Note: Descriptions are shown in the official language in which they were submitted.
SS82
This invention relates to an apparatus for
sequentially depositing layers of different materials with
rigid control of the interface composition on a substrate
by sputtering.
In sputter deposition, material is deposited as
a result of ion bombardment of a target. The bombarding
ions cause atoms of the target to be ejected at high
~elocity and become deposited on an appropriately exposed
surface, usually referred to as a substratè. Typically, the
target is physically and electrically connected to a cathode
and the substrate is positioned on an anode. rrhe ions are
produced from an inert gas or gas mixture present between
the anode and cathode across which a DC or RF potential is
applied.
In many applications, it is necessary to produce
! ~ a multilayer structure of different materials in which each
layer is of a very precLse thickness and the interface
between layers is absolutely free of contamination. This is
particularly the case for electronic circuits or devices
used in space exploration~ where the presence of any con-
tamination between layers is not permissible due to its
unXnown effect on the device's performance in space environ-
ments or over long periods of operation.
Sputtering apparatus capable of depositing several ~-
layers of different materials on a singl substrate are known.
Generally, each target is supported on a separate cathode
with its separate power network. After one layer is deposited
from a first target, which is on one cathode, the power
network of another cathode is activated. Then~ after a
period of target cleansing, which can be as long as severa].
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~urs, the first layer is exposed to the cleansed target
and a second layer is deposited from the second target.
~nfortunately, in the interim period between the deposition
of the first layer and the start of the deposition of the
second layer, the top surface of the first layer tends to
become contaminated. Such contamination prevents perfect
interface between deposited layers.
; Manufacturers of multilayered units ignore the
presence of the contamination between layers since for
general commercial applications its effect can be minimized
by baking, i.e., annealing the multilayered structures.
However, for applications in which the presence of any
contamination cannot be permitted, the annealing is of no
value. Also, in prior art sputtering equipment in which
matter ls depositable from different targets on a single
substrate there is no capability to individually control
the rate of deposition of the material of each target. As -~ 1
i5 know, materials used in sputter deposition have different
rates of deposition, and therefore being able to individually ; ;~
control their sputtering rates is important. The prior art
also employs several separate cathodes, one per target, with
each cathode having its own separate power network. This
;; greatly increases the initial cost and maintenance require- ments.
This invention successfully overcomes the above --
noted disadvantages of the prior art by providing a sputtering
apparatus comprising: a chamber containing an inert gas at a
selected pressure with 2 single stationary cathode in the
chamber. A rotatable anode is provided in the chamber spaced
apart from the cathode along a chamber axis. A plurality of
different target materials are connected to and supported by
the single cathode. A plurality of spaced apart elements are
provided supported between the anode and the cathode, each
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element defining a plurality of apertures, whereby each of
the targets is exposable through a different set of apertures
of the plates to a selected area of the anode aligned with
the target material along a different axis paralleI to the
chamber axis. Power means are provided for applying a poten-
; tial difference across the anode and cathode to ionize the
gas to form a plasma containing gas ions and electrons, the
ions striking the targets to dislodge neutral material
particles therefrom, at least some of which are directed to
the anode. Potential means are provided for controlling the
potentials of the elements so as to control the ionization
current of each plasma between each target and directed to
the anode through a different set of apertures of the elements,
the plates and apertures being spaced between the anode and
cathode whereby when the selected area of the anode is aligned
with a first of the targets only neutral material particles
from the first target reach the selected area, with neutral
material particles from either or both the first and second
elements reaching the selected anode area continuously as
the anode is rotated and the selected anode area is moved
i from alignment with the first target to alignment with the
second target.
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The plurality of apertured plates confine the plasma
to extend in the form of a column from one target in the
direction of the anode, and to prevent its spreading as well
as to prevent sputtered material cross contamination between
the targets.
