U.S. patent application number 10/793735 was filed with the patent office on 2004-09-02 for methods of polishing, interconnect-fabrication, and producing semiconductor devices.
This patent application is currently assigned to Renesas Technology Corporation. Invention is credited to Homma, Yoshio, Kondo, Seiichi, Sakuma, Noriyuki.
Application Number | 20040171264 10/793735 |
Document ID | / |
Family ID | 18733721 |
Filed Date | 2004-09-02 |
United States Patent
Application |
20040171264 |
Kind Code |
A1 |
Kondo, Seiichi ; et
al. |
September 2, 2004 |
Methods of polishing, interconnect-fabrication, and producing
semiconductor devices
Abstract
The present invention provides a technique to reduce and
suppress scratches and delamination, to suppress and control the
development of dishing and erosion, and to polish at high polishing
rate. Polishing is performed using a polishing solution, which
contains an oxidizer, phosphoric acid, organic acid, a chemical to
form inhibition layer, and water.
Inventors: |
Kondo, Seiichi; (Leuven,
BE) ; Sakuma, Noriyuki; (Hachioji, JP) ;
Homma, Yoshio; (Hinode, JP) |
Correspondence
Address: |
Stanley P. Fisher
Reed Smith Hazel & Thomas LLP
3110 Fairview Park Drive, Suite 1400
Falls Church
VA
22042-4503
US
|
Assignee: |
Renesas Technology
Corporation
|
Family ID: |
18733721 |
Appl. No.: |
10/793735 |
Filed: |
March 8, 2004 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
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10793735 |
Mar 8, 2004 |
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10396410 |
Mar 26, 2003 |
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6750128 |
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10396410 |
Mar 26, 2003 |
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09828919 |
Apr 10, 2001 |
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6562719 |
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Current U.S.
Class: |
438/691 ;
438/692 |
Current CPC
Class: |
H01L 21/3212 20130101;
C09G 1/02 20130101; H01L 21/7684 20130101; B24B 37/044
20130101 |
Class at
Publication: |
438/691 ;
438/692 |
International
Class: |
H01L 021/302; H01L
021/461 |
Foreign Application Data
Date |
Code |
Application Number |
Aug 4, 2000 |
JP |
2000-242750 |
Claims
What is claimed is:
1. A method for producing at least one semiconductor device,
comprising the steps of preparing a base material having an
impurity doping layer; forming an insulating film having an opening
on the impurity doping layer; forming a barrier metal film on the
insulating film; forming a Cu film on the barrier metal film;
polishing the Cu film using a first polishing solution comprising
an oxidizer, a phosphoric acid, a lactic acid, and an inhibitor
comprising anti-corrosive agent; exposing the barrier metal film,
upon said polishing, by mechanically scrubbing the Cu film;
polishing the barrier metal film using a second polishing solution
comprising an abrasive powder; and exposing the insulating film by
mechanically scrubbing the barrier metal film.
2. The method of claim 1, further comprising: washing the base
material after said exposing the insulating film by mechanically
scrubbing the barrier metal film; and drying the washed base
material.
3. A method for producing at least one semiconductor device,
comprising the steps of preparing a base material having thereon an
interconnect layer; forming an insulating film having an opening
wherethrough the interconnect layer is exposed; forming a barrier
metal film on the base material whereon the insulating film is
formed; forming a Cu film on the barrier metal film; polishing the
Cu film using a first polishing solution comprising an oxidizer, a
phosphoric acid, a lactic acid, an inhibitor comprising
anti-corrosive agent, and water; exposing the barrier metal film by
mechanically scrubbing the Cu film; polishing using a second
polishing solution comprising an abrasive powder; exposing the
insulating film by mechanically scrubbing at least one of the Cu
film and the barrier metal film; washing the base material; and
drying the washed base material.
4. A method for producing at least one semiconductor device,
comprising the steps of preparing a base material having thereon a
metal interconnect layer; forming an insulating film having an
opening on the metal interconnect layer; forming a barrier metal
film on the base material whereon the insulating film is formed;
forming a Cu film on the barrier metal film; polishing using a
first polishing solution comprising hydrogen peroxide, phosphoric
acid, lactic acid, and an inhibitor comprising anti-corrosive
agent; mechanically scrubbing the Cu film upon said polishing using
a first polishing solution; polishing using a second polishing
solution after said mechanically scrubbing the Cu film;
mechanically scrubbing the Cu film and the barrier metal film after
said polishing using the second polishing solution; washing the
base material; and drying the washed base material.
5. The method of claim 4, wherein the second polishing solution
comprises an abrasive powder.
