U.S. patent application number 11/329093 was filed with the patent office on 2006-05-18 for electroless plating method, electroless plating device, and production method and production device of semiconductor device.
This patent application is currently assigned to HITACHI, LTD.. Invention is credited to Haruo Akahoshi, Takeyuki Itabashi, Hiroshi Nakano.
Application Number | 20060102485 11/329093 |
Document ID | / |
Family ID | 34100647 |
Filed Date | 2006-05-18 |
United States Patent
Application |
20060102485 |
Kind Code |
A1 |
Nakano; Hiroshi ; et
al. |
May 18, 2006 |
Electroless plating method, electroless plating device, and
production method and production device of semiconductor device
Abstract
The invention is purposed to reduce the amount of the
electroless plating solution used for plating, to facilitate
compositional control of the plating solution, and to prevent
degradation of quality of the plating film (deposit) by oxygen
dissolved in the plating solution. An electroless plating method in
which a previously prepared electroless plating solution is exposed
to a depressurized atmosphere to decrease the gas components
existing in the solution, and while maintaining the plating
solution in the form of a continuous thin layer, the surface to be
plated of the substrate on which to form an electroless plating
film is brought into contact with said layer of the plating
solution and maintained in this state for a required period of time
to perform electroless plating. An electroless plating device, and
a production method and a production device of semiconductor
devices are also disclosed.
Inventors: |
Nakano; Hiroshi; (Hitachi,
JP) ; Itabashi; Takeyuki; (Hitachi, JP) ;
Akahoshi; Haruo; (Hitachi, JP) |
Correspondence
Address: |
McDermott Will & Emery LLP
600 13th Street, N.W.
Washington
DC
20005-3096
US
|
Assignee: |
HITACHI, LTD.
Tokyo
JP
|
Family ID: |
34100647 |
Appl. No.: |
11/329093 |
Filed: |
January 11, 2006 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
10898201 |
Jul 26, 2004 |
|
|
|
11329093 |
Jan 11, 2006 |
|
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Current U.S.
Class: |
205/88 ;
257/E21.174; 257/E23.16 |
Current CPC
Class: |
H01L 23/53223 20130101;
H01L 2924/0002 20130101; C23C 18/1683 20130101; H01L 21/76849
20130101; H01L 21/288 20130101; C23C 18/1619 20130101; H01L 2924/00
20130101; C23C 18/1682 20130101; H01L 21/76843 20130101; H01L
2924/0002 20130101; H01L 21/76874 20130101 |
Class at
Publication: |
205/088 |
International
Class: |
C25D 5/00 20060101
C25D005/00 |
Foreign Application Data
Date |
Code |
Application Number |
Oct 18, 2004 |
JP |
JP 2003-203788 |
Claims
1. An electroless plating method comprising the step of carrying
out an electroless plating treatment by, while keeping an
electroless plating solution beforehand prepared at a continuous
thin liquid layer, bringing a surface to be plated of a substrate,
on which an electroless plating is to be formed, into contact with
the liquid layer and by maintaining the contacting state for a
prescribed period of time.
2. The method according to claim 1 wherein, in the electroless
plating treatment step, the electroless plating solution is exposed
to a depressurized atmosphere to decrease gas components staying
dissolved in the solution.
3. The method according to claim 1 wherein said electroless plating
treatment is conducted on each of the substrates piece by piece,
and an amount of the electroless plating solution used per
substrate is 5 to 150 ml.
4. The method according to claim 1 wherein the electroless plating
solution, at least in a region where the electroless plating is to
be conducted, is kept in a substantially closed atmosphere shut off
from an outer air.
5. The method according to claim 1 wherein the layer of the plating
solution is kept in a non-oxidizing atmosphere.
6. The method according to claim 1 wherein the liquid layer of the
solution is substantially kept horizontally, and a downward facing
surface to be plated of the substrate is brought into contact with
the surface of the plating solution.
7. The method according to claim 1 wherein the surface to be plated
has a copper interconnect, and an interconnect protective film is
formed on said copper interconnect by said electroless plating.
8. The method according to claim 4 wherein the electroless plating
treatment is carried out in a nitrogen gas or argon gas
atmosphere.
9. The method according to claim 1 wherein, at least during the
electroless plating treatment, an opening of a container forming
the layer of the electroless plating solution is closed by the
surface to be plated of the substrate.
10. The method according to claim 1 wherein a thickness of the
layer of the electroless plating solution is 0.01 to 5 mm.
11. The method according to claim 1 wherein a flow of the
electroless plating solution is stopped during the electroless
plating treatment.
12-18. (canceled)
19. A method for producing a semiconductor device comprising the
steps of: holding a semiconductor substrate so as to bring a
region, at which an interconnect protective film on the
semiconductor substrate having a metal interconnect is to be
formed, into contact with a thin layer of an electroless plating
solution beforehand prepared; degassing the electroless plating
solution to decrease gas components therein; and conducting an
electroless plating treatment while shutting off an atmosphere of
the electroless plating solution from an outer air to form the
interconnect protective film.
20. (canceled)
Description
FIELD OF THE INVENTION
[0001] The present invention relates to an electroless plating
method, an electroless plating device, and a production method and
a production device of semiconductor devices. More particularly, it
relates to electroless plating techniques available for producing
electronic devices such as semiconductor devices having a basic
structure comprising a wiring system using copper or the like as
wiring material and having an interconnect protective film.
BACKGROUND OF THE INVENTION
[0002] Request is rising for the improvement of operating speed of
semiconductor devices for realizing a higher degree of integration
and higher performance of the semiconductor devices, and in line
with this, efforts have been made for further miniaturization and
layer multiplication of internal wiring of LSI. Such
miniaturization and layer multiplication of wiring system lead to
an increase of wiring resistance and inter-wiring capacitance,
which affects interconnecting signal transfer speed. Since this
signal transfer delay time encumbers speed-up of operation of
semiconductor devices, it has been tried to lower dielectric
constant of the interlayer insulating films for controlling the
inter-wiring capacitance and to lower resistance of the wiring
material to reduce wiring resistance, thereby to elevate operation
speed.
[0003] It has been proposed to use copper, whose specific
resistance is as low as 1.7 .mu..OMEGA.cm, as wiring material. But
this material has the problem that it is liable to oxidize on the
surface to cause an increase of wiring resistance or lower
reliability of wiring or elements. Also, copper tends to react with
the insulating films or diffuse into these films, so that in order
to secure reliability of interconnection, it needs to provide a
protective film between copper interconnect and insulating films,
but formation of a conductive film as an interconnect protective
film on the surface of wiring enables a reduction of electric
capacity.
[0004] As means for forming the interconnect protective films,
there are known methods making use of electroless plating for
forming the conductive films. For instance, U.S. Pat. No. 5,695,810
(CLAIMS) shows the idea of forming a cobalt-tungsten-phosphorus
conductive film as an interconnect protective film by electroless
plating. Also, JP-A-2002-151518 (abstract) discloses means of
forming a cobalt-tungsten-boron conductive film.
[0005] As the method of such electroless plating, JP-A-2001-342573
(abstract) and JP-A-2002-129343 (abstract) propose application of
an electroless plating solution by circulation. In this method,
however, since the plating solution is kept dropped onto the
surface to be plated of a semiconductor substrate throughout the
process, the plating solution is used in large quantities for
circulation. Further, in such use of the plating solution by
circulation, fine particles tend to be generated from the component
parts of the apparatus, and such generation of fine particles may
become a momentum to start decomposition of the plating solution,
causing deposition of fine particles on the semiconductor substrate
to lower reliability of wiring.
[0006] Further, the electroless plating solution has the property
that its concentration varies in accordance with the progress of
reaction, so that the formed film composition changes with
variation of the solution composition, resulting in loss of the
normal function of the film to protect the wiring. Moreover, in
order to maintain the solution composition, scale-up of the
apparatus becomes essential because of the necessity of
incorporating a compositional analyzer, replenishing means, etc.,
making it difficult to form a functional film with high
reproducibility.
[0007] In the method of JP-A-2002-129343 (abstract), in order to
save the amount of the plating solution used, plating is carried
out by placing the plating solution on rotary wafer holder surface,
but since the semiconductor substrate is not in a state of being
sealed airtight, air is taken in to increase the amount of oxygen
staying dissolved in the plating solution. It has been confirmed
that the presence of such dissolved oxygen has the effect of
retarding the progress of plating reaction, adversely affecting the
in-plane uniformity of the film thickness.
