U.S. patent application number 10/147952 was filed with the patent office on 2003-02-06 for method for forming carbonaceous hard films.
Invention is credited to Kirkpatrick, Allen R., Kitagawa, Teruyuki, Matsuo, Jiro, Yamada, Isao.
Application Number | 20030026990 10/147952 |
Document ID | / |
Family ID | 23763046 |
Filed Date | 2003-02-06 |
United States Patent
Application |
20030026990 |
Kind Code |
A1 |
Yamada, Isao ; et
al. |
February 6, 2003 |
Method for forming carbonaceous hard films
Abstract
A method for enabling the formation of a carbonaceous hard film
having a high hardness, strong adherence to the substrate, a wide
range of substrate compatibility, and structural stability, which
can be formed at room temperature and may cover a large area. The
method includes vapor depositing a hard film of a carbonaceous
material onto a substrate under vacuum by depositing a vaporized,
hydrogen free carbonaceous material, which may be ionized or
non-ionized, onto the substrate surface while irradiating the
carbonaceous material with gas cluster ions, generated by ionizing
gas clusters to form the film.
Inventors: |
Yamada, Isao; (Himeji,
JP) ; Matsuo, Jiro; (Kyoto, JP) ; Kitagawa,
Teruyuki; (Ako-gun, JP) ; Kirkpatrick, Allen R.;
(Carlisle, MA) |
Correspondence
Address: |
PERKINS, SMITH & COHEN LLP
ONE BEACON STREET
30TH FLOOR
BOSTON
MA
02108
US
|
Family ID: |
23763046 |
Appl. No.: |
10/147952 |
Filed: |
May 17, 2002 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
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10147952 |
May 17, 2002 |
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09443995 |
Nov 19, 1999 |
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6416820 |
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Current U.S.
Class: |
428/408 |
Current CPC
Class: |
C23C 14/58 20130101;
Y10T 428/30 20150115; H01J 2237/0812 20130101; B82Y 30/00 20130101;
C23C 14/5833 20130101; C23C 14/0605 20130101 |
Class at
Publication: |
428/408 |
International
Class: |
B32B 009/00 |
Claims
What is claimed is:
1. A carbonaceous hard film vapor phase-formed on a substrate
material and having a Vickers hardness of 4,000 kg/mm.sup.2 or more
and a coefficient of friction of 0.15 or less.
2. A carbonaceous hard film of claim 1 wherein said film does not
contain hydrogen.
Description
CROSS REFERENCE TO RELATED APPLICATIONS
[0001] This application is a divisional of U.S. application Ser.
No. 09/443,995 entitled "Method for Forming Carbonaceous Hard
Film", filed Nov. 19, 1999, such application being incorporated
herein by reference.
BACKGROUND OF THE INVENTION
[0002] The invention is directed to a method and apparatus for
forming a carbonaceous hard film and a device therefor. In
particular, the invention is directed to a method and apparatus for
forming a novel carbonaceous hard film having a dramatic
surface-improving effect, which is useful in tools and moving parts
where a high hardness, wear resistance, and reduced friction are
required, and in precision electronic instrument parts and the
like.
[0003] In recent years, higher hardness and higher functionality
are being required more and more from hard coatings for industrial
use. In these circumstances, hard carbonaceous coatings,
represented by diamond-like carbon films, have drawn attention as a
material satisfying the more rigorous demands of a new era. Such
hard carbonaceous coatings have been subject to attempts at vapor
phase film deposition by various methods, foremost among them
chemical vapor deposition (CVD), but there are various problems in
the path to practical use, and the range of application has been
limited so far.
[0004] For example, in the most successful instances, a maximum
level of 3,000 kg/mm.sup.2 Vickers hardness has been attained in a
hard carbonaceous film through plasma assisted CVD methods, but a
problem exists in that 3,000 kg/mm.sup.2 has been an actual limit.
Adhesion characteristics and the substrate temperature during film
formation also present problems to be solved with regard to
conventional hard carbonaceous films resulting from vapor phase
film deposition.
