U.S. patent number 3,824,398 [Application Number 05/292,348] was granted by the patent office on 1974-07-16 for method for plasma treatment of substrates.
This patent grant is currently assigned to Celanese Corporation. Invention is credited to Abraham A. Boom.
United States Patent |
3,824,398 |
Boom |
July 16, 1974 |
METHOD FOR PLASMA TREATMENT OF SUBSTRATES
Abstract
A method and apparatus for efficiently generating a gaseous
plasma particularly for the treatment of substrates. A radio
frequency electrical signal is applied to two electrodes disposed
exteriorly of an electrically insulative, gas impervious envelope.
A central passage extends into the envelope and one electrode is
disposed in the central passage. The electrodes are separated at
least in part by the envelope and the radio frequency signal
applied to the electrodes excites the gas within the envelope to
thereby generate a gaseous plasma therein. The gas conditions
within the envelope differ from the gas conditions exteriorly
thereof and the amplitude of the radio frequency signal is
insufficient to generate a plasma outside the chamber defined by
the envelope. Since the plasma does not contact the electrodes,
efficiency is maximized and the plasma is not contaminated by the
electrodes. In addition, the surface areas of the electrodes differ
substantially thereby creating a plasma within the envelope which
varies in concentration in a predetermined manner, with the
concentration being greatest near the center of the envelope. A
substrate may therefore be contacted by varying plasma
concentration as it passes through the envelope and the outer wall
of the envelope is not contaminated by the plasma. A vacuum lock
for preventing gas leakage into the envelope is also disclosed.
Inventors: |
Boom; Abraham A. (Martinsville,
NJ) |
Assignee: |
Celanese Corporation (New York,
NY)
|
Family
ID: |
26866919 |
Appl.
No.: |
05/292,348 |
Filed: |
September 26, 1972 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
Issue Date |
|
|
171282 |
Aug 12, 1971 |
3723289 |
|
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|
Current U.S.
Class: |
250/325; 204/164;
219/121.6; 250/492.1; 422/186.18; 422/186.29; 422/906 |
Current CPC
Class: |
H01J
37/32091 (20130101); B29C 59/14 (20130101); H05H
1/30 (20130101); D06M 10/025 (20130101); D06M
14/34 (20130101); D01F 11/16 (20130101); H01J
37/3277 (20130101); H01J 37/32743 (20130101); Y10S
422/906 (20130101); H01J 2237/336 (20130101) |
Current International
Class: |
B29C
59/14 (20060101); B29C 59/00 (20060101); D01F
11/00 (20060101); D01F 11/16 (20060101); D06M
10/02 (20060101); D06M 14/34 (20060101); H01J
37/32 (20060101); D06M 10/00 (20060101); D06M
14/00 (20060101); H05H 1/30 (20060101); H05H
1/26 (20060101); G01n 023/00 (); H01j 037/00 () |
Field of
Search: |
;204/164,165,168
;250/324,325,326,492,531,532,539 ;317/4,262A |
References Cited
[Referenced By]
U.S. Patent Documents
Primary Examiner: Lindquist; William F.
Parent Case Text
This is a division of application Ser. No. 171,282 filed Aug. 12,
1971, now issued as U.S. Pat. No. 3,723,289 and assigned to the
assignee hereof.
Claims
What is claimed is:
1. A method for creating a plasma for the treatment of a substrate
without exposure of the substrate to a high current density
comprising the steps of:
providing an electrically insulative, gas-impervious envelope
between first and second electrodes of significantly different
configuration;
modifying at least one of the pressure and the constituency of the
gas within the envelope;
applying a radio frequency electrical signal to the electrodes to
thereby create a plasma of varying concentration within the
envelope without creating a plasma exteriorly thereof and to
thereby reduce the current flow between the electrodes; and
passing a substrate to be treated along a predetermined path
through said plasma.
2. A method for treating a substrate comprising the steps of:
providing a pair of electrodes differing significantly in surface
area;
applying a radio frequency electrical signal to the electrodes to
create a gaseous plasma of varying concentration therebetween;
and,
passing a substrate to be treated along a predetermined path
through a selected plasma concentration to treat the substrate.
