U.S. patent application number 10/131324 was filed with the patent office on 2003-05-08 for copper plating solution for embedding fine wiring, and copper plating method using the same.
This patent application is currently assigned to Electroplating Engineers of Japan Limited (Japanese Corporation). Invention is credited to Kuzushima, Toshio, Totsuka, Takashi.
Application Number | 20030085133 10/131324 |
Document ID | / |
Family ID | 26619354 |
Filed Date | 2003-05-08 |
United States Patent
Application |
20030085133 |
Kind Code |
A1 |
Totsuka, Takashi ; et
al. |
May 8, 2003 |
Copper plating solution for embedding fine wiring, and copper
plating method using the same
Abstract
The present invention provides a copper plating solution for
embedding fine wiring, wherein it contains copper sulfate at 100 to
300 g/L as copper sulfate pentahydrate, sulfuric acid at 5 to 300
g/L, chlorine at 20 to 200 mg/L, a macromolecular surfactant at
0.05 to 20 g/L for controlling the electrodeposition reaction,
sulfur-based saturated organic compound at 1 to 100 mg/L for
accelerating the electrodeposition reaction, leveling agent
composed of a macromolecular amine compound at 0.01 to 10 mg/L and
reductant at 0.025 to 25 g/L for stabilizing the copper plating
solution. The copper plating solution of the present invention for
embedding fine wiring can plate the wafer surface provided with
fine wiring patterns with sub-micron order gaps in-between and
coated with copper serving as the metallic seed film, to fill the
gaps neither leaving any defect therein nor dissolving the metallic
seed film.
Inventors: |
Totsuka, Takashi; (Naka-gun,
JP) ; Kuzushima, Toshio; (Hiratsuka-shi, JP) |
Correspondence
Address: |
ARENT FOX KINTNER PLOTKIN & KAHN
1050 CONNECTICUT AVENUE, N.W.
SUITE 400
WASHINGTON
DC
20036
US
|
Assignee: |
Electroplating Engineers of Japan
Limited (Japanese Corporation)
|
Family ID: |
26619354 |
Appl. No.: |
10/131324 |
Filed: |
April 25, 2002 |
Current U.S.
Class: |
205/291 ;
205/296 |
Current CPC
Class: |
C25D 3/38 20130101 |
Class at
Publication: |
205/291 ;
205/296 |
International
Class: |
C25D 003/38 |
Foreign Application Data
Date |
Code |
Application Number |
Jul 26, 2001 |
JP |
P2001-226559 |
Nov 9, 2001 |
JP |
P2001-344200 |
Claims
What is claimed is:
1. A copper plating solution for embedding fine wiring, containing
100 to 300 g/L of copper sulfate as copper sulfate pentahydrate, 5
to 300 g/L of sulfuric acid, 20 to 200 mg/L of chlorine, 0.05 to 20
g/L of a macromolecular surfactant for controlling the
electrodeposition reaction, 1 to 100 mg/L of a sulfur-based
saturated organic compound for accelerating the electrodeposition
reaction, 0.01 to 10 mg/L of a leveling agent composed of a
macromolecular amine compound and 0.025 to 25 g/L of a reductant
for stabilizing the copper plating solution.
2. The copper plating solution for embedding fine wiring according
to claim 1, containing 0.01 to 20 mg/L of an organic dye compound
for controlling leveling of deposited copper.
3. The copper plating solution for embedding fine wiring according
to claim 1 or 2, wherein said leveling agent composed of a
macromolecular amine compound is polyethylene imine or
polypropylene imine.
4. The copper plating solution for embedding fine wiring according
to claim 3, wherein said macromolecular amine compound has an
average molecular weight of 5,000 to 100,000.
5. The copper plating solution for embedding fine wiring according
to any one of claims 1 to 4, wherein said reductant for stabilizing
the copper plating solution contains at least one organic compound
containing at least one type of functional group selected from
aldehyde, hydroxyl and carboxyl, alcohol, and organocarboxylic
acid.
6. A method of copper plating for embedding fine wiring, with the
copper plating solution for embedding fine wiring according to any
one of claims 1 to 5 under the conditions of a cathode current
density of 0.05 to 5 A/dm.sup.2 and liquid temperature of 5 to
30.degree. C.
