Note: Descriptions are shown in the official language in which they were submitted.
WO 95123652 218 4 7 3 8 p~~S95ro2762
-1-
ION BEAM PROCESS FOR DEPOSTfION OF HIGHLY
ABRASION-RESISTANT COATINGS
FIELD OF THE INVENTION
This invention relates generally to a process for depositing coatings
which protect a substrate from wear and abrasion. More particularly, the
invention
relates to a process for protecting such substrates as plastic sunglass
lenses,
ophthalmic lenses, bar codes scanner windows, and industrial wear parts from
scratches and abrasion.
BACKGROUND OF THE INVENTION
There we numerous prior art methods for coating substrates to improve
their performance, e.g. lifetime, abrasion wear resistance and similar
properties.
For example, consider the case of plastic sunglass lenses or plastic
prescription
eyewear. Due to the ease of scratching plastic, abrasion-resistant coatings
are
deposited onto the surface of plastic lenses. These hard outer coatings
increase the
useful life of the lenses. To make such coatings marketable, the process for
depositing these hard coatings must be inexpensive, reliable and reproducible.
Plastic lenses sold into the ophthalmic lens market are largely coated by
acrylic and polysiloxane dip-coatings or spin coatings. These coatings
significantly
improve the abrasion resistance of the lens compared to the uncoated lens.
This is
particularly true for the case of polycarbonate which is very subject to
abrasion
However, improved abrasion resistance of coated lenses is still a major
problem in
the ophthalmic lens industry. The industrial goal is to obtain plastic lenses
which
exhibit the same abrasion resistance as glass lenses. Current commercial
plastic
lenses have abrasion resistance characteristics which are poor compared to
glass.
Therefore, when purchasing lenses, one must choose between glass, which is
very
abrasion resistant but is heavier, or plastic which is lighter but much less
abrasion-
resistant.
Other coatings have been suggested for plastic substrates, including lenses.
Most of these coatings are so-called "plasma polymers" which are largely
produced
by creating a plasma from siloxane precursor gases. The substrates are exposed
to
the plasma, but they are not biased to cause energetic ion bombardment. The
WO95l23652 - PCT/US95/02762
2184738
_2_
performance of these plasma polymers is often only marginally better than that
of
the polysiloxane and acrylic spin and dip coatings, and the performance of
these
coatings does not approach the performance of glass. These films are often
quite
soft and are not useable as protective coatings except on extremely soft
substrates.
Other coating processes have been suggested in which energetic ion
bombardment is caused by mounting the substrates on the powered electrode in a
radio frequency (RF) plasma system and exposing the parts to the plasma,
thereby
creating a negative bias on the substrate surface. The resultant coatings are
often
more abrasion resistant than the "plasma polymers". These plasma systems are
not
readily scaled to a throughput required for mass production nor are they
easily
operated in a reproducible, controlled fashion in a production environment.
The
RF plasma process also suffers in that the deposition process, and the
propetrties of
the resultant coating are dependent on whether the substrate to be coated is
an
electrical conductor or insulator. Furthermore, if the substrate is an
insulator, the
thickness of the substrate strongly influences the deposition process
energetics and
the properties of the resultant coating. This means that for production
coating of
insulating substrates of different size and shape, e.g. plastic lenses, it may
be
necessary to have different coating processes for each type of substrate. This
reduces the flexibility of the process for use in production. Additionally,
systems
with large area electrodes are not widely available. For example, there are no
readily available commercial parallel plate RF deposition systems having large
electrodes, i.e. at least one meter in diameter.
The following references illustrate prior art coating processes in which
plasmas are used in direct contact with the surface of the substrate:
Rzad et. al., U.S. Pat. No. 5,156,882, describe a method of preparing a
transparent plastic article having an improved protective stratum thereon. The
protective stratum is deposited by plasma enhanced chemical vapor deposition
(PECVD).
BaIian et. al., U.S. Pat. No. 5,206,060, describe a process and device for
depositing thin layers on a substrate using a plasma chemical vapor deposition
(PCVD) technique. The substrate must be made conductive, and is used as an
electrode in the PCVD process.
wo 95~z3652 218 4 7 3 8 P~~S95/02762
-3-
Reed et. al., U.S. Pat. No. 5,051,308, describe an abrasion-resistant article
and a method for producing the same. The article includes a plastic substrate
and a
gradational coating applied by a PECVD process.
Devins et. al., U.S. Pat. No. 4,842,941, also describe an abrasion-resistant
article and a method for making the same. The article includes a polycarbonate
substrate, an interfacial layer of an adherent resinous composition on the
substrate,
and an abrasion-resistant layer applied on top of the interfacial layer by
PECVD.
Brochot et. al., U.S. Pat. 5,093,153 describe a coated object comprising a
glass substrate coated with an organomineral film by a PECVD process.
Kubacki, U.S. Pat. No. 4,096,315, describes a low-temperature plasma
polymerization process for coating an optical plastic substrate with a single
layer
coating for the purpose of improving the durability of the plastic.
Enke et. al., U.S. Pat. No. 4,762,730, describe a PECVD process for
producing a transparent protective coating on a plastic optical substrate
surface.
All of the prior art plasma deposition methods for application of wear and
abrasion-resistant coatings suffer from one or more of the following
deficiencies
and shortcomings:
(1) difficulty in pre-cleaning of substrates prior to deposition;
(2) adhesion of the protective, abrasion-resistant coating;
(3) permeation of the coatings by water vapor and oxygen;
(4) fabrication of coherent, dense coatings;
(5) control of coating properties during a deposition run and
batch-to-batch variation of coating characteristics;
(6) coating thickness control and reproducibility of thickness;
(7) part-to-part and batch-to-batch control of coating uniformity;
(8) difficulty in coating substrates of complex geometry or
configuration; and
(9) production readiness and ability to scale-up the deposition process for
mass production.
These shortcomings are highlighted in the following review of the two
preferred prior art methods for deposition of abrasion-resistant coatings on
plastic
optical substrates: plasma polymerization and biased RF plasma deposition.
W0 95123652 PCdIUS95102762
2184738
-4-
The first problem encountered by both methods is the difficulty in pre-
cleaning the substrates prior to deposition of the adhesion layer or abrasion-
resistant film. Typically substrates are pre-cleaned in an inert gas or glow
discharge (plasma) prior to deposition. This pre-cleaning technique suffers
from
low cleaning rate, and re-contamination of the substrate by sputtered
contaminants
which are deposited back onto the substrate.
One of the key requirements for a protective coating on a variety of
substrates, including optics, is the need to provide a barrier to moisture,
oxygen,
and other environmental elements. This requires formation of a coating
structure
with optimal atom packing density. This atom packing density is maximized by a
high degree of ion bombardment during film growth, which is not easily
attainable
or optimized by the plasma polymerization methods of the prior art.
Regarding the control of the coating properties within a single deposition
run, and from batch-to-batch, it is well known that control is difficult with
the
plasma deposition methods. For the case of deposition of electrically
insulating
coatings on electrically conductive substrates by the biased RF plasma
technique, it
is known that as the deposited coating thickness increases, there will be a
gradual
decrease of the surface bias on the growing film; see Meyerson et al., U.S.
Pat.
No.4,647,494,
column 6, line 67 through column 7, line 3. This decrease results in a change
in
the properties of the deposited coating, i.e. hardness, stress and hydrogen
concentration.
Because the size and shape of the particular part to be coated, and its
method of fixturing influence the plasma uniformity and plasma density around
the
part, it is difficult to predict and control deposition thickness uniformity
across
multiple parts coated within a single coating run using the plasma deposition
methods of the prior art.
