U.S. patent application number 11/759606 was filed with the patent office on 2010-03-11 for system and method for plasma plating.
This patent application is currently assigned to Basic Resources, Inc.. Invention is credited to Craig D. Harrington, Daniel N. Hopkins, Jerry D Kidd.
Application Number | 20100058986 11/759606 |
Document ID | / |
Family ID | 38290282 |
Filed Date | 2010-03-11 |
United States Patent
Application |
20100058986 |
Kind Code |
A1 |
Kidd; Jerry D ; et
al. |
March 11, 2010 |
SYSTEM AND METHOD FOR PLASMA PLATING
Abstract
An exemplary system and method for plasma plating are disclosed.
The system may comprise a vacuum chamber, a filament positioned
within the vacuum chamber and operable to receive a depositant, and
a depositant positioned at the filament. The system may also
comprise a platform positioned within the vacuum chamber, a
substrate positioned at the platform, a DC power supply generating
a DC signal, a radio frequency transmitter generating a radio
frequency signal, an electrically conductive path that electrically
couples the DC signal and the radio frequency signal to the
substrate, and a filament power control electrically coupled to the
filament and generating a current through the filament at an
amplitude to generate heat in the filament to melt the
depositant.
Inventors: |
Kidd; Jerry D; (Granbury,
TX) ; Harrington; Craig D.; (Cleburne, TX) ;
Hopkins; Daniel N.; (Fort Worth, TX) |
Correspondence
Address: |
HUNTON & WILLIAMS LLP;INTELLECTUAL PROPERTY DEPARTMENT
1900 K STREET, N.W., SUITE 1200
WASHINGTON
DC
20006-1109
US
|
Assignee: |
Basic Resources, Inc.
Dallas
TX
|
Family ID: |
38290282 |
Appl. No.: |
11/759606 |
Filed: |
June 7, 2007 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
09427775 |
Oct 26, 1999 |
7250196 |
|
|
11759606 |
|
|
|
|
Current U.S.
Class: |
118/723I |
Current CPC
Class: |
C23C 14/32 20130101;
C23C 14/505 20130101 |
Class at
Publication: |
118/723.I |
International
Class: |
C23C 16/505 20060101
C23C016/505; C23C 16/00 20060101 C23C016/00 |
Claims
1. A system for plasma plating comprising: a vacuum chamber at a
pressure defined by a range that extends from 0.1 milliTorr to 4
milliTorr; a filament positioned within the vacuum chamber and
operable to receive a depositant; a depositant positioned at the
filament; a platform positioned within the vacuum chamber; a
substrate positioned at the platform; a DC power supply generating
a DC signal at a voltage amplitude defined by a range that extends
from 1 volt to 5000 volts; a radio frequency transmitter generating
a radio frequency signal at a power level defined by a range that
extends from 1 watt to 50 watts; an electrically conductive path
that electrically couples the DC signal and the radio frequency
signal to the substrate; and a filament power control electrically
coupled to the filament and generating a current through the
filament at an amplitude to generate heat in the filament to melt
the depositant.
2. The system of claim 2, further comprising a gas in the vacuum
chamber.
3. The system of claim 2, wherein the gas is a noble gas.
4. The system of claim 2, wherein the gas is an inert gas.
5. The system of claim 2, wherein the gas is argon.
6. The system of claim 1, further comprising: a vacuum system
operable to assist with maintaining the pressure in the vacuum
chamber at the pressure defined by the range that extends from 0.1
milliTorr to 4 milliTorr; and a gas flowing into the vacuum chamber
operable to assist with maintaining the pressure in the vacuum
chamber at the pressure defined by the range that extends from 0.1
milliTorr to 4 milliTorr.
7. The system of claim 1, wherein the filament and the depositant
are positioned at a distance no greater than 6 inches from the
substrate.
8. The system of claim 1, wherein the vacuum chamber is at a
pressure defined by a range that extends from 0.5 milliTorr and 1.5
milliTorr.
9. The system of claim 1, wherein the DC power supply is generating
a DC signal at a voltage amplitude defined by a range that extends
from 500 volts to 750 volts.
10. The system of claim 1, wherein the DC signal is provided at a
negative polarity.
11. The system of claim 1, wherein the radio frequency transmitter
is generating a radio frequency signal at a power level defined by
a range that extends from 5 watt to 15 watts.
12. The system of claim 1, wherein the vacuum chamber is at a
pressure defined by a range that extends from 0.5 milliTorr and 1.5
milliTorr, the DC power supply is generating a DC signal at a
voltage amplitude defined by a range that extends from negative 500
volts to negative 750 volts, and the radio frequency transmitter is
generating a radio frequency signal at a power level defined by a
range that extends from 5 watt to 15 watts.
13. The system of claim 1, further comprising: a DC signal/radio
frequency signal mixer mixing the DC signal and the radio frequency
signal before the electrically conductive path electrically couples
the DC signal and the radio frequency signal to the substrate.
14. The system of claim 13, further comprising: a radio frequency
balancing network receiving the DC signal and the radio frequency
signal generated by the DC signal/radio frequency signal mixer and
minimizing the standing wave reflected power.
15. The system of claim 14, wherein the minimizing the standing
wave reflected power is performed using an automatic control.
16. The system of claim 14, wherein the minimizing the standing
wave reflected power is performed using a manual control.
17. The system of claim 1, wherein a magnet is not introduced to
produce a magnetic field near the substrate.
Description
CROSS-REFERENCE TO RELATED APPLICATIONS
[0001] This patent application is a divisional of U.S. patent
application Ser. No. 09/427,775, filed Oct. 26, 1999, which is
hereby incorporated by reference herein in its entirety.
FIELD OF THE INVENTION
[0002] This invention relates in general to the field of deposition
to technology for plating and coating materials and, more
particularly, to a system and method for plasma plating.
BACKGROUND OF THE INVENTION
[0003] Various deposition technologies exist for plating and
coating materials. These various technologies include, for example,
vacuum deposition or physical vapor deposition ("PVD"), chemical
vapor deposition ("CVD"), sputtering, and ion plating. All of these
deposition technologies suffer from disadvantages such as poor
deposition layer adhesion, high cost, generation of environmentally
wasteful products that are expensive and cumbersome to dispose,
damage to the substrate, elevated substrate temperatures,
non-uniform deposition layers, inefficient use of expensive
depositants, and inconsistent application of deposition layers are
among some of the disadvantages suffered by one or more of the
prior deposition technologies.
SUMMARY OF THE INVENTION
[0004] From the foregoing it may be appreciated that a need has
arisen for a system and method for plasma plating that generates a
controllable and repeatable deposition layer on a substrate. In
accordance with the present invention, a system and method for
plasma plating are provided that substantially eliminate one or
more of the disadvantages and problems outlined above.