[0008] JP-A-2001-342573 (abstract) discloses a method in which the
electroless plating solution is sprayed from the shower head on the
upwardly disposed surface to be plated of the substrate, but this
method involves the same problem as encountered in JP-A-2002-129343
(abstract) since the plating solution is brought into contact with
air to take in oxygen.
SUMMARY OF THE INVENTION
[0009] As explained above, in order to form a continuous functional
film by an electroless plating device which has been used for
forming the interconnect protective films, the plating solution is
used in circulation, so that analytical control of the plating
solution is necessary, and because of the large volume of the
solution used, scale-up of the equipment is indispensable, inviting
a rise of running cost. Researches have been made for a plating
film forming method that can solve these problems, but there is yet
known no electroless plating method and device that can meet the
said film forming conditions.
[0010] An object of the present invention is to form films,
typically interconnect protective films, with high uniformity by
easy control of the plating solution, and to provide therefor an
electroless plating method, an electroless plating device, and a
production method and a production device of semiconductor
devices.
[0011] According to the present invention, there is provided an
electroless plating method comprising the step of carrying out an
electroless plating treatment by, while keeping an electroless
plating solution beforehand prepared at a continuous thin liquid
layer, bringing a surface to be plated of a substrate, on which an
electroless plating is to be formed, into contact with the liquid
layer and by maintaining the contacting state for a prescribed
period of time. The above electroless plating treatment is
conducted on each of the substrates piece by piece, and an amount
of the electroless plating solution used per substrate is
preferably 5 to 150 ml. Particularly a good plating film can be
obtained by carrying out the above electroless plating treatment by
exposing the electroless plating solution to a depressurized
atmosphere to decrease gaseous components staying dissolved in the
solution.
[0012] The electroless plating solution, at least in a region where
the electroless plating is to be carried out, is preferably kept in
a substantially closed atmosphere shut off from an outer air. This
makes it possible to prevent air, especially oxygen, from getting
into the plating solution to impair the progress of plating. Any of
the above four patent documents are silent on the conception of
shutting off the plating atmosphere from the outer air. In order to
create such an inert atmosphere, it is preferable to maintain the
layer of said plating solution in a non-oxidative atmosphere, for
instance, a nitrogen or argon atmosphere.
[0013] It is a practical and simple way of embodying the method of
the present invention that the liquid layer of the solution is
substantially kept horizontally and a downwardly facing surface to
be plated of the substrate is brought into contact with the surface
of the plating solution.
[0014] A principal example of application of the present invention
is forming an interconnect protective film for a semiconductor
device. The substrate surface to be plated has a copper
interconnect, and an interconnect protective film is formed on said
copper interconnect by the electroless plating. Currently, in the
production of semiconductor devices, it is the most popular
practice in the art to work e.g. 12-inch (about 30 cm in diameter)
wafers one by one, with this operation being called "leaf
processing". Formation of the interconnect protective film by
electroless plating is also included in this leaf processing. The
present invention is especially suited for this leaf processing,
and the "surface to be plated" referred to in this specification
means a surface of each unit wafer.
[0015] In the present invention, at least during the electroless
plating treatment, an opening of a container forming the layer of
the electroless plating solution is closed by the surface to be
plated of the substrate. This is helpful to protect the rear side
of the semiconductor substrate from the plating solution when it is
desired not to contaminate the rear side of the substrate with the
plating solution or other matter. It also keeps the plating
solution free from oxygen.
[0016] The present invention is purposed to form the films with a
very small thickness of tens to hundreds nm such as interconnect
protective films for semiconductor devices. For the adjustment of
solution composition, temperature control, temperature management
and cost reduction, it is necessary to minimize the volume of the
plating solution used for one piece of wafer. For this reason, the
electroless plating liquid layer thickness is confined to a range
of 0.01 to 5 mm. Especially a layer thickness in the range of
around 0.1 to 1 mm is optimum. The smaller the volume of the
plating solution, the easier the temperature control. Control of
the plating solution composition, for example, correct adjustment
of the plating solution composition during the plating operation,
is by no means easy. According to the present invention, by
minimizing the amount of the plating solution used per wafer,
control of the plating solution composition during the plating
operation is made unnecessary and the plating solution is discarded
on the conclusion of every plating operation without compositional
adjustment of the plating solution, so that control of the plating
solution is strikingly simplified and also cost of the plating
solution (material cost, control cost, etc.) is greatly
reduced.
[0017] In the present invention, it is preferable to stop a flow of
the electroless plating solution during the electroless plating
treatment. In the conventional electroless plating process, it has
been the common practice to adjust the plating solution composition
or to stir or circulate the plating solution during the plating
operation. According to such practice, however, it becomes
necessary to control the plating solution composition and there is
a possibility to take in oxygen to cause troubles.
[0018] The present invention provides an electroless plating device
comprising: an electroless plating treatment container having an
opening and forming a continuous thin liquid layer of electroless
plating solution; a first plating solution supply means comprising
a pump and piping for feeding the electroless plating solution to
said container; and a second plating solution supply means
comprising a pump and piping for lowering a gas in the plating
solution during the electroless plating treatment.
[0019] An internal capacity of said plating container is preferably
5 to 150 ml, the optimal volume being around 30 to 50 ml, in case
where 12-inch wafers are treated. As mentioned above, the opening
of the plating container and the substrate to be plated are
preferably designed such that the area of said opening of the
container be smaller than the area of the surface to be plated of
the substrate, and that said opening be closed by the
substrate.
[0020] As mentioned above, it is preferable to form a continuous
thin layer of electroless plating solution between the bottom of
said plating container and the surface to be plated of the
substrate. No good plating film can be obtained with a
discontinuous or non-uniform layer of plating solution. The
distance between the surface to be plated of the substrate and a
bottom side of the electroless plating treatment container is
preferably 0.01 to 5 mm.
[0021] Means are provided for keeping the thin layer of electroless
plating solution substantially horizontally and for holding the
surface to be plated of the substrate in a downwardly facing
position to contact the thin layer of plating solution. This
ensures contact between the plating solution and the surface to be
plated of the substrate, making it possible to obtain a good
plating film.
[0022] In accordance with the present invention, there is also
provided an electroless plating in which in addition to a tank of
the electroless plating solution tank, there is provided at least
one kind of treating solution tank. This plating device is
preferably provided with a gas supply pipe for substituting a
plating space with an inert gas atmosphere lowered in oxygen
concentration.
[0023] The present invention is further intended to provide a
device for producing a semiconductor device comprising: means for
setting a region, at which an interconnect protective film on a
semiconductor substrate having a metal interconnect is to be
formed, and for holding said semiconductor substrate so as to being
said region of the substrate into contact with a thin layer of an
electroless plating solution beforehand prepared; a degassing means
for degassing the plating solution to decrease gas components
therein; and a closure means for shutting off an atmosphere of the
electroless plating solution from an outer air.
[0024] According to the present invention, control of the
electroless plating solution becomes easy and also the electroless
plating conditions can be set with good reproducibility, making it
possible to realize a further dimensional reduction of the
electroless plating device and to attain the object to prevent rise
of running cost. Further, reproducibility of the formed
interconnect protective film composition and uniformity of the
worked wafers are improved to elevate reliability of semiconductor
interconnect.
[0025] Other objects, features and advantages of the invention will
become apparent from the following description of the embodiments
of the invention taken in conjunction with the accompanying
drawings.
BRIEF DESCRIPTION OF THE DRAWINGS
[0026] FIG. 1 is a flow chart illustrating a process of forming an
interconnect protective film for a semiconductor device.
[0027] FIG. 2 is a schematic plan showing the general layout of an
electroless plating device according to another embodiment of the
present invention.
[0028] FIG. 3 is a plan for illustrating a principal part of the
electroless plating device of the present invention.
[0029] FIG. 4 is a cross-sectional view showing the structure of a
principal part of the electroless plating device of the present
invention.
[0030] FIG. 5 is a plan, partly shown in section, showing the
structure of the electroless plating device according to the first
embodiment of the present invention.