Description
BACKGROUND OF THE INVENTION
[0001] 1. Field of the Invention
[0002] The present invention relates to a plating treatment
technique for the surface of a wafer as an electronic device, more
particularly to a plating solution of copper sulfate for embedding
copper by plating on the wafer surface on which fine wiring
patterns with sub-micron order gaps in-between are formed.
[0003] 2. Description of the Related Art
[0004] Recently, the fine processing techniques for a wafer as an
electronic device have made rapid progress, and the plating
techniques for processing wafers have been also extensively under
development. The plating techniques for processing wafers include
copper plating based on electrolysis, and the representative
electrolytic plating solution includes strongly acidic solutions of
copper sulfate, and alkaline solutions of cyan- and pyrophosphoric
acid-based ones. Among these plating solutions, a strongly acidic
solution of copper sulfate has been widely used, because it can be
more easily managed and controlled for electrodeposition rate than
the alkaline ones.
[0005] The plating solution of copper sulfate is basically composed
of copper sulfate, sulfuric acid and an organic compound, e.g.,
surfactant. Various plating solutions of copper sulfate are known,
in which various additives, e.g., polymer and those known as
brightener and leveler, are contained at a given content. Addition
of these additives controls an electrodeposition rate of the
plating metal, thereby providing a plating solution of copper
sulfate which allows uniform copper plating.
[0006] Recently, wafers are frequently treated through a copper
plating on the surface thereof which has been provided with fine
wiring patterns with sub-micron order gaps in-between. In this
case, it is required to completely fill these gaps with deposited
copper. In other words, the very narrow gap of the sub-micron order
must be filled with copper through a plating treatment.
[0007] Completely filling these fine gaps by deposited copper has
been coped with by adjusting various additives contained in the
plating solution. More specifically, the additives which affect
electrodeposition of copper, e.g., leveler, brightener and polymer,
are adequately adjusted and incorporated in the plating solution,
to provide a copper solution which can be filled in the fine gaps
between the wiring patterns. However, it has been pointed out that
use of the additive-containing plating solution of copper sulfate
may cause the following problems.
[0008] The wafers of late are coated with a metallic film, referred
to as seed, by physical vapor deposition (PVD) before being treated
by plating, and copper is frequently deposited to cover the wafer
as the metallic seed film. The wafer coated with the copper seed
film may not be uniformly plated with the copper sulfate solution,
because the solution tends to dissolve the copper seed film. More
specifically, filling the fine gaps between the wiring patterns
with the copper plating solution may produce defects, e.g., voids
and seams, in the gaps. In addition, thickness of the deposited
copper was sometimes uneven between the wafer surface portion with
the fine wiring pattern and that without them.
[0009] The uneven copper plating is mainly caused by dissolution of
the copper seed film, and one countermeasure will be to prevent
dissolution of the metallic seed film even when copper comes into
contact with the plating solution of copper sulfate. More
specifically, use of a plating solution of copper sulfate having a
composition of high-concentration copper and low-concentration
sulfuric acid will be one countermeasure against dissolution of the
metallic seed film.
[0010] However, the plating solution of unbalanced composition will
be less stable than the common plating solution of copper sulfate,
and deteriorate uniformity of the copper plating treatment, because
it tends to decompose the additive used for controlling
electrodeposition. As a result, it is difficult to continuously
keep the uniform copper plating.
SUMMARY OF THE INVENTION
[0011] The present invention, developed under these circumstances,
provides a copper plating solution for embedding fine wiring which
plates, with copper from a plating solution of copper sulfate, the
wafer surface provided with fine wiring patterns with sub-micron
order gaps in-between and coated with copper serving as the
metallic seed film, characterized in that it can control
dissolution of the metallic seed film, plate the wafer surface by
filling the fine gaps with copper without leaving defects in the
gaps and cover the entire surface of the wafer to be plated with
copper of uniform thickness, and is very high in solution
stability.
[0012] The inventors of the present invention have reached the
copper plating solution of the present invention for embedding fine
wiring, after having intensively studied copper sulfate plating
solutions of unbalanced composition containing copper at a high
concentration and sulfuric acid at a low concentration.
