coating technology produces a 10 time higher yield
than alternative coating techniques.
- ATOMIC LEVEL
CONTROL OF FILM THICKNESS AND UNIFORMITY.
<0.1% variation in 25 um thick films covering a 7,088
mm2 wafer. <0.0003 variation in optical
refractive index over a 7,088 mm2 wafer.
- HIGH OPTICAL
TRANSMISSION.
Less than 5 ppm intrinsic loss insures high optical transmission
and greater film design flexibility and easier power budget
management.
- LOW STRESS COATINGS.
DRM coatings have less stress than alternative coatings.
This provides greater flexibility in thin film design
enabling the construction of thicker film structures on
thinner substrates without the concern of excessive deformation
and cracking of the coating or substrate. Coatings of
over 300 layers are possible on 1.2 mm thick glass substrates.
- HIGH ENVIRONMENTAL
STABILITY.
Coatings have been certified to pass Telcordia requirements
for telecommunication applications. Thermal drift is less
than 0.5 pm/°C for telecom filters. This means that
test results in your QC lab will reflect the same results
in the field.
- HIGH PROCESS
REPEATABILITY.
Large volumes of coated parts exhibit high performance
uniformity from run to run both when parts are coated
on the same coating system and when parts are coated on
multiple coating systems operating around the world. This
ensures a steady supply of reliable parts from multiple
locations within Precis.
- APPLICATION
FLEXIBILITY.
As your product lines change and even if your industry
focus diversifies, Precis DRM coating technology can still
be applied to your evolving coating needs.
Block
Diagram and Operational Theory of DRM Coatings
There are dramatic
differences between traditional fixed target sputtering
and DRM sputtering.
In traditional
sputtered coating systems the target material is fixed.
The sputtering of target material occurs around the racetrack
shaped plasma containment induced by the magnet assembly
behind the fixed target as shown in Figure 1.0. The sputtering
process slowly erodes a ractrack, V-shaped groove into the
target.
Figure
1.0. Traditional Fixed Target Assembly for Sputtered Coating
Systems
As the process continues, the changing
geometry created by the deepening groove causes variations
in both the sputtering rate and coating uniformity. In reactive
sputtering, increased process instability can also occur
as dielectric coating material builds up on the unsputtered
areas of the target. This build up results from the target’s
inability to continually clean all parts of its surface
as it sputters. Electric charge collects on the built up
dielectric material. This eventually raises the voltage
above the breakdown potential of the material and arcing
occurs adding more instability to the process.
In a Dual Rotary Magnetron Sputtering
System the targets are cylindrical as shown in Figure 2.0.
Figure
2.0. Photograph of a Cylindrical Target Used in a DRM Coating
System.
During the coating process the targets
rotate continuously around fixed magnetic assemblies as
shown in Figures 3.0 and 4.0.
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| Figure 3.0. Block Diagram
of a Dual Rotary Magnetron (DRM) Coating |
Figure 4.0. Dual Rotary Magnetron
(DRM) Assembly (shown with belt drive for automatic
rotation). |
As shown in Figure 3.0, material is sputtered
on to the substrate as it passes by the cylindrical targets.
Figure 5.0 shows the glowing plasma configuration around
the dual rotary targets during the coating process.
Figure 5.0. Photograph of Plasma
Formation Around Dual Rotary Targets.
Arcing, previously a serious problem,
is greatly reduced using AC sources at frequencies of 40
KHz and above. The cylindrical targets remain essentially
free of dielectric buildup over their lifetime because the
sputtering rate exceeds the dielectric buildup rate and
constant rotation ensures that the entire target surface
is exposed to the same conditions. Since at any given time
one target is sputtering while the other acts as the anode,
anode drift, or the “disappearing anode” as it
is often referred to, is eliminated. The thickness of the
target material is kept below approximately an eighth of
an inch to minimize geometric changes over its sputtering
lifetime. The small net change in target thickness is a
very small fraction of the target-to-substrate distance,
leading to almost imperceptible changes in process conditions
over weeks of operation. Deposition rates remain high relative
to RF sputtering and the absorption in the films is very
low (typically a few ppm).
The benefits of very dense films created
by high-energy oxygen bombardment, originally realized in
other coating techniques by using an auxiliary ion gun,
are achieved automatically in DRM sputtering without the
use of an ion gun. The AC process of DRM sputtering efficiently
produces negatively charged oxygen species that accelerate
into the growing film when the target is sputtering at high
negative potential. Since this magnetron process is very
stable over time and over a wide area, improved coating
uniformity is achieved and large areas of the substrate
surface yield usable parts. This is dramatically different
than conventional ion-beam sputtering techniques that coat
only a thin annulus on the substrate and produce no usable
parts on the majority of the substrate surface.
Films with high optical performance and
environment stability are created with DRM sputtering while
coating at temperatures below 90°C versus the 200°
to 300°C required by other coating processes. This allows
DRM to greatly reduce thermally induced stress and coat
on temperature sensitive substrates such as plastics. Lower
stress also allows coatings to be made directly on to substrates
as thin as 200 um. This is not possible with other coating
techniques, which typically have 5 to 10 times higher stress
components in their coatings. In order to cope with the
high stress and prevent deformation and cracking, substrates
as thick as 10 mm are used. Later, the thick substrates
are ground and polished to achieved the desired substrate
thickness. Grinding increases risk, reduces yield and adds
cost. With DRM coating, grinding is unnecessary, making
DRM coating a more effective and productive approach.
Precis
Coating Systems Using DRM Coating Technology:
The DRM coating technology is used in
the Precis Design OCS 1000 Coating System as shown in Figure
6.0.
Figure
6.0. Precis Design OCS 1000 Coating System Using the DRM
Coating Technology
The DRM Sources are mounted in the door
of the OCS 1000 Coating System as indicated in Figure 6.0
and shown in Figure 7.0.
Opening the door of the Precis OCS 1000
System reveals the coating chamber, which contains the DRM
Sources and the Turntable upon which the substrates are
mounted.
Figure 7.0. Photograph of Precis
OCS 1000 Coating Chamber.
During the coating process
the rotating Turntable places each substrate in front of
each DRM Source for coating. To ensure extreme accuracy
during this coating process, internal optical monitoring
systems track the optical performance of the layered structure
as it is produced on the substrates. Any errors in refractive
index or optical thickness are detected. Dynamic design
adjustments are made so that later layers compensate for
errors in prior layers. This technique is called quarter-wave
optical thickness (QWOT) Tuning. QWOT Tuning is only feasible
because of the high correlation between the thin film modeling,
the film design tools and the OCS 1000 coating capability.
Figure 7.0 shows the OCS
1000 equipped to handle 12 circular wafers with diameters
of 95 mm (3.7 inches). The system can accommodate circular
wafers with diameters up to 152 mm (~6.0 inches). Square
substrates can also be installed.
Inline coating systems using
DRM sources are also used at Precis to accommodate flat
substrates up to 1 meter square as shown in Figures 8.0
and 9.0.
FIGURE 8.0. Photograph of Precis
Design’s Automated Inline Coating System
Using DRM Coating Technology.
FIGURE
9.0. Photograph of 1-Meter Long Cylindrical Targets
Used in Precis Design’s Automated Inline Coating System.
Summary:
The powerful and proprietary capabilities of Dual Rotary
Magnetron Coating Technology uniquely qualify the Precis
Design Corporation to offer you new technical and financial
opportunities. It also opens the possibility of new cost
structures and higher performance requirements for several
industries.
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