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Claims  |
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What is claimed is:
1. Apparatus for metal plating walls of minute passages contained within a
platable substrate comprising:
substrate support means for supporting within a confined walled region
capable of sustaining an electrical plasma a substrate containing holes to
be plated, with said support means being formed of electrically conductive
material;
electron cyclotron resonance heating type plasma generating means for
generating a plasma with said plasma including positive metal ions of the
plating metal and directing said plasma in a path toward said substrate
support means;
said plasma generating means including a longitudinal magnetic field
oriented in the direction of and extending at least to said substrate and
said substrate support means to confine the transverse movement of said
ions in said plasma and to focus movement of said ions in said plasma
toward said substrate support means, whereby said ions may travel in
helical paths toward said substrate;
said plasma generating means further including metal sputter source means
for providing metal to form metal ions;
screen means having front and back sides, said screen means being located
in front of said substrate support means and in the part of and in
confronting relationship with said plasma and also being spaced along said
path of said plasma from said metal sputter source means with said front
side thereof facing said metal sputter source means and with said back
side thereof facing said substrate support means, for permitting passage
of metal ions therethrough for travel toward said substrate support means
and to decouple electric fields associated with said plasma generating
means present on the side of said screen means away from said substrate
support means and to permit the establishment of an electric field between
said location of said screen means and said substrate support means;
said screen means containing a plurality of contiguous apertures to form a
sieve like wall in the path of said plasma and comprising an electrically
conductive non-magnetic metal material, with said screen means being
electrically grounded;
electric field means for providing an electric field between said screen
means and said substrate support means to add energy to those of said
positive metal ions traveling through said screen means to increase the
pitch of said helical paths of travel of said positive metal ions, whereby
said higher energy ions interact with said magnetic field to cause
movement of a greater percentage of said ions so that they arrive at the
substrate at or near parallel to the passages in said substrate; said
electric field means including bias voltage source means coupled to said
substrate support means for applying a negative polarity voltage to said
substrate support means.
2. The invention as defined in claim 1 wherein said screen means comprises
a wire mesh formed of tungsten.
3. The invention as defined in claim 1 wherein said bias voltage source
means is adjustable for permitting adjustment of the level of said
negative polarity voltage applied to said substrate support means; and
wherein said plasma generating means further includes adjustable high
voltage supply means coupled to said sputter source means for applying a
high negative voltage thereto.
4. The invention as defined in claim 3 wherein said bias voltage supply
means provides a voltage level to said substrate support means that is on
the order of one tenth the voltage level of said high negative voltage
applied to said sputter source means by said adjustable high voltage
supply means.
5. The invention as defined in claim 1 wherein said plasma generating means
includes: a vacuum chamber defining an elongate passage having an axis and
means for maintaining said chamber in vacuum with said sputter source
means being disposed at one end of said chamber; a microwave energy source
for radiating energy in the vicinity of said sputter source means to
provide energy for the generation of ions; high voltage supply means for
placing said sputter source means at a high negative voltage; and magnetic
field generating means for creating a static solenoidal magnetic field
axial of said vacuum chamber for inhibiting movement of ions in said
plasma toward the sidewalls of said chamber.
6. The invention as defined in claim 1 wherein said screen means comprises:
an electrically conductive non-magnetic metal mesh screen located at an
intermediate position in and along the path of said plasma; and
wherein said bias voltage source means is located external of said chamber
with said source means including a positive polarity terminal and a
negative polarity terminal, said positive polarity terminal being
electrically connected to ground and said negative polarity terminal being
electrically connected to said substrate support means.
7. Apparatus for metal plating walls of minute passages contained within a
platable substrate comprising:
substrate support means for supporting within a confined walled region
capable of sustaining an electrical plasma a substrate containing holes to
be plated ;
plasma generating means for generating an electrical plasma with said
plasma containing positive ions of the plating metal and directing said
plasma in a path toward said substrate support means;
said plasma generating means including means for providing a longitudinal
magnetic field oriented in the direction of and extending at least to said
substrate to confine the transverse movement of said ions in said plasma
and to focus movement of said ions in said plasma toward said substrate
support means, whereby said ions may travel in helical paths toward said
substrate;
screen means located in front of said substrate support means and in the
path of said plasma for permitting passage of metal ions therethrough
toward said substrate support means and to decouple electric fields
associated with said plasma means from said substrate support means and
permit the establishment of an electric field between said location of
said screen means and said substrate support means;
said screen means being of an electrically conductive non-magnetic metal
material and being electrically grounded;
electric field means for providing an electric field between said screen
means and said substrate support means to add energy to those of said ions
travelling through said screen means to increase the pitch of said helical
paths, whereby said higher energy ions interacts with said magnetic field
to cause movement of a greater percentage of said ions at or near parallel
to the passages in said susbtrate; and wherein said plasma means includes
a sputter plate and wherein said screen means is spaced a first distance
from said sputter plate and a second distance from said substrate, with
said first distance being substantially larger than said second distance.