[0013] The copper sulfate plating solution of the present invention
for embedding fine wiring is characterized in that it contains
copper sulfate at 100 to 300 g/L as copper sulfate pentahydrate,
sulfuric acid at 5 to 300 g/L, chlorine at 20 to 200 mg/L, a
macromolecular surfactant at 0.05 to 20 g/L for controlling the
electrodeposition reaction, sulfur-based saturated organic compound
at 1 to 100 mg/L for accelerating the electrodeposition reaction,
leveling agent composed of a macromolecular amine compound at 0.01
to 10 mg/L and reductant at 0.025 to 25 g/L for stabilizing the
copper plating solution.
[0014] The function(s) and effect(s) of each component for the
copper plating solution composition of the present invention are
described for the plating treatment involving embedding fine
wiring. First of all, the copper plating solution of the present
invention is basically composed of copper sulfate, sulfuric acid
and hydrochloric acid. Of these components, copper sulfate and
sulfuric acid are contained at 100 to 300 g/L as copper sulfate
pentahydrate and 5 to 300 g/L, respectively, because of necessity
for giving the solution of high-concentration copper and
low-concentration sulfuric acid. The sulfuric acid concentration by
itself may be in a general range for the common solution. Viewed
from its relationship with concentration of copper sulfate (more
specifically copper), however, it satisfies the unbalanced
composition of high-concentration copper sulfate and
low-concentration sulfuric acid.
[0015] The plating solution composition containing copper sulfate
and sulfuric acid in the above ratio dissolves no copper seed, even
when the metallic seed film of copper covers the wafer surface. The
solution containing sulfuric acid at below 100 g/L as copper
sulfate pentahydrate tends to dissolve the copper seed. At a copper
sulfate concentration above 300 g/L, on the other hand, salting-out
of copper sulfate in the plating solution tends to occur, which
accelerates decomposition of each additive, as described later. A
sulfuric acid concentration below 5 g/L is accompanied by decreased
current efficiency, and difficulty in the uniform plating
treatment. At a sulfuric acid concentration above 300 g/L, on the
other hand, the plating solution tends to dissolve the copper seed.
Chlorine is preferably contained at a concentration in a range of
20 to 200 mg/L. At below 20 mg/L, uniform electrodeposition will be
no longer expected. At above 200 mg/L, on the other hand, copper
chloride tends to be precipitated on the copper anode surface.
Moreover, the plating solution declines in capacity to fill the
gaps between the fine wiring patterns at a chlorine concentration
beyond 20 to 200 mg/L, tending to leave voids in the plated
gaps.
[0016] The macromolecular surfactant, added to the copper plating
solution of the present invention for embedding fine wiring to
control the electrodeposition reaction, is adsorbed on the wafer
surface where the fine wiring patterns with voids are exposed to
the plating solution (i.e., portion other than the gap inside), to
perform a function of controlling the electrodeposition reaction
there. In particular, plating current tends to be concentrated at
the edge, which is exposed to the surface side when the gaps are
formed, with the result that the plating electrodeposition reaction
tends to proceed faster and deposit copper more thickly at the edge
than gap inside. Therefore, the macromolecular surfactant is used
to be adsorbed on the portions, e.g., edge, which tend to be plated
more thickly, and control the plating electrodeposition reaction
there. It is adsorbed in the gap inside to a lesser extent, and
allows the plating electrodeposition reaction to proceed, because
it is not retarded much.
[0017] The macromolecular surfactants useful for the present
invention include 1,3-dioxolan polymer, polypropylene glycol,
polypropylene propanol, polyethylene glycol, polyethylene glycol
derivative, oxyl alkylene polymer and copolymer of ethylene oxide
and propylene oxide, which may be used either individually or in
combination.
[0018] The macromolecular surfactant for the copper plating
solution of the present invention for embedding fine wiring to
control the electrodeposition reaction may not fully exhibit its
function of controlling the electrodeposition reaction, when
contained at below 0.05 g/L. At above 20 g/L, on the other hand, it
may excessively control the reaction, with the result that the
reaction may not proceed uniformly, tending to produce seams in the
fine gaps. The macromolecular surfactant preferably has a molecular
weight (weight-average molecular weight Mw) of 100 to 50,000. The
one having a molecular weight of less than 100 may not be effective
because of the insufficient capacity of controlling the
electrodeposition reaction. One the other hand, the one having a
molecular weight above 50,000 may be adsorbed unevenly.
