U.S. patent application number 11/051624 was filed with the patent office on 2005-10-06 for method of manufacturing semiconductor device.
Invention is credited to Fukushima, Dai, Kurashima, Nobuyuki, Minamihaba, Gaku, Yano, Hiroyuki.
Application Number | 20050218008 11/051624 |
Document ID | / |
Family ID | 35053090 |
Filed Date | 2005-10-06 |
United States Patent
Application |
20050218008 |
Kind Code |
A1 |
Fukushima, Dai ; et
al. |
October 6, 2005 |
Method of manufacturing semiconductor device
Abstract
Disclosed is a method for manufacturing a semiconductor device,
comprising depositing an electrically conductive film on an
insulating film formed above a semiconductor substrate and having a
recessed portion, polishing the surface of the electrically
conductive film constituting a processing surface with an alkaline
slurry on a polishing cloth to expose the surface of the insulating
film to the outside while leaving the electrically conductive film
selectively within the recessed portion of the insulating film,
treating the processing surface, in which the surface of the
insulating film is exposed to the outside by the polishing
treatment with the alkaline slurry, with a deionized water and,
then, with an acidic washing solution so as to render the
processing surface acidic, and transferring the semiconductor
substrate from the position on the polishing cloth into a washing
unit while keeping the processing surface acidic.
Inventors: |
Fukushima, Dai;
(Kamakura-shi, JP) ; Minamihaba, Gaku;
(Yokohama-shi, JP) ; Yano, Hiroyuki;
(Yokohama-shi, JP) ; Kurashima, Nobuyuki;
(Yokohama-shi, JP) |
Correspondence
Address: |
FINNEGAN, HENDERSON, FARABOW, GARRETT & DUNNER
LLP
901 NEW YORK AVENUE, NW
WASHINGTON
DC
20001-4413
US
|
Family ID: |
35053090 |
Appl. No.: |
11/051624 |
Filed: |
January 27, 2005 |
Current U.S.
Class: |
205/640 ;
205/157; 257/E21.304 |
Current CPC
Class: |
H01L 21/3212 20130101;
H01L 21/6723 20130101; H01L 21/67219 20130101; H01L 21/02074
20130101 |
Class at
Publication: |
205/640 ;
205/157 |
International
Class: |
C25D 007/12; C25D
007/12 |
Foreign Application Data
Date |
Code |
Application Number |
Apr 2, 2004 |
JP |
2004-110411 |
Claims
What is claimed is:
1. A method for manufacturing a semiconductor device, comprising:
depositing an electrically conductive film above an insulating film
formed above a semiconductor substrate and having a recessed
portion; polishing the surface of the electrically conductive film
constituting a processing surface with an alkaline slurry on a
polishing cloth to expose the surface of the insulating film to the
outside while leaving the electrically conductive film selectively
within the recessed portion of the insulating film; treating the
processing surface, in which the surface of the insulating film is
exposed to the outside by the polishing treatment with the alkaline
slurry, with a deionized water and, then, with an acidic washing
solution so as to render the processing surface acidic; and
transferring the semiconductor substrate from the position on the
polishing cloth into a washing unit while keeping the processing
surface acidic.
2. The method according to claim 1, wherein the electrically
conductive film comprises a Cu film deposited above the insulating
film with a liner material interposed therebetween.
3. The method according to claim 1, wherein the insulating film
comprises a film formed of a hydrophobic material.
4. The method according to claim 1, wherein the washing solution is
an aqueous solution containing at least one selected from the group
consisting of citric acid, oxalic acid, maleic acid, and malonic
acid.
5. A method for manufacturing a semiconductor device, comprising:
depositing an electrically conductive film above an insulating film
formed above a semiconductor substrate and having a recessed
portion; polishing the surface of the electrically conductive film
constituting a processing surface with an acidic slurry on a
polishing cloth so as to make the processing surface acidic and to
expose the surface of the insulating film to the outside while
leaving the electrically conductive film selectively within the
recessed portion of the insulating film; and transferring the
semiconductor substrate from the position on the polishing cloth
into a washing unit while keeping acidic the processing surface in
which the surface of the insulating film is exposed to the
outside.