While the plasma deposition methods offer high deposition rates, it is
difFcult to reproducibly control deposition rate, deposition thickness and
deposition
uniformity acrosslarge areas with plasma deposition methods. Because of the
interdependence of process variables such as pressure, gas flow rate, power,
and
substrate bias, accurate control of deposition thickness is difficult. Thus,
it is very
W 0 95123652 PCl/US95/02762
2184738
-s-
difficult to manufacture coating layers with thickness less than 0.1 micron,
and
with run-to-run thickness variation of less than approximately 10%. This is a
significant disadvantage of the plasma deposition techniques of the prior art
for the
deposition of optical coatings, especially those requiring the use of
multiple, thin
s layers of varying refractive index, such as antireflection coatings.
Finally, because of the sensitivity of the plasma deposition processes to
substrate geometry, it is often impossible to coat parts of complex geometry
or
configuration. Examples of complex geometry include optical lenses with high
corrective power which may be edged to a variety of shapes, industrial molds
used
to fabricate plastic parts, and other industrial machine parts, including
shafts, gears,
bearings, and the like. The current industrial trend is to fabricate many of
these
industrial machine parts from electrically insulating plastics and ceramics.
These
electrically insulating industrial machine parts we especially difficult to
coat
uniformly by the plasma deposition methods.
is All of the difficulties above combine to make mass production of
protective,
abrasion-resistant coatings on a variety of substrates by the plasma
deposition
processes of the prior art very problematic indeed. Clearly, an improved
method
for flexible, reproducible, and high quality mass production of abrasion-
resistant
coatings has long been sought.
Ion beam etching and deposition of many materials is known in the prior
art. For example, ion milling is commonly used in semiconductor processing.
Ion
beam systems typically are more controllable than RF plasma systems in that
the
deposition and etching process parameters, e.g. plasma potential, substrate
bias,
plasma current, gas flows and chamber pressures are not as strongly coupled as
2s they are in the RF plasma process. This results in a wider process window
and
better control for ion beam processing, as compared to plasma processing.
Additionally, ion beam deposition equipment is available which is capable of
processing in excess of 1000 square inches of substrate material per batch. It
is
believed that RF equipment is not commercially available which approaches this
level of scale. The combination of the higher degree of control for ion beam
processing and the ability to scale to large areas allows for a process which
is more
easily moved into production and is more robust. However, one major
WO 95123652 PCTYUS95I02762
2184738
-6-
disadvantage to prior art ion beam deposition processes, e.g. for deposition
of DLC
films, is their relatively low deposition rate which leads to long production
times
for thick coatings, and hence high production cost.
In an article published in Clinical Materials, Vol. 12, pages 237-244 (1993),
G. Dearnaley describes a process in which low vapor pressure materials are
condensed on the surface of the article to be coated and simultaneously
bombarded
by a high energy nitrogen ion beam. In this case, the ion energy required is
greater than 10 kV. These large voltages are difficult to control and become
problematic in a production environment. In addition, the coatings
manufactured
by this method are opaque and not useable for applications where a transparent
coated product is required.
Kimock, et al., U.S. Pat. Nos. 5,135,808, 5,190,807, 5,268,217 disclose
direct ion beam deposition processes using a hydrocarbon gas or carbon vapor
for
producing abrasion wear resistant products comprising substrates with hard
outer
coatings of substantially optically transparent diamond-like carbon (DLC)
useful for
commercial articles such as optical lenses, sunglass lenses, and bar code
scanner
windows.
SUMMARY OF THE INVENTION
The invention provides an improved method for deposition of an abrasion-
resistant coating onto substrates. More particularly, this invention provides
an ion
beam deposited coating to the surface of a substrate which is highly adherent,
and
exhibits greatly improved wear resistance and environmental durability. Still
more
particularly, this invention provides a low cost and efficient process for
mass-
producing coated substrates with improved wear resistance and superior
lifetime.
The method is especially usefulfor applying an abrasion-resistant coating to
the
surface of plastic optical substrates, such as lenses.
In the method of the present invention, the substrate is first chemically
cleaned to remove unwanted materials and other contaminants. In the second
step,
the substrate is inserted into a vacuum chamber, the air in said chamber is
evacuated and the substrate surface is sputter-etched by a beam of energetic
ions to
assist in the removal of residual contaminants such as residual hydrocarbons
and
surface oxides, and to activate the surface. After the substrate surface has
been
WO 95123652 218 4 7 3 8 pCT/US95/02762
sputter-etched, a protective, abrasion-resistant coating is deposited using
selected
precursor gases by ion beam deposition. The ion beam-deposited coating may
contain one or more layers. Once the chosen thickness of the coating has been
achieved, the deposition process on the substrates is terminated, the vacuum
chamber pressure is increased to atmospheric pressure, and the coated
substrates
having improved abrasion-resistance are removed from the vacuum chamber.
The present invention provides amorphous, confotmal, protective, abrasion-
resistant coatings containing a combination of the elements selected from the
group
consisting of C, Si, H, O and N. More particularly, the coatings of the
present
invention are selected from at least one of the following combinations of
elements:
Si and C; Si, C and H; Si and N; Si, N and H; Si and O; Si, O and H; Si, O and
N; Si, O, N and H; Si, C and N; Si, C, H and N; Si, C and O; Si, C, H and O;
Si,
C, O and N; and Si, C, H, O and N.
The process for deposition of these coatings uses an ion beam source which
operates with precursor gases comprising at least one of the following
combinations of elements selected from the group consisting of Si and C; Si, C
and
H; Si and N; Si, N and H; Si and O; Si, O and H; Si, O and N; Si, O, N and H;
Si, C and N; Si, C, H and N; Si, C and O; Si, C, H and O; Si, C, O and N; and
Si,
C, H, O and N. The process of the present invention is particularly well-
suited to
the manufacture of optically transparent coatings with tailored hardness,
stress, and
chemistry. These properties make the coatings of the present invention ideally
suited to plastic substrates, such as sunglass and ophthalmic lenses. Coatings
which exhibit glass-like or quartz-like properties can be made by the present
process. Coatings which have properties resembling silicon carbide, silicon
nitride,
and hydrogenated and oxygenated forms of these materials can also be made by
this process.
Additionally, diamond-like carbon coatings can be made by the process of
the present invention. The term "diamond-like carbon" is meant to include
amorphous materials composed of carbon and hydrogen, whose properties
resemble, but do not duplicate, those of diamond. Some of these properties are
high hardness (HV = about 1,000 to about 5,000 kg/mm=), low friction
coefficient
(approximately 0.1), transparency across the majority of the electromagnetic
WO 95/23652 218 4 7 3 8 PCT~S95102762
_g_
spectrum, and chemical inertness. At least some of the carbon atoms in DLC are
bonded in chemical structures similar to that of diamond, but without long
range
crystal order. These DLC materials can contain to 50 atomic percent of
hydrogen.
The DLC coatings made by the present invention are hwd, inert and slippery,
and
are ideal for use in optical as well as many non-optical applications.
BRIEF DESCRIPTION OF THE DRAWING
Further features and advantages will become apparent from the following
and more particular description of the preferred embodiment of the invention,
as
illustrated in the accompanying drawing in which:
FIG. 1 is a diagrammatic view of an illustrative ion beam deposition
apparatus used to manufacture coated substrate products in accordance with the
present invention.
DETAILED DESCRIPTION OF THE INVENTION
The method of the present invention substantially reduces or eliminates the
disadvantages and shortcomings associated with the prior art techniques by
providing:
(I) for the deposition of highly abrasion-resistant coatings on a variety of
substrates, including metals, ceramics, glasses, and plastics;
(2) for the deposition of highly optically transparent, highly abrasion-
resistant coatings on optically transparent plastic substrates such as lenses;
(3) for the deposition of highly abrasion-resistant coatings which is
independent of the electrical conductivity and thickness of the substrate;
(4) for the deposition of a protective abrasion-resistant coating onto the
surface of a substrate, in which the layer thickness and uniformity of the
coating
are reproducibly controlled to a high degree of accuracy;
(5) for the application of an abrasion-resistant coating which is highly
repeatable and reliable;
(6) a process which is readily scaleable to large areas and has high
throughput for mass production;
(7) a process in which the substrate is not limited to any particular material
or geometry; and
W O 95123652 218 4 7 3 8 P~~S95/02762
-9-
(8) for the protection of a substrate from abrasion, wear and corrosion
damage during normal, or severe use conditions, and for significantly
extending the
lifetime of the substrate.
