U.S. patent application number 10/078766 was filed with the patent office on 2003-08-21 for process for electroplating silicon wafers.
This patent application is currently assigned to Shipley Company, L.L.C.. Invention is credited to Miura, Takeshi, Ota, Yasuo, Seita, Masaru.
Application Number | 20030155247 10/078766 |
Document ID | / |
Family ID | 27732897 |
Filed Date | 2003-08-21 |
United States Patent
Application |
20030155247 |
Kind Code |
A1 |
Miura, Takeshi ; et
al. |
August 21, 2003 |
Process for electroplating silicon wafers
Abstract
An electroplating solution comprising copper ions and a
complexing agent for the copper ions and has a pH in the range of 4
to 10. The electroplating solution of the present invention makes
it possible to fill trenches or via holes on silicon wafers for
providing copper wiring with copper in a defect-free manner by
preventing the seed layer from dissolving in the plating
solution.
Inventors: |
Miura, Takeshi;
(Saitama-shi, JP) ; Seita, Masaru;
(Kitaadachi-gun, JP) ; Ota, Yasuo; (Tokyo,
JP) |
Correspondence
Address: |
EDWARDS & ANGELL, LLP
P.O. BOX 9169
BOSTON
MA
02209
US
|
Assignee: |
Shipley Company, L.L.C.
Malborough
MA
|
Family ID: |
27732897 |
Appl. No.: |
10/078766 |
Filed: |
February 19, 2002 |
Current U.S.
Class: |
205/157 ;
205/291 |
Current CPC
Class: |
C25D 7/123 20130101;
C25D 3/38 20130101 |
Class at
Publication: |
205/157 ;
205/291 |
International
Class: |
C25D 003/38; C25D
007/12 |
Claims
What is claimed is:
1. An electroplating solution comprising copper ions and a
complexing agent for the copper ions and having a pH in the range
of 4 to 10.
2. An electroplating process using an electroplating solution
comprising copper ions and a completing agent for the copper ions
and having a pH in the range of 4 to 10.
3. The electroplating process according to claim 2, wherein the
plating is applied on the silicon wafer on which a conductive seed
layer has been formed.
4. A silicon wafer plated with an electroplating solution
comprising copper ions and a complexing agent for the copper ions
and having a pH in the range of 4 to 10.
Description
BACKGROUND OF THE INVENTION
[0001] 1. Field of the Invention
[0002] The present invention relates to an electroplating solution
that can provide a microdefect-free plated copper layer with
improved adherence to form Cu wiring on a silicon wafer. The
present invention also relates to a plating process using such an
electroplating solution, as well as to a silicon wafer obtained
through such a plating process.
[0003] 2. Description of the Related Art
[0004] In response to the trend toward development of electronic
devices such as personal computers with higher performance than
ever and miniaturization of these devices, a process of forming
wiring on silicon wafers has been devised and become widely used,
in which, in place of conventional aluminum wiring, a copper layer
with extremely high electroconductivity is deposited in trenches
and/or via holes formed on the silicon wafer to form wiring with
improved performance.
[0005] When it is desired to deposit the electroconductive layer in
trenches or via holes of silicone wafers to form wiring, dry
processes such as CVD and PVD including sputtering and ion plating
have been conventionally used. Drawbacks of these techniques
include low work efficiency in the dry process and unreliable Cu
wiring due to the voids that, when the Cu layer is formed by
sputtering, remain in trenches or via holes that have been
incompletely filled with copper. This incomplete filling arises
because in the dry processes, the Cu layer is formed at a
substantially faster rate at the openings of the trenches and via
holes than inside them, plugging up the openings before the
trenches and via holes have been completely filled.
