Note: Descriptions are shown in the official language in which they were submitted.
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RC~ 76, 636
-NOVEL AND IMPROVED DIAMOND~I.IKE FILM AND PROCESS
FOR PRODUCING SAME
This invention relates to an improved amorphous,
carbonaceous, diamond-like film. Additionally, the
; 5 invention pertains to an improved process for producing
such an amorphous, carbonaceous film having diamond-like
properties.
sack~round of the Invention
Carbonaceous diamond-like film o~ films having
diamond-like properties, s~ch as the film of this
invention, are well-known in the prior ar~. These fi~ms
are particularly useful in applications such as thè coating
of optical lenses to increase the optical transmission
throuyh the lens and the coating of mirrors to improve the
light reflectivity from the mirror. Such films also find
useful applications as protective films in abrasive
applications, such as the coating of writing instruments,
as a general anti-reflective coating, and as a dielectric
or protective coating for silicon and silicon-containing
devices. In fact, the diamond-like films disclosed in
this invention find many other useful applications in
commerce and industry where film~ which are clear,
extremely hard, extremely adherent, abrasion-resistant,
corrosion-resistant, and which possess good optical
properties; are needed.
While the amorphous, carbonaceous/ diamond-like
~ilms of the prior art have much to commend them, the
search has continued for improved amorphous, carbonaceous
films having diamond-like properties. Particularly such
a film having increased hardness and increased adherence
to various substrates has continued to be sought, as well
as a process for producing such a filmr
The novel and improved carbonaceous diamond-like
film of this invention is an improvement over presently-
3S known films in that it has an extremely low stress, hasthe ability to tenaciously adhere to many, varied
substrates, has a low hydrogen content, and is extremely
hard.
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1 Su~ar~ of the Invention
With this invention, I have produced a novel and
improved, amorphous, carbonaceous, diamond-like ~ilm which
has an extremely low hydrogen content and an extremely low
stress. This film is resistant to both acids and alkalis
and has a hardness similar to that of diamond. The film
has a refractive index, a dielectric constant, and a
thermal coefficient of expansion similar to that of diamond~
In addition, the film adheres well to many types of
substrates, such as glasses, plastics, metals, semi~
conductors and the likeO
Detailed Description of the Invention
The improved amorphous, carbonaceous, diamond-
like film o~ this invention, in addition to possessing
the above-enumerated properties and qualities, differ~
from other presently-known carbonaceous films in that it
possesses an extremely low hydrogen content; on the order
of about one atomic percent or less of hydrogen. Tha prior
art carbonaceous films contain hydrogen in an amount of up
2~ to about 25 atomic percen~ or more.
The diamond-like film of this invention
addit.ionally differs ~rom prior art carbonaceous films in
that is has an extremely low stress; the stress may be
either a compressive or a tensile stress~ The film of this
invention exhibits a stress on the order of 107 to 108
dynes/cm2, while the ilms of the prior art exhibit a
stress on the order of 10ll dynes/cm2. It is believed
that the stress of these carbonaceous films is related to
their hydrogen content, and that the lower the hydrogen
content of the film, the lower the stress in the filmO
Due to the extremely low stress~ the film of this invention
is extremely adherent and adheres tenaciously to a great
number and variety of substrates on which it is deposited.
The carbonaceous, diamond-like films o this
invention are extremely resistant to acids, such as H2SO4,
HF, HC1, and HCl:HNO3, and alkalis such as NaOH, XOH,
RbOH, and CsOH.
The amorphous, carbonaceous, diamond-like film
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1 Of this invention is produced by a hybrid process in a
deposition chamber using a radio frequency plasma
decomposition from an alkane, such as n-butane, using a
pair of spaced, generally parallel, carbon electrodes,
preferably ultra pure carbon electrodes. While most
films of this invention were deposited using normal butane,
other alkan~s, such as methane, ethane, propane, pentane,
and hexane can be substituted in the process of this
invention to produce the improved carbonaceous, diamond-
like film thereof.
The deposition chamber, such as a stainlesssteel chamber, includes a pair of generally parallel and
horizontal, vertically spaced, pure carbon electrodes with
the substrate to be coated positioned on the lower carbon
electrode. The electrodes are typically positioned about
2 up to about 8 centimeters apart from each other, with the
preferred electrode spacing being approximately 2.5
centimeters. The chamber is evacuated to its ultimate
pressurej generally in the region of about 10 7 torr, and
2~ then backfilled with an alkane, such as n-butane, to ~
pressure of approximately 8 x 10-4 torr. Thereafter, the
vacuum system is throttled to a pressure in the range of
approximately 25 to 100 millitorr~ After stabilization
of the pressure, the radio frequency power is applied to
the pair of pure carbon elactrodes with the lower
electrode (substrate target~ being biased in the range of
about 0 to about -lO0 volts, and the upper electrode being
biased in the range of about -200 to about -3500 volts.