It has been unexpectedly found that the ion beam deposition process for the
manufacture of the coatings of the present invention produced remarkable
performance on a variety of substrates, especially soft optical plastics. The
remarkable performance compared to prior art techniques is the result of the
combination of the critical features and attributes listed below. The method
of the
present invention is capable of:
(I) Overcoming the difficulties in obtaining an atomically clean surface by
sputter-etching the substrates using an ion beam of controlled shape, current,
and
energy. The ion beam "shape" is controlled by focusing the beam with
electrostatic or magnetic fields. In this way, the beam can be efficiently
delivered
to the substrates to be processed, with maximum utilization. It has been found
that
the control of ion beam current and beam energy to within 1% is consistently
achieved which results in a highly repeatable and predictable rate of removal
of
surface contaminant layers. In addition, the ion beam sputter-etching process
is
conducted in high vacuum conditions, such that oxidation or contamination of
the
surface with residual gases in the coating system is negligible. Finally, the
apparatus geometry can be easily configured such that the sputtered
contaminants
deposit on the vacuum chamber walls, and they do not re-deposit onto the
surface
of the pan as it is being sputter-etched.
(2) Producing excellent adhesion of the protective ion beam deposited
layers) by generating an atomically clean surface prior to the deposition of
the
coating. For most applications, the deposited protective layer contains
silicon. For
applications in which the topmost layer of the coating does not contain
silicon,
adhesion can be enhanced via the use of silicon-containing adhesion-promoting
interlayers between the top coating, e.g. DLC, and the substrate. In either
case, the
ion beam deposited layer is preferably deposited immediately upon completion
of
the ion beam sputter-etching step to achieve maximum adhesion to the
substrate.
Deposition of the coating layers) immediately upon completion of the ion beam
sputter-etching step minimizes the possibility for re-contamination of the
sputter-
WO 95123652 218 4 7 3 8 p~T~S95102762
-10-
etched surface with vacuum chamber residual gases or other contaminants. The
silicon-containing layers include a variety of amorphous materials, such as
silicon
oxide, silicon nitride, silicon oxy-nitride, silicon carbide, silicon oxy-
carbide,
silicon carbonitride, the so-called silicon-doped DLC, mixtures thereof and
chemical combinations thereof. Each of the silicon-containing interlayers may
contain hydrogen.
(3) Controlling and minimizing excessive compressive stress in the coatings
deposited by the method of the present invention allows for the deposition of
highly adherent coatings.
(4) Producing highly dense ion beam protective coatings. This makes the
coatings excellent barriers to water vapor and oxygen. The high density
of the ion beam deposited coatings presumably results from the extremely high
degree of ion bombardment during film growth, compared to prior art methods.
(5) Producing a coating in which its properties do not change with layer
thickness as is found for the prior art RF plasma deposition processes. This
attribute is achieved because the coating deposition step is conducted with a
charge
neutralized ion beam. The charge neutrality- of the ion beam deposition
process
also allows for coating of parts with complex geometry without interference to
the
process. Parts of varying geometry can be coated within a single coating run
with
no adverse effect on the deposition conditions. For example, lenses of various
sizes and shapes can easily be coated with the same coating material in the
same
run. The ease of fixturing substrates for coating is one of the highly
important
technical advantages and distinguishingfeatures of the presentinvention.
(6) Coating all portions of substrates, which contain electrically conducting
and electrically insulating materials, with the same high-quality coating. In
the
case of the plasma deposition methods, DLC coatings of different properties
may
be deposited on different locations of the same substrate, depending upon
whether
the area being coated is an electrical conductor or an electrical insulator,
and upon
the electrical connections between the substrates and the vacuum chamber.
Substrate conductivity has no effect on the properties of the ion beam
deposited
coating of the present invention, which is in sharp contrast to that of plasma
deposition methods of the prior art.
R'O 95123652 PCTYUS95/02762
-11-
(7) Obtaining minimal batch-to-batch variation in the properties of the
coatings. This is the case because process parameters such as ion energy, ion
current density, gas flow rate, and deposition chamber pressure are largely de-
coupled in the ion beam deposition method of the present invention, and
because
each of these process parameters can be accurately controlled and reproduced
to a
high degree of certainty, often to within I%. In addition, the process
endpoint
coating thickness is easily defined and reproduced.
(8) Producing part-to-part thickness uniformity, e.g. a variation of less than
2% can be easily achieved. This is the case because of the compatibility of
the
method of the present invention with commercially available substrate holders
incorporating motion, i.e. rotation and/or planetary motion.
(9) Being readily scaled-up to accommodate mass production because large
scale ion beam sources are commercially available. For example, commercially
available 38 cm ion beam sources have been used to deposit DLC coatings
simultaneously over four 18-inch diameter platens with a thickness variation
across
all parts of less than +/- 2%. Similar ion beam sources can be used to
practice the
process of the present invention. Plasma deposition systems for application of
abrasion-resistant coatings are not presently commercially available on this
scale.
The apparatus for carrying out the preferred embodiment of the present
invention is illustrated schematically in FIG. I. The coating process is
carried out
inside a high vacuum chamber 1, which is fabricated according to techniques
known in the art. Vacuum chamber I is evacuated into the high vacuum region by
first pumping with a rough vacuum pump (not shown) and then by a high vacuum
pump, 2. Pump 2 can be a diffusion pump, turbomolecular pump, cryogenic pump
("cryopump"), or other high vacuum pumps known in the art. Use of a diffusion
pump with a cryogenically cooled coil for pumping water vapor is a preferred
high
vacuum pumping arrangement for the present invention. The use of cryopumps
with carbon adsorbents is somewhat less advantageous than other high vacuum
pumps because such cryopumps have a low capacity for hydrogen which is
generated by the ion beam sources used in the method of the presentinvention.
The low capacity for hydrogen results in the need to frequently regenerate the
adsorbent in the cryopumps.
CA 02184738 2004-12-30
-12-
It is understood that the process of the present invention can be carried out
in a batch-type vacuum deposition system, in which the main vacuum chamber is
evacuated and vented to atmosphere after processing each batch of parts; a
load-
locked deposition system, in which the main vacuum deposition chamber is
maintained under vacuum at all times, but batches of parts to be coated are
shuttled
in and out of the deposition zone through vacuum-to-air load locks; or in-line
processing vacuum deposition chambers, in which parts are flowed constantly
from
atmosphere, through differential pumping zones, into .the deposition chamber,
back
through differential pumping zones, and returned to atmospheric pressure.
Substrates to be coated are mounted on substrate holder 3, which may
incorporate tilt, simple rotation, planetary motion, or combinations thereof.
For
coating lenses, domed planetary substrate holders may be used. The substrate
holder can be in the vertical or horizontal orientation, or at any angle in
between.
Vertical orientation is preferred to minimize particulate contamination of the
substrates, but if special precautions such as low turbulence vacuum pumping
and
careful chamber maintenance are practiced, the substrates can be mounted in
the
horizontal position and held in place by gravity. This horizontal mounting is
advantageous from the point of view of easy fixturing of small substrates
which are
not easily clamped in place. This horizontal geometry can be most easily
visualized
by rotating the illustration in FIG. 1 by 90 degrees.