8. The invention as defined in claim 7 wherein said electric field means
and said magnetic field means of said plasma generating means are
sufficient in level to cause said ions that pass through said screen means
to move in a helix of a pitch having a pitch angle on the average equal to
or less than angle defined by the arc tangent determined by the width of
the substrate passage divided by one half of said passage depth.
9. The invention as defined in claim 7 wherein said electric field means is
adjustable in level to change the amount of energy added to said metal
ions.
10. The method of plating passage walls of passages formed in a substrate
wherein the length of the passage in the substrate is substantially
greater than the width of the passage opening thereby defining a high
aspect ratio passage, comprising the steps of:
supporting said substrate on an electrically conductive substrate support
within a confined evacuated region and applying a negative polarity
voltage of a bias voltage source to said substrate support;
creating a magnetically confined electron cyclotron resonance heated plasma
within said confined evacuated region with said plasma containing
positively charged metal ions and permitting said metal ions to move in
helical paths toward said substrate including the step of subjecting a
metal atom source located at a predetermined position in said confined
region to ion bombardment,
passing said plasma through an electrically grounded metal sieve like
screen located longitudinally spaced from said metal atom source in the
path of and confronting said plasma and longitudinally spaced from said
substrate to place said plasma at electrical ground potential, whereby
metal ions from said metal atom source traveling to said substrate must
pass through said screen;
increasing the longitudinal velocity of said metal ions in said plasma from
a location longitudinally spaced from said screen and in the proximity of
said substrate prior to said ions reaching said substrate in an amount
sufficient to permit metal ions of said plasma approaching a passage in
said substrate to enter said substrate passage traveling longitudinally
relatively in line with said passage, whereby said passage becomes
relatively uniformly filled up following entry of successive quantities of
metal ions over a period of time.
11. In a metal plating apparatus of the electron cyclotron resonance
heating plasma type containing within a chamber a metal atom source and a
substrate support means and in which a plasma, containing metal ions
derived from said metal atom source, is directed in said chamber toward
substrate support means intended to hold a substrate containing relatively
deep passages with passage walls to be plated and further including
magnetic field means for producing a longitudinally extending solenoidal
field extending at least from said metal atom source through to said
substrate and substrate support means to confine said plasma precluding
said plasma from grounding to walls of said chamber and to cause said
metal ions to travel in helical paths toward said substrate support means,
the improvement therein comprising in combination therewith;
means for electrically grounding the plasma at a predetermined position
between said metal atom source and said substrate support means and for
increasing the longitudinal velocity of said metal ions at a position
along the length of the plasma spaced from said predetermined position and
laterally displaced from said substrate and substrate support means to a
level sufficient to permit metal ions of said plasma to reach the bottom
of said substrate passage, whereby said metal ions relatively uniformly
fill said passages and contact said passage walls, said last named means
including:
a non-magnetic metal sieve like screen maintained at electrical ground
potential, said screen having a front side oriented facing said metal atom
source and a back side oriented facing said substrate support means; and
bias voltage source means electrically connected to said substrate support
means for applying a negative polarity voltage to said substrate support
means, said bias voltage source being adjustable to permit change in the
level of said negative polarity voltage.
12. The invention as defined in claim 11 further including: high voltage
supply means connected in circuit with said metal atom source for applying
a high negative polarity voltage thereto; and wherein said high negative
polarity voltage is on the order of ten times larger than said negative
polarity voltage applied to said substrate support means.
13. The invention as defined in claim 11 wherein said screen comprises a
wire mesh.