3. A method for creating a plasma for the treatment of a substrate
without contamination of the plasma comprising the steps of:
providing an electrically insulative, gas-impervious envelope
between first and second electrodes of significantly different
configuration, the envelope defining a chamber isolated from the
electrodes;
modifying the gas conditions within the envelope;
applying a radio frequency electrical signal to the electrodes of
sufficient amplitude to create a plasma of varying concentration
within the chamber, the plasma being isolated from the electrodes
to prevent contamination of the plasma by the electrodes; and
passing a substrate to be treated along a predetermined path
through a selected plasma concentration to treat the substrate.
Description
BACKGROUND OF THE INVENTION
The present invention relates to a method for treating substrates
and specifically to a method for more efficiently generating a
plasma for the treatment of substrates and for subjecting a
substrate to varying plasma concentrations during the treatment
thereof.
Various substrates have been treated in gaseous plasmas to obtain
desired substrate characteristics. An example of one such process
is disclosed and claimed in U.S. Pat. application Ser. No. 93,350
filed Nov. 27, 1970, by Forschirm et al for "Surface Modification
of Organic Polymeric Materials" and assigned to the assignee of the
present invention. In the Forschirm et al application, an organic
polymeric fiber is introduced into a gaseous plasma for
modification of the surface thereof. For example, a polymeric
continuous filament yarn may be exposed to a gaseous plasma formed
by exciting argon or other suitable gases at a pressure of about 2
mm Hg. with a 4 megahertz, 1,000 watt radio frequency signal, to
modify the yarn to obtain desirable surface characterisitcs.
Another process for treating fibers in a gaseous plasma is
disclosed and claimed in U.S. Pat. application Ser. No. 88,358
filed Nov. 10, 1970, for "Vapor Phase Boron Deposition by Pulse
Discharge" by Kenneth C. Hou and assigned to the assignee of the
present invention. In the Hou process, a boron coating is deposited
on a suitable substrate by generating a boron-hydrogen excited gas
species or plasma and contacting the substrate with the plasma. The
plasma is generated by applying pulsed high frequency electrical
power to a gaseous mixture of boron and hydrogen at a pressure of
about 1 to 3 atmospheres. For example, a 3,000 volt peak-to-peak
a.c. signal having a frequency of 13.6 megahertz in pulses of 100
microseconds duration at a pulse repetition rate of 1 kilohertz may
be utilized to excite the gaseous mixture within a coating zone
into which the substrate is introduced to provide a smooth, firmly
adhering layer of boron 1 to 2 mils in thickness.
Carbonaceous fibrous materials have been treated in plasmas as is
described in U.S. Pat. application Ser. No. 99,169 filed Dec. 17,
1970, for "Surface Modification of Carbon Fibers," by Kenneth C.
Hou and assigned to the assignee of the present invention. In this
Hou process, a carbonaceous fibrous material is contacted for a
brief time with an excited gas species generated by applying high
frequency electrical energy in pulsed form to a gaseous mixture of
a monotonic inert gas and a surface modification gas. For example,
a carbonaceous yarn may be passed through a gaseous mixture of
helium and oxygen wherein the oxygen is present in the mixture in a
concentration of about 0.5 percent by weight. A 3 kilovolt
peadk-to-peak a.c. signal having a frequency of 13.56 megahertz may
be utilized to excite the gaseous mixture thereby contacting the
yarn with the excited gas species to modify the surface
thereof.
In the above-described processes, the excited gas species or plasma
is generated by electrically exciting the gas or gaseous mixture.
For example, energy may be imparted to gas capacitively and a
plasma thereby generated. The plasma is highly electrically
conductive and a high conduction current flows between the
capacitor plates or electrodes because of the resultant decrease in
the electrical resistance of the gas between the electrodes. In the
treatment of fibers for commercial uses, the cost of the power
required to generate the plasma becomes an important factor.
It is desirable to keep current flow to a minium since the
efficiency of the processes decreases and the cost of treating
fibers increases with an increase in current. In addition, the
amount of wasted power in transmission lines will be reduced as
current requirements decrease. Moreover, by providing control of
the location of the major concentration of the generated plasma,
the plasma may be utilized in a more efficient manner.
The cost of treating substrates may also be dependent upon the
length of time during which a reaction chamber may be operated
without shutdown for maintenance. It may be necessary to frequently
change the gas within the chamber if the gas is contaminated by the
electrodes. Also, the useful life of the reaction chamber may be
adversely affected by material buildup on the walls thereof during
the treatment operation.