[0005] According to an aspect of the present invention, a method
for plasma plating is provided to generate a deposition layer on a
substrate. The method for plasma plating includes positioning a
substrate within a vacuum chamber, positioning a depositant in a
filament within the vacuum chamber, reducing the pressure in the
vacuum chamber to a level at or below 4 milliTorr, and introducing
a gas into the vacuum chamber at a rate to raise the pressure in
the vacuum chamber to a level at or between 0.1 milliTorr and 4
milliTorr. In other embodiments, the gas is not required to be
introduced. The method also includes applying a DC signal to the
substrate at a voltage amplitude at or between 1 volt to 5000
volts, applying a radio frequency signal to the substrate at a
power level at or between 1 watt and 50 watts, and heating the
depositant to a temperature at or above the melting point of the
depositant to generate a plasma in the vacuum chamber. The plasma
will preferably include both positively charged gas and depositant
ions that will be attracted to the substrate, which will,
preferably, be provided at a negative potential if the DC signal is
provided at a negative polarity.
[0006] According to another aspect of the present invention, an
system for plasma plating is provided that generates a deposition
layer on a substrate. The system for plasma plating includes a
vacuum chamber at a pressure that extends from 0.1 milliTorr to 4
milliTorr, a filament with an associated depositant located on or
in the filament, a platform positioned within the vacuum chamber, a
substrate positioned at or on the platform, a DC power supply
generating a DC signal at a voltage in a range that extends from 1
volt to 5000 volts, a radio frequency transmitter generating a
radio frequency signal at a power level defined by a range that
extends from 1 watt to 50 watts, an electrically conductive path
that electrically couples the DC signal and the radio frequency
signal to the substrate, and a filament power control electrically
coupled to the filament and generating a current through the
filament at an amplitude to generate heat in the filament to melt
the depositant.
[0007] The present invention provides a profusion of technical
advantages that include the capability to controllably, repeatably,
and reliably plate a substrate using plasma plating to develop a
deposition layer with a high adherence to the substrate.
[0008] Another technical advantage of the present invention
includes the capability to control the thickness of the deposition
layer to around 500 Angstroms, while developing a more uniform
deposition layer thickness that is repeatable from one application
to the next.
[0009] Another technical advantage of the present invention
includes the capability to efficiently use depositants to minimize
the consumption of depositants, which often are expensive precious
metals such as gold and even platinum. These efficiencies are
achieve through the proper placement of filaments and the use of
proper operational parameters. This significantly reduces overall
costs.
[0010] Yet another technical advantage of the present invention
includes the capability to perform plasma plating without heating
up the substrate to extreme temperatures that often damage the
substrate through molecular and/or metallurgical changes. This
ensures that a deposition layer can be developed without the danger
of possibly unknowingly damaging a substrate. This is especially
significant when the failure of a substrate in its system or
intended use results in a safety hazard. This also provides the
significant advantage of allowing the substrate to be handled and
used immediately after the plasma plating process.
[0011] Still yet another technical advantage of the present
invention includes the capability to perform plasma plating without
bombarding the substrate with high energy ions, like ion plating,
which could damage or alter the substrate through molecular,
metallurgical, and possibly chemical changes. This is because
plasma plating is believed to be achieved at medium energy levels,
such as at a medium energy level on the average of between 10 eV
and 90 eV, such that good adhesion is achieved but no metallurgical
or chemical changes occur to the substrate due to the relatively
shallow depth of embedment of the deposition layer.
[0012] Still yet another technical advantage includes the
capability plate a substrate with a deposition layer with a
thickness that is small enough so as not to change the functional
shape of the substrate, such as a bolt, a nut, a fastener, and
other components with strict tolerances. The present invention will
also work in the presence of an oxidation layer.
[0013] Yet another technical advantage includes the capability to
plate a substrate with a deposition layer without generating waste
by products or any environmentally hazardous waste. This is
significant.
[0014] Other technical advantages are readily apparent to one
skilled in the art from the following figures, description, and
claims.
BRIEF DESCRIPTION OF THE DRAWINGS
[0015] For a more complete understanding of the present invention
and the advantages thereof, reference is now made to the following
brief description, taken in connection with the accompanying
drawings and detailed description, wherein like reference numerals
represent like parts, in which:
[0016] FIG. 1 is a schematic diagram that illustrates a system for
plasma plating that can be used to plate materials, according to an
embodiment of the present invention;
[0017] FIG. 2 is a top view of a vacuum chamber of a system for
plasma plating that illustrates one embodiment of a platform
implemented as a turntable;
[0018] FIG. 3 is a side view that illustrates the formation and
dispersion of a plasma around a filament to plasma plate a
substrate according to an embodiment of the present invention;
[0019] FIG. 4 is a sectional view that illustrates a deposition
layer that includes a base layer, a transition layer, and a working
layer;
[0020] FIG. 5 is a flowchart that illustrates a method for plasma
plating according to an embodiment of the present invention;
and
[0021] FIG. 6 is a flowchart that illustrates a method for
backsputtering using the system of the present invention, according
to an embodiment of the present invention.
DETAILED DESCRIPTION OF THE INVENTION
[0022] It should be understood at the outset that although an
exemplary implementation of the present invention is illustrated
below, the present invention may be implemented using any number of
techniques, whether currently known or in existence. The present
invention should in no way be limited to the exemplary
implementations, drawings, and techniques illustrated below,
including the exemplary design and implementation illustrated and
described herein.
[0023] FIG. 1 is a schematic diagram that illustrates a system 10
for plasma plating that can be used to plate any of a variety of
materials, according to an embodiment of the present invention. The
system 10 includes various equipment used to support the plasma
plating of a substrate 12 within a vacuum chamber 14. Once
appropriate operating parameters and conditions are achieved, a
depositant provided in a filament 16 and a filament 18 may be
evaporated or vaporized to form a plasma. The plasma will contain,
generally, positively charged ions from the depositant and will be
attracted to the substrate 12 where they will form a deposition
layer. The plasma may be thought of as a cloud of ions that
surround or are located near the substrate 12. The plasma will
generally develop a dark region, near the closest surface of the
substrate 12 from the filament 12 and the filament 18, that
provides acceleration of the positive ions into the substrate
12.
[0024] The filament 12 and the filament 14 reside within the vacuum
chamber 14 along with a platform 20, which supports the substrate
12. A drive assembly 22 is shown coupled between a drive motor 24
and a main shaft of the platform 20 within the vacuum chamber 14.
In the embodiment shown in FIG. 1, the platform 20 is provided as a
turntable that rotates within the vacuum chamber 14. The drive
assembly 22 mechanically links the rotational motion of the drive
motor 24 with the main shaft of the platform 20 to impart rotation
to the platform 20. The rotation of the main shaft of the platform
20 is enhanced through various support bearings such as a base
plate bearing 28 and a platform bearing 30.
[0025] As is illustrated, the vacuum chamber 14 resides or is
sealed on a base plate 32. The vacuum chamber 14 may be provided
using virtually any material that provides the appropriate
mechanical characteristics to withstand an internal vacuum and an
external pressure, such as atmospheric pressure. For example, the
vacuum chamber 14 may be provided as a metal chamber or as a glass
bell. In an alternative embodiment, the base plate 32 serves as the
platform 20 to support the substrate 12. The base plate 32 may be
thought of as part of the vacuum chamber 14.
