U.S. patent application number 10/980320 was filed with the patent office on 2005-06-16 for plating method, plating apparatus and a method of forming fine circuit wiring.
Invention is credited to Kimizuka, Ryoichi, Kubota, Makoto, Mishima, Koji, Nakada, Tsutomu, Sahoda, Tsuyoshi.
Application Number | 20050126919 10/980320 |
Document ID | / |
Family ID | 34656159 |
Filed Date | 2005-06-16 |
United States Patent
Application |
20050126919 |
Kind Code |
A1 |
Kubota, Makoto ; et
al. |
June 16, 2005 |
Plating method, plating apparatus and a method of forming fine
circuit wiring
Abstract
A copper plating film has a lower chlorine ion content. Circuit
wiring of high electromigration resistance is formed by
electroplating. In a method of copper plating using a leveler
containing a nitrogen-containing high molecular compound, the
leveler is dechlorinated prior to its use for plating. A plating
apparatus has a tank for preparing a plating solution, a device for
dechlorinating a leveler, a leveler supply station for supplying
the dechlorinated leveler to the tank and a plating station. A
method of forming fine circuit wiring includes forming a circuit
with a phosphorus-doped copper plating layer on a substrate for an
electronic circuit having a fine circuit pattern, a barrier layer
and any necessary seed layer formed thereon.
Inventors: |
Kubota, Makoto; (Yamato-shi,
JP) ; Sahoda, Tsuyoshi; (Chigasaki-shi, JP) ;
Nakada, Tsutomu; (Yokohama-shi, JP) ; Mishima,
Koji; (Fujisawa-shi, JP) ; Kimizuka, Ryoichi;
(Setagaya-ku, JP) |
Correspondence
Address: |
WENDEROTH, LIND & PONACK, L.L.P.
2033 K STREET N. W.
SUITE 800
WASHINGTON
DC
20006-1021
US
|
Family ID: |
34656159 |
Appl. No.: |
10/980320 |
Filed: |
November 4, 2004 |
Current U.S.
Class: |
205/125 ;
204/242; 205/297 |
Current CPC
Class: |
C25D 21/14 20130101;
C25D 3/38 20130101; H05K 3/423 20130101 |
Class at
Publication: |
205/125 ;
205/297; 204/242 |
International
Class: |
C25D 005/02; C25D
017/00 |
Foreign Application Data
Date |
Code |
Application Number |
Nov 7, 2003 |
JP |
2003-377719 |
Nov 11, 2003 |
JP |
2003-380831 |
Claims
What is claimed is:
1. A method of copper plating using a leveler containing a
nitrogen-containing high molecular compound, wherein the leveler is
dechlorinated prior to its use for plating.
2. The method of copper plating according to claim 1, wherein the
dechlorinated leveler has a chlorine ion content of 0.1 g or less
per gram of nitrogen-containing high molecular compound.
3. The method of copper plating according to claim 1, wherein the
dechlorinated leveler has a chlorine ion content of 1 g/l or
less.
4. The method of copper plating according to claim 1, wherein the
dechlorination is carried out by sedimentation or electrolysis.
5. A leveler for copper plating containing a nitrogen-containing
high molecular compound, the leveler having a chlorine ion content
of 0.1 g or less per gram of nitrogen-containing high molecular
compound.
6. A plating apparatus comprising a tank for preparing a plating
solution, a device for dechlorinating a leveler, a leveler supply
station for supplying the dechlorinated leveler to the tank and a
plating station.
7. A plating apparatus for forming a metal film on a seed layer on
a substrate surface by electroplating, the apparatus comprising a
loading and unloading station, a substrate conveying device, a
cleansing unit, a plating tank, a tank for preparing a plating
solution and supplying it to the plating tank, a station for
measuring the concentrations of additives, a device for
dechlorinating a leveler and a leveler supply station for supplying
the dechlorinated leveler to the plating solution, the
concentration measuring station measuring the concentration of the
leveler in the plating solution and in accordance with the result
of the measurement, the leveler supply station adding the
dechlorinated leveler to the plating solution.
8. A method of forming fine circuit wiring, comprising forming a
circuit with a phosphorus-doped copper plating layer on a substrate
for an electronic circuit having a fine circuit pattern, a barrier
layer and any necessary seed layer formed thereon.
9. The method of forming fine circuit wiring according to claim 8,
wherein the plating layer has a phosphorus content of
1.times.10.sup.-6 to 10 atom %.
10. The method of forming fine circuit wiring according to claim 8,
wherein the plating layer has a volume resistivity of 5
.mu..OMEGA..multidot.cm or less.
11. The method of forming fine circuit wiring according to claim 8,
wherein the plating layer is formed by electroplating.