6. The method according to claim 5, wherein the electrically
conductive film comprises a Cu film deposited above the insulating
film with a liner material interposed therebetween.
7. The method according to claim 5, wherein the insulating film
comprises a film formed of a hydrophobic material.
8. A method for manufacturing a semiconductor device, comprising:
supplying a liquid onto a polishing cloth under the state that a
processing surface formed on a semiconductor substrate is abutted
against the polishing cloth so as to treat the processing surface
while monitoring a property value on the polishing cloth, the
property value being an acid concentration or a pH value; and
allowing the semiconductor substrate to be retreated from the
position on the polishing cloth into a washing unit upon detection
that the property value has been deviated from within a prescribed
range set in advance.
9. The method according to claim 8, wherein the processing surface
is formed of the surface of the insulating film formed above the
semiconductor substrate and includes an electrically conductive
film buried in a recessed portion of the insulating film.
10. The method according to claim 9, wherein the liquid comprises a
washing solution formed of an acidic aqueous solution and a
deionized water supplied after the washing solution.
11. The method according to claim 10, wherein the washing solution
is an aqueous solution containing at least one selected from the
group consisting of citric acid, oxalic acid, maleic acid and
malonic acid.
12. The method according to claim 9, further comprising: depositing
the electrically conductive film above the insulating film formed
above the semiconductor substrate and having the recessed portion;
and polishing the surface of the electrically conductive film with
a slurry on the polishing cloth to leave selectively the
electrically conductive film within the recessed portion of the
insulating film, thereby obtaining the insulating film having the
electrically conductive film buried in the recessed portion.
13. The method according to claim 12, wherein the insulating film
having the electrically conductive film buried in the recessed
portion is obtained by polishing the surface of the electrically
conductive film with an alkaline slurry and, then, with a deionized
water on the polishing cloth.
14. The method according to claim 9, wherein the insulating film
comprises a film formed of a hydrophobic material.
15. The method according to claim 8, wherein the processing surface
is constituted by the surface of the electrically conductive film
deposited above the insulating film formed above the semiconductor
substrate and having a recessed portion.
16. The method according to claim 15, wherein the liquid comprises
an acidic slurry and a deionized water supplied after the acidic
slurry.
17. The method according to claim 16, wherein the electrically
conductive film is polished with the acidic slurry to leave
selectively the electrically conductive film within the recessed
portion of the insulating film, thereby exposing the surface of the
insulating film to the outside, followed by supplying the deionized
water onto the surface of the insulating film having the
electrically conductive film buried in the recessed portion.
18. The method according to claim 15, wherein the insulating film
comprises a film formed of a hydrophobic material.
19. The method according to claim 8, wherein the acid concentration
constitutes the property value, and the prescribed range set in
advance is a range having a lower limit that is not lower than 0.1%
by weight.
20. The method according to claim 8, wherein the pH value
constitutes the property value, and the prescribed range set in
advance is a range having an upper limit that is not higher than pH
3.
Description
CROSS-REFERENCE TO RELATED APPLICATIONS
[0001] This application is based upon and claims the benefit of
priority from prior Japanese Patent Application No. 2004-110411,
filed Apr. 2, 2004, the entire contents of which are incorporated
herein by reference.
BACKGROUND OF THE INVENTION
[0002] 1. Field of the Invention
[0003] The present invention relates to a method of manufacturing a
semiconductor device, particularly, to a CMP (Chemical-Mechanical
Planarization) process for forming, for example, a Cu damascene
wiring for a system LSI or a high speed LOGIC-LSI.
[0004] 2. Description of the Related Art
[0005] A high degree of integration of the elements is critical to
the realization of a high speed LSI of the next era. In this
connection, the design rule for the damascene wiring that is formed
by the CMP process is going to increase in severity to enable a
wiring width of 0.07 to 30 .mu.m and film thickness of 100 nm.
[0006] For forming a damascene wiring having a film thickness of
100 nm, a CMP process using a slurry is carried out in general.
