U.S. patent application number 08/971867 was filed with the patent office on 2001-12-20 for plasma vapor deposition with coil sputtering.
Invention is credited to HONG, LIUBO.
Application Number | 20010052455 08/971867 |
Document ID | / |
Family ID | 27129489 |
Filed Date | 2001-12-20 |
United States Patent
Application |
20010052455 |
Kind Code |
A1 |
HONG, LIUBO |
December 20, 2001 |
PLASMA VAPOR DEPOSITION WITH COIL SPUTTERING
Abstract
A method and apparatus for depositing a layer of a material
which contains a metal on a workpiece surface, in an installation
including a deposition chamber; a workpiece support providing a
workpiece support surface within the chamber; a coil within the
chamber, the coil containing the metal that will be contained in
the layer to be deposited; and an RF power supply connected to
deliver RF power to the coil in order to generate a plasma within
the chamber, a DC self bias potential being induced in the coil
when only RF power is delivered to the coil. A DC bias potential
which is different in magnitude from the DC self bias potential is
applied to the coil from a DC voltage source. In order to place a
deposition chamber of a physical vapor deposition apparatus in
which metal or other material is sputtered from a target and a coil
in condition to effect deposition of a layer consisting of the
sputtered material on a substrate subsequent to deposition, in the
apparatus, of a layer containing a reaction compound of the
sputtered material, the chamber is filled with a non-reactive gas
and a voltage is applied to sputter from the target and coil any
reaction compound which has coated the target and coil during
deposition of the layer containing the reaction compound of the
sputtered metal.
Inventors: |
HONG, LIUBO; (SAN JOSE,
CA) |
Correspondence
Address: |
WILLIAM K KONRAD
PATENT COUNSEL
APPLIED MATERIALS INC
P O BOX 450A
SANTA CLARA
CA
95052
|
Family ID: |
27129489 |
Appl. No.: |
08/971867 |
Filed: |
November 19, 1997 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
08971867 |
Nov 19, 1997 |
|
|
|
08907382 |
Aug 7, 1997 |
|
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|
Current U.S.
Class: |
204/192.12 ;
204/192.13; 204/192.15; 204/298.03; 204/298.06; 204/298.07;
204/298.08; 204/298.12 |
Current CPC
Class: |
H01J 37/32082 20130101;
H01J 37/3408 20130101 |
Class at
Publication: |
204/192.12 ;
204/192.13; 204/192.15; 204/298.03; 204/298.06; 204/298.07;
204/298.08; 204/298.12 |
International
Class: |
C23C 014/34 |
Claims
What is claimed is:
1. Apparatus for depositing a layer of a metal-containing material
on a workpiece surface, said apparatus comprising: a deposition
chamber; a workpiece support providing a workpiece support surface
within said chamber; a coil within said chamber, said coil
containing the metal of the metal-containing material to be
deposited; an RF power supply connected to deliver RF power to said
coil in order to generate a plasma within said chamber, a DC self
bias potential being induced in said coil when only RF power is
delivered to said coil; and a DC voltage source connected to apply
to said coil a DC bias potential which is different in magnitude
from the DC self bias potential.
2. The apparatus according to claim 1 wherein metal is sputtered
from said coil when RF power is delivered to said coil, the plasma
is generated in said chamber and the additional DC bias potential
is applied to said coil.
3. The apparatus according to claim 2 wherein the additional DC
potential enhances sputtering of metal from said coil.
4. The apparatus according to claim 3 wherein said coil is a single
turn coil.
5. The apparatus according to claim 4 wherein: the workpiece
support surface has a central region and a peripheral region
surrounding the central region; said coil is dimensioned and
positioned so that metal sputtered therefrom is directed primarily
to the peripheral region of the workpiece support surface; and said
apparatus further comprises a sputtering target disposed in said
deposition chamber so that metal is sputtered from said target when
the plasma is generated in said chamber, and metal sputtered from
said target is directed to the central region of the workpiece
support surface.
6. The apparatus according to claim 3 wherein: the workpiece
support surface has a central region and a peripheral region
surrounding the central region; said coil is dimensioned and
positioned so that metal sputtered therefrom is directed primarily
to the peripheral region of the workpiece support surface; and said
apparatus further comprises a sputtering target disposed in said
deposition chamber so that metal is sputtered from said target when
the plasma is generated in said chamber, and metal sputtered from
said target is directed to the central region of the workpiece
support surface.
7. The apparatus according to claim 3 wherein said coil is the sole
source of sputtered metal in said chamber.
8. The apparatus according to claim 7 wherein said coil comprises a
plurality of turns.
9. The apparatus according to claim 8 wherein said turns have
respectively different diameters.
10. The apparatus according to claim 9 wherein said coil is a
planar coil whose turns lie in a plane substantially parallel to
the workpiece support surface.
11. The apparatus according to claim 9 wherein said coil is a
dome-shaped coil.
12. The apparatus according to claim 1 further comprising an RF
power blocking filter connected between said RF power supply and
said DC voltage source.
13. The apparatus according to claim 11 wherein the DC bias
potential applied by said DC voltage source is greater in magnitude
than the DC self bias potential.
14. Apparatus for depositing a layer of a metal-containing material
on a workpiece surface, said apparatus comprising: a deposition
chamber; a workpiece support providing a workpiece support surface
within said chamber; a coil within said chamber, said coil
containing the metal of the metal-containing material to be
deposited; means for delivering RF power to said coil in order to
generate a plasma within said chamber while a DC self bias
potential is induced in said coil when only RF power is delivered
to said coil; and means for applying a DC bias potential to said
coil, the DC bias potential being different in magnitude from the
DC self bias potential.
15. The apparatus according to claim 14 wherein the DC bias
potential applied by said means is greater in magnitude than the DC
self potential.
16. Apparatus for depositing a layer of a metal-containing material
on a workpiece surface, said apparatus comprising: a deposition
chamber; a workpiece support providing a workpiece support surface
for supporting a workpiece within said chamber; a coil within said
chamber, said coil containing the metal of the metal-containing
material to be deposited; means for delivering RF power to said
coil in order to generate a plasma within said chamber while a DC
self bias potential is induced in said coil when only RF power is
delivered to said coil, for sputtering material from said coil and
directing the sputtered material onto the workpiece; means for
applying a DC bias potential to said coil, the DC bias potential
being different in magnitude from the DC self bias potential;
wherein said coil is the sole source of sputtered material within
said chamber.
17. The apparatus according to claim 16 wherein said coil comprises
a plurality of turns.
18. The apparatus according to claim 17 wherein said turns have
respectively different diameters.
19. The apparatus according to claim 18 wherein said coil is a
planar coil whose turns lie in a plane substantially parallel to
the workpiece support surface.