Description
PRIORITY TO FOREIGN APPLICATIONS
[0001] This application claims priority to Japanese Patent
Application No. P2000-242750.
BACKGROUND OF THE INVENTION
[0002] 1. Field of the Invention
[0003] The present invention relates to polishing of a metal film,
and in particular, to a method of polishing in an
interconnect-fabrication process for producing semiconductor
devices.
[0004] 2. Description of the Background
[0005] In recent years, with rapid progress and development in the
techniques available to produce semiconductor integrated circuits,
such as large scale semiconductor integrated circuits (hereinafter
referred as "LSI"), with greater integration and improved
performance characteristics, new techniques for fabrication have
been developed. One of these techniques is chemical-mechanical
polishing (hereinafter referred as "CMP"), which is a technique
frequently used in processes such as LSI manufacturing--in
particular, CMP is used in the flattening of an inter-layer
insulating film, the formation of metal plug, and the formation of
buried interconnect layer in the process to form a multi-level
interconnection. This technique is disclosed, for example, in U.S.
Pat. No. 4,944,836.
[0006] Further, attempts have been made in recent years to utilize
copper (Cu) alloy with low resistance as the material for
interconnection, rather than the aluminum (Al) alloy used in the
past, with the purpose of producing high-performance LSIs. However,
for Cu alloy, it is difficult to carry out fine fabrication based
on dry etching methods, which methods have been frequently used for
the formation of Al alloy interconnects. For this reason, the
"damascene" method has been primarily adopted, wherein a Cu alloy
thin film is deposited on an insulating film formed with grooves
fabricated thereon, and the Cu alloy thin film other than that
buried in the grooves is removed by CMP, and buried interconnect is
thereby prepared. This technique is disclosed, for example, in
JP-A-2-278822. It is generally practiced to place a barrier metal
film, such as a titanium nitride (TiN) film, a tantalum (Ta) film
or a tantalum nitride (TaN) film, of several tens of nm in
thickness, for the purposes of improving adhesive properties and of
providing Cu diffusion barrier between the Cu alloy thin film and
the insulating film.
[0007] In the past, the polishing solutions used in CMP, for metal
films such as the Cu alloy commonly used for interconnects,
generally contained abrasive power and oxidizer (oxidizing
chemicals) as the main components. The basic CMP mechanism is
oxidization of the surface of a metal film by the oxidizing action
of the oxidizer, and the mechanical removal of the oxides by the
abrasive powder. This technique is disclosed, for example, in "The
Science of CMP" (edited by Masahiro Kashiwagi; published by Science
Forum Co., Ltd.; Aug. 20, 1997, p.299)
[0008] Abrasive powders, such as alumina abrasive powder or silica
abrasive powder, of several tens to several hundreds of nm in grain
diameter, are known in the art. Most types of abrasive powder for
metal CMP that are commercially available are alumina type
powders.
[0009] As the oxidizer, hydrogen peroxide (H.sub.2O.sub.2), ferric
nitrate (Fe(NO.sub.3).sub.3), and potassium periodate (KIO.sub.3)
are generally used. These are described, for example, in "The
Science of CMP" (pp.299-300). Among these substances, hydrogen
peroxide has been more frequently used in recent years, due to the
fact that it does not contain metal ions.
[0010] However, when interconnects and/or plugs are fabricated
using the polishing solution, which contains an abrasive powder for
conventional type metal CMP as the main component, the following
problems occur:
[0011] (1) Development of dishing (depression on interconnect) and
erosion (corrosion.And scraping of the insulating film on the
peripheral portion of the interconnect);
[0012] (2) Development of scratches (polishing scratches);
[0013] (3) Delamination;
[0014] (4) The need to remove abrasive powder by ishing after
CMP;
[0015] (5) High cost for abrasives;
[0016] (6) High cost for abrasive supply system and iste liquid
processing system; and
[0017] (7) Dust in clean room originated from CMP system.
[0018] The above problems are caused by the fact that CMP is
performed using abrasive powder. In the conventional CMP methods,
however, the abrasive powder is needed to quickly remove oxide
layers formed by the oxidizer. If abrasive powder is not added,
it.is not possible to reach a polishing rate (i.e. a polishing
speed) that is suitable for practical use.
[0019] In contrast, JP-A-11-135466 discloses a method for polishing
metal film using a polishing solution not containing abrasive
powder, and for fabricating a buried interconnect structure.