Where the washing step after the CMP process is insufficient so as
to render the finished state of the wiring poor, e.g., where a
local abnormality is included in the finished state, the
performance of the manufactured semiconductor device is markedly
lowered. Also, since it is possible for the wiring to be broken
during operation of the semiconductor device, vigorous research is
currently being carried out on the washing method of the
semiconductor wafer after the CMP process.
[0007] In the case of forming a Cu damascene wiring, it is critical
to eliminate, as much as possible, the defects such as Cu
corrosion, Cu dissolution, scratches, and the reattachment of dust
(e.g., contamination due to the abrasive particles, the materials
formed by the polishing treatment, or the materials from the
polishing cloth) after the washing process. In recent years, the
influence of the defects on the product yield has been clarified in
accordance with progress in the miniaturization of the
semiconductor device, with the result that the demands for the
reduction in defects have been greatly increased. The corrosion
generated in a special pattern portion alone and a very small
erosion in the tip portion of the wiring have been confirmed by the
enhancement in the level of defect evaluation. It has also been
clarified that dust and scratches are not negligible factors.
[0008] Under the circumstances, a method for manufacturing a
semiconductor device, which permits overcoming the defects pointed
out above so as to make it possible to manufacture a semiconductor
device of a high reliability, has not yet been developed.
BRIEF SUMMARY OF THE INVENTION
[0009] A method for manufacturing a semiconductor device according
to one aspect of the present invention comprises depositing an
electrically conductive film above an insulating film formed above
a semiconductor substrate and having a recessed portion; polishing
the surface of the electrically conductive film constituting a
processing surface with an alkaline slurry on a polishing cloth to
expose the surface of the insulating film to the outside while
leaving the electrically conductive film selectively within the
recessed portion of the insulating film; treating the processing
surface, in which the surface of the insulating film is exposed to
the outside by the polishing treatment with the alkaline slurry,
with a deionized water and, then, with an acidic washing solution
so as to render the processing surface acidic; and transferring the
semiconductor substrate from the position on the polishing cloth
into a washing unit while keeping the processing surface
acidic.
[0010] A method for manufacturing a semiconductor device according
to another aspect of the present invention comprises depositing an
electrically conductive film above an insulating film formed above
a semiconductor substrate and having a recessed portion; polishing
the surface of the electrically conductive film constituting a
processing surface with an acidic slurry on a polishing cloth so as
to make the processing surface acidic and to expose the surface of
the insulating film to the outside while leaving the electrically
conductive film selectively within the recessed portion of the
insulating film; and transferring the semiconductor substrate from
the position on the polishing cloth into a washing unit while
keeping acidic the processing surface in which the surface of the
insulating film is exposed to the outside.
[0011] Further, a method for manufacturing a semiconductor device
according to still another aspect of the present invention
comprises supplying a liquid onto a polishing cloth under the state
that a processing surface formed on a semiconductor substrate is
abutted against the polishing cloth so as to treat the processing
surface while monitoring a property value on the polishing cloth,
the property value being an acid concentration or a pH value; and
allowing the semiconductor substrate to be retreated from the
position on the polishing cloth into a washing unit upon detection
that the property value has been deviated from within a prescribed
range set in advance.
BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWING
[0012] FIGS. 1A and 1B are cross sectional views collectively
showing a method of manufacturing a semiconductor device according
to one embodiment of the present invention;
[0013] FIG. 2 schematically shows the state of the CMP process;
[0014] FIG. 3 schematically shows the construction of a polishing
apparatus used in the manufacturing method of the semiconductor
device according to the embodiment of the present invention;
[0015] FIG. 4 is a cross sectional view showing the state of an
insulating film after the polishing treatment by the conventional
method; and
[0016] FIG. 5 is a cross sectional view showing a process step
included in the manufacturing method of a semiconductor device
according to another embodiment of the present invention.
DETAILED DESCRIPTION OF THE INVENTION
[0017] Some embodiments of the present invention will now be
described.