12. A phosphorus-doped copper plating solution containing
1'10.sup.-6 to 50% by weight of elemental phosphorus in the form of
a phosphorus compound in a copper sulfate plating solution
containing copper sulfate, sulfuric acid and chlorine ions.
13. The phosphorus-doped copper plating solution according to claim
12, wherein the phosphorus compound is selected from the group
consisting of phosphoric acid, phosphorus oxide or copper
sulfate.
14. A plating apparatus having an anode plate and a substrate to be
plated which are positioned opposite each other in a plating tank
containing a phosphorus-doped copper plating solution for
electroplating the surface of the substrate by supplying an
electric current between the anode plate and the substrate from a
power source, the apparatus having at least a device for supplying
a solution containing a phosphorus compound as a device for
supplying a constituent composing the plating solution.
15. The plating apparatus according to claim 14, further including
a device for controlling at least the concentration of phosphorus
in the plating solution.
16. The plating apparatus according to claim 14, wherein the anode
plate is an insoluble plate.
Description
BACKGROUND OF THE INVENTION
[0001] 1. Field of the Invention
[0002] This invention relates to a copper plating method and more
particularly to a copper plating method employing a dechlorinated
leveler and the leveler and plating apparatus employed
therefor.
[0003] This invention relates also to a method of forming fine
circuit wiring by plating on a substrate having a fine circuit
pattern, such as a semiconductor or a printed wiring board, and
particularly to a method of forming fine circuit wiring in which
phosphorus-doped copper plating is relied upon for preventing the
electromigration of the fine circuit wiring as formed, and a
plating solution and a plating apparatus therefor.
[0004] 2. Description of the Related Art
[0005] Aluminum or an aluminum alloy has hitherto been used as a
material for forming a wiring circuit on a semiconductor wafer. An
improved degree of integration has, however, created a demand for a
material of higher electric conductivity. Copper has drawn
attention as a material satisfying such a demand and has come to be
used for plating a substrate.
[0006] Various additives, such as a surface active agent, an
unsaturated organic compound and chlorine ions, are used in copper
plating to form a uniform plating film. Among these additives, it
is said that chlorine ions are necessary for assisting the
dissolution of the anode and the action of a brightener (Handbook
of Plating, Society for the Study of Electroplating, The Nikkan
Kogyo Shinbun, Ltd., page 76). The additives also include a leveler
so called, since it is used for leveling the growth of a plating
film, and a nitrogen-containing high molecular compound is usually
used as the leveler. The nitrogen-containing high molecular
compound is often supplied in the form of a hydrochloride as a
tertiary or quaternary nitrogen salt and therefore, the leveler
often contains chlorine ions.
[0007] While the chlorine ions play an important role in a plating
solution as stated above, it has been a problem that the chlorine
ions incorporated in a copper plating film lower its electric
conductivity. Another problem has been due to the corrosiveness of
chlorine ions, as they cause the corrosion and deterioration of
plated wiring.
[0008] On the other hand, copper is used as a material for wiring
on an LSI or printed circuit board owing to its low electric
resistivity. Fine copper wiring is, for example, formed on a
semiconductor wafer by forming first a wiring pattern by via or
other holes and trenches and then plating the wafer with copper to
fill the holes and trenches with the copper to thereby form copper
wiring.
[0009] There has recently been growing a strong demand for still
smaller, higher capacity and faster LSI devices and printed circuit
boards calling for finer and more highly integrated copper wiring.
Accordingly, copper wiring has come to be required to allow a
steady flow of an electric current at a higher current density, but
has come to present a problem of electromigration.
[0010] When an electric current is passed through copper wiring,
the copper ions (electrons) in the wiring are subjected to a
coulomb force from an electrical field and a force of bombardment
with the flowing electrons. At a high current, a balance between
those forces is lost and the migration (diffusion) of copper ions
occurs, which is a phenomenon known as electromigration.
Electromigration is likely to cause the formation of voids in
copper wiring or its insulation and thereby exert a serious effect
on electronic devices. Moreover, electromigration causes stress
migration as a secondary phenomenon and is likely to increase the
frequency of occurrence of the serious effect as stated above.
[0011] Accordingly, a copper plating film forming copper wiring is
required to have a high degree of electromigration resistance.
[0012] There are, however, only a few reports made so far in
respect of methods of imparting electromigration resistance to
copper, including a method in which tin is added to copper. As tin
is a metal which is electrochemically baser than copper, it has
been difficult to form a deposited copper film containing tin
uniformly by electroplating, since copper is deposited more
actively than tin. Accordingly, there has been no effective way to
form copper wiring having a high level of electromigration
resistance by copper plating.
SUMMARY OF THE INVENTION
[0013] It is, therefore, an object of this invention to provide a
method of forming a plating film containing less chlorine ions.
[0014] It is another object of this invention to provide a method
of forming circuit wiring having a high level of electromigration
resistance by electroplating.