[0026] The base plate 32 also provides mechanical support for the
system 10 while allowing various devices to feed through from its
bottom surface to its top surface within the vacuum chamber 14. For
example, the filament 16 and the filament 18 receive power from a
filament power control module 34. It should be noted that although
two filament power control modules 34 are shown in FIG. 1,
preferably, these two modules are implemented as one module. In
order to provide power to the filament 16 and the filament 18,
electrical leads must feed through the base plate 32 as illustrated
in FIG. 1. Similarly, the drive motor 24 must also penetrate or
feed through the base plate 32 to provide mechanical action to the
drive assembly 22 so that the platform 20 may be rotated. The
electrical feed through 26, described more fully below, also feeds
through the base plate 32 and provides an electrical conductive
path between the platform 20 and various signal generators, also
described more fully below. In a preferred embodiment, the
electrical feed through 26 is provided as a commutator that
contacts the bottom surface of the platform 20, in the embodiment
where the platform 20 is implemented as a turntable. The electrical
feed through 26 may be implemented as a commutator and may be
implemented as a metal brush which can contact the bottom surface
of the platform 20 and maintain an electrical contact even if the
platform 20 rotates.
[0027] The filament power control module 34 provides an electric
current to the filament 16 and the filament 18. In one embodiment,
the filament power control module 34 can provide current to the
filament 16 for a particular duration, and then provide current to
the filament 18 during a second duration. Depending upon how the
filaments are configured, the filament power control module 34 may
provide current to both the filament 16 and the filament 18 at the
same time or during separate intervals. This flexibility allows
more than one particular depositant material to be plasma plated
onto the substrate 12 at different times. The filament power
control module 34 preferably provides alternating current to the
filaments, but may provide a current using any known method of
generating current. In a preferred embodiment, the filament power
control module 34 provides current at an amplitude or magnitude
that is sufficient to generate enough heat in the filament 16 to
evaporate or vaporize the depositant.
[0028] In order to ensure even heating of the depositant, which
will be provided at or in the filament 16 or the filament 18, the
current provided by the filament control module 34 will preferably
be provided using incremental staging so that a more even heat
distribution will occur in the depositant that is being melted
within the vacuum chamber 14.
[0029] In a preferred embodiment, the platform 20 is implemented as
a turntable and rotates using the mechanical linkage as described
above. A speed control module 36, as shown in FIG. 1, may be
provided to control the speed of the rotation of the platform 20.
Preferably, the rotation of the platform 20 occurs at a rate from
five revolutions per minutes to 30 revolutions per minute. It is
believed that an optimal rotational rate of the platform 20 for
plasma plating is provided at a rotational rate of 12 revolutions
per minute to 15 revolutions per minute. The advantages of rotating
the platform 20 are that the substrate 12 can be more evenly plated
or coated. This is especially true when multiple substrates are
provided on the surface of the platform 20. This allows each one of
the multiple substrates to be similarly positioned, on average,
within the vacuum chamber 14 during the plasma plating process.
[0030] In other embodiments, the platform 20 may be provided at
virtually any desired angle or inclination. For example, the
platform 20 may be provided as a flat surface, a horizontal
surface, a vertical surface, an inclined surface, a curved surface,
a curvilinear surface, a helical surface, or as part of the vacuum
chamber such as a support structure provided within the vacuum
chamber. As mentioned previously, the platform 20 may be stationary
or rotate. In an alternative embodiment, the platform includes
rollers that may be used to rotate one or more substrates.
[0031] The platform 20, in a preferred embodiment, provides or
includes an electrically conductive path to provide a path between
the electrical feed through 26 and the substrate 12. In one
embodiment, platform 20 is provided as a metal or electrically
conductive material such that an electrically conductive path is
provided at any location on the platform 20 between the electrical
feed through 26 and the substrate 12. In such as a case, an
insulator 21, will be positioned between the platform 20 and the
shaft that rotates the platform 20 to provide electrical
isolation.
[0032] In another embodiment, the platform 20 includes electrically
conductive material at certain locations on its top surface that
electrically coupled to certain locations on the bottom surface. In
this manner, the substrate 12 can be placed at an appropriate
location on the top side of the platform 20 while the electrical
feed through 26 may be positioned or placed at an appropriate
location on the bottom side of the platform 20. In this manner, the
substrate 12 is electrically coupled to the electrical feed through
26.
[0033] The electrical feed through 26 provides a DC signal and a
radio frequency signal to the platform 20 and the substrate 12. The
desired operational parameters associated with each of these
signals are described more fully below. Preferably, the DC signal
is generated by a DC power supply 66 at a negative voltage and the
radio frequency signal is generated by an RF transmitter 64 at a
desired power level. The two signals are then preferably mixed at a
DC/RF mixer 68 and provided to the electrical feed through 26
through an RF balancing network 70, which provides signal balancing
by minimizing the standing wave reflected power. The RF balancing
network 70 is preferably controlled through a manual control.
[0034] In an alternative embodiment, the platform 20 is eliminated,
including all of the supporting hardware, structures, and
equipment, such as, for example, the drive motor 24, and the drive
assembly 22. In such a case the substrate 12 is electrically
coupled to the electrical feed through 26.
[0035] The remaining equipment and components of the system 10 of
FIG. 1 are used to create, maintain, and control the desired vacuum
condition within the vacuum chamber 14. This is achieved through
the use of a vacuum system. The vacuum system includes a roughing
pump 46 and a roughing valve 48 that is used to initially pull down
the pressure in the vacuum chamber 14. The vacuum system also
includes a foreline pump 40, a foreline valve 44, a diffusion pump
42, and a main valve 50. The foreline valve 44 is opened so that
the foreline pump 40 can began to function. After the diffusion
pump 42 is warmed or heated to an appropriate level, the main valve
50 is opened, after the roughing pump 40 has been shut in by
closing the roughing valve 44. This allows the diffusion pump 42 to
further reduce the pressure in the vacuum chamber 14 below a
desired level.
[0036] A gas 60, such as argon, may then be introduced into the
vacuum chamber 14 at a desired rate to raise the pressure in the
vacuum chamber 14 to a desired pressure or to within a range of
pressures. A gas control valve controls the rate of the flow of the
gas 60 into the vacuum chamber 14 through the base plate 32.
[0037] Once all of the operating parameters and conditions are
established, as will be described more fully below in connection
with FIGS. 5 and 6 according to the teachings of the present
invention, plasma plating occurs in system 10. The substrate 12 may
be plasma plated with a deposited layer, which may include one or
more layers such as a base layer, a transitional layer, and a
working layer, through the formation of a plasma within the vacuum
chamber 14. The plasma will preferably include positively charged
depositant ions from the evaporated or vaporized depositant along
with positively charged ions from the gas 60 that has been
introduced within the vacuum chamber 14. It is believed, that the
presence of the gas ions, such as argon ions, within the plasma and
ultimately as part of the depositant layer, will not significantly
or substantially degrade the properties of the depositant layer.