In addition, a plurality of spaced apart apertured
biasing rings are positioned after the plates toward the
anode. These biasing rings are charged with a potential
gradient rising toward the anode potential in order to control,
simultaneously, the cross section and therefore the plasma
current in each column. Positioned in the path of each plasma
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column between the anode and the last blasing ring is a
separate suppressor ring, which is connectable to a different
biasing voltage. Its function is to control the individual
current to each plasma and thereby individually control the
rate of deposition from each target, independently of the
rate of deposition from the other targets.
The plates, the biasing rings and the suppression
rings are so positioned as to prevent any cross contamination
between the targets. In addition, the apparatus includes
movable shutters which are intially positioned so as to
; inhibit any material from any of the targets from reaching
the substrate while the targets are being cleansed. There-
after, the shutters are positioned to expose the substrate
on the anode to a Eirst target. After the desired layer
thickness is deposited, the shutters and the anode, supporting
the substrate, are rotated so as to expose the latter to a
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second target from which ma~ter is to be deposited. The ~
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targets are arranged so that as the substrate is moved
from one position to the next during the transition period,
matter is continuously deposited thereon, first from the
~ first target, and then from both targets when the substrate
is at a midpoint between the two targets and finally only
from the second target when the substrate is aligned there-
. w.ith. The continuous deposition of matter on the substrate .
eliminates the possibility of contamination between deposited
layers and insures perfect interface therebetween~ .
In the drawings: .
Figure 1 is a side cross-sectional view of the ~.:
. basic embodiment of the invention;
Figures 2 and 3 are top view of diffexent parts,
shown in Figure l;
Figure 4 is a partial side view useful in explain- ~. :
ing one aspect of the invention; and .-:
Figures 5 and 6 are additional top views of .
different parts, shown in Figure 1.
In Figure 1, numeral 10 represents an airtight
chamber which is connected to a vacuum system 12, and to a
:; reservoir 14 of metered gas, e.g., argon. As is known, the
chamber is first evacuated to a low pressure, e.g., 1 x 10
Torr and is then backfilled with a small amount of ~as from
source 14 to an appropriate pressure on ~he order of several
micxons.
Supported in chamber 10 is a single cathode 15 which
is shown suspended from a top plate 16. The cathode is cooled
by a cooling liquid from an appropriate source (not shown)
~y means of interconnecting insulated conduits 180 Also
supported in chamber 10 is an anode 20 which is rotatable by
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an external drive unit or motor 22, to which it is connected
by shaft 23. A stationary liquid-cooled plate 25, with which
the rotatable anode is in thermal contact, is fixedly posi-
tioned in the chamber, such as by means of brackets 260
Cooling liquid flows to and from plate 25 through conduits
270 The function of plate 25 is to remove heat from anode
20. The arrangement described so far is similar to prior
art sputtering apparatus.
As shown in Figure 1, an adapter plate 28 is
attached to the cathode 15, such as by means of screw 29.
Attached to the plate 28 are a plurality of targets 30.
Since the plate 28 is at the cathode potential, hereafter
the targets will be thought of as being connected to and
supported by the cathode 15. Figure 2 is a top view of
plate 28 and three circular targets 30, designated Tl, T2,
and T3. As shown, the targets are not positioned symmetrically
about the plate center. Rather, the angles between Tl and T2,
between T2 and T3, and between T3 and Tl, are 110, 110, and
140, respectively, for reasons to be explained hereinafter.
Each target is of a different material, a layer of which is
to be deposited either directly on the anode 20 or on a
substrate supported thereon. Such a substrate is shown in
Figure 1 and is designated by numeral 32.
As in the case in the prior art, a potential ~-
difference is established between the anode and cathode in
the chamber. Typically, the anode is at ground potential and
the cathode is at minus several Kv~ The large potential
- diference produces a glow discharge or plasma as a result of
the ionization of the gas in the chamber. The ions strike
the taryets causing neutral atoms to become separated
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therefrom, generally referred to as sputtering, while the
electrons travel to the positive anode. At least some of
the neutral atoms reach the substrate on the anode to form
the desired deposition layer. In the present invention, the
anode is assumed to be at ground potential, and the negative
potential is assumed to be applied to the cathode 15 from a
network 33.
