U.S. patent application number 10/837630 was filed with the patent office on 2004-10-14 for method and apparatus for forming interconnects, and polishing liquid and polishing method.
Invention is credited to Hongo, Akihisa, Kimizuka, Ryoichi, Matsuda, Naoki, Ohno, Kanji.
Application Number | 20040200728 10/837630 |
Document ID | / |
Family ID | 27481399 |
Filed Date | 2004-10-14 |
United States Patent
Application |
20040200728 |
Kind Code |
A1 |
Hongo, Akihisa ; et
al. |
October 14, 2004 |
Method and apparatus for forming interconnects, and polishing
liquid and polishing method
Abstract
A method and apparatus for forming interconnects embedding a
metal such as copper (Cu) into recesses for interconnects formed on
the surface of a substrate such as a semiconductor substrate. The
method includes providing a substrate having fine recesses formed
in the surface, subjecting the surface of the substrate to plating
in a plating liquid, and subjecting the plated film formed on the
surface of the substrate to electrolytic etching in an etching
liquid.
Inventors: |
Hongo, Akihisa;
(Yokohama-shi, JP) ; Matsuda, Naoki;
(Yokohama-shi, JP) ; Ohno, Kanji; (Sagamihara-shi,
JP) ; Kimizuka, Ryoichi; (Tokyo, JP) |
Correspondence
Address: |
WENDEROTH, LIND & PONACK, L.L.P.
2033 K STREET N. W.
SUITE 800
WASHINGTON
DC
20006-1021
US
|
Family ID: |
27481399 |
Appl. No.: |
10/837630 |
Filed: |
May 4, 2004 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
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10837630 |
May 4, 2004 |
|
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09891472 |
Jun 27, 2001 |
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Current U.S.
Class: |
205/220 ;
205/223; 257/E21.174; 257/E21.175; 257/E21.303; 257/E21.304;
257/E21.309; 257/E21.582; 257/E21.583 |
Current CPC
Class: |
H05K 3/107 20130101;
H01L 21/76849 20130101; H01L 21/2885 20130101; H01L 21/7684
20130101; H05K 2201/09036 20130101; C25F 3/02 20130101; H01L
21/3212 20130101; H05K 3/108 20130101; C25F 7/00 20130101; H01L
21/32115 20130101; H01L 21/76843 20130101; H01L 21/32134 20130101;
H05K 2201/0376 20130101; H01L 21/76838 20130101; H01L 21/288
20130101; H01L 21/76864 20130101; H05K 3/07 20130101 |
Class at
Publication: |
205/220 ;
205/223 |
International
Class: |
C25D 005/48 |
Foreign Application Data
Date |
Code |
Application Number |
Jun 29, 2000 |
JP |
2000-196993 |
Nov 22, 2000 |
JP |
2000-356590 |
Mar 16, 2001 |
JP |
2001-77154 |
Mar 16, 2001 |
JP |
2001-77155 |
Claims
1-47. (cancele)
48. A method for forming interconnects on a substrate, comprising:
providing a substrate having fine recesses in a surface of the
substrate; plating a film of a conductive material on the surface
of the substrate in a plating liquid; and electrolytic-etching a
surface of the plated film formed on the surface of the substrate
in an etching liquid.
49. The method according to claim 48, wherein the etching liquid
contains at least one additive selected from the group consisting
of an additive which forms a complex compound or an organic complex
with the metal of the plate film and an additive which can lower
the corrosion potential of the metal of the plated film.
50. The method according to claim 48, wherein a waveform of current
flowing in said electrolytic-etching is a pulse waveform or a PR
pulse waveform.
51. A method for forming interconnect on a substrate, comprising:
providing a substrate having a recess in a surface of the
substrate, plating the substrate with copper to form a copper film
on the surface and to fill copper into the recess of the substrate;
electrolytic-polishing or chemical-polishing a surface of the
copper film on the substrate in a polishing liquid; and annealing
the substrate after said polishing.
52. The method according to claim 51, wherein the annealing the
substrate is carried out in such a state that the copper film
remains on the entire surface of the substrate.
53. The method according to claim 51, further comprising
chemical-mechanical-polishing the surface of the copper film on the
surface of the substrate, after said annealing.
54. The method according to claim 53, further comprising
cap-plating the substrate to selectively cover an exposed surface
of a copper interconnect with a protective film, after said
chemical-mechanical-polis- hing.
55. A method for forming interconnect on a substrate, comprising:
providing a substrate having a recess in a surface of the
substrate, plating the substrate with copper to form a copper film
on the surface and to fill copper into the recess of the substrate;
annealing the substrate having the copper film thereon; and
electrolytic-polishing or chemical-polishing a surface of the
copper film on the substrate in a polishing liquid, after said
annealing.
56. The method according to claim 55, wherein the polishing is
carried out to form an exposed surface of a copper
interconnect.
57. The method according to claim 55, further comprising
cap-plating the substrate to selectively cover the exposed surface
of the copper interconnect with a protective film.
58. A method for forming interconnect on a substrate, comprising:
providing a substrate having recesses in a surface of the substrate
and a copper film on the surface and in the recesses of the
substrate; electrolytic-polishing or chemical-polishing a surface
of the copper film on the surface of the substrate, where only
copper is exposed thereon, in a first polishing liquid in which the
dissolution of copper is suppressed; and electrolytic-polishing or
chemical-polishing the surface of the substrate, where only copper
is exposed, or copper and a conductive material other than copper
are exposed, in a second polishing liquid in which the dissolution
of copper is further suppressed than in a first polishing
liquid.
59. The method according to claim 58, further comprising removing a
copper remaining on the surface of said other conductive material
by electrolytic-polishing or chemical-polishing.
60. The method according to claim 58, further comprising removing
said other conductive material remaining on the surface of the
substrate.
61. The method according to claim 60, wherein said copper on the
recesses and said other conductive material remaining on the
surface of the substrate is removed by passivating a surface of
said copper and preferentially electrolytic-polishing or
chemical-polishing said other conductive material.
62. The method according to claim 60, wherein said copper on the
recesses and said other conductive material remaining on the
surface of the substrate is removed by passivating an entire
surface including said copper and said other conductive material
and composite-electrolytic-poli- shing said entire surface.
63. A method for forming interconnects on a substrate, comprising:
providing a substrate having a small recess and a large recess in a
surface of the substrate, wherein the surface of the substrate
being covered with a seed layer; plating a film of a conductive
material on a surface of the seed layer with a plating liquid to
deposit the conductive material in the small recess and the large
recess, said plated film having a raised portion on the small
recess; and electrolytic-etching a surface of the plated film to
selectively remove the raised portion on the small recess.
64. A method for forming interconnects on a substrate, comprising:
providing a substrate having a recess in a surface of the
substrate, wherein the surface of the substrate being covered with
a seed layer; plating a film of a conductive material on a surface
of the seed layer with a plating liquid to deposit the conductive
material in the recess, said plated film having a raised portion;
forming a passivated film on a surface of said raised portion; and
removing the passivated film and the plated film, selectively, of
the raised portion.
65. A method for forming interconnects on a substrate, comprising:
providing a substrate having a recess in a surface of the
substrate, wherein the surface of the substrate being covered with
a seed layer; plating a film of a conductive material on a surface
of the seed layer with a plating liquid to deposit the conductive
material in the recess; forming a passivated film on a surface of
the plated film; and removing the passivated film and the plated
film while leaving the plated film on the recess of the substrate.
Description
[0001] This is a Divisional Application of U.S. patent application
Ser. No. 09/891,472, filed Jun. 27, 2001.
BACKGROUND OF THE INVENTION
[0002] 1. Field of the Invention
[0003] This invention relates to a method and an apparatus for
forming interconnects, and a polishing liquid and a polishing
method, and more particularly to a method for forming interconnects
by embedding a metal such as copper (Cu) in recesses for
interconnects formed in the surface of a semiconductor substrate,
and to a polishing liquid and a polishing method for use in such
method and apparatus.
[0004] 2. Description of the Related Art
[0005] In recent years, instead of using aluminum or aluminum
alloys as a material for forming interconnection circuits on a
semiconductor substrate, there is an eminent movement towards using
copper (Cu) which has a low electric resistance and high
electro-migration resistance. Copper interconnects are generally
formed by filling copper into fine recesses formed in the surface
of a substrate. There are known various techniques for producing
such copper interconnects, including CVD, sputtering, and plating.
According to any such technique, a copper is deposited on the
substantially entire surface of a substrate, followed by removal of
unnecessary copper by chemical mechanical polishing (CMP).
[0006] FIGS. 32A through 32C illustrate, in a sequence of process
steps, an example of producing such a substrate W having copper
interconnects. As shown in FIG. 32A, an insulating film 2 of an
oxide SiO.sub.2 or of a low-K material is deposited on a conductive
layer 1a formed on a semiconductor base 1 bearing semiconductor
devices. A contact hole 3 and a trench 4 for interconnects are
formed in the insulating film 2 by the lithography/etching
technique. Thereafter, a barrier layer 5 of TaN or the like is
formed on the entire surface, and a seed layer 7 as an electric
feed layer for electroplating is formed on the barrier layer 5.
[0007] Then, as shown in FIG. 32B, copper plating is carried out
onto the surface of the substrate W to fill the contact hole 3 and
the trench 4 with copper and, at the same time, deposit a copper
film on the insulating film 2. Thereafter, the copper film 6 on the
insulating film 2 is removed by chemical mechanical polishing (CMP)
so as to make the surface of the copper film 6 filled in the
contact hole 3 and the trench 4 for interconnects, and the surface
of the insulating film 2 lie substantially on the same plane. An
interconnect composed of the copper film 6, as shown in FIG. 32, is
thus formed.
[0008] By the way, as shown in FIG. 33, when the copper film 6 is
formed by plating on the surface of the substrate W in which a fine
hole(s) 8 with a diameter d.sub.1, e.g., on the order of 0.2 .mu.m,
and a large hole(s) 9 with a diameter d.sub.2, e.g., on the order
of 100 .mu.m are present, the growth of plating is likely to be
promoted at the portion above the fine hole 8, whereby the copper
film 6 is raised at that portion, even when the effect of a plating
liquid or an additive contained in the plating liquid is optimized.