It is therefore an object of the present invention to provide a
novel method and apparatus for more efficiently generating a
plasma.
It is a further object of the present invention to provide a novel
method for generating a plasma within a reaction chamber for the
treatment of fibers.
It is another object of the present invention to provide a novel
method for reducing the current flow between electrodes in a
capacitive plasma generator, and particularly in chambers adapted
for the treatment of fibers.
It is still another object of the present invention to provide a
novel method wherein contamination of the plasma by the electrodes
is prevented.
It is yet a further object of the present invention to provide a
novel method wherein contamination of the interior walls defining
the chamber is minimized.
In some applications utilizing the present invention, it is
desirable to selectively expose a substrate to a plasma to achieve
selectable surface modification or coating of the substrate. For
example, the amount of time during which the substrate is exposed
to the plasma may be selectively varied to provide the desired end
product. This may be accomplished through control of the speed at
which the substrate passes through the plasma, assuming that other
conditions remain constant.
Moreover, other conditions to which the substrate is subjected
within a plasma reaction chamber may have an effect on the
resultant treated substrate. The substrate may, for example, be
adversely affected by excess heat or the sudden exposure to high
temperatures. It may therefore be desirable to expose the substrate
to the plasma in a controllable manner.
It is therefore yet another object of the present invention to
provide a novel method for selectively exposing a substrate to a
plasma.
It is still a further object of the present invention to provide a
novel method for selectively exposing the substrate to varying
concentrations of a plasma within a reaction chamber.
These and other objects of the present invention will become
apparent to one skilled in the art to which the invention pertains
from a perusal of the following description when read in
conjunction with the appended drawings.
THE DRAWINGS
FIG. 1 is a schematic representation of a reaction chamber
embodying the present invention;
FIG. 2 is a view in cross section of the reaction chamber of FIG.
1, taken along the line 2--2;
FIG. 3 is a schematic representation of the reaction chamber of
FIG. 1 with a substrate being treated therein;
FIG. 4 is a view in cross section of the reaction chamber of FIG.
3, taken along the line 4--4;
FIG. 5 is a schematic representation of a reaction chamber similar
to the chamber shown in FIG. 3 with a plurality of substrates being
treated therein;
FIG. 6 is a view in partial cross section of the reaction chamber
of FIG. 5 illustrating the vacuum lock of the present invention;
and,
FIGS. 7A and 7B are end views of the vacuum lock of FIG. 6, taken
along the line 7--7 thereof, and illustrate two of the alternative
shapes which the vacuum lock may have.
DETAILED DESCRIPTION
Referring to FIGS. 1 and 2 wherein a preferred embodiment of a
reaction chamber constructed in accordance with the present
invention is illustrated, a reaction chamber 10 is formed by a
substantially gas impervious, generally electrically non-conductive
or insulative envelope 12 into which a central passage 14 extends.
An electrode 16 extends into the central passage 14 and is isolated
from the chamber 10 by the radially inward wall of the envelope 12.
An electrode 18 is disposed radially outward of the envelope 12,
and is separated at least in part from the centrally disposed
electrode by at least a portion of the envelope 12, thereby
defining an area within the envelope 12, i.e., at least a portion
of the chamber 10, which is disposed between the electrodes 16 and
18.
A high frequency electrical potential is applied between the
electrodes 16 and 18 from a suitable source such as a variable
frequency and amplitude radio frequency (FR) generator 20 to
thereby subject the chamber as defined by the envelope 12 between
the electrodes 16 and 18 to a selectable time varying electrical
field. A suitable fill tube 22 may be provided communicating with
the chamber 10 through the envelope 12 and having a valve or other
suitable closure means 24 therein to selectively control the nature
and pressure of the gas within the envelope 12.
With continued reference to FIGS. 1 and 2, the envelope 12 defining
the chamber 10 preferably comprises an outer elongated hollow glass
cylindrical member 26, an inner elongated hollow glass cylindrical
member 28, and apertured end plates 30 and 32 sealed therebetween
in a suitable conventional manner. The cylindrical member 28
illustrated is substantially coextensive with the member 26 and is
disposed in telescoping relationship thereto coaxially within the
member 26 to define a chamber annular in cross section as is shown
in FIG. 2.
