A diamondlike carbon film is deposited in the surface of a substrate by exposing the surface to an argon ion beam containing a hydrocarbon. The current density in the ion beam is low during initial deposition of the film. Subsequent to this initial low current condition, the ion beam is increased to full power. At the same time, a second argon ion beam is directed toward the surface of the substrate. The second ion beam has an energy level much greater than that of the ion beam containing the hydrocarbon. This addition of energy to the system increases mobility of the condensing atoms and serves to remove lesser bound atoms

Banks, B. A.

Mirtich, M. J.

Sovey, J. S.

English

NASA Technical Reports Server

United States Patent 1191 [II]  Patent Number: 4,490,229 
Mirtich et al. [45] Date of Patent: Dec. 25, 1984 
DEPOSITION OF DIAMONDLIKE CARBON 
FILMS 
Inventors: Michael J. Mirtich, North Olmsted; 
James S. Sovey, Strongsville; Bruce 
A. Banks, Olmsted Township, 
Cuyahoga County, all of Ohio 
The United States of America as 
represented by the Administrator of 
the National Aeronautics and Space 
Administration, Washington, D.C. 
Assignee: 
Appl. No.: 628,866 
Filed: Jul. 9, 1984 
Int. Cl.3 .............................................. C23C 15/00 
U.S. Cl. ............................ 204/192 C; 204/192 R; 
204/192 SP; 423/414; 423/445; 423/446; 
423/449; 423/DIG. 10 
423/445, 446, 449,414, DIG. 10 
Field of Search ......... 204/192 C, 192 R, 192 SP; 
References Cited 
U.S. PATENT DOCUMENTS 
3,859,422 1/1975 Home et ai. ........................ 423/445 
3,949,062 4/1976 Vereschagin ....................... 423/446 
4,060,660 11/1977 Carlson et al. ...................... 428/408 
4,173,522 1/1976 Pulker et ai. .................... 204/192 C 
4,191,736 3/1980 Nelson et al. 
4,228,142 10/1980 Holcombe et 
4,288,353 9/1981 Eckel et ai. . 
4,346,123 SA982 Kaufmann ... 
4,351,712 9/1982 Cuomo et ai. ....... 
4,412,903 11/1983 Green et al. 
4,437,962 3/1984 Banks .................................. 204/192 
Primary Examiner-Arthur P. Demers 
Attorney, Agent, or Firm-Norman T. Musial; John R. 
Manning 
1571 ABSTRACT 
A diamondlike carbon film is deposited in the surface of 
a substrate by exposing the surface to an argon ion beam 
containing a hydrocarbon. The current density in the 
ion beam is low during initial deposition of the film. 
Subsequent to this initial low current condition, the ion 
beam is increased to full power. At the same time a 
second argon ion beam is directed toward the surface of 
the substrate. The second ion beam has an energy level 
much greater than that of the ion beam containing the 
hydrocarbon. This addition of energy to the system 
increases mobility of the condensing atoms and serves 
to remove lesser bound atoms. 
19 Claims, 1 Drawing Figure 
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U.S. Patent Dec. 25, 1984 
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DEPOSITION OF DIAMONDLIKE CARBON 
FILMS 
DESCRIPTION 
ORIGIN O F  THE INVENTION 
The invention described herein was made by employ- 
ees of the US.  Government and may be manufactured 
and used by or for the Government for governmental 
purposes without the payment of any royalties thereon 
or therefor. 
TECHNICAL FIELD 
This invention is concerned with making thin films 
having the properties of diamond. The thicknesses of 
films are usually between thousands of angstroms and a 
few microns. 
Various procedures have been utilized in an effort to 
produce carbon thin films with diamondlike properties. 
These films have numerous applications as scratch resis- 
tant coatings for polymers, weather resistant coatings, 
and biocompatable coatings on biomedical implants. A 
variety of plasma and ion beam techniques have been 
employed to produce such carbon films. 
By way of example, rf plasma decomposition of hy- 
drocarbon gas has been suggested. Such plasma decom- 
position of other alkanes has also been utilized, and low 
energy carbon ion beam deposition has been reported. 
Ion plating and dual ion techniques using a carbon tar- 
get have also been used. 
The quality of the films produced by the prior art 
methods is such that the films appear to have a low 
electrical resistivity of about 1 to 10 ohm cm and high 
optical absorption of about 105 cm-1. These films also 
have less resistance to chemical attack of H2S04/- 
HNO3. The films are also softer than desired, and their 
densities are lower than optimum. 