Radio Erequency plasma decomposition is begun, and an
amorphous, carbonaceous, diamond like film is deposited
onto the substrate at rates varying between about 8 up to
about 35 angstroms per minute, to produce a film of up
to about 5 mic~ometers in thickness.
The films produced by the above process have an
extremely low stress. The stress for the films prodllced
by the process has been measured and determined to be in
the range of about 107 to 108 dynes/cm2. As has been
previously stated, the stress may be either a compressive
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1 'or tensile stress. It has been determined that the
resultant stress of ~he film produced by this proceSs, be
it either a compressive or tensile stress, is dependent
on the potential applied to the upper carbon electrode.
The following specific examples are included '
in order to illus~rate the invention and the improvements
thereof with greater particularity. However, it is to be
understood that these examples are not intended to limit
the invention in any way.
EX~M
In this example, a stainless steel deposition
chamber, as described above, was prepared for deposition
of the improved carbonaceous diamond-like film of this
invention.~ The~deposition chamber was stabilized with
n-butane at a deposition pressure of approximately 50
millitorr with the pair of ultra pure carbon eIectrodes
being horizontally positioned and at a vertical spacing
of approximately 6 centimeters from each other. A glass
substrate for deposition of the film was positioned on the
lower carbon electrode. The lower electrode (substrate
target) was maintained at a potentiaI of -50 volts and the
upper electrode was maintained at a potential of -500
volts.
A film was then deposited by radio frequency
plasma decomposition from n-butane onto the glass
substrate under the above conditions at a rate of about
10 angstroms per minute to a thickness of approximately
1.45 micrometers. The stress of the resultant film was
measured and determined to be a stress of about 7 x loB
dynes/cm2, tensile stress. The resultant film had a
hydrogen content of less than 1~0 atomic percent.
In a similar experiment, it was determined that
when the potential of the upper electrode was decreased
and maintained at a -300 volts, while maintaining the
potential of the lower electrode (substrate target) at,
-50 volts, the film deposited under such conditions at a
rate of approximately lO angstroms per minute to a
thickness of 1.5 micrometers had a compressive stress.
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1 The stre~s of the film in this experiment was measured and
determined to be about 8 x 1o8 dynes/cm2, compressive
stress. The hydrogen content of the film obtained in this
experiment was measured and determined to be less than
l.O atomic.percent hydrogen.
In a series of additional experiments, similar
to the above, improved carbonaceous diamond-like films,
like the above, were deposited on other substrates. These
substrates included~metals, such as stainless steel,
molybdenum, tungstén, and tantalum; various gla~ses,
sîlicon, silicon dioxide, and aluminum oxide, as well a5 .
plastics, such as polycarbonate, s~yrene, acrylic~
styrene~acrylic copolymer, and other resins.
: EXAMPLE II
1.5 In this example, a series of experiments were
performed as in Example I to deposit the improved
carbonaceous, diamond-like film of this invention under a
varie-ty of potentials applied to the upper electrode and
lower electrode or substrate karget. The voltage~ employed
and the results obtained in each of these experiments
are set forth hereinbelow;
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- 7 - RCA 76,636
The hydrogen content of the above films was measured
and determined to be less than 1.0 atomic percent
hydrogen.
EX~MPLE III
In this example, a number of high quality
plastic lenses were coated with the improved carbonaceous,
diamond-like film of this invention using the stainless
steel deposition chamber and process of this invention as
described in Example I. After evacuation~ the chamber
was backfilled with normal butane. and stabilized at a
deposition pressure of approximately 80 millitorr. The
pair of ultra pure carbon electrodes were positioned at a
spacing of about 2.5 centimeter with the plastic lens to
be coated positioned on the lower electrodeO This lower
electrode (substrate target) was maintained at a potential
of -50 volts while the upper elec~rode was maintained at
a potential of -2500 volts. A film was th n r.f. plasma
deposited onto the plastic lens under these conditions at
a rate of approximately 25 angstroms per minute to a
thickness of llO0 angstroms. Another lens was coated on
both of its sides with the film of this inventionJ wi~h
the film on each side having a thickness of llO0
angstroms A third plastic lens was coated on one side with
the fi~m of this invention to a thickness of ll,000
angstroms. In all cases, the films of this example
2B exhibited the same low stress and low hydrogen content as
the films produced in the previous examples set orth
above. Additionàlly, the optical properties (absorption,
transmission, and reflection) of the coated plastic
lenses were maintained at approximately the same level,
and .Ln many cases these optical properties were improved
by the film of this invention having been coated on their
surface.