20. The apparatus according to claim 18 wherein said coil is a
dome-shaped coil.
21. Apparatus for depositing a layer of a metal-containing material
on a workpiece surface, said apparatus comprising: a deposition
chamber; a workpiece support providing a workpiece support surface
for supporting a workpiece within said chamber; a coil within said
chamber, said coil containing the metal of the metal-containing
material to be deposited; and means for delivering RF power to said
coil in order to generate a plasma within said chamber while a DC
self bias potential is induced in said coil when only RF power is
delivered to said coil, for sputtering material from said coil and
directing the sputtered material onto the workpiece, wherein said
coil is shaped and positioned so that material sputtered from said
coil is substantially uniformly deposited on said workpiece surface
and wherein said coil is the sole source of sputtered material
within said chamber.
22. The apparatus according to claim 21 wherein said coil comprises
a plurality of turns.
23. The apparatus according to claim 22 wherein said turns have
respectively different diameters.
24. The apparatus according to claim 23 wherein said coil is a
planar coil whose turns lie in a plane substantially parallel to
the workpiece support surface.
25. The apparatus according to claim 23 wherein said coil is a
dome-shaped coil.
26. The apparatus according to claim 21 wherein said coil is a
spiral-shaped coil.
27. A method of depositing a layer of a metal-containing material
on a workpiece surface in a deposition chamber, said method
comprising: disposing a workpiece having a surface in the chamber;
disposing a coil within the chamber, the coil containing the metal
of the metal-containing material to be deposited; generating a
plasma in the chamber by delivering RF power to the coil so that
the metal is sputtered from the coil, whereby a DC self bias
potential is induced in the coil when only RF power is delivered
thereto; creating a DC bias potential in the coil, which potential
is different in magnitude from the DC self bias potential; and
directing metal sputtered from the coil to the workpiece surface to
form the layer.
28. The method according to claim 27 wherein the plasma and the DC
bias potential cause the metal to be sputtered from the coil at a
rate which varies directly with the magnitude of the DC bias
potential, and further comprising adjusting the magnitude of the DC
bias potential to sputter metal from said coil at a selected
rate.
29. The method according to claim 27 wherein: the workpiece surface
has a central region and a peripheral region surrounding the
central region; said step of directing metal sputtered from the
coil is carried out to direct sputtered metal primarily to the
peripheral region; and said method further comprises sputtering
metal from a target within the chamber and directing metal
sputtered from the target primarily to the central region.
30. The method according to claim 29 wherein said step of adjusting
the magnitude of the DC bias potential is performed to minimize
differences between the thickness of the layer in the peripheral
region and the thickness of the layer in the central region.
31. The method according to claim 27 wherein all sputtered metal
directed to the workpiece surface is metal which has been sputtered
from the coil.
32. The method according to claim 31 wherein the coil is configured
to cause a layer of uniform thickness to be deposited on the
workpiece surface.
33. The method according to claim 27 wherein the DC bias potential
created in the coil is greater in magnitude than the DC self bias
potential.
34. A method of depositing a layer of a metal-containing material
on a workpiece surface in a deposition chamber, said method
comprising: disposing a workpiece having a surface in the chamber;
disposing a coil within the chamber, the coil containing the metal
of the metal-containing material; generating a plasma in the
chamber by delivering RF power to the coil so that the metal is
sputtered from the coil, whereby a DC self bias potential is
induced in the coil when only RF power is delivered thereto;
creating a DC bias potential in the coil, which potential is
different in magnitude from the DC self bias potential; and
directing metal sputtered from the coil to the workpiece surface to
form the layer, wherein all sputtered metal directed to the
workpiece surface is metal which has been sputtered from the
coil.
35. The method according to claim 34 wherein the coil comprises a
plurality of turns.
36. The method according to claim 35 wherein the coil turns have
respectively different diameters.
37. The method according to claim 36 wherein the coil is a planar
coil whose turns lie in a plane substantially parallel to the
workpiece support surface.
38. The method according to claim 36 wherein the coil is a
dome-shaped coil.
39. The method according to claim 36 wherein the coil is a
spiral-shaped coil.
40. A method of depositing a layer of a metal-containing material
on a workpiece surface in a deposition chamber, said method
comprising: disposing a workpiece having a surface in the chamber;
disposing a coil within the chamber, the coil containing the metal
of the metal-containing material; generating a plasma in the
chamber by delivering RF power to the coil so that the metal is
sputtered from the coil, whereby a DC self bias potential is
induced in the coil when only RF power is delivered thereto; and
directing metal sputtered from the coil to the workpiece surface to
form the layer, wherein said coil is shaped and positioned so that
material sputtered from said coil is substantially uniformly
deposited on said workpiece surface and wherein all sputtered metal
directed to the workpiece surface is metal which has been sputtered
from said coil.
41. The method according to claim 40 wherein the coil comprises a
plurality of turns.
42. The method according to claim 41 wherein the coil turns have
respectively different diameters.
43. A method of depositing a layer on a substrate, comprising:
sputtering a sputter material source which includes a coil while
biasing said coil at a first biasing level to provide a first
sputtering rate of said coil to deposit a layer of a reaction
compound on a substrate in a chamber, said reaction compound
comprising a material sputtered from said sputter material source
and a second constituent other than said sputter source material;
sputtering said sputter material source a second time while biasing
said coil at a second biasing level, higher than said first biasing
level, to provide a second sputtering rate to remove a coating of
reaction compound from said sputter material source; and after said
reaction compound coating removal sputtering, sputtering said
sputter material source a third time to deposit a layer of sputter
source material substantially free of said reaction compound on a
substrate in said chamber.
44. The method of claim 43 wherein said second sputtering rate is
higher than said first sputtering rate so that said reaction
compound coating removal sputtering is at a higher rate than said
sputter source material layer sputtering.
45. The method of claim 44 wherein said sputter material source
further includes a target separate from said coil.
46. The method of claim 45 wherein said sputter source material
layer sputtering comprises biasing said target at a first level to
provide a first sputtering rate of said target, and said reaction
compound coating removal sputtering comprises biasing said target
at a second level, higher than said first biasing level, to provide
a second sputtering rate, higher than said first sputtering rate so
that said reaction compound coating removal sputtering is at a
higher rate than said sputter source material layer sputtering.
47. The method of claim 44 wherein said biasing of said coil at a
second biasing level includes coupling a DC voltage source to said
coil sputter material source.
48. The method of claim 43 further comprising removing said
substrate having said reaction compound layer prior to said
reaction compound coating removal sputtering and covering a
substrate support during said reaction compound coating removal
sputtering.