14. Apparatus for metal filling of minute passages contained within a
platable substrate comprising:
substrate support means for supporting within a confined region capable of
sustaining an electrical plasma a substrate containing holes to be plated;
electron cyclotron resonance heating type plasma means for generating an
electrical plasma with said plasma containing ions of the plating metal
and directing said plasma in a path toward said substrate support means;
said plasma means including a source of metal ions with said source of
ions being located at a first predetermined position at one end of said
path and providing a longitudinally directed magnetic field that extends
through said substrate support means;
screen means having front and back sides and including a plurality of
contiguous apertures therethrough, with one of said sides being oriented
facing said source of ions and the remaining one of said sides being
oriented facing said substrate support means; said screen means being
positioned in front of said substrate support means and in the path of
said plasma displaced along said path from said source of ions for
permitting passage of said metal ions therethrough toward said substrate
support means and for isolating any electric fields to the side of said
screen means away from said substrate support means, said screen means
being of a non-magnetic electrically conductive material;
means for applying a negative polarity voltage supplied by a bias voltage
source to said substrate support means to add energy to and cause change
to the motion of said ions that pass through said screen means in the
vicinity of said substrate support means, whereby the longitudinal
velocity of movement of said ions is increased.
15. Apparatus for metal plating walls of minute passages contained within a
platable substrate comprising:
substrate support means for supporting within a confined walled region
defining a vacuum chamber capable of sustaining an electrical plasma a
substrate containing holes to be plated, with said substrate support means
being of electrically conductive material;
electron cyclotron resonance type plasma generating means for generating an
electrical plasma in said chamber with said plasma containing positive
ions of the plating metal and directing said plasma in a path toward said
substrate support means;
said plasma generating means including a sputter plate; a source of
microwave energy for heating ions in the vicinity of said sputter plate;
high voltage source means having a positive polarity terminal and negative
polarity terminal with said positive polarity terminal connected to
electrical ground potential and said negative polarity terminal being
connected to said sputter plate; means for admitting an ionizable gas in
the vicinity of said sputter plate for exposure to microwave energy;
magnetic field means for producing a longitudinal magnetic field oriented
in the direction of said substrate to confine the transverse movement of
ions in said plasma and to focus movement of ions in said plasma
longitudinally toward said substrate support means with said magnetic
field extending through said substrate and substrate support means;
screen means located in front of said substrate support means and in the
path and in confronting relationship with said plasma and axially spaced
from said sputter plate for permitting passage of metal ions therethrough
toward said substrate support means and to decouple electric fields
associated with said plasma means on the side of said screen away from
said substrate support means;
said screen means containing a large plurality of apertures to form a sieve
like structure and comprising an electrically conductive non-magnetic
metal;
means connecting said screen means to electrical ground potential;
said substrate support means being located a first predetermined distance
to one side of said screen means and said sputter plate being located a
second predetermined distance on the opposite side of said screen means,
with said first predetermined distance being lesser than said second
predetermined distance;
electric field means for providing an electric field between said screen
means and said substrate support means to add energy to ions following
passage thereof through said screen means, whereby said higher energy ions
interacts with said magnetic field to cause movement of a greater
percentage of ions in a direction essentially perpendicular to the
substrate and into the passages in said substrate supported in said
substrate support means;
said electric field means including adjustable low voltage source means
having positive and negative polarity terminals with said positive
polarity terminal connected to electrical ground potential and with said
negative polarity terminal connected to said substrate support means.
16. The invention as defined in claim 15 wherein said vacuum is adapted to
provide a vacuum of approximately 2.times.10.sup.-5 millimeters of
Mercury; wherein said sputter plate is of the metal Copper; wherein said
magnetic field means produces a magnetic field that measures approximately
4,000 Gauss; said high voltage source means is approximately -1000 volts
in level; said low voltage source means is approximately 100 volts in
level; said ionizable gas comprises Argon; said first predetermined
distance between said substrate support and said screen is approximately
two inches; and said second predetermined distance between said screen and
said sputter plate is between thirty six to forty eight inches.
17. The invention as defined in claim 16 wherein said screen means
comprises a metal wire mesh. |
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Claims |
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Description |
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FIELD OF THE INVENTION
The present invention relates to apparatus for metal plating of
semiconductor substrates that incorporate microelectronic circuitry and,
more particularly, to an improved apparatus and method for filling high
aspect ratio passages in microelectronic substrate with an electrically
conductive material.
BACKGROUND
An integrated semiconductor circuit contains large numbers of electronic
devices within a single substrate or "chip" with the electronic devices
being selectively connected by electrical conductors to form functional
circuits. Such semiconductor devices are formed in layers, quite often
including an electrical conductor as a base or bottom most layer; and,
additionally, different electronic devices are formed within different
levels of layers with such devices being strategically placed over the
available surface area or "geography" of the minute chip. This integrated
circuit structure is accomplished by known processes.