[0018] As a result of extensive research on the defects such as the
corrosion generated in a special pattern portion alone and a very
small erosion generated in the wiring edge, the present inventors
have found that these defects are caused by the finishing method or
the washing method, not by the CMP process itself. In the case of,
for example, a Cu film, the corrosion or the erosion of the wiring
edge is not generated in the polishing stage with the conventional
alkaline slurry or in the subsequent polishing stage with a
deionizid water (DIW) because the Cu film is protected by a
protective film formed by a complexing agent within the slurry.
However, the corrosion or the erosion in a special pattern portion
is generated if the polishing is performed with a DIW after the
polishing treatment with an acidic washing solution. As a result of
extensive research on the causes of these defects, it has been
found that the protective film on the surface of the Cu film is
removed by the polishing treatment using an acidic washing
solution, and that the defects noted above are generated by the
polishing treatment with a DIW after removal of the protective
film.
[0019] It has also been found that a DIW is involved in the
increases in dust and scratches. To be more specific, during the
polishing treatment with a washing solution, dust either on the
wafer or the polishing cloth tends to be washed away easily.
However, if the polishing treatment is performed with a DIW, a
reverse contamination of the semiconductor wafer from the polishing
cloth is invited, with the result that the dust tends to remain on
the surface of the semiconductor wafer or the polishing cloth. In
other words, if a DIW is used for the finish washing treatment, the
reverse contamination of the semiconductor wafer from the polishing
cloth is generated so as to increase the dust, leading to a
secondary increase in scratches. It should be noted that the
reverse contamination derived from the DIW is generated on the
polishing cloth during the polishing treatment with a DIW after the
washing step.
[0020] Under the circumstances, the present inventors have found
that, in order to suppress the defects noted above, it is necessary
to avoid the polishing with a DIW after exposure of a pure Cu
surface to the outside by the polishing with a washing solution. To
be more specific, it has been found that, for suppressing the
particular defects, it is necessary to make the processing surface
acidic after exposure of the Cu surface to the outside by the
processing on the polishing cloth. In the manufacturing method of a
semiconductor device according to the embodiment of the present
invention, the processing surface should not be excessively washed
with a DIW, but should be put under an acidic state after
completion of the polishing treatment with a washing solution and,
in general, before the transfer of the wafer into the washing unit.
Also, where the semiconductor wafer is polished with a slurry alone
without using a washing solution and, then, transferred into the
washing unit, it is necessary for the processing surface after the
polishing treatment with the slurry to be put under an acidic
state. The processing surface can be kept acidic by maintaining the
pH value or the acid concentration of the processing surface after
the processing on the polishing cloth within a prescribed range. To
be more specific, the processing surface can be kept acidic by
allowing the pH value to be smaller than 7. Also, the processing
surface can be kept acidic by allowing the acid concentration to be
not lower than 0.05% by weight in the case of using, for example,
citric acid as the acid, though the actual acid concentration
differs depending on the kind of acid used.
[0021] In the embodiment of the present invention, the processing
surface is processed on a polishing cloth by using an acidic
processing solution, and the semiconductor substrate after the
processing is transferred directly into the washing unit so as to
overcome the defects in respect of the corrosion in a special
pattern portion and the erosion in the wiring edge. It is possible
for the acidic processing solution to be formed of either a slurry
or a washing solution. Where the polishing treatment is carried out
by using an acidic slurry having a pH value lower than 7, the
semiconductor substrate after the polishing treatment can be
transferred as it is directly into the washing unit. Alternatively,
it is possible to carry out the washing with an acidic washing
solution after the polishing treatment with an acidic slurry,
followed by transferring the semiconductor substrate into the
washing unit. In the case of using an acidic washing solution, it
is possible to use an alkaline slurry having a pH value exceeding
7. In this case, the polishing treatment with a DIW is carried out
after the polishing treatment with an alkaline slurry, followed by
carrying out the washing and polishing treatment with an acidic
washing solution. In the case of using the alkaline slurry, it is
desirable to carry out the polishing treatment with a DIW in order
to shift the processing surface to an acidic side before the
semiconductor substrate is transferred into the washing unit. By
carrying out the polishing treatment with a DIW after the polishing
treatment with the alkaline slurry, the state of the polishing
cloth can be once changed into a neutral region so as to make it
possible to prevent scratches and the corrosion of the wiring that
is caused by the agglomeration of the abrasive particles that is
brought about by a rapid change in the pH value. In order to
enhance the effect of removing the abrasive particles, it is
possible to carry out the polishing treatment with a DIW even in
the case of using an acidic slurry as far as the acidic state can
be maintained on the processing surface.