The introduction of the gas into the vacuum chamber 14 is also
useful in controlling the desired pressure within the vacuum
chamber 14 so that a plasma may be generated according to the
teachings of the present invention. In an alternative embodiment,
the plasma plating process is achieved in a gasless environment
such that the pressure within the vacuum chamber 14 is created and
sufficiently maintained through a vacuum system.
[0038] The generation of the plasma within the vacuum chamber 14 is
believed to be the result of various contributing factors such as
thermionic effect from the heating of the depositant within the
filaments, such as the filament 16 and the filament 18, and the
application of the DC signal and the radio frequency signal at
desired voltage and power levels, respectively.
[0039] The vacuum system of the system 10 may include any of a
variety of vacuum systems such as a diffusion pump, a foreline
pump, a roughing pump, a cryro pump, a turbo pump, and any other
pump operable or capable of achieving pressures within the vacuum
chamber 14 according to the teachings of the present invention.
[0040] As described above, the vacuum system includes the roughing
pump 46 and the diffusion pump 42, which is used with the foreline
pump 40. The roughing pump 46 couples to the vacuum chamber 14
through the roughing valve 48. When the roughing valve 48 is open,
the roughing pump 46 may be used to initially reduce the pressure
within the vacuum chamber 14. Once a desired lower pressure is
achieved within the vacuum chamber 14, the roughing valve 48 is
closed. The roughing pump 46 couples to the vacuum chamber 14
through a hole or opening through the base plate 32. The roughing
pump 46 will preferably be provided as a mechanical pump. In a
preferred embodiment of the vacuum system of the system 10 as shown
in FIG. 1. The vacuum system in this embodiment includes a foreline
pump coupled to a diffusion pump 42 through a foreline valve 44.
The foreline pump 40 may be implemented as a mechanical pump that
is used in combination with the diffusion pump 42 to reduce the
pressure within the vacuum chamber 14 to a level even lower than
that which was produced through the use of the roughing pump
46.
[0041] After the roughing pump has reduced the pressure within the
vacuum chamber 14, the diffusion pump 42, which uses heaters and
may require the use of cooling water or some other substance to
cool the diffusion pump 42, couples with the vacuum chamber 14
through a main valve 50 and through various holes or openings
through the base plate 32 as indicated in FIG. 1 by the dashed
lines above the main valve 50 and below the platform 20. Once the
diffusion pump 42 has been heated up and made ready for operation,
the main valve 50 may be opened so that the pressure within the
vacuum chamber 14 may be further reduced through the action of the
diffusion pump 42 in combination with the foreline pump 44. For
example, the pressure within the vacuum chamber 14 may be brought
below 4 milliTorr. During a backsputtering process, the pressure in
the vacuum chamber 14 may be dropped to a level at or below 100
milliTorr on down to 20 milliTorr. Preferably, the pressure within
the vacuum chamber 14 during a backsputtering process will be at a
level at or below 50 milliTorr on down to 30 milliTorr. During
normal operation of the system 10 during a plasma plating process,
the pressure within the vacuum chamber 14 may be reduced by the
vacuum system to a level at or below 4 milliTorr on down to a value
of 0.1 milliTorr. Preferably, the vacuum system will be used during
a plasma plating process to reduce the pressure within the vacuum
chamber 14 to a level at or below 1.5 milliTorr on down to 0.5
milliTorr.
[0042] FIG. 2 is a top view of a vacuum chamber of a system for
plasma plating that illustrates one embodiment of a platform
implemented as a turntable 20. The turntable 20 is shown with
substrates 12a, 12b, 12c, and 12d positioned, symmetrically on the
surface of the turntable 20. The turntable 20 may rotate either
clockwise or counterclockwise. The substrates 12a-12d may be
virtually any available material and are shown in FIG. 2 as round,
cylindrical components such that the top view of each of the
substrates presents a circular form.
[0043] The filament power control module 34 is electrically coupled
to a first set of filaments 94 and 96 and a second set of filaments
90 and 92. Although the electrical connections are not fully
illustrated in FIG. 2, it should be understood that the filament
power control module 34 may supply current to the first set of
filaments 94 and 96 or to the second set of filaments 90 and 92. In
this manner, the deposition layer may be provided with two
sublayers such as a base layer and a working layer. The base layer
will preferably be applied first through depositants provided in
the first set of filaments 94 and 96 while the working layer will
be deposited on the base layer of the substrates 12a-12d using the
depositants provided at the second set of filaments 90 and 92.
[0044] The arrangement of the substrates in FIG. 2 may be described
as an array of substrates that include inwardly facing surfaces,
which are closer to the center of the turntable 20, and outwardly
facing surfaces, which are closer to the outer edge of the
turntable 20. For example, the inwardly facing surfaces of the
array of substrates 12a-d will be presented to the filament 92 and
the filament 96, at different times of course, as they are rotated
near the filaments. Similarly, the outwardly facing surfaces of the
substrates 12a-d will be presented to the filaments 90 and 94 as
they rotate near these filaments.
[0045] As mentioned previously, the filament power control module
34 may provide a current in virtually any form, such as a direct
current or an alternating current, but preferably provides current
as an alternating current.
[0046] In operation, turntable 20 rotates, for example, in a
clockwise direction such that after substrate 12b passes near or
through the filaments, the next substrate that will pass near or
through the filaments is substrate 12c, and so on. In one example,
the first set of filaments 94 and 96 are loaded with a depositant,
such as nickel (or titanium), and the second set of filaments are
loaded with a depositant such as the metal alloy silver\palladium.
This example illustrates a two shot application or a two layer
deposition layer.
[0047] After all of the operating parameters have been established
within the vacuum chamber, as described throughout herein, the
filament power control module 34 may energize or provide
alternating current to the first set of filaments 94 and 96 so that
the nickel will evaporate or vaporize to form a plasma with the
gas, such as argon gas, within the vacuum chamber. The positively
charged nickel ions and the positively charged argon ions in the
plasma will be attracted to the substrates 12a-d, which are at a
negative potential. Generally, the closer the substrate is to the
first set of filaments 90 and 92 as it rotates, the more material
will be deposited. Because the turntable is rotating, a uniform or
more even layer will be applied to the various substrates.
[0048] After the first plasma has been plated onto the array of
substrates 12a-d to form a base layer of the depositant layer on
the substrates, the filament power control module 34 is energized
so that a sufficient amount of current is provided to the second
set of filaments 90 and 92. Similarly, a plasma is formed between
the argon ions and the silver\palladium ions and the working layer
is then formed to the substrates that are being rotated.
[0049] During the first shot when the base layer is being applied,
the outwardly facing surfaces of substrates 12a-d are primarily
coated through the nickel depositant located in the filament 94.
Similarly, the inwardly facing surfaces of the substrates are
coated by the nickel depositant located in the filament 96. The
same relation holds true for the second shot where the
silver\palladium is plasma plated onto the substrates to form the
deposit layer.