Prior to deposition, the substrates are ion beam sputter-etched with an
energetic ion beam generated by ion beam source 4. Ion beam source 4 can be
any
ion source known in the prior art, including Kaufman-type direct current
discharge
ion sources, radio frequency or microwave frequency plasma discharge ion
sources,
microwave electron cyclotron resonance ion sources, each having one, two, or
three
grids, or gridless ion sources such as the Hall Accelerator and End Hall ion
source
of U.S. Pat. No. 4,862,032. The ion source beam is charge neutralized by
introduction of
electrons into the beam using a neutralizer (not shown), which may be a
thermionic filament,
plasma bridge, hollow cathode, or other types known in the prior art.
Ion source 4 is provided with inlets S and 6 for introduction of gases
directly into the
ion source plasma chamber. Inlet 5 is used for introduction of
W 0 95123652 PCT/US95/02762
-13-
inert gases, such as argon, krypton, and xenon, for the sputter-etching.
Additionally, during the sputter-etching step, oxygen may be introduced in
inlet 6,
and used independently or mixed with an inert gas to provide chemically-
assisted
sputter-etching, e.g. for plastic substrates. Inlet 6 is used for introduction
of
reactive gases such as hydrocarbons (e.g. methane, acetylene, cyclohexane),
siloxanes, silazanes, oxygen, nitrogen, hydrogen, ammonia, and similar gases
for
the coating deposition. During the coating deposition, the reactive gases can
be
mixed with an inert gas to modify the properties of the resultant coating and
improve the stability of the ion source. The reactive gases can also be
introduced
away from the ion source plasma chamber, but into the ion beam by inlet 7.
Inlet
7 may contain multiple holes for the introduction of reactive gases, or may be
a
"gas distribution ring". Finally, reactive gases for the deposition, e.g.
oxygen and
ammonia, can be introduced at or near the substrate by inlet 8, or into the
chamber
background by inlet 9. The reactive gases introduced by inlet 8 modify the
properties of the coating by chemical reaction at the surface of the coating
during
deposition.
Additionally, to improve the deposition rate and throughput of the coating
machine, multiple ion sources 4 can be utilized and operated simultaneously.
Operation of the ion sources can be sequenced for the case in which different
coating materials are deposited from each ion source. As described in U.S.
Pat.
No. 4,490>229, an additional ion source (not shown) can be used to co-bombard
the
substrates during coating deposition to alter the film properties.
According to the method of the present invention, the substrate is first
chemically cleaned to remove contaminants, such as residual hydrocarbons and
other contaminants, from the substrate manufacturing and handling processes.
Ultrasonic cleaning in solvents, or other aqueous detergents as known in the
art is
effective. Details of the cleaning procedure depend upon the nature of the
contamination and residue remaining on the part after manufacture and
subsequent
handling. It has been found that it is critical for this chemical cleaning
step to be
effective in removing surface contaminants and residues, or the resulting
adhesion
of the coating will be poor.
WO 95123652 218 4 7 3 8 POT~S95102762
-14-
In the second step of the process, the substrate is inserted into a vacuum
chamber, and the air in said chamber is evacuated. Typically, the vacuum
chamber
is evacuated to a pressure of 1 x 10'' Torr or less to ensure removal of water
vapor
and other contaminants from the vacuum system. However, the required level of
vacuum which must be attained prior to initiating the next step must be
determined
by experimentation. The exact level of vacuum is dependent upon the nature of
the substrate material, the sputter-etching rate, the constituents present in
the
vacuum chamber residual gas, and the details of the coating process. It is not
desirable to evacuate to lower pressures than necessary, as this slows down
the
process and reduces the throughput of the coating system.
In the third step of the process, the substrate surface is bombarded with a
beam of energetic ions from an ion beam to assist in the removal of residual
contaminants, e.g. any residual hydrocarbons, surface oxides and other
contaminants, not removed in the first step, and to activate the surface. By
the
term "ion beam", it is intended to mean a beam of ions generated from a plasma
which is remote from the substrate. The ions can be extracted from the plasma
by
a variety of techniques which include, but are not limited to the use of
electrostatic
grids which are biased to promote extraction of positive ions, e.g. Kaufman-
type
ion source, or magnetic fields coupled with electrostatic fields, e.g. End
Hall-type
ion source and Hall accelerators. After extraction, the ions are directed from
the
ion source toward the substrates due to the potential difference between the
source
of the ions (plasma) and the samples, typically at or near ground potential.
The
ion beam is typically charge neutralized with electrons obtained from a
variety of
possible sources including but not limited to a thermionic hot filament, a
plasma
bridge neutralizer or a hollow cathode. Charge neutralization of the ion beam
allows the processing of electrically insulating substrates in a very stable
fashion
since the potential of the substrate is maintained. Typical pressures in the
deposition zone around the substrate for the invention are in the range of
about 10-6
Totr to about 5 x 10'' Torr so that ion-gas collisions can be minimized,
thereby
maintaining the high energy ion bombardment of the surface which is necessary
for
the formation of dense, hard coatings. This sputter-etching of the substrate
surface
is required to achieve high adhesion between the substrate surface and the
coating
W O 95123652 218 4 7 3 8 PCT~S95102762
-15-
layer(s). The sputter-etching can be carried out with inert gases such as
argon,
krypton, and xenon. Additionally, hydrogen or oxygen may be added to the ion
beam to assist in activation of the surface. The sputter-etching source gas
can be
introduced in a variety of different ways, including direct introduction into
the
plasma chamber of the ion source, introduction near the ion source but not
directly
into the source, i.e. through inlet 7, or introduction into a location remote
from the
source, as the vacuum chamber background gas through inlet 9. Typically, in
order
to achieve efficient and rapid ion sputter-etching, the ion beam energy is
greater
than 20 eV. Ion energies as high as 2000 eV can be used, but ion beam energies
less than 500 eV result in the least amount of atomic scale damage to the
substrate.
Immediately after the substrate surface has been sputter-etched, a coating
layer is deposited on the substrate by a beam of ions containing two or more
of the
elements of C, Si, H, O, N or subgroups of these elements. This ion beam is
generated by introducing precursor gases containing two or more of the
elements of
C, Si, H, O, N or subgroups of these elements into the ion source plasma, near
the
ion source plasma, or remote from the ion source plasma. These precursor gases
may be blended with other inert gases; e.g. argon. The precursor gases undergo
"activation" in the ion source plasma or in the ion beam itself. Examples of
"activation" include, but are not limited to simple electronic excitation,
ionization,
chemical reaction with other species, ions and neutrals, which may be
electronically excited, and decomposition into simpler ionic or neutral
species
which may be electronically excited. Ions are extracted from the remote plasma
to
form an ion beam which is charge neutralized by addition of electrons. Some of
these activated precursor species then condense on the surface of the
substrate to
be coated. The ions strike the surface with energies from 10 to 1500 eV. The
ion
impact energy depends on-the electric field between the point of origin of the
ion
and the sample, and the loss of energy due to collisions which occur between
the
ion and other ionic or neutral species prior to the impingement of the ion
onto the
substrate. The neutrals will strike the surface with a variety of energies,
from
thermal to 100's of eV, depending on the origin of the neutral. This highly
energetic deposition process produces highly adherent, very dense and hard
W095123652 ~ ~ ~ a ~ ~ ~ PCTIUS95102762
-16-
coatings on the substrate surface. The density, hardness and other properties
of the
coating are all very dependent on the energetics of the deposition process as
well
as the precursor gases used.
The following describes several different forms of the ion beam deposited,
abrasion-resistant coating. In the simplest case, the deposition process
conditions
are not changed during the coating process resulting in a single layer
coating. The
thickness of this layer can be from about 50 A to about 100 microns, depending
on
the degree of abrasion protection required by the application. Generally,
thicker
coatings provide greater wear and abrasion-resistance.