[0006] For this reason, a plating technique known as copper sulfate
plating has recently been employed for forming an electroconductive
film and filling trenches and via holes in silicon wafers and
thereby form Cu wiring. While the copper sulfate plating, a wet
process, offers high work efficiency and achieves complete filling
of the trenches and via holes with copper, leaving no void, it
requires that an electroconductive layer be deposited on the
surfaces of the silicon wafers, as well as on the inner surfaces of
the trenches and via holes, prior to application of the plating,
due to the nature of the copper sulfate plating as an
electroplating technique. This surface conductive layer, which
serves as an undercoat of the plating, is commonly referred to as a
seed layer and is generally formed by CVD or PVD including
sputtering and ion plating.
[0007] Although the seed layer is generally formed to an average
thickness of 100 to 200 nm in the flat region of a silicon wafer
and to an average thickness of 10 nm on the inner sides of trenches
and via holes, the thickness can vary significantly with the
thinnest part having a thickness less than half the average
thickness.
[0008] Thus, when electroplating is applied on top of the seed
layer by using the copper sulfate plating solution, which is
strongly acidic, the seed layer often dissolves in the plating
solution at a significantly fast rate so that relatively thin parts
of the seed layer may completely dissolve upon electroplating,
which makes it difficult to ensure sufficient adhesion between the
seed layer and the plating. Moreover, as it dissolves during the
electroplating, the seed layer may be partially lost and, as a
result, copper deposition may not take place in some part in the
trenches or via holes, or, in an extreme case, electric current may
not be able to flow through the trenches or via holes due to the
missing seed layer and copper deposition may not take place at all,
resulting in defects in plating. For this reason, copper sulfate
plating cannot be applied to silicon wafers with particularly small
trenches and via holes.
[0009] In short, formation of micro patterns of wiring, an
essential requirement for improving the performance of
semiconductor devices, cannot be achieved through the use of the
copper sulfate plating solution.
[0010] Since such defects are more likely to occur in the trenches
or via holes with smaller sizes, it is difficult to design smaller
patterns on the silicon wafers. Accordingly, novel plating
techniques have been longed for that can provide copper plating
without causing deterioration of the seed layer and thus make it
possible to pursue smaller patterns on the silicon wafers and
semiconductor devices so as to improve their performances.
[0011] Electroless copper deposition, on the other hand, does not
require a highly acidic plating solution like the copper sulfate
plating solution so that the seed layer is less susceptible to the
plating solution. In this technique, however, catalysts such as
palladium must be adsorbed onto the inside of trenches or via holes
prior to plating. As a result, the heterogeneous metal may
contaminate the Cu layer that serves as wiring, lowering the
electric characteristics as well as reliability of the wiring.
Furthermore, the bath control is more difficult in the electroless
copper plating than in the electrolytic copper plating since
reducing agents would decompose while the plating solution is used.
Also, the electroless copper plating solution contains harmful
substances such as formaldehyde, which serves as a reducing agent,
and a cyanide compound, which serves as a stabilizing agent.
SUMMARY OF THE INVENTION
[0012] Accordingly, it is an objective of the present invention to
provide an efficient plating solution that can completely fill
trenches or via holes without a defect such as voids when it is
used to form copper wiring on silicon wafers. It is also an
objective of the present invention to provide a plating process
that takes advantage of such a plating solution.
[0013] In an effort to find a way to solve the above-mentioned
problems, the present inventor has found that, when copper wiring
is to be formed on silicon wafers, it is possible to fill up
trenches or via holes of the silicon wafers with copper, without
causing any defects such as void, by applying electroplating to the
silicon wafers on top of the conductive seed layer using a plating
solution that contains copper ions and a complexing agent for the
copper ions and has a pH in a predetermined range.
[0014] Accordingly, the present invention provides an
electroplating solution that contains copper ions and a complexing
agent for the copper ions and has a pH in the range of 4 to 10. The
present invention further provides a plating process using such an
electroplating solution. When the plating process of the present
invention is used to form copper wiring on a silicon wafer, the
plating is applied on the silicon wafer on which a conductive seed
layer has been formed. The present invention also provides a
silicon wafer plated with the electroplating solution of the
present invention.