[0019] Next, the sulfur-based saturated organic compound for the
copper plating solution of the present invention for embedding fine
wiring to accelerate the electrodeposition reaction works to
accelerate the electrodeposition rate of copper on the wafer
surface to be plated. It has a lower molecular weight than the
macromolecular surfactant, penetrating into the fine gaps more
smoothly, to accelerate the electrodeposition reaction for copper
plating within the gap, where the plating reaction is more
difficult to proceed.
[0020] The sulfur-based saturated organic compound capable of
accelerating the electrodeposition reaction is preferably a
dithiobis-alkane-sulfonic acid or salt thereof. More specifically,
these compounds include 4,4-dithiobis-butane-sulfonic acid,
3,3-dithiobis-propane-sulfonic acid, 2,2-dithiobis-ethane-sulfonic
acid and salts thereof, which may be used either individually or in
combination.
[0021] The sulfur-based saturated organic compound for accelerating
the electrodeposition reaction is preferably contained at 1 to 100
mg/L. At below 1 mg/L, it cannot sufficiently accelerate the
electrodeposition reaction within the gaps on the wafer surface to
be plated. At above 100 mg/L, on the other hand, it will start
accelerating the reaction in the area other than the fine gap
inside, tending to produce voids in the gaps, and the uniform
copper plating treatment may not be realized.
[0022] Each of the macromolecular surfactant for controlling the
electrodeposition reaction and sulfur-based saturated organic
compound for accelerating the electrodeposition reaction works as
the additive which helps the plating solution fill the fine gaps
between the fine wiring patterns by deposited copper. These
components, although contributing to filling the gaps with
deposited copper, little exhibit a function of controlling
thickness of deposited copper corresponding to the surface shape in
the surface on which fine wiring patterns are provided and that
which carries no wiring patterns, i.e., flat surface. In other
words, the plating solution cannot plate the whole surface with
copper of uniform thickness only with the aid of the macromolecular
surfactant for controlling the electrodeposition reaction and
sulfur-based saturated organic compound for accelerating the
electrodeposition reaction, although capable of plating the wafer
surface treated to have fine wiring patterns thereon.
[0023] The inventors of the present invention have found that the
plating solution significantly deteriorates, when it contains
copper at a high concentration and sulfuric acid at a low
concentration to prevent dissolution of the metallic seed film,
because of tendency of the components to decomposition, notably the
sulfur-based saturated organic compound contained to accelerate the
electrodeposition reaction.
[0024] Therefore, the copper plating solution of the present
invention for embedding fine wiring contains a leveling agent
composed of an amine compound and reductant for stabilizing the
copper plating solution, in addition to the macromolecular
surfactant and sulfur-based saturated organic compound.
[0025] The leveling agent composed of a macromolecular amine
compound for the copper plating solution of the present invention
for embedding fine wiring has a function of leveling final
thickness of the deposited copper. More specifically, it levels
thickness of the deposited copper both in the surface on which fine
wiring patterns are provided and that which carries no wiring
patterns, i.e., flat surface. The examples of the macromolecular
amine compounds having a leveling function include polyethylene
imine and polypropylene imine. It preferably has an average
molecular weight of 5,000 to 100,000. The one having an average
molecular weight below 5,000 easily diffuses into the gaps between
fine wiring patterns, tending to diminish the function of the
sulfur-based saturated organic compound for accelerating the
electrodeposition reaction. On the other hand, the one having an
average molecular weight above 100,000 tends to make the plating
treatment for embedding wiring unstable, conceivably resulting from
uneven adsorption of the compound. The macromolecular amine
compound having an average molecular weight of 5,000 to 100,000 is
difficult to diffuse into the gaps between fine wiring patterns,
preventing to a lesser extent the function of the sulfur-based
saturated organic compound for accelerating the electrodeposition
reaction.
[0026] For the effect of average molecular weight of the
macromolecular amine compound on extent of improving uniformity
(leveling) of deposited copper thickness, it is found that the
effect is exhibited by a small quantity of the compound, when it
has a relatively low average molecular weight (100 to 2,000).
However, it will not contribute much to the improved uniformity,
unless its content is increased to some extent, when it has a
relatively high average molecular weight (10,000 to 100,000).
Nevertheless, however, it is preferable to use the amine compound
of relatively high molecular weight for the copper plating solution
of the present invention for embedding fine wiring, because of
easiness in analysis and concentration management of the
compound.