[0031] FIG. 6 is a side elevation, partly shown in section, showing
the structure of the electroless plating device according to the
third embodiment of the present invention.
[0032] FIG. 7 is a schematic diagram of the plating system in the
semiconductor producing device in an embodiment of the present
invention.
[0033] FIG. 8 is a schematic diagram of the plating system in the
semiconductor producing device in another embodiment of the present
invention.
[0034] FIG. 9 is a cross-sectional view showing arrangement of
semiconductor, insulating film, wiring film and protective film of
a semiconductor device to which the present invention was
applied.
[0035] FIG. 10 is a plan showing the plane structure of a
semiconductor device to which the present invention was
applied.
DESCRIPTION OF REFERENCE NUMERALS
[0036] 1: interconnect protective film, 2: copper interconnect, 3:
barrier film, 4: insulating film, 5: seed layer, 6: copper film, 7:
groove for wiring, 8: SiN interconnect protective film, 9:
palladium film, 10: connecting hole, 11: wiring plug, 12: wiring
oxidized layer, 13: abnormal deposition, 14: inter-wiring
shorting.
DETAILED DESCRIPTION OF THE INVENTION
[0037] The semiconductor producing device according to the present
invention and its preferred embodiments are explained below.
[0038] A semiconductor device is produced from a process comprising
the following steps (a) to (g):
[0039] (a) An insulating film 4 is formed on a semiconductor
substrate (here, a sublayer wiring layer already having an
insulating film 3b and sublayer wiring 2b formed on the inside
surface of each groove as shown in FIG. 1 (a) is used as
substrate), and a barrier film 3b and wiring material 2b are formed
by sputtering in each groove formed in said insulating film. (FIG.
1 (b)).
(b) Wiring grooves 7 and connecting holes 10 are formed in the
insulating film 4. (FIG. 1 (c)).
(c) Barrier film 3 for preventing diffusion of wiring material is
formed on insulating film 4. (FIG. 1 (d)).
(d) Seed layer 5 which becomes ground for electrolytic copper
plating is formed on barrier film 3 (FIG. 1 (e)).
(e) Wiring grooves 7 and holes 10 are filled up with copper 6 by
electrolytic copper plating on copper seed layer 5. (FIG. 1
(f)).
(f) The film of copper 6 formed on barrier film 3 excluding grooves
7 and holes 10 is removed so that copper 6 is left only in the
inside of each groove 7 and hole 10 to form wiring 2 and wiring
plug 11. (FIG. 1 (g)).
(g) Interconnect protective film 1 is formed only on the surface of
wiring 2 and wiring plug 11 by electroless plating. (FIG. 1
(h)).
[0040] The above steps (a) to (g) are repeated a necessary number
of times to form a semiconductor device having multiple laminated
wiring layers. Any of the steps (a) to (f) can be carried out in
the same way as the conventional wiring forming process, and the
conventional materials can be used for the substrate and insulating
film.
[0041] For instance, as the substrate, it is possible to use one
comprising a silicon wafer such as used in the conventional LSI
process, with elements formed thereon, or a wafer having sublayer
wiring 2b formed thereon as described above. Also, as the
insulating film 4 formed in step (a), there can be used the known
insulating materials such as SiO.sub.2, silsesquioxane hydride
(SiOF) and methylsiloxane, various kinds of low dielectric constant
materials and their laminate films. (FIG. 1 (b)).
[0042] Conventional lithographic and etching techniques can be
employed for forming wiring grooves 7 and holes 10 in step (b).
(FIG. 1 (c)).
[0043] As barrier film 3 formed in step (c), it is possible to use
a film made of a known high-melting point material such as
titanium, tantalum, tungsten, etc., or their alloys, or a nitride
film made of titanium nitride, tantalum nitride, tungsten nitride
or such. These films can be formed by the known techniques such as
chemical vapor growth and sputtering. (FIG. 1 (d)).
[0044] The known techniques such as chemical vapor growth and
sputtering can be used for forming seed layer 5 in step (d). (FIG.
1 (e)).
[0045] In step (e), copper film 6 is formed by electroplating.
(FIG. 1 (f)).
[0046] In step (f), copper and barrier film at the unnecessary
parts are removed by chemical machine grinding. (FIG. 1 (g)).
[0047] The step of forming interconnect protective film 1 by
electroless plating on the surfaces of grooves 7 and holes 10
(wiring 2 and wiring plug 11) formed in step (g) is a step
characteristic of the present invention. This step is carried out
by dipping the chemical machine ground substrate in an electroless
plating bath. As electroless plating, cobalt-based plating with
high thermal stability is suited.
[0048] The cobalt-based electroless plating bath is composed of a
metal salt, a reducing agent, a complexing agent, a pH adjuster and
other additives. As cobalt salt, cobalt sulfate, cobalt chloride
and the like can be used. As tungsten salt, ammonium tungstate,
tungstic acid and the like can be used.
[0049] As reducing agent, in order to form an interconnect
protective film selectively on copper interconnect alone, the boron
compounds which can react on the copper interconnect surface and
the cobalt plating film are preferably used. Examples of such boron
compounds are dimethylamineborane, diethylamineborane, almineborane
and sodium hydride. Use of such a reducing agent makes it possible
to form an interconnect protective film directly on copper
interconnect without needing a plating catalyst such as palladium.
Ammonium, tetramethylammonium and the like are preferably used as
alkali solution for pH adjustment.
[0050] Citrates and the like are suited for use as completing
agent. As additives, thiourea, saccharine, thioglycollic acid,
known surfactants, etc., can be used. The plating solution
temperature is preferably in the range from 40.degree. C. to
90.degree. C. In case of using hypophosphorous acid or
hypophosphite as reducing agent, it is necessary to apply a
catalytic treatment with Pd on the surface of Cu wiring before
conducting electroless plating.
[0051] As the material of the film to be formed, tungsten-based and
molybdenum-based alloys such as cobalt-tungsten-boron alloy and
cobalt-tungsten-phosphorus alloy are preferably used. It is
advisable to add a pretreatment step of cleaning wafers before
conducting electroless plating. This can eliminate the influences
such as variation of plating speed by contamination of the copper
interconnect surface or deposition of organic matter, affording an
improvement of film thickness uniformity in the wafer plane.
[0052] As the pretreatment solution, it is recommendable to use an
acidic solution such as sulfuric acid diluted to about 5%, an
alkaline solution such as organic alkali, or a reducing solution
which can reduce the copper surface. The acidic solution has the
effect of dissolving oxides on the copper interconnect surface but
has the risk of enlarging surface unevenness, so that the treatment
should be completed in a short time. The reducing solution has the
effect of reducing oxides on the copper surface and is capable of
enhancing activity of the copper surface while maintaining the
surface unevenness, so that it is suited for the pretreatment.
[0053] As the reducing pretreatment solution, it is advisable to
use a solution prepared by mixing appropriate amounts of a
complexing agent such as citric acid or succinic acid, a boron
compound such as dimethylamineborane, a copper reducing agent, e.g.
aldehydes such as formaldehyde, an organic alkali agent such as
aqueous tetramethylammonium solution for pH adjustment, and
additives such as surfactant. Treating temperature is preferably 20
to 70.degree. C., more preferably 40 to 60.degree. C. pH is
adjusted to stay in the range from neutrality to 12.
[0054] The interconnect protective film 1 formed by using a
cobalt-based electroless plating bath as described above
selectively covers copper interconnect 2 as exemplified in FIG. 9.
Since interconnect protective film 1 selectively covering copper
interconnect 2 grows isotropically from copper interconnect, it is
not only formed just above copper interconnect but extends onto the
barrier film or insulating film from the edge of copper
interconnect equally to the desired thickness of the interconnect
protective film. In FIG. 9, the same reference numerals as used in
FIG. 1 designate the same elements.
[0055] The system for carrying out such cobalt-based electroless
plating will be explained concretely in relation to the
semiconductor device producing device and chemical solution
treating device (particularly plating device) used in the
respective Examples, with reference to FIG. 2.
A. Structure of Plating Device
[0056] As an example of the plating device incorporated in the
semiconductor device manufacturing apparatus of the present
invention, the automatic wafer plating device used in the Examples
described below is here illustrated.