[0022] (Embodiment 1)
[0023] A method of forming a Cu damascene wiring will now be
exemplified. FIGS. 1A and 1B are cross sectional views collectively
showing the Cu-CMP process.
[0024] In the first step, an insulating film 11 was deposited to a
thickness of 6,000 .ANG. on a semiconductor substrate 10 having an
element (not shown) formed thereon, followed by forming a groove 14
as a recessed portion in the insulating film 11, as shown in FIG.
1A. The insulating film 11 was formed by using TEOS (tetraethoxy
silane).
[0025] In the next step, a TaN film was formed as a liner material
12 on the entire surface of the insulating film 11 by a sputtering
method to a thickness of 100 .ANG., followed by forming a Cu film
as a wiring material film 13 to a thickness of 6,000 .ANG. on the
liner material 12 by a plating method. Incidentally, the liner
material 12 is not limited to the TaN film. For example, it is
possible for the liner material 12 to be of a single layer
structure formed of Ta, TaN, Ti, or TiN or to be of a laminate
structure formed of the films of the materials noted above. This is
also the case with the other embodiments of the present invention
described herein later.
[0026] Further, the undesired portions of the Cu film 13 and the
TaN film 12 are removed by the CMP process so as to form a Cu
damascene wiring. To be more specific, a top ring 23 holding a
semiconductor substrate 22 was abutted against a turntable 20
having a polishing cloth 21 attached thereto while rotating the
turntable 20 at a rotation speed of 100 rpm, as shown in FIG. 2.
The semiconductor substrate 22 was abutted against the polishing
cloth 21 with a polishing load of 300 gf/cm.sup.2. During the
polishing treatment, a slurry used as a processing solution 27 was
supplied from a processing solution supply nozzle 25 onto the
polishing cloth 21 at a flow rate of 200 cc/min with the rotation
speed of the top ring 23 set at 100 rpm. The polishing treatment
was carried out for 80 seconds until the undesired portion of the
Cu film 13 outside the groove 14 was removed so as to expose the
TaN film 12 positioned below the Cu film 13 to the outside by using
"CMS 7401/CMS 7452" (trade name, manufactured by JSR Inc.) as the
slurry, and "IC 1000" (trade name, manufactured by RODEL Inc.) as
the polishing cloth. Incidentally, a water supply nozzle 24 and a
dresser 26 are also shown in FIG. 2.
[0027] After removal of the undesired portion of the Cu film 13,
the undesired portion of the TaN film 12 was removed by the CMP
process so as to expose the surface of the insulating film 11 to
the outside, as shown in FIG. 1B. In this case, the polishing
treatment was carried out for 60 seconds under the conditions equal
to those for the previous polishing treatment, except that the
rotation speed of each of the top ring 23 and the turntable 20 was
changed to 50 rpm, that the polishing load was changed into 400
gf/cm.sup.2, and that "CMS 8301" (trade name, manufactured by JSR
Inc.) was used as the slurry. The slurry "CMS 8301" is an alkaline
slurry having a pH value of 9.5 and is mixed with a corrosion
preventing agent. It is desirable to use an acidic slurry. However,
it is possible to use an alkaline slurry if a corrosion preventing
agent is added to the slurry.
[0028] After the polishing treatment, a DIW was supplied from the
water supply nozzle 24 for carrying out a polishing treatment for
15 seconds in preparation for the shifting of the pH value toward
the acidic side, followed by supplying an aqueous solution
containing 0.2% by weight of citric acid, said aqueous solution
being used as the washing solution, from a washing solution supply
nozzle (not shown) so as to carry out the polishing treatment for
30 seconds. The process steps until the polishing treatment with
the aqueous solution of citric acid were carried out consecutively
on the single turntable 20 shown in FIG. 2, followed directly by
the next process step such as the roll washing step. Since the
aqueous solution of citric acid has a pH value of 3, the roll
washing step is carried out with the processing surface kept
acidic. It is possible to use an acidic aqueous solution of, for
example, citric acid, oxalic acid, maleic acid, or malonic acid as
the washing solution.
