U.S. patent application number 10/529315 was filed with the patent office on 2006-08-24 for method for depositing multilayer coatings.
Invention is credited to Dennis Teer.
Application Number | 20060188660 10/529315 |
Document ID | / |
Family ID | 9944790 |
Filed Date | 2006-08-24 |
United States Patent
Application |
20060188660 |
Kind Code |
A1 |
Teer; Dennis |
August 24, 2006 |
Method for depositing multilayer coatings
Abstract
The invention relates to a method and apparatus for the
generation of multilayered coatings onto substrates. Typically the
apparatus used is a closed field unbalanced magnetron configuration
in conjunction with one or more cylindrical and rotatable shields
and a substrate carrier on which the substrates to be coated are
carried. The shields and substrate holder are provided for rotation
about a common axis of rotation. The shields are provided with
apertures to allow the selective positioning of the apertures to
define a passage or passages along which material from the targets
can pass onto the substrates. The targets can be cleaned prior to
the coating stage by operation of the targets with the shields
selectively positioned to prevent the deposited material from
reaching the substrates.
Inventors: |
Teer; Dennis; (Hartlebury,
GB) |
Correspondence
Address: |
Nixon Peabody
Clinton Square
Po Box 31051
Rochester
NY
14603-1051
US
|
Family ID: |
9944790 |
Appl. No.: |
10/529315 |
Filed: |
December 26, 2003 |
PCT Filed: |
December 26, 2003 |
PCT NO: |
PCT/GB03/04189 |
371 Date: |
March 29, 2005 |
Current U.S.
Class: |
427/524 ;
118/723ME |
Current CPC
Class: |
C23C 14/505 20130101;
C23C 14/352 20130101; C23C 14/568 20130101; H01J 37/3405 20130101;
C23C 14/3492 20130101; H01J 37/3447 20130101 |
Class at
Publication: |
427/524 ;
118/723.0ME |
International
Class: |
C23C 14/42 20060101
C23C014/42 |
Foreign Application Data
Date |
Code |
Application Number |
Sep 26, 2002 |
GB |
0222331.1 |
Claims
1. Apparatus for the application of a coating of material or
materials, said coating comprising at least first and second layers
of material or material compositions, said apparatus including at
least first and second magnetrons from which material can be
selectively applied, a substrate holder, on which the substrates to
be coated are held and characterised in that positioned between the
magnetrons and the substrate holder, is at least one shield, said
shield including at least one aperture through which material
deposited from a magnetron can pass for application onto the
substrates when the aperture is suitably positioned with respect to
the said magnetron and substrate holder by selective rotation of
the shield with respect to the magnetrons so as to define a passage
through which the material deposited from the target of said
magnetron can pass.
2. Apparatus according to claim 1 characterised in that the
movement of the shield in use means that when the aperture or any
part of the aperture is not in front of a particular magnetron,
deposition of the material onto the substrates from that magnetron
is prevented or at least significantly reduced.
3. Apparatus according to claim 1 characterised in that the shield
is rotatable so that the aperture moves from a position in front of
a first magnetron to a position in front of a second magnetron and
so on in sequence to provide a multi layered coating.
4. Apparatus according to claim 3 characterised in that a coating
with alternate layers of materials from the targets of the first
and second magnetrons is achieved.
5. Apparatus according to claim 1 characterised in that the
thickness of the individual layers of material is controlled by the
power applied to the magnetron and/or the time of a shield aperture
being positioned in front of that particular magnetron.
6. Apparatus according to claim 1 characterised in that a closed
field unbalanced magnetron (CFUBM) configuration is used.
7. Apparatus according to claim 1 characterised in that the
substrates are mounted on the holder which is rotatable.
8. Apparatus according to claim 1 characterised in that the shield
is replaced by two shields with one positioned inside the other,
having a common axis of rotation and each having at least one
aperture therein.
9. Apparatus according to claim 8 wherein the shield are
cylindrical and concentric with the substrate holder, and rotate
about a common axis of rotation.
10. Apparatus according to claim 9 characterised in that the
shields are selectively rotated to bring the apertures in each into
line and define a passage for the deposition of material from a
magnetron target therethrough when positioned in front of said
target.
11. Apparatus according to claim 9 characterised in that the
shields are selectively positioned so as to prevent material
passing through the apertures and onto the substrates during the
preparation of the magnetron targets.