BRIEF DESCRIPTION OF THE DRAWINGS
[0015] These and other objectives and advantages of the present
invention will become apparent from the following description with
reference to the accompanying drawings, wherein:
[0016] FIG. 1 is a scanning ion micrograph showing a cross-section
of via holes formed on a silicon wafer fabricated in accordance
with Example 3 of the present invention; and
[0017] FIG. 2 is a scanning ion micrograph showing a cross-section
of via holes formed on a silicon wafer fabricated in accordance
with Comparative Example.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
[0018] The present invention will now be described in further
detail.
[0019] An electrolytic copper plating solution of the present
invention contains cupper ions and a complexing agent for the
copper ions. The copper ions may be added to the electrolytic
copper plating solution in the form of salts. Any known copper salt
that can serve as a copper ion source may be used in the
electrolytic copper plating solution. In this regard, various types
of copper salts can be used to serve as the copper salt of the
present invention provided that their anions do not impose adverse
effects on the electrolytic copper plating solution.
[0020] Examples of the preferred copper salt include, but are not
limited to, copper sulfate, copper chloride, copper hydroxide,
copper acetate, copper sulfamate, copper pyrophosphate, copper
carbonate and copper oxide. Of these, copper sulfate, copper
hydroxide, copper chloride and salts of copper with the
later-described complexing agent are particularly preferred.
[0021] For example, the electrolytic copper plating solution has a
copper concentration of 0.5 to 60 g/L, preferably 5 to 20 g/L.
[0022] Alternatively, an anode may be used to serve as the source
of copper ions. Examples of the preferred anode include soluble
anodes including oxygen-free copper anodes and
phosphorus-containing copper anodes. Insoluble anodes such as
platinum, titanium, stainless, iridium oxide and graphite may also
be used.
[0023] Examples of the preferred complexing agent for use in the
present invention include any material that can form a complex with
copper ions, such as polyamine and salts thereof, aminocarboxylic
acid and salts thereof, aminealkanol compounds, oxycarboxylic acid
and salts thereof, cyclic acid-imide compounds, and organic
phosphonic acid and salts thereof.
[0024] The polyamine may be either a straight-chained or cyclic
polyamine. Examples of the straight-chained polyamine include
ethylenediamine, diethylenetriamine, diethylenetetramine and
triethylenetetramine while examples of the cyclic polyamine include
piperazine, imidazolidine and pyrazolidine. These compounds may be
provided in the forms of salts such as sulfates, chlorides,
nitrates and acetates.
[0025] Examples of the amino carboxylic acid include glycine,
iminodiacetic acid, nitrilotriacetic acid,
hydroxyethylethylenediaminetri- acetic acid,
tetrahydroxyethylenediamine, dihydroxymethylethylenediaminedi-
acetic acid, ethylenediaminetetracetic acid,
cyclohexane-1,2-diaminetetrac- etic acid,
ethyleneglycoldiethyletherdiaminetetracetic acid,
ethylenediaminetetrapropionic acid and
N,N,N',N'-tetrabis-2-(2-hydroxypro- pyl)ethylenediamine. These
compounds may be provided in the forms of salts including salts
formed with alkali metals such as sodium and potassium, and
ammonium salts.
[0026] Examples of the alkanolamine compounds include
monoethanolamine, diethanolamine and triethanolamine.
[0027] Examples of the oxycarboxylic acid include tartaric acid,
citric acid, gluconic acid, succinic acid and malic acid. These may
be provided in the forms of salts including salts formed with
alkali metals such as sodium and potassium, and ammonium salts.
[0028] Examples of the cyclic acid-imide compound include cyclic
acid-imide compounds that contains one or two nitrogen atoms in one
molecule of that compound, such as succinimide, phthalimide,
hydantoin and 5,5-dimethylhydantoin.