[0057] The main body of the automatic wafer plating device used in
the Examples comprises, as shown in FIG. 2, a conveyor mechanism
(conveyor robots) 26 for conveying wafers 13, loading stage 27,
pre-plating stage 28, plating stage 29, cleaning stage 30, drying
stage 31 and unloading stage 32. There are also provided a chemical
solution supply system and a chemical solution recovering system
(not shown).
[0058] There are provided wafer cassette 33 at loading stage 27,
plating pretreatment solution tank 34 at pre-plating stage 28,
plating solution tank 35 at plating stage 29, cleaning tank 36 at
cleaning stage 30, dryer 37 at drying stage 31, and wafer cassette
38 at unloading stage 32. Plating pretreatment solution tank 34 and
plating solution tank 35 are the tanks in which treatment with a
chemical solution is conducted. Each of these tanks is equipped
with piping for supplying a chemical solution and a temperature
controller (not shown). Spinner treatment may be conducted in
cleaning tank 36.
[0059] Each of these stages 27-32 may be provided in plurality for
improving throughput capacity. Pre-plating stage 28 and cleaning
stage 30 may be excluded. Particularly in the case of cobalt-based
electroless plating using a boron compound such as
dimethyl-amineborane as reducing agent, the pre-treating stage can
be excluded as catalyzation of Pd, etc., is unnecessary. Conveyor
robot 26, as shown in FIG. 3, has a wafer carrier arm 40 and a
wafer holder 39, and is designed to hold wafer 13 and carry it to a
predetermined position (for example, chemical solution treating
tank 17).
[0060] The chemical solution treating tank 17 of the automatic
wafer plating device in this example may be of a mechanism such as
shown in FIG. 4 and FIG. 5 (a) and (b). FIG. 5 (a) is a cross
section of treating tank 51, and FIG. 5 (b) is a top plan thereof.
This treating tank 51 is provided with a wafer support 52 along the
top opening of a thin saucer-like container 51a, and at a position
opposing the side of said support 52 is provided a chemical
solution supply line 53 which passes into the inside of treating
tank 51 from its outside. The chemical solution supplied from its
supply line 53 is discharged out of treating tank 5 from chemical
solution discharge port 54 via valve 55. The surface to be treated
of wafer 13 carried on support 52 and fixed in position by wafer
holder 56 is brought into contact with the layer 57 of chemical
solution to undergo treatment therewith.
[0061] Treating container 51a is provided with treating solution
inlets 60, a solution passage 61 and a solution discharge port 62.
Thickness (h) of the solution layer is preferably set at 5 mm or
less, especially 1 mm or less. The internal volume of the treating
container (the portion occupied by the solution which contributes
to the plating treatment, pretreatment and after-treatment, not
including the rise-up portion at the end of the solution layer in
FIG. 4) is 150 cm.sup.3 or less, preferably about 20 to 70
cm.sup.3.
[0062] In case this chemical solution treatment is plating, an
electric heating element 58 such as a heater is built in the
opposite wall (viz. bottom surface of the treating container) for
controlling the temperature, and the temperature in the plating
space is measured and controlled. If air gets into the plating
solution, the progress of plating reaction is retarded, so that the
plating space is preferably filled with an inert gas such as
nitrogen or argon or reduced in pressure. It is also effective to
introduce nitrogen gas or argon gas into the chemical solution tank
containing the plating solution and shut off air to hinder
dissolution of oxygen into the solution. Particularly vacuum
degassing of the plating solution supplied to the plating container
51a is recommended as it does not affect the quality of the plating
film.
[0063] The plating container, or chemical solution treating tank 51
for conducting the plating treatment, is provided in plating stage
29. Two or more of such plating tank may be provided in this stage.
Instead of the horizontal treating tank illustrated, it is also
possible to use a vertical treating tank 130 such as shown in FIG.
6 (a) and (b). Plating tank 51 shown in FIG. 6 (a) and (b) is
erected almost vertically. The thin layer of the chemical solution
such as plating solution is formed almost vertically, and the
surface to be plated of the wafer is held vertically and brought
into contact with the layer of the chemical solution. In FIG. 6 (a)
and (b), the same reference numerals as used in FIG. 4 and FIG. 5
(a) and (b) designate the same elements.
[0064] In the embodiment of FIGS. 4 and 5, the chemical solution
layer is formed substantially horizontally. Although the chemical
solution layer may be formed non-horizontally as in FIG. 6, it is
more rational and advantageous in terms of ease of treatment to
form and hold the solution layer substantially horizontally.
[0065] The material composing the plating tank is preferably
selected from those which are resistant to high temperature of up
to 80.degree. C. and alkalinity. For example, materials with
excellent chemical resistance such as Teflon (registered trade
mark), heat-resistant vinyl chloride and the like are suited for
use as tank material. When higher mechanical strength is required
of the plating tank, it is suggested to use a metallic material
coated with a highly chemically resistant substance such as Teflon.
In this case, it should be noted that if a metal active to the
electroless plating reaction is left exposed, the plating reaction
advances locally, so that care should be taken to eliminate any
exposure of metal.
[0066] The plating chamber where electroless plating is carried out
is preferably designed so that the distance therefrom to the
opposite wall 59 is from 10 .mu.m to 5 mm to lessen the volume of
the plating space defined by the object to be plated and said
opposite wall 59. By thus restricting the volume of the plating
space, it is possible to reduce the amount of the plating solution
required for one round of plating operation and to facilitate
control of the plating solution such as temperature control.
Further, it is possible to shorten the time required for the
replacement of the treating solution and to correctly set the time
for the plating operation.
[0067] The plating solution may be discarded after used once. The
electroless plating reaction causes deposition of the metallic
components while consuming the reducer components in the plating
solution, and induces grdual accumulation of the oxidized product
of the reducing agent, so that the respective ionic components in
the plating solution are varied in accordance with the progress of
the plating reaction. Since the once used solution is discarded,
control of the plating solution such as compositional analysis of
the solution becomes unnecessary or is remarkably simplified.
[0068] Arrangement of the equipment is horizontal in FIG. 4 but not
limited to this form; it may be vertical or skewed. Horizontal
arrangement has the advantage in that it allows easy control of the
plating time since the period of time in which the plating solution
is kept in contact with the entirety surface of the wafer can be
easily controlled. Vertical arrangement is advantageous in that
feed and discharge of the plating solution is easy.
[0069] Opposite wall 59 is disposed parallel to wafer 13 in FIG. 4,
but it may be set non-parallel to the wafer. Non-parallel
arrangement of opposite wall 59 and wafer 13 facilitates feed and
discharge of the plating solution. In the opposite wall may be
formed grooves for controlling flow of the solution. This can
uniformize the mode of hitting of the plating solution against the
wafer.
[0070] The electroless plating solution is divided into two or more
portions and stored in the respective reservoir tanks. Immediately
before entering the plating chamber, the plating solution is mixed
with a solution containing metallic ions and a solution containing
a reducing agent to prevent the self-decomposition reaction from
occurring in the plating solution, thereby solving the problem of
formation of fine particles in the plating solution and their
adhesion to the substrate.
[0071] Mixing of the plating solution may be effected by a blender
provided in the piping or may be performed in a pre-plating chamber
provided for the adjustment of the plating solution. Also, there
may be provided the reservoir tanks and corresponding piping for
the pre-cleaning solution and the after-cleaning solution,
respectively, making arrangement to allow replacement of the
solution in the plating tank. This can dispense with the
pretreatment tank to contribute to the miniaturization of the
equipment. Further, in order to perform cleaning of wafers with an
organic solvent or such, it is advisable to install exclusive
piping and waste solution discharge line.
[0072] Still further, provision of a pure water line for cleaning
of the tank and drain for waste acids will facilitate maintenance
of the plating tank. A heating means such as electric heater and a
temperature control unit are provided for conducting preliminary
heating in the reservoir tanks so that the plating solution will
have an optimal temperature for plating when it enters the plating
chamber.
B. Operation of the Device
[0073] Here, the process of treatments by the plating device in the
embodiments of the present invention is described with reference to
FIG. 7. The treatments described below are controlled by
information processor for control 25. This information processor 25
is a system comprising central processing unit (CPU), main memory,
external memory and input-output device. In the following
embodiments, processing by this information processor 25 is once
stored in a memory medium such as optical disc, magnetic disc or
magneto-optical disc, and actualized as the program written in the
main memory is executed by CPU, but the present invention is not
limited to the actualization means according to such a program.