Another disadvantage to these prior art techniques is 
that the size of the substrate to be coated is limited. Also 
the deposition rates are undesirably low. The prior art is 
further deficient in that the films produced are stressed 
because of the inability to control enough independent 
parameters. 
It is, therefore, an object of the present invention to 
provide thin carbon films having diamondlike proper- 
ties which include extreme mechanical hardness charac- 
terized by high scratch resistance, high dielectric 
strength and electrical resistivity together with a large 
band gap, high thermal conductivity, chemical inertness 
including insolubility in concentrated H2S04/HNO3, 
and optical properties that include high transmittance at 
visible wavelengths. 
BACKGROUND ART 
Green et a1 U.S. Pat. No. 4,412,903 describes a dia- 
mondlike carbon coating deposited from methane in a 
direct current glow discharge m-ocess. The substrate 
may be precleaned with argon ion bombardment. Carl- 60 uses argon gas. In addition, neutralization of the ion 
son et a1 U.S. Pat. No. 4,060,660 also refers to the depo- beam may be achieved by secondary electons released 
sition of an amorphous carbon thin-film in a glow dis- by ion bombardment of the walls of a vacuum facility 
charge process. (not shown) which houses the ion source 16. 
Cuomo et a1 US. Pat. No. 4,351,712 is concerned This vacuum facility is sufficiently large to minimize 
with a low energy ion beam deposition/oxidation pro- 65 back sputtered facility material from contaminating the 
cess. The deposition takes place at low energy levels material being ion bombarded. Such a facility having a 
from about 30 eV to about 180 eV. Banks U.S. Pat. No. diameter of about 1.5 meters and a length of about 7.3 
4,437,962 is directed to the production of diamondlike meters has been satisfactory. The vacuum facility nor- 
L 
flakes which are mixed with a binder or matrix material 
to form composites. 
DISCLOSURE OF INVENTION 
This invention provides thin carbon films of superior 
quality having the properties of diamond. The films are 
generated by a deposition employing a hollow cathode 
with hydrocarbon/argon ion sources. 
Low current densities are utilized during initial depo- 
10 sition of the film. The ions or charge-exchanged neu- 
trals have energy levels between about 80 eV and about 
150 eV. The flowrate ratio of methane to argon is about 
28%. 
The resulting films have a potential for use in micro- 
15 electronic applications. These films are also used in high 
energy laser and plastic windows. It is further contem- 
plated that the films may be utilized for corrosion pro- 
tection for metal. 
BRIEF DESCRIPTION OF THE DRAWING 
The objects, advantages and novel features of the 
invention will be more fully apparent from the follow- 
ing description when read in connection with the ac- 
companying drawing which is a schematic view of a 
25 dual beam ion source system utilized for the deposition 
of films having diamondlike properties. 
5 
2o 
BEST MODE FOR CARRYING OUT THE 
INVENTION 
In referring now to the drawing there is shown a 
substrate 10 of quartz, silicon, or other metal upon 
which a diamondlike carbon film is generated. Accord- 
ing to the present invention the substrate 10 is first 
exposed to an argon ion beam 12 to clean absorbed 
35 gasses and contaminants from the exposed surface 14. 
The beam 12 has an energy level between about 500  eV 
and about lo00 eV. The current density of the beam 12 
is between about 0.5 ma/cm2 to about 2 ma/cm2. 
The argon ion beam 12 is preferably generated by a 
40 30 centimeter electron bombardment ion source 16 that 
is connected to a suitable reservoir of argon gas through 
a supply pipe 18. The argon gas is fed through a hollow 
cathode 20 into a main discharge chamber 22. 
The ion beam source 16 may be of the type developed 
45 from electrical propulsion technology. Such an ion 
source is described in “Advances in Electronics and 
Electron Physics” by H. R. Kaufman, Vol. 36, pages 
265-373, 1974. Liquid nitrogen is used in cold traps of 
diffusion pumps and the cryoliner of the vacuum system 
Beam extraction is accomplished by a dished, two 
grid ion optics system of the type described in AIAA 
Paper No. 76-1017 entitled “A 30 cm Diameter Argon 
Ion Source”. This system includes an upstream grid 24 
5 5  and a downstream grid 26. The 30-cm argon ion beam 
source preferably has its ion optics masked down to an 
ion beam diameter of about 10 cm. 