The targets must be cleansed before depo!,ition can
take place. Therefore, a shutter 57 is incorporated. It is
placed near the anode and is at the anode potential, i.e.,
ground in the present example. The shutter has an opening
which in the present invention is positioned so that when
targets are cleansed the substrate is not exposed to the
sputtered material from any of the targets.
To insure the successive deposition of layers of
' the different target materials, in which each layer consists
of only one target material, it is of primary importance to
prevent any cross-contamination between the plasmas and
the materials sputtered from the various targets. This can
be achieved only by limiting the plasma from each target to
be directed to the substrate as a separate column which is
isolated from the other plasma columns, and by insuring that
sputtered matter from any target reaches the substrate only
when the latter is exposed to the particular plasma columM.
As shown in Figure 1, the apparatus includes a -
pluxality of plates 35. Two such plates are shown. Each
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plate 35 includes three apertures 36 as shown in Figure 3.
Each aperture diameter is greater than the target diameter,
by about O.S inch. The plates are fixedly positioned so
that the centers of the apertures are aligned along vertical
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axes with the targets' centers. Thus, in a horizontal
plane, the periphery of each aperture 36 is about 1/4 inch
from the projected edge of the target. The plates are
spaced apart 1/4 inch from one another, with the plate 35
closest to the targets being shown as flush with the
targets' front faces.
Also included i~ a plate 37 with a single aperture
38 shown in Figure 20 Plate 37 surrounds the cathode plate
28. The diameter of aperture 38 is about 1/2 inch greater
than the diameter of plate 28. The plate 37 is positioned
so that it is about 1/4 inch from the periphery of plate 28
and about 1/4 inch from the top plate 35. The plates 35 and
37 are connected to ground potential. They perform two
functions. The first is to prevent both plasma and sputtér
matter cross-contamination. The second function is to
facilitate the plasma formation along each column.
As is known, plasma tends to ~low along the
~, longest path. As the plasma is formed near each target, it
tends to move outwardly toward the walls of chamber 10. The -~
presence of the plates at ground potential confines t~e
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plasma to flow toward the anode, and the plasma is ~ as
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; a column with its outer surface being undulatea as shown in
Figure 4 for a single target. The plasma is designated by
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numeral 40. It is thus seen that the plates restrict the ;~
- plasma within the desired column and prevent spattered
material cross-contamination between columns.
In addition to the plates, the apparatus of the
present invention includes a plurality of biasing shields 42.
Three such shields are shown in Figure 1. Physically, the
shields are identical to the plates 35. This is, each has
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three apertures 36, as shown in Figure 3. The shields 42
are also spaced apart 1/4 inch toward the anode. However,
unlike plates 35 which are at ground potential, the shields
42 are connected to a divider network 45, represented as a
resistor 45a connected between ground and a minus potential
-V. The shield 42 closest to the anode is at a higher
potential than the shields closest to lowest plate 35. Thus,
all the shields 42 are at a lower potential than the anode
which is at ground.
Due to the shields' potentials, the cross section
of the plasma passing through each set of apertures of the
shields is restricted thereby reducing plasma current which
reduces the deposition rate. It should be pointed out that
the biasing shields 42 simultaneously control the plasmas
from all three targets in the three columns since the three
plasmas flow through the same three biased ~hields. In
addition, the shields 42, like plates 35, prevent cross- ~ -
contamination between the three columns and cause the shape
of the plasma in each column to have the undulated outer
surface as shown in Figure 4.
The apparatus also includes a separate biasing
ring 50 for each column. A top view of one ring 50 is shown
in Figure 5. Its aperture 52 i5 of the same size as each
aperture 36 of a shield 42. The three individual rings 50
are located in the same plane about 1/4 inch below the lowest
shield 42. Each ring S0 is connected to a separate bias
source 55 (Figure 5) of negative voltage. Such voltage,
like the ones applied to shield 42, reduces plasma current
, and therefore the deposition rate. However, since each
co}wnn has a separately biasable rinq 50, the plasma in each
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column is controllable independently of the plasmas in the
: other columns.