49. A method for placing a plasma vapor deposition apparatus in
condition to effect deposition of a layer consisting of a metal on
a substrate subsequent to deposition, in the apparatus, of a layer
containing a reaction compound of the metal, the apparatus
including a deposition chamber containing at least one component
including a coil from which metal is sputtered during deposition
and which is coated with the metal reaction compound during
deposition of the metal reaction compound, the metal reaction
compound being formed by reacting metal sputtered from the
component with a reactive gas within the chamber, a first DC bias
potential being inherently induced in the coil during deposition of
the metal reaction compound, said method comprising removing a
metal reaction compound coating which has formed on at least one
component by the steps of: removing the reactive gas from the
chamber; introducing a non-reactive gas into the enclosure; and
sputtering substantially all metal reaction compound from the
component in an atmosphere containing substantially only the
non-reactive gas and metal reaction compound material being
sputtered from the component while applying a DC voltage to the
coil in order to place the coil at a second DC bias potential
having a magnitude greater than the first DC bias potential.
50. The method according to claim 49 wherein the at least one
component also includes a sputtering target separate from said
coil.
51. The method according to claim 50 wherein the metal reaction
compound is one of a nitride and an oxide.
52. The method according to claim 51 wherein said coil is mounted
within the chamber and connected for receiving RF power to generate
an RF electromagnetic field which interacts with gas within the
chamber to produce a plasma, the plasma containing gas ions which
ionize material sputtered from at least one component.
53. The method according to claim 52 wherein sputtering of the
metal from the component during deposition of the metal reaction
compound is effected while supplying a first RF power level to the
coil, and wherein said step of sputtering substantially all metal
reaction compound from the component comprises supplying a second
RF power level which is higher than the first RF power level.
54. The method according to claim 49 wherein said coil is mounted
within the chamber and connected for receiving RF power to generate
an RF electromagnetic field which interacts with gas within the
chamber to produce a plasma, the plasma containing gas ions which
ionize material sputtered from at least one component.
55. The method according to claim 54 wherein sputtering of the
metal from the component during deposition of the metal reaction
compound is effected while supplying a first RF power level to the
coil, and wherein said step of sputtering substantially all metal
reaction compound from the component comprises supplying a second
RF power level which is higher than the first RF power level.
56. The method according to claim 49 further comprising preventing
deposition of any material on a substrate during said step of
sputtering substantially all metal reaction compound from the
component.
57. The method according to claim 56 wherein said step of
preventing deposition of any material on a substrate is carried out
by having no substrate in the enclosure during said step of
sputtering substantially all metal reaction compound from the
component.
58. The method according to claim 49 wherein the apparatus further
includes a substrate support within the chamber, the substrate
support having a support surface on which a substrate rests during
deposition of a layer, and wherein said method further comprises
covering the support surface during said step of sputtering
substantially all metal reaction compound from the component.
59. An apparatus for depositing a layer on a substrate, comprising:
a chamber having a sputter material source which includes an RF
coil, a biasing power supply for applying a DC biasing voltage to
said RF coil, a support for a substrate positioned to receive
material sputtered from said sputter material source onto said
substrate, and at least one port for admitting a reactive material
other than said sputter source material and for expelling said
reactive material; and a programmable chamber controller, said
controller being programmed to cause said chamber to 1) admit
reactive material; 2) sputter said sputter material source to
deposit a layer of a reaction compound on said substrate, said
reaction compound comprising said source material sputtered from
said sputter material source and said reactive material; 3) expel
reactive material from said chamber; 4) sputter said sputter
material source a second time to remove a coating of reaction
compound from said sputter material source; and 5) after said
reaction compound removal sputtering, sputter said sputter material
source a third time to deposit a layer of sputter source material
substantially free of said reaction compound on a substrate in said
chamber, wherein said controller is further programmed to control
said biasing power supply to 1) bias said coil at a first level to
provide a first sputtering rate of said sputter material source
during said sputter source material layer; and 2) bias said coil at
a second level, higher than said first biasing level, to provide a
second sputtering rate during said reaction compound coating
removal sputtering, higher than said first sputtering rate.
60. The apparatus of claim 59 wherein said reaction compound
coating removal sputtering is at a higher rate than said sputter
source material layer sputtering.
61. The apparatus of claim 59 wherein said sputter material source
further includes a target.
62. The apparatus of claim 59 wherein said biasing power supply is
a DC voltage source coupled to said coil.
63. Apparatus for selectively depositing, on a surface of a
substrate, either a layer consisting essentially of a metal, in an
atmosphere consisting essentially of non-reactive gas, or a layer
of a reaction compound of the metal, in an atmosphere containing a
reactive gas, said apparatus comprising: a closed deposition
chamber for containing the substrate and the atmosphere; a coil
disposed in said chamber; and power supply means connected to said
coil for applying to said coil a voltage for creating, within said
chamber, an inductively coupled plasma which acts to sputter metal
from a metal body within said deposition chamber and to ionize the
sputtered metal for deposition on the substrate surface, wherein
said power supply means are controllable for applying a voltage
having a first magnitude to said coil during deposition of a layer
and for applying a voltage having a second magnitude, larger than
the first magnitude, after deposition of a layer of a reaction
compound of the metal and before deposition of a layer consisting
essentially of the metal, and while the atmosphere within said
chamber consists essentially of the non-reactive gas, and further
wherein said power supply means comprise a DC power supply for
selectively applying a DC bias to said coil to create at least a
portion of the voltage having the second magnitude.
64. The apparatus according to claim 63 wherein said power supply
means further comprise an RF power source for controllably
supplying either a first RF power level to said coil, to create the
voltage having the first magnitude, or a second RF power level
which is higher than the first RF power level to create the voltage
having the second magnitude.
65. The apparatus according to claim 63 wherein said power supply
means further comprise an RF power source for supplying RF power to
said coil to create the voltage having the first magnitude.
66. The apparatus according to claim 63 further comprising: a
substrate support within said chamber, said substrate support
having a support surface on which a substrate rests during
deposition of a layer; and a cover plate for covering the support
surface when the voltage having the second magnitude is being
applied to said coil.
Description
CROSS-REFERENCE TO RELATED APPLICATIONS
[0001] This is a continuation-in-part of my copending application
No. 08/907382, filed Aug. 7, 1997, entitled PLASMA VAPOR DEPOSITION
WITH COIL SPUTTERING, Attorney Docket 1957/PVD/DV.
BACKGROUND OF THE INVENTION
[0002] The present invention relates to the deposition of layers,
or films, of metals and metal compounds on a workpiece, or
substrate, during fabrication of integrated circuits, display
components, etc. In connection with the fabrication of integrated
circuits, the substrate may be constituted by one or more
semiconductor wafers, while in the case of fabrication of a
display, such as a liquid crystal display, the substrate may be one
or more glass plates. The substrate could also be a hard disc that
will be used for data storage, or read/write heads for a disc
drive.