[0005] In hard carbonaceous films formed using plasma enhanced CVD
processes, adhesion characteristics to various steel and other
metallic substrate materials, primarily tools, are in reality poor,
and implementation into practical applications has been
problematic. The reason is that the coefficient of thermal
expansion of a hard carbonaceous film is extremely low
(0.80.times.10.sup.-6/K). Thus, when a film is formed on a
substrate material with a large coefficient, such as stainless
steel 13.8.times.10.sup.-6/K in primary material, iron), it has not
been possible to avoid reaching relatively high temperatures in the
substrate material during formation of the hard carbonaceous film.
When the substrate material temperature cools down from the high
temperature reached during film-formation to ambient temperature
after film-formation, stress develops between the film and the
substrate material, and consequently the film peels off.
[0006] Conventional methods investigated for improving the poor
adhesion of a film include forming an intermediate layer between
the substrate material and the film (a silicon compound or the
like), and roughening of the substrate material surface. However,
while the first method initially appears to improve adhesion
between the hard carbonaceous film and the intermediate layer, in
actual application in tools and the like, adhesion has still been
insufficient, and the film peels off. It has also not been possible
to obtain an intermediate layer having a sufficient hardness to
allow placement under a high-hardness carbonaceous film. The second
method, like the first method, does not obtain adequate adhesion
strength in actual use.
[0007] During film-formation, a substrate heating temperature of at
least 200'C or more has been required to obtain a high-hardness
carbonaceous film. Thus, it has not been practical to apply hard
carbonaceous films to substrate materials that experience
deformation or deterioration at high temperatures, e.g., substrate
materials having a low melting point or that become annealed and
lose their hardness within this range of temperatures.
[0008] In various conventional CVD processes, gas mixtures of
hydrogen and methane, or other hydrocarbon gases, have been used as
the source for film formation material and the incorporation of
hydrogen into the carbonaceous film was deliberate. However, as
noted above, the hardness thus obtained has been merely 3,000
kg/mm.sup.2 Vickers hardness at maximum. In terms of
heat-resistance, in hard carbonaceous films containing hydrogen,
graphitization begins at 350'C, whereas in a film not containing
hydrogen, graphitization does not begin unless the temperature is
500'C or higher. The onset of graphitization causes a decline in
hardness and a degradation of characteristics.
[0009] With hydrogen, the danger of ignition is also extremely
high, and use of methane gas or other such hydrocarbon gas at the
same time presents a flammability hazard.
[0010] Methods for forming a hard carbonaceous film not containing
hydrogen include sputtering methods, electron beam deposition
methods, and direct ion beam methods, but in these methods,
hardness, wear resistance, and other such characteristics have been
found to be inadequate, and for reasons including the narrow range
of parameters in which the fllmforming process operates an article
adequate for practical use cannot presently be obtained.
[0011] CVD methods and other such plasma processes also entail
problems in that generation of films having a uniform, large
surface area has been difficult. When plasma is generated adjacent
to an insulating hard carbonaceous film, once the plasma has been
extinguished, growth does not again appear in the same location
even if the plasma is regenerated, thus posing a major problem to
the creation of a large, uniform surface area film.
SUMMARY OF THE INVENTION
[0012] Accordingly, the invention provides a method and apparatus
for forming a novel carbonaceous hard film, which has a high
hardness surpassing the hardness level previously deemed a
conventional limit, is superior in adherence to a substrate
material, obviates effects resulting from substrate temperature,
and is also superior in potential for creation of a large surface
area.
[0013] The invention provides a method and apparatus for forming a
carbonaceous hard film by irradiation with gas cluster ions during
or following the deposition of a layer of carbonaceous material
from vapor which may, or not, be partially ionized, wherein said
method is a method for vapor phase film deposition of a
carbonaceous hard film on a substrate material under a
vacuum-reduced pressure. The vaporized carbonaceous material, which
may be ionized or non-ionized, is deposited onto a substrate
surface. Gas clusters made up of atomic or molecular aggregate of a
material, which is gaseous at ambient temperature and pressure, are
ionized, accelerated and irradiated onto the surface containing the
layer of carbonaceous material.