Further, the growth of plating with an adequately high levelling
property cannot be made within the large hole 9. This results in a
difference (a+b) in the level of the copper film 6 deposited on the
substrate W, i.e. the height a of the raised portion above the fine
hole 8 plus the depth b of the depressed portion above the large
hole 9. Thus, in order to obtain the desired flat surface of
substrate W with the fine hole 8 and the large hole 9 being fully
filled with copper, it is necessary to provide the copper film 6
having a sufficiently large thickness beforehand, and remove by CMP
the extra portion corresponding to the above difference (a+b) in
the level.
[0009] This involves problems in that the large thickness of the
plated film requires a prolonged time for processing by CMP in
order to polish away the large amount. Increasing the rate of CMP
processing to avoid the prolongation of processing time can cause
dishing in the large hole.
[0010] In order to solve the above problems, it is required to make
the thickness of the plated film as thin as possible, and prevent
the formation of the raised and depressed portions in the plated
film, despite the co-presence of fine and large holes in the
surface of the substrate, thereby improving the flatness of the
plated film. In this regard, when the plating treatment is carried
out in an electrolytic copper sulfate bath, for example, it has not
been possible to decrease both of the rise and the depression in
the plated film merely by the action of the plating liquid or with
an additive. It is possible to reduce the degree of rise in the
plated film by temporarily using a reversed electric field as a
power source, or by using a PR pulse power source during the film
deposition process. This approach, however, cannot prevent the
formation of depressed portions and, in addition, denatures the
film at its surface portion.
[0011] Further, there is a strong demand for not resorting to CMP
processing which, in general, needs a complicated operation and
control, takes a considerably long processing time, and in
addition, may be carried out, in general, in a separate apparatus
from that of a plating treatment.
[0012] It is to be pointed out that though a low-K material, which
has a low dielectric constant, is expected to be predominantly used
in the future as a material for an insulating film, the low-K
material has a low mechanical strength and therefore has difficulty
enduring the stress applied during CMP processing. Thus, there is a
demand for a method which enables the flattening of the substrate
without giving stress thereto.
[0013] Further, a method has been reported which carries out CMP
processing simultaneously with plating, viz. chemical mechanical
electrolytic polishing. According to this method, the mechanical
processing is carried out to promote the growing defect of plating,
causing the problem of denaturing of the resulting film.
SUMMARY OF THE INVENTION
[0014] The present invention has been made in view of the above
drawbacks in the prior art. It is therefore a first object of the
present invention to provide a method and apparatus for forming
interconnects which can obtain a plated film with improved flatness
even when fine and large holes are co-present in the surface of a
substrate, and which can carry out the subsequent CMP processing in
a short time without suffering from dishing.
[0015] It is a second object of the present invention to provide a
method and apparatus for forming interconnects which, while
omitting a CMP treatment entirely or reducing a load upon a CMP
treatment to the least possible extent, can successively carry out
a series of copper interconnects-forming steps including a
copper-filling step.
[0016] Further, it is a third object of the present invention to
provide a polishing liquid which, when used in electrolytic
polishing or chemical polishing, can polish a plated copper film
formed on the surface of a substrate into a flatter film surface
and can polish the surface of a substrate, in which copper and a
conductive material other than copper are co-present, uniformly at
the same polishing rate; and provide a polishing method which, due
to the use of the above polishing liquid, can omit a CMP treatment
entirely or can reduce the load from a CMP treatment to the least
possible load.
[0017] In order to achieve the first object, the present invention
provides a method for forming interconnects, comprising providing a
substrate having fine recesses formed in a surface thereof plating
the surface of the substrate in a plating liquid and electrolytic
etching the plated film formed on the surface of the substrate in
an etching liquid.
[0018] This method, when applied to a substrate having fine holes
and large holes in the surface, promotes a bottom-up growth of
plating in a large hole by carrying out plating in a plating liquid
having a high levelling property, whereby it is possible to fill
the large hole with a thinner plated film. Concomitantly with the
bottom-up of plating in a large hole, the raised portion of plating
above a fine hole becomes thicker. The raised portion can be
selectively removed by the electrolytic etching. The above method
can thus improve the flatness of a plated film.
[0019] In the present invention, the plating is carried out in a
plating liquid for exclusive use in plating, and the etching in an
etching liquid for exclusive use in etching, so as to prevent the
plated film from deteriorating.
[0020] The etching liquid may preferably contain at least one
additive selected from the group consisting of an additive which
forms a complex compound or an organic complex with the metal of
the plated film and an additive which can lower the corrosion
potential of the metal of the plated film. The additive for forming
the complex compound may specifically be pyrophosphoric acid or
aminocarboxylic acid (e.g. glycine). The additive for forming the
organic complex may be ethylenediamine, EDTA, DTPA, iminodiacetic
acid, TETA, or NTA. When the plated film is a copper film, the
additive which can lower the corrosion potential of copper includes
thiourea and its derivatives.
[0021] A waveform of current flowing in the electrolytic etching
may be, for example, a pulse waveform or a PR pulse waveform. Such
waveforms can improve diffusion of the additive contained in the
etching liquid.
[0022] The apparatus for forming interconnects of the present
invention comprises a plating section for holding a plating liquid
and plating a surface of a substrate having fine recesses formed in
the surface thereof in the plating liquid and an etching section
for holding an etching liquid and electrolytic etching the plated
film formed on the surface of the substrate.
[0023] According to the apparatus, plating and electroetching can
be carried out in a successive manner. Further, repeating the
plating and electroetching treatments can further improve the
flatness of the plated film.
[0024] The etching section may include, for example, a substrate
holder for holding a substrate with its surface downward, a cathode
plate immersed in the etching liquid and located facing the lower
surface of the substrate held by the substrate holder, and a
relative movement mechanism for allowing the substrate held by the
substrate holder and the cathode plate to move relatively. The
relative movement between the substrate and the cathode plate
prevents a plated film from being locally etched excessively to
worsen the flatness of the film.
[0025] The relative movement mechanism may comprise a
substrate-rotating mechanism for rotating the substrate and a
cathode plate-moving mechanism for rotating, reciprocating,
eccentrically rotating the cathode plate, or making a scroll motion
of the cathode plate.
[0026] This mechanism makes the velocities of the substrate at its
various points relative to the cathode plate closer to one another
so as to make the flow conditions of the etching liquid between the
various points of the substrate and the cathode plate uniform,
thereby avoiding the generation of a singular point in the flow of
etching liquid. The distance between the cathode plate and the
substrate (anode) should preferably be made as small as possible
mechanically, and is preferably 1.0 mm or less, more preferably 0.5
mm or less.
[0027] According to a preferred aspect of the present invention,
the apparatus further comprises a plurality of grooves extending
over the full length of the cathode plate in the surface thereof,
and a plurality of etching liquid feed holes formed in the cathode
plate for feeding the etching liquid to the grooves, the plurality
of etching liquid feed holes communicating with the grooves.
[0028] During the electroetching, the etching liquid is fed from
the grooves formed in the surface of the cathode plate to between
the two electrodes, i.e. the cathode plate and the substrate, while
particles floating in the etching liquid is allowed to pass through
the grooves to the outside by the action of centrifugal force. This
makes it possible that a fresh etching liquid is always present
between the electrodes. The grooves may preferably be formed in
parallel or in a lattice arrangement so as not to make a difference
in current density between the center and the periphery of the
cathode plate and, in addition, to allow the etching liquid to flow
smoothly to the outside.
[0029] The substrate holder may be constructed to hold the
substrate in a vacuum attraction manner or in an electrostatic
chucking manner. Such a substrate holder can hold the substrate by
attracting the entire surface of the substrate, thereby absorbing
undulations present in the substrate, so that the substrate holder
can be held with a flattened state.
[0030] The cathode plate may be composed of a material having a
poor adhesion to copper. When the electroetching is carried out,
for example, to a plated copper film by using a cathode plate made
of e.g. titanium whose oxide shows poor adhesion to copper, the
dissolved copper ions are precipitated onto the cathode plate side
but the precipitate is immediately released from the cathode plate
to float as copper particles in the etching liquid. The etching
liquid containing the floating copper particles is allowed to flow
to the outside. The etching can thus be carried out without
suffering from the deterioration with time of the surface flatness
of the cathode plate. Further, the generation of hydrogen gas
during the etching can be prevented. The etching can thus provide
the etched surface with excellent flatness.
[0031] In order to achieve the second object, the present invention
provides an apparatus for forming interconnects by forming a copper
film on a surface of a substrate to fill copper into fine recesses
formed in the surface of the substrate, comprising a housing, a
transport route provided in the housing for transporting the
substrate, and a copper-plating section, an electrolytic or
chemical polishing section, and an annealing section which are
disposed along the transport route.
[0032] According to this apparatus, the flattening process after
copper plating is carried out mainly by means of electrolytic or
chemical polishing. Thus, the apparatus can omit a CMP treatment
entirely or reduce a load upon a CMP treatment, and can
successively carry out a series of flattening steps including
annealing in the same housing.
[0033] A cleaning section may be provided in the housing for
cleaning the substrate.
[0034] At least two of the electrolytic or chemical polishing
sections may be provided for carrying out a first-stage
electrolytic or chemical polishing and a second-stage electrolytic
or chemical polishing. This enables such two-stage electrolytic or
chemical polishing treatment to the surface of copper that the rate
of polishing or the polishing selectivity to the base is made
different between the first and the second stages so as to obtain a
flatter copper surface, or that the surface of copper is polished
in the first stage, and in the second stage, the exposed copper and
other conductive materials (e.g. TaN) are polished evenly at the
same polishing rate.
[0035] The apparatus may be provided a cap-plating treatment
section for forming a protective film which selectively covers and
protects the exposed surface of copper interconnects. The
cap-plating treatment for protecting the exposed surface of copper
interconnects by the selective coating of a protective film thereon
can thus be carried out successively in the same housing.
[0036] The present invention provides a method for forming
interconnects by forming a copper film on a surface of a substrate
to fill copper into fine recesses formed in the surface of the
substrate, comprising plating the substrate with copper to form the
copper film on the surface and to fill copper into the fine
recesses of the substrate, electrolytic or chemical polishing the
surface of the substrate having the copper film thereon in a
polishing liquid and annealing the substrate in such a state that
the copper film remains on the entire surface of the substrate,
after the polishing.