[0029] The organic phosphonic acid may be any compound that has a
plurality of phosphonic acid groups in one molecule of that
compound and has one of the chemical structures shown below, and
salts thereof:
[0030] Formula 1
[0031] where X.sup.1 is selected from the group consisting of
hydrogen atom, C.sub.1-5 alkyls, aryl, arylalkyl, amino, or
C.sub.1-5 alkyls substituted with hydroxyl, carboxyl (--COOH) or
phosphonic acid group (--PO.sub.3MM'); M and M' are each selected
from the group consisting of hydrogen atom, sodium, potassium and
ammonium (NH.sub.4) and may or may not be identical to one another;
and m and n are each an integer from 0 to 5;
[0032] Formula 2
[0033] where X.sup.2 is one selected from the group consisting of
--CH.sub.2--, --CH(OH)--, --C(CH.sub.3)(OH)--, --CH(COOM)-- or
--C(CH.sub.3)(COOM)--; or
[0034] Formula 3
[0035] where X.sup.3 through X.sup.7 are each independently
selected from hydrogen atom, C.sub.1-5 alkyls, aryl, arylalkyl,
amino, phosphonic acid group (--PO.sub.3H.sub.2), or C.sub.1-5
alkyls substituted with hydroxyl, carboxyl (--COOH) or phosphonic
acid group (--PO.sub.3H.sub.2), given that at least two of X.sup.3
through X.sup.7 are phosphonic acid group (--PO.sub.3H.sub.2) or
C.sub.1-5 alkyl substituted with phosphonic acid group
(--PO.sub.3H.sub.2).
[0036] The C.sub.1-5 alkyl may be either straight-chained or
branched and includes methyl, ethyl, propyl, isopropyl, butyl,
isobutyl and sec-butyl. The aryl may be phenyl or naphthyl. The
arylalkyl may be any combination of the aforementioned alkyls and
aryls.
[0037] Specific examples of the complexing agent for use with the
above-mentioned organic phosphonic acid having a plurality of
phosphonic acid groups include aminotrimethylenephosphonic acid,
1-hydroxyethylidene-1,1-diphosphonic acid,
ethylenediaminetetramethylenep- hosphonic acid,
diethylenetriaminepentamethylenephosphonic acid or salts thereof
formed with sodium, potassium or ammonium.
[0038] The complexing agent for use in the present invention may be
either a single agent or a mixture of two or more agents.
[0039] The complexing agent for use in the present invention is
used in the concentration range of, for example, 0.05 to 2.0 mol/L,
preferably 0.2 to 1.0 mol/L. It is particularly preferred that the
amount of the complexing agent be equal to or greater than that of
copper ions in the plating solution for use in the present
invention. Preferably, the molar ratio of copper ions to the
complexing agent is in the range of 1:1 to 1:25, more preferably
1:1 to 1:10 (copper ion:complexing agent). If the concentration of
the complexing agent is lower than either 0.05 mol/L or the molar
concentration of copper ion in the plating solution, the complexing
agent cannot keep copper ions in the plating solution in a stable
manner, leading to the formation of copper precipitation. On the
other hand, a concentration of the complexing agent higher than 2.0
mol/L is economically unfavorable since further increase in its
effect is hardly expected.
[0040] The electroplating solution of the present invention can be
obtained by adding an acidic or basic compound to a solution
containing the copper salt and the complexing agent to adjust the
solution to a pH of 4 to 10, preferably 7 to 10. It is particularly
important to maintain the solution in this pH range since the
dissolving rate at which the seed layer deposited in the trenches
or via holes of a silicon wafer into the plating solution can be
substantially decreased by performing plating in this pH range.
[0041] Examples of the basic compound for adjusting the pH of the
plating solution include sodium hydroxide, potassium hydroxide,
ammonium hydroxide, monoethanolamine, diethanolamine,
triethanolamine, ethylenediamine, diethylenetriamine and
triethylenetetramine, while examples of the acidic compound include
sulfuric acid, hydrochloric acid, phosphoric acid, organic sulfonic
acids, phosphonic acids and carboxylic acids. These basic compounds
and acidic compounds may or may not be the same as the
above-mentioned complexing agents.