[0014] The invention also provides a formation method, wherein the
carbonaceous material is one or more of a fullerene, a carbon
nanotube, graphite, amorphous carbon, or a carbene not containing
hydrogen. The formation method is such that the atoms or molecules
comprising the gas clusters are comprised of one or more of a rare
gas, oxygen, a carbon oxide, nitrogen, a nitride, a halogen, or a
halide. The Vickers hardness of the carbonaceous hard film is more
than 4,000 kg/mm.sup.2 and the coefficient of friction is 0.15 or
less. In addition, the carbonaceous hard film does not contain
hydrogen.
[0015] The invention provides an apparatus for forming a
carbonaceous hard film on a substrate through irradiation with gas
cluster ions, wherein the apparatus is equipped with a gas cluster
beam generation means, a gas cluster ionization means, ionized gas
cluster acceleration means, means for generating vaporized
particles of carbonaceous material, vaporized particles ionization
means, means for acceleration of the vaporized and ionized
particles of carbonaceous materials, and a film formation unit
therefore, which are disposed as necessary, and vacuum exhaust
means. The gas cluster ionization and acceleration units and the
carbonaceous material vaporized particle product, or the product of
ionization and acceleration units added thereto, are directed
towards a substrate surface disposed in the film formation unit
such that individual gas cluster ions and ionized or non-ionized
carbonaceous material vaporized particles are irradiated onto the
substrate.
[0016] The invention also provides a carbonaceous hard film
deposited on a substrate material from vapor phase, wherein the
Vickers harness is more than 4,000 kg/mm2 and the coefficient of
friction is 0.15 or less, and the invention offers a carbonaceous
hard film not containing hydrogen.
BRIEF DESCRIPTION OF THE DRAWINGS
[0017] FIG. 1 is a schematic block diagram of a film forming
apparatus that utilizes a gas cluster ion beam in accordance with
the invention;
[0018] FIGS. 2A-2D are graphs showing the change in the Raman
spectrum when the cluster ion accelerating energy is varied;
[0019] FIG. 3 is a graph showing the change in the Vickers
hardness; and FIG. 4 is a graph showing the results of measurements
of the friction coefficient.
[0020] FIG. 4 is a graph showing the results of measurements of the
friction coefficient.
DETAILED DESCRIPTION OF THE INVENTION
[0021] A method of forming a carbonaceous hard film according to
the invention is structured according to a method characterized by
vapor phase film formation by gas cluster ion beam assisted
deposition. Specifically, a method of vapor-phase film formation of
a carbonaceous hard film on a substrate material under a
vacuum-reduced pressure is described. When a vaporized carbonaceous
material is deposited onto a substrate material surface with or
without ionization, a gas cluster comprising an aggregate of atoms
or molecules of a material, which is gaseous at ambient temperature
and pressure, is ionized, and film formation is carried out by
irradiating the gas cluster ions onto said layer of the
carbonaceous vapor deposited on the surface of a substrate
material.
[0022] In accordance with the invention, the carbonaceous material
may be of various types excluding diamond, and examples include one
or more of a fullerene, a carbon nanotube, graphite, amorphous
carbon, or a carbene not containing hydrogen. These several
carbonaceous materials are appropriate in that do not contain
hydrogen other than as a possible impurity. Among these, fullerenes
and carbon nanotubes, or homologues thereof, have drawn recent
attention from the perspective of novel carbon material technology
and are cited as ideal starting materials.
[0023] These carbonaceous materials are vaporized and deposited
onto a substrate surface either directly or after ionization. The
means for vaporization may be an appropriate process such as
sputtering, laser ablation, ion or electron beam, or crucible
heating. In the case of ionized particles, these may be accelerated
and deposited on a substrate surface. The atoms or molecules
comprising a gas cluster are a gas under conditions of ambient
temperature and ambient pressure. Examples include one or more of
argon, helium, neon, and other rare gases; oxygen; CO.sub.2 and
other carbon oxides; nitrogen; nitrides; halogens; and SF.sub.6 and
other halides.