[0037] After the annealing treatment, the substrate may be
subjected to a CMP treatment, and the treated substrate may then be
subjected to the above described cap-plating treatment to
selectively cover the exposed surface of copper interconnects with
a protective film. The above manner of first carrying out the wet
treatments, followed by the dry treatments, has the merit that the
wet treatment sections and the dry treatment sections can be
arranged in separate divisions in an apparatus. It is however
possible to follow the sequence of plating.fwdarw.annealing.fwdar-
w.electrolytic or chemical polishing.fwdarw.CMP.
[0038] The present invention further provides a method for forming
interconnects by forming a copper film on a surface of a substrate
to fill copper into fine recesses formed in the surface of the
substrate, comprising plating the substrate with copper to form the
copper film on the surface and to fill copper into the fine
recesses of the substrate, annealing the substrate having the
copper film thereon and electrolytic or chemical polishing the
surface of the substrate in a polishing liquid after the annealing.
This method can omit a CMP treatment entirely.
[0039] The substrate may have a cap-plating treatment applied there
to to selectively cover the exposed surface of the copper
interconnects with a protective film after the polishing.
[0040] In order to achieve the third object, the present invention
provides a polishing liquid for use in electrolytic or chemical
polishing of copper by immersing therein a substrate having fine
recesses in a surface thereof which are filled with copper by
forming copper film, comprising at least one inorganic acid and/or
an organic acid capable of dissolving copper and at least one
viscosity-increasing agent selected from the group consisting of
polyhydric alcohols, high-molecular weight polyhydric alcohols and
alkylene glycol alkyl or aryl ethers.
[0041] The polishing liquid, when used in the electrolytic or
chemical polishing of the surface of a copper film formed on a
substrate, can enlarge the diffusion layer on the substrate in
which a copper complex is present, and therefore can raise the
polarization potential and suppress the conductivity of the entire
surface of the substrate in the liquid, thereby suppressing the
dissolution of copper over the entire substrate surface and/or the
movement of copper ions in the liquid and making the surface not
sensitive to a minute change in current density, whereby the
polished surface endured with high-flatness can be obtained. In
this connection, it has been found that the enlargement of the
diffusion layer, the rise in polarization potential and the
suppression of conductivity depend largely on the viscosity of the
polishing liquid used.
[0042] Examples of the polyhydric alcohols include ethylene glycol,
propylene glycol and glycerin. Examples of the high-molecular
weight polyhydric alcohols include polyethylene glycol and
polypropylene glycol. Examples of the alkylene glycol alkyl or aryl
ethers include ethylene glycol ethyl ether, ethylene glycol methyl
ether, ethylene glycol propyl ether, ethylene glycol phenyl ether,
propylene glycol ethyl ether, propylene glycol phenyl ether and
dipropylene glycol monomethyl ether.
[0043] The polishing liquid preferably has a viscosity of 10 cP
(0.1 Pa.multidot.s) or more and a conductivity of 20 mS/cm or
lower.
[0044] It is preferred that the polishing liquid further contains
an additive which can adhere to the surface of copper and
electrically and/or chemically suppress the dissolution of copper.
The use of the polishing liquid containing such an additive in the
electrolytic or chemical polishing can provide the polished copper
surface with improved flatness. Further, when copper and other
conductive materials (such as TaN) are exposed on the surface of a
substrate, the electrolytic or chemical polishing of the substrate
with the use of the additive-containing polishing liquid can polish
the copper and the other conductive material (such as TaN) evenly
at the same polishing rate. Specific examples of the additive may
include imidazole, benzimidazole, benzotriazole and phenacetin.
[0045] The polishing liquid may preferably contain a basic liquid
or an additive which forms a strong complex with copper or promotes
the formation of a passivated film on the surface of copper. The
use of the polishing liquid containing such a basic liquid or an
additive can provide the polished copper surface with improved
flatness.
[0046] Further, when copper and other conductive materials (such as
TaN) are exposed on the surface of a substrate, the electrolytic or
chemical polishing of the substrate with the use of such polishing
liquid can polish the copper and the other materials (such as TaN)
evenly at the same polishing rate. Chromic acid may be mentioned as
an example of the basic liquid for promoting the formation of a
passivated film on the surface of copper. EDTA and quinaldin may be
mentioned as examples of the additive, and pyrophosphoric acid as
an example of the basic liquid, for forming a complex with
copper.
[0047] The present invention provides a method for polishing a
substrate having fine recesses in a surface thereof which are
filled with copper by forming copper film, comprising electrolytic
or chemical polishing the surface of the substrate, where only
copper is exposed thereon, in a polishing liquid in which the
dissolution of copper is suppressed and electrolytic or chemical
polishing the surface of the substrate, where only copper is
exposed, or copper and a conductive material other than copper are
exposed, in a polishing liquid in which the dissolution of copper
is further suppressed.
[0048] According to this method, the unnecessary portion of plated
copper film can be remove by the electrolytic polishing into a flat
surface, and the flatness can be improved by the subsequent
electrolytic or chemical polishing. Alternatively, the first
electrolytic polishing to remove the unnecessary copper is allowed
to proceed until a conductive material other than copper (such as
TaN) becomes exposed on the surface, and the exposed material (such
as TaN), together with the exposed copper, can then be polished
away at the same rate by the second electrolytic or chemical
polishing into a flatter surface. The polishing method of the
present invention can thus omit a CMP treatment entirely, or reduce
a load upon a CMP treatment to the least possible extent.
[0049] Copper remaining on the surface of the other conductive
material is removed by electrolytic or chemical polishing. The
removal of such copper can avoid a rise in polishing rate of
copper, which would be caused if the copper would remain unremoved,
in the subsequent electrolytic or chemical polishing.
[0050] The other conductive material, not having been removed, may
be removed. After the electrolytic or chemical polishing, the other
conductive material, not having been removed by the polishing and
remaining on the insulating film, e.g. a SiO.sub.2 oxide film or a
film of low-K material, may be removed without resorting to a CMP
processing.
[0051] The copper and/or the other conductive material remaining on
the surface of the substrate may be removed either by passivating
only the surface of the copper and preferentially electrolytic or
chemical polishing the other conductive material, or by passivating
the entire surface including the copper and the other conductive
material, and composite electrolytic polishing said entire
surface.
[0052] The above and other objects, features, and advantages of the
present invention will be apparent from the following description
when taken in conjunction with the accompanying drawings which
illustrates preferred embodiments of the present invention by way
of example.
BRIEF DESCRIPTION OF THE DRAWINGS
[0053] FIG. 1 is a plan view of an embodiment of an
interconnects-forming apparatus in accordance with the present
invention;
[0054] FIG. 2 is a schematic view of a plating section used in the
apparatus of FIG. 1;
[0055] FIG. 3 is a schematic view of an etching section used in the
apparatus of FIG. 1;
[0056] FIG. 4 is a schematic view of another embodiment of an
etching section;
[0057] FIG. 5 is a flow diagram showing the flow of process steps
in the interconnects-forming apparatus of FIG. 1;
[0058] FIGS. 6A and 6B are conceptual cross-sectional views
illustrating the progress of plating on a substrate;
[0059] FIG. 7 is a conceptual cross-sectional view showing the
state of a plated substrate;
[0060] FIGS. 8A and 8B are conceptual cross-sectional views
illustrating an example of selective etching in an etching
section;
[0061] FIGS. 9A and 9B are conceptual cross-sectional views
illustrating another example of selective etching in an etching
section;
[0062] FIG. 10 is a conceptual cross-sectional view showing the
state of a substrate after the etching treatment;
[0063] FIG. 11 is a cross-sectional view of yet another embodiment
of an etching section;
[0064] FIG. 12 is a plan view of a cathode plate used in the
etching section of FIG. 11;
[0065] FIG. 13 is a diagram showing an example of a current pulse
to be applied in the etching section of FIG. 11;
[0066] FIG. 14 is a plan view of another embodiment of an
interconnects-forming apparatus in accordance with the present
invention;
[0067] FIG. 15 is a schematic view of a copper-plating section used
in the apparatus of FIG. 14;
[0068] FIG. 16 is a schematic view of an electrolytic or chemical
polishing section used in the apparatus of FIG. 14;
[0069] FIG. 17 is a schematic view of another embodiment of an
electrolytic or chemical polishing section;
[0070] FIG. 18 is a longitudinal sectional view of an annealing
section;
[0071] FIG. 19 is a horizontal sectional view of the annealing
section;
[0072] FIG. 20 is a flow diagram showing the flow of process steps
in the interconnects-forming apparatus of FIG. 14;
[0073] FIG. 21A through 21D are diagrams illustrating steps of the
formation of copper interconnects according to the process flow of
FIG. 20;
[0074] FIG. 22 is a graph showing the relationship between the
viscosity and conductivity of a polishing liquid and the polishing
effect in an electrolytic or chemical polishing using the polishing
liquid;
[0075] FIG. 23 is a graph showing the relationship between the
liquid temperature and the polishing effect in an electrolytic or
chemical polishing using the polishing liquid;
[0076] FIG. 24 is a graph showing the relationship between the
waveform of current and the polishing effect in an electrolytic or
chemical polishing using the polishing liquid;
[0077] FIG. 25 is a flow diagram showing the flow of process steps
that are to be added to the process steps of FIG. 20;
[0078] FIG. 26A through 26C are diagrams illustrating the formation
of copper interconnects according to the process flow of FIG.
25;
[0079] FIG. 27 is a diagram illustrating a composite electrolytic
polishing;
[0080] FIG. 28 is a plan view of yet another embodiment of an
interconnects-forming apparatus in accordance with the present
invention;
[0081] FIG. 29 is a flow diagram showing the flow of process steps
in the apparatus of FIG. 28;
[0082] FIG. 30 is a cross-sectional view of yet another embodiment
of an electrolytic or chemical polishing section;
[0083] FIG. 31 is a plan view of a plate used in the electrolytic
or chemical polishing section of FIG. 30;
[0084] FIGS. 32A through 32C are diagrams illustrating, in a
sequence of process steps, the formation of copper interconnects
through copper plating; and
[0085] FIG. 33 is a cross-sectional view illustrating the state of
a substrate having a problem which has been plated with copper
according to a conventional method.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
[0086] Preferred embodiments of the present invention will now be
described with reference to the drawings.
[0087] FIG. 1 is a plan view of an interconnects-forming apparatus
in accordance with the present invention. The interconnects-forming
apparatus comprises pairs of loading/unloading sections 10,
cleaning/drying sections 12, temporary storage sections 14, plating
sections 16, washing sections 18 and etching sections 20. The
apparatus is also provided with a first transport mechanism 22 for
transporting a substrate between the loading/unloading sections 10,
the cleaning/drying sections 12 and the temporary storage sections
14, and a second transport mechanism 24 for transporting a
substrate between the temporary storage sections 14, the plating
sections 16, the washing sections 18 and the etching sections
20.