[0029] FIG. 3 schematically shows the construction of the polishing
apparatus used for the manufacturing method of the semiconductor
device according to the first embodiment (embodiment 1) of the
present invention. As apparent from the drawing, which shows the
general construction of the polishing apparatus, the polishing
apparatus comprises a CMP section 30, in which the polishing is
carried out in two systems, and a washing section 31 for washing a
semiconductor wafer 33 transferred from each of the two systems
included in the CMP section 30. A CMP processing is applied to the
semiconductor wafer 33 on a turntable 32 arranged in the CMP
section 30 and, then, the semiconductor wafer 33 is held by a
polishing unit 34. In the example described above, the polishing
treatment with an aqueous solution of citric acid is applied first
to the semiconductor wafer 33 and, then, the semiconductor wafer 33
is transferred under the state that the surface of the
semiconductor wafer 33 is held acidic. Incidentally, a dressing
unit 35 is also shown in the CMP section 30.
[0030] In the washing section 31, a wafer hanger (not shown) of a
wafer transfer robot 36 receives the semiconductor wafer 33 from
the polishing unit 34 and, then, the semiconductor wafer 33 is
transferred into a double-sided roll washing device 37. The both
surfaces of the semiconductor wafer 33 are washed with, for
example, water by the double-sided roll washing device 37 and,
then, the semiconductor wafer 33 is transferred by the wafer
transfer robot 36 into an inverting device 38. The inverted wafer
is washed and, then, dried in a pencil washing device 39. Finally,
the semiconductor wafer 33 is housed in a cassette 40.
[0031] In the first embodiment of the present invention, the roll
washing is applied to the semiconductor wafer 33 under the state
that the processing surface of the semiconductor wafer 33 is held
acidic. The defects such as the corrosion of Cu and the erosion of
the Cu wiring edge, which were not found on the processing surface
of the semiconductor wafer before the roll washing treatment, were
not found even after the roll washing treatment. Also, the degree
of the scratches on the Cu film was found to be low, i.e., as low
as 10 scratches/cm.sup.2. Further, as a result of observation with
a defect evaluating apparatus, the dust degree was also found to be
low, i.e., as low as 60 dust particles/cm.sup.2.
[0032] For comparison, the polishing treatment was carried out by
the conventional method. To be more specific, the process steps up
to the polishing treatment with an aqueous solution of citric acid
were carried out as described above. In addition, a polishing
treatment with a DIW was carried out for 15 seconds after the
polishing treatment with the aqueous solution of citric acid. As
shown in FIG. 4, an erosion 50 in the Cu wiring edge was generated
in the insulating film 11 after the polishing treatment with the
DIW. The erosion 50 was found to be very deep, i.e., the maximum
depth was found to be 500 .ANG.. Also, the scratch degree on the Cu
film was found to be high, i.e., as high as 98 scratches/cm.sup.2,
and the dust degree was also found to be high, i.e., as high as 170
dust particles/cm.sup.2. In conclusion, it has been confirmed that
the defects are increased by the polishing treatment with a
DIW.
[0033] (Embodiment 2)
[0034] A film structure equal to that shown in FIG. 1A was formed
on the semiconductor substrate 10 as in the first embodiment
(embodiment 1), except that the insulating film 11 shown in FIG. 1A
was changed into a laminate structure comprising a first insulating
film 51 formed of LKD 5109 (trade name, manufactured by JSR Inc.)
and having a thickness of 3,000 .ANG. and a second insulating film
52 formed of LKD 27 (trade name, manufactured by JSR Inc.) and
having a thickness of 1,500 .ANG., and that the liner material 12
shown in FIG. 1A was changed into a Ta/TaN film 53, as shown in
FIG. 5. The material "LKD 27" used for forming the second
insulating film 52 is a hydrophobic material.