[0027] The leveling agent composed of the macromolecular amine
compound is preferably contained at 0.01 to 10 mg/L. It is
difficult to fully exhibit its function of leveling thickness of
the deposited copper at below 0.01 mg/L. At above 10 mg/L, on the
other hand, it may excessively exhibit the leveling effect to
prevent the effect of the sulfur-based saturated organic compound
for accelerating the electrodeposition reaction and to cause the
conformal separation in which the deposited copper is deposited in
the gaps between fine wiring patterns to the same thickness as is
on the surface side, with the result that seams and voids tend to
be formed in the gaps.
[0028] The reductant for stabilizing the copper plating solution of
the present invention for embedding fine wiring (hereinafter
referred to as the plating-solution-stabilizing reductant) works to
control decomposition of the sulfur-based saturated organic
compound, which is sensitive to changes in concentrations of copper
and sulfuric acid. The sulfur-based saturated organic compound is
decomposed significantly, especially in the plating solution having
a composition of high-concentration copper and low-concentration
sulfuric acid, to reduce serviceability of the solution. Therefore,
the copper plating solution of the present invention for embedding
fine wiring is incorporated with the plating-solution-stabilizing
reductant, to control decomposition of the sulfur-based saturated
organic compound. This allows the copper plating treatment for
embedding wiring to be continuously effected, with the sulfur-based
saturated organic compound stably present even in the plating
solution of high-concentration copper and low-concentration
sulfuric acid composition, and also improves serviceability of the
plating solution itself.
[0029] The preferable reductants for stabilizing the plating
solution of the present invention include an organic compound
containing at least one type of functional group selected from
aldehyde, hydroxyl and carboxyl, alcohol, and organocarboxylic
acid. The organic compounds having at least one functional group of
hydroxyl or carboxyl include glyoxal, benzaldehyde,
succindialdehyde, acetoaldehyde and propionaldehyde. The alcohols
include ethanol, methanol and propanol. The organic carboxylic
acids include citric acid, oxalic acid, glyoxylic acid and ascorbic
acid. These reductants have a function of effectively preventing
decomposition of the sulfur-based saturated organic compound.
[0030] The plating-solution-stabilizing reductant is preferably
contained at 0.025 to 25 g/L. It will have an insufficient function
of preventing decomposition of the sulfur-based saturated organic
compound to cause deterioration of the plating solution, when
contained at below 0.025 g/L. At above 25 g/L, on the other hand,
it may cause self-decomposition of the plating solution, conversely
tending to make the solution unstable.
[0031] The copper plating solution of the present invention for
embedding fine wiring may be further incorporated with an organic
dye compound which has a function of controlling leveling of the
deposited copper. Such a compound works to promote uniform
electrodeposition of copper for plating, irrespective of shape of
the surface to be plated, when the electrodeposition of copper
proceeds to some extent, although exhibiting its function only to a
limited extent during the initial stage of plating treatment, i.e.,
electrodeposition of copper. It is particularly useful for plating
copper on a hole (the so-called via) , where the hole inside is
plated with copper in such a way that the via opening is not
closed.
[0032] These organic dye compounds useful for the present invention
include safranine, phenazine, thioflavin, Dye 300, Dye 1556, Dye
3100, Absorber Dye ADI and Cy5, which may be incorporated either
individually or in combination. See Japanese Patent Application
Laid-Open No. P2000-248397 for details of these compounds. The
organic dye compound is preferably contained at 0.01 to 20 mg/L. It
may not fully exhibit its leveling function at below 0.01 mg/L,
deteriorating the final appearances of the plated product. At above
20 mg/L, on the other hand, it may not effectively fill the gap
insides with copper.
[0033] The copper plating solution of the present invention for
embedding fine wiring will be most effective for securely
preventing dissolution of the copper seed film, when it contains
copper sulfate at 150 to 250 g/L as copper sulfate pentahydrate and
sulfuric acid at 10 to 100 g/L. Such a solution with a composition
of high-concentration copper and low-concentration sulfuric acid
can plate the wafer surface uniformly with copper, while little
dissolving the copper seed film on the wafer.