In the second case, it is desirable to provide multiple coating layers on a
substrate. One example of this situation is the case of a plastic ophthalmic
lens
with an anti-reflective coating. For this case, a thick, transparent coating
is first
deposited to provide abrasion resistance. Using the process of the present
invention, materials with different indices of refraction are made simply by
varying
the deposition conditions such as precursor gas composition or ion beam
energy.
By alternating layers of precise thicknessesand sufficiently different
refractive
indices on top of the thick layer, an anti-reflective coating is created. The
range of
suitable layer thicknesses and refractive indices are well known in the prior
art. In
this way, a highly abrasion-resistant, anti-reflective plastic lens product is
created.
Using the same type of layering of materials with different indices one can
design
specific reflective colors, e.g, quarter-wave stacks, using techniques that
are well
known in the prior att.
The third case is applicable in situations where the hard, abrasion-resistant,
or low-friction layer does not adhere well to the substrate. In this
situation, it is
desirable to use a first adhesion-promoting layer or interlayer. Such a layer
may
utilize different precursor gases or different deposition conditions in order
to
enhance chemical bonding of the abrasion-resistant, or low-friction layer to
the
substrate, or to reduce film stress to enhance adhesion to the substrate.
Therefore,
the first layer must adhere well to the substrate and the subsequent, abrasion-
resistant layer must adhere well to the first layer. For this situation, a
thin (less
than 1 micron) adhesion promoting layer is typically used with a thick (about
2 to
about 100 microns) abrasion-resistant outer layer on top.
W 0 95123652 PCT/U595/02762
-17-
There are other cases in which a thick, abrasion-resistant layer may adhere
well to the substrate but is lacking in some other property, such as low
friction, so
that one or more additional top coatings are required. An example of this
situation
is discussed in Kimock et al., U.S. Pat. No. 5,268,217, for coated wear
resistant
S glass bar-code scanner windows. For this product, a thick, hard, silicon oxy-
nitride
coating layer material which is abrasion-resistant under most conditions is
used.
When a piece of glass is rubbed over the silicon oxy-nitride layer, glass
debris is
left on the surface of the coating due to the high friction between glass and
silicon
oxy-nitride. If a thin layer of low-friction DLC or other low-friction
material is
deposited over the silicon-oxy-nitride, rubbing with glass does not leave
debris on
the surface. The present invention can be used to deposit an adhesion layer, a
thick, abrasion-resistant layer, e.g. silicon oxy-nitride, and the low-
friction, DLC
top layer. Additionally, the DLC could be deposited by other known methods.-
Finally, other low-friction top layers such as boron nitride, tin oxide,
indium tin
1S oxide, aluminum oxide, and zirconium oxide can be used.
DLC is an outstanding abrasion-resistant material. Therefore, for cases
where an extremely hard, inert, abrasion-resistant coating is required, DLC is
a
preferred coating. It has been found that deposition of interlayer materials
which
contain silicon atoms onto the substrate prior to deposition of the DLC layer
results
in highly adherent DLC coatings with outstanding wear resistance properties.
It is
currently believed that reaction between silicon atoms in the interlayer
material and
the carbon atoms in the DLC layer is critical for the DLC coating to exhibit
excellent adhesion. Direct ion beam deposition of interlayers containing
silicon
and one or more of the elements hydrogen, oxygen, carbon, and nitrogen can be
2S performed by the present invention by operating ion source 4 on gases which
contain these elements. For example, ion source 4 can be operated on
diethylsilane
gas to produce an interlayer containing silicon, carbon, and hydrogen. The
thickness of these interlayers is typically in the range of about 10 .~ to I
micron in
thickness.
The silicon-containing layers of the present invention, previously referred
to, contain the following combinations of elements: Si and C; Si, C and H; Si
and
N; Si, N and H; Si and 0; Si, O and H; Si, O and N; Si, O, N and H; Si, C, H
and
WO 95123652 PCTIITS95I02762
2184738
-18-
N; Si, C, H and O; Si, C and N; Si, C and O; Si, O, C and N; and Si, C, H, O
and
N, may be referred by the names of amorphous silicon carbide, silicon nitride,
silicon oxide, and silicon oxy-nitride, and mixtures thereof and chemical
combinations thereof, such as "silicon carbonitride", "silicon oxy-carbide",
and
"silicon oxy-carbonitride". By "silicon carbide", it is meant to include
materials
which are composed of the elements silicon.~nd carbon, and possibly hydrogen.
Stoichiometric and non-stoichiometric amounts of silicon and carbon are
included
in the defroition of this silicon carbide material. By "silicon nitride", it
is meant to
include materials which are composed of the elements silicon and nitrogen, and
possibly hydrogen. Stoichiometric and non-stoichiometric amounts of silicon
and
nitrogen are included in the definition of this silicon nitride material. By
"silicon
oxide", it is meant to include materials which are composed of the elements
silicon
and oxygen, and possibly hydrogen. By "silicon oxy-nitride", it is meant to
include
materials which are composed of the elements silicon, oxygen, and nitrogen,
and
possibly hydrogen. Materials falling under the chemical formula SiOxNYH~ are
considered to be within the definition of this silicon oxy-nitride material.
The
amorphous silicon oxy-carbide (Si, O, C, H) and silicon oxy-carbonitride (Si,
O, C,
N, and H) materials deposited by the process of the present invention are
particularly advantageous as abrasion-resistant coatings for plastic
substrates.
It is advantageous to deposit the DLC layer immediately following the
deposition of the adhesion promoting layer to minimize the possibility of re-
contamination of the interlayer surface with vacuum chamber residual gases or
other contaminants. The thickness of the ion beam deposited DLC coating can be
between 50 ~ and approximately 100 microns. Thinner DLC coatings, on the
order of 50 ~$ are useful when the main function of the DLC is to provide a
low
friction surface, or chemical protection. Thicker DLC layers are useful when
the
protection from severe abrasion is required.
Several ion beam deposition methods may be used for the formation of the
DLC coatings of the present invention, including direct ion beam deposition,
and
direct ion beam deposition with ion assist as in U.S. Pat. No. 4,490,229,
referred to
above.
WO 95123652 218 4 7 3 8 pCT~S951D2762
-19-
For sake of process simplicity, rapid deposition, and ease of scale-up to
mass production, direct ion beam deposition from a hydrocarbon gas source is
the
most preferred DLC deposition process for this invention. Methane or
cyclohexane
are preferred as the hydrocarbon source gases, but other hydrocarbon gases,
such as
acetylene, butane, and benzene can be used as well. Hydrogen and inert gases,
e.g.
argon, krypton, and xenon, may be introduced into the ion source plasma to
modify
the DLC film properties. The ion energy used in the DLC deposition process may
be in the range of approximately 20 eV to approximately 1000 eV. Ion energies
in
the range of 20 eV to 300 eV are most preferred to minimize heating of the
substrate during deposition.
Once the chosen thickness of the top coating layer has been achieved, the
deposition process on the substrates is terminated, the vacuum chamber
pressure is
increased to atmospheric pressure, and the coated substrates are removed from
the
vacuum chamber.
The examples which follow illustrate the superior performance of the
method of this invention. The examples are for illustrative purposes only and
are
not meant to limit the scope of the claims in any way.
Example A
A three inch diameter Si(001) wafer and a 1" x 1" piece of fused silica
were cleaned in isopropyl alcohol, dried with nitrogen gas and mounted onto a
graphite disk using Kapton tape. The graphite plate was mounted into a
stainless
steel vacuum chamber pumped by a 10" diffusion pump and the chamber was
evacuated to a pressure of 9.2 x 10-6 Torr. The substrates were sputter-etched
for
one minute by an argon ion beam generated from an End Hall ion source
(manufactured by Commonwealth Scientific as Mark II) operated on S stem of
argon, at an anode potential of 171 volts, and an anode current of 1.08 amps.