[0015] We, the inventors of this invention, have discovered that
the chlorine ions incorporated in a plating film are not the
chlorine ions added intentionally to a plating solution, but a
small amount of chlorine ions which a leveler contains. This
invention is based on our discovery.
[0016] According to one aspect of this invention, therefore, there
is provided a method of copper plating using a leveler containing a
nitrogen-containing high molecular compound, wherein the leveler is
dechlorinated prior to its use for plating.
[0017] According to another aspect of this invention, there is
provided a leveler for copper plating containing a
nitrogen-containing high molecular compound, the leveler having a
chlorine ion content of 0.1 g or less per gram of
nitrogen-containing high molecular compound.
[0018] According to still another aspect of this invention, there
is provided a plating apparatus comprising a tank for preparing a
plating solution, a device for dechlorinating a leveler, a leveler
supply station for supplying the dechlorinated leveler to the tank
and a plating station.
[0019] According to a further aspect of this invention, there is
provided a plating apparatus for forming a metal film on a seed
layer on a substrate surface by electroplating, the apparatus
comprising a loading and unloading station, a substrate conveying
device, a cleansing unit, a plating tank, a tank for preparing a
plating solution and supplying it to the plating tank, a station
for measuring the concentrations of additives, a device for
dechlorinating a leveler and a leveler supply station for supplying
the dechlorinated leveler to the plating solution, the
concentration measuring station measuring the concentration of the
leveler in the plating solution and in accordance with the result
of the measurement, the leveler supply station adding the
dechlorinated leveler to the plating solution.
[0020] We have studied various possibilities of forming copper
wiring having a high level of electromigration resistance by copper
plating, and discovered that a phosphorus-doped copper plating film
deposited by using a copper plating solution containing phosphorus
or phosphoric acid ions in addition to copper ions has a higher
level of electromigration resistance than that of an ordinary
copper plating film. We have found that the use of such a plating
solution makes it possible to form copper wiring having a high
level of electromigration resistance on a semiconductor wafer, or
the like, and we have made this invention.
[0021] According to a still further aspect of this invention,
therefore, there is provided a method of forming fine circuit
wiring, comprising forming a circuit with a layer of
phosphorus-doped copper plating on a substrate for an electronic
circuit having a fine circuit pattern, a barrier layer and any
necessary seed layer formed thereon.
[0022] According to a still further aspect of this invention, there
is provided a phosphorus-doped copper plating solution containing
1.times.10.sup.-6 to 50% by weight of elemental phosphorus in the
form of a phosphorus compound in a copper sulfate plating solution
containing copper sulfate, sulfuric acid and chlorine ions.
[0023] According to a still further aspect of this invention, there
is provided a plating apparatus having an anode plate and a
substrate to be plated which are positioned opposite each other in
a plating tank containing a phosphorus-doped copper plating
solution for electroplating the surface of the substrate by
supplying an electric current between the anode plate and the
substrate from a power source, the apparatus having at least a
device for supplying a solution containing a phosphorus compound as
a device for supplying a constituent composing the plating
solution.
[0024] The use of any copper plating method, leveler or plating
apparatus according to this invention makes it possible to reduce
the amount of the chlorine ions incorporated in any copper plating
film and thereby the possibility of corrosion and deterioration of
any copper-plated wiring.
[0025] The fine circuit wiring formed by phosphorus-doped copper in
accordance with this invention has a higher level of
electromigration resistance than that of any wiring formed by
copper alone, allows an electric current to pass therethrough at a
higher current density and therefore copes with a demand for finer
and higher density circuit wiring.
BRIEF DESCRIPTION OF THE DRAWINGS
[0026] FIGS. 1A to 1C are a series of sectional views showing an
example of plating processes;
[0027] FIG. 2 is a diagram showing a plating apparatus embodying
this invention;
[0028] FIG. 3 is a diagram showing a dechlorinating device and a
raw leveler tank in the apparatus embodying this invention;
[0029] FIG. 4 is a diagram showing a plating station in the
apparatus embodying this invention;
[0030] FIG. 5 is a diagram showing another form of plating
station;
[0031] FIGS. 6A to 6D are a series of views showing the steps of a
method embodying this invention;
[0032] FIG. 7 is a phase diagram of copper and phosphorus; and
[0033] FIG. 8 is a diagram showing another form of plating
apparatus embodying this invention.
DETAILED DESCRIPTION OF THE INVENTION
[0034] A leveler used in copper plating is usually employed for
leveling the growth of a plating film and contains a
nitrogen-containing high molecular compound. The
nitrogen-containing high molecular compound used herein may be any
high molecular compound containing a nitrogen element in its
molecule, for example, poly(dialkylaminoethyl acrylate),
poly(diallyl dimethyl ammonium), polyethyleneimine, polyvinyl
pyridine, polyvinyl amidine, polyallylamine or polyaminesulfonic
acid. The nitrogen-containing high molecular compound is used in
the form of a hydrochloride as a tertiary or quaternary nitrogen
salt so that its solubility in water may be improved. Accordingly,
the leveler contains a nitrogen-containing high molecular compound
and chlorine ions.
