U.S. patent number 3,644,191 [Application Number 04/806,972] was granted by the patent office on 1972-02-22 for sputtering apparatus.
This patent grant is currently assigned to Tokyo Shibaura Electric Co., Ltd.. Invention is credited to Katsuo Matsushima.
United States Patent |
3,644,191 |
Matsushima |
February 22, 1972 |
SPUTTERING APPARATUS
Abstract
In a sputtering apparatus a plasma is formed between a
cylindrical first electrode and a second electrode concentric with
the first electrode. Either one of the electrodes is made of a
material to be sputtered and the surface of the other electrode is
covered by a thin film of the sputtered material.
Inventors: |
Matsushima; Katsuo
(Kawasaki-shi, JA) |
Assignee: |
Tokyo Shibaura Electric Co.,
Ltd. (Kawasaki-shi, JA)
|
Family
ID: |
12012180 |
Appl.
No.: |
04/806,972 |
Filed: |
March 13, 1969 |
Foreign Application Priority Data
|
|
|
|
|
Mar 15, 1968 [JA] |
|
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43/19904 |
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Current U.S.
Class: |
204/298.06;
204/298.16 |
Current CPC
Class: |
C23C
14/35 (20130101); H01J 37/3402 (20130101) |
Current International
Class: |
C23C
14/35 (20060101); H01J 37/34 (20060101); H01J
37/32 (20060101); C23c 015/00 () |
Field of
Search: |
;204/298 |
References Cited
[Referenced By]
U.S. Patent Documents
Primary Examiner: Mack; John H.
Assistant Examiner: Kanter; Sidney S.
Claims
What is claimed is:
1. A sputtering apparatus comprising:
an evacuable chamber;
means for introducing an ionizable gas into said chamber;
a cylindrical target electrode disposed in said evacuable
chamber;
a rodlike metallic electrode electrically connected to ground and
disposed coaxially within said cylindrical target and spaced from
said cylindrical target;
means disposed on the base of said evacuable chamber for supporting
said rodlike electrode and for supporting a cylindrical member to
be coated with sputtered material, said member to be coated being
supportable coaxially around and adjacent to said rodlike
electrode;
an anode electrode and a cathode electrode disposed within said
evacuable chamber spaced from respective ends of said cylindrical
target electrode;
power supply means for impressing a predetermined voltage across
said anode electrode and said cathode electrode, a negative
potential to said target electrode and a positive potential to said
rodlike electrode to establish a plasma which passes through the
space between said target and rodlike electrodes;
means disposed adjacent to said evacuable chamber to focus said
plasma within the space between said target and rodlike electrodes,
and whereby material is sputtered from the target onto the outer
surface of the cylindrical member.
2. The plasma sputtering apparatus according to claim 1 wherein
said ionizable gas is argon gas.
3. The plasma sputtering apparatus according to claim 1 wherein
said means to focus said plasma is a cylindrical focusing
magnet.
4. The plasma sputtering apparatus according to claim 1 wherein
said anode is an anode disc electrode and said cathode is a cathode
filament electrode.
Description
This invention relates to sputtering apparatus capable of forming
thin films having uniform thickness and crystal structure on
cylinders or columns.
The term sputtering means as technique wherein a material mounted
on a cathode electrode electrode is sputtered by the bombardment of
ions formed by electric discharge and then deposited on an anode
electrode or a substrate located close to the anode electrode to
form a thin film of the material.
There have been proposed many types of the sputtering apparatus
including diode or triode structure apparatus. More particularly,
in one type electrodes themselves act as a target and a member to
be coated with sputtered material respectively. In the other type,
a third electrode is provided to form a plasma. In still another
type a magnet is used to focus a plasma. However, direct current
(DC) sputtering apparatus including two electrodes for creating
glow discharge is used most widely.
FIG. 1 schematically illustrates such a DC sputtering apparatus. A
cathode electrode 2 and an anode electrode 3, each in the form of a
flat plate, are disposed in parallel opposed relationship in a
vacuum chamber 1 connected to an evacuating system, not shown. The
target material is mounted on the cathode electrode, or the cathode
electrode itself is comprised by the target material, and a
substrate 4 on which the sputtered material is to be deposited is
secured on the surface of the anode electrode facing the target.