As further shown in Figure 1, a pair of shutters
57 and 58 are included in chamber 10~ Each is coupled by a
separate shaft to motor 22. Each shutter has an aperture 59
: (see Figure 6) with a diameter which is generally equal to
the diameter of the layer to be deposited. Shutter 57 is
utilized as a barrier when the surfaces of the targets are
cleansed, while shutter 58 is a target selector, used to
select the particular target from which material is deposited.
Except during cleansing, both shutters are moved together
by motor 22.
'rhe use of the apparatus will now be described in :
; connection with the specific example in which it is assumed
that a unit or structure consisting of layers from targets ;.
Tl, T2, and T3 is to be produced. Either after or before
placing the substrate 32 on the anode and before establishing -~
the necessary gas pressure in chamber 10, shutter 58 is :
~ rotated so that its aperture is aligned with the column of Tl
and shutter 58 is rotated so that its aperture is in the 140 ~ .
zone ~see Figure 2) between T3 and Tl. Then the potentials
are applied to the cathode and anode. As a result, target
sputtering takes place, thereby cleansing all three targets. :~
The potentiaI is applied continuously throughout the entire : .
operation. ~s the targets are cleansed due to the position :
o~ shutter 57l none of the sputtered material reaches the
substrate 32. .....
After the targets are cleansed, the shutter 57 is
rotated to align its aperture with the column Tl. Thus, the
substrate 32 is exposed to target Tl and theFefore the first
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layer is deposited thereon. The bias on ring 50 in this
column may be controlled to control the deposition rate from
Tl. After the layer from Tl reaches the desired thickness,
both shutters 57 and S8 are rotated together (clockwise in
Figure 2) with the anode 20 toward the column of T2.
As the anode and the shutters move from the
position in which the substrate 32 and the shutters' apertures
- are aligned with the column of Tl to that of T2, a deposition
transition takes place. The spacing between columns in the
chamber and the movement of the anode shutters are such that
during the entire transition some material is always deposited
on the substrate. As the substrate and the shutters move
away from the column of Tl, less material fro~ Tl is deposited
on the substrate until the substrate is completely blocked
off from the Tl column and is aligned with the T2 column.
Then only material from T2 is deposited to form the second
layer. In operation, when the substrate and the apertures of
shutters 57 and 58 are midpoint between the Tl and T2 columns,
i.e., about 55 (see Figure 2) from either column, some matter
from each of targets Tl and T2 gets deposited on the substrate.
However, as the substrate becomes aligned with the T2 column,
only matter from T2 is deposited thereon. Any matter from
either Tl or T3 is blocked off by the plates, shields, and
xings, as well as by the shutters which are between the
targets and the substrate.
The continuous deposition during the transition
from Tl to T2 eliminates the presence of any contaminant
between the deposited layers. Also, it insures perfect
interface between the two deposited layers of materials from
Tl and T2. After reaching the T2 column, the shutters remain
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thereat until the layer of T2 material reaches the desired
thickness. Then the anode and the shutters are moved to
column T3 to deposit the T3 material. Again t during the
transition from T2 to T3, material is continuously deposited
on the substrate to eliminate contamination between the
second and third layers and provide nearly perfect interface
therebetween.
The apparatus of the present invention was used to
deposit layers of molybdenum and gold on nickel foil with -~
perfect adhesion. It was also used to deposit in sequence
layers of titanium, molybdenum and gold on an aluminum oxide
substrate. When etched the layers which were on the order of
; SOO to lOOO A(angstrom) in thickness were found to be with- ;
out fault. That is, the interfaces between layers were
perfect and did not contain any contaminants. It should be
appreciated that the invention is not intended to be limited
for use with the above-mentioned materials. Any sputterable
materials may be used therein. Also, more than one substrate
may be simultaneously exposed in the same column.
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