[0003] It is known to deposit layers on such substrates by
processes such as physical vapor deposition. By way of example, as
described in copending application Ser. No. 08/680,335, filed Jul.
10, 1996 (Attorney Docket No. 1390CIP/PVD/DV), entitled "Coils for
Generating a Plasma and for Sputtering" by Jaim Nulman et al.,
which is assigned to the assignee of the present application and
incorporated herein by reference in its entirety, processes of this
type may be performed in apparatus including a deposition chamber
which contains a target, a coil and a support for the substrate.
The target is made of a material such as a metal which will form a
metal layer or the metal component of a metal compound layer. The
coil will be supplied with an RF current that will generate, within
the chamber, an RF electromagnetic field.
[0004] When a gas is introduced into the chamber at an appropriate
pressure, a dense plasma (10.sup.11-10.sup.13 ions/cm.sup.3) may be
ignited inside the chamber by the RF electromagnetic field. The
target may be associated with a magnetic field producing device,
such as a magnetron, and may be biased by a DC or RF voltage
applied to the target from a voltage source. The magnetic field
traps electrons, while the DC bias voltage on the target attracts
ions to the target. These ions dislodge, or sputter, atoms or
clusters of atoms of material from the target. The sputtered atoms
travel toward the support and a certain proportion of these atoms
are ionized in the plasma. The support provides a surface for
supporting the substrate and may be biased, usually by an AC
source, to bias the substrate with a polarity selected to attract
ionized target material to the substrate surface. The bottom
coverage of high aspect ratio trenches and holes on the substrate
can be improved by this substrate bias. Alternatively, the chamber
may sputter target material without an RF coil or other devices for
generating an ionizing plasma such that substantially all the
material deposited is not ionized.
[0005] Although the RF electromagnetic field is generated by
applying an alternating RF current to the coil, a DC potential may
be induced in the coil as described in the aforementioned copending
application Ser. No. 08/680,335. This potential which may be
referred to as a self bias, combines with the RF potential on the
coil. The combined DC and RF potentials have the net effect of
attracting ions from the plasma to the coil. If the coil is made of
the same material as the target, the coil can constitute an
additional source of deposition material which will be sputtered
from the coil by ions attracted from the plasma to be deposited on
the substrate.
[0006] If a film consisting essentially of only the sputtered
material is to be formed on a substrate, then the gas within the
chamber is preferably nonreactive with respect to the sputtered
atoms. If, on the other hand, a compound film formed by a chemical
reaction of the target material with another constituent is to be
formed, the gas introduced into the chamber may have a composition
selected to react with the sputtered target material ions and atoms
to form molecules of the compound, which are then deposited on the
substrate. Alternatively, the gas may react with the target
material while or after it is deposited.
[0007] For example, plasma and nonionizing plasma sputtering
deposition processes of the type described above can be used to
deposit either a pure metal or metal alloy, such as titanium,
tantalum, aluminum, copper, aluminum-copper, etc., or a metal
compound, such as titanium nitride (TiN), aluminum oxide
(Al.sub.2O.sub.3), etc. Also, other non metallic materials may be
deposited such as silicon and silicon dioxide. For deposition of a
pure metal or metal alloy, the target, and possibly the coil, will
be made of this metal and the plasma gas is preferably a
non-reactive gas, i.e. a gas such as argon, helium, xenon, etc.,
which will not react with the metal. For deposition of a metal
compound, the target, and possibly the coil, will be made of one
component of the compound, typically the metal or metal alloy, and
the chamber gas will include a reactive gas composed of, or
containing, the other component or components of the compound, such
as nitrogen or oxygen. The sputtered metal reacts with gas atoms or
molecules to form the compound, molecules of which are then
deposited on the substrate. In the same manner, a nonmetallic
target material may be sputtered in a nonreactive environment to
deposit relatively pure target material onto the substrate.
Alternatively, the target material may be sputtered in a reactive
environment to produce on the substrate a layer of a compound of
the target material and a reactive component. Hereinafter, a
compound formed of a target or coil material and a reactive
component will be referred to as a reaction compound, whether the
sputtered material is metallic or otherwise.
[0008] One factor determining the performance of such apparatus is
the density of gas, and hence the density of the plasma, in the
chamber. A relatively dense plasma can provide an increased
ionization rate of the sputtered material atoms, thus improving
bottom coverage of trenches and holes on the substrate. However,
under high pressure conditions, material sputtered from the target
tends to be deposited preferentially in a central region of the
substrate support surface. Such nonuniformity can often increase at
higher deposition rates or higher pressures.
[0009] This nonuniformity is disadvantageous because the thickness
of the deposited layer preferably should correspond to a nominal
value, within a narrow tolerance range, across the entire support
surface. Therefore, when the substrate is, for example, a wafer
which will ultimately be diced into a plurality of chips, and there
is a substantial variation in the thickness of the layer across the
wafer surface, many of the chips may become rejects that must be
discarded.
[0010] As described in the aforementioned copending application
Ser. No. 08/680,335, it has been recognized that material sputtered
from the coil may be used to supplement the deposition material
sputtered from the primary target of the chamber. Because the coil
can be positioned so that material sputtered from the coil tends to
deposit more thickly at the periphery of the wafer, the center
thick tendency for material sputtered from the primary target can
be compensated by the edge thick tendency for material sputtered
from the coil. As a result, uniformity can be improved.
[0011] The quantities of material sputtered from the coil and the
target are a function of several factors including the DC power
applied to the target and the RF power applied to the coil.
However, the freedom to adjust these and other factors may be
limited in some applications by the requirements of other process
parameters which are often interdependent. Thus, a need exists for
further control over the quantity of material sputtered from the
coil to facilitate further increases in the degree of uniformity of
deposition that may be achieved.
[0012] In addition, when such apparatus is used to deposit a
reaction compound layer, some of the reaction compound typically
also coats the target and the coil. For example, when titanium
nitride is deposited in a chamber having a titanium metal target in
a nitrogen atmosphere, titanium nitride typically coats the target
and coil. Therefore, if it were then attempted to deposit a pure
target material layer, i.e., a layer of just titanium, in the same
apparatus, the reaction compound molecules of titanium nitride
would likely also be sputtered from the target, and also from the
coil, and thus could contaminate the titanium metal layer.
Therefore, it has generally not been practical to sputter deposit a
metal or metal alloy layer from a target of the same material
immediately after having deposited a metal compound layer in the
same apparatus.
[0013] Some efforts have been made to deal with this drawback by
sputtering away the metal compound layer coating on the target, and
covering over the metal compound layer coating on the coil with a
layer of the metal sputtered from the target, this procedure being
known as "pasting". However, such attempts have generally been
found to be unacceptably costly and time-consuming, and otherwise
unsatisfactory.