To electrically connect together selected electronic devices located at
different vertical positions in this three dimensional solid matrix
characterizing the chip, into an electrical circuit, integrated circuits
employ metal "plated through" holes. That is, minute sized passages,
formed by known photolithographic etching technique, extend through the
matrix intersecting electrically conductive material, the metal lines or
layers located at different vertical levels; and a metal plating, an
electrical conductor, is applied to the walls of the passages and, as
desired, fills the entire passage. The metal plating provides an
electrically conductive path between the conductive material at the two
levels, much like the vertically extending plumbing pipes that extend
through the different vertical levels of a high rise office building. The
conductive path thus formed allows voltages and currents to pass between
the circuits on one level or "floor" and another vertically spaced level.
For additional background the reader may refer to the patent and technical
literature on this subject.
Those skilled in the integrated circuit art have made increased efforts to
effectively squeeze greater numbers of electronic devices within a given
area of semiconductor substrate, increasing the "device density", by
further reducing the size of individual semiconductor devices. As this
device density increases, the channels and holes through the substrate
layers necessarily are formed increasingly deep relative to the width of
the hole; the holes have a "high aspect" ratio, greater than three to one.
For example, typical holes may be one micron in diameter and three to four
microns in depth for an aspect ratio of 3:1 to 4:1.
The high aspect ratio of the holes makes it difficult to attain quality
metal plating: known metal sputtering processes and vapor deposition
techniques appear to fail due to "shadowing" effects, wherein some metal
atoms or ions traveling in random or uncontrolled directions strike the
walls at an angle thus causing a metal growth along the top of the hole,
causing "sidewall" growth, at the top of the hole, which is eventually
closed. This leaves an internal void in the plating and results in poor
electrical conductivity. Existing plasma techniques made known to
applicant also failed to solve that problem.
Recognizing this technological difficulty, other workers in this subject
have reported experiments in which a plasma containing a slightly ionized
flux of aluminum atoms, approximately two per cent or less positively
charged ions, are accelerated onto a target substrate, negatively biased
by a very large voltage, to improve the filling of the high aspect ratio
holes. As reported by S. N. Mei, S. N. Yang, & T. M. Lee & S. Roberts in a
paper, "High Aspect Ratio via Filling with Al Using Partially Ionized Beam
Deposition", presented at the AVS 34th National Symposium; Anaheim, CA.
November 2-6, 1987, those experiments show that plasma plating of high
aspect ratio holes is possible. It is noteworthy that the foregoing method
and apparatus did not use a confining magnetic field, characteristic of
the present invention, and used a low ion percentage plasma. The present
invention provides a different and more effective solution to the
technological difficulty encountered.
Likewise, the patent to Homma et. al. U.S. Pat. No. 4,717,462 granted
January 5, 1988 for a "Sputtering Apparatus" describes a plasma plating
apparatus in which a plasma is produced without a magnetic field
generating apparatus as a solution to the problem of plating of high
aspect ratio holes in substrate. That apparatus includes a metal screen,
preferably of magnetic material, but which may also be non-magnetic, and
in which either rf power or dc current power is applied to the substrate,
the latter dc voltage being given in the example as of the same dc voltage
level as the screen, electrical ground potential.
In its operation, Homma's screen appears to collimate the moving atoms in
the plasma by preventing passage of atoms which are traveling toward the
screen skew to the axis at too great an angle. Because of the random
uncontrolled direction of movement of atoms and ions produced in the
plasma generator if all such particles are allowed to travel to the
substrate, the plating building up outside the holes would occur more
quickly than inside - hence, the shadowing. By preventing those ions that
do not follow generally an axial path from reaching the substrate, the
build up of the metal in the holes and a more even metal coating on the
surface of the substrate is possible, but at a reduced plating rate, since
fewer atoms pass through the screen. In making the holes in the screen
into tunnel like "high aspect ratio" passages the Homma patent notes that
a more even coating is obtainable since more atoms cannot make it through
the screen and the plating speed drops dramatically.
As becomes more apparent hereafter, the present invention does not seek to
screen out ions or slow down the plating rate as a compromise to obtain a
more even plating as appears to be the arrangement in the different
apparatus of the Homma et. al. patent.