The anode electrode is grounded while a high potential is applied
to the cathode electrode. While maintaining a steady flow of argon
gas, for example, through the vacuum chamber a high potential is
applied across the anode and cathode electrodes to create glow
discharge between them so as to bombard cathode electrode 2 with
positively charged argon ions thus depositing the material of the
cathode electrode on the substrate 4.
With the sputtering apparatus referred to above, however, as anode
and cathode electrodes are made of parallel flat plates, the
distribution of electric field established between these electrodes
is not uniform at the edges thereof. Thus, at the central portion
of electrodes, lines of electric force are perpendicular to the
surface of electrodes but are bowed at the edges. This means that
the speed of deposition of the sputtered material on the substrate
secured to the surface of the anode electrode is different at the
central portion and at the edge thus resulting in the nonuniformity
of thickness and crystal structure of the deposited film.
Moreover, because both the substrate and target are flat, the
resulted film is also limited to flat one. Where a cylindrical
substrate is used, it is necessary to provide a mechanism for
rotating the substrate.
An object of this invention is to provide a sputtering apparatus
capable of establishing a uniform field distribution in a discharge
space.
Another object of this invention is to provide a new and improved
sputtering apparatus which can form sputtered films having crystals
of uniform thickness and structure.
Yet another object of this invention is to provide a sputtering
apparatus capable of forming thin films on the surface of
cylindrical or columnar substrate.
According to this invention, these and other objects can be
accomplished by providing a sputtering apparatus comprising a
vacuum chamber in which a gas is introduced a first cylindrical
electrode disposed in said chamber, a second electrode disposed in
said first electrode, said second electrode having an outer
peripheral surface of substantially the same configuration as the
inner peripheral surface of said first electrode, and means to
establish a plasma between said first and second electrodes.
The first electrode acts as the cathode while the second electrode
as the anode. The cathode electrode is supplied with a negative
high potential whereas the anode electrode is grounded. For
example, the cathode electrode is made of copper and the anode
electrode is made of tungsten. After introducing a suitable gas in
vacuum chamber, when discharge is created by impressing a high
voltage across the anode and cathode electrodes, the copper
comprising the cathode electrode is bombarded by the ions of the
gas to deposit copper on the surface of the anode electrode. With
the above described arrangement the cathode electrode serves as of
target material and the anode electrode acts also as a substrate on
which the sputtered material is to be deposited.
Because cathode and anode electrodes are cylinders disposed
concentrically, the field distribution between them is quite
uniform thus increasing the effective discharge space region which
is particularly effective to obtain uniform thickness and crystal
structure of the deposited film. Further, in accordance with this
invention it is very easy to form thin films on the surface of
cylinders without the necessity of rotating the substrate by a
rotating mechanism of special design as heretofore been the
practice.
While in the above described arrangement a thin film is formed
directly on the surface of the anode electrode, such film may be
formed on an independent cylinder which is concentrically disposed
around the anode electrode.
By reversing the relative position of cathode and anode electrodes,
a thin film may be formed on the inner surface of a cylindrical
body.
In accordance with a modified embodiment of this invention the
sputtering apparatus comprises a vacuum chamber an
electroconductive rod disposed in the chamber, a cylindrical target
coaxially disposed about the rod, and a cathode electrode and an
anode electrode disposed adjacent opposite openings, respectively
of the target. This embodiment is a sputtering apparatus of the
three electrode type. In operation, a suitable gas is introduced in
the vacuum chamber, a low voltage is impressed across the anode and
cathode electrodes to create electric discharge and a negative
potential is applied to the target. Positive ions of the gas formed
by the discharge are caused to bombard the target so that sputtered
target material is deposited on the surface of the rod through the
plasma. With this embodiment the rate of deposition of the film is
increased, contamination by the residual gas is decreased and a
film of uniform thickness and crystal structure can be formed on
the surface of the cylindrical or columnar rod.