[0014] Therefore, facilities in which layers of a metal and layers
of a compound of that metal are to be deposited on substrates are
typically equipped with two apparatuses, each for depositing a
respective type of layer. This, of course, may entail twice the
investment cost associated with one apparatus. Moreover, in
production systems having multiple chambers coupled to a central
transfer chamber, valuable perimeter space of the transfer chamber
is occupied by an extra chamber that could otherwise be used by
another chamber to increase throughput or provide additional
processes.
BRIEF SUMMARY OF THE INVENTION
[0015] It is an object of the present invention to alleviate the
above difficulties.
[0016] A more specific object of the invention is to improve the
uniformity with which a layer of material is deposited on a
substrate.
[0017] Another object of the invention is to achieve such
improvement in uniformity without any significant increase in the
cost or complexity of the deposition apparatus.
[0018] Still another object of the invention is to improve
deposited film uniformity while, at the same time, improving
apparatus throughput.
[0019] Still another object of the invention is to improve
deposited film uniformity while at the same time reducing the cost
and complexity of the deposition apparatus.
[0020] Still another object of the invention is to allow added
control of the rate of deposition of material on a substrate.
[0021] A further specific object of the invention is to facilitate
deposition of a layer of a target material such as an elemental
metal or metal alloy in a single deposition apparatus a short time
after completion of deposition of a layer of a reaction compound of
the target material and another constituent.
[0022] A still more specific object of the invention is to rapidly
remove reaction compound material which has been deposited on the
target or coil in a deposition chamber subsequent to a reaction
compound layer deposition process and prior to a target material
layer deposition process which does not include a reactive
constituent.
[0023] The above and other objects are achieved, according to the
present invention, by a method and apparatus for sputter depositing
a layer on a substrate in which following deposition of a layer of
reaction compound formed from constituents which includes a
reactive material and a material sputtered from a target or coil, a
layer of material sputtered from the same target or coil may be
deposited in the same chamber in which the subsequent layer is
substantially free of contamination by the reaction compound or the
reactive material. In the illustrated embodiment, this may be
achieved by removing the reactive material from the sputter chamber
following the deposition of the reaction compound, introducing a
non-reactive gas into the enclosure; and sputtering substantially
all reaction compound from the target or coil which provided the
source of the sputtered material. As a consequence, the same
chamber is then ready to deposit another layer except that the
layer may be a layer consisting essentially of only material
sputtered from the source. In this manner, a chamber may be used to
deposit a metal compound such as titanium nitride and then after
sputter cleaning, be ready to deposit a layer of relatively pure
titanium in the same chamber without substantial contamination by
titanium nitride.
[0024] This aspect of the invention is particularly applicable to
apparatus which includes a chamber containing a sputtering target
and a plasma generating coil. According to the invention, a
suitable voltage is applied to the coil, while the chamber is
filled with a non-reactive gas and does not contain any substrate,
to produce a plasma which will rapidly sputter deposited metal
compound material from the target, and possibly also from the
coil.
[0025] The above and other objects are further achieved, according
to the present invention, by a method and an apparatus for
depositing a layer of a material which contains a metal on a
workpiece surface in which both RF energy is supplied to a coil to
generate a plasma to ionize the deposition material, and a separate
DC bias is applied to the coil to control the coil sputtering rate.
In the illustrated embodiment, a DC voltage source is coupled to
the coil through an RF filter to provide a DC bias potential which
is different in magnitude from the coil DC self bias potential
which results from the applied RF power. In this manner, the coil
bias potential and hence the coil sputtering rate may be controlled
with a degree of independence from the RF power applied to the
coil.
[0026] In another aspect of the invention, the coil may be shaped
and positioned to permit use as the sole source of sputtered
material within said chamber while maintaining good uniformity. As
a consequence, in some applications, the need for a separate target
and associated magnetron may be eliminated.
BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS
[0027] FIG. 1 is a simplified, elevational, cross-sectional view of
deposition apparatus constructed according to one embodiment of the
invention.
[0028] FIG. 2 is a circuit diagram illustrating electrical systems
associated with the apparatus of FIG. 1.
[0029] FIG. 3 is a view similar to that of FIG. 1 showing another
embodiment of deposition apparatus according to the invention.
[0030] FIG. 4 is a cross-sectional view of another embodiment of a
coil which may be employed in apparatus according to the present
invention.
DETAILED DESCRIPTION OF EMBODIMENTS
[0031] FIG. 1 shows the basic components of one embodiment of a
deposition apparatus constructed according to a first preferred
embodiment of the invention.
[0032] The illustrated apparatus includes a deposition chamber 2, a
sputtering target 4, a plasma generating coil 6 and a workpiece
support 8, all of which are disposed within chamber 2. Outside of
chamber 2, and above target 4, there is provided a magnetic field
generating assembly, such as a magnetron, 10. Target 4 is made of a
conductive material, for example a metal, such as titanium, which
is to be sputtered and then deposited on a workpiece provided on a
workpiece support surface 14 of workpiece support 8. Other
materials which are currently deposited in such apparatus include
metals and alloys such as aluminum, copper, tantalum,
aluminum-copper alloys and metal compounds such as titanium nitride
and tantalum nitride.
[0033] In order to make possible the generation of a plasma within
chamber 2, a suitable quantity of an ionizable gas, such as argon,
is introduced into the chamber through a port 15 and RF power is
supplied to coil 6 from an RF power supply 16 via an appropriate
matching network 20. One end of coil 6 is connected to matching
network 20 and the other end of coil 6 is connected to ground via a
DC blocking capacitor 22 (FIG. 2). The RF power supplied to coil 6
results in the generation of an electromagnetic field that produces
a plasma. Assembly 10 also contributes to generation of a plasma
within chamber 2. In the absence of RF current in coil 6, a plasma
of lower density can also be generated in the vicinity of target 4
and magnetron 10 by applying a DC or RF voltage to target 4.
[0034] Under these conditions, a material to be deposited on a
substrate disposed on surface 14 will be sputtered from target 4,
at least partially ionized in the plasma field and directed to the
workpiece.
[0035] The sputtering of material from target 4 is aided by biasing
target 4, by means of a biasing voltage source 24, such as a DC
source, with a polarity to attract ions in the plasma. The
attracted ions impact on target 4 and dislodge atoms or clusters of
atoms of the material making up target 4.
[0036] A proportion of the atoms sputtered from target 4 will be
ionized in the plasma to become, in the case of a metal, positive
ions. In order to promote deposition of these positive ions on the
workpiece surface, workpiece support 8 is connected to a suitable
bias voltage source 26 such as an AC source. In the illustrated
embodiment, sources 24 and 26 cause a negative bias to develop on
the target 6 and the substrate 14, respectively.