[0035] The leveler is usually provided in the form of an aqueous
solution containing, say, 5 to 20 g of nitrogen-containing high
molecular compound and 3 to 10 g of chlorine ions per liter.
[0036] The leveler is added to a plating solution to the extent
that the plating solution usually contains 5 to 20 mg of
nitrogen-containing high molecular compound per liter. When the
leveler is added to the plating solution, the chlorine ions which
the leveler contains are carried over into the plating solution and
the plating solution usually contains several milligrams of
chlorine ions per liter.
[0037] Other additives used in a copper plating solution include
chlorine ions. The chlorine ions are usually added in the amount of
40 to 80 mg per liter, as it is said that they are necessary for
assisting the dissolution of the anode and the action of a
brightener.
[0038] As the amount of the chlorine ions carried over from the
leveler into the plating solution is by far smaller than that of
the chlorine ions added to the plating solution for assisting the
dissolution of the anode and the action of the brightener, it has
been considered that the chlorine ions which are carried over from
the leveler do not exert any effect on plating.
[0039] Our study has, however, ascertained that the chlorine ions
carried over from the leveler into the plating solution are
incorporated predominantly into a plating film, as will become
obvious from the description of examples. Accordingly, the chlorine
ions contained in the leveler are dechlorinated to reduce the
amount of chlorine ions incorporated into a plating film.
[0040] While any method can be employed for dechlorinating the
leveler in accordance with this invention if it can reduce the
amount of chlorine ions, a method relying upon sedimentation or
electrolysis is preferred.
[0041] The dechlorination of the leveler by sedimentation may, for
example, be carried out by adding to it a substance forming a
hardly soluble salt with chlorine ions, e.g. silver nitrate, as
shown by expression I:
AgNO.sub.3+Cl.sup.-.fwdarw.AgCl.dwnarw.+NO.sub.3.sup.- (I)
[0042] The dechlorination by electrolysis may, for example, be
carried out by removing chlorine gas at the anode, as shown by
expression II:
2Cl.sup.-.fwdarw.Cl.sub.2.Arrow-up bold.+2e.sup.- (II)
[0043] The dechlorinated leveler used in accordance with this
invention preferably has a chlorine ion content of 0.1 g or less,
more preferably 0.05 g or less and still more preferably 0.01 g or
less per gram of nitrogen-containing high molecular compound. If
its chlorine ion content exceeds 0.1 g per gram of
nitrogen-containing high molecular compound, it is likely that an
undesirably large amount of chlorine ions may be incorporated into
a plating film.
[0044] Moreover, the dechlorinated leveler used in accordance with
this invention preferably has a chlorine ion content of 1 g or less
per liter. If it is exceeded, it is likely that an undesirably
large amount of chlorine ions may be incorporated into a plating
film.
[0045] The invention will now be described in further detail with
reference to the drawings, though the drawings are not intended for
limiting the scope of this invention.
[0046] The plating method, leveler for plating and plating
apparatus according to this invention are mainly used for forming
copper layers of wiring by electroplating on the surface of a
semiconductor wafer to be plated. Reference is first made to FIGS.
1A to 1C showing an example of plating processes.
[0047] A semiconductor wafer W has a conductive layer la formed on
a substrate 1 having a semiconductor device formed thereon, an
insulating film 2 of SiO.sub.2 deposited thereon, a contact hole 3
and a wiring trench 4 formed therein by lithography and etching, a
barrier layer 5 formed thereon from e.g. TiN and a seed layer 7
formed thereon as a feed layer for electrolytic plating, as shown
in FIG. 1A.
[0048] The semiconductor wafer W has its surface plated with
copper, so that a copper layer 6 maybe deposited on the insulating
film 2, while the contact hole 3 and trench 4 of the substrate 1
are filled with copper, as shown in FIG. 1B. Then, the copper layer
6 on the insulating film 2 is removed by chemical mechanical
polishing (CMP), so that the copper layer 6 filling the contact
hole 3 and wiring trench 4 may have a surface substantially flush
with the surface of the insulating film 2. As a result, wiring is
formed by the copper layer 6, as shown in FIG. 1C.