[0088] As shown in FIG. 2, the plating section 16 includes a
top-opened cylindrical plating tank 32 for accommodating a plating
liquid 30, and a substrate holder 34 for detachably holding a
substrate W with its front surface downward at such a position that
the substrate W covers the top opening of the plating tank 32. In
the inside of the plating tank 32, an anode plate 36 in a flat
plate shape, which makes an anode electrode when immersed in the
plating liquid 30 with the substrate as a cathode, is disposed
horizontally. The center portion of the bottom of the plating tank
32 is connected to a plating liquid injection pipe 38 for spurting
a plating liquid upwardly to form a jet flow. Further, a plating
liquid receiver 40 is provided around the upper outer periphery of
the plating tank 32.
[0089] In operation, a substrate W held with its front surface
downward by the substrate holder 34 is positioned above the plating
tank 32 and a given voltage is applied between the anode plate 36
(anode) and the substrate W (cathode) while the plating liquid 30
is allowed to spurt upwardly from the plating liquid injection pipe
38 so that the jet flow of the plating liquid 30 hits vertically
against the lower surface (to be plated surface) of the substrate
W, whereby a plating current is allowed to pass between the anode
plate 36 and the substrate W, and a plated film is thus formed on
the lower surface of the substrate W.
[0090] As shown in FIG. 3, the etching section 20 includes a
top-opened cylindrical etching tank 52 for accommodating an etching
liquid 50, and a substrate holder 56 for detachably holding the
substrate W with its front surface downward by a holding member 54,
such as an electrostatic chuck, at such a position that the
substrate W covers the top opening of the etching tank 52. In the
inside of the etching tank 52, a cathode plate 58 in a flat plate
shape, which makes a cathode electrode when immersed in the etching
liquid 50 with the substrate as an anode, is disposed horizontally.
The substrate holder 56, at its center, is connected to the lower
end of a drive shaft 62 that is connected to a motor 62, so that it
is allowed to rotate together with the substrate W. The cathode
plate 58 is connected to one end of a reciprocating rod 66 which is
driven by an actuator 64 such as a cylinder, so that it is allowed
to reciprocate horizontally by the actuation of the actuator
64.
[0091] In operation, while the lower surface (to be etched surface)
of the substrate W, which is held with its front surface downward
by the substrate holder 56, is kept in contact with the etching
liquid 50, the substrate W is allowed to rotate together with the
substrate holder 56 and, at the same time, the cathode plate 58 is
allowed to reciprocate, while a given voltage is applied between
the cathode plate 58 (cathode) and the substrate W (anode) to pass
an electric current therebetween so as to electrolyticaly etch a
plated film on the substrate W.
[0092] FIG. 4 shows another embodiment of an etching section 20
which employs a cathode plate 58 having a larger diameter than that
of the substrate W. The cathode plate 58 is connected at its center
to the upper end of a drive shaft 70 that is connected to a motor
68, so that it is allowed to rotate by the actuation of the motor
68.
[0093] An interconnects-forming process will now be described by
referring to FIGS. 5 through 10.
[0094] First, the substrate W, which has in the surface a fine
hole(s) 8 and a large hole(s) 9 for interconnects (see FIG. 7) and
has a seed layer 7 (see FIG. 32A) as an uppermost layer, is taken
out one by one from the loading/unloading section 10 by the first
transport mechanism 22, and is transported, via the temporary
storage section 14, to the plating section 16 (step 1).
[0095] Next, plating is carried out onto the substrate W in the
plating section 16, thereby forming a plated copper film 6 on the
surface of the substrate W as shown in FIGS. 6A, 6B and 7 (step 2).
In carrying out the plating, with a primary view to reducing a
depression 6a in the plated copper film 6 caused by the presence of
the large hole 9, there is used, as the plating liquid 30 shown in
FIG. 2, a plating liquid having a high levelling property, for
example a liquid of a high levelling composition with a high copper
sulfate concentration and a low sulfuric acid concentration, e.g. a
composition of 100-300 g/l of copper sulfate and 10-100 g/l of
sulfuric acid. An additive for improving the levelling property,
e.g. polyalkylene imine, a quaternary ammonium salt and a cationic
dye, may be added to the plating liquid. By the term "levelling
property" is herein meant a property of inducing a bottom-up growth
of plating in the hole.
[0096] The use of such a high-levelling plating liquid 30 in the
plating onto the substrate W promotes the bottom-up growth of
plating in the large hole 9 and, as a result, as shown in FIGS. 6A
and 6B, the thickness t.sub.2 of the plated copper film 6 in the
large hole 9 becomes larger than the thickness t.sub.1 of the
plated copper film 6 on the plane surface portion. This means that
the large hole 9 can be filled with copper with the small thickness
t.sub.1 of plated film. On the other hand, as shown in FIG. 7, the
use of the high-levelling polishing liquid increases the height a
of the raised portion of the copper film 6 above the fine hole
8.
[0097] After the completion of plating, the plated substrate W is,
according to necessity, transported to the washing section 18 for
washing by water (step 3), and the substrate is then transported to
the etching section 20.
[0098] Next, the surface (plated surface) of the substrate W is
subjected to electrolytic etching in the etching section 20 to
effect etching of the copper film 6 formed on the substrate W (step
4). In carrying out the etching, there is used, as the etching
liquid 50 shown in FIGS. 3 and 4, an etching liquid containing an
additive which can form with copper a complex compound or an
organic complex, including an additive which acts as an
etching-promoting agent, such as pyrophosphoric acid,
ethylenediamine, aminocarboxylic acid, EDTA, DTPA, iminodiacetic
acid, TETA, NTA, and their derivatives, or an additive which acts
as an etching-suppressing agent, such as a quaternary ammonium salt
and a polymer, or an additive which can lower the corrosion
potential of copper, such as thiourea or its derivatives. As the
base bath, acids such as sulfuric acid, hydrochloric acid, sulfuric
peroxide mixture, and hydrofluoric peroxide mixture, and alkalis
such as ammonium peroxide mixture may be used, though use is not
limited thereto.
[0099] When etching is carried out by using, as the etching liquid,
an etching liquid containing the additive which preferentially
adheres to a high-current density site in the copper film and acts
to lower the potential at that site or the additive which can form
with copper a complex compound or an organic complex, and by
providing an electric field between the substrate W as the anode
and the cathode plate 58 (cathode) that are disposed opposite to
each other as shown in FIGS. 3 and 4, the additive A adheres
selectively to the raised portions of high current density as shown
in FIG. 8A and the additive A lowers the potentials at the raised
portions, whereby etching portions B, indicated by the image lines
in FIG. 8A, are etched away. Selective etching of the raised
portions in the copper film 6 is thus effected. On the other hand,
when etching is carried out in the same manner but using an etching
liquid containing the additive which preferentially adheres to a
low-current density site and acts to suppress etching, the additive
A adheres selectively to the valley portions as shown in FIG. 9A
and suppresses etching at the valley portions, whereby etching
portion B, indicated by the image line in FIG. 9B, are etched away.
Selective etching of the raised portions is thus effected.
[0100] The selective etching of the raised portions in the copper
film 6 can thus decrease the level difference L between the top of
the raised portion and the bottom of the depressed portion as shown
in FIG. 10, providing the copper film with improved flatness. When
such a flattened substrate is subjected to a CMP processing, the
processing can be carried out at a relatively low CMP rate, and
therefore without suffering from dishing, in a short time.
[0101] The waveform pulse of the electric current applied in the
above electroetching may be a pulse waveform or a PR pulse
waveform. The use of such a waveform pulse can improve the
diffusion of the additive contained in the etching liquid. As the
case may be, the etching liquid may be composed solely of the base
bath, i.e. not containing any additive.
[0102] During the etching process, in the case of the etching
section 20 shown in FIG. 3, the substrate W is allowed to rotate
while the cathode plate 58 is allowed to reciprocate. In the case
of the etching section 20 shown in FIG. 4, the substrate W and the
cathode plate 58 are both allowed to rotate in the same direction.
In either case, the substrate W and the cathode plate 58 are thus
made to move relatively so as to make the velocities of the
substrate W at its various points relative to the cathode plate 58
closer to one another, thereby making the flow conditions of the
etching liquid between the various paints of the substrate W and
the cathode plate 58 uniform so as not to make a singular point in
the flow of etching liquid. This can prevent the plated film on the
substrate W from being locally etched excessively to worsen the
flatness of the substrate surface.
[0103] After the completion of the etching treatment, the substrate
W is, according to necessity, transported to the washing section 18
for washing by water (step 5), and the substrate W is then
transported to the cleaning/drying section 12 for cleaning and
drying of the substrate W (step 6). Thereafter, the substrate is
returned to a cassette in the loading/unloading section 10 by the
first transport mechanism 22 (step 7).
[0104] The above plating and etching steps can be carried out
repeatedly, as shown by the image line in FIG. 5. Repetition of the
respective plating followed by the selective etching of the raised
portions in the plated copper film, can further improve the
flatness of the copper film. Though the plating treatment and the
etching treatment are carried out successively in the same
apparatus according to the embodiment of FIG. 1, the treatments may
be carried out independently in separate apparatuses.
[0105] In order to make the plated surface of the substrate as flat
as possible by the electrolytic etching, it is important to hold
the substrate with its best flattened state and use a cathode plate
(cathode) having the flattest possible finish, and also to allow
them to move relatively while they are kept as close as possible so
as not to make, within the area of the substrate surface, any
singular points in the flow of etching liquid and in the electric
field.
[0106] FIGS. 11 and 12 show yet another embodiment of an etching
section 20 which meets the above demands. The etching section 20
includes a top-opened cylindrical etching tank 52 for accommodating
an etching liquid 50, and a substrate holder 56 for detachably
holding a substrate W with its front surface downward at such a
position that the substrate W covers the top opening of the etching
tank 52.
[0107] The etching tank 52 comprises a substantially discoidal
bottom plate 72, a cylindrical overflow weir 74 fixed to the
peripheral end of the bottom plate 72, and an outer shell 78
surrounding the outer periphery of the overflow weir 74 and
defining an etching liquid drainage zone 76 between itself and the
overflow weir 74. A cathode plate 58 in a plain plate shape, which
makes a cathode when immersed in the etching liquid 50, is disposed
horizontally on the upper surface of the bottom plate 72 of the
etching tank 52.