[0042] When necessary, a brightener is added to the electroplating
solution of the present invention in order to improve
characteristics of the electroplating solution and film
characteristics of the deposits. Any known material that has been
conventionally used in copper plating can be used as the
brightener. Examples thereof include sulfur compounds such as
sulfides and thio-compounds and nitrogen-containing heterocyclic
compounds that are soluble in the plating solution.
[0043] A wetting agent may be added to the electroplating solution
of the present invention in order to improve wetting
characteristics of articles to be plated. Any known material that
has been conventionally used in copper plating can be used as the
wetting agent. Examples of such material include nonionic
surfactants, anionic surfactants, cationic surfactants and
amphoteric surfactants. The cationic surfactants and the amphoteric
surfactants to serve as the wetting agent may or may not be the
same material as the above-described additives or the complexing
agents.
[0044] While the electrolytic copper plating solution of the
present invention has a substantially high conductivity, a
conductive salt may further be added if necessary. Examples of the
conductive salt include sulfates, organic sulphonates, phosphates
and salts of carboxylic acids.
[0045] If necessary, any known additive may be added to the
electrolytic copper plating solution of the present invention.
[0046] While the electroplating solution of the present invention
and the electroplating process using the same plating solution may
be used in practically any electroplating application, they are
particularly useful for electroplating silicon wafers, especially
those with trenches and via holes. The term "trench" as used herein
means a groove formed on a silicon wafer and may be of any
cross-sectional shape such as rectangular, square or trapezoidal
shape. A trench can be characterized by its aspect ratio, which is
given by the depth divided by the width of the trench. Preferably,
a trench has an aspect ratio of 0.1 to 30, particularly 0.5 to
10.
[0047] The term "via hole" as used herein means a hole formed on a
wafer and may be formed as a blind hole with one end closed. While
a via hole may be of any cross-sectional shape, it preferably has a
rectangular or trapezoidal cross-sectional shape. A via hole
generally has a diameter of 0.05 to 1.0 .mu.m while one with the
diameter of 0.15 to 0.5 .mu.m is particularly preferred.
[0048] Trenches or via holes can be formed on silicon wafers by
using dry etching techniques such as reactive ion etching (RIE) and
plasma etching.
[0049] A barrier layer may be provided on the surface of silicon
wafers, trenches or via holes. The purpose of the barrier layer is
to prevent the deposited copper from dispersing on the surface of
the silicon wafer to alter the semiconductor characteristics. The
barrier layer can be formed on the surface of the silicon wafer, or
inside the trenches or via holes, by depositing a layer of Ti, TiN,
Ta, TaN, W and WN using PVD techniques including sputtering and ion
plating or CVD techniques.
[0050] A conductive seed layer is deposited on the surface of
silicon wafer, or inside the trenches or via holes, prior to
application of electrolytic copper plating. The seed layer is
formed by depositing a layer of a highly conductive metal (e.g.,
copper) using PVD techniques such as sputtering and ion plating or
CVD techniques. While the seed layer may be of any thickness, the
layer that is 1 nm thick is sufficient to be formed inside the
trenches or via holes.
[0051] When the electrolytic copper plating is applied in the
trenches or via holes of a silicon wafer, the trenches or via holes
may be filled completely with copper using the electrolytic copper
plating solution of the present invention, or they may first be
filled halfway and then applied with a highly acidic or highly
basic copper plating solution to be filled completely. The
electrolytic copper plating solution of the present invention
reinforces the seed layer and adds thickness to the seed layer
within the trenches or via holes of silicon wafers so that a highly
acidic or highly basic copper plating solution, which would
otherwise corrode the seed layer, can be used to plate the silicon
wafer.
[0052] In the present invention, electrolysis is carried out at a
temperature of 10 to 70.degree. C., preferably 20 to 40.degree. C.
Sufficient conductivity cannot be obtained if the temperature is
lower than, or equal to, 10.degree. C., whereas decomposition of
the complexing agent unfavorably accelerates at temperatures higher
than, or equal to, 70.degree. C.