[0049] FIG. 2 is a diagram showing a plating apparatus 10 embodying
this invention. The plating apparatus 10 of this invention has a
plating solution tank 12 for preparing and holding a plating
solution 14, a concentration measuring station 16, a carrier supply
station 40, a surface active agent supply station 50 and a leveler
supply station 30 connected to the plating solution tank 12 by
pipelines 15, 48, 58 and 38, respectively, a dechlorinating device
60 connected to the leveler supply station 30 by a pipeline 67, a
raw leveler tank 90 connected to the dechlorinating device 60 by a
pipeline 94, a control station 18 connected to all of the
concentration measuring station 16, leveler supply station 30,
carrier supply station 40 and surface active agent supply station
50, and a plating station 70 connected to the plating solution tank
12 by a pipeline 100, a pump 102, a filter 104, a pipeline 108 and
a pump 106, as shown in FIG. 2.
[0050] The leveler supply station 30 has a leveler tank 32 holding
a dechlorinated leveler 34 and a pump 36 connected to the control
station 18, the carrier supply station 40 has a carrier tank 42
holding a carrier 44 and a pump 46 connected to the control station
18 and the surface active agent supply station 50 has a surface
active agent tank 52 holding a surface active agent 54 and a pump
56 connected to the control station 18, as shown in FIG. 2.
[0051] FIG. 3 is a diagram showing details of the dechlorinating
device 60 and raw leveler tank 90 by example. The de-chlorinating
device 60 has a dechlorinating tank 62, a cathode 64, an anode 65
and a stirrer 66, as shown in FIG. 3. The raw leveler tank 90 holds
a raw leveler 92 and is connected to the dechlorinating tank 62 by
the pipeline 94 with a pump 96.
[0052] FIG. 4 is a diagram showing details of the plating station
70 by example. A plating tank 76 connected to the pipelines 100 and
108 holds a plating solution 14 in which a wafer W mounted on a jig
and an anode 72 are disposed opposite each other, while a power
source 74 is connected between the wafer W and the anode 72, as
shown in FIG. 4.
[0053] FIG. 5 is a top plan view of another form of plating station
70. The plating station 70 has four loading and unloading units 80
holding a plurality of substrates W therein, four plating units 82
for performing plating and auxiliary treatment, two conveying
robots 84 and 85 for conveying the substrates W between the loading
and unloading units 80 and the plating units 82, two bevel and rear
surface cleansing units 86, a film thickness measuring device 87
and a temporary wafer support 88, as shown in FIG. 5. The plating
units 82 are all connected to the pipelines 100 and 108, though
they are only partly shown. In FIG. 5, the conveying robots 84 and
85 constitute s substrate conveying device according to this
invention.
[0054] All the equipment shown in FIG. 2 for preparing the plating
solution may be installed within the plating station shown in FIG.
5 so as to form an integral part thereof.
[0055] Description will now be made of the operation of the plating
apparatus of this invention constructed as described above. The raw
leveler 92 held in the raw leveler tank 90 and still to be
dechlorinated is drawn by the pump 96 through the pipeline 94 into
the dechlorinating device 60, whereby it is dechlorinated. The raw
leveler 92 pumped into the dechlorinating tank 62 is uniformly
stirred by the stirrer 66. Upon application of a voltage to the
anode 65 and cathode 64, the reaction shown by the expression II
occurs at the anode 65 and chlorine gas (Cl.sub.2) emerges. This
indicates the dechlorination of the leveler. The dechlorinated
leveler 34 is transferred by the pump 69 through the pipeline 67
into the leveler tank 32 in the leveler supply station 30.
2Cl.sup.-.fwdarw.Cl.sub.2.Arrow-up bold.+2e.sup.- (III)
[0056] The plating solution 14 held in the plating solution tank 12
is transferred to the concentration measuring station 16, in which
the concentrations of the leveler, carrier and surface active agent
in the solution are measured. The results of the measurements are
sent to the control station 18 and if the concentration of any of
those additives is lower than the pre-set control range, the
dechlorinated leveler 34, carrier 44 or surface active agent 54 is
supplied by the pump 36, 46 or 56 from the leveler supply station
30, carrier supply station 40, or surface active agent supply
station 50 to the plating solution tank 12 through the pipeline 38,
48 or 58, so that the concentration of each additive may be kept
within the control range by the control station 18.
[0057] The plating solution 14 having its additives controlled in
concentration as described is drawn by the pump 102 through the
pipeline 100 and the filter 104 into the plating station 70 and
used for plating the substrate or substrates W in the plating tank
76 or the plating units 82. The plating solution having lowered
concentrations of surface active agent, carrier and leveler as a
result of their consumption by plating is returned by the pump 106
into the plating solution tank 12 through the pipeline 108.
[0058] Description will now be made of the operation of the plating
station 70. Referring first to one form of plating station 70 as
shown in FIG. 4, the plating solution 14 having its additives
controlled in concentration is supplied by the pump 102 through the
pipeline 100 and the filter 104 into the plating tank 76. A voltage
is applied between the anode 72 and the wafer W by the power source
74, whereby the wafer W has its surface plated with copper. After
plating, the plating solution is returned by the pump 106 into the
plating solution tank 12 through the pipeline 108.