12. A method for controlling the application of a multilayered
coating onto at least one substrate in a coating chamber, said
method comprising positioning a plurality of magnetrons with
targets of material to be deposited in the coating chamber to face
towards a substrate holder in the chamber, interposing between the
substrate holder and the magnetrons, first and second shields,
providing in said shields at least one aperture which, when
selectively positioned with respect to a magnetron, allows material
deposited from the magnetron target to pass therethrough and onto
the substrates and characterised in that the shields are
selectively rotatable so as to move and position the respective
apertures to define a passage for selected periods of time to allow
the passage of material deposited from a magnetron target and then
to move the shields to repeat the same as required with respect to
the first and second magnetrons as required to apply the
multilayered coating onto the substrates.
13. A method according to claim 12 characterised in that the
magnetrons are continuously operated during the deposition process
to deposit material from the respective target and when the
apertures of the shields are not positioned to define a passage for
the material the deposited material applies to the wall of the
shield which faces the target.
14. A method according to claim 12 wherein when no passage is
defined by the shield apertures at a particular magnetron at a
particular time during the coating procedure that magnetron can be
moved to a shut down or standby condition.
15. A method according to claim 12 characterised in that the
movement of one or both of the shields is continuous at a selected
speed which can be varied or fixed to suit particular coating
requirements.
16. A method according to claim 12 characterised in that the
movement of one or both of the shields is stepwise with a selected
dwell time of the shields to allow a blanking of the passage of
deposited material to the substrates or deposition of material from
a target or targets for a period of time.
17. A method according to claim 16 characterised in that the
shields are selectively moved between dwell times to define the
blanking or deposition passage configurations as required.
18. A method according to claim 12 wherein a reactive gas is
introduced into the coating chamber during the coating procedure to
allow the deposited material to form a compound material on the
substrates.
19. A method according to claim 12 characterised in that the method
includes the step of conditioning or preparing the material targets
in each of the magnetrons prior to operation of the shields to form
deposition passages, during which preparation stage material is
deposited from the magnetron targets and the shields are positioned
to prevent material from the targets reaching the substrates.
20. A method according to claim 12 characterised in that the
relative positions of the shields when forming a passage for the
deposited material from a magnetron target are selected to define
the width of the passage defined by the apertures.
21. A method according to claim 20 wherein the apertures are
positioned in line to define a full width passage.
22. A method according to claim 20 wherein the apertures are offset
or of differing widths to define a passage of a width less than the
width of the largest width aperture.
23. A method for the control of operation of apparatus for applying
a coating onto at least one substrate, said coating comprising a
series of layers and said apparatus including within a coating
chamber at least two magnetrons for the selective deposition of
material from magnetron targets onto the substrates, and a
plurality of cylindrical shields positioned between the targets and
the substrate holder, said shields including apertures which can be
selectively positioned to define a passage for deposited material
from the targets onto the substrates and characterised in that the
method comprises the steps of: preparing the targets by operating
the magnetrons to deposit material from the targets in the coating
chamber and positioning the shields to prevent the passage of
deposited material onto the substrates; and applying a
predetermined power level to the magnetrons and maintaining said
power level during the application of the deposited material onto
the substrates and the apertures in the shields are selectively
positioned to allow the selective application of the material onto
the substrates through passages defined by the apertures.
24. A method according to claim 23 wherein the deposition of
material is to be by reactive deposition and a reactive gas is
introduced into the coating chamber to a defined level after the
magnetron target preparation steps have been completed.
25. A method according to claim 24 wherein when the appropriate gas
level is reached and maintained, the apertures in the shields are
selectively positioned to allow the selective application of the
material onto the substrates through passages defined by the
apertures.
26. A method according to claim 24 wherein the defined level of
reactive gas is selected with reference to the metal intensity of
the target as cleaned and prepared which is regarded as 100%.
27. A method according to claim 24 wherein monitoring means are
provided in the coating chamber and when the appropriate gas level
is reached to match a predetermined value the same is monitored for
a period of time to ensure the same is stable and if so the gas
continues to flow at that same rate.
28. A method according to claim 27 wherein a gas control method is
used including any of magnetron power supply voltage variation or
mass spectrometer control of gas partial pressures.
29. A method according to claim 27 wherein Optical emission
monitoring (OEM) is used to control the gas flow.
30. A method according to claim 29 wherein OEM is used to control
the reactive gas flow at the required level for a stoichiometric
coating to be applied to the substrates.