[0050] FIG. 3 is a side view that illustrates the formation and
dispersion of a plasma around a filament 100 to plasma plate a
substrate 12 according to an embodiment of the present invention.
The filament 100 is implemented as a wire basket, such as tungsten
wire basket, and is shown with a depositant 102 located, and
mechanically supported, within the filament 100. As the filament
power control module 34 provides sufficient current to the filament
100, the depositant 102 melts or vaporizes and a plasma 104 is
formed. Of course, all of the operating parameters of the present
invention must be present in order to achieve the plasma state so
that plasma plating may takes place.
[0051] The substrate 12, which is provided at a negative potential,
attracts the positive ions of the plasma 104 to form a deposition
layer. As is illustrated, the dispersion pattern of the plasma 104
results in most of the positive ions of the plasma 104 being
attracted to the side adjacent or nearest to the filament 100 and
the depositant 102. Some wrap around will occur such as that
illustrated by the plasma 104 contacting the top surface of the
substrate 12. Similarly, some of the positive ions of the plasma
104 may be attracted to the platform or turntable. As is
illustrated, the present invention provides an efficient solution
for the creation of a deposition layer by ensuring that most of the
ions from the depositant are used in the formation of the
deposition layer.
[0052] FIG. 4 is a sectional view that illustrates a deposition
layer of the substrate 12 that includes a base layer 110, a
transition layer 112, and a working layer 114. It should be noted
at the outset that the thickness of the various layers that form
the deposition layer are grossly out of proportion with the size of
the substrate 12; however, the relative thicknesses of the various
sublayers or layers of the deposition layer are proportionate to
one another, according to one embodiment of the present
invention.
[0053] Generally, the thickness of the entire deposition layer on
the substrate, according to the teachings of the present invention,
are believed to generally range between 500 and 20,000 Angstroms.
In a preferred embodiment, the entire thickness of the deposition
layer is believed to range between 3,000 and 10,000 Angstroms. The
present invention provides excellent repeatability and
controllability of deposition layer thicknesses, including all of
the sublayers such as the base layer 110, the transition layer 112,
and the working layer 114. It is believed that the present
invention can provide a controllable layer thickness at an accuracy
of around 500 Angstroms. It should also be mentioned that the
present invention may be used to form a deposition layer with one
or any multiple of sublayers.
[0054] The thickness of the deposition layer is normally determined
based on the nature of intended use of the plasma plated substrate.
This may include such variables as the temperature, pressure, and
humidity of the operating environment, among many other variables
and factors. The selection of the desired metal or depositant type
for each layer is also highly dependant upon the nature of the
intended use of the plasma plated substrate.
[0055] For example, the present invention prevents or substantially
reduces galling or mating or interlocking components. Galling
includes the seizure of mated components that often occur when two
surfaces, such as threaded surfaces, are loaded together. Galling
can cause components to fracture and break, which often results in
severe damage. Plasma plating may be used to prevent or reduce
galling by plating one or more contacting surfaces.
[0056] Various depositants may be used to achieve this beneficial
effect. It is believed, however, that galling is preferably reduced
through a plasma plating process that deposits a base layer of
nickel or titanium and a working layer of a silver/palladium metal
alloy on one or more contacting surfaces. For high temperature
applications, such as over 650 degrees Fahrenheit, it is believed
that the galling is preferably reduced through a plasma plating
process that deposits a nickel or titanium base layer and a working
layer of gold.
[0057] It has been found through experimentation that chromium does
not work well to reduce galling, this includes when the chromium is
deposited as either the base layer, the transition layer, or the
working layer. It is believed that chromium may be a depositant
that is more difficult to control during the plasma plating
process.
[0058] Plasma plating may also be used to plate valve parts, such
as valve stems in non-nuclear applications, and are preferably
plasma plated using a titanium base layer, a gold transition layer,
and an indium working layer. In nuclear applications, such as
nuclear power plant applications, indium is not a preferred plasma
plating depositant because it is considered to be too much of a
radioactive isotope absorber. Instead, valve stems in nuclear
applications are preferably plasma plated using a nickel base layer
and a silver/palladium metal alloy working layer.
[0059] As is illustrated in FIG. 4, the working layer 14 is
normally provided at a substantially larger thickness than the
corresponding transition layer 112 and the base layer 110. It
should also be noted that the coating of the top of the substrate
12 is shown to be thin at or near the center or middle of the
substrate 12. This effect is due to how the filaments are
positioned during the plasma plating process. For example, if the
filaments are positioned similarly to that illustrated in FIGS.
2-3, the middle or center portion of the substrate 12 will
generally have a thinner overall profile than the side of the
deposition layer.
[0060] Although various ranges of thicknesses have been discussed
herein, it should be understood that the present invention is not
limited to any maximum deposition layer thickness. The thickness of
the deposition layer, especially the thickness of the working layer
114, can be provided at virtually any desired thickness, normally
depending upon the operating environment in which the plasma plated
substrate 12 will be introduced. The base layer 110 and the
transition layer 112 and any other layers below the working layer
114 will preferably be provided at a substantially smaller
thickness than the corresponding thickness of the working layer
114. For example, the base layer 110 and the transition layer 112
may be provided at a thickness ranging from 500 to 750 Angstroms
while the working layer 114 may be provided at virtually any
thickness such as for example 18,000 Angstroms.
[0061] FIG. 5 is a flow chart of a method 500 for plasma plating
according to an embodiment of the present invention. The method 500
begins at block 502 and proceeds to block 504. At block 504, the
material or substrate that will be plasma plated is prepared for
the process. This may include cleaning the substrate to remove any
foreign materials, contaminants, and oils. Any of a variety of
known cleaning processes may be used such as those defined by the
Steel Structures Painting Council (SSPC). For example, the SSPC-5
standard may be employed to ensure that a substrate is cleaned to a
white metal condition. Similarly, the SSPC-10 standard may be
employed. Preferably, the substrate will undergo an abrasive
blasting, such as for example, bead blasting to further ensure that
any foreign materials or contaminants are removed. It should be
noted that an oxidation layer may be present on the surface of the
substrate. The present invention allows for a deposition layer to
be plasma plated onto the substrate surface, even in the presence
of an oxidation layer, with excellent adhesion and mechanical
properties.
[0062] The method 500 proceeds next to block 506 where the plasma
plating system prerequisites are established. Depending upon the
implementation of the system for plasma plating, this may involve
any of a variety of items. In the situation where a diffusion pump
is used as part of the vacuum system, items such as the
availability of cooling water must be established. Similarly, the
adequate availability of lube oil and air to operate the various
equipment, valves, and machinery associated with the system for
plasma plating must be established. An adequate supply of gas, such
as argon gas, should also be verified and checked at this point
before proceeding to block 510.
[0063] At block 510, assuming that a diffusion pump is used as part
of the vacuum system, the diffusion pump is prepared for operation.
This may include opening a foreline valve and the starting of the
foreline vacuum pump which is used in combination with the
diffusion pump. Once a foreline vacuum has been drawn, the heaters
of the diffusion pump may be energized. This places the diffusion
pump in service.