[0108] A cylindrical boss 72a is provided integrally to the central
portion of the lower surface of the bottom plate 72 of the etching
tank 52, and the boss 72a is rotatably mounted, through a bearing
80, on a crank portion 82a located at the upper end of a rotating
shaft 82. Thus, the central axis O.sub.1 of the crank portion 82a
is eccentric to the central axis O.sub.2 of the rotating shaft 82
with an eccentricity e, whereas the central axis O.sub.1 of the
crank portion 82a coincides with the central axis of the boss 72a.
The rotating shaft 82 is rotatably mounted, through bearings 85a
and 85b, on the outer shell 78. Though not shown in FIGS. 11 and
12, rotation-prevention mechanisms for preventing rotation of the
bottom plate 72 about its own axis are provided between the bottom
plate 72 and the outer shell 78.
[0109] When the rotating shaft 82 is rotated, the crank portion 82a
is allowed to make a revolutionary movement with the eccentricity e
as a radius, and the revolutionary movement of the crank portion
82a causes the bottom plate 72 to make, together with the cathode
plate 58, a scroll movement (translational rotation) with the
eccentricity e as radius, i.e., a revolutionary movement with the
eccentricity e as a radius, with rotation about its own axis being
inhibited.
[0110] As shown in FIG. 12, the diameter d.sub.3 of the cathode
plate 58 is determined so that even when the substrate W of
diameter d.sub.4 makes a scroll movement, the substrate W does not
move out of the area of the cathode plate 58. The diameter d.sub.5
of the etching liquid feed zone, which contains the below-described
etching liquid feed holes 58b, is determined so that even when the
substrate W of diameter d.sub.5 makes a scroll movement, the
etching liquid feed zone remains within the area of the substrate
W.
[0111] The bottom plate 72 is provided, on its inside, with a
etching liquid chamber 72b communicated with an etching liquid feed
line 88 extending from a circulation tank 84 and including midway a
pressure pump 86, and a plurality of etching liquid discharge holes
72c extending upwardly from the etching liquid chamber 72b. The
circulation tank 84 communicates with the etching liquid drainage
zone 76 through a return line 90.
[0112] When the cathode plated 58 is used in the electrolytic
etching of a plated copper film, it is made of such material as
titanium that forms an oxide thereof on the surface of the plate,
whose oxide has a poor adhesion to copper. When the electroetching
is carried out onto a plated copper film by using such a cathode
plate, the dissolved copper ions are precipitated onto the cathode
plate 58 (cathode) side, but the precipitate is immediately
released from the cathode plate 58 due to the poor adhesion between
copper and the cathode plate 58, and the released precipitate comes
to float as copper particles in the etching liquid. Further, the
generation of hydrogen gas during the etching process can be
prevented. The electrolytic etching can thus provide the etched
surface with excellent flatness.
[0113] In the surface of the cathode plate 58, there are formed a
number of grooves 58a extending linearly over the full length of
the cathode plate 58 in a lattice form, and in the inside of the
cathode plate 58, a plurality of etching liquid feed holes 58b,
each disposed to correspond to each etching liquid discharge hole
72c and communicated with the groove 58a, are provided.
[0114] During the electroetching, the etching liquid 50 is fed from
the grooves 58a formed in the surface of the cathode plate 58 to
between the two electrodes, i.e. the cathode plate 58 and the
substrate W, while particles floating in the etching liquid 50 is
allowed to pass through the grooves 58a to the outside smoothly by
the action of centrifugal force. This makes it possible that a
fresh etching liquid 50 is always present between the electrodes.
Further, selection for the cathode plate 58 of such material as
titanium, whose oxide formed on the surface exhibits poor adhesion
to copper, in carrying out the electroetching of a plated copper
film makes it possible that the copper, once precipitated onto the
cathode plate side from its dissolved ion state, is immediately
released from the cathode plate 58 to float as copper particles in
the etching liquid. The etching liquid containing such copper
particles is allowed to pass through the grooves 58a and flow
smoothly to the outside. This prevents the deterioration with time
of the surface flatness of the cathode plate 58, thus ensuring the
flatness of the cathode plate 58.
[0115] In order to prevent making a difference in current density
between the center and the periphery of the cathode plate 58 and
also to allow the etching liquid 50 to flow smoothly through the
grooves 58a, the grooves 58a are preferably formed in a lattice
arrangement when the substrate W makes a scroll movement. When the
substrate W makes a reciprocating movement, the grooves 58a are
preferably arranged in parallel in the movement direction.
[0116] The substrate holder 56 is housed in an under-opened housing
92, and is designed to be capable of moving up and down by a
lifting rod 94, and rotating together with the housing 92 through a
motor 60. The substrate holder 56, on its inside, is provided with
a vacuum chamber 56a that communicates with a vacuum source, and a
number of vacuum attraction holes 56b penetrating downwardly from
the vacuum chamber 56a. The substrate holder 56 is thus constructed
to hold the substrate W in a vacuum attraction manner.
[0117] Usually, small undulations are present on the substrate W.
Further, the substrate can further deform depending on how it is
held. With such a deformed substrate, it is generally not possible
to flatten with 0.1 .mu.m or less of irregularity. According the
vacuum attraction method herein employed, the substrate W is held
with its entire surface being kept attracted, whereby the
undulations present on the substrate can be absorbed and thus the
substrate can be held with a flatter state. Accordingly, it becomes
possible to obtain flatness of less than 0.1 .mu.m irregularity by
the electroetching treatment.
[0118] An electrostatic chucking manner for holding the substrate
may be adopted instead of the vacuum attraction manner.
[0119] When the substrate W held by the substrate holder 56 is
lowered down to a position for etching treatment, the distance S
between the lower surface of the substrate W and the upper surface
of the cathode plate 58 should be made as small as possible
mechanically, preferably is 1.0 mm or less, and more preferably 0.5
mm or less. By thus making the anode-cathode distance S as small as
possible mechanically, i.e., preferably 1.0 mm or less and more
preferably 0.5 mm or less, the concentration of electric current on
the raised portions on the surface of the substrate W, which are to
be preferentially etched, is promoted, and a vertical electric
field can be formed between the substrate W and the cathode plate
58, whereby the entire surface (plated surface) of the substrate W
can be successfully etched into an evenly flattened surface.
[0120] In the housing 92, electric contacts 96 are provided which,
when the substrate W is attracted and held by the substrate W,
contact with the bevel portion or the peripheral portion of the
substrate W to make the substrate anode. Further, a packing 98 is
provided on the lower surface of the substrate holder 56 which,
when the substrate W is held by the holder, makes a pressure
contact with the upper surface of the substrate for sealing.
[0121] Operations for carrying out electroplating in the above
etching section 20 will now be described.
[0122] First, the etching liquid 50 is fed into the etching tank 52
and, while the etching liquid 50 is overflowing from the overflow
weir 74, the bottom plate 72 is allowed to make, together with the
cathode plate 58, a scroll movement. Under these conditions, as
described above, the substrate holder 56 holding the substrate W
with its plated (e.g. copper-plated) surface downward is lowered,
while rotating the substrate W, down to a position for
electroetching.
[0123] The relative movement between the substrate W and cathode
plate 58 makes the velocities of the substrate W at its various
points relative to the cathode plate 58 closer to one another so as
to make the flow conditions of the etching liquid 50 between the
various points of the substrate W and the cathode plate 58 uniform,
that is to say, so as not make a singular point in the flow of
etching liquid.
[0124] Under the above conditions, a pulse current as shown in FIG.
13, for example, with a time t.sub.1 to be applied of 1 .mu.m-10
.mu.m, preferably 10 .mu.m, and with a current density to be
applied of 5-50 A/dm.sup.2, is applied a plurality of times with
stoppage times t.sub.2, each time t.sub.2 larger e.g. by about 5-20
times the time t.sub.1, being interposed. Upon passing of current,
oxidation dissolution of the plated film occurs first at the raised
portion of the substrate, and then shifts to the plane portion.
Accordingly, passing of current and immediate shutoff of the power
feed, when repeated, enables selective etching of the raised
portion.
[0125] The etching liquid 50 is fed from the grooves 58a formed in
the surface of the cathode plate 58 to between the two electrodes,
i.e. the cathode plate 58 and the substrate W, while particles
floating in the etching liquid is allowed to pass through the
grooves 58a to the outside smoothly by the action of centrifugal
force, whereby a fresh etching liquid 50 is always present between
the electrodes. Selection for the cathode plate 58 of such material
as titanium, whose oxide formed on the surface exhibits poor
adhesion to copper, in carrying out the electroetching of a plated
copper film makes it possible that the copper, once precipitated
onto the cathode plate side from its dissolved ion state, is
immediately released from the cathode plate 58 to float as copper
particles in the etching liquid. The etching liquid containing such
copper particles is allowed to pass through the grooves 58a and
flow smoothly to the outside. This prevents the deterioration with
time of the surface flatness of the cathode plate 58, thus ensuring
the flatness of the cathode plate 58. Moreover, since the
anode-cathode distance S can thus be kept constant during the
operation and the generation of hydrogen gas can be prevented, the
electroetching can provide the etched surface with excellent
flatness.
[0126] As described above, the substrate W after the etching
treatment is, according to necessity, transported to the washing
section 18 (see FIG. 1) for washing by water, followed by the same
procedure as described above.
[0127] According to the above described embodiment, a substrate
having fine holes and large holes in the surface is first subjected
to the plating carried out in the plating liquid having a high
levelling property so as to promote the bottom-up growth of plating
in the large holes, and the substrate is then subjected to the
electrolytic etching (electroetching) to selectively remove the
raised portions in the plated film, whereby the flatness of the
plated film can be improved. This enables a later CMP processing to
be carried out, without suffering from dishing, in a short
time.