[0037] Since it is often desired to be able to move workpiece
support 8 vertically within chamber 2, while the interior of
chamber remains sealed, workpiece support 8 may be coupled to
chamber 2 by an appropriate bellows 28.
[0038] When the only voltage applied to coil 6 is an alternating RF
voltage, it is believed that a DC self bias is inherently induced
on coil 6 across blocking capacitor 22. In the illustrated
embodiment, this bias will have a negative polarity and can be of
the order of -100 volts. If coil 6 is made of a sputterable
material, then ions in the plasma will be attracted to coil 6 as a
result of the DC self bias and these ions will sputter, or
dislodge, atoms or clusters of atoms of material from the surface
of coil 6. Therefore, by making coil 6 of the same material as
target 4, the rate of generation of material for deposition on the
workpiece surface can be increased. Still further, the target and
coil 6 provide spatially separated sources of sputter material,
which can be used to improve film properties.
[0039] Since coils, such as coil 6, may be dimensioned and
positioned so as to be outside the periphery of workpiece support
surface 14, it has been found that sputtered material originating
from coil 6 will tend to be deposited thicker in the peripheral
region of the workpiece support surface than in the center region.
This is beneficial because in many installations, and particularly
those operating with high pressures, material sputtered from target
4 tends to be deposited thicker in the central region of the
workpiece support surface than in the peripheral region. Thus, the
sputtering of deposition material from coil 6 can help to
counteract the tendency of material sputtered from target 4 to be
deposited to a greater thickness in the central region of the
workpiece support surface.
[0040] To obtain the best deposition uniformity, the coil
sputtering rate is preferably sufficiently high relative to the
target sputtering rate to compensate for any deposition
nonuniformity of material from the target. One way this might be
achieved is to reduce the target sputtering rate. But a lower
target sputtering rate usually results in a lower deposition rate
on the substrate, and therefore a lower system throughput. Another
approach is to increase the coil sputtering rate by increasing RF
power level. However, the optimum value of the RF power applied to
the coil is a function of several process parameters and chamber
design considerations. Hence, in many applications a particular RF
power level which may provide a useful self bias on the coil 6 to
provide a desired coil sputtering rate, may have a disadvantageous
effect on these other factors or may be higher than that which may
be provided by the particular system. Thus, the RF power level
which provides the best uniformity of deposition may not be
appropriate for the particular chamber or may adversely affect
other film properties.
[0041] In accordance with one aspect of the invention, the coil
sputtering rate may be controlled with a degree of independence of
the RF power level. In the illustrated embodiment, not only is RF
energy supplied to the coil to generate a plasma to ionize the
deposition material, but a separate DC bias is also applied to the
coil to separately control the coil bias level and hence control
the coil sputtering rate. As a result, one need not be limited to
the DC self bias which is created when only an alternating RF
current is applied to the coil.
[0042] Thus, according to the invention, the DC bias on coil 6 is
altered, independently of the magnitude and frequency of the RF
power delivered by supply 16, by also connecting coil 6 to a DC
voltage source 30. Preferably, an RF blocking filter 32 is
connected between coil 6 and DC voltage source 30. Such an RF
blocking filter, when designed properly, can eliminate or reduce
substantially RF current flowing to the DC source 30. Filter 32
provides a negligibly small DC impedance between source 30 and coil
6 so that coil 6 will be placed at a DC bias essentially equal to
the voltage provided by voltage source 30. While voltage source 30
is represented schematically by a battery, it will be appreciated
that any suitable DC voltage source can be employed and the output
voltage thereof can be adjusted to produce the desired level of DC
bias on coil 6.
[0043] While the RF generator 16 and matching network 20 are
preferably coupled to one end of the coil 6, the DC source 30 and
RF filter 32 may be coupled to the coil anywhere along its length.
For example, as shown in FIG. 2, the DC source 30 and filter 32 may
be coupled to end of coil 6 to which is the end to which the
blocking capacitor 22 is coupled which is opposite to the end to
which RF generator 16 is coupled.
[0044] As an alternative to the arrangement illustrated in FIG. 1,
it will be appreciated that a separate voltage source 30 need not
be provided and RF filter 32 could, instead, be connected between
coil 6 and the DC voltage source 24. Since there is no DC path from
coil 6 to ground, the current flow between voltage source 30 and
coil 6 will be a function primarily of the sputtering current as
ions impact the coil 6 and secondary electrons are emitted into the
plasma. Therefore, voltage source 30, or voltage source 24, if used
in place of source 30, preferably should be capable of producing a
sufficiently high output current to accommodate the anticipated
sputtering rate.
[0045] FIG. 2 is a circuit diagram illustrating one example of
circuitry employed for supplying RF current and a DC bias voltage
to coil 6. Here coil 6 is represented by its equivalent circuit,
which is a series arrangement of an inductance and a
resistance.
[0046] Matching network 20 is a conventional network which includes
two adjustable capacitors and an inductor. As is known, the purpose
of circuit 20 is to match the output impedance of RF power supply
16 to the impedance of the load to which it is connected. In
addition, the DC blocking capacitor 22 connected between coil 6 and
ground serves to prevent flow of a DC current from coil 6 to
ground. To improve deposited layer uniformity, RF frequency and
power levels may be periodically altered during deposition. In
addition, impedances of the components of the matching network and
blocking capacitor may be periodically varied during
deposition.
[0047] Filter 32 is constructed, in a conventional manner, of
impedances such as capacitors and inductors, to block transmission
of RF power from coil 6 to voltage source 30.
[0048] In the embodiment shown in FIG. 1, if it is desired to
reduce the rate at which metal is sputtered from target 4 in order
to improve the deposited layer thickness uniformity across the
substrate surface, this can be achieved by reducing the DC power
applied to target 4.
[0049] Since plasma generating coil 6 can be converted into an
effective source of sputtered material by application thereto of a
suitable DC bias potential, then, according to a further feature of
the present invention, the possibility exists of completely
eliminating target 4 and its associated assembly 10 and using the
coil as the sole source of sputtering material.
[0050] However, if the coil is to be used as the only sputtering
material source, then it would be desirable to configure the coil
to produce sputtered material in such a manner that the resulting
layer deposited on the workpiece will have a substantially uniform
thickness across the workpiece surface area. For example, coil 6
could be replaced by a flat multi-turn coil, as represented by coil
36 in FIG. 3. Apart from the different configuration of the coil
and the elimination of target 4, assembly 10 and voltage supply 24,
the apparatus shown in FIG. 3 may be identical to that shown in
FIG. 1 and described above.
[0051] It is believed that the rate of production of sputtered
material can be readily controlled by adjusting the level of
voltage produced by source 30. Thus, source 30 is preferably an
adjustable voltage source.