The
Ar gas was introduced directly into the plasma chamber of the ion source. The
pressure in the chamber was 7.4 x 10'5 Totr. A hot filament was used as the
electron source. After sputter-etching, methane gas was inu~oduced directly
into
the plasma chamber of the ion source at a flow of 10 stem resulting in a
pressure
of 6.6 x 10-5 Totr. The anode voltage was 172 volts and the anode current was
1.08 amps. After 5 minutes of operation at these conditions, an adherent 2880
A
W0 95123652 PCTIUS95102762
2184738
-20-
thick DLC coating was deposited. The compressive stress of the coating was 1.5
x
10'° dynes/cmz. The coating on the fused silica substrate was brown in
color when
viewed in visible light.
Example B
A three inch diameter 5i(001) wafer and a I"x 1" piece of fused silica were
cleaned in isopropyl alcohol, dried with nitrogen gas and mounted onto a
graphite
disk using Kapton tape. The graphite plate was mounted into a stainless steel
vacuum chamber pumped by a 10" diffusion pump and the chamber was evacuated
to a pressure of 2.3 x 10-6 Torr. The substrates were sputter-etched for two
minutes by an argon ion beam generated from the End Hall ion source
(Commonwealth Scientific's Mark I1) operated on 5 sccm of argon, at an anode
potential of 170 volts and an anode current of 1.25 amps. The argon gas was
introduced directly into the plasma chamber of the ion source. The pressure in
the
chamber was 4.8 x 10'' Totr. A hot filament was used as the electron source.
After sputter-etching, the argon was shut off and cyclohexane gas was
inu~oduced
directly into the plasma chamber of the ion source resulting in a chamber
pressure
of 1.4 x 10'' Ton. The anode voltage was 26.6 volts and the anode current was
1
amp. After 15 minutes of operation at these conditions, a 2650 .~ thick DLC
coating was obtained. The coating had a compressive stress of 3.6 x 109
dynes/cm=. The film on the fused silica substrate was yellow in color when
viewed
in visible light.
Example C
A three inch diameter Si(001) wafer and a 1" x I" piece of fused silica
were cleaned in isopropyl alcohol, dried with nitrogen gas and mounted onto a
graphite disk using Kapton tape. The graphite plate was mounted into a
stainless
steel vacuum chamber pumped by a 10" diffusion pump and the chamber was
evacuated to a pressure of 2.5 x 10'" Torr. The substrates were sputter-etched
for
two minutes by an argon ion beam generated from the End Hall ion source
(Commonwealth Scientific's Mark II) operated on 6.4 sccm of argon, at an anode
potential of 160 volts and an anode current of 0.98 amp. The Ar gas was
introduced directly into the plasma chamber of the ion source. The pressure in
the
chamber was 2.1 x 10'' Tom. A hot filament was used as the electron source.
WO 95123652 218 4 7 3 8 P~~~95~2762
-21-
After the sputter-etching was complete, tetramethylcyclotetrasiloxane was
introduced into the plasma chamber of the ion source and the argon was turned
off
resulting in a chamber pressure of 6.7 x 10-' Torn. The source was operated at
an
anode potential of 100 volts at a current of 1.56 amps (ion beam current
approximately 0.31 amp). After four minutes of operation at these conditions,
the
source was shut off and allowed to cool, and the chamber was vented. The
coating
deposited was adherent and 3775 A thick, and the compressive stress of the
coating
was 1.05 x 10'° dynes/cm~. The deposition rate was approximately 945
1~/min.
The coating was optically clear to visible light and had a refractive index of
1.8.
Example D
A 1" x 1" piece of fused silica, a CR-39 lens, a 2" x 2" x 0.125" CR-39
sample, a 2" x 2" x 0.125" polycarbonate sample, and a piece of 5i were all
cleaned in isopropyl alcohol and blown dry with nitrogen gas. The samples were
mounted onto an 18-inch diameter aluminum plate which was subsequently
mounted in a stainless steel vacuum chamber pumped by a 10" diffusion pump and
the chamber was evacuated to a pressure of 2.4 x 10-6 Torr. These substrates
were
sputter-etched for 10 minutes by an argon ion beam generated from the End Hall
ion source (Commonwealth Scientific's Mark I1) operated on 4.7 sccm of argon
gas, at an anode voltage of 150 volts and an anode current of 1.02 amps. The
argon gas was introduced directly into the plasma chamber of the ion source.
The
chamber pressure was L1 x 10-' Torr. After this sputter-etch, the argon flow
was
increased to 37.5 sccm and the anode voltage was reduced to 50 volts.
Hexamethyldisiloxane vapor was introduced into the argon ion beam through a
nozzle located approximately 1" downstream of the ion source plasma. The
pressure in the chamber was 1.4 x 10-' Ton. The ion source was then operated
at
an anode current of 5.10 amps. After 30 minutes of deposition at this
condition, an
adherent coating of 2500 t~ thickness was obtained. In visible light, the
coating
appeared yellow in color on the fused silica substrate.
Example E
A I" x 1" piece of fused silica, a CR-39 lens, a 2" x 2" x 0.125" CR-39
sample, a 2" x 2" x 0.125" polycarbonate sample, and a piece of Si were all
cleaned in isopropyl alcohol and blown dry with nitrogen gas. The samples were
WO 95123652 218 4 7 3 8 PCTIUS95I02762
mounted onto an 18" diameter aluminum plate which was subsequently mounted in
a stainless steel vacuum chamber which was pumped by a 10" diameter diffusion
pump and the chamber was evacuated to a pressure of 2 x 10-5 Tos. The
substrates were sputter-etched for S minutes by an argon ion beam generated
from
the End Hall ion source (Commonwealth Scientific's Mark II] operated on 14
sccm of argon gas (introduced directly into the plasma chamber of the ion
source),
at an anode voltage of 115 volts and an anode current of 3.56 amps. The
pressure
in the chamber was 2.5 x 10'' Ton. The electron source was a hollow cathode
operated on 3 sccm of argon gas. After this sputter-etch, the argon flow was
decreased to 7 sccm and the anode voltage was reduced to 67 volts and
hexamethyldisilazane was introduced into the argon ion beam through a nozzle
approximately I" downstream of the ion source. The ion source was operated at
5.1 amps current, and the deposition was continued for 30 minutes. The chamber
pressure was 1.1 x 10-' Torr. An adherent, 2.1-micron thick film was obtained
which was very transparent and water-clear when viewed in visible light.
Example F
A 1" x 1" piece of fused silica and a 3" diameter Si(001) wafer were
cleaned in isopropyl alcohol and blown dry with nitrogen gas. The samples were
mounted onto a 6" diameter graphite plate which was subsequently mounted in a
stainless steel vacuum chamber, and the vacuum chamber was evacuated to a
pressure of 1.3 x 10's Torr using a 10" diffusion pump. The samples were
sputter-
etched for 30 seconds with a 500 eV, 137 mAmp argon ion beam generated in
Kaufman-type ion source with I I cm diameter grids. After sputter-etching the
substrates, tetraethoxysilane was introduced into the ion source after the
argon was
turned off. The ion source was operated for 10 minutes at an anode potential
of
500 volts and a beam current of 62 mAmps. An adherent coating of 2300 .pi
thickness was deposited. The compressive stress of the coating was 6.1 x 109
dynes/cm-. The coating appeared yellow in visible light.