[0128] FIG. 14 is a plan view showing another embodiment of an
interconnects-forming apparatus in accordance with the present
invention. The interconnects-forming apparatus comprises a housing
110 that houses the following: loading/unloading sections 111; a
transport route 125; a copper-plating section 112, a
cleaning/drying section 114, an annealing section 116, a first
electrolytic or chemical polishing section 118, a second
electrolytic or chemical polishing section 120 and a
cleaning/drying section 122, which are arranged in the above order
along the transport route 125 on one side thereof; and a
cap-plating treatment section 124 including a pretreatment section
124a, a Pd-attaching treatment section 124b, a pre-plating
treatment section 124c, an electroless CoWP-plating section 124d
and a cleaning/drying section 124e, which are arranged along the
transport route 125 on the other side thereof. Further, the
apparatus is provided with a transporting device 126 movable along
the transport route 125 for transporting a substrate between the
above sections.
[0129] As shown in FIG. 15, the plating section 112 includes a
top-opened cylindrical plating tank 132 for accommodating a plating
liquid 130, and a substrate holder 134 for detachably holding a
substrate W with its front surface downward at such a position that
the substrate covers the top opening of the plating tank 132. The
other construction of the plating section 112 is the same as the
plating section 16 shown in FIG. 2, and hence a description thereof
is herein omitted, with the same reference numerals being given to
the same members.
[0130] As shown in FIG. 16, the electrolytic or chemical polishing
sections 118 and 120 each include a top-opened cylindrical
polishing tank 152 for accommodating a polishing liquid (an
electrolyte or a chemical agent) 150, and a substrate holder 156
for detachably holding the substrate W with its front surface
downward by a holding member 154, such as an electrostatic chuck,
at such a position that the substrate W covers the top opening of
the polishing tank 152. On the inside of the polishing tank 152, a
plate 158 in a flat plate shape, which makes a cathode electrode
when immersed in the polishing liquid 150 with the substrate as an
anode, is disposed horizontally. The other construction of the
electrical or chemical polishing sections 118 and 120 is the same
as the etching section 20 shown in FIG. 3, and hence a description
thereof is herein omitted, with the same reference numerals being
given to the same members.
[0131] In operation, while the lower surface (polishing surface) of
the substrate W, which is held with its front surface downward by
the substrate holder 156, is kept in contact with the polishing
liquid 150, the substrate W is allowed to rotate together with the
substrate holder 156 and, at the time, the plate 158 is allowed to
reciprocate, while a given voltage is applied between the plate 158
(cathode) and the substrate W (anode) to pass an electric current
therebetween so as to electrolyticaly polish a plated film on the
substrate W, whereas a chemical polishing is effected by stopping
the electric current.
[0132] Thus, in the electrolytic or chemical polishing sections 118
and 120, the surface of the substrate W can be chemically polished
merely by immersing the substrate surface in the polishing liquid
(a chemical agent) 150 due to the corrosion effect of the polishing
liquid, whereas the surface of the substrate W can be
electrolyticaly polished by immersing the plate 158 and the
substrate W in the etching liquid (an electrolyte) 150 and applying
a given voltage therebetween.
[0133] FIG. 17 shows another embodiment of electrolytic or chemical
polishing sections 118 and 120, each of which employs a plate 158
having a larger diameter than that of the substrate W. The plate
158 is connected at its center to the upper end of a drive shaft 70
that is connected to a motor 68, so that it is allowed to rotate by
the actuation of the motor 68.
[0134] FIGS. 18 and 19 show the annealing section 116. The
annealing section 116 comprises a chamber 1002 having a gate 1000
for taking in and out the substrate W, a hot plate 1004 disposed at
an upper position in the chamber 1002 for heating the substrate W
to e.g. 400.degree. C., and a cool plate 1006 disposed at a lower
position in the chamber 1002 for cooling the substrate W by, for
example, flowing a cooling water inside the cool plate 1006. The
annealing section 1002 also has a plurality of vertically movable
elevating pins 1008 penetrating the cool plate 1006 and extending
upward and downward therefrom for placing and holding the substrate
W on them. The apparatus further includes a gas introduction pipe
1010 for introducing an antioxidant gas between the substrate W and
the hot plate 1004 during annealing, and a gas discharge pipe 1012
for discharging the gas which has been introduced from the gas
introduction pipe 1010 and has flowed between the substrate W and
the hot plate 1004. The pipes 1010 and 1012 are disposed on both
sides of the hot plate 1004.
[0135] The gas introduction pipe 1010 is connected to a mixed gas
introduction line 1022, which is connected to a mixer 1020, where a
N.sub.2 gas introduced through a N.sub.2 gas introduction line 1016
containing a filer 1014a, and a H.sub.2 gas introduced through a
H.sub.2 gas introduction line 1018 containing a filter 1014b, are
mixed to form a mixed gas which flows through the line 1022 into
the gas introduction pipe 1010.
[0136] In operation, the substrate W, which has been carried in the
chamber 1002 through the gate 1000, is held on the elevating pins
1008 and the elevating pins 1008 are raised up to a position at
which the distance between the substrate W held on the elevating
pins 1008 and the hot plate 1004 becomes e.g. 0.1-1.0 mm. The
substrate W is then heated to e.g. 400.degree. C. through the hot
plate 1004 and, at the same time, the antioxidant gas is introduced
from the gas introduction pipe 1010 and the gas is allowed to flow
between the substrate W and the hot plate 1004 while the gas is
discharged from the gas discharge pipe 1012, thereby annealing the
substrate W while preventing its oxidation. The annealing treatment
may be completed in about several tens of seconds to 60 seconds.
The heating temperature of the substrate W may arbitrarily be
selected in the range of 100-600.degree. C.
[0137] After the completion of the annealing, the elevating pins
1008 are lowered down to a position at which the distance between
the substrate W held on the elevating pins 1008 and the cool plate
1006 becomes e.g. 0-0.5 mm. By introducing a cooling water into the
cool plate 1006, the substrate W is cooled by the cool plate 1006
to a temperature of 100.degree. C. or lower in e.g. 10-60 seconds.
The cooled substrate W is transported to the next step.
[0138] A mixed gas of N.sub.2 gas with several % of H.sub.2 gas is
used as the above antioxidant gas. However, N.sub.2 gas may be used
singly.
[0139] An example of the process for forming interconnects will now
be described by referring to FIG. 20 and FIGS. 21A to 21D. This
example illustrates a case where the surface of the substrate W,
which is plated with copper to form a plated copper film 6 as shown
in FIG. 32B, is flattened without resorting to a CMP processing to
thereby form copper interconnects, and the surface of the copper
interconnects is subjected to a cap-plating treatment.
[0140] First, the substrate W having a seed layer 7 (see FIG. 32A)
as an outermost layer is taken out one by one from the
loading/unloading section 111 by the transport device 126 and is
transported to the copper-plating section 112 (step 1).
[0141] Next, plating with copper by e.g. electroplating is carried
out onto the substrate W in the copper-plating section 112, thereby
forming a plated copper film 6 on the surface of the substrate W as
shown in FIG. 21A (step 2). In carrying out the plating, with a
primary view to reducing a depression in the plated copper film
caused by the presence of the large hole, there is used, as the
plating liquid 130 shown in FIG. 15, a plating liquid having a high
bottom-up composition with a high copper sulfate concentration and
a low sulfuric acid concentration, e.g. a composition of 100-300
g/l of copper sulfate and 10-100 g/l of sulfuric acid. An additive
for improving the bottom-up property may be added to the plating
liquid. By the term "bottom-up property" is herein meant a property
of inducing a bottom-up growth of plating in the large hole.
[0142] After the completion of plating, the plated substrate W is
transported to the cleaning/drying section 114 for cleaning and
drying (step 3), and the substrate W is then transported to the
annealing section 116 where the substrate W having the plated
copper film 6 thereon is heat-treated to anneal the copper film 6
(step 4). Thereafter, the annealed substrate W is transported to
the first electrolytic or chemical polishing section 118.
[0143] Next, in the first electrolytic or chemical polishing
section 118, a first-stage electrolytic or chemical polishing is
carried out to the surface (plated surface) of the substrate W to
polish and remove the copper film 6 formed on the surface of the
substrate W (step 5). In the case of the electrolytic etching, a
polishing liquid is used, as the polishing liquid (electrolyte) 150
shown in FIGS. 16 and 17, which comprises at least one inorganic
acid and/or organic acid capable of dissolving copper and at least
one thickening agent selected from the group consisting of
polyhydric alcohols, high-molecular weight polyhydric alcohols and
alkylene glycol alkyl or aryl ethers, and which thus has an
increased viscosity by the addition of the thickening agent.
[0144] The use of such a polishing liquid 150 having an increased
viscosity in the electrolytic etching of the surface of the copper
film 6 formed on the substrate W can enlarge the diffusion layer on
the substrate, in which a copper complex is present, and therefore
can raise the polarization potential and suppress the conductivity
of the entire surface of the substrate in the liquid, thereby
suppressing the dissolution of copper over the entire substrate
surface and/or the movement of copper ions in the liquid and making
the surface not sensitive to a minute change in current density,
whereby a polished surface endowed with high flatness can be
obtained. In this regard, the enlargement of the diffusion layer,
the rise in polarization potential and the suppression of
conductivity depend largely on the viscosity of the polishing
liquid, and the use of the above polishing liquid having an
increased viscosity can provide an improved flatness to the
polished surface. For obtaining a sufficiently high flatness, the
polishing liquid 150 should preferably have a viscosity of 10-100
cP, more preferably 20-60 cP and a conductivity of 1-20 mS/cm, more
preferably 5-18 mS/cm. The temperature of the polishing liquid 150
is preferably 0-30.degree. C., more preferably 5-25.degree. C.
[0145] The above electrolytic polishing removes the seed layer 7 on
the barrier layer 5 as well as the copper film 6 on the seed layer
7 to thereby expose the surface of the barrier layer 5, and
flattens the exposed surface of the barrier layer 5 together with
the surface of the copper film 6 filled in the contact hole 3 and
the trench 4 for interconnects, as shown in FIG. 21B, and then the
polishing process is completed. The electrolytic polishing, during
the processing, may be switched to a chemical polishing in the same
treatment section.
[0146] Phosphoric acid may be mentioned as an example of the
inorganic acid capable of dissolving copper. Examples of the
organic acid capable of dissolving copper may include citric acid,
oxalic acid and gluconic acid. Examples of the polyhydric alcohols
as the thickening agent include ethylene glycol, propylene glycol
and glycerin. Examples of the high-molecular weight polyhydric
alcohols as the thickening agent include polyethylene glycol and
polypropylene glycol. Examples of the alkylene glycol alkyl or aryl
ethers as the thickening agent include ethylene glycol ethyl ether,
ethylene glycol methyl ether, ethylene glycol propyl ether,
ethylene glycol phenyl ether, propylene glycol ethyl ether,
propylene glycol methyl ether, propylene glycol phenyl ether and
dipropylene glycol monomethyl ether.