31. A method according to claim 24 wherein the power level applied
to the magnetrons during the preparation stage is higher than that
applied during the material deposition.
32. A method according to claim 24 wherein stable operating
conditions are established prior to the deposition of the material
onto the substrates by enabling the preparation and cleaning of the
targets without contaminating the substrates by positioning the
shields to prevent the passage of the material onto said substrates
during the preparation stage.
Description
[0001] The invention to which this application relates is to the
provision of a method for the deposition of multilayered coatings,
in terms of layers of different materials or different material
compositions, onto a substrate with the coating and/or the layers
in the coating having controlled thickness characteristics.
[0002] The method utilised in this invention is based on sputtering
and preferably magnetron sputter cathodes, and yet further,
unbalanced magnetrons used in accordance with apparatus in the
Patent GB2258343.
[0003] Conventionally, in a typical coating system with two
magnetrons which face each other, the first magnetron is provided
with a target of material A to be deposited on the substrate and
the second magnetron is provided with a target of material B also
to be deposited onto the substrate. Typically two power supplies
are provided for each of the magnetrons and the conditions
controlled via control of the power supplies so that the rate of
deposition of material from the magnetron is controlled. The
substrates are mounted on a central rotating holder and receive a
coating flux from the targets so that material A and material B are
alternatively applied to the substrate in layers to form a
multilayer coating. The thickness of the individual layers of
material is typically defined by the power level applied to the
magnetrons and by the speed of rotation of the holder of the
substrates.
[0004] A common problem with this method of application is that the
interfaces between the respective layers in the coating are not
well defined or sharp.
[0005] It has previously been proposed to solve this problem by
providing the magnetrons in a manner so that they can be switched
on and off to give alternative levels of control. An adaptation of
this process is to provide shutters provided in front of each of
the magnetron targets which can be operated to move between open
and closed conditions to provide additional control.
[0006] The provision of shutters and/or switching on and off of
magnetrons can provide difficulties in the control of the
deposition. This is particularly problematic for the deposition of
coatings for uses which have relatively low tolerance to coating
imperfections and where imperfection can cause significant
problems. An example of this is the application of coatings on
optical substrates, where the required degree of control of both
composition and thickness is extreme.
[0007] A further problem is that when the coating process is to
include reactive sputtering i.e. the application of materials in a
reactive gas in the coating chamber to form a particular material
coating composition problems arise with regard to the control of
the gas flow. The problems of controlling gas flow in turn mean
that the control of the coating composition can be difficult and as
a result the coating composition varies beyond acceptable coating
parameters. With the use of conventional shutter arrangements it is
not possible to establish stable gas flow in the coating chamber
and/or stable magnetron target poisoning conditions behind the
shutter. As a result, the electrical potential, magnetic field and
gas flow close to the magnetrons is adversely affected.
[0008] The aim of the present invention is to provide a system for
the control and application of multilayered coatings onto the
substrate which avoids the control and application problems
conventionally encountered.
[0009] In a first aspect of the invention there is provided
Apparatus for the application of a coating of material or
materials, said coating comprising at least first and second layers
of material or material compositions, said apparatus including at
least first and second magnetrons from which material can be
selectively applied, a substrate holder, on which the substrates to
be coated are held and characterised in that positioned between the
magnetrons and the substrate holder, is at least one shield, said
shield including at least one aperture through which material
deposited from a magnetron can pass for application onto the
substrates when the aperture is suitably positioned with respect to
the said magnetron and substrate holder by selective rotation of
the shield with respect to the magnetrons so as to define a passage
through which the material deposited from the target of said
magnetron can pass.
[0010] In one embodiment the magnetrons utilised are unbalanced
magnetrons and yet further and preferably the magnetron deposition
apparatus is in the form of a closed field unbalanced magnetron
material deposition apparatus. In one embodiment the magnetron
arrangement used is as disclosed in the patent GB2258343.
[0011] Typically, the movement of the shield in use means that when
the aperture or any part of the aperture is not in front of a
particular magnetron, deposition of the material onto the
substrates from that magnetron is prevented or the amount of
deposition is reduced.
[0012] Typically each shield provided is cylindrical and is rotated
so that the aperture moves from a position in front of a first
magnetron to a position in front of a second magnetron and so on,
thus allowing, if desired, continuous operation of the magnetrons,
so that deposition of a layered coating with alternate layers of
materials from the targets of the first, second and further
magnetrons is achieved.