The central electrode 16 is preferably an elongaged metallic
cylindrical member, e.g., a wire, telescoped within the central
passage 14, but may be hollow. The outer electrode 18 is preferably
a hollow cylindrical electrically conductive member
circumferentially disposed round at least a portion of the
insulative member 26 and may, for example, be a metallic foil
conformed to the radially outer surface of the envelope. The
central electrode 16 preferably extends axially into the central
passage 14 sufficiently so that an elongated annular portion of the
chamber 10 is located between the electrodes 16 and 18.
The application of a potential between the electrodes 16 and 18
creates an electric field between these electrodes, as is indicated
by the lines 34 in FIG. 2. The electrode configuration, i.e., the
relative positions of the electrode and the relative dimensions
thereof, cause the electric field to be more concentrated or dense
in the vicinity of the central electrode 16 near the axis of the
annular chamber 10.
If the intensity of the electric field is sufficient, the gas in
the chamber 10 will be excited sufficiently to create a gaseous
plasma in the chamber. The plasma generally comprises highly
reactive species such as ions, electrons and neutral fragmented
particles in highly excited states. Since the exciting of the gas
by the electric field creates the plasma, the plasma concentration
of density generally conforms to the electric field concentration
or density. Thus, the concentration or density of the plasma
generated within the gas impervious envelope 12 varies between the
outer cylindrical member 26 and the inner cylindrical member 28 in
a manner related to the electric field concentration of
density.
The plasma is thereby concentrated around the inner cylindrical
member 28 rather than being dispersed evenly throughout the chamber
10. This central concentration permits more efficient utilization
of the plasma for treating substrates and permits selective
exposure of the substrate to the plasma as will hereinafter be
described. In addition, this central concentration of the plasma
prevents excessive buildup of material on the inner wall of the
outer cylindrical member 26.
The relationship between the gas conditions within the envelope 12
and the gas conditions exteriorly thereof is desirably such that
the plasma may be confined to the chamber 10. The electric
potential applied to the electrodes 16 and 18 may thus be lower and
the current density will be correspondingly less. This desirable
relationship may be obtained by utilizing selected gases at
predetermined pressures within the chamber 10, while exposing the
electrodes outside the envelope 12 to the atmosphere.
By way of example, a monatomic inert gas, such as argon or helium
at atmospheric or slightly less than atmospheric pressure may be
utilized in the chamber 10. When the RF signal is applied to the
electrodes 16 and 18, a plasma will be more readily generated
within the chamber 10 than exteriorly thereof. With the potential
of the RF signal applied to the electrodes set at a value
corresponding to the potential required to generate a plasma within
the chamber 10, but below the potential required to generate a
plasma in the vicinity of the electrodes 16 and 18 externally of
the chamber 10, the current which flows between the electrodes 16
and 18 will not be appreciably affected by the ion flow within the
highly electrically conductive plasma since these electrodes are
electrically isolated from the plasma. The plasma within the
chamber 10 is not contacted by the electrodes 16 and 18 and
therefore not contaminated by the electrodes.
Referring now to FIG. 3, a substrate 36 to be treated within the
generated plasma may be introduced into the chamber 10 through a
vacuum lock 38 subsequently described in greater detail in
connection with FIGS. 6 and 7. The substrate 36 may be passed
through the chamber 10 in contact with the plasma therein at a rate
determined by the particular treatment process to which the
substrate is being subjected. For example, the substrate 36 may be
an organic polymeric fiber, such as a thermoplastic or
thermosetting polyester, polyamide, cellulosic or polyolefin
material, the surface of which is to be treated in the plasma to
obtain a paticular surface modification as is described in greater
detail in the previously discussed U.S. Pat. application Ser. No.
93,350, by Florschirm et al. The substrate 36 may alternatively be
a carbonaceous fibrous material to be treated in the plasma within
the chamber 10 as is described in greater detail in the previously
discussed U.S. Pat. application Ser. No. 99,169, by Kenneth C. Hou.
In a further application of the present invention to the treatment
of substrates, a coating may be deposited on a suitable substrate
by generating a suitable gaseous plasma and contacting the
substrate with this plasma. A more detailed description of the
substrate and gases utilized in one such coating technique may be
had by reference to the previously discussed U.S. Pat. application
Ser. No. 88,358, by Kenneth C. Hou. The above referenced Forschirm
and Hou patent applications are hereby incorporated herein by
reference.