Neutralization of the ion beam 12 may be achieved by 
a hot wire or hollow cathode neutralizer 28 which also 
30 
50 during operation of the ion source 16. 
4.490,229 
3 
maily is maintained at a pressure of about 3 X torr 
during the operation of the ion source 16. 
The 30 cm hollow cathode ion source 16 is then used 
to directly deposit a diamondlike carbon film on the 
surface 14. Argon gas is used in the hollow cathode 20 
to establish and maintain a discharge. Methane (CH4) or 
another hydrocarbon is introduced into the main dis- 
charge chamber 22 from a supply pipe 30 whereupon c ,  
C&, CH,, C+, (CH,)+ molecules and ions are intro- 
duced into the beam 12 through the ion optics system 
24. The ideal flowrate ratio of methane to argon re- 
quired to generate a diamondlike carbon film on the 
surface 14 is 28%. 
The energy level required of the beam 12 is between 
about 80 eV and 150 eV to generate the diamondlike 
carbon film on the surface 14. The optimum energy 
level of the beam 12 is 100 eV. With this energy level it 
is necessary to have a voltage of -600 volts on the 
downstream grid 26 to extract the beam 12. 
A novel feature of the invention is the utilization of a 
second ion beam source 32 during this deposition as will 
be described below in greater detail. The source 32 is 
preferably an 8 centimeter electron bombardment ion 
source which is similar to the source 16. Argon is sup- 
plied to the source 32 through a supply pipe 34, and an 
argon in beam 36 is produced. Neutralization of this 
beam is achieved by the neutralizer 28 used to neutralize 
the 30 cm ion source beam 12. Only one neutralizer is 
required for the system. 
An important requirement of the present invention is 
that in order to initiate the deposition of a diamondlike 
carbon film on the surface 14, it is necessary for the 
current density in the beam 12 to be low during initial 
deposition at the substrate 10. A typical value is $ or less 
of the current density during full deposition. This re- 
quired low current density is for a period of time vary- 
ing from 3 minutes to 30 minutes, depending upon the 
substrate material. 
Subsequent to this initial low current condition the 30 
centimeter hollow cathode ion source 16 is set at full 
power current conditions. At the same time the 8 centi- 
meter ion source 30 using argon ions at 200 eV to 500 
eV is turned on with the current density at the substrate 
of 25 microamperes/cm*. This addition of energy to the 
system increases mobility of the condensing atoms and 
serves to remove lesser bound atoms. Typical deposit 
rates at these conditions is between 70 and 80 angstroms 
per minute. 
A number of advantages are realized using the 
method of the present invention. For example, thermal 
control of the substrate 10 to change stress levels in the 
film can be achieved. It is further contemplated that the 
films can be laser annealed during deposition. 
Other gasses can be introduced at the substrate 10 to 
change the composition of the film to achieve a desired 
property. For example, the addition of hydrogen gas to 
the films on the surface 14 increases their transparency. 
Biasing of the substrate 10 during deposition may be 
varied using either R F  or DC. The angles of incidence 
of the energetic argon ion beam 34 or the low energy 
hydrocarbon ion beam 12 may be varied. It is further 
contempiated that the substrate may be rotated to coat 
complex geometric configurations. In certain applica- 
tions the diameters of the ion sources 16 and 32 may be 
made larger or smaller than those presently described. 
5 
10 
15 
20 
25 
30 
35 
40 
45 
50 
55  
60 
65 
The advantages of the disclosed process over those of 
the prior art are that the films produced though amoro- 
phous are clear, extremely hard, chemically inert, of 
4 
high resistivity and have an index of refraction of 3.2. 
These properties &re similar to those of a single crystal 
diamond. 
These films have uses in microelectronic applications, 
high energy laser and plastic windows, and corrosion 
protection for metal. This process has other applications 
where the desired properties the diamondlike film can 
be shaped, using the many independent parameters, 
during the film formation process. 
Failure to follow the critical process steps of this 
invention may result in no film being deposited on the 
surface 14. In other instances the film may spa11 or it 
may be loosely bound carbon or soot. 
The utilization of the hollow cathode ion source 16 