[0035] Further, the undesired portion of the Cu film 13 was removed
by applying a CMP process (polishing treatment) under the
conditions equal to those for the first embodiment so as to expose
the surface of the Ta/TaN film 53 to the outside, followed by
further applying a CMP process under the conditions equal to those
described previously so as to expose the surface of the second
insulating film 52 to the outside.
[0036] After the polishing treatment, an additional polishing
treatment was carried out for 15 seconds by supplying a DIW from
the water supply nozzle 24. Further, a washing solution was
supplied from the washing solution supply nozzle (not shown) so as
to carry out the polishing treatment for 30 seconds. An aqueous
solution containing 1% by weight of citric acid, which was prepared
by diluting CITREX (trade name, manufactured by Wako Junyaku Kogyo
K. K.) with a DIW, was used as the washing solution. The processing
after the polishing of the Ta/TaN film 53 with a slurry was carried
out while monitoring the citric acid concentration on the polishing
cloth. To be more specific, the acidity was measured by using a
near infrared spectrometer so as to monitor the citric acid
concentration on the polishing cloth.
[0037] When the washing solution supplied onto the processing
surface was switched to a DIW, the citric acid concentration on the
polishing cloth was found to be lower than 0.1% by weight.
Therefore, the semiconductor substrate was immediately retreated
from the position on the polishing cloth into a washing unit.
[0038] It is possible to control the polishing apparatus such that
the operations described above are interlocked. To be more
specific, it is possible to permit the polishing apparatus body to
be interlocked when the citric acid concentration detected by a
sensor has been lowered below a prescribed level, e.g., 0.1% by
weight, set in advance. The washing and polishing treatments are
carried out while monitoring the citric acid concentration on the
polishing cloth by using a sensor. When the citric acid
concentration has deviated from a prescribed range, the polishing
apparatus body is interlocked upon receipt of an electronic signal
from the sensor. As a result, the top ring is guided immediately to
the waiting position so as to transfer the semiconductor substrate
into the washing unit.
[0039] If the citric acid concentration is slightly lower than 0.1%
by weight, the acidic state can be maintained sufficiently. Such
being the situation, the washing treatment is carried out in the
washing unit under the state that the acidic state is kept at the
processing surface in the second embodiment (embodiment 2) of the
present invention, too. The surface of the semiconductor substrate
immediately after the retreat from the position on the polishing
cloth was observed, with the result that no defect was recognized
as in embodiment 1. In other words, it was possible to avoid the Cu
abnormality.
[0040] The prescribed value of the acid concentration is a value
that can be determined in accordance with the lowest acid
concentration that permits the processing surface abutting against
the polishing cloth to assume an acidic state. It follows that the
prescribed value of the acid concentration can be determined
appropriately in accordance with the kind of the acid used. In
general, the acidic state can be formed under an acid concentration
of 0.05% by weight. However, it is desirable for the prescribed
value of the acid concentration to be set at about 0.1% by weight
in order to maintain an acidic state of the processing surface
without fail.
[0041] For comparison, a polishing treatment with a DIW was carried
out for 15 seconds after the washing and polishing treatment with
the washing solution. The erosion as shown in FIG. 4 was generated
on the processing surface after the polishing treatment with the
DIW.
[0042] In general, a reverse contamination tends to be accelerated
by a DIW when it comes to the insulating film formed of a
hydrophobic material. The known hydrophobic insulating materials
include, for example, SiLK (trade name, manufactured by Dow
Chemical, Co., Ltd.), Coral (trade name, manufactured by Novellus
Systems, Inc.), and BD (black diamond) (trade name, manufactured by
Applied Materials Inc.) in addition to LKD 27 referred to above. As
described above, it is possible to avoid the use of a DIW by
allowing the acid concentration on the polishing cloth to fall
within a prescribed range so as to make it possible to suppress the
reverse contamination of the insulating film.
[0043] (Embodiment 3)
[0044] As shown in FIG. 5, the Ta/TaN film 53 was exposed to the
outside as in the second embodiment (embodiment 2) described above.