[0013] Typically the substrate can be rotated and in one embodiment
the holder rotates at a faster rate than the cylindrical
shutter.
[0014] In a preferred embodiment the axis of rotation of the
substrate holder is common with the axis of rotation of any of
shield which is provided. This means that with the substrate holder
substantially cylindrical and the shields which are provided being
of cylindrical shape that the coating apparatus as herein described
is symmetrical hence improving the controllability of the
apparatus.
[0015] Typically, the thickness of the individual layers of
material is controlled by the power applied to the magnetron and/or
the time of a shield aperture being positioned in front of that
particular magnetron. It is found that accurate and close control
of the thickness of the material layer with improved and sharp
interfaces between the layers is achieved by the invention.
[0016] Typically the magnetrons can be round or rectangular and the
aperture is shaped so as to match the requirements for the
particular magnetron shape used.
[0017] Typically, the size and shape of each aperture in the shield
is chosen to ensure uniformity in the thickness of the material
coating on the substrates.
[0018] Preferably two shields ate provided, both typically
cylindrical, and with one positioned inside the other and with
common axes of rotation, and each having at least one aperture
therein. The speed of rotation, direction of rotation and
positioning of each shield can be independently controlled but with
an aim of ensuring that when required the apertures in the
respective shields are positioned so as to ensure that the
deposition of material from the magnetron targets onto the
substrates is entirely prevented during the preparation of the
magnetron targets and, thereafter, the apertures are positioned at
the correct location with respect to the magnetron targets to allow
the selected and controlled deposition of material onto the
substrates. In a further embodiment three or more shields can be
provided between the substrate holder and the magnetron depositions
means.
[0019] Typically, the shields have a radius so that one fits inside
the other and both can be positioned close to the magnetrons or
close to the substrates or any position between these extremes to
suit particular coating requirements.
[0020] In one embodiment a range of shields can be provided to be
selectively positioned in the coating chamber to suit particular
coating requirements and may be replaced, as required, by
alternative shields with different radii and/or aperture
dimensions. Alternatively, shields can be provided which allows
adjustment to provide suitable dimensions. When two shields are
used it is only when the apertures in each are wholly or partially
aligned that the material can pass through the same to be deposited
onto the substrates.
[0021] It should also be appreciated that the apparatus and method
herein described can be used for the non-reactive or reactive
deposition of material to form the coatings on the substrates, the
reactive sputtering being achieved by the controlled introduction
of reactive gases as required.
[0022] In a further aspect of the invention there is provided a
method for controlling the application of a multilayered coating
onto at least one substrate in a coating chamber, said method
comprising positioning a plurality of magnetrons with targets of
material to be deposited in the coating chamber to face towards a
substrate holder in the chamber, interposing between the substrate
holder and the magnetrons, first and second shields, providing in
said shields at least one aperture which, when selectively
positioned with respect to a magnetron, allows material deposited
from the magnetron target to pass therethrough and onto the
substrates and characterised in that the shields are selectively
rotatable so as to move and position the respective apertures to
define a passage for selected periods of time to allow the passage
of material deposited from a magnetron target and then to move the
shields to repeat the same as required with respect to the first
and second magnetrons as required to apply the multilayered coating
onto the substrates.
[0023] In one embodiment the magnetrons are continuously operated
during the deposition process to deposit material from the
respective targets and when the apertures of the shields are not
positioned to define a passage for the material the deposited
material applies to the wall of the shield which faces the target.
Although it is envisaged that the operation of the targets to
deposit material continuously may be advantageous in terms of
control it is possible that when the apertures of the shields are
not to be positioned to allow the passage of material from a
particular target, then that target and magnetron may be moved to a
shut down condition or a reduced operating condition so as to avoid
or reduce respectively the deposition of material onto the shield
wall and hence reduce material wastage. In this embodiment when the
control system for the apparatus determines that a passage is to be
provided in the near future for the deposition of material from
said target, the magnetron and target are returned to full
operating conditions.
[0024] In one embodiment, the movement of one or both of the
shields is continuous. If continuous the speed can be varied or
fixed to suit particular coating requirements. Alternatively, the
movement of the shields is stepwise with a selected dwell time of
the shields to allow a total blanking of the passage of deposited
material or the maintenance of the apertures to define a passage in
front of one or other or both of the magnetrons.
[0025] Typically, when two shields are provided they will be moved
in opposing rotating directions.