[0074] In the system of FIG. 7, plating solution 16 in plating tank
17 having a cover is degassed by vacuum pump VP. Pretreatment
solution 76 in plating pretreatment solution tank 73 is supplied to
the plating tank 17 via electromagnetic valve 24. Electroless
plating solution is blended in the blender 72 with predetermined
amount of the solution 19 from the tank 18. After adjusted with
pure water, if needed, the electroless plating solution is supplied
into the tank 17 via electromagnetic valve 24, while pure water 77
in pure water tank 74 is supplied via electromagnetic valve and
filter 22 and mixed with the plating solution components, and the
mixed solution is forwarded into plating solution tank 17.
[0075] First, conveyor robot 26 shown in FIG. 2 takes out waters 13
one by one from wafer feed cassette 33 set on loading stage 27,
conveys the taken-out wafer to pre-plating stage 28 and places it
in plating pretreatment tank 34. Plating pretreatment is conducted
on wafer 13 in said tank 34. Then wafer 13 is further carried to
plating stage 29 by robot 26 and set to the supporting portion of
plating tank 35. A plating film is formed in this plating tank
35.
[0076] Wafer 13 is then conveyed to cleaning stage 30 by robot 26,
and after undergoing the cleaning and drying treatments, it is
taken in recovery cassette 38 at unloading stage 32. If arrangement
is made such that wafer 13 is taken in cassette 38 and this
cassette 38 is unloaded at drying stage 31, the device can be
reduced in size.
[0077] The plating procedure at plating stage 29 is explained with
reference to FIGS. 2 and 7. By the operation of information
processor for control 25, wafer 13 which has undergone plating
pretreatment at pre-plating stage 28 is conveyed to plating stage
29 by conveyor robot 26 and set to the wafer support at the opening
of the plating tank. Wafer 3 is secured to the support by wafer
holder 9 to inhibit the plating solution 16 from getting round to
the non-plated side of the wafer, and then inflow of the treating
solution into plating tank 35 is started.
[0078] Information processor 25 also operates to beforehand heat
the reservoir tanks of the plating pretreatment solution and the
plating solution and control them at an optimal temperature, and
before the plating solution is led into the plating tank,
appropriate amounts of the solutions from the respective reservoir
tanks are blended and supplied to plating tank 35.
[0079] The plating pretreatment solution is thus stored in plating
tank 35, and wafer 13, which is the object to be plated, is brought
into contact with the plating pretreatment solution. On completion
of fill-up of the plating chamber with the treating solution,
counting of the treating time is started. After the lapse of a
predetermined period of time, the plating solution is led into the
plating tank, whereby the pretreatment solution is forced out and
replaced with the plating solution. As replacement is completed,
supply of the plating solution is ceased, and after the lapse of a
certain period of time, for example 2 to 30 minutes, pure water is
introduced.
[0080] Supply and discharge of pure water is continued until
cleaning of wafer 3 is completed after the lapse of a predetermined
period of time. After completion of cleaning, the plating solution
in plating tank 35 is discharged out and wafer 13 is set free and
carried to final cleaning stage 30 by robot 26. This completes the
plating film forming process.
EXAMPLE 1
[0081] The following example is illustrated with reference to FIG.
1. Elements were formed on a silicon substrate of 200 mm in
diameter. On the substrate having sublayer wiring 2b (FIG. 1 (a)),
a 1 .mu.m thick SiO.sub.2 insulating film 4 was formed (FIG. 1
(b)). Then grooves 7 for wiring and connecting holes 10 were formed
by conventional dry etching (FIG. 1 (c)). The grooves were 0.2
.mu.m wide and the connecting holes were 0.15 .mu.m in diameter.
Then a 50 nm thick Ta film was formed as barrier film 3 by
sputtering (FIG. 1 (d)), after which a 150 nm thick copper film was
formed as seed layer 5 (FIG. 1 (e)).
[0082] The copper seed layer was formed at a rate of 200 to 400
nm/min by a long distance copper sputtering apparatus Ceraus
ZX-1000 (Nippon Shinku Gijutsu Co., Ltd.). This substrate was
dipped in a plating solution of the following composition and
subjected to 5-minute electroplating (6) at a solution temperature
of 24.degree. C. and a current density of 1 A/dm.sup.2 using
phosphorus-containing copper as anode electrode.
(Electroplating Conditions)
[0083] Copper sulfate 0.4 mol/dm.sup.3 [0084] Sulfuric acid 2.0
mol/dm.sup.3 [0085] Chloride ion 1.5.times.10.sup.-3 mol/dm.sup.3
[0086] MICROFAV Cu2100 10.times.10.sup.-3dm.sup.3/dm.sup.3 (copper
plating additive produced by Nippon Electroplating Engineers Co.,
Ltd.)
[0087] Then, for separating the metals precipitated by
electroplating, chemical machine grinding was carried out by a
chemical machine grinder Model 472 mfd. by IPEC Ltd. using
alumina-dispersed abrasive grains containing 1 to 2% of hydrogen
peroxide and a pad (IC-1000 mfd. by Rodel Corp.). The substrate was
ground to the barrier film under a grinding pressure of 190
g/cm.sup.2 to separate the wiring conductors (FIG. 1 (g)).
[0088] Then, an interconnect protective film was formed by using
the electroless plating device shwon in FIG. 4 and the electroless
plating system shown in FIG. 8. Connected to the electroless
plating device were piping for organic solvent, piping for cleaning
with an alkaline solution, piping for electroless plating solution,
and piping for water washing. In FIG. 8, the same reference
numerals as used in FIG. 7 designate the same elements. No
degassing pump is provided in the system of FIG. 8, but the plating
solution components are supplied by using pumps P.
[0089] The distance between the wafer to be plated and the opposing
wall was set at 1 mm. For disposal of the waste solutions, a waste
organic solvent discharge line and a waste inorganic solution
discharge line were connected. Before conducting plating on the
wafer, the alkaline aqueous solution used for pretreatment, the
solution containing metal ions used as the plating solution and the
solution containing a reducing agent were heated respectively to
55.degree. C., and nitrogen was bubbled through the solutions in
the reservoir tanks.
[0090] The plating tank and the wafer holder were preheated to
50.degree. C. For cleaning before plating, isopropyl alcohol was
introduced at a rate of 750 ml/min, and the supply of the solution
was suspended for 3 minutes after the wafer came into contact with
the solution. Then the pretreatment solution (alkaline aqueous
solution) was introduced for 10 seconds at a rate of 750 ml/min to
replace the solution in the tank, and the supply of the solution
was suspended for 3 minutes.
[0091] Thereafter, the plating solution was introduced for 10
seconds at a rate of 750 ml/min to replace the solution in the tank
with the plating solution, then the supply of the solution was
suspended for a predetermined period of time and cobalt-based
electroless plating was conducted. Then pure water was introduced
into the plating tank for one minute for cleaning. Since the
reducing agent used here is reacted on copper, the cobalt-based
electroless plating reaction proceeds on copper interconnect
without a step of catalyzation such as introduction of palladium
(FIG. 1 (h)).
[0092] Since in this devic the plating tank and the wafer holder
have been preheated, the temperature distribution in the wafer
plane during electroless plating was satisfactorily narrow, with
the disparity being 0.5.degree. C. at the most. Also, in this
device, diaphragm pumps were employed for the introduction of the
solution, and the supply of the solution was stopped after
introduction of the treating solution was completed. By stopping
the supply of the solution, it was possible to reduce the amount of
the plating solution required.
[0093] Stirring of the plating solution was effected by moving the
plating solution back and forth in the plating chamber and flow
passages by idling the diaphragm pumps. Since the volume of the
plating chamber was as small as 35 cm.sup.3 in this example, it was
possible to secure sufficient movement of the plating solution and
to improve stirring performance even when the volume of the plunger
portion of the pump was 5 cm.sup.3.