[0064] The method 500 proceeds next to block 512 where the vacuum
chamber is set up. This includes any number of processes such as
positioning the substrate within the vacuum chamber. This is
normally achieved by positioning or placing the substrate at a
specified location on a platform or turntable located within the
vacuum chamber. Before accessing the internal volume of the vacuum
chamber, the vacuum chamber seal must be broken and the bell jar or
outer member is preferably lifted away from its base plate. Once
the substrate is positioned on the platform, the filaments may be
positioned relative to the placement of the substrate.
[0065] The positioning of the filaments may involve any number of
techniques and includes such variables as the amount and type of
depositant to be provided at the filament, and the distance, not
only relative to the substrate, but relative to other filaments.
Generally, the filament will be located a distance ranging from 0.1
inches to 6 inches from the substrate, as measured from the center
line of the filament, or from the depositant, to the closest point
of the substrate. Preferably, however, the distance between the
filament or the depositant and the substrate will range anywhere
from 2.75 inches to 3.25 inches when the depositant will serve as
the base layer or transition layer of the deposition layer.
Similarly, when the depositant will serve as the working layer of
the deposition layer that will be deposited on the substrate, the
distance between the filament or the depositant and the substrate
is preferably provided at a distance between 2 inches and 2.5
inches.
[0066] In the situation where multiple depositants or multiple
shots will be performed in the plasma plating process, it is
necessary to consider the placement of the filaments that will hold
the first depositant relative to those that will hold the second
depositant as well as each of the filament's position relative to
each other and the substrate. Generally the distance of a second
filament from a first filament, which will include a depositant
that will serve as a base layer, transition layer, or a working
layer of a deposition layer, should be anywhere between 0.1 inches
and 6 inches.
[0067] The spacing between filaments that include depositants that
will serve as a base layer, is generally provided between 0.1
inches and 6 inches. Preferably, this distance shall be between 3
inches and 4 inches. The foregoing filament spacing information
also applies when the depositant provided in the filaments will
serve as the transition layer in the deposition layer. Similarly,
the spacing between filaments, which include a depositant that will
serve as the working layer of the deposition layer, should
generally be between 0.1 inches and 6 inches, but, preferably, will
be between 2.5 inches and 3 inches.
[0068] The chamber setup of block 512 may also need to take into
account the arrangement of an array of substrates on the platform
that are being plasma plated. For example, a filament that is
positioned in the vacuum chamber so that it will provide a
dispersion pattern to provide depositant coverage to inwardly
facing surfaces of an array of substrates, it may require anywhere
from 20 to 80 percent less mass or weight of depositant when
compared with a filament positioned in the vacuum chamber to
provide coverage for the array of outwardly facing surfaces. The
reference to inwardly and outwardly are relative to the platform or
turntable with inwardly referring to those surfaces closer to the
center of the platform or turntable. This is because the efficiency
of the plasma plating process is greater for the inwardly facing
surfaces of an array of substrates than at the outwardly facing
surfaces of the array of substrates because of the forces
attracting the, generally, positive ions of the plasma. This also
ensures that the thickness of the deposition layer on the inwardly
facing surfaces and the outwardly facing surfaces are more uniform.
In such a case, the weight or mass of the depositant will,
preferably, need to vary between such filament positions.
Generally, the variance in mass or weight between the two locations
may be anywhere from 20 to 80 percent different. Preferably, the
depositants in the filaments covering the inwardly facing surfaces
will use 40 to 50 percent less mass or weight than the depositants
of the filaments covering the outwardly facing surfaces. The amount
of the depositant placed in the filaments corresponds to the
desired thickness of the deposition layer, and any sublayers
thereof. This was discussed more fully and is illustrated more
fully in connection with FIG. 3.
[0069] The type of filament affects the dispersion pattern achieved
through the melting or evaporation of its depositant during the
creation of the plasma. Any of a variety of filament types, shapes,
and configurations may be used in the present invention. For
example, the filament may be provided as a tungsten basket, a boat,
a coil, a crucible, a ray gun, an electron beam gun, a heat gun, or
as any other structure, such as a support structure provided within
the vacuum chamber. The filaments are generally heated through the
application of an electric current through the filament. However,
any method or means of heating the depositant within the filament
may be used in the present invention.
[0070] The setup of the vacuum chamber also includes placing the
depositants in the one or more filaments. The present invention
contemplates the use of virtually any material that is capable of
being evaporated under the conditions and parameters of the present
invention so that a plasma will form. For example, the depositant
may include virtually any metal, such as a metal alloy, gold,
titanium, chromium, nickel, silver, tin, indium, lead, copper,
palladium, silver/palladium and any of a variety of others.
Similarly, the depositant may include any other materials such as
carbon, nonmetals, ceramics, metal carbides, metal nitrates, and
any of a variety of other materials. The depositants will generally
be provided in a pellet, granule, particle, powder, wire, ribbon,
or strip form. Once the filaments have been properly positioned and
loaded, the vacuum chamber may be closed and sealed. This may
include sealing the bell portion of the vacuum chamber with its
base plate.
[0071] The method 500 proceeds next to block 514 where preparations
are made to begin establishing a vacuum condition within the vacuum
chamber. In one embodiment, such as the system 10 shown in FIG. 1,
a roughing pump is started to begin evacuating the vacuum chamber
and to bring the pressure down within the vacuum chamber to a
sufficient level so that additional pumps may take over to further
reduce the pressure within the vacuum chamber. In one embodiment,
the roughing vacuum pump is a mechanical pump that may be started,
and a roughing valve may then be opened to provide access to the
vacuum chamber. Once the roughing vacuum pump has achieved its
desired function and has reduced the pressure in the vacuum chamber
to its desired or designed level, the roughing valve is shut. At
this point, the method 500 transitions to block 516.
[0072] At block 516, the pressure within the vacuum chamber is
further reduced using another vacuum pump. For example, in one
embodiment, a diffusion pump/foreline pump is utilized to further
reduce the pressure within the vacuum chamber. In the embodiment of
the present invention as illustrated in FIG. 1, this is achieved by
opening the main valve and allowing the diffusion pump, supported
by the mechanical foreline pump, to further pull or reduce the
pressure in the vacuum chamber.
[0073] Generally, the pressure in the vacuum chamber is reduced to
a level that is at or below 4 milliTorr. Preferably, the pressure
in the vacuum chamber is reduced to a level that is at or below 1.5
milliTorr. In the event that backsputtering, which is described
below in connection with block 518 of the method 500, is to be
performed, the pressure in the vacuum chamber is reduced to a level
below 100 milliTorr and generally in a range between 20 milliTorr
and 100 milliTorr. In a preferred embodiment when backsputtering is
to be performed, the pressure is reduced in the vacuum chamber at a
level below 50 milliTorr, and generally at a level between 20
milliTorr and 50 milliTorr.