[0026] In one embodiment the method includes the step of
conditioning or preparing the material targets in each of the
magnetrons to ensure that each is entirely clean prior to operation
of the shields during which material is deposited from the
magnetron targets without the presence of reactive gas and the
shields positioned to prevent material from the targets reaching
the substrates during this stage. In this case the shields are
positioned such that the aperture(s) in one shield are spaced apart
as far as possible from the aperture(s) in the other shield, the
exact spacing and positioning being dependent upon each shield
aperture configuration. The provision of the shields in this
configuration ensures the prevention of material reaching the
substrate surfaces and hence prevents the same from being adversely
affected prior to the controlled application of the coating
materials.
[0027] In one embodiment, when two shields are utilised, the
relative positions of the apertures in each of the shields when
forming a passage for the deposited material from a magnetron
target can be selected to vary the width of the passage. For
example, if the apertures are fully aligned a fully open passage is
provided which allows a full deposition rate whereas, if only
partially aligned, the size of the passage is reduced and hence the
deposition rate to the substrates is reduced.
[0028] Typically, if the shields are rotated in the reverse
direction to the direction of rotation of the substrate holder as
this provides a more clearly defined "cut off" of the deposited
material as the apertures leave a position in front of the
magnetron.
[0029] In one embodiment one of the shields includes a greater
number of apertures than the other thereby allowing for the
selective positioning of the apertures to define material
deposition passages.
[0030] In a further aspect of the invention there is provided a
method for the control of operation of apparatus for applying a
coating onto at least one substrate, said coating comprising a
series of layers and said apparatus including within a coating
chamber at least two magnetrons for the selective deposition of
material from magnetron targets onto the substrates, and a
plurality of cylindrical shields positioned between the targets and
the substrate holder, said shields including apertures which can be
selectively positioned to allow the passage of deposited material
from the targets onto the substrates and characterised in that the
method comprises the steps of: [0031] preparing the targets by
operating the magnetrons to deposit material from the targets in
the coating chamber and positioning the shields to prevent the
passage of deposited material onto the substrates; and [0032]
applying a predetermined power level to the magnetrons and
maintaining said power level during the application of the
deposited material onto the substrates and the apertures in the
shields are selectively positioned to allow the selective
application of the material onto the substrates through passages
defined by the apertures.
[0033] In one embodiment if the deposition of material is to be by
reactive deposition the reactive gas is introduced into the coating
chamber to a defined level after the magnetron target preparation
steps have been completed and when the appropriate gas level is
reached and maintained, the apertures in the shields are
selectively positioned to allow the selective application of the
material onto the substrates through passages defined by the
apertures. As the magnetron targets are so effectively cleaned and
prepared in accordance with the invention prior to the commencement
of the deposition of material onto the substrates the defined level
of reactive gas is selected with reference to the metal intensity
of the target as prepared which is regarded as 100%.
[0034] As the current invention allows the accurate and controlled
cleaning of the targets and the power level can be maintained at
constant during the coating process as the targets continuously
deposit material even if the apertures are not located adjacent the
same, so it is the level of reactive gas introduced into the
coating chamber which can be used as the controlling parameter to
control the composition of the coatings on the substrates. This is
in addition to control of any of the speed of rotation of the
substrate holder and the speed and/or dwell time of the shields to
allow more accurate control of the coating application, greater
definition between the coating layers and the ability to provide a
multilayered multi material coating which is dense, has good
optical quality and can be closely defined in more easily
repeatable coating procedures.
[0035] Typically the amount of reactive gas which is introduced
into the chamber is in response to a user selection of a required
percentage level of the metal intensity. Monitoring means are
provided in the chamber and when the appropriate gas level is
reached to match the percentage level the same is monitored for a
period of time to ensure the same is stable and if so the gas
continues to flow at that same rate. Thus this can be achieved by
use of the Optical emission monitoring (OEM) method to control the
gas flow and hence the composition of the coating. This method, to
operate successfully depends on the operation commencing with
"clean" targets and, as already explained above this is achieved
with the current method and apparatus by the operation of the
magnetrons and targets to sputter deposit the material prior to the
introduction of any reactive gas into the coating chamber.
Furthermore the ability to arrange the shields as described blocks
the passage of the sputtered material to the substrates and hence
ensures that there is no contamination of the substrates during
this preparation stage. Typically the preparation and cleaning
steps are further enhanced by applying a power level higher than
that used during deposition.