[0052] When target 4 is no longer needed as a sputtered material
source, the system designer has greater freedom to select the
configuration of the plasma generating coil. Heretofore, it was
considered preferable to construct the coil in such a manner as to
not obstruct the movement of sputtered material from the target 4
to the workpiece. When target 4 is no longer provided, this
limitation no longer exists. In addition, when a target is no
longer present, one has greater freedom to select the height of the
coil above workpiece support surface 14. Depending on the shape of
processing chamber 2 and the configuration of the plasma generating
coil, it may be found to be preferable to move the coil either up
or down relative to the height which the coil would have in that
chamber when a separate target 4 is also provided. However, as a
general rule, displacing the coil upwardly may result in ionization
of a higher percentage of the sputtered material prior to reaching
the substrate surface and thus could increase the percentage of the
deposited material reaching the bottoms of grooves in the
substrate. Furthermore, elimination of target 4 and magnetic field
generating assembly 10 could represent a substantial simplification
of the design of the apparatus and provide a corresponding
reduction in the cost of manufacturing the apparatus.
[0053] The coil configuration shown in FIG. 3 thus represents one
of many possibilities made available by the present invention.
[0054] Another preferred form of construction for a coil which
could serve as a sole source of sputtered material according to one
aspect of the invention is coil 46 shown in FIG. 4 and is wound to
conform to a dome shape. In certain apparatus configurations, this
shape could be found to result in a deposited layer having a
particularly high uniformity. FIG. 4 illustrates a non-inverted
dome shape. It is anticipated that dome shapes which are inverted
may be utilized as well.
[0055] Embodiments of the present invention which utilize a coil as
the sole source of sputtering material should be expected to
deliver such material to the workpiece at a lower rate than would
occur if another target were also provided. However, in many cases,
the layer which is to be deposited may be very thin and a lower
sputtering and deposition rate would allow the thickness of such a
layer to be more accurately controlled. Thus, for certain purposes,
apparatus exhibiting a lower sputtering and deposition rate is
desirable.
[0056] On the other hand, when material is to be sputtered and
deposited at a high rate, apparatus according to the invention
which combines a separate target with a coil which is separately DC
biased may be preferred. Because the deposition nonuniformity from
target 4 alone may be aggravated at higher deposition rates in some
applications, more coil sputtering may be needed to maintain good
overall deposition uniformity. Therefore, additional DC bias on the
coil will be advantageous in such applications.
[0057] Apparatus according to the invention can be employed for
depositing metal layers, such as layers of titanium, tantalum,
aluminum, etc., in which case the gas introduced to generate a
plasma may be selected to not react with ions of the metal to be
deposited. A typical gas employed for this purpose is argon.
[0058] The invention can also be employed for forming layers of
metal compounds, such as TiN, TaN, etc. In this case, the coil, and
target, if provided, would be made of the metal component of such a
compound, while the gas introduced into chamber 2 would be composed
of or consist of another component, such as nitrogen.
[0059] In general, embodiments of the invention will be operated to
give the bias potential on the coil a magnitude which is greater
than its DC self bias potential. A bias potential of greater
magnitude will cause material to be sputtered from the coil at a
higher rate. Furthermore, when a coil is employed as the sole
source of sputtering material, material may be sputtered from the
coil at a rate required by certain deposition operations even if
the only DC bias on the coil is the self bias. Therefore, according
to certain embodiments of the invention in which the coil is the
sole source of sputtering material, voltage source 30 and blocking
filter 32 are removed, so that the coil end which is remote from RF
power supply 16 is connected only to capacitor 22.
[0060] The parameters of the RF current supplied to a coil, the
component values for the circuitry shown in FIG. 2, the temperature
and pressure conditions within chamber 2 and all other operating
parameters not specified herein would be selected according to
principles known in the art.
[0061] Similarly, the precise shape and dimensions of each plasma
generating coil can be determined on the basis of principles known
in the art. To cite one specific example, in apparatus according to
the invention for depositing a layer on a workpiece in the form of
a silicon wafer having a diameter of 8 inches, the coil could be
constructed in the manner described in copending application Ser.
No. 08/857,719, filed May 16, 1997, and entitled "Central Spiral
Coil Design for Ionized Metal Plasma Deposition" (Attorney Docket
No. 1752/PVD/DV). The plasma generating coils shown in the drawings
of the present application are constructed from stock having a
circular cross section. However, coils employed in embodiments of
the present invention can also be made from stock having other
cross-sectional shapes, including square, rectangular, flat ribbon,
oval, etc. cross-sectional shapes. For those embodiments in which
DC voltage source 30 is employed to increase the magnitude of the
DC bias on the coil, i.e. to make that bias more negative, the coil
is preferably provided with a cooling fluid channel and a cooling
fluid, most commonly water, is caused to flow through the channel
for cooling purposes.
[0062] Apparatus of the type described above may be employed to
form an elemental metal or metal alloy layer or a layer of other
types of target material in which formation of a compound which
includes the target material is not desired. In this case, the gas
filling chamber 2 will preferably be a non-reactive gas, such as
argon, helium, xenon, etc. If a metal reaction compound layer is to
be deposited in such apparatus, chamber 2 may be filled through
port 15 with an appropriate reactive gas which is ionized in the
plasma and then combines with ions and atoms of the sputtered metal
to form the compound. Typical metal compounds which are formed in
this manner include TiN, TaN and Al.sub.2O.sub.3. In each case, the
target will be made of the metal component or metal alloy component
of such compound. When the compound is a nitride, the gas
introduced into chamber 2 will contain nitrogen. When the compound
is an oxide, the gas introduced into chamber 2 will contain
oxygen.
[0063] When the illustrated apparatus is operated to form a metal
reaction compound layer on a workpiece surface, molecules of the
metal compound will typically also be deposited on target 4, as
well as on coil 6. If these molecules can be removed from target 4
in a sufficiently short time, then the apparatus can be utilized to
deposit a layer of just the target material which is typically a
metal or metal alloy. In addition, if, during a deposition of a
metal layer, material will be sputtered from coil 6, then metal
reaction compound molecules which may have been deposited on coil 6
during the metal compound layer deposition operation should also be
removed.
[0064] According to the present invention, the apparatus may be
placed in a condition to permit deposition of a high purity
elemental metal layer or other target material in a short period of
time after completion of deposition of a reaction compound layer
comprising the elemental metal or other target material as a
constituent, by removing all reactive gas from the interior of
chamber 2 through an exhaust port such as port 15 and replacing the
gas with a suitable non-reactive gas and then creating conditions
necessary to sputter the metal reaction compound material off of
the target and the coil. In the example described below, the target
4 and coil are made of a high purity elemental metal such as
titanium. However, in alternative embodiments, the target and the
coil may be made of a variety of target materials including metal
alloys and semiconductor materials as described above.