[0147] A pulse waveform or a PR pulse waveform may be employed as
the waveform pulse of the electric current applied in the
electrolytic polishing. The use of such a pulse waveform can
improve the diffusion of the additive contained in the polishing
liquid.
[0148] FIGS. 22 through 24 show the experimental results of
electrolytic or chemical polishing carried out by using various
polishing liquids. FIG. 22 shows the relationship between the
viscosity and conductivity of a polishing liquid and the polishing
effect; FIG. 23 shows the relationship between the liquid
temperature and the polishing effect; and FIG. 24 shows the
relationship between the waveform of current and the polishing
effect. In these Figures, a-1, a-2, c-1 and c-2 denote the
following charge conditions shown in Table 1.
1 TABLE 1 a-1 DC 5 A/dm.sup.2 a-2 DC 10 A/dm.sup.2 c-1 Pulse 5
A/dm.sup.2 .times. 10 mS OFF .times. 10 mS c-2 Pulse 10 A/dm.sup.2
.times. 10 mS OFF .times. 10 mS
[0149] FIG. 22 shows the results of a polishing experiment in which
various polishing liquids, which mutually consist of phosphoric
acid as a base liquid, dipropylene glycol monomethyl ether as a
thickening agent, and water, but have different viscosities due to
different contents of the water, were used. As can be seen from
FIG. 22, the polishing effect increases with an increase in the
liquid viscosity and with a decrease in the liquid conductivity,
and the polishing effect index shows its peak at the viscosity
20-60 cP and the conductivity 17-9 mS/cm.
[0150] FIG. 23 shows the results of a polishing experiment in which
polishing liquids, which mutually consist of 100 ml of phosphoric
acid, 150 ml of dipropylene glycol monomethyl ether and 150 ml of
water, but differ in the liquid temperature, were used. It can be
seen from FIG. 23 that the polishing effect varies with the various
electrolytic conditions employed, and shows a high effect at the
liquid temperature of 30.degree. C. or lower, especially 25.degree.
C. or lower.
[0151] FIG. 24 shows the results of a polishing experiment in which
a polishing liquid consisting of 100 ml of phosphoric acid, 150 ml
of dipropylene glycol monomethyl ether and 50 ml of water, was used
and the pulse waveform was varied. In FIG. 24, 10/10 sec indicates
10 sec at ON and 10 sec at OFF. FIG. 24 shows that a pulse waveform
of 1 mS-1 sec ON/OFF, especially of 1 mS-100 mS ON/OFF, is
preferred.
[0152] During the polishing process, in the case of the electrical
or chemical polishing section 118 shown in FIG. 16, the substrate W
is allowed to rotate while the plate 158 is allowed to reciprocate.
In the case of electrolytic or chemical polishing section 118 shown
in FIG. 17, the substrate W and the plate 158 are both allowed to
rotate in the same direction. In either case, the substrate W and
the plate 158 are thus made to move relatively so as to make the
velocities of the substrate at its various points relative to the
plate 158 closer to one another, thereby making the flow conditions
of the polishing liquid between the various points of the substrate
and the plate 158 uniform so as not to make a singular point in the
flow of polishing liquid. This can prevent the plated film on the
substrate W from being locally etched excessively to worsen the
flatness of the substrate surface. This holds also for the
subsequent electrolytic or chemical polishing carried out in the
second electrolytic or chemical polishing section 120.
[0153] The substrate, which has undergone the first-stage
electrolytic or chemical polishing treatment in the first
electrolytic or chemical polishing section 118, is then transported
to the second electrolytic or chemical polishing section 120 where
the second-stage electrolytic or chemical polishing is carried out
to the surface of the substrate (step 6). In case a chemical
polishing is carried out as the second-stage polishing, a polishing
liquid is used as the polishing liquid (chemical agent) 150 which
comprises the polishing liquid having an increased viscosity used
in the first electrolytic or chemical polishing (step 5) and added
thereto, an additive which can adhere to the surface of copper and
chemically suppress the dissolution of copper, or a basic liquid or
additive which forms a strong complex with copper or promotes the
formation of a passivated film on the surface of copper.
[0154] Electrolytic or chemical polishing of the surface of copper
film 6 and the surface of the barrier film 5 composed of a
conductive material, such as TaN, by the use of the above polishing
liquid 150 containing the basic liquid or the additive, can polish
the copper film 6 and the barrier film (TaN, Ta, WN, TiN, etc.) 5
evenly at the same polishing rate. The polishing treatment thus
removes the barrier layer 5 on the insulating film 2, and flattens
the exposed surface of the insulating film 2 together with the
surface of the copper film 6 filled in the contact hole 3 and the
trench 4 for interconnects, as shown in FIG. 21C, and then the
second-stage electrolytic or chemical polishing process is
completed.
[0155] Specific examples of the additive which can
electrochemically suppress the dissolution of copper may include
imidazole, benzimidazole, benzotriazole and phenacetin. Chromic
acid may be mentioned as an example of the basic liquid which
promotes the formation of a passivated film on the surface of
copper. ETDA and quinaldin may be mentioned as examples of the
additive, for forming a strong complex with copper, and
pyrophosphoric acid may be mentioned as an example of the basic
liquid, for forming a strong complex with copper.
[0156] As described above, the electrolytic and/or chemical
polishing treatment can effectively remove the unnecessary copper
film 6 on the insulating film 2 such as an oxide film or a film of
low-K material, together with the barrier film 5, and can
successfully flatten the surface of the insulating film 2 and the
surface of the copper film 6 filled in the contact hole 3 and the
trench 4 for interconnects. A CMP treatment can therefore be
omitted.
[0157] After the completion of the second-stage electrolytic or
chemical treatment, the substrate W is transported to the
cleaning/drying section 122 for cleaning and drying (step 7), and
is then transported to the pretreatment section 124a in the
cap-plating treatment section 124, where the substrate is subjected
to a pretreatment, for example, additional cleaning of the
substrate surface (step 8). Then, in the Pd-attaching treatment
section 124, Pd is attached to the surface of the copper film 6 to
activate the exposed surface of the copper film 6 (step 9). The
substrate is then subjected to a pre-plating treatment, for
example, a neutralizing treatment, in the pre-plating treatment
section 124c (step 10). Thereafter, the substrate is transported to
the electroless CoWP-plating section 124d, where selective
electroless plating with COWP is carried out onto the activated
surface of the copper film 6 so as to cover and protect the exposed
surface of the copper film 6 with a COWP film P as shown in FIG.
21D (step 11). A plating liquid usable in the electroless plating
may be, for example, a mixture of a cobalt salt and a tangstic
salt, which contain as additives a reducing agent, a complexing
agent, a pH buffer and a pH adjusting agent. Alternatively, plating
covering may be effected by subjecting the exposed surface after
the polishing to electoless Ni--B plating so as to selectively form
a protective film (plated film) P of Ni--B alloy on the exposed
surface of the interconnects 6, thereby protecting the
interconnects 6. The thickness of the protective film P is
generally in the range of 0.1-500 nm, preferably 1-200 nm, more
preferably 10-100 nm.
[0158] The electroless Ni--B plating for forming the protective
film P may be carried out by using, for example, a plating liquid
containing nickel ions, a complex agent for nickel ions, an
alkylamine borane or a borohydride as a reducing agent for nickel
ions, and TMAH (tetramethyl ammonium hydroxide) as a pH adjusting
agent for adjusting the liquid pH in the range of 5-12.
[0159] After the completion of the cap-plating treatment, the
substrate W is transported to the cleaning/drying section 124e for
cleaning and drying (step 12), and the substrate W is then returned
to the cassette of the loading/unloading section 111 by the
transporting device 126 (step 13).
[0160] Though the selective electroless CoWP plating has been
described above as an example of the cap-plating treatment which is
carried out onto the activated exposed surface by attaching Pd, in
advance, of the copper film 6 with a COWP film selectively, the
cap-plating treatment of the present invention, of course, is not
limited to this specific example.
[0161] As shown in FIG. 25, it is preferred in the present
invention to additionally carry out a chemical polishing or an
electrolytic polishing (step 5-1) between the electrolytic or
chemical polishing of step 5 and the electrolytic or chemical
polishing of step 6, and a chemical polishing or a composite
electrolytic polishing (step 6-1) between the electrolytic or
chemical polishing of step 6 and cleaning/drying treatment of step
7.
[0162] In this regard, there is a case where in the electrolytic
polishing of the surface of the substrate W for removing the copper
film 6 formed thereon (step 5), a copper 6a still remains unremoved
on the barrier film 5, as shown in FIG. 26, due to the polishing
conditions, etc. If the electrolytic polishing is continued to such
a substrate, only the copper in the hole and the trench for
interconnects is polished whereas the copper 6a on the barrier film
is left unremoved.
[0163] In order to overcome the drawback in the above case, the
electrolytic polishing (step 5) can be shifted to a chemical
polishing (step 5-1) by shutting off the power source to stop
applying a given voltage between the plate 158 and the substrate W,
and by using the polishing liquid used in the electrolytic
polishing as a chemical agent, whereby the copper 6a remaining on
the surface of the barrier layer 5 can be removed as shown in FIG.
26B.
[0164] Though the electrolytic polishing (step 5) and the chemical
polishing (step 5-1) are carried out in the same polishing tank
using the same polishing liquid in the above example, it is also
possible to carry out a polishing in a separate polishing tank,
either by a chemical polishing using e.g. a polishing liquid
(chemical agent) containing an additive which, due to the effect of
the additive that preferentially adheres to a high-current density
area, can preferentially remove the remaining copper-film 6a, or by
an electrolytic polishing using the same polishing liquid
(electrolyte). Imidazole, benzimidazole, benzotriazole or
phenacetin may be used as the additive.
[0165] Further, there is also a case where after the chemical or
electrolytic polishing of the surface of the substrate W for
removing the barrier layer 5 and the copper film 6 (step 6), a
conductive material 5a such as TaN, which is the material of the
barrier layer 5, still remains on the insulating film 2 such as an
oxide film or a film of a low-K material, as shown in FIG. 26c, due
to the polishing conditions, etc. This necessitates an additional
processing by CMP, that is, a CMP treatment can not be omitted.