[0036] Thus, in one embodiment the power level applied in the
preparation step is higher than the power level applied during the
coating stage.
[0037] As already stated the method for reactive material
deposition can utilise Optical Emission Monitoring (OEM) for
control purposes although it should be appreciated that other
control systems can also be utilised as required.
[0038] A description of the prior art arrangements and specific
embodiments of the present invention are now described with
reference to the accompanying drawings wherein:
[0039] FIG. 1 illustrates a conventional, prior art coating
system,
[0040] FIG. 2 illustrates the provision of shutters in a
conventional manner;
[0041] FIGS. 3a and b illustrate one embodiment of the present
invention in plan with a cross section along line A-A of the
shields of FIG. 5;
[0042] FIG. 4 illustrates a further embodiment of the invention in
plan with a cross section along line C-C of the shields shown in
FIG. 5;
[0043] FIG. 5 illustrates three shields in different embodiments in
accordance with the invention; and
[0044] FIG. 6 illustrates a further embodiment of the invention in
plan with a cross section along lines A-A and B-B of the two
shields in FIG. 5 to illustrate the aperture in each.
[0045] Referring firstly to FIG. 1 there is illustrated a coating
system with two facing magnetrons, magnetron 1 with the target
material A and magnetron 2 with target material B. In operation,
power is applied to the magnetrons under controlled conditions via
power supplies 31,33 respectively so that the substrates 3, which
are mounted on a central rotating holder 4, receive a coating flux
from targets A and B alternately and are as a result coated by a
multilayer coating.
[0046] FIG. 2 illustrates a known system of the type of FIG. 1
which includes a system to attempt to provide improved definition
and sharpness between layers in the multilayer coating. The system
comprises the provision of magnetrons 1 and 2 which can be switched
on and off and also provided with shutters 6 which can be
selectively open as shown by shutter 6' and closed, as shown by
shutter 6'' to provide additional control of the application of the
coating material.
[0047] In FIG. 2 a "double door" shutter arrangement is used
although this can be replaced by a single door or a sliding
parallel door. What they all have in common is that for the
conventional shutter to operate it needs to be close to the
magnetron to provide a relatively small, typically the same size as
the magnetron target, barrier close to the magnetron. If the
conventional shutters were spaced any distance from the magnetron
they would be less effective in blocking the coating flux. The
present invention provides a solution to this problem and the
general problem of preconditioning material targets effectively and
the control of the material deposition in an effective manner.
[0048] The deposition system can be simple sputtering in which case
the substrates can be at earth potential. Alternatively, sputter
ion plating can be used in which case the substrate can be at any
negative potential up to -5 kv but more typically about -50 v.
Furthermore the substrate can be provided at a floating potential
but/and in order to ensure stable conditions during the deposition
process, the shield can be earthed, floating or biased to a
negative potential as required.
[0049] With reference to FIGS. 3a and b, one embodiment of the
invention of the current application is shown with the apparatus
and method used to deposit coatings in the following manner. The
apparatus is provided in a coating chamber 9 and two shields 10, 11
are provided, both of which are cylindrical. The shield 10 is
provided with an aperture 12 and the shield 11 is provided with an
aperture 13. The aperture in each shield is located such that, by
rotation of the shields each aperture can be selectively positioned
in front of the other and, together, form a passage between either
of the magnetrons 1, 2 and the substrate holder 4. In that position
with the passage formed, as shown in FIG. 3b, material deposited 17
from the magnetron target A passes through the passage 15 defined
by apertures 12,13 and onto the substrates 3 on the holder 4 which
is rotated. The shields are selectively rotatable so that the
apertures 12,13 can be moved between a position in front of one
magnetron A, to a position in front of the other magnetron B, or
indeed yet further magnetrons if provided, and then held with the
aperture at the selected magnetron for the required time for
depositing material from that magnetron onto the substrates to
create a layer with the required depth.
[0050] FIG. 3a illustrates how the material 17 can be deposited
from the targets A and B but if the apertures 12,13 are not aligned
the material is simply deposited onto the wall of the shield
10.
[0051] Thus, with the shields provided, the magnetrons can be
continually operated but, it is only when the apertures 12,13 are
located in front of a magnetron, that the material from that
magnetron target can reach the substrates.