[0074] Preceding next to block 518, a backsputtering process may be
performed to further clean and prepare the substrate. It should be
understood, however, that such a process is not mandatory. The
backsputtering process is described in more detail below in
connection with FIG. 6. The backsputtering process may include the
rotation of the platform or turntable within the vacuum chamber. In
such a case, the turntable will generally be rotated at a rate at
or between 5 revolutions per minute and 30 revolutions per minute.
Preferably, the turntable will be rotated at a rate between 12
revolutions per minute and 15 revolutions per minute. The operation
of the turntable, which also will preferably be used as the
deposition layer is being formed on the substrate according to the
teachings of the present invention.
[0075] Method 500 proceeds next to block 520 where an operating
vacuum is established. Although a vacuum condition has already been
established within the vacuum chamber, as previously discussed in
connection with block 514 and 516, an operating vacuum can now be
established through the introduction of a gas into the vacuum
chamber at a flow rate that will raise the pressure in the vacuum
chamber to a level generally at or between 0.1 milliTorr and 4
milliTorr. Preferably, the introduction of the gas is used to raise
the pressure in the vacuum chamber to a level that is at or between
0.5 milliTorr and 1.5 milliTorr. This will ensure that there are no
depositant ion collisions within the plasma, which will increase
the depositant efficiency and provide a clean, highly adhered
deposition layer to the substrate. The gas that is introduced into
the vacuum chamber may be any of a variety of gases but will
preferably be provided as an inert gas, a noble gas, a reactive gas
or a gas such as argon, xenon, radon, helium, neon, krypton,
oxygen, nitrogen, and a variety of other gases. It is desirable
that the gas is a noncombustible gas. It should be understood that
the present invention does not require the introduction of a gas
but may be performed in the absence of a gas.
[0076] At block 522, various operating parameters and values of the
system are established. This will generally include the rotation of
a turntable, if desired, the application of a DC signal, and the
application of a radio frequency signal. Assuming that the platform
includes a turntable or some other rotating device, the turntable
rotation will preferably be established at this point. This
assumes, of course, that the rotation of the turntable was not
previously started and the discretionary backsputtering block
518.
[0077] Once the rotation of the turntable has been established, the
DC signal and the RF signal may be applied to the substrate. The
application of the DC signal to the substrate will generally be
provided at a voltage amplitude that is at or between one volt and
5,000 volts. Note that the polarity of the voltage will preferably
be negative; however, this is not always required. In a preferred
embodiment, the application of the DC signal to the substrate will
be provided at a voltage level at or between negative 500 volts and
negative 750 volts.
[0078] The application of the radio frequency signal to the
substrate will generally be provided at a power level that is at or
between 1 watt and 50 watts. Preferably, the power level of the
radio frequency signal will be provided at 10 watts or between a
range defined by 5 watts and 15 watts. The frequency of the radio
frequency signal will generally be provided at an industrial
specified frequency value in either the kilohertz range or the
megahertz range. Preferably, the frequency signal will be provided
at a frequency of 13.56 kilohertz. Although the term radio
frequency has been used throughout to describe the generation and
application of the radio frequency signal to the substrate, it
should be understood that the term radio frequency should not be
limited to its commonly understood definition of signals having
frequencies roughly between 10 kilohertz and 100,000 megahertz. The
term radio frequency shall also include any signal with a frequency
component that is operable or capable of assisting with the
creation or excitation of a plasma in a vacuum chamber.
[0079] Block 522 will also preferably include the mixing of the DC
signal and the radio frequency signal, using mixer circuitry, to
generate a mixed signal. This allows only one signal to be applied
to the substrate. This is generally achieved using the electrical
feed through that extends through the base plate of the vacuum
chamber and contacts an electrically conductive portion of the
platform, which in turn electrically couples to the substrate or
substrates. Block 522 may also include the balancing of the mixed
signal through the use of a radio frequency balancing network.
Preferably, the mixed signal is balanced by minimizing the standing
wave reflected power. This is preferably controlled through a
manual control.
[0080] As the output or load characteristics of the antenna or
output changes, as seen from the mixer circuitry, problems can
arise when electrical signals or waves are reflected from the
output load back to the mixer or source. These problems may include
damage to the radio frequency transmitter and a reduction in the
transfer of power to the substrate and vacuum chamber to ensure the
formation of a sufficient plasma to achieve a successful plasma
plating process.
[0081] This problem can be reduced or solved by including the radio
frequency balancing network that can adjust its impedance,
including in one embodiment its resistance, inductance, and
capacitance, to match or reduce the presence of reflected waves.
The impedance and electrical characteristics of the output load or
antenna are affected by such things as the presence and/or absence
of a plasma and the shape and properties of the substrate or
substrates on the platform. Because of such changes during the
plasma plating process, the radio frequency balancing network may
need to be adjusted during the process to minimize the standing
wave reflected power or, stated differently, to prevent or reduce
the standing wave ratio return to the radio frequency
transmitter.
[0082] Preferably, these adjustments are performed manually by an
operator during the plasma plating process. In other embodiments,
the radio frequency balancing network is automatically adjusted.
Care must be taken, however, to ensure that the automatic
adjustment does not over compensate or poorly track the changes in
the output load.
[0083] The method 500 proceeds next to block 524 where the
depositant or depositants are melted or evaporated so that a plasma
will be generated. The generation of the plasma at the conditions
provided by the present invention will result in a deposition layer
being formed on the surface of the substrate through plasma
plating. It is believed that the deposition layer is formed at a
medium energy level on the average of between 10 eV and 90 eV.
[0084] The depositants are generally evaporated or vaporized by
providing a current through the filament around the depositant. In
a preferred embodiment, the depositants are slowly or incrementally
heated to achieve a more even heat distribution in the
depositant.
[0085] This also improves the formation of the plasma. The current
may be provided as an alternating current or as any other current
that is sufficient to generate heat in the filament that will melt
the depositant. In other embodiments, the depositant may be heated
through the introduction of an agent that is in chemical contact
with the depositant. In still other embodiments, the depositant may
be heated through the use of electromagnetic or microwave
energy.
[0086] The conditions in the vacuum chamber will be correct for the
formation of a plasma. The plasma will generally include gas ions,
such as argon ions, and depositant ions, such as gold, nickel, or
palladium ions. The gas ions and the depositant ions will generally
be provided as positive ions due to the absence of one or more
electrons. The creation of the plasma is believed to be assisted
through the introduction of the radio frequency signal and because
of thermionic phenomena due to the heating of the depositants. It
is contemplated that in some situations, a plasma may be generated
that includes negatively charged ions.
[0087] The negative potential established at the substrate due to
the DC signal will attract the positive ions of the plasma. Once
again, this will primarily include depositant ions and may include
gas ions, such as argon gas ions from the gas that was introduced
earlier in method 500. The inclusion of the gas ions, such as argon
ions, are not believed to degrade the material or mechanical
characteristics of the deposition layer.
[0088] It should be noted that some prior literature has suggested
that the introduction of a magnet at or near the substrate is
desirable to influence the path of the ions of the plasma as they
are attracted to the substrate to form the deposition layer.