[0059] Referring now to another form of plating station 70 as shown
in FIG. 5, a wafer W to be plated is taken out by the conveying
robot 84 from a wafer cassette installed in any of the loading and
unloading stations 80 and is conveyed to the film thickness
measuring device 87 in which the thickness of a plating film for
the wafer W to be plated is measured. Then, the wafer W is taken
out by the robot 84 from the film thickness measuring device 87 and
mounted on the temporary wafer support 88. Then, the wafer W on the
temporary wafer support 88 is taken by the hands of the other
conveying robot 85 and charged into any of the plating units 82
through its wafer charge and discharge opening, while its surface
to be plated is held upside. The plating solution 14 having its
additives controlled in concentration is supplied from the plating
solution tank 12 by the pump 102 through the pipeline 100 and the
filter 104 into the plating unit 82 to plate the wafer. After
plating, the plating solution is returned by the pump 106 through
the pipeline 108 into the plating solution tank 12.
[0060] After its plating, the wafer W is discharged from the
plating unit 82 by the robot 85. The wafer W as discharged is
conveyed to one of the bevel and rear surface cleansing units 86
and after its cleansing and drying, it is mounted on the temporary
wafer support 88 by the robot 85 and is, then, conveyed by the
robot 84 to the film thickness measuring device 87, in which the
thickness of the plating film formed on the wafer W is measured,
and it is conveyed by the robot 84 into the wafer cassette
installed in any of the loading and unloading stations 80. This is
the end of the whole process of plating a single wafer W.
[0061] The method of this invention is carried out by, for example,
employing a substrate for an electronic circuit having a fine
circuit pattern formed thereon as shown in FIG. 6A, forming a
barrier layer on the substrate as shown in FIG. 6B, forming a seed
or catalyst layer thereon as shown in FIG. 6C and forming a
phosphorus-doped copper plating layer thereon to fill the fine
holes and trenches defining the fine circuit pattern as shown FIG.
6D. In FIGS. 6A to 6D, 201 and 203 denote interlayer insulating
layers formed on the substrate, 202 a conductive layer, 204 the
barrier layer, 205 the seed or catalyst layer, and 206 the
phosphorus-doped copper plating layer.
[0062] The substrate on which fine circuit wiring is formed by the
method of this invention is a semiconductor wafer, or printed
circuit substrate having a fine circuit pattern formed on its
surface. Such a pattern is, for example, formed by fine trenches
and holes, such as via holes, and the trenches and holes are filled
with phosphorus-doped copper to form circuit wiring.
[0063] The method of forming fine circuit wiring according to this
invention is carried out after the substrate is pre-treated by a
customary method. The pretreatment of, for example, a silicon
substrate such as a silicon wafer is done to form a barrier layer
of, for example, Ta, TaN, TiN, WN, SiTiN, CoWP or CoWB (FIG. 6B).
If electroplating is thereafter carried out, a copper seed layer
serving as a power feed layer is formed by e.g. PVD as pretreatment
after the formation of a barrier layer. If electroless plating is
carried out, pretreatment is done to form a catalytic layer (FIG.
6C).
[0064] The substrate pretreated as described has a phosphorus-doped
copper plating layer formed thereon (FIG. 6D). This plating is so
done as to fill the whole fine trenches and holes forming a fine
circuit pattern. Finally, the phosphorus-doped copper film
deposited on any other surface than the area of the circuit wiring
is removed by e.g. CMP, leaving a fine circuit wiring formed by the
phosphorus-doped copper film.
[0065] The phosphorus-doped copper plating solution used to form a
phosphorus-doped copper film in accordance with this invention,
which has been discovered by us, the inventors of this invention,
contains, for example, the following constituents:
1 Copper sulfate pentahydrate 150 to 250 g/l Sulfuric acid 10 to
100 g/l Chlorine ion 30 to 90 mg/l Phosphorus compound 100 to
10,000 mg/l (as phosphoric acid ion) Polymer component 10 to 40
ml/l Carrier component 1 to 20 ml/l Leveler component 1 to 20
ml/l
[0066] When electrolytic copper sulfate plating is employed to fill
wiring trenches and holes in the surface of e.g. a semiconductor
wafer, it is often the case to add three kinds of organic additives
called the polymer, carrier and leveler components to the basic
components, copper sulfate (CuSO.sub.4.5 H.sub.2O), sulfuric acid
(H.sub.2SO.sub.4) and chlorine (Cl), in order to make it possible
to form a plating film of improved quality and fill the trenches
and holes in an improved way.
[0067] Firstly, the polymer component is a component added to
suppress the deposition of adsorbed copper ions on the cathode
surface to thereby increase activation polarization and improve
uniformity of electrodeposition, and also called a suppressor or
carrier. A surface active agent, such as polyethylene glycol (PEG)
or polypropylene glycol (PPG), is usually employed.