Example G
Two 2" x 2" x 0.125" CR-39 flat substrates, a CR-39 lens, a 2" x 2" x
0.125" polycarbonate substrate and a 3" diameter Si(001) wafer were
ultrasonically
cleaned in isopropanol followed by drying with nitrogen gas. The samples were
W095123652 218 4 7 3 8 PCT~S95/02762
-23-
mounted on a 18" diameter aluminum plate with Kapton tape and the plate was
mounted in a stainless steel vacuum chamber which was subsequently evacuated
to
a pressure of 4.4 x 10-' Torr by a 10" diameter diffusion pump. The samples
were
sputter etched for 5 minutes with an argon ion beam generated in the End Hall
ion
source (used in the above examples) using 10 sccm argon gas introduced
directly
into the plasma chamber of the ion source. The anode potential was 30 volts
while
the current was 5.8 amps. The electron source for the End Hall ion source was
a
hollow cathode operated on 3 sccm argon gas. After sputter-etching the
substrates,
approximately 16 sccm of octamethylcyclotetrasiloxane was introduced into the
argon beam through nozzles located approximately I" downstream of the ion
source. The anode potential was 58 volts while the anode current was 5.8 amps.
After operating for 3.5 minutes with these conditions, 10 scan of oxygen gas
were
introduced. After operating for an additional 30 seconds, the oxygen flow was
increased to 30 scan. After an additional 30 seconds, the oxygen flow was
increased to 50 sccm. After an additional 30 seconds, the oxygen flow was
increased to 70 scan and the argon was shut off. The anode potential was 56
volts
and the anode current was 5.72 amps. The chamber pressure was 1.45 x 10-' Ton.
The ion source plasma and ion beam were extinguished 40 minutes after the
first
introduction of the octamethylcyclotetrasiloxane. The chamber was brought to
atmospheric pressure and the samples were removed. The coated samples were
water-clear when viewed in visible light. Approximately 5.5 microns of coating
was deposited onto the samples.
The stress of the coating was 7.7 x 10$ dynes/cmz. The haze measured on
the CR-39 samples was less than 0.4%. The 2" x 2" x 0.125" piece of coated CR-
39 was tested with a Taber abrader using 500 grams. load with CS-lOF wheels
(total of 1 kg load). After 500 cycles, the change in haze was determined to
be
0.65°!0. Glass tested in an identical fashion had a change in haze of
0.69% after
500 cycles. The coating contained silicon, oxygen, carbon and hydrogen (Si, O,
C
and H).
Example H
Two CR-39 lenses, and two CR-39 2" x 2" x 0.125" pieces were
ultrasonically cleaned in isopropanol and then dried using nitrogen gas. The
WO 95/23652 2 ~ g 4 7 3 8 P~~S95102762
-24-
samples were mounted on a 18" diameter aluminum disk with Kapton tape. The
disk was mounted into a stainless steel vacuum chamber which was pumped with a
10" diffusion pump. The chamber was evacuated to a pressure of 1.6 x 10''
Torr.
The samples were sputter-etched for 5 minutes using an argon ion beam
generated
in the End Hall ion source (used in the above examples) with 17.4 sccm of
argon
gas directly into the plasma chamber of the ion source, an anode potential of
80
volts, and an anode current of 4.22 amps. The electron source for the End Hall
ion
source was a hollow cathode. A shutter was then placed between the ion source
and the substrates to block the ion beam, and 100 sccm of oxygen gas was run
into
the plasma chamber of the ion source, the argon was turned off, and
octamethylcyclotetrasiloxane was allowed into the chamber through nozzles
located
approximately 1" downstream of the ion source. The anode potential was 72
volts
and the anode cuwent was S.S7 amps. The pressure during this process was 1.25
x
10'' Torr. After 72 minutes of operation at this condition, the ion source
plasma
1S and ion beam were extinguished and the chamber was brought to atmospheric
pressure, and the substrates were removed. The samples were water-clear in
visible light. The coating thickness was 7.6 microns and the compressive
stress
was 5.7 x IOR dynes/cm2. The hardness of the coating (measured by
nanoindentation) was 3.4 GPa. For reference, the hardness of quartz measured
by
the same technique was 10 GPa.
Example I
Two pieces of Si and six metal alloy substrates were ultrasonically cleaned
in trichloroethane followed by isopropanol and then dried with nitrogen gas.
The
parts were mounted on a 6" diameter graphite plate using Kapton tape. The
fixture
2S was mounted into a stainless steel vacuum chamber which was pumped by a 10"
diffusion pump. The chamber was evacuated to a pressure of 1.0 x 10-5 Torr.
The
samples were sputter etched with an argon ion beam generated by a 11 cm ,
Kaufman-type ion source operated with 6 sccm of argon, at an anode potential
of
S00 volts and a beam current of 137 mAmps for two minutes. The chamber -
pressure was 1.3 x 10' Torr. After sputter-etching, approximately 200 I~ layer
of
Si was deposited by ion beam sputtering from a Si target. A 1000 eV, 0.1 amp
ion
beam from a S cm Kaufman-type ion source was operated on 7 sccm of Ar gas
WO 95123652 218 4 7 3 8 P~~S95/02762
were used to sputter the Si target for 1.5 minutes. After deposition of the Si
layer,
the 11 cm ion source was operated on 12 sccm of methane gas and approximately
12 sccm of diethylsilane gas at an anode potential. of 500 volts and a beam
current
of 0.185 amp for 71 minutes. The chamber pressure was 1.4 x 10' Torr. The ion
source plasma and ion beam were extinguished and the chamber was brought to
atmospheric pressure and the samples were removed. The samples were coated
with 2 microns of a coating containing carbon, silicon, and hydrogen. The
coating
appeared shiny black in visible light and had a nanoindentation hardness of 13
GPa.
Example J
Two 2" x 2" x 0.375" pieces of common float glass are ultrasonically
cleaned in isopropanol. The substrates are then mounted onto an aluminum disk
with Kapton tape and the disk is mounted into a stainless steel vacuum
chamber.
The chamber is evacuated to a pressure of 5 x 10'6 Ton. The glass is sputter-
etched with an argon ion beam generated in an End Hall ion source operating on
argon gas which is introduced directly into the plasma chamber of the ion
source.
The samples are sputter-etched for two minutes with the anode potential at 50
volts
and the anode current at 5 amps. The electron source for the ion beam source
is a
hollow cathode operating on argon and the chamber pressure is 5 x 10-0 Torr.
After sputter-etching, the argon is turned off and 50 sccm of oxygen gas are
introduced into the plasma chamber of the ion source. Additionally, 50 sccm of
silane are introduced through a nozzle 1" downstream of the ion source. The
anode potential is 50 volts and the anode current is 5 amps. These conditions
result in deposition of an amorphous Si0=-like film on the substrates. These
conditions are maintained for 3 minutes. Then, 50 scan of ammonia gas are
introduced into the plasma chamber of the ion source and the oxygen gas flow
is
,, reduced to 5 sccm. The anode potential is 50 volts and the anode current is
S
amps. These conditions produce a silicon-oxy-nitride-like coating material on
the
substrate. After operation at these conditions for 2 hours, the silane,
ammonia, and
oxygen gas flows are turned off, and 20 sccm of methane gas is introduced into
the
plasma chamber of the ion source. The anode potential is 50 volts and the
anode
current is 5 amps. These conditions produce a DLC coating on the.substrate.
WO 95123652 PCTlUS95102'762
2184738
-26-
After operation at these conditions for 2 minutes, the ion source plasma and
ion
beam are extinguished, the chamber is brought to atmospheric pressure, and the
coated glass windows are removed. The total thickness of the coating is S.S
microns and contains carbon, silicon, hydrogen, oxygen and nitrogen. The
samples
S have a very light brown color when viewed in visible light. The adhesion,
abrasion resistance, and chemical resistance of the coating are excellent.
The above Example J process produces a glass substrate with a first layer of
amorphous silicon oxide-like material (thickness less than 2,00011), a second
thick
layer of amorphous silicon oxy-nitride material, and a thin (200 A thick) top
layer
of DLC.
Examvle K
One glass and one polysiloxane-coated polycarbonate sunglass lens are
ultrasonically cleaned in isopropanol and blown dry with nitrogen gas. The
lenses
are mounted on an aluminum disk with Kapton tape and mounted into a stainless
1S steel vacuum chamber. The chamber is evacuated to a pressure of S x 10'6
Torr.