[0024] The number of atoms (molecules) comprising a cluster or
cluster ion can be controlled by controlling the formation
conditions of the gas cluster, and in the method of the invention,
the number thereof is not limited but can be made, for example,
10-10,000.
[0025] The gas clusters, made up of aggregates comprising a number
of atoms (molecules) between 10-10,000 (which can be
predetermined), are ionized by electron bombardment, for example,
and endowed with energy by acceleration to form a cluster ion beam
which is then irradiated.
[0026] Conditions in the film formation of a carbonaceous hard film
also include the degree of vacuum pressure reduction during film
formation, the substrate material temperature during film
formation, the ratio of the number of atoms or molecules in the
vaporized particles of the carbonaceous material or the ionized
particles thereof to the number of gas cluster ions, and the gas
cluster ion accelerating voltage. These conditions can also be set
as appropriate considering such factors as the type of carbonaceous
material or the characteristics of the carbonaceous hard film, and
the rate of film formation.
[0027] For example, a quantity of 1-10 gas cluster ions per 1-5,000
molecules comprising the carbonaceous material is considered. There
is also no particular limitation with respect to the cluster ion
accelerating voltage, and the voltage is set within a range forming
a carbonaceous film of desirable quality. For example, the cluster
ion accelerating voltage may be set in the range of 1
KeV-10OKeV.
[0028] Unlike the plasma CVD methods conventionally employed, there
is absolutely no need to heat the substrate in the method of the
invention. Rather, a carbonaceous hard film can be formed on a
substrate held at room temperature without heating. Of course, it
is also acceptable to perform heating if desired, within limits
that do not interfere with the method.
[0029] Unlike conventional plasma film forming methods, there is
negligible increase in the temperature of the substrate during the
process of forming the film in the method herein described. For
this reason, the method can be utilized without any particular
restrictions on the type of substrate employed. Moreover, the
problem that has been encountered in the conventional art, wherein
there is a substantial increase in the temperature of the substrate
during film formation, does not occur with the present method. In
addition, pre-treatments such as the provision of an intermediate
layer or roughening of the substrate surface are not required in
the method of the invention.
[0030] In the method for forming a carbonaceous hard film in
accordance with the invention, if the Ar atoms which form an Ar
cluster ion are present in the amount of 1,000 atom/ion, for
example, and an accelerating energy of 5 keV is applied to this gas
cluster ion, then the energy per atom is the value obtained when
the total energy is divided by the number of atoms forming the
cluster. In this case, this energy is 5 eV/atom. Accordingly, since
this is an equivalently low energy ion beam, it is possible to form
a high quality carbonaceous hard film in which there is minimal
radiation damage such as voids.
[0031] Moreover, in the case of a gas cluster ion, a localized,
instantaneous high-temperature, high-pressure state can be achieved
on the surface during multiple impacts with the surface of the
substrate. Thus, it becomes possible to approach the
high-temperature, high-pressure state required for diamond
synthesis. As a result, a carbonaceous hard film can be obtained
which has high hardness, is resistant to friction and wear, and
which includes many sp.sup.3 diamond bonds which could not be
achieved with the conventional methods for forming films.
[0032] FIG. 1 is a schematic block diagram of a film forming
apparatus 100 that utilizes a Gas cluster ion beam in accordance
with the invention. The apparatus 100 includes a gas cluster
generating chamber 102 and a film formation chamber 120. The gas
cluster generating chamber includes a source of gas 104, a nozzle
108, and a vacuum pump 106. A skimmer 112 separates un-clustered
gas from gas clusters prior to their entry into a differential
pumping chamber 114 that includes a vacuum pump 110.
[0033] The film formation chamber includes a first ionizer 122, a
first accelerator 124, and a deflection system 126. The chamber 120
also includes a second ionizer 130 and an associated crucible 128,
and a second accelerator 132. A vacuum pump 134 serves to evacuate
the chamber in which a substrate 141 is positioned by a substrate
holder 140.