[0034] The plating treatment with the copper plating solution of
the present invention for embedding fine wiring is preferably
effected at a cathode current density of 0.05 to 5A/dm.sup.2. The
treatment will fill the gap inside completely with copper, even
when it is very fine, of the order of sub-micron in size, at a
cathode current density in the above range, and gives a very well
leveled copper layer on the wafer surface. At a cathode current
density below 0.05A/dm.sup.2, the electrodeposition reaction
proceeds almost simultaneously in the gap and other areas, with the
result that voids tend to be formed in the gap filled with the
deposited copper. At above 5A/dm.sup.2, on the other hand, hydrogen
tends to be generated, to deteriorate current efficiency and
plating efficiency by electrodeposition. The plating solution is
preferably kept at 5 to 30.degree. C. The salting-out tends to
occur at below 5.degree. C., whereas the additive tends to be
decomposed at above 30.degree. C. Particularly preferably, it is
kept at 10 to 20.degree. C., when the plating solution contains
copper sulfate at 150 to 250 g/L as copper sulfate pentahydrate and
sulfuric acid at 10 to 100 g/L, because salting-out tends to occur
in the solution of such high-concentration copper and
low-concentration sulfuric acid composition as solution temperature
decreases. The solution stably realizes uniform copper plating,
when kept at a temperature in the above range, and is serviceable
for extended periods.
[0035] It is preferable, when the plating treatment is effected
with the copper solution of the present invention for embedding
fine wiring, to adequately add each component consumed for the
treatment, e.g., the macromolecular surfactant, sulfur-based
saturated organic compound, leveling agent composed of a
macromolecular amine compound, plating-solution-stabilizing
reductant or organic dye compound, while taking into consideration
the quantity consumed to keep it at a desired concentration. Each
component for the copper plating solution of the present invention
for embedding fine wiring is consumed during the treatment process,
and the highly uniform copper plating treatment can be effected for
extended periods when each component is adequately added while
taking into consideration the quantity consumed to keep it at a
concentration in the above-described range.
BRIEF DESCRIPTION OF THE DRAWINGS
[0036] FIG. 1 schematically shows a cross-sectional view of test
pieces for evaluation of plating for embedding wiring, provided
with gap grooves;
[0037] FIG. 2 presents a SEM microgram showing cross-sectional view
of the test pieces for evaluation of plating for embedding wiring,
treated with the copper plating solution prepared in Example 2;
[0038] FIG. 3 presents a SEM microgram showing cross-sectional view
of the test pieces for evaluation of plating for embedding wiring,
treated with the copper plating solution prepared in Comparative
Example 2;
[0039] FIG. 4 presents a SEM microgram showing cross-sectional view
of the test piece for evaluation of plating for embedding wiring,
evaluated for running characteristics with the copper plating
solution prepared in Example 7;
[0040] FIG. 5 presents a SEM microgram showing cross-sectional view
of the test piece for evaluation of plating for embedding wiring,
evaluated for running characteristics with the copper plating
solution prepared in Comparative Example 3; and
[0041] FIG. 6 shows a relationship between average molecular weight
of polyethylene imine and the leveling characteristics.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
[0042] Embodiments according to the present invention will be
described more particularly by way of Examples and Comparative
Examples listed in Table 1. Symbols and Ratings are shown in Table
2.
1 TABLE 1 Difference in thickness Running of deposited Embed-
character- A B C D E copper (.mu.m) dability istics Example 1 1.0
20 0.01 2.5 0.5 0.55 .largecircle. .largecircle. Example 2 1.0 20
0.1 2.5 0.5 0.05 .largecircle. .largecircle. Example 3 1.0 20 1.0
2.5 0.5 0.07 .largecircle. .largecircle. Example 4 1.0 20 10.0 2.5
0.5 0.05 .DELTA. .DELTA. Example 5 1.0 20 20 2.5 0.5 0.06 X X
Example 6 1.0 20 0.1 0.025 0.5 0.05 .largecircle. .DELTA. Example 7
1.0 20 0.1 2.5 0.5 0.06 .largecircle. .largecircle. Example 8 1.0
20 0.1 5.0 0.5 0.06 .largecircle. .largecircle. Example 9 1.0 20
0.1 25 0.5 0.05 .DELTA. .DELTA. Example 10 1.0 20 0.1 30 0.5 0.05 X
X Example 11 1.0 20 10.0 2.5 0.5 0.05 .largecircle. .largecircle.