Another existing plasma apparatus inherently capable of applying or
depositing metal plating on microelectronic circuit substrate is the
Plasma Immersion Implantation Apparatus ("PII" apparatus) produced by TRW,
Inc., Redondo Beach, CA, the assignee of the present invention that is
described in U.S. Pat. No. 4,059,761 granted Nov. 22, 1977 to Dawson
entitled "Separation of Isotopes By Time of Flight" (Dawson '761).
Reference may be made to the Dawson '761 patent as additional background
to the present invention. As shown in the patent, plasma apparatus is used
to create positive ions of two different materials which can be separated
or sorted and teaches techniques for creating a plasma containing positive
ions.
More specifically, Dawson '761 discloses an apparatus for generating a
plasma using a tungsten sputter plate, a source of potassium to be ionized
and an RF source to expose the potassium to RF "heating" energy within an
evacuated longitudally extending chamber with longitudal magnetic fields
for confining the plasma away from the chamber walls, allowing positive
ions to drift toward a metal collector at the distant end of the chamber
as part of the described arrangement for separating isotopes. Although
intended for a purpose different from plating of holes in microelectronic
chip substrate, the present invention recognizes that the apparatus shown
in the Dawson patent can employ metal ions to provide a metal coating on a
substrate. A similar structure to Dawson is presented in U.S. Pat. No.
4,123,316 granted Oct. 31, 1978 to Tsuchimoto et. al. to which reference
may be made for further background in magnetically confined plasma
apparatus.
In applying the aforementioned Dawson apparatus to plating of
microelectronic substrates it was found that one experienced the same
unsatisfactory result as that encountered with vapor deposition plating
techniques in plating high aspect ratio holes. It was discovered that the
application of a voltage to the substrate and support had no energy adding
effect on the ions of the plasma increasing the negative voltage on the
substrate as was expected to attract positive metal ions to the substrate,
to add longitudinal velocity to such ions, failed. Unexpectedly, the
plasma appeared to change in lock step with the change in voltage.
Effectively the plasma remained latched to the voltage of the substrate.
When the voltage applied to the substrate increased, the plasma voltage
increased. Since there was no increase in the potential difference between
the plasma and the substrate, energy could not be added to individual
ions.
A dramatic change occurred upon the introduction of an electrically
grounded screen to the plasma apparatus and a voltage was applied between
the screen and the substrate support to create the structure described in
this specification. The plasma voltage no longer locked to the voltage on
the substrate support. Energy could be added to the metal ions. Successful
hole plating occurred.
In retrospect it is surmised that the screen effectively "grounded" the
plasma, decoupling the plasma from the substrate voltage and placing the
plasma at electrical ground. When the voltage on the substrate was varied,
the plasma voltage no longer changed with it; an electric field could thus
be established through the portion of the plasma and permitted addition of
energy increasing the longitudinal velocity of the plasma ions, while
repelling the electrons in the plasma.
An object of the present invention therefor is to provide a new and more
efficient apparatus and process for "through hole" plating of high aspect
ratio holes in microelectronic integrated circuit substrate. A further
object of the invention is to provide a plasma apparatus that is capable
of plating minute hole walls with copper or aluminum metals with great
speed. An additional object of the invention is to provide a
microelectronic substrate hole plating apparatus that is adjustable or
variable to ensure effective plating of different size holes and to ensure
complete plating of any particular high aspect ratio passage in the
substrate. A still further object of the invention is to achieve
modifications to existing plasma plating apparatus to form new plasma
plating apparatus capable of providing quality plating of high aspect
ratio holes so as to retain the benefit of redeploying existing apparatus.
And a still additional object of the invention is to improve integrated
circuit fabrication processes.
SUMMARY OF THE INVENTION
The plasma type metal plating apparatus according to the invention is
characterized by an electrical plasma, magnetically confined, containing a
high percentage of positive metal ions, that is directed toward the target
substrate, the latter containing the passages with passage walls to be
plated; and means for increasing the longitudinal velocity of the moving
ions of the plasma in the region of the substrate prior to incidence of
those ions on the substrate.
In a more specific aspect the invention is characterized by a substrate
support means for supporting a substrate containing holes to be plated in
a confined region capable of sustaining an electrical plasma; plasma means
for generating an electrical plasma with said plasma containing positive
ions of the plating metal and directing said plasma in a path toward the
substrate support means that holds the target substrate; with the plasma
means including a magnetic field oriented longitudinally in the direction
of said plasma toward said substrate support means to confine the plasma,
keeping the plasma from the region walls; screen means located in front of
said substrate support means and in the path of said plasma for permitting
passage of metal ions therethrough toward said substrate support means and
for decoupling electric fields associated with the plasma means from said
substrate support means, effectively electrically grounding the plasma,
with the screen being of an electrically conductive non-magnetic metal;
and electric field means for providing an electric field between the metal
screen and said substrate support means to add energy to the ions that
pass through the screen means in the vicinity of support means, increasing
the longitudal velocity of the ions whereby the higher energy ions
interact with said magnetic field to cause movement of ions into the
substrate passages.