[0034] In an exemplary embodiment, the gas clusters are generated
and radiated as follows. A high-pressure source gas 104 is expanded
from the nozzle 108 of the gas cluster generating element 103 into
the vacuum in the gas cluster generating chamber 102. The energy of
the source gas atoms is converted into translational motion energy,
while at the same time reducing their thermal energy by adiabatic
expansion. The source gas atoms or molecules, which super cooled
due to the loss of thermal energy, nucleate the atoms or molecules
to form gas clusters.
[0035] These neutral clusters which have formed are passed through
a skimmer 112 to the differential pumping chamber 114 and
eventually to the film formation chamber 120. After being ionized
by ionizer 122, the gas cluster ions are accelerated by accelerator
124 towards the substrate 141. Deflection system 126 scans the gas
cluster ion beam over the surface of the substrate 141.
[0036] In the example shown in FIG. 1, a carbonaceous material is
vaporized by heating it within the crucible 128, which is the
element for generating the vaporized particles of the carbonaceous
material. Thereafter, as needed, the vaporized particles of
carbonaceous material may be partially ionized by ionizer 130 and
the ionized particles are further accelerated by accelerator 132.
The vaporized carbonaceous particles, ionized or non-ionized, are
deposited on the substrate surface. During film formation, the gas
cluster ion beam bombards the substrate material. Optionally, the
deposited film may also be removed from the device in which it was
produced, to be irradiated by the cluster ion beam in a separate
suitable device.
[0037] In accordance with the invention, a carbonaceous hard film
can be provided in which (1) it is a carbonaceous hard film
deposited in vapor phase onto a substrate, (2) the Vickers hardness
is higher than 4,000 kg/mm.sup.2, (3) the friction coefficient is
0.15 or less, and (4) the carbonaceous hard film of the invention
does not contain hydrogen atoms in the hard film.
[0038] The term "carbonaceous hard film" as employed herein in
reference to the invention means that the primary film component is
carbon, and that the film material is composed only of carbon, with
the exception of atoms or molecules which become unintentionally
mixed in as impurities from the starting materials for vapor phase
film formation or as otherwise unintended contaminants.
[0039] The carbonaceous hard film of the invention, formed in vapor
phase as described above, has not been known nor concretely offered
previously. For example, specifically, by employing the invention,
it is possible to provide a material having a Vickers hardness of
in excess of 4,000 kg/mm' and a friction coefficient of 0.15 or
less. The thickness of the carbonaceous hard film is not
particularly restricted, but may be within the range of 1.about.5
.mu.m, for example.
[0040] Further explanation in greater detail will now be made using
the following examples.
[0041] Carbonaceous hard films were formed using a method in which
a carbonaceous material was vapor deposited, while employing gas
cluster ions, on each of a silicon, SUS 304, Cr, Ni, and organic
substrate.
[0042] A pure carbon fullerene (mainly C,O) was used here as the
carbonaceous material, with argon employed as the cluster source
gas. As shown in FIG. 1, by heating the crucible, the fullerene was
vaporized and vapor deposited onto the substrate. The argon cluster
ions were ionized and accelerated to 1.about.10 keV, and then
bombarded onto the room temperature substrate.
[0043] By performing vapor deposition and radiation at a proportion
of 1-10 argon cluster ions per 1.about.5,000 fullerene molecules
that reach the substrate, it was possible to form a solid
carbonaceous hard film on the various substrates noted above within
the wide ion accelerating energy range of 3.about.9 keV. The Raman
spectra of carbonaceous hard films formed following radiation in
which the argon cluster ion accelerating energy was varied among 3,
5, 7 and 9 keV are shown respectively in the graphs of FIGS. 2A-2D.
Broad Raman spectra in the range of 1200 cm.sup.-1.about.1600
cm.sup.-1 which verified the carbonaceous hard film could be
obtained.