Experimental evidence now suggests that the introduction of such a
magnet is actually undesirable and produced unwanted effects. The
presence of the magnet may lead to uneven deposition thicknesses,
and prevent or significantly impede the controllability,
repeatability, and reliability of the process.
[0089] Whenever the deposition layer is designed to include
multiple sublayers, multiple shots must be performed at block 524.
This means that once the base layer depositants have been melted
through the heating of their filaments, the transition layer
depositants (or the depositant of the next layer to be applied) are
heated and melted by the introduction of heat at their filaments.
In this manner, any number of sublayers may be added to the
deposition layer. Before successive depositant sublayers are
formed, the preceding layer shall have been fully or almost fully
formed. The method 500 thus provides the significant advantage of
allowing a deposition layer to be created through multiple
sublayers without having to break vacuum and reestablish vacuum in
the vacuum chamber. This can significantly cut overall plasma
plating time and costs.
[0090] The method 500 proceeds next to block 526 where the process
or system is shut down. In the embodiment of the system shown in
FIG. 1, the main valve is closed and a vent valve to the vacuum
chamber is opened to equalize pressure inside the vacuum chamber.
The vacuum chamber may then be opened and the substrate items may
be immediately removed. This is because the method 500 does not
generate excessive heat in the substrates during the plasma plating
process. This provides significant advantages because the material
or mechanical structure of the substrate and deposition layer are
not adversely affected by excessive temperature. The plasma plated
substrates may then be used as needed. Because the temperature of
the substrates are generally at a temperature at or below 125
Fahrenheit, the substrates can generally be immediately handled
without any thermal protection.
[0091] The method 500 provides the additional benefit of not
generating any waste byproducts and is environmentally safe.
Further, the method 500 is an efficient process that efficiently
uses the depositants such that expensive or precious metals, such
as gold and silver, are efficiently utilized and are not wasted.
Further, due to the fact that the present invention does not use
high energy deposition techniques, no adverse metallurgical or
mechanical effects are done to the substrate. This is believed to
be due to the fact that the deposition layer of the present
invention is not deeply embedded within the substrate, but
excellent adherence, mechanical, and material properties are still
exhibited by the deposition layer. After the substrates have been
removed at block 528, the method 500 ends at block 530.
[0092] FIG. 6 is a flow chart of a method 600 for backsputtering
using the system and method of the present invention, according to
an embodiment of the present invention. As mentioned previously,
backsputtering may be used to further clean the substrate before a
deposition layer is formed on the substrate through plasma
plating.
[0093] Backsputtering generally removes contaminants and foreign
materials. This results in a cleaner substrate which results in a
stronger and more uniform deposition layer. The method 600 begins
at block 602 and proceeds to block 604 where a gas is introduced
into the vacuum chamber at a rate that maintains or produces a
desired pressure within the vacuum chamber. This is similar to what
was previously described in block 520 in connection with FIG. 5.
Generally, the pressure in the vacuum chamber should be at a level
at or below 100 milliTorr, such as at a range between 20 milliTorr
and 100 milliTorr. Preferably, the pressure is provided at a level
at or between 30 milliTorr and 50 milliTorr.
[0094] The method 600 proceeds next to block 606 where rotation of
the platform or turntable is established, if applicable. As
mentioned previously, the rotation of the turntable may be provided
at a rate between 5 revolutions per minute and 30 revolutions per
minute but is preferably provided at a rate between 12 revolutions
per minute and 15 revolutions per minute.
[0095] Proceeding next to block 608, a DC signal is established and
is applied to the substrate. The DC signal will generally be
provided at an amplitude at or between one volt and 4,000 volts.
Preferably, the DC signal will be provided at a voltage between
negative 100 volts and negative 250 volts.
[0096] Block 608 also involves the generation of a radio frequency
signal that will be applied to the substrate. The radio frequency
signal will generally be provided at a power level at or between 1
watt and 50 watts. Preferably, the radio frequency signal will be
provided at a power level of 10 watts or at or between 5 and 15
watts. The DC signal and the radio frequency signal are preferably
mixed, balanced, and applied to the substrate as a mixed signal. As
a consequence, a plasma will form from the gas that was introduced
at block 604. This gas will generally be an inert gas or noble gas
such as argon. The formation of the plasma includes positive ions
from the gas. These positive ions of the plasma will be attracted
and accelerated to the substrate, which will preferably be provided
at a negative potential. This results in contaminants being
scrubbed or removed from the substrate. Once the contaminants or
foreign matter are removed from the substrate, they are sucked out
of the vacuum chamber through the operation of the vacuum pump,
such as the diffusion pump.
[0097] Proceeding next to block 610, the backsputtering process
continues for a period of time that is generally between 30 seconds
and one minute. Depending on the condition and cleanliness of the
substrate, the backsputtering process may continue for more or less
time. Generally, the backsputtering process is allowed to continue
until the capacitance discharge, created by the backsputtering
process is substantially complete or is significantly reduced. This
may be visually monitored through the observation of sparks or
light bursts that coincide with the capacitive discharge from the
is contaminants from the substrate. This may be referred to as
microarcing.
[0098] During the backsputtering process, the DC signal must be
controlled. This is normally achieved through manual adjustments of
a DC power supply. Preferably, the voltage of the DC signal is
provided at a level that allows the voltage to be maximized without
overloading the DC power supply. As the backsputtering process
continues, the current in the DC power supply will vary because of
changes in the plasma that occur during the backsputtering process.
This makes it necessary to adjust the voltage level of the DC
signal during the backsputtering process.
[0099] The method 600 proceeds next to block 612 where the DC
signal and the radio frequency signal are removed and the gas is
shut off. The method 600 proceeds next to block 614 where the
method ends.
[0100] Thus, it is apparent that there has been provided, in
accordance with the present invention, a system and method for
plasma plating that satisfies one or more of the advantages set
forth above. Although the preferred embodiment has been described
in detail, it should be understood that various changes,
substitutions, and alterations can be made herein without departing
from the scope of the present invention, even if all, one, or some
of the advantages identified above are not present. For example,
the DC signal and the radio frequency signal may be electrically
coupled to the substrate using virtually any available electrically
conductive path. The present invention may be implemented using any
of a variety of materials and configurations. For example, any of a
variety of vacuum pump systems, equipment, and technology could be
used in the present invention. The present invention also does not
require the presence of a gas, such as argon, to form a plasma, and
the backsputtering process is not a mandatory process to practice
the present invention. These are only a few of the examples of
other arrangements or configurations of the system and method that
is contemplated and covered by the present invention.
[0101] The various components, equipment, substances, elements, and
processes described and illustrated in the preferred embodiment as
discrete or separate may be combined or integrated with other
elements and processes without departing from the scope of the
present invention. The present invention may be used to plasma
plate virtually any material, object, or substrate using any of a
variety of depositants. Other examples of changes, substitutions,
and alterations are readily ascertainable by one skilled in the art
and could be made without departing from the spirit and scope of
the present invention.
* * * * *