[0053] In the present invention, electrolysis is carried out at a
cathode current density of 0.1 to 4.0 A/dm.sup.2, preferably 0.5 to
2.0 A/dm.sup.2. If the cathode current density is excessively
small, it takes considerable amount of time to achieve the plated
layer of desired thickness, reducing productivity, whereas if the
cathode current density is excessively large, copper deposits
cannot be obtained as desired since copper ions are depleted at the
surface of the cathode, especially within the trenches and via
holes.
[0054] While a general-purpose DC power source can be used to apply
plating using the plating solution of the present invention, a
pulse power source or a PR power source is particularly effective
in improving uniformity of electroplating. Current-reverse
electrolysis, which switches polarity faster than the conventional
PR electrolysis, is also effective.
[0055] Unlike the conventional sulfuric acid copper plating
solution, which is highly acidic, the electrolytic copper plating
solution of the present invention has a pH ranging from weakly
acidic to weakly basic pH (pH 4-10), preferably from neutral to
weakly basic pH (pH 7-10). For this reason, the electrolytic copper
plating solution of the present invention makes it possible to fill
the trenches or via holes with copper without causing any defects
such as voids while minimizing damage to the seed layer formed on a
silicon wafer, which is susceptible to highly acidic conditions.
Accordingly, copper wiring is achieved using defect-free trenches
or via holes.
EXAMPLES
[0056] The present invention will now be described with reference
to Examples and Comparative Examples in further detail. Examples
and Comparative Examples are only illustrative and are not intended
to limit the scope of the invention in any way.
[0057] A typical process of the present invention involves
following steps:
[0058] 1. formation of trenches and via holes.
[0059] 2. deposition of a TaN barrier layer using sputtering
technique.
[0060] 3. deposition of a Cu seed layer using sputtering
technique.
[0061] 4. application of electrolytic copper plating in accordance
with the present invention, the pH of which ranges from weakly
acidic to weakly basic.
Example 1
A Weakly Acidic Plating Solution 1 in Accordance with the Present
Invention
[0062]
1 Cu ions 10 g/L (added as copper sulfate) citric acid 0.25 mol/L
potassium hydroxide 45 g/L pH 4.5 temperature 25.degree. C. current
density 0.5 A/dm.sup.2 time 10 min.
Example 2
A Weakly Acidic Plating Solution 2 in Accordance with the Present
Invention
[0063]
2 Cu ions 10 g/L (added as copper sulfate) ethylenediamine 0.5
mol/L sulfuric acid 20 g/L pH 5.0 temperature 25.degree. C. current
density 0.5 A/dm.sup.2 time 10 min.
Example 3
A Weakly Basic Plating Solution 1 in Accordance with the Present
Invention
[0064]
3 Cu ions 10 g/L (added as copper sulfate)
hydroxyethylethylenediaminetriacetic acid 0.15 mol/L
triethanolamine 0.65 mol/L pH 8.4 temperature 25.degree. C. current
density 0.5 A/dm.sup.2 time 10 min.
Example 4
A Weakly Basic Plating Solution 2 in Accordance with the Present
Invention
[0065]
4 Cu ions 10 g/L (added as copper acetate) aminotri
(methylenephosphonic acid) 0.5 mol/L potassium hydroxide 90 g/L pH
9.0 temperature 25.degree. C. current density 0.5 A/dm.sup.2 time
10 min.
Example 5
A Weakly Basic Plating Solution 3 in Accordance with the Present
Invention
[0066]
5 Cu ions 15 g/L (added as copper hydroxide)
1-hydroxyethylene-1,1-diphosphonic acid 0.5 mol/L potassium
hydroxide 110 g/L pH 9.6 temperature 25.degree. C. current density
0.5 A/dm.sup.2 time 10 min.
Example 6
A Weakly Basic Plating Solution 4 in Accordance with the Present
Invention
[0067]
6 Cu ions 15 g/L (added as copper acetate) ethylenediaminetetra
(methylenephosphonic acid) 0.5 mol/L aqueous ammonia (35%) 100 mL/L
pH 7.4 temperature 25.degree. C. current density 0.5 A/dm.sup.2
time 10 min.