[0094] The plating pretreatment conditions and the plating
conditions are shown below. TABLE-US-00001 (Plating pretreatment
solution) Citric acid 0.30 mol/dm.sup.3 Dimethylamineborane 0.06
mol/dm.sup.3 RE610 (surfactant produced 0.05 g/dm.sup.3 by Toho
Chemical Co., Ltd.) (Plating pretreatment conditions) pH 9.5
(adjusted with tetramethylammonium solution) Solution temperature
55.degree. C. Pretreatment time 3 min. (Cobalt-based electroless
plating solution) Cobalt sulfate 0.1 mol/dm.sup.3 Citric acid 0.3
mol/dm.sup.3 Dimethylamineborane 0.06 mol/dm.sup.3 Tungstic acid
0.03 mol/dm.sup.3 RE610 (surfactant produced by 0.05 g/dm.sup.3
Toho Chemical Co., Ltd.) (Plating conditions) pH 9.5 (adjusted with
tetramethylammonium solution) Solution temperature 55.degree. C.
Plating time 2 min.
[0095] Cobalt-based electroless plating was carried out under the
above plating conditions. After cleaning with pure water, wafer 3
was unlocked and conveyed to final cleaning stage 30 by conveyor
robot 26. At the final cleaning stage, the wafer was cleaned for 2
minutes by rotating it at 500 rpm by a spinner while spraying pure
water against the surface and the rear side of the wafer, then
spray of pure water was stopped and the wafer was rotated at 2,000
rpm to scatter away the liquid and thereby dried. Then the wafer
was carried to the unloading stage by the conveyor robot. This
completed the process of forming a cobalt-based electroless plating
film serving as an interconnect protective film.
[0096] The thus formed substrate was worked by the focused ion
beams (FIB). Observation of a cross section of the substrate
including the grooves and holes by a scanning electron microscope
(SEM) showed that a 30 nm thick cobalt-tungsten-boron alloy film
was deposited uniformly on the copper surface.
[0097] No discrepancy in film thickness was noted between the
peripheral and central parts of the wafer in the SEM observation of
the formed film. Also, no deposition of cobalt-tungsten-boron alloy
was seen on the insulating film. Auger electron spectroscopic
analysis of the obtained cobalt alloy confirmed that it was an
electroless plating film composed of 79 atomic % of cobalt, 20
atomic % of tungsten and 1 atomic % of boron.
[0098] From the foregoing, it was confirmed, as the effect of the
instant embodiment of the present invention, that an interconnect
protective film can be formed uniformly in the wafer plane only on
the copper embedded in the wiring grooves and holes by using the
plating device according to the described example of the present
invention.
[0099] Then the thus obtained copper interconnect substrate with a
protective film was annealed for 30 minutes by heating to
500.degree. C. in a 2% hydrogen/98% helium gas atmosphere. As a
result of Auger electron spectroscopic examination of its surface,
no copper was detected from the surface and also no diffusion of
copper, or wiring material, was seen. The wiring resistance before
and after the heat treatment was not greater than 3% on the entire
wafer surface, and it could be confirmed that no increase of wiring
resistance was caused by oxidation of copper. Further, as no change
of resistance was admitted before and after formation of the
interconnect protective film as a result of measurement of
inter-wiring resistance, it could be confirmed that no abnormal
deposition occurred between wiring.
[0100] From the foregoing, it could be confirmed that by using the
electroless plating method according to the instant embodiment of
the present invention, it is possible to form a
cobalt-tungsten-boron alloy film uniformly in the wafer plane as a
copper interconnect protective film, to prevent oxidation and
diffusion of copper, and to obtain high reliability of the
semiconductor devices having copper interconnect.
EXAMPLE 2
[0101] In this example, electroless plating was carried out using a
horizontal film plating device 130 similar to that used in Example
1 shown in FIG. 4, with a vacuum pump provided on the treating
solution discharge piping as shown in FIG. 7. The composition of
the plating solution 16 and the plating conditions were the same as
used in Example 1.
[0102] Before carrying out plating on the wafers, an alkaline
solution used for pretreatment, a solution containing metallic ions
used as plating solution, and a solution containing a reducing
agent were heated respectively to 55.degree. C., and nitrogen was
bubbled into the respective reservoir tanks. The plating tank and
the wafer holder were preheated to 50.degree. C. The vacuum chamber
was evacuated by a vacuum pump, and the reservoir tanks of the
chemical solutions were closed airtight. Then the valve connecting
the vacuum chamber and the plating chamber was opened, followed by
opening of the valve connecting the pre-cleaning tank and the
plating chamber to admit the pre-cleaning fluid into the plating
chamber.
[0103] For pre-cleaning (cleaning before plating), isopropyl
alcohol was introduced at a rate of 600 ml/min, and after the wafer
came into contact with the fluid, the valve connecting the plating
chamber and the pre-cleaning tank was closed to suspend supply of
the fluid for 3 minutes. Then the valve connecting the plating
chamber and the plating pretreatment tank was opened to introduce
an alkaline aqueous solution as a pretreatment solution at a rate
of 600 ml/min for 15 seconds to replace the solution in the tank,
followed by suspension of supply of the solution for 3 minutes.
Then the plating solution was introduced at a rate of 600 ml/min
for 15 seconds to replace the solution in the tank with the plating
solution, after which supply of the solution was stopped for a
predetermined period of time and cobalt-based electroless plating
was conducted.
[0104] Thus by introducing the solution in a depressurized state,
it was possible to prevent the air bubbles produced in the plating
solution or the bubbles of the surfactant from adhering to the
wafer surface, thereby inhibiting the possibility of non-deposition
of the plating film due to adhesion of air bubbles. Then pure water
was introduced into the plating tank for one minute for cleaning.
Stirring of the plating solution in this device was effected by
moving the plating solution back and forth in the plating chamber
and the flow passages by opening and closing the valve of the
vacuum chamber.
[0105] Cobalt-based electroless plating was carried out under the
said plating conditions, followed by cleaning with pure water, and
then wafer 13 was unlocked and conveyed to final cleaning stage 30
by robot 26. At the final cleaning stage, the wafer was cleaned for
2 minutes by rotating it at 500 rpm by a spinner while spraying
pure water to the surface and rear side of the wafer. Then spray of
pure water was stopped, and the wafer was rotated at 2,000 rpm to
scatter away the liquid to dry the wafer. The wafer was then
further conveyed to the unloading stage by the convenyor robot,
thereby completing the process of forming a cobalt-based
electroless plating film used as an interconnect protective
film.
[0106] The thus formed substrate was worked by FIB. SEM observation
of its cross section including the grooves and holes showed that a
30 nm thick cobalt-tungsten-boron alloy film was uniformly
deposited on the copper surface. Also, as a result of observation
of the formed film, there was admitted no discrepancy in film
thickness between the peripheral part and the central part of the
wafer, and no non-deposition area existed. Further, no deposition
of cobalt-tungsten-boron alloy was noted on the insulating
film.
[0107] Auger electron spectroscopic analysis of the obtained cobalt
alloy confirmed that it was an electroless plating film composed of
79 atomic % of cobalt, 20 atomic % of tungsten and 1 atomic % of
boron.
[0108] From the foregoing, it was confirmed that an interconnect
protective film can be formed uniformly in the wafer plane only on
the copper embedded in the wiring grooves and holes by using the
plating device according to the instant embodiment of the present
invention.
[0109] Then the thus formed copper interconnect substrate with a
protective film was subjected to 30-minute annealing by heating to
500.degree. C. in a 2% hydrogen/98% helium gas atmosphere. As a
result of Auger electron spectroscopic examination of its surface,
no copper was detected from the surface and also no diffusion of
copper (wiring material) was seen. The wiring resistance before and
after the heat treatment was not greater than 2% on the entire
wafer surface, from which it could be confirmed that there took
place no increase of wiring resistance due to oxidation of
copper.
[0110] Further, as no change of resistance was admitted before and
after formation of the interconnect protective film as a result of
measurement of inter-wiring resistance, it could be confirmed that
no abnormal deposition occurred between wiring.
[0111] From the foregoing, it could be confirmed that by using the
electroless plating method according to the instant embodiment of
the present invention, it is possible to form a
cobalt-tungsten-boron alloy film uniformly in the wafer plane as a
copper interconnect protective film, to prevent oxidation and
diffusion of copper, and to obtain high reliability of the
semiconductor devices having copper interconnect.
