The method and equipment used for sputtering by use of an apertured electrode and a pulsed substrate bias are discussed. The technique combines the advantages of ion plating with the versatility of a radio frequency sputtered source. Electroplating is accomplished by passing a pulsed high voltage direct current to the article being plated during radio frequency sputtering

Przybyszewski, J. S.

Shaltens, R. K.

English

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(NASA-Case-LEW-10920-1) METHOD AND
APPARATUS FOR SPUTTERING UTILIZING AN
APERTURED ELECTRODE AND A PULSED
SUBSTRATE BIAS Patent (NASA) 3 p
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May 8, 1973 j. s. PRZYBYSZEWSKI ETAL 3,732,158
METHOD AND APPARATUS FOR SPUTTERING UTILIZING AN APERTURED
ELECTRODE AND A PULSED SUBSTRATE BI/S
Filed Jan. 14. 1971
RADIO FREQUENCY
POWER SOURCE
HIGH VOLTAGE
O.C.
(0-5 KV.)
BY
INVENTORS
JOHM S. PRZYBYSZEWSKI
RICHARD K. SHALTENS
ATTORNEYS
United States Patent Office 3,732,158Patented May 8, 1973
3,732,158
METHOD AND APPARATUS FOR SPUTTERING
UTILIZING AN APERTURED ELECTRODE AND
A PULSED SUBSTRATE BIAS
John S. Przybyszewski, North Olmsted, and Richard K.
Shaltens, Lakewood, Ohio, assignors to the United
States of America as represented by the Administrator
of the National Aeronautics and Space Administration
Filed Jan. 14, 1971, Ser. No. 106,424
Int. Cl. C23c 15/00
U.S. Cl. 204—192 7 Claims
ABSTRACT OF THE DISCLOSURE
Combining the advantages of ion plating with the versa-
tility of a radio frequency sputtered source. A pulsed high
voltage direct current is passed to the article being plated
during radio frequency sputtering. •
15
ORIGIN OF THE INVENTION
The invention described herein was made by employees
of the United States Government and may be manufactured
and used by or for the Government for governmental pur-
poses without the payment of any royalties thereon or
therefor.
BACKGROUND OF THE INVENTION
This invention is concerned with plating adherent films
on objects having complex geometries. The invention is
particularly directed to ion plating alloy films on such
objects using a radio frequency sputtered source. The ion
plating process is modified because this source supplies film
material at a much slower rate than the usual thermal
evaporation source.
In the past several methods were used to deposit various
types of films on simple as well as geometrically complex
objects. While each process is satisfactory for certain
applications, problems have been encountered with all
of these methods.
Conventional vapor deposition is conducted in a vacu-
um of 10~6 to 10~8 torr. The use of conventional vapor
deposition has been generally restricted to the elemental
metals, although some metal alloy systems as well as cer-
tain semiconductors and nonconductors have been vapor
deposited. The high vacuum used in vapor deposition re-
duces the concentration of gas molecules which increases
the mean free path. Very little scattering of the film mate-
rial results, and the process is limited to line-of-sight
deposition. The coating of complex geometries by vapor
deposition is conditioned on the rotation of the object to
be coated. Adherence of a vapor dep'osited film is poor
because of the low energy of the impinging film material.
The film adhesion is improved when either direct cur-
rent or radio frequency sputtering is used. Direct current
sputtering has been successful for depositing elemental
metals, semiconductors, and metal alloy systems. This type
of sputtering is not useful for depositing nonconductors.
Radio frequency sputtering has been used for depositing
elemental metals, metal alloy systems, semiconductors,
and nonconductors. This type of sputtering is not limited
by the nature of the film material. It can be used to sput-
ter almost any material from insulators through semi-
conductors to metals.
Radio frequency and direct current sputtering are gen-
erally done in an atmosphere having a pressure in the range
of about 5 to 20 microns. Because of this relatively high
pressure the sputtered material is scattered. The mean free
path is short, and the material is diffused rapidly as it
leaves the source. Even though this scattering effect causes
film formation on surfaces not directly facing the source
material, both RF and DC sputtering are considered to
be line-of-sight deposition processes. The low energy of
the impinging film material adversely affects film ad-
herence.
Ion plating is performed at about the same pressure as
RF and DC sputtering. A high voltage is applied to the ob-
ject to be coated. This results in a uniform coating on all
sides without rotating or moving either the object or the =3
source of film material. While the coating has excellent ad-
JQ hesion, problems have been encountered because the proc-
ess utilizes a thermal evaporation source. This limits the