The substrate 36 may be introduced into the chamber 10 at an a
angle with respect to the central electrode 16 as is illustrated in
FIG. 3. The substrate 36 might thereby follow a path generally
indicated at 40 which subjects the substrate 36 to varying
concentrations of the plasma as it passes through the chamber 10.
Alternatively, as is shown in FIG. 5, one or more substrates 36 may
be passed through the chamber 10 substantially parallel to the
electrodes 16 at a selected radial distance thereform, thereby
permitting the exposure of the substrates 36 to a selected plasma
concentration.
Referring now to FIGS. 6 and 7 wherein the vacuum lock 33 of FIGS.
3 and 5 is illustrated in greater detail, a hollow tube 40 sealed
to the end plate 30 of the envelope 12 communicates interiorly with
the chamber 10 and provides a passage through which the substrate
36 may be introduced into the chamber 10. The substrate 36 may be,
for example, a loosely packed fiber bundle through which air
leakage ordinarily occurs during the passage thereof between
chambers at different pressures.
The tube 40 generally conforms in cross-section to the shape of the
substrate, i.e., the bundle of fibers, but is slightly smaller in
cross-section than the bundle causing the fibers to be inwardly
compressed against each other and against the internal wall of the
tube 40. For example, if the fiber bundle is generally circular in
cross-section as in FIG. 7(A), the tube 40 may also be circular in
cross-section with a slightly smaller diameter than that of the
bundle. Likewise, if the bundle is elliptical in cross-section as
in FIG. 7(B), the tube 40 preferably conforms to that shape and is
scaled down to slightly smaller dimensions.
One end 42 of the tube 40 is flared or funnel-shaped providing a
transition zone for gently compressing the fiber bundle without
damage thereto. If desired, the tube 40 may also narrow slightly
along the length thereof to further compress the fiber bundle
during the introduction thereof into the chamber 10. It should be
noted that when the substrate is a tightly packed fiber bundle or a
single filament substrate, the diameter of the tube 40 may be the
same or slightly larger than the substrate to prevent damage
thereto.
At least two fluid passages 44 and 46 are spaced along the length
of the tube 40 and communicate with the interior thereof. Each of
the passages 44 and 46 is connected to associated pressure sources
48 and 50, respectively.
The gas pressure applied to the passage 46 preferably approximates
the pressure in the chamber 10, while the pressure applied through
the passage 44 is preferably slightly higher than the pressure in
the chamber 10, thereby creating a pressure differential along the
interior of the tube 40. This pressure differential, together with
the mechanical compression of the substrate, prevents gas leakage
into the chamber 10 when, for example, the pressure in the chamber
10 is less than the pressure outside the chamber 10.
With the two passages 44 and 46 illustrated in FIG. 6, gas leakage
into the chamber 10 is minimized since a very slight pressure
differential, e.g., 1 mm. Hg., can be maintained between the
chamber 10 and the passage 46. An even smaller pressure
differential between these two points may be obtained by increasing
the number of lateral fluid passages 44 and 46, thereby providing
even greater gas integrity between the spaces.
SUMMARY OF ADVANTAGES AND SCOPE OF THE INVENTION
It is apparent from the description of the invention that numerous
advantages result therefrom. For example, the electrodes are
isolated from the highly conductive plasma created within the
envelope, resulting in greater efficiency as well as greater
current control and eliminating contamination of the plasma by the
electrodes.
Control of the substrate treatment process is facilitated by the
controlled plasma concentration achieved in the present invention.
The substrate may be selectively contacted by the proper
concentration of plasma by selecting the path which the substrate
follows through the generated plasma. Additionally, the plasma is
concentrated in one location within the chamber resulting in more
efficient substrate treatment and less material buildup on the
interior walls of the envelope.
Moreover, continuous substrates may be treated without adverse
effects on the conditions within the reaction chamber since
isolation is provided between the interior and exterior of the
envelope. For example, the substrate may pass from an area at one
pressure, into the envelope which may be at another pressure, and
then into an area at yet a different pressure without any
substantial gas leakage.
The present invention may thus be embodied in other specific forms
without departing from the spirit or essential characteristics
thereof. The presently disclosed embodiments are therefore to be
considered in all aspects as illustrative and not restrictive, the
scope of the invention being indicated by the appended claims
rather than by the foregoing description, and all changes which
come within the meaning and range of equivalency of the claims are
therefore intended to be embraced therein.
* * * * *