[0052] The deposition method and apparatus as herein described can
be used to deposit coatings in a non reactive gas such as argon
and/or can be used for deposition of material in a reactive mode by
the introduction of a reactive gas into the coating chamber 9. If
nitrogen gas is introduced then nitride coatings can be deposited,
if a hydrocarbon gas is introduced then carbide coatings can be
deposited, if oxygen is introduced then oxide coatings can be
deposited and so on. Yet further, it should be appreciated that
coatings comprising pure metals or compounds produced by reactive
methods can be produced.
[0053] When reactive deposition is to be provided the reactive gas
flow into the chamber 9 can be controlled by a needle valve or mass
flow valve or by magnetron power supply voltage variation or mass
spectrometer control of gas partial pressures but preferably by a
method relying on optical emission monitoring (OEM) with feed back
control to a piezo electric valve would be used to ensure close
control of the composition of the compound coating.
[0054] Using the OEM method it is necessary initially to establish
the selected stable conditions for stoichiometric coatings.
Movement of conventional shutters close to the magnetron targets
affects the stability of the gas flow and so causes the deposition
of coatings with undesirable compositions. Also movement of the
conventional types of shutter can affect the magnetic field and
plasma conditions of the magnetron and cause variations in
deposition rates.
[0055] The shields 10,11 in accordance with this invention have
several advantages. Because of the fact that the shields and
substrate holder 4 and configuration of the deposition apparatus
can all be in a substantially cylindrical form and with a common
central axis 19 so the apparatus is symmetrical and hence the
substrate holder and particularly the shields have very little and
significantly reduced affect on the stability of the system as they
rotate. Also the shields can be positioned at different radii and
the optimum radius for each can be selected so that any effect on
stability is minimised as the cylindrical shields rotate. Also it
is easy to bias the cylindrical shields electrically and the
optimum bias for stability can be selected.
[0056] When controlling the thickness of layers applied to close
tolerances it is necessary to maintain stability at the sputter
magnetrons and any shield movement should change the magnetic and
plasma environment at the sputter electrodes as little as possible.
This is particularly true for magnetron electrodes. During
deposition of compound coatings by reactive techniques the
deposition conditions are particularly sensitive to changes in the
magnetic and plasma environment of the sputter electrode. A
conventional shutter of the type shown in FIG. 2 will influence the
flow of gas to the sputter target causing serious instability in
the control of coating composition. As the cylindrical shields in
accordance with the invention are symmetrical, and can be
sufficiently distant from the sputter electrode they have little
effect on the magnetic and plasma environment at the electrode and
have little effect on the gas flow conditions close to the
electrode. Also, the electrical potential of the shields can be
selected to minimise any effects on the potential field of the
whole deposition system and the conditions close to the substrates
are maintained stable.
[0057] It has been found that a particularly successful and simple
arrangement is to position the shield between the substrates and
unbalanced magnetron sputter electrodes in a closed field
unbalanced magnetron (CFUBM) deposition arrangement as in the
patent previously mentioned. For most coatings a substrate bias
voltage of less than -50 v ensures excellent coating quality. Under
these conditions the floating potential of the cylindrical shutter
is about -20 v and good long term stability is maintained in the
system as the shutter is moved.
[0058] The applied bias can be RF or DC with RF provided for
insulating substrates or insulating coatings. One convenient method
is to have both the substrates and the shields floating.
[0059] For most compound coatings deposited reactively, the OEM
control method ensures that the reactive gas flow can be controlled
adequately at one of the magnetrons. The power on the other
magnetrons can be selected so that it produces stoichiometric
coating at the gas flow resulting from the control system at the
first magnetron. The required layer thicknesses can then be
obtained by controlling the dwell time for the passage formed by
the apertures in the shields in front of each target.
[0060] It may be necessary to have separate OEM gas flow control
systems at two or more magnetrons but these can relatively easily
be provided.
[0061] The provision of two shields 10,11 also means that movement
of the shields is sufficiently rapid to give the required sharpness
of interface between the layers of the applied coating. Typically,
both shields can be independently controlled and can, in one
embodiment be rotated in opposite directions 24, 22 as shown in
FIG. 6 or, alternatively, both could be moved in the opposite
direction to the rotation 23 of the substrate holder. The two
shield arrangement also has the advantage that the magnetrons A, B
can be run with no possibility of deposition on the substrates 3
when the apertures 12, 13 in the two shields 10, 11 are out of line
as also shown in FIG. 6. This is an important feature as, during
the preparation of the magnetrons the targets of the same are
operated to sputter deposit material which acts as a cleaning step
and established the required stable conditions. The provision of
the two shields with the apertures out of line and removed from the
magnetron locations ensures that none of the sputtered material can
reach the substrates.