film materials to the elemental metals and those com-
pounds which do not dissociate 'before they evaporate.
SUMMARY OF THE INVENTION
These problems have been solved by the present inven-
tion which utilizes radio frequency sputtering with a pulsed
high voltage direct current. The process is not limited to a
line-of-sight deposition, and complex geometries can be
plated without rotation. The process is useful for plating
adherent films of elemental metals, metal alloy systems,
semiconductors, and nonconductors.
OBJECTS OF THE INVENTION
It is, therefore, an object of the present invention to
plate an adherent alloy film on an object having a geometri-
cally complex configuration.
Another object of the invention is to provide an im-
proved plating method which combines the advantages of
„„ ion plating with the versatility of a radio frequency sput-ou ,tered source.
A further object of the invention is to provide an im-
proved method for plating alloy films on complex geom-
etries without rotation during the plating process.
These and other objects of the invention will be appar-
ent from the specification which follows and from the
drawing wherein like numerals are used throughout to
identify like parts.
25
35
40
45
DESCRIPTION OF THE DRAWING
The figure is a schematic diagram of a system construct-
ed in accordance with the invention for plating adherent
alloyed films on geometrically complex objects.
DESCRIPTION OF THE PREFERRED
EMBODIMENT
Referring now to the drawing there is shown an object
10 which is to be coated in accordance with the present
invention. The object 10 may be any electrically conductive
50 article having either a simple or geometrically complex
configuration. By way of example the invention has been
utilized to coat bearings with a solid lubricant. The object
10 is mounted in a chamber 12 that is connected at 14
to a suitable vacuum pumping system.
55 A target 16 of the material to be sputtered is likewise
located in the chamber 12. The target 16 is connected to a
radio frequency power source 18 through a matching net-
work 20. This RF sputtered source 16 is utilized instead of
a thermal evaporation source 'normally used in ion plating.
go As stated earlier, certain modifications are required be-
cause the RF sputtered source 16 supplies film material
at a much slower rate than a thermal evaporation source.
A suitable gas is supplied to the chamber 12 at an inlet
22. Argon is preferably used. The object 10 to be plated
65 is connected to a high voltage, direct current source 24.
The source 24 preferably has a range of 0 to 5 kilovolts.
In this manner the ion plating is carried out in a low
pressure ionized gaseous atmosphere with the object 10
to be plated forming a cathode that is maintained at a
70 high negative potential from the source 24. Consequently,
the object 10 to be plated is continuously bombarded or
sputtered by ions before, during and after film material
3,732,158
10
15
20
25
30
35
enters the ionized gas. If the evaporation rate of the film
material is too slow the film on the object to be plated will
be sputtered away as fast as it develops, and no film will
result. Because the RF sputtered source 16 is inherently
slow, no film would develop under normal ion plating con-
ditions.
According to the present invention the ion plating proc-
ess has been modified to reduce the rate of sputtering off
of the newly formed .film by providing a timed switch 26
between the source 24 and the object 10. The reduction in
the sputtering off rate is accomplished by pulsing the
negative high voltage DC from the source 24 to the object
10 by means of the timed switch 26.
A third electrode 28 is positioned in the chamber 12 to
establish a common electrode between the RF power
source 18 and the DC power source 24. The electrode 28
is connected to the high voltage DC power source 24
through an RF choke 30. The electrode 28 forms an anode
with respect to the cathode 10. The radio frequency power
source 18 is connected to the electrode 28 through a ca-
pacitor 32. A bypass capacitor 34 is likewise provided.
This third electrode 28 is preferably in the form of a
perforated plate or screen that is located between the sput-
tered source 16 and the object 10. The screen has an aper-
ture in the center to enable sputtered material to pass to
the object to be plated.
In operation, the object 10 is mounted in the chamber
12 together with the target 16 of material to be sputtered.
The chamber 12 is partially evacuated and a gaseous at-
mosphere from about 10-20 microns pressure is estab-
lished. A high voltage DC negative potential of 2 to 5
kilovolts with respect to the screen 28 is continuously
applied to the object 10. This establishes a glow discharge
within the vacuum chamber 12 to sputter clean the ob-
ject 10.
After a predetermined period of sputter cleaning, the