The invention is now described in conjunction with a preferred
embodiment with reference to the accompanying drawing, in
which:
FIG. 1 is a longitudinal sectional view schematically illustrating
an electrode arrangement of a prior art sputtering apparatus;
FIG. 2 shows a side elevation, partly in section, of one embodiment
of the sputtering apparatus according to the present invention;
FIG. 3 is a perspective view of electrodes of a modified sputtering
apparatus according to the present invention; and
FIG. 4 shows a longitudinal side elevation, partly in section, of
another modification of this invention.
The sputtering apparatus of this invention will be described in
detail by referring to FIGS. 2 to 4 of the accompanying
drawing.
EXAMPLE 1
As shown in FIG. 2, within a vacuum chamber 11 of glass or metal,
tungsten, for example and connected on an evacuating system, not
shown, is disposed a cylindrical cathode electrode 12 or a first
electrode of tantalum and having dimensions of 1.0 mm. thick, 30
mm. inside diameter and 50 mm. height. Within the cathode electrode
is concentrically disposed a cylindrical or columnar nickel anode
13, of 1.8 mm. in diameter. The anode electrode 13 is secured to a
support 14 which is grounded. A negative high voltage is supplied
to cathode electrode 12 through a conductor 15 connected to a power
source of high voltage, not shown, the conductor 15 being insulated
from the support 16 by means of an insulator 17.
If desired a cooling device for the cathode electrode 12 and a
cylindrical shutter may be provided between anode and cathode
electrodes.
In operation, the interior of the vacuum chamber 11 is evacuated by
the evacuating system. When a pressure of the order of
1.times.10.sup..sup.-6 torr. is reached, argon gas is introduced
into the chamber through a variable leak valve 18 to a pressure of
10.sup..sup.-1 -10.sup..sup.-2 torr. and a voltage of from 3 to 5
kv. is impressed across the cathode and anode electrodes. It is
advantageous to utilize a high reactance transformer to prevent an
abnormal discharge.
Generally the current capacity is determined dependent upon the
area of the cathode electrode. In this case the current density
amounts to several milliamperes/cm..sup.2 on the average. Under
these conditions a maximum rate of deposition of tantalum of 10
A./min. can be obtained, and the deposited film has substantial
adhesion and hardness. With this sputtering apparatus a film
comprised by sputtered particles can be formed on the external
surface of anode electrode 13. Of course cathode electrode 12 acts
as a target during sputtering.
Positively charged ions of gas created by the electric discharge
bombard cathode electrode 12 with high energy to sputter atoms of
the material comprising the target. Under this condition
substantially equal number of positively charged ions and
negatively charged particles or electrons exist to form a plasma.
In front of the cathode cylinder 12 facing to the plasma there is
formed a region termed as the cathode drop in which the density of
the charged particles is low and the intensity of the electric
field is high. Positively charged ions are accelerated in this
cathode drop region to bombard cathode electrode 12 thus causing
sputtering as well as secondary electron emission (.gamma.
function). Electrons emitted by the .gamma. function are
accelerated to further ionize the discharge gas to sustain
discharge.
While in FIG. 2, cathode and anode electrodes 12 and 13 are shown
concentric, it is not always necessary. Thus for example, even when
the axes of anode and cathode electrodes are not in exact alignment
the thickness of the film deposited on the surface of anode
electrode 13 becomes slightly thinner at portions remote from the
inner surface of the cathode electrode. Where it is desired to
locally vary the thickness of the deposited film, cathode and anode
electrodes may be arranged eccentrically. Should both electrodes
become eccentric by some reason, where it is desired to obtain a
film of uniform thickness, the anode electrode may be rotated.
Although in the above described example films are formed on the
surface of anode electrode 13, such films can be formed on the
inner surface of a cylinder in the following manner. This can be
accomplished by mere change of the electrode material and the
relative polarity of the potential. More particularly, in the
arrangement shown in FIG. 2, anode electrode 13 is made of a target
material, cathode electrode 12 is grounded and a high negative
potential is applied to anode electrode 13. Then the target
material comprising the anode will be sputtered and deposited on
the inner surface of cathode electrode 12.
While in the sputtering apparatus shown in FIG. 2, films are formed
on the surface of anode electrode 13, in the modification shown in
FIG. 3, the films are deposited on the surface of a cylinder
independent of the anode electrode.