The samples are sputter-etched with an argon ion beam generated by the End
Hall
ion source (used in the above examples) operated on argon introduced directly
into
the plasma chamber of the ion source with an anode potential of SO volts and
an
anode current of 5 amps for 2 minutes. The electron source for the ion beam
source is a hollow cathode operated on argon gas. After sputter-etching, the
argon
is turned off and 50 sccm oxygen are introduced directly into the plasma
chamber
and SO scan of silane are introduced through a nozzle 1" downstream of the ion
source. The anode potential is SO volts and the anode current is S amps. These
conditions result in deposition of an amorphous silica-like material on the
substrate.
After operation at these conditions for 2 minutes, the silane and oxygen gases
are
turned off, and 20 scan of methane gas are introduced directly into the plasma
chamber of the ion source. The anode potential is SO volts and the anode
current
is 5 amps. These conditions produce a DLC coating on the surface of the
substrate. After operation at these conditions for 10 minutes, the ion source
plasma
and ion beam are extinguished, the chamber is brought to atmospheric pressure,
and the lenses are removed. The lenses have a gold-brown reflected color when
W 0 95123652 PCT/fJS95/02762
2184738
_27_
viewed in visible light. The coating has excellent adhesion, abrasion-
resistance,
and chemical resistance.
The Example K process described above provides a coated sunglass lens
with a 500 ~-thick layer of amorphous silica-like interlayer material and a
1000 r~-
' S thick layer of DLC.
Example L
Two 2" x 2" x 0.125" CR-39 flat substrates, a CR-39 lens, a 2" x 2" x
0.125" polycarbonate substrate, a 8" diameter x 0.125" thick polycarbonate
substrate and a 3" diameter Si(001) wafer were ultrasonically cleaned in
isopropanol followed by drying with nitrogen gas. The samples were mounted on
8.5" diameter disks with Kapton tape and the disks were mounted in a stainless
steel vacuum chamber on a planetary drive which was subsequently evacuated to
a
pressure of 5 x 10~fi Torr by a 10" diameter diffusion pump. The samples were
sputter etched for 2 minutes with an argon ion beam generated in the End Hall
ion
source (used in the above examples) using 3 scan argon gas introduced directly
into the plasma chamber of the ion source. The anode potential was 50 volts
while
the current was 5.6 amps. The electron source for the End Hall ion source was
a
hollow cathode operated on 3 sccm argon gas. After sputter-etching the
substrates,
approximately 16 sccm of octamethylcyclotetrasiloxane was introduced into the
argon beam through nozzles located approximately I" downstream of the ion
source. The anode potential was 59 volts while the anode current was 5.8 amps
(ion beam current approximately LS amps). After operating for 3.0 minutes with
these conditions, 70 sccm of oxygen gas was introduced into the plasma chamber
of the ion source and the argon flow was reduced to 0.0 sccm. The anode
potential was 57 volts and the anode current was 5.79 amps (ion beam current
approximately L5 amps). The chamber pressure was 1.4 x 10'' Torr. The ion
source plasma and ion beam were extinguished 40 minutes after the first
introduction of the octamethylcyclotetrasiloxane. The chamber was brought to
atmospheric pressure and the samples were removed. The coated samples were
water-clear when viewed in visible light. Approximately 4.8 microns of coating
was deposited onto the samples.
CA 02184738 2004-12-30
-28-
The stress of the coating was 6.4 x 108 dynes/cm~. The tensile strain to
microcracking of the coating was determined using a four point bend technique.
Coated polycarbonate pieces, 1 cm x 10 cm, were cut from the 8" diameter disk
and mounted in the four point bend apparatus. The samples were bent until
microcracking of the coating was observed. The radius of curvature was
measured
and the strain was calculated. The results indicate that the strain to
microcracking
was 2.1 - 2.2%.
Examples G, H and L demonstrate that the present invention can produce
highly optically transparent, water-clear, low stress, adherent, hard,
abrasion-
resistant coatings containing silicon, carbon, oxygen, and hydrogen on plastic
substrates at high deposition rates. For high rate depositon of these
materials, the
End Hall source is a preferred ion beam source because of its ability to
produce
high ion beam currents. Additionally, these high ion beam currents are
produced at
low ion beam energies, which results in reduced substrate heating and other
advantageous properties of the coating.
In a preferred embodiment of the present invention, coatings comprising
silicon, oxygen, carbon, and hydrogen, having the properties of
Nanoindentation
hardness in the range of about 2 to about 5 GPa and a tensile strain to
microcracking greater than about 1% are deposited. These coatings comprising
silicon, oxygen, carbon, and hydrogen are set forth in detail in applicant's
Canadian
application 2,184,736 published September 14, 1995. When applied to plastic
substrates,
these coatings produced Taber abrasion resistance test results equivalent to
that of glass.
These coatings are particularly useful in applications where optical plastic
substrates require
improved abrasion protection (e.g. plastic sunglass or ophthalmic lenses).
Example E
demonstrated that the invention can produce similar coatings which contain
nitrogen.
The properties of the coatings in Examples E, G, H, and L which make them
highly
attractive and unique are hardness which is much greater than that of plastics
such as
polycarbonate and CR-39 (typical hardness 0.2-0.3 GPa), or polymer coatings,
and high
flexibility and high tensile strain to microcracking. Compositionally, the
coatings are not
SiO2m but rather contain significant amounts
W O 95123652 218 4 7 3 8 P~~S95102762
_29_
(>5 aromic peroent) of carbon and, therefore, do not show brittle fracture
failure as
is exhibited by glass or quartz coatings.
A unique advantage of the use of the ion beam method for producing these
materials is the relationship between stress and hardness. It is well known in
the
prior art that stress and hardness are often strongly related. Typically, the
greater
the compressive stress, the harder the material. For the case of the Si-O-C-H
materials produced by injecting siloxane precursors into an oxygen ion beam,
it
was unexpectedly found that by increasing the ratio of oxygen to siloxane
precursor, the coating hardness was increased, while the compressive stress
was
simultaneously decreased. By this method, it is possible to produce hard,
abrasion-
resistant coatings which are under tensile stress, or are nearly stress-free.
This is a
very unexpected result for an energetic deposition process, and a key
technical
advantage of the presentinvention.
It is believed that the reduction in compressive stress with increasing
hardness is due to the etching of carbon from the growing surface by the
oxygen
ions, or activated oxygen in the ion beam. It has been observed by Energy
Dispersive Spectroscopy that the carbon signal in the deposited coatings
decreases
with increasing oxygen flow rate for a fixed siloxane precursor flow rate. It
is
believed that the reduction is in compressive stress with increasing coating
hardness is unique to the ion beam process of the presentinvention.
Using the process of the present invention, very high deposition rates can be
achieved while maintaining low substrate temperature. This invention produces
coatings which are very adherent and provide outstanding abrasion protection.
For
example, coated plastic substrates such as lenses, which have abrasion
resistance
equal to that of glass can be produced. Because of the high coating deposition
rates which can be attained, the invention provides an economical
manufacturing
process. The process of the present invention is also readily scaled-up to
mass
production using commercially available equipment.
From the foregoing description, one of ordinary skill in the art can easily
ascertain that the presentinvention provides an improved method for producing
highly protective and abrasion-resistant coatings on a variety of substrates,
including optical plastics. Highly important technical advantages of the
present
WO 95123652 PCTIUS95102762
2184738
-30-
invention include outstanding adhesion of the ion beam deposited coatings,
outstanding abrasion resistance, and ease and flexibility of mass production.
Without departing from the spirit and scope of this invention, one of
ordinary skill in the art can make various changes and modifications to the
invention to adapt it to various usages and conditions. As such, these changes
and
modifications are properly, equitably, and intended to be, within the full
range of
equivalents of the following claims.