high voltage DC source 24 is deenergized and the gaseous
pressure is lowered to about 10 microns. The RF power
source 18 to the film material 16 is energized, and sput-
tering of the film material begins. At this point the high 40'
voltage DC source 24 is switched to a timed on-off mode
by the switch 26. In this manner the high voltage DC is re-
energized and reapplied to the object 10.
The pulsed high voltage direct current RF sputtering
process produces an intense electric field which com-
pletely surrounds the object 10. This can be seen as a dark
space around this object. Any ionized material entering
this region gains kinetic energy from the field and impacts
on the surface of the object 10 with great force. This con-
tributes to improved adhesion. The dark space, in effect,
represents essentially a source of film material which
takes on the general outline of the object 10.
The high voltage DC negative potential on the object
10 is maintained throughout the plating. The process is
continued until the desired film is obtained. The reduced
sputtering rate of the film on the object 10 results in the
formation of a visible film having excellent adherence
and covering the entire object.
EXAMPLE
Pulsed high voltage direct current radio frequency sput-
tering was used to plate antifriction bearing components
with a solid lubricant film of molybdenum disulfide. The
plating conditions are as follows:
Total coating time each component: 3 hours
Radio Frequency Input Power to Source Material: 700
watts at 7 megahertz
Maximum pulse amplitude to specimen: 2000 V-DC,
negative ' ;
Pulse form: 15 seconds on; 5 minutes off; 5% duty cycle
Specimen to screen distance: 2.5 inches
45
50
Specimen to source distance: approximately 6 inches
Chamber pressure: 5 microns; argon
The components were assembled and the bearing was
tested. The bearing was satisfactory for its intended use.
While one embodiment of the invention has been shown
and described it will be apperciated that various modifica-
tions to the invention may be made without departing
from the spirit of the invention or the scope of the sub-
joined claims.
What is claimed is:
1. In a sputtering apparatus, including a vacuum cham-
ber, means for admitting a gas into said chamber, target
holding means for supporting the material to be sput-
tered, substrate holding means for supporting a substrate
to be coated, means for applying RF potential to said
target to sputter said material, and means for applying a
high voltage direct current to said substrate;
the improvement wherein an apertured electrode is dis-
posed between said substrate holding means and said
target holding means, said electrode being connected
to said means for applying RF potential and said
means for applying a high voltage direct current
whereby a high voltage direct current negative po-
tential with respect to said electrode is applied to
said substrate holding means and an RF potential
is applied to said target holding means to sputter said
material, and
timed switch means connected to said means for apply-
ing a high voltage direct current, said timed switch
means enabling said high voltage direct current nega-
tive potential to be pulsed from of about 15 seconds
on and about 5 minutes off.
2. Apparatus as claimed in claim 1 wherein said aper-
tured electrode is a screen.
3. Apparatus as claimed in claim 2 wherein the screen
has a centrally disposed aperture therein.
4. In an RF sputtering process wherein an RF potential
is applied to a target to sputter material from the target
onto a substrate, the improvement comprising disposing
an apertured electrode between the target and the sub-
strate, connecting said electrode to a source of RF poten-
tial and to a source of high voltage direct current, and
applying to said substrate a high voltage direct current
negative potential pulse from of about 15 seconds on and
about 5 minutes off.
5. A method as. claimed in claim 4 wherein said pulsed
voltage is a potential of about 2 to 5 kilovolts.
6. A method as claimed in claim 4 including disposing
said target about 2.5 inches from said apertured electrode
and said substrate about 6 inches from said apertured elec-
trode.
7. A method as claimed in claim 6 wherein argon is
utilized at a pressure of about 10 microns.
55
60
References Cited
UNITED STATES PATENTS
3,361,659 1/1968 Bertelsen 204—298
3,526,584 9/1970 Shaw 204—298
3,528,906 9/1970 Cash et al 204—295
3.461.054 8/1969 Uratny 204—192
3,479,269 11/1969 Byrnes et al. 204—192
3.530.055 9/1970 Maissel et al 204—192
3,589,994 6/1971 Schwartz et al. 204—192
65
JOHN H. MACK, Primary Examiner
S. S. KANTER, Assistant Examiner
U.S. Cl. X.R.
70 204—298


Method and apparatus for sputtering utilizing an apertured electrode and a pulsed substrate bias

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