Comparative Example
[0068] 1. formation of trenches and via holes.
[0069] 2. deposition of a TaN barrier layer using sputtering
technique.
[0070] 3. deposition of a Cu seed layer using sputtering
technique.
[0071] 4. application of copper sulfate plating.
[0072] Plating Solution A Copper Sulfate Plating Solution of Known
Composition
7 Cu ions 17.5 g/L (added as copper sulfate) sulfuric acid 175 g/L
Cl ions 50 mg/L Additive 5 mL/L pH 1 or less temperature 25.degree.
C. current density 1 A/dm.sup.2 time 5 min.
[0073] Evaluation Test 1 Dissolving Rate of Seed Layer.
[0074] Small pieces of a silicon wafer with a deposited seed layer
were immersed in the plating solutions. The thickness of the seed
layer was measured for each piece using a fluorescent X-ray film
thickness meter, and the dissolving rate of the seed layer was
determined from the decrease in thickness.
[0075] Temperature of plating solution: 25.degree. C.
[0076] Immersion time: 10 min.
[0077] Solution: not stirred
[0078] Measurement was taken by fluorescent X-ray film thickness
meter. Average of five measurements was taken.
[0079] Seed layer: made of copper; formed by sputtering to a
thickness of 100 nm.
8TABLE 1 Results Dissolving rate of seed layer Weakly acidic copper
plating 0.3 nm/min. bath 1 of the present invention Weakly acidic
copper plating 0.7 nm/min. bath 2 of the present invention Weakly
basic copper plating 0.3 nm/min. bath 1 of the present invention
Weakly basic copper plating 0.9 nm/min. bath 2 of the present
invention Weakly basic copper plating 0.8 nm/min. bath 3 of the
present invention Weakly basic copper plating 0.5 nm/min. bath 4 of
the present invent ion Copper sulfate plating bath 2.5 nm/min.
[0080] Evaluation Test 2: Test for Plating Applied to via Holes on
a Silicon Wafer.
[0081] Copper plating was applied to the silicon wafer having via
holes by the above-described steps. It was observed that the via
holes were filled with copper. The via holes, the barrier layer and
the seed layer were formed under the same conditions for all of
Examples and Comparative Example.
[0082] Via hole size: 0.35 .mu.m in diameter, 1.6 .mu.m in
depth.
[0083] Barrier layer: made of TaN; formed by sputtering.
[0084] Seed layer: made of copper; formed by sputtering.
[0085] Observation: Silicon wafer was cut by a focused ion beam
(FIB), and the cross-section was observed using scanning ion
microscopy (SIM).
9TABLE 2 Results Plating bath Degree of via Occurrence of used hole
filling defects Example 1 Weakly acidic Completely 0/5 bath 1
filled Example 2 Weakly acidic Completely 0/6 bath 2 filled Example
3 Weakly basic Completely 0/5 bath 1 filled Example 4 Weakly basic
Completely 0/6 bath 2 filled Example 5 Weakly basic Completely 0/6
bath 3 filled Example 6 Weakly basic Completely 0/6 bath 4 filled
Comparative Copper sulfate Seed layer was 6/6 Example 1 bath lost
and no copper deposits formed at the bottom of via holes.
[0086] It has been made clear from the results of Examples 1 to 6
according to the present invention that, through the use of the
method of the present invention, the seed layer was prevented from
dissolving into the plating solution and copper wiring can be
provided by filling trenches or via holes of silicon wafers with
copper in a defect-free manner.
[0087] On the other hand, the seed layer dissolved in the plating
solution in Comparative Example, in which a copper sulfate solution
was used. Thus, it has been shown that via holes cannot be filled
with copper through this process.
[0088] While there has been described what are at present
considered to be preferred embodiments of the present invention, it
will be understood that various modifications may be made thereto,
and it is intended that the appended claims cover all such
modifications as fall within the true spirit and scope of the
invention.
* * * * *