[0166] In order to overcome the drawback in the above case,
electrolytic or chemical polishing is carried out using a polishing
liquid containing an additive which has a higher effect than the
above described additive added to the electrolyte used in the
preceding electrolytic polishing (step 6) using a basic liquid
which can passivate copper, electrolytic polishing is carried out
using a basic liquid which can passivate copper or under
passivating electrolytic conditions, thereby flattening the surface
of the insulating film 2 (an oxide film or a film of low-K
material) and the surface of the copper film 6 filled in the
contact hole 3 and the trench for interconnects, as shown in FIG.
21C.
[0167] Instead of such electrolytic or chemical polishing,
composite electrolytic polishing may be carried out by passivating
the entire surface of the copper layer 6 and the remaining barrier
film 6 composed of a conductive material such as TaN, and polishing
and removing both the copper and the conductive material at the
same time. It is also possible to first carry out the electrolytic
or chemical polishing, and subsequently carry out such a composite
electrolytic polishing.
[0168] The composite electrolytic polishing can be carried out by
using a polishing liquid containing abrasive particles. As shown in
FIG. 27, the abrasive particles G polish and remove protuberances P
of the passivated copper or TaN remaining on the surface of the
substrate W, and the barrier layer 5 composed of a conductive
material such as TaN, which is present beneath the passivated layer
to be polished away by the grains G, is preferentially polished and
removed by electrolytic or chemical polishing. The copper and the
conductive material such as TaN can thus be polished at the same
time. When a finish surface of a surface roughness of 100 .ANG. or
less is desired, for example, it is preferred to use an abrasive of
a #5000 size or smaller.
[0169] FIG. 28 is a plan view of yet another embodiment of an
interconnects-forming apparatus in accordance with the present
invention. The apparatus comprises a housing 110 that houses the
following: loading/unloading sections 111; transport route 125; a
copper-plating section 112, a cleaning/drying section 114, a first
electrolytic or chemical polishing section 118, a second
electrolytic or chemical polishing section 120, a cleaning/drying
section 122 and an annealing section 116, which are arranged in the
above order along the transport route 125. Further, the apparatus
is provided with a transporting device 126 movable along the
transport route 125 for transporting a substrate between the above
sections. The constructions of the copper-plating section 112, the
electrolytic or chemical sections 118 and 120, the annealing
section 116, etc. are the same as described above.
[0170] An example of the process for forming interconnects will now
be described by referring to FIG. 29. This example illustrates a
case where the surface of the substrate W, which is plated with
copper to form a plated copper film 6 as shown in FIG. 32B, is
flattened through a CMP processing to form copper interconnects.
Though the final flattening process is thus carried out by CMP, a
load upon the CMP is reduced.
[0171] First, the substrate W having a seed layer 7 (see FIG. 32A)
as an outermost layer is taken one by one from the
loading/unloading section 111 by the transport device 126, and is
transported to the copper-plating section 112 (step 1).
[0172] Next, plating with copper by e.g. electroplating is carried
out onto the substrate W in the copper-plating section 112, thereby
forming a plated copper film 6 (see FIG. 32B) on the surface of the
substrate W (step 2). After the completion of plating, the plated
substrate W is transported to the cleaning/drying section 114 for
cleaning and drying (step 3), and the substrate W is then
transported to the first electrolytic or chemical polishing section
118.
[0173] Next, in the first electrolytic or chemical polishing
section 118, a first-stage electrolytic or chemical polishing is
carried out to the surface (plated surface) of the substrate W to
polish and remove the copper film 6 formed on the surface of the
substrate W (step 4). In the case of the electrolytic etching, as
described above, a polishing liquid is used as the polishing liquid
(electrolyte) 150 shown in FIGS. 16 and 17 which comprises at least
one inorganic acid and/or organic acid capable of dissolving copper
and at least one thickening agent selected from the group
consisting of polyhydric alcohols, high-molecular weight polyhydric
alcohols and alkylene glycol alkyl or aryl ethers, and which thus
has an increased viscosity by the addition of the thickening agent,
thereby enlarging the diffusion layer on the substrate, raising the
polarization potential and suppressing the conductivity of the
entire surface of the substrate in the liquid, to thereby obtain a
high flatness of the polished surface.
[0174] Next, the substrate which has undergone the first-stage
electrolytic or chemical polishing treatment is transported to the
second electrolytic or chemical polishing section 120 where the
second-stage electrolytic or chemical polishing is carried out to
the surface of the substrate (step 5). As described above, in case
a chemical polishing is carried out as the second-stage polishing,
a polishing liquid is used as the polishing liquid (chemical agent)
which comprises the polishing liquid having an increased viscosity
used in the electrolytic polishing and added thereto, an additive
which can adhere to the surface of copper and chemically suppress
the dissolution of copper, or a basic liquid or an additive which
forms a strong complex with copper or promotes the formation of a
passivated film on the surface of copper, thereby further improving
the flatness of the copper film 6 (see FIG. 32B). The chemical
polishing treatment may be omitted.
[0175] As described above, instead of the chemical polishing, an
electrolytic polishing may be carried out by using the same
polishing liquid containing the same additive. Further, the
chemical polishing may be carried out using the same polishing
liquid as used in the preceding electrolytic polishing (step 4), by
shutting off the power source for the electrolytic polishing. When
the thickness of the copper film 6 has reached the minimum
thickness necessary for annealing, e.g. 300 nm, the chemical
polishing is terminated, and the substrate is then transported to
the cleaning/drying section 122.
[0176] The substrate is cleaned and dried in the cleaning/drying
section 122 (step 6), and is then transported to the annealing
section 116 where the substrate having the plated film 6 thereon is
heat-treated to anneal the copper film 6 (step 7). Thereafter, the
annealed substrate W is returned to the cassette of the
loading/unloading section 111 by the transporting device 126 (step
8).
[0177] Thereafter, the substrate W is subjected to a CMP treatment
in a separate apparatus (step 9) to make the surface of the copper
film 6 filled in the contact hole 3 and the trench 4 for
interconnects and the surface of the insulating film 2 lie
substantially on the same plane, thereby forming interconnects
composed of the copper film 6 (see FIG. 32C). If necessary, the
above described cap-plating treatment is then carried out (step
10).
[0178] According to this embodiment, the flatness of the copper
film on a substrate after electrolytic or chemical polishing can be
improved, even when fine holes and large holes are co-present in
the surface of the substrate, by either carrying out one stage of
the electrolytic polishing, or carrying out at least two stages of
the electrolytic polishing and the electrolytic or chemical
polishing. A later CMP processing can therefore be carried out in a
shout time without suffering from dishing.
[0179] In order to make the plated surface of the substrate as flat
as possible by the electrolytic polishing, it is important to hold
the substrate with its best flattened state and use a plate
(cathode) having the flattest possible finish, and also to allow
them to move relatively while they are kept as close as possible so
as not make, within the area of the substrate surface, any singular
points in the flow of polishing liquid and in the electric
field.
[0180] FIGS. 30 and 31 show yet another embodiment of electrolytic
or chemical polishing sections 118 and 120 which meet the above
demands. The polishing section 118 (120) includes a top-opened
cylindrical polishing tank 152 for accommodating a polishing liquid
150, and a substrate holder 156 for detachably holding a substrate
W with its front surface downward at such a position that the
substrate W covers the top opening of the polishing tank 152. A
plate (cathode plate) 158 in a plain plate shape, which makes a
cathode when immersed in the polishing liquid 150, is disposed
horizontally on the upper surface of the bottom plate 72 of the
polishing tank 152. The diameter d.sub.3 of the plate 158 is
determined so that even when the substrate W of diameter d.sub.4
makes a scroll movement, the substrate W does not move out of the
area of the plate 158; and the diameter d.sub.5 of the polishing
liquid feed zone, which contains a polishing liquid feed holes
158b, is determined so that even when the substrate W of diameter
d.sub.4 makes a scroll movement, the polishing liquid feed zone
remains within the area of the substrate W. In the surface of the
plate 158, there are formed a number of grooves 158a in a lattice
from. The substrate holder 156, on its inside, is provided with a
vacuum chamber 156a that communicates with a vacuum source, and a
number of vacuum attraction holed 156b penetrating downwardly from
the vacuum chamber 156a. The other construction of the electrolytic
or chemical polishing sections 118 and 120 is the same as the
etching section 20 shown in FIGS. 11 and 12, and hence a
description thereof is herein omitted, with the same reference
numerals being given to the same members.
[0181] In carrying out electrolytic polishing in the electrolytic
or chemical sections 118 and 120, the etching liquid 150 is fed
into the etching tank 152 and, while the etching liquid 150 is
overflowing from the overflow weir 74, the bottom plate 72 is
allowed to make, together with the plate 158, a scroll movement.
Under these conditions, the substrate holder 156 holding the
substrate W with its plated surface downward is lowered, while
rotating the substrate W, down to a position for polishing.
[0182] Under the above conditions, a pulse current as shown in FIG.
13, for example, with a time t.sub.1 to be applied of 1 mS-20 mS,
preferably 10 mS, and with a current density to be applied of 2-20
A/dm.sup.2, is applied a plurality of times with stoppage times
t.sub.2, each time t.sub.2 equal to the time t.sub.1, being
interposed. Upon passing of current, oxidation dissolution of the
plated film occurs first at the raised portion of the substrate,
and then shifts to the plane portion. Accordingly, passing of
current and immediate shutoff of the power feed, when repeated,
enables selective etching of the raised portion.
[0183] As described hereinabove, according to the
interconnects-forming method and apparatus, the flattening process
after copper plating is carried out mainly by electrolytic or
chemical polishing. Thus, the present invention can omit a CMP
treatment entirely or reduce a load upon a CMT treatment and,
except for the case of resorting to CMT solely for the finishing
processing, can successively carry out a series of flattening steps
including annealing in the same housing.
[0184] Further, the polishing liquid of the present invention, when
used in electrolytic polishing or chemical polishing, can polish a
plated copper film formed on the surface of a substrate into a
flattened film surface and can polish copper and a conductive
material other than copper at the same polishing rate. The
polishing method of the present invention can provide the polished
surface with excellent flatness and therefore can omit a CMT
treatment entirely or reduce a load upon CMP to the least possible
extent.
[0185] Although certain preferred embodiments of the present
invention have been shown and described in detail, it should be
understood that various changes and modifications may be made
therein without departing from the scope of the appended
claims.
* * * * *