Comparative 1.0 20 -- -- 0.5 0.74 X X Example 1 Comparative 1.0 20
-- 2.5 0.5 0.79 .largecircle. .largecircle. Example 2 Comparative
1.0 20 0.1 -- 0.5 0.06 .DELTA. X Example 3
[0043]
2TABLE 2 A Concentration [g/L] of a macromolecular, triol type
surfactant of polypropylene glycol (PPG) having an average
molecular weight of 5,000 B Concentration [mg/L] of
3,3-dithiobis-propane-sodium sulfonate C Concentration [mg/L] of
polyethylene imine having an average molecular weight of 1,000 D
Concentration [g/L] of glyoxyl E Concentration [g/L] of safranine
Difference in Difference between thickness of deposited copper on
the surface with the thickness of gap and that on the surface
without the gap, determined by observation deposited copper of the
cross section of the test piece for evaluation of plating for
embedding wiring (.mu.m). Embeddability Extent of the deposited
copper filled in the groove and via hole formed on the wafer
surface, determined by observation of the cross section of the test
piece for evaluation of plating for embedding wiring. It was
evaluated according to the three-grade system: .largecircle.: the
gap is completely filled with copper without forming any defect,
e.g., void or seam; .DELTA.: the gap is filled with copper to some
extent, although some defects, e.g., void or seam, are observed;
and X: the gap is not well filled with deposited copper, showing
voids or seams inside. Running The test piece was continuously
plated with the copper plating solution characteristics at 25
Ahr/L, and extent of embeddability was evaluated by the observation
of the cross section according to the three-grade system, described
above.
[0044] The copper sulfate plating solution used in each of Examples
and Comparative Examples described in Table 1 was basically
composed of Cu at 50 g/L (adjusted by copper sulfate pentahydrate),
sulfuric acid at 50 g/L and chlorine at 70 mg/L. The basic
composition was incorporated with various additives given in Table
1, to prepare the plating solution for each of Examples and
Comparative Examples. More specifically, the basic composition bath
was prepared, to which the components A to E given in Table 1 were
added, to prepare the plating solution.
[0045] Examples 1 to 10 described in Table 1 used the same contents
of the additive components A, B and E, and varying contents of the
components C and D. Polyethylene imine as the additive C had an
average molecular weight of 1,000 for all Examples except Example
11, which used the component C having an average molecular weight
of 10,000. The plating solutions prepared in Comparative Examples 1
to 3 contained the components A, B and E each at the same content
as Examples, but contained only C or D or none of them.
[0046] The plating treatment conditions were liquid temperature:
20.degree. C., anode: phosphorus-containing copper, and plating
current: supplied at a cathode current density of 1A/dm.sup.2. The
object to be plated was the test piece for evaluation of plating
for embedding wiring, which was composed of a silicon wafer coated
beforehand with a metallic seed film of copper, sputtered to a
thickness of approximately 0.1 .mu.m (1000 .ANG.). The surface to
be plated consisted of the area provided with a total of 11 grooves
(position Nos. 1 to 11) of different gap width (the cross-sectional
view of which was similar to that of the test piece for evaluation
of plating for embedding wiring, shown in FIG. 1), and the flat
surface provided with no groove. Each gap groove had a depth D of 1
.mu.m, and the gap width was narrowed as the position number
increased, as shown in Table 3.
3TABLE 3 Position No. 1 2 3 4 5 6 7 8 9 10 11 Gap width 1.65 0.39
0.31 0.27 0.23 0.22 0.20 0.18 0.16 0.15 0.14 (.mu.m)
[0047] The test piece for evaluation of plating for embedding
wiring was embedding-plated with copper, to evaluate each plating
solution, where the piece cross section was analyzed by a scanning
electron microscope, to determine to what extent the solution
filled the gap, and its leveling capacity by measuring thickness of
deposited copper on the surface provided with the gap groove and
that provided with no groove. Moreover, the running characteristics
of each plating solution was determined by plating the test piece
with the solution at 25 Ahr/L for embedding wiring to observe to
what extent the gap was filled with copper.
[0048] As shown in Table 1, it is confirmed that the surface is
plated with copper to a greatly different thickness whether it is
provided with the gap or not, when the plating solution is free of
the component C (Comparative Examples 1 and 2). By contrast, the
surface is plated uniformly with copper whether it is provided with
the gap or not, when the plating solution prepared in each of
Examples 2 to 10.