[0068] Secondly, the carrier component is a component added to
improve the density and brightness of a plating film and also
called a brightener. A sulfur compound, such as
mercapto-alkylsulfonic acid or HS--C.sub.nH.sub.2n--SO.sub.3, is
usually employed. It is in the form of anions in the plating
solution, inhibits the deposition of copper ions and thereby
promotes the formation of a finer deposit.
[0069] Thirdly, the leveler component is a compound containing
nitrogen, such as polyamine. It is in the form of cations in the
plating solution. The adsorption of the leveler is more likely to
occur in a place having a high current density and in the place
where the adsorption of the leveler is more likely to occur,
activation overvoltage increases and the deposition of copper is
suppressed. At the bottom of any fine trench or hole, on the other
hand, the adsorption of the leveler is less likely to occur and the
deposition of copper is predominant.
[0070] Examples of the phosphorus compounds in the phosphorus-doped
copper plating solution are, for example, phosphoric acid, copper
sulfate and phosphorus oxides such as phosphorus pentoxide.
[0071] In order to have a phosphorus-doped copper film deposited
from the above plating solution, it is desirable to control the
deposition potentials of copper and phosphorus so that they may be
close to each other. Moreover, it is possible to add to the plating
solution any organic additive known as used in any known acidic
copper plating solution, such as a deposition inhibitor or
accelerator, if required.
[0072] When the above plating solution is used to form a
phosphorus-doped copper plating film, it may have a temperature of,
say, 15.degree. C. to 40.degree. C. and a current density of, say,
0.3 to 30 mA/cm.sup.2 may be employed. In order to form a
phosphorus-doped copper film which is stable in composition, it is
desirable to use an insoluble substance, such as platinum (Pt) or
iridium oxide (Ir.sub.2O.sub.3), as the anode instead of metallic
copper and add a solution of the component to be deposited.
[0073] The phosphorus-doped copper plating film formed as described
is a film of copper containing a very small amount of phosphorus or
a phosphorus compound incorporated therein. Although the phase in
which phosphorus or a compound thereof is present in copper is not
clearly known, it is obvious from the Cu--P phase diagram in FIG. 7
that when copper has a temperature of 300.degree. C. or below, for
example, 0.6 atm % or less of phosphorus may be incorporated in the
crystal grain boundary of copper, or its crystal and form a solid
solution with it, and its presence in such a phase is, therefore,
possible. It is considered that phosphorus provides an improved
electro-migration resistance, as it inhibits the diffusion of
copper atoms. The same is true with a phosphorus compound.
[0074] FIG. 8 shows an example of plating apparatus which can be
employed to form fine circuit wiring by a phosphorus-doped copper
film in accordance with this invention.
[0075] FIG. 8 is a diagram showing the layout of the plating
apparatus by example, which includes a plating tank 210 holding a
phosphorus-doped copper plating solution Q, in which an anode plate
211 and a substrate 212 to be plated are disposed opposite each
other, and if a plating current is supplied between the anode 211
and the substrate 212 from a power source E, the substrate 212 has
its surface plated electrolytically.
[0076] 213 is a plating solution preparing tank for preparing a
phosphorus-doped copper plating solution. A standard copper sulfate
plating solution Q1 (basic solution), an additional solution Q2
obtained by adding the polymer component to the basic solution, an
additional solution Q3 obtained by adding the carrier component to
the basic solution, an additional solution Q4 obtained by adding
the leveler component to the basic solution, sulfuric acid
(H.sub.2SO.sub.4) Q5 and hydrochloric acid (HCl) Q6 can be supplied
to the plating solution preparing tank 213 from a standard solution
tank 214 through a pump P1 and a valve V1, from an additional
solution tank 215 through a pump P2 and a valve V2, from an
additional solution tank 216 through a pump P3 and a valve V3, from
an additional solution tank 217 through a pump P4 and a valve V4,
from a sulfuric acid tank 218 through a pump P5 and a valve V5 and
from a hydrochloric acid tank 219 through a pump P6 and a valve V6,
respectively. Phosphoric acid (H.sub.3PO.sub.4) Q7 can be supplied
from a phosphoric acid tank 226 through a pump P7 and a valve
V7.
[0077] The phosphorus-doped copper plating solution Q8 prepared in
the plating solution preparing tank 213 is supplied by a pump P8 to
the plating tank 210 through a filter 220. The plating solution Q
exceeding a predetermined surface level in the plating tank 210 is
returned to the plating solution preparing tank 213. Thus, the
plating solution is circulated between the plating solution
preparing tank 213 and the plating tank 210. 221 is a sampling
device for taking a sample of the phosphorus-doped copper plating
solution Q8 supplied to the plating solution 210 and 222 is an
automatic analyzing device for analyzing automatically the
composition of the sample of the plating solution Q8 taken by the
sampling device 221. 223 is a waste solution tank, 224 is a level
sensor for measuring the surface level of the plating solution Q8
in the plating solution preparing tank 213 and 225 is a control
unit.