EXAMPLE 3
[0112] In this example, a vertical film plating device 130
illustrated in FIG. 6 was used. The composition of the plating
solution 16 and the plating conditions were the same as used in
Example 1. In the plating device of this example, a vertical
plating tank was used, and the solution was pumped into the tank
from its bottom.
[0113] Connected to the plating device were piping for organic
solvent, piping for cleaning with an alkaline aqueous solution,
piping for electroless plating solution and piping for water
washing. The distance between the wafer to be plated and the
opposing wall was set at 1 mm. For discharge of waste solution, a
waste organic solvent discharge line and a waste inorganic aqueous
solution discharge line were connected to the device. Isopropyl
alcohol was introduced at a rate of 750 ml/min for pre-cleaning.
After the wafer came into contact with the fluid, the three-way
valve connecting the plating chamber and pre-cleaning tank was
closed to suspend supply of the fluid for 3 minutes.
[0114] Thereafter, the plating chamber and the discharge port were
connected by using the three-way valve to discharge the
pre-cleaning fluid, and then the three-way valve was converted to a
flow inlet. A pretreatment solution comprising an alkaline aqueous
solution was introduced at a rate of 750 ml/min for 5 seconds, and
after the tank was filled up with the pretreatment solution, supply
of the solution was suspended for 3 minutes. Then the plating
chamber and the discharge port were connected by the three-way
valve to discharge the pretreatment solution, and then the
three-way valve was converted to a flow inlet through which the
plating solution was introduced at a rate of 750 ml/min for 5
seconds. After the tank was filled with the plating solution,
supply of the solution was suspended for a predetermined period of
time and cobalt-based electroless plating was carried out.
[0115] Then pure water was introduced into the plating tank for one
minute for cleaning the tank. Stirring of the plating solution in
this device was effected by moving the plating solution back and
forth in the plating chamber and flow passages by a diaphragm pump
as in Example 1. This was followed by cleaning and drying in the
same manner as in Example 1 to complete the process of forming a
cobalt-based electroless plating film serving as an interconnect
protective film. In this example, because of use of a vertical
tank, discharge of the treating solution was easy and could be
completed in about 2 seconds.
[0116] The thus formed substrate was worked by FIB, and its cross
section including the grooves and holes was observed by SEM, which
showed that a 25 nm thick cobalt-tungsten-boron alloy film was
deposited uniformly on the copper surface. As a result of
observation of the film formed at the upper, central and lower
parts of the wafer, it was found that the film deposition was
approximately 4% thicker at the lower part than at the central part
due to the difference in time required for the introduction and
discharge of the plating solution, but scatter of film thickness
was less than 5% in the entire wafer. No deposition of the
cobalt-tungsten-boron alloy on the insulating film was
admitted.
[0117] Auger electron spectroscopic analysis of the obtained cobalt
alloy film confirmed that it was an electroless plating film
composed of 79 atomic % of cobalt, 20 atomic % of tungsten and 1
atomic % of boron.
[0118] The foregoing results confirmed the effect of this
embodiment that an interconnect protective film can be formed
uniformly in the wafer plane only on the copper embedded in the
wiring grooves and holes by using the plating device according to
the instant embodiment of the present invention.
[0119] Then the thus obtained copper inter-connect substrate with a
protective film was subjected to 30-minute annealing by heating to
500.degree. C. in a 2% hydrogen/98% helium gas atmosphere. In the
Auger electron spectroscopic examination of its surface, there was
detected no copper from the surface nor was observed any diffusion
of copper as wiring material. Wiring resistance before and after
the heat treatment was less than 2% in the entire wafer, which
confirmed that no increase of wiring resistance attributable to
oxidation of copper took place. Also, since no change of resistance
was admitted before and after formation of the interconnect
protective film in the measurement of inter-wiring resistance, it
was ascertained that no abnormal deposition occurred between
wiring.
[0120] From the foregoing, it was confirmed that by using the
electroless plating method according to the instant embodiment of
the present invention, it is possible to form a
cobalt-tungsten-boron alloy film uniformly in the wafer plane as a
copper interconnect protective film, to prevent oxidation and
diffusion of copper, and to obtain high reliability of the
semiconductor devices having copper interconnect.
EXAMPLE 4
[0121] In this example, instead of forming a cobalt-tungsten-boron
alloy film, a cobalt-tungsten-phosphorus alloy film was formed on
the copper interconnect by the electroless plating method of the
present invention.
[0122] Copper interconnect was formed on a silicon substrate in the
same way as in Example 1. Since hypophosphorous acid is used as
reducing agent in cobalt-tungsten-phosphorus plating, no direct
reaction takes place on the copper, so that no direct plating on
the copper is possible. For carrying out plating in this case, it
is necessary to beforehand apply a catalyst 9 such as palladium on
the copper. Since the plating chamber is contaminated if the
palladium treatment is conducted in the plating chamber, the
following palladium catalyzation step was carried out at the
pre-plating stage. TABLE-US-00002 (Palladium catalyzation step)
Palladium chloride 0.003 mol/dm.sup.3 Hydrochloric acid 1 .times.
10.sup.-3 dm.sup.3/dm.sup.3 Acetic acid 0.5 dm.sup.3/dm.sup.3
Hydrofluoric acid 5 .times. 10.sup.-3 dm.sup.3/dm.sup.3 Temperature
24.degree. C. Time 10 seconds
[0123] By the catalyzation treatment, palladium was deposited on
the islet with an average size of 20 nm. After washing with pure
water for one minute, the wafer was transferred to the plating
stage by a robot. Then electroless plating was carried out with the
same process as used in Example 1. The electroless plating solution
used is shown below. TABLE-US-00003 (Electroless plating solution)
Cobalt sulfate 0.1 mol/dm.sup.3 Citric acid 0.3 mol/dm.sup.3
Hypophosphorous acid 0.2 mol/dm.sup.3 Tungstic acid 0.03
mol/dm.sup.3 RE610 (surfactant produced by 0.05 g/dm.sup.3 Toyo
Chemical Co., Ltd.) (Plating conditions) pH 9.5 (adjusted with
tetramethylammonium solution) Solution temperature 75.degree. C.
Plating time 5 min.
[0124] Cobalt-based electroless plating was carried out under the
above plating conditions, and after washing with pure water, wafer
3 was unloosed and conveyed to final cleaning stage 30 by conveyor
robot 26. At the final cleaning stage, the wafer was cleaned for 2
minutes by rotating it at 500 rpm by a spinner while spraying pure
water over the surface and the rear side of the wafer, then spray
of pure water was stopped and the wafer was rotated at 2,000 rpm to
scatter away the liquid to dry the wafer. Then the wafer was
carried to the unloading stage by a conveyor robot, completing the
process of forming a cobalt-based electroless plating film as an
interconnect protective film.
[0125] SEM observation of a cross section of the obtained substrate
showed that a cobalt-tungsten-phosphorus alloy plating film was
selectively deposited as shown in FIG. 9. Also, as a result of
similar SEM observation, it was found that, as shown in FIG. 10,
beside interconnect protective film 1 deposited on the copper
interconnect pattern, there existed abnormal deposits 63 between
wiring and inter-wiring shorting 64, at 5 spots in all in the
wafer, but an interconnect protective film was formed selectively
on other part.
[0126] Cross-sectional observation of the FIB-worked wafer showed
that the copper interconnect surface was enlarged in unevenness due
to replacement with palladium, and that a uniform interconnect
protective film was formed, with the film thickness at the center
and periphery of the wafer being 35 nm.
[0127] Auger electron spectroscopic analysis of the obtained cobalt
alloy film showed that it was an electroless plating film composed
of 84 atomic % of cobalt, 8 atomic % of tungsten and 8 atomic % of
phosphorus.
[0128] From the foregoing, it was confirmed that by using the
plating device according to the instant embodiment of the present
invention, it is possible to form an interconnect protective film
uniformly in the wafer plane only on the copper embedded in the
wiring grooves and holes.
[0129] Then the produced copper interconnect substrate with a
protective film was subjected to 30-minute annealing by heating to
400.degree. C. in a 2% hydrogen/98% helium gas atmosphere. In Auger
electron spectroscopic examination of its surface, there was
detected no copper from the surface nor was admitted any diffusion
of wiring copper. Wiring resistance before and after the heat
treatment was less than 6% on the entire wafer surface, which
confirmed that there took place no rise of wiring resistance due to
oxidation of copper.