[0049] The plating solution prepared in Example 2 was compared with
that prepared in Comparative Example 2 by thickness of deposited
copper, observed by scanning electron microscopic analysis. FIGS. 2
and 3 present the SEM micrograms showing the thickness of copper
deposited in the respective examples. In each microgram, the white
portion represents the deposited copper, where copper shown in the
left side is deposited on the flat wafer surface with no gap,
compared with the one in the right side deposited on the wafer
surface with gap.
[0050] FIG. 2 shows the wafer surface plated with copper in Example
2, where difference between thickness of deposited copper on the
flat surface and that on the surface with the gap is around 0.05
.mu.m. On the other hand, the difference is much larger at 0.79
.mu.m on the surface plated in Comparative Example 2, shown in FIG.
3. Comparing the surface plated in Example 4 with that plated in
Example 11, the plating solution filled the gap well in Example 11,
even when it contained polyethylene imine as the component C at the
upper limit content, when its average molecular weight was 10,000,
as shown in Table 1. The solution containing the imine having an
average molecular weight of 10,000 gave a larger embedding
margin.
[0051] The running characteristics results of each plating solution
revealed that the copper solutions prepared in Examples 1 to 4 and
7 to 9 show no deterioration in its embeddability even when used
for extended periods. On the other hand, the surfaces plated in
Examples 6 and 10 and Comparative Examples 1 and 3 showed
deteriorated embeddability when used for extended periods.
Comparing the microgram shown in FIG. 4 with that shown in FIG. 5,
which present the plated surface conditions to be observed for the
running characteristics, the surface plated in Example 7 was smooth
(FIG. 4) whereas that plated in Comparative Example 3 was fairly
roughened. Similarly, the surfaces plated with the solutions
prepared in Examples 6 and 10 and Comparative Example 1 were fairly
roughened, although not shown, when observed for their running
characteristics at 25 Ahr/L.
[0052] Finally, the relationship between average molecular weight
of polyethylene imine as the component C and leveling
characteristics were investigated. The results are described. A
total of four levels of average molecular weights of polyethylene
imine (hereinafter referred to as PEI), given in Table 4, were
investigated, and the silicon wafer surface was plated with the
copper plating solution of varied PEI content, where contents of
the additives other than the component C, copper, sulfuric acid and
chlorine were set at the same levels as in Example 1. The leveling
characteristics of the copper plating treatment were evaluated by
difference in thickness of deposited copper, where thickness of
deposited copper on the flat surface with no circuit patterns and
that on the surface provided with gaps continuously formed at
intervals of 0.39 .mu.m were determined by the SEM analysis of the
wafer cross-sections, to find the difference. The plating
conditions were liquid temperature: 20.degree. C., anode:
phosphorus-containing copper, and plating current: supplied at a
cathode current density of 1 A/dm.sup.2, where the target thickness
of deposited copper was set at 0.7 .mu.m.
4 TABLE 4 Average molecular weight of PEI Example 12-1 600 Example
12-2 1800 Example 12-3 10000 Example 12-4 70000
[0053] FIG. 6 plots difference in thickness of deposited copper
against concentration of PEI added for the copper plating solutions
prepared in Examples 12-1 to 12-4, given in Table 4. The average
film thickness was 0.68 .mu.m. It is found, as shown in FIG. 6,
that the leveling characteristics are affected at a low PEI
content, when its average molecular weight is low (Examples 12-1
and 12-2). It is also found that the surface will not be uniformly
plated when PEI having a high average molecular weight such as that
for Examples 12-3 and 12-4 is used, unless its content is increased
to some extent. These results indicate that it is preferable to use
polyethylene imine having an average molecular weight of 10,000 or
more, because its analysis and management become easier as its
content in the plating solution increases.
[0054] As discussed above, the copper plating solution of the
present invention for embedding fine wiring can plate the wafer
surface provided with fine wiring patterns with gaps in-between, to
completely fill the gaps even when they are very fine, of the order
of sub-micron in width, and also allows copper to be deposited to a
uniform thickness over the entire wafer surface. It can also
realize uniform copper plating continuously and stably for extended
periods, in spite of its composition characterized by high copper
concentration and low sulfuric acid concentration.
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