An added feature allows for adjusting or changing the electric field,
whereby the amount of energy added to the metal ions is increased to cause
the ion to change its path of travel to the substrate by interaction with
the magnetic field. By varying the electric field, metal plating of the
hole walls at all depths is assured.
The associated method is characterized by the steps of directing an
electrical plasma containing a high percentage of metal ions toward the
microelectronic substrate; and increasing the longitudinal velocity of the
ions in the vicinity of said substrate to enter the holes in the targeted
substrate in a direction parallel or near parallel to the hole's axis,
resulting in a build up of metal from the bottom of the hole to its top,
without producing voids or shadowing.
The foregoing and additional objects and advantages of the invention
together with the structure characteristic thereof, which was only briefly
summarized in the foregoing passages, becomes more apparent to those
skilled in the art upon reading the detailed description of a preferred
embodiment, which follows in this specification, taken together with the
illustrations thereof presented in the accompanying drawings.
DESCRIPTION OF THE DRAWINGS
In the Drawings:
FIG. 1 illustrates the invention in schematic form;
FIG. 2 is a graph of the magnetic field intensity as a function of distance
as used in the embodiment of FIG. 1; and
FIG. 3 is a graph of the potential distribution of the plasma as a function
of distance as prescribed for the embodiment of FIG. 1.
DETAILED DESCRIPTION
Reference is made to FIG. 1 in which the preferred embodiment is
illustrated in schematic form and is shown to include a plasma generating
device that includes a vacuum chamber 1, represented by dash lines, a
microwave energy source 3, sputter plate 5, a substrate support plate 7, a
metal screen 9, which is positioned in front of the support plate, and an
aperture plate 11. A region or zone 14 is identified within the chamber,
which is referred to as an electron cyclotron resonance heating zone or,
simply, "ECRH" zone, later herein more fully described. The chamber is
typically formed of stainless steel or aluminum; materials which are of a
non-magnetic characteristic and are vacuum tight.
A pump 18 of conventional structure is included for creating a vacuum
within the chamber and is illustrated to the right in the figure. A source
of gas 20 and valve 22 is included and is located to the left in the
figure. Closure members that allow access to the chamber, and other common
elements all of which accompany a practical structure, are known and are
necessarily included, but are not separately illustrated. In as much as
those additional known elements do not add to an understanding of the
present invention those additional elements need not be described further
or discussed in detail.
A magnetic field generator, suitably of the electromagnet type formed of a
series of "pancake" type wound coils of electrical insulated wires placed
side by side and which are connected to a source of electrical dc current,
not illustrated, located external to the chamber, is represented by the
symbol 13. The magnetic field generator produces a solenoidal field as
represented by the arrow B. The magnetic field is directed along the axis
and extends the length of the chamber, including the substrate support
member. By way of example, the electromagnet and the current supplied to
it should be capable of providing a magnetic field of between 400 to 4000
gauss. A cooling source 16 of conventional structure is provided to remove
heat from the chamber walls.
A first source of dc voltage 15 is applied to the sputter plate via
electrical feed through lead 17 with the negative polarity of the dc
applied to the sputter plate; the positive polarity of source 15 is
connected to electrical ground, symbolically illustrated. A second source
of dc voltage 19 is connected to substrate support member 7 with the
negative polarity terminal connected via feed through lead 21 to the
support member and the positive polarity terminal connected to electrical
ground. Each of the dc sources is adjustable or variable as represented by
the arrow in the battery symbol, the purpose of which becomes more
apparent from the further description of operation later herein addressed.
By way of example source 15 is adjustable between zero and 1,000 volts and
source 19 is adjustable between zero and 100 volts, the latter being only
one tenth the level as the former source.
Microwave energy from source 3, which may be a klystron type oscillator, is
accessible to and directed within the chamber onto and in the region about
the sputter plate, the latter of which contains the metal to be ionized,
suitably Copper or Aluminum by way of example, and causes the release of
ions in a plasma, according to known principles the theor | | |