[0130] Further, as a result of measurement of inter-wiring
resistance, there was admitted no change of resistance before and
after formation of the interconnect protective film, excepting the
7 spots in the wafer where a notable decrease of inter-wiring
resistance occurred, from which it was confirmed that no abnormal
deposition took place between wiring except for the above 7
spots.
[0131] The foregoing endorses the fact that by using the
electroless plating method in the instant embodiment of the present
invention, it is possible to form a cobalt-tungsten-phosphorus
alloy film uniformly in the wafer plane as a copper interconnect
protective film, to prevent oxidation and diffusion of copper, and
to obtain high reliability of the semiconductor devices having
copper interconnect.
EXAMPLE 5
[0132] This example is identical with Example 1 except for use of
an organic insulating material for the inter-wiring insulating film
and the step of forming such an insulating film.
[0133] Elements were formed on a 200 mm-diameter silicon substrate,
and an organic insulating film with a low dielectric constant was
formed on the substrate having sublayer wiring. For forming said
organic insulating film, a hydrocarbon (including aromatic
hydrocarbon)-based organic insulating film material with a low
dielectric constant was spin coated to a thickness of 300 nm on the
substrate and cured by a 30-minute, 400.degree. C. heat treatment
in a nitrogen (N.sub.2) atmosphere. A typical example of the
hydrocarbon (including aromatic hydrocarbon)-based organic
insulating film materials with a low dielectric constant usable
here is commercially available under the trade name of "SiLK" from
Dow Chemical Co., Ltd., which has a dielectric constant of
approximately 2.65.
[0134] Although in this example "SiLK" was used as the low
dielectric constant organic insulating film material, it is
possible to use other known organic insulating film materials such
as, for example, "BCB" available from Dow Chemical Co., Ltd.,
"FLARE" available from Allied Signal Co., Ltd., and "VELOX"
available from Schumacher Co., Ltd.
[0135] Then, after ordinary patterning and formation of grooves 7
for wiring and connecting holes 10, copper interconnect was formed
on the silicon substrate in the same way as in Example 1, followed
by cobalt-based electroless plating thereon to form a
cobalt-tungsten-boron film.
[0136] The thus formed substrate was worked by FIB, and its cross
section including the grooves and holes was observed by SEM, which
showed that an 180 nm thick cobalt-tungsten-boron alloy film was
deposited uniformly on the copper surface. No deposition of
cobalt-tungsten-boron alloy was observed on the organic insulating
film. Auger electron spectroscopic analysis of the obtained cobalt
alloy film confirmed that it was an electroless plating film
composed of 79 atomic % of cobalt, 20 atomic % of tungsten and 1
atomic % of boron.
[0137] From the foregoing, it was confirmed that when using an
organic insulating film in this embodiment of the present
invention, it is possible to form an interconnect protective film
only on the copper embedded in the wiring grooves and holes by the
electroless plating method of this invention.
[0138] Then the obtained copper interconnect substrate having a
protective film was subjected to 30-minute annealing by heating to
400.degree. C., 450.degree. C. and 500.degree. C. in a 2%
hydrogen/98% helium gas atmosphere. In Auger electron spectroscopic
observation of the surface of each substrate, no copper was
detected from the surface nor diffusion of wiring copper was
admitted in any of the substrates treated at 400.degree. C.,
450.degree. C. and 500.degree. C. Also, there was seen no change of
wiring resistance before and after the heat treatment at
500.degree. C., from which it was confirmed that there took place
no rise of wiring resistance due to oxidation of copper.
[0139] From the above, it was confirmed that even when using an
organic insulating film with a low dielectric constant as the
inter-wiring insulating film, it is possible to form a
cobalt-tungsten-boron alloy film selectively on the copper as a
copper interconnect protective film in the same way as in Example
1, to prevent diffusion of copper, and to secure reliability of
wiring.
[0140] Shown below are the important embodiments of the present
invention. These embodiments are implemented in conjunction with
the inventive concepts set forth in the appended Claims.
(1) An electroless plating method according to any one of the
Claims wherein plural treating solutions are introduced
successively, either before or after the electroless plating
treatment, to the surface to be plated of the substrate to be
worked.
[0141] (2) An electroless plating method according to any one of
the Claims wherein the components of the electroless plating
solution are prepared as the respective chemical solutions and
reserved in the respective chemical solution tanks, then these
chemical solutions are mixed in the introduction passage to form a
plating solution, and this plating solution with its components
adjusted is introduced to the area where electroless plating is to
be conducted.
[0142] (3) An electroless plating method according to any one of
the Claims wherein before conducting electroless plating, a
pretreatment is carried out with a pretreatment solution at least
adjusted in pH by a reducing agent, a complexing agent and an
organic alkali.
(4) An electroless plating method according to any one of the
Claims wherein a boron compound or an aldehyde is used as the
reducing agent for the pretreatment solution.
(5) An electroless plating method according to any one of the
Claims wherein the layer of said plating solution is maintained
non-horizontally, and the area to be plated is brought into contact
with the surface of said plating solution.
(6) An electroless plating method according to any one of the
Claims wherein the thickness of the layer of said electroless
plating solution is 0.05 to 3 mm.
(7) An electroless plating method according to any one of the
Claims wherein the thickness of the layer of said electroless
plating solution is 0.1 to 1 mm.
(8) An electroless plating method according to any one of the
Claims wherein said electroless plating solution and the area to be
plated are kept in contact during the period until the deposit
thickness becomes 5 to 100 nm.
[0143] (9) An electroless plating method according to any one of
the Claims wherein the electroless plating solution and the surface
to be plated of the substrate are brought into contact with each
other so that a deposit thickness of 10 to 60 nm will be
obtained.
[0144] (10) An electroless plating method according to any one of
the Claims wherein said electroless plating operation is conducted
on each of said substrates respectively, and the amount of the
electroless plating solution used per substrate is 10 to 100
ml.
[0145] (11) An electroless plating method according to any one of
the Claims wherein said electroless plating operation is conducted
on each of said substrates respectively, and the amount of the
electroless plating solution used per substrate is 20 to 70 ml.
[0146] (12) An electroless plating method according to any one of
the Claims wherein said electroless plating operation is conducted
on each of said substrates respectively, and the amount of the
electroless plating solution used per substrate is 30 to 50 ml.
(13) An electroless plating device according to any one of the
Claims wherein piping is provided for supplying the different
treating solutions successively into the electroless plating
container.
[0147] (14) An electroless plating device according to any one of
the Claims wherein means are provided for holding the substrate to
be plated so that it will be positioned non-horizontally and that
the surface to be plated of the substrate will face downwardly so
that it will contact the surface of the plating solution.
[0148] (15) An electroless plating device according to any one of
the Claims wherein a thin layer of the electroless plating solution
is formed between the underside of the electroless plating
container and the surface to be plated of the substrate to be
worked.
[0149] (16) An electroless plating program for executing
electroless plating described in any one of the Claims whereby a
computer used for the electroless plating method for forming an
interconnect protective film on the copper interconnect surface of
a semiconductor substrate is operated to function as a means for
introducing an appropriate amount of the treating solution into the
plating space, a means for controlling the temperature of the
heating device for maintaining the treating solution at a
predetermined temperature, and a means for discharging the treating
solution after the lapse of a predetermined period of time.
[0150] (17) An electroless plating program for executing
electroless plating described in any one of the Claims wherein the
computer functions as a means for mixing the plural chemical
solutions each in an appropriate amount to prepare a treating
solution and introducing it into the plating space.
[0151] (18) An electroless plating program for executing
electroless plating described in any one of the Claims wherein the
computer functions as a means for properly introducing the plural
treating solutions to replace the treating solution in the plating
space.
(19) A memory medium readable by a computer characterized in that
it maintains the electroless plating program described in any one
of the Claims.
[0152] It should be further understood by those skilled in the art
that although the foregoing description has been made on
embodiments of the invention, the invention is not limited thereto
and various changes and modifications may be made without departing
from the spirit of the invention and the scope of the appended
claims.
EFFECT OF THE INVENTION
[0153] According to the present invention, a high-quality
electroless plating film can be obtained with stability. Also,
according to the present invention, a high-quality protective film
for wiring of semiconductor devices can be produced with ease.
* * * * *