[0044] The Vickers hardness of carbonaceous hard films (film
thickness: 2 .mu.m) formed following irradiation in which the argon
cluster accelerating energy was varied among 5, 7, and 9 keV are
shown in the graph of FIG. 3. The highest hardness was obtained at
an argon cluster ion accelerating energy of 7 keV, this hardness
being approximately 5,000 kg /MM2. The results of measurements of
the friction coefficient are shown in the graph of FIG. 4. It was
found that the friction coefficient was extremely small, at a value
of 0.1.
[0045] In addition, a carbonaceous hard film that was sufficiently
adhered to the substrate could be obtained for all the substrates
without carrying out a pre-treatment such as providing an
intermediate layer.
[0046] In contrast, in the CVD method that is currently employed in
industry, it is not Possible to adhere the hard carbonaceous film
without performing a pre-treatment to the metal substrate.
Accordingly, it was understood that the film obtained using the
method of the invention could not be achieved through conventional
methods for forming a hard carbonaceous film.
[0047] In addition, in the case of an organic substrate, it was
also possible to form a carbonaceous hard film without any
accompanying change in the character or shape of the substrate, and
the substrate itself did not reach a high temperature.
[0048] As explained in detail heretofore, the invention provides a
formation method in which a carbonaceous hard film can be directly
deposited onto a substrate, irrespective of whether that substrate
is a metal or non-metal, without performing a pretreatment such as
provision of an intermediate layer. The carbonaceous hard film
provided by the invention may be applied to processes which require
high hardness or low friction or both, or may be used as a high
quality protective film for non-lubricated sliding parts in the
various types of machinery which have been put into operation in
clean environments in recent years, as well as optical lenses and
filters. In addition, the carbonaceous hard film of the invention
may also be utilized as a surface material for a variety of
metal-molded industrial equipment parts, such as the various
rollers for precision molding, which must be reflective, shock
resistant and resistant to chemicals, as well as have a smooth
surface and be wear resistant. Accordingly, the carbonaceous hard
film of the invention can be utilized as a surface improving film
for various parts in any industrial field. As a result of the
present invention, it is possible to provide a carbonaceous hard
film that has a Vickers hardness in excess of 4,000 kg/mm.sup.2,
and offers superior resistance to friction and wear, and excellent
chemical stability.
[0049] Specifically, the invention provides the following effects.
The film can be formed at room temperature when forming the film
using a gas cluster ion beam. Accordingly, it was possible to form
a carbonaceous hard film of sufficient adhesion on a metal
substrate, such as stainless steel, in which there is a large
difference in the coefficient of thermal expansion between the
substrate material and the carbonaceous hard film. Furthermore, it
was possible to form a film onto an organic substrate having a low
thermal deformation temperature, something that had been
problematic to achieve with the conventional technology.
[0050] In the method of the invention, there is absolutely no need
to employ the hydrogen that is used in many conventional CVD
processes. As a result, a carbonaceous hard film is formed which,
as compared to the hard carbonaceous films formed using CVD
processes and the like, does not contain hydrogen. Accordingly,
none of the problems observed in hard carbonaceous films containing
hydrogen occur in the described method, so that, as a result, it is
possible to form a carbonaceous hard film that has superior thermal
stability.
[0051] By applying an electric field to a gas cluster ion beam
following acceleration, scanning thereof becomes possible by means
that are well known in the ion beam art. By such scanning it
becomes easy to increase the area over which it is possible to
obtain a film of uniform 5 character and thickness, which cannot be
done using a CVD method.
[0052] Accordingly, the invention enables the formation of a
carbonaceous hard film having a high hardness, strong adherence to
the substrate, a wide range of substrate selections, and structural
stability, which can be formed at room temperature and may have a
larger area, the formation of this type of film having been
difficult to achieve using any of the conventional 10 methods for
forming a hard carbonaceous film.
[0053] Although the present invention has been shown and described
with respect to several preferred embodiments thereof, various
changes, omissions and additions to the form and detail thereof,
may be made therein, without departing from the spirit and scope of
the invention.
* * * * *