[0078] The composition of the plating solution Q8 as analyzed by
the automatic analyzing device 222 and the level of the plating
solution Q8 as measured by the level sensor 224 are inputted to the
control unit 225. In accordance with the results of analysis of the
plating solution Q8 by the automatic analyzing device 222, the
control unit 225 controls the pumps P1 to P7 and the valves V1 to
V7 to control the standard solution Q1 supplied from the standard
solution tank 214, the additional solution Q2 supplied from the
additional solution tank 215, the additional solution Q3 supplied
from the additional solution tank 216, the additional solution Q4
supplied from the additional solution tank 217, sulfuric acid Q5
supplied from the sulfuric acid tank 218, hydrochloric acid Q6
supplied from the hydrochloric acid tank 219 and phosphoric acid Q7
and thereby regulate the composition of the plating solution Q8 in
the plating solution preparing tank 213.
[0079] The invention will now be described in further detail by
examples, though these examples are not supposed at all to limit
the scope of this invention.
EXAMPLE 1
[0080] A test was conducted to ascertain that chlorine ions
incorporated into a plating film were of a leveler.
[0081] One liter of a plating solution was so prepared as to
contain 200 g of CuSO.sub.4.5H.sub.2O, 10 g of H.sub.2SO.sub.4, 60
mg of chlorine ions, 200 mg of polyethylene glycol having a
molecular weight of about 3000 and 5 mg of
bis(3-sulfopropyl)disulfide.
[0082] A quaternary ammonium hydrochloride salt of polyvinyl
pyridine yet to be dechlorinated was employed as a leveler and was
so added to the plating solution that the plating solution might
contain 10 mg of polyvinyl pyridine per liter. The leveler yet to
be dechlorinated contained 16 g of polyvinyl pyridine and 4 g of
chlorine ions per liter. The plating solution was used for the
copper plating of a silicon wafer. The plating solution to which no
leveler had been added was also used for the copper plating of a
silicon wafer.
[0083] The copper-plated silicon wafers were examined by a
secondary ion mass spectrometer (SIMS) for the chlorine ions
incorporated in their copper plating films. As a result, it was
confirmed that the amount of chlorine ions in the copper plating
film formed by using the leveler containing chlorine ions was about
10 times larger than in the plating film formed without using any
leveler.
[0084] It is, therefore, obvious that the chlorine ions carried
over from the leveler into the plating solution are predominantly
incorporated into the plating film.
EXAMPLE 2
[0085] The leveler used in Example 1 was dechlorinated to prepare a
leveler having a chlorine ion concentration reduced to 1 g/l.
[0086] The dechlorinated leveler and the same plating solution as
in Example 1 were used for the copper plating of a silicon
wafer.
[0087] The examination of the wafer by SIMS as in Example 1 can
confirm a reduction in the amount of chlorine ions incorporated in
its copper plating film.
EXAMPLE 3
[0088] A phosphorus-doped copper plating solution was prepared by
adding 5 ml of 50% phosphoric acid to one liter of a copper sulfate
plating solution (basic solution) having the composition shown
below. The plating solution was used for one minute of
phosphorus-doped copper plating at a temperature of 25.degree. C.
and a current density of 30 mA/cm.sup.2 on a semiconductor wafer in
which via holes having a width of 150 nm and an aspect ratio of 5
had been formed. The semiconduct or wafer had a barrier and a seed
layer formed by customary methods.
[0089] Composition of the Copper Sulfate Plating Solution:
2 Copper sulfate pentahydrate 200 g/l Sulfuric acid 50 g/l Chlorine
ion 50 mg/l Phosphorus compound 100 mg/l (as phosphoric acid ion)
Polymer component 30 ml/l Carrier component 10 ml/l Leveler
component 10 ml/l
[0090] There was obtained a phosphorus -doped copper plating film
having a phosphorus content of 1.times.10.sup.-6 atom % or more
along its depth. Its examination by a scanning electron microscope
did not reveal any void in any of the via holes in the substrate.
Its electromigration resistance was higher than that of any copper
plating film not containing phosphorus.
[0091] As is obvious from the foregoing, the plating method,
plating apparatus and leveler according to this invention make it
possible to reduce the amount of chlorine ions incorporated in a
plating film.
[0092] The phosphorus-doped copper plating film formed in
accordance with this invention can form copper wiring having a
higher level of electromigration resistance than that of any
ordinary copper plating film.
[0093] The phosphorus-doped copper wiring is widely useful as
wiring for a smaller and more highly integrated substrate for an
electronic circuit, such as a semiconductor wafer.
* * * * *