More particularly, as shown in FIG. 3, an additional cylinder 19 of
glass, for example is mounted on support 14 to coaxially surround
anode electrode 13. Upon application of high voltage across cathode
and anode electrodes 12 and 13 to create glow discharge
therebetween, the material, tantalum for example, of the cathode
will be sputtered to deposit on the outer surface of glass cylinder
19. By vertically reciprocating the glass cylinder the width of the
deposited film can be increased. Where it is desired to deposit a
film on the inner surface of glass cylinder 19, as above described,
the relative potential of anode and cathode electrodes is reversed
and the anode electrode is made of a target material such as
tantalum. As diagrammatically shown in FIG. 3, the lower end of
anode electrode 13 is received in an opening (not shown) in support
14 and secured thereto by means of a set screw 20. The glass
cylinder 19 may be merely placed on support 14.
To prepare a thin film of an insulator a cylinder of the insulator
such as SiO.sub.2, Si.sub.3 N.sub.4, metal oxides of high melting
point such as Ta, Nb, Zr, Ti and the like is fit in the cathode
electrode 12 shown in FIG. 2 and a high-frequency voltage of about
10 MHz. is applied to the cathode electrode. Then positively
charged particles collected on the surface of the cylindrical
insulator will be periodically neutralized by negatively charged
particles having a mobility several thousand times larger than the
former so that the surface of the insulator will become negative
with respect to the grounded anode electrode at each half cycle of
the high-frequency voltage, during which sputtering is effected to
deposit a film of the insulator on the surface of anode electrode
13.
EXAMPLE 2
This example illustrates a modified sputtering apparatus employing
three electrodes. Thus, as shown in FIG. 4, a cylindrical target or
a first electrode 32 of tantalum and having dimensions of 1.5 mm.
thick, 70 mm. inside diameter and 50 mm. height is disposed in a
vacuum chamber 31 connected to an evacuating system, not shown, and
a glass or quartz tube to be coated 33, 10 mm. inside diameter, 80
mm. height and 1.0 mm. wall thickness is mounted on a support 34 of
stainless steel for example. Within tube 33 is disposed an
electroconductive metal rod 35, or a second electrode made of
stainless steel and having a diameter of 5 mm., which is also
supported by support 34. An anode electrode 36 comprising a metal
circular disk is disposed close to and in parallel with the upper
surface of target 32. A cathode electrode 37 is disposed spaced
from the lower end of target 32. Target 32 is maintained at a high
negative potential with respect to metal rod 35 while the metal rod
35 and the cathode electrode 37 are grounded. Anode electrode 36 is
maintained at a low positive potential. As shown, a focusing magnet
38 is disposed on the outside of vacuum chamber 31 in parallel with
target 34. The purpose of the focusing magnet is to combine the
plasma created between anode electrode 36 and cathode electrode 37
within a predetermined region.
The operation of this modification is as follows:
When the interior of the vacuum chamber 31 is evacuated to a vacuum
of the order of 1.times. 10.sup..sup.-6 torr. argon gas is
introduced into the chamber through a variable leak valve 39 to a
pressure of 1.times. 10.sup..sup.-3 torr.
Then a potential of 50 V is impressed across anode electrode 36 and
cathode electrode 37 to establish a plasma while at the same time a
DC power of 1.0 kv. and 60 milliamperes is applied to target 32.
The plasma is formed inside target cylinder 32 and the positively
charged ions in the plasma bombard the target 32 to deposit a
tantalum film on the outer surface of tube 33.
In the foregoing examples 1 and 2 although sputtered films are
deposited on the outer surface of a cylindrical member, no film is
formed on the inner surface thereof. Where it is desired to form
films on the inner surface of tube 33, target 32 and
electroconductive metal rod 35 may be interchanged with consequent
reversal of the polarity of the potential as has been discussed
with reference to Example 1.
As above described, since in accordance with this invention,
parallel plate electrodes are not employed as in the prior art but
instead a target cylinder and an electroconductive metal rod
respectively acting as a cathode electrode and an anode electrode
are disposed concentrically, it is possible to increase the volume
of uniform discharge, thus resulting in uniform thickness and
crystal structure of the deposited film. Further, it is possible to
deposit films on both inside and outside surfaces of a
cylinder.
* * * * *