[0065] The non-reactive gas may be of any of the types described
above, and, more generally, may be of any type which does not
include a chemical element that will react with ions of the metal
contained in target 4, and possibly in coil 6. In addition, any
substrate which has been processed in chamber 2 is preferably
removed and work piece support 8 may be covered with a disk, or
shutter, 34 of a suitable material, such as a metal, in order to
prevent deposition of unwanted material on the upper surface of
support 8.
[0066] Then, an RF voltage is applied to coil 6 in order to
generate an inductively coupled plasma which will cooperate with
the magnetic field produced by assembly 10 and the bias voltage on
target 4 to sputter metal reaction compound molecules off target 4.
At the same time, most or all of the metal reaction compound
molecules which have been deposited on coil 6 may be sputtered off.
The sputtered metal reaction compound material may be deposited on
the walls of chamber 2, where they will not interfere with the
subsequent operation of depositing an elemental layer. In addition,
a flow of non-reactive gas may be established through port 15 of
the chamber 2 in order to carry off some or most of the metal
reaction compound molecules, or ions thereof.
[0067] In accordance with preferred embodiments of the invention,
the cleaning operation will be accelerated by increasing the RF
power provided by supply 16 above that supplied during a deposition
operation. The power can be increased to any arbitrarily high
level, the only requirement being that the power level be
maintained below a value which would damage or destroy any
component within the chamber, such as coil 6.
[0068] A typical RF power level for sputtering a Ti coil is 2.5 kW.
This may be doubled to 5 kW or more, for example, during coil
cleaning.
[0069] In accordance with a further feature of the invention, the
sputtering of metal reaction compound molecules from target 4 may
be accelerated by increasing the power level of the negative bias
applied to target 4 by voltage source 24. Because a film is not
being formed on a production substrate during the cleaning
operation, limitations which may normally be present on the target
power level are not present during this cleaning operation.
Accordingly, the DC power level applied to the target 4 may be
substantially increased over the value normally used during sputter
deposition onto the workpiece. As a consequence, the sputtering
rate may be substantially increased to reduce the time needed to
clean the target. Again, the power level should not be raised to a
level which could damage chamber components. For example, a typical
power level for a Ti target is 4 kW. This power level may be raised
to 8 to 20 kW or more to clean the target. If the target becomes
cleaned before the coil is completely cleaned, the target power
level may be reduced to levels just high enough to sputter off any
materials being deposited on the target while the coil continues to
be sputtered, preferably at higher level, to clean the coil
further.
[0070] In accordance with preferred embodiments of the invention,
the sputtering of metal compound molecules from coil 6 and hence
the cleaning of coil 6 is accelerated by increasing the DC bias on
coil 6 in the manner described above.
[0071] The DC bias imposed on coil 6 by voltage source 30 can have
any arbitrarily high value, subject only to the condition that this
bias not be so high as to cause damage or destruction to any
component within chamber 2. By way of example, in an apparatus in
which the self bias on coil 6 would be of the order of -100V during
a deposition operation, it is preferred that the DC bias imposed on
coil 6 by voltage source 30 have a magnitude greater than -200V in
order to assure that the cleaning operation will be performed in a
sufficiently short period of time. Also, the power level may be
doubled or more, for example, during cleaning.
[0072] In accordance with a further preferred embodiment of the
invention, the sputtering of metal reaction compound molecules from
target 4, and possibly also from coil 6, can be effected by both
increasing the RF voltage from power supply 16 and providing a DC
bias voltage from source 30, each voltage being produced in the
manner described above.
[0073] Conceivably, cleaning could be performed, in the presence of
a suitably non-reactive gas, by applying to coil 6 only RF power at
the same level employed during a deposition operation. However, the
time required to perform the cleaning operation would then be
comparatively long. Therefore, a cleaning operation of this type
would not provide the full benefits offered by the present
invention.
[0074] According to alternative embodiments of the invention,
voltage source 30 can be connected, via filter 32, to other points
in the circuit shown in FIG. 2. For example, instead of connecting
the coil of filter 32 to the high voltage side of capacitor 22,
this end of the coil could be connected to either end of the coil
which forms a component of matching network 20.
[0075] RF power supply 16 may be constructed to produce an
adjustable voltage, as shown in FIGS. 1 and 2. Thus, during
cleaning the RF voltage may be substantially increased to minimize
cleaning time. Following cleaning, the RF voltage may be
substantially reduced to the normal value used for sputtering a
film onto a workpiece. When DC voltage source 30 is provided to
create, or contribute to, the increased DC bias, or cleaning
voltage, on coil 6, source 30 is preferably connected to filter 32
via a switch, as shown in FIGS. 1 and 2. This switch may,
alternatively, be connected to the end of the coil of filter 32
which is remote from source 30.
[0076] In all of the disclosed embodiments of the invention for
cleaning a target and/or coil, any combination of increased RF
power and increased DC bias on the coil can be utilized, so long as
the destruction of, or damage to, any component of the apparatus is
avoided. The component values for the circuitry shown in FIG. 2,
the temperature and pressure conditions within chamber 2 and all
other operating parameters not specified herein would be selected
according to principles known in the art.
[0077] Similarly, the precise shape and dimensions of each plasma
generating coil can be determined on the basis of principles known
in the art. To cite one specific example, in apparatus according to
the invention for depositing a layer on a workpiece in the form of
a silicon wafer having a diameter of 8 inches, the coil could be
constructed in the manner described in copending application Ser.
No. 08/857,719, filed May 16, 1997, and entitled "Central Spiral
Coil Design for Ionized Metal Plasma Deposition" (Attorney Docket
No. 1752/PVD/DV). The plasma generating coils shown in the drawings
of the present application are constructed from stock having a
circular cross section. However, coils employed in embodiments of
the present invention can also be made from stock having other
cross-sectional shapes, including square, rectangular, flat ribbon,
oval, etc. cross-sectional shapes. Since, according to the present
invention, a DC voltage source is employed to increase the
magnitude of the DC bias on the coil, i.e. to make that bias more
negative, the coil is preferably provided with a cooling fluid
channel and a cooling fluid, most commonly water, is caused to flow
through the channel for cooling purposes.
[0078] The operations of the chamber 2 are preferably controlled by
a programmable controller 50 (FIG. 1) such as a microprocessor
based workstation. Thus, the switching on and off of the power
supplies and generators, the opening and closing of the ports 15,
the operation of the magnetron 10 and other functions of the
chamber 2 may be controlled automatically by the controller 50.
[0079] While particular embodiments of the present invention have
been shown and described, it will be apparent to those skilled in
the art that changes and modifications may be made without
departing from this invention in its broader aspects and,
therefore, the aim in the appended claims is to cover all such
changes and modifications as fall within the true spirit and scope
of this invention.
* * * * *