The slurry for polishing the Ta/TaN film 53 was prepared by adding
5% by weight of colloidal silica used as abrasive particles, 0.1%
by weight of BTA (benzotriazole) used as a corrosion preventing
agent, and 0.1% by weight of nitric acid used as a pH adjusting
agent to a DIW. The slurry thus prepared was found to exhibit a pH
value of 1.5. The undesired portion of the Ta/TaN film 53 was
removed under the conditions equal to those for embodiment 1,
except that used was the slurry prepared as described above. In the
third embodiment (embodiment 3) of the present invention, the
polishing treatment of the Ta/TaN film 53 was carried out while
monitoring the pH value of the processing surface by using a sensor
having a high resolution in the vicinity of the pH value of 2.5. To
be more specific, the ion concentration was measured by using a
conductivity meter so as to monitor the pH value on the polishing
cloth.
[0045] After the polishing treatment with the slurry, a DIW was
supplied from the water supply nozzle 24. As a result, the pH value
of the processing surface instantly exceeded 2.5 and, thus, the
semiconductor substrate was immediately retreated from the position
on the polishing cloth into the washing unit.
[0046] It is possible to control the polishing apparatus such that
the operations described above are interlocked. To be more
specific, the polishing apparatus body is interlocked when the pH
value detected by the sensor has exceeded a prescribed value, e.g.,
2.5. The polishing treatment with a DIW is carried out while
monitoring the pH value on the polishing cloth by using a sensor.
When the monitored pH value has exceeded the prescribed value, the
polishing apparatus body receives an electric signal from the
sensor so as to be interlocked. Then, the top ring is immediately
guided to the waiting position so as to transfer the semiconductor
substrate to the washing unit.
[0047] Since an acidic state is formed if the pH value is not
larger than about 2.5, the washing is carried out in the washing
unit under the state that the processing surface is put under the
acidic state in the third embodiment (embodiment 3) of the present
invention, too. The processing surface before the roll washing
stage was observed, with the result that no defect was observed as
in embodiment 1, supporting that it was possible to avoid the Cu
abnormality.
[0048] The prescribed pH value is the largest pH value that permits
the processing surface abutting against the polishing cloth to be
put under the acidic state. It is reasonable to state that an
acidic state is formed, if the pH value is less than 7. However, it
is desirable for the prescribed pH value to be low, i.e., not
larger than about 3, in order to maintain without fail the acidic
state of the processing surface.
[0049] For comparison, a polishing treatment was carried out on the
polishing cloth as above, except that a DIW was supplied until the
pH value on the processing surface exceeded 7.0. In this case, the
erosion as shown in FIG. 4 was generated on the polishing surface
after the polishing treatment with the DIW. In other words, it has
been confirmed that a defect is generated even if the processing
surface is polished by using an acidic slurry, if the polishing
treatment is carried out with a DIW in the subsequent step until
the processing surface is rendered neutral.
[0050] Incidentally, it is possible to monitor the acid
concentration as in the second embodiment (embodiment 2) in
supplying a DIW after the polishing treatment with an acidic
slurry. Alternatively, it is also possible to monitor the pH value
in supplying a DIW after the washing and polishing treatment with
an acidic washing solution. The combination between the kind of the
acidic processing solution and the property value to be monitored
is not particularly limited, and it is possible to employ a desired
combination appropriately.
[0051] The description given above is directed to the formation of
a Cu damascene wiring. However, the wiring material is not limited
to Cu. It is possible to avoid abnormalities after the polishing
treatment by transferring the semiconductor substrate into the
washing unit under an acidic state even in the case of using Al or
W as the wiring material.
[0052] As described above, the embodiment of the present invention
provides a method of manufacturing a semiconductor device that
permits avoiding the defect generation so as to enhance the
reliability of the semiconductor device.
[0053] Additional advantages and modifications will readily occur
to those skilled in the art. Therefore, the invention in its
broader aspects is not limited to the specific details and
representative embodiments shown and described herein. Accordingly,
various modifications may be made without departing from the spirit
or scope of the general inventive concept as defined by the
appended claims and their equivalents.
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