[0062] The examples given so far are for a two magnetron system.
The method is suitable for multi magnetron systems with any number
of magnetrons. For a 4 magnetron system as shown in FIG. 4 two
cylindrical shields 30,31 are provided and each, in this
embodiment, is provided with two apertures, although it should be
appreciated that the number of apertures provided and the spacing
of the same is dependent upon the particular coating requirements
and configurations. Here, magnetrons 1 and 3 have targets of the
same material A and magnetrons 2 and 4 have targets of material B.
However it should be appreciated that in other embodiments each of
the magnetrons can have a target of a different material or other
combinations of target materials can be used to suit particular
coating formation requirements. Two diametrically opposed apertures
12,12' in shield 30 and 13,13' in shield 31 are positioned as
shown. This method is similar to that for the two magnetron system
but, in this example, gives double the deposition rate of materials
A or B as the same can be deposited from the two magnetron pairs,
1,3 or 2,4, respectively through the two passages defined by the
apertures 12,13 and 12',13' respectively.
[0063] FIG. 5 illustrates three shields 10, 11 and 30 which can be
selectively used and each can be selectively used individually or
in combination for any of the embodiments shown in FIGS. 3a,b, 4
and 6 to suit particular purposes. The drives used to rotate and
stop the shields can be any suitable powered and controlled drive
means.
[0064] Another embodiment of the invention is shown in FIG. 7 where
there is provided the coating chamber 9 with the rotatable
substrate holder 4 and substrates 3 thereon. In this embodiment a
single cylindrical shield 20 is used with an aperture 21. Again two
magnetrons 1,2 are provided with materials A,B respectively. The
operating method is similar to that previously described with
respect to the two shield arrangement with the passage 15 being
formed by the provision of the aperture 21 at the required location
with respect to the magnetrons. In practice it has been found that
the use of the two shields ensures maximum stability and gives
excellent control of layer thickness by ensuring the improved
preparation of the targets and avoiding the deposition of material
from the targets onto the substrates during the target preparation
stage.
[0065] It will also be seen from the embodiment of the invention
described that the shields can be positioned a significant distance
away from the magnetrons in contrast to the conventional system
where the shutter is required to be positioned close to the
magnetron to be most effective. Thus the present invention allows
the shield to be associated with the position of the substrates to
be coated rather than the magnetron positions. This in turn allows
the improved efficiency of the shield with the aperture controlling
the area of the application of the material rather than
conventional systems where the shutter is required to close the
aperture in order to prevent application of material which is
frequently not effective.
[0066] When the magnetrons and target are operated continuously in
accordance with one operating embodiment of the invention there is
the disadvantage that the material from one magnetron (or 2
magnetrons in the case of the 4 magnetron system) is not exposed to
a passage to the substrates and so that material is deposited on
the surface of the cylindrical shield. However this disadvantage is
of less importance than the improvements in stability and operating
control which is achieved by the invention. However if one or both
of the targets in a non reactive coating process, was a precious
metal such as gold or platinum the same could be recovered from the
surface of the cylindrical shield with close to 100% recovery
rate.
[0067] There is now provided a specific example of operation of
apparatus and utilisation of the method in accordance with the
invention;
[0068] By way of example, a coating comprising nineteen layers
[alternate layers of niobia and silica] was deposited using the
apparatus and method as herein described with the cylindrical
shields each having an aperture therein. The target in each
magnetron was either of niobia or silica. The specific thicknesses
of each layer of material applied were controlled by exposing the
substrate to the magnetron with relevant target material for the
necessary time to achieve the required layer thickness.
[0069] On completion of each layer, the cylindrical shields were
rotated such that the apertures in the same formed a passage to the
magnetron with the alternate material and the shields maintained in
this position until the required thickness of that material layer
was deposited. The steps were then repeated for the next material
layer and so on until the required nineteen layers had been
applied.
[0070] The following graph shows the comparison of a theoretical
spectral transmission characteristic of the optical coating with
the measured spectral transmission characteristic of the nineteen
layer multilayer optical coating formed utilising the invention as
described above.
[0071] It is clearly seen from this graph that there is extremely
close agreement between the theory and measured data. This
indicates that the individual layer thickness control to <.+-.1%
has been achieved.
* * * * *