with a mix of hydrocarbon gasses and argon operated at 
low energies for direct deposition of the film on the 
substrate 10, in addition to the use of a second ion 
source 30, provides an independent source of argon ions 
with various energies and current density levels. This 
independently controls the mobility of the condensing 
atoms and sputters away loosely bound atoms. 
While the preferred embodiment of the invention has 
been disclosed and described it will be appreciated that 
various modifications may be made without departing 
from the spirit of the invention or the scope of the sub- 
joined claims. 
We claim: 
1. A method of making diamondlike carbon films on 
exposing said substrate to a first ion beam having a 
first current density and a first energy level, 
introducing a hydrocarbon into said first ion beam 
whereby an initial portion of a diamondlike carbon 
film is deposited on said substrate, 
increasing the current density of said first ion beam to 
a second current density whereby a remaining 
portion of a diamondlike carbon film is deposited 
on said substrate, and 
exposing said substrate to a second ion beam having a 
second energy level greater than said first energy 
level during the deposition of said remaining por- 
tion of said diamondlike carbon film. 
2. A method of making a diamondlike carbon film as 
claimed in claim 1 wherein the substrate is mounted in a 
vacuum environment having a pressure of about 
3 x 10-5 torr. 
3. A method of making a diamondlike carbon film as 
claimed in claim 1 wherein the first ion beam contains 
argon ions. 
4. A method of making a diamondlike carbon film as 
claimed in claim 1 wherein the first current density of 
the first ion beam is less than one half the second current 
density of the first ion beam. 
5. A method of making a diamondlike carbon film as 
claimed in claim 4 wherein the first current density is 
maintained for a period of time between about three 
minutes and about thirty minutes. 
6. A method of making a diamondlike carbon film as 
claimed in claim 1 wherein the first energy level of the 
first ion beam is between about 80 eV and about 150 eV. 
7. A method of making a diamondlike carbon film as 
claimed in claim 6 wherein the first energy level is about 
100 eV. 
8. A method of making a diamondlike carbon film as 
claimed in claim 6 wherein the second energy level of 
said second ion beam is between about 200 eV and 
about 500 eV. 
a substrate comprising the steps of 
4,490,229 
5 6 
9. A method of making a diamondlike carbon film as 
claimed in claim 1 wherein the current density of the 
second ion beam at the substrate is about 25 mi- 
croamoperes/cm*. 
on a substrate surface comprising the steps of 
the second ion beam has an energy level bet 
200 eV and about 500 eV. 
14. A method of depositing a diamondlike 
as claimed in claim 10 wherein the substrate is biased 
10. A method of depositing a diamondlike carbon film 5 during film deposition. 
15. A method of depositing a diamondlike c 
mounting the substrate in a vacuum environment, as claimed in claim 10 wherein hydrogen gas is added to 
directing a first ion beam containing a hydrocarbon said film during deposition thereby increasing the trans- 
parency. toward said surface, and 
directing a second ion beam having an energy level 10 16. A method of depositing a diamondlike carbon film greater than that of said first ion beam toward said as claimed in claim 10 wherein the substrate is rotated surface. 
11. A method of depositing a diamondlike carbon film during deposition. 
as claimed in claim 10 wherein the substrate is mounted 17. A method of depositing a diamondlike carbon film 
in a vacuum environment having a pressure of about 15 as claimed in claim 10 wherein the film is annealed 
3~ 10-5 torr. during deposition. 
12. A method of depositing a diamondlike carbon film 18. A method of depositing a diamondlike carbon film 
as claimed in claim 10 wherein said first and second ion as claimed in claim 17 wherein the film is laser annealed. 
beams contain argon ions. 19. A substrate having a diamondlike carbon film 
13. A method of depositing a diamondlike carbon film 20 deposited thereon in accordance with the method of 
* * * * *  as claimed in claim 10 wherein the first ion beam has an energy level between about 80 eV and about 150 eV and 
claim 1. 
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Deposition of diamondlike carbon films

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