According to this method, using a polishing solution containing an
oxidizer, a substance to turn the oxides to water-soluble, water
and, if necessary, an anti-corrosive substance (for forming
inhibition layer), the surface of the metal film is mechanically
scrubbed, and a buried metal interconnect can be prepared on the
surface. For example, a Cu interconnect is produced using an
abrasive-free polishing solution, which contains hydrogen peroxide,
citric acid, and benzotriazole (hereinafter referred as "BTA").
[0020] The problems (1) to (7) described hereinabove may be solved
when the above abrasive-free polishing solution method is used,
while a acceptable polishing rate (speed) under normal polishing
conditions of 80-150 nm/min is maintained. Even when high polishing
load of 300 g/cm.sup.2 or more is applied, the polishing rate
reaches the saturation level and does not go beyond 200 nm/min, and
thus it is not possible to increase the throughput beyond this
limit. In the case wherein a commercial alumina polishing solution
is used, a polishing rate as high as 300-500 nm/min may be reached
by applying a high polishing load. In this case, however, the
problems of scratches and delamination become more serious.
[0021] On the other hand, a number of different approaches to these
difficulties are available. One such approach is presented in
JP-A-7-94455, which discloses a phosphoric acid aqudous solution as
one of abrasive polishing solutions for Cu (see Example 4 of the
above publication). It is described therein that the ratio of
polishing rate of Cu to the insulating film can be increased up to
14.5 by using the abrasive polishing solution containing phosphoric
acid of 3% concentration (see FIG. 5 of the above publication,
wherein the Cu content is 100%). However, using experimentation, it
is very difficult to attain a polishing rate of 50 nm/min. or more
under practical polishing condition (i.e. polishing load of 500
g/cm.sup.2 or less; rotational speed of platen at 90 rpm or less)
by the simple combination of abrasive powder and phosphoric acid
aqueous solution. If the abrasive powder is removed, the polishing
rate is less than 20 nm/min. Therefore, although the ratio of
polishing rate is high using this abrasive polishing solution, it
is not possible to carry out polishing with a sufficient throughput
and high accuracy (without developing erosion).
[0022] In the abrasive polishing solution for tungsten CMP
disclosed in JP-A-10-265776, phosphoric acid or organic acid is
used as a stabilizer. In this case, the stabilizer is a chemical to
suppress and control the reaction between a catalyst (ferric
nitrate) added in the polishing solution, and the oxidizer
(hydrogen peroxide). According to experimentation, an etching rate
for Cu of this polishing solution is more than 100 nm/min, and,
using this solution, it is possible to polish Cu film, but a Cu
interconnect is eliminated by the etching. This polishing solution
is specifically directed to tungsten CMP and is not generally
applicable for Cu-CMP. Thus, using the teachings of JP-A-10-265776,
it is not possible to achieve high-speed polishing of Cu by
simultaneously adding phosphoric acid and organic acid (in
particular, lactic acid) to the polishing solution not containing
abrasive powder.
[0023] A polishing solution for Cu-CMP is disclosed in
JP-A-11-21546. This polishing solution includes abrasive powder, an
oxidizer (e.g. urea--hydrogen peroxide), a chemical to form complex
salt (e.g. ammonium oxalate or organic acid such as lactic acid), a
film forming agent (e.g. BTA, imidazole), and a surface active
agent. It is described in the above patent publication that
inorganic acid, such as phosphoric acid, may be added in order to
adjust the pH value of the polishing solution, or to promote the
polishing rate of the barrier metal film. The surface active agent
as described in this publication is used to reduce or suppress
setting, agglutination and decomposition of the abrasive powder. By
experimentation, it is practically difficult to polish Cu film
using the polishing solution when the abrasive powder is removed
from the polishing solution described in the above publication.
That is, in this polishing solution, it is essential to
mechanically remove Cu oxides via the abrasive powder. Thus, using
the teachings of this publication, it is not possible to achieve
high-speed polishing of Cu by simultaneously adding phosphoric acid
and organic acid (in particular, lactic acid) using the polishing
solution not containing abrasive powder as a main component.
[0024] A polishing solution not containing abrasive powder is
disclosed in JP-A-52-21222 as a chemical polishing solution to be
used for Cu ornaments on camera components. The polishing solution
comprises a surface active agent, hydrogen-peroxide, sulfuric acid,
and phosphoric acid, and this teaching provides improved luster by
polishing a Cu surface using emery abrasive paper with abrasive
powder attached on it. The surface active agent has an effect to
provide better luster by improving wettability of the polishing
surface. According to experimentation, the etching rate of the
polishing solution is 1000 nm/min. or more, and it is not possible
to use this as the polishing solution for fabricating a buried Cu
interconnect on the level of several hundreds of nm.
[0025] JP-A-55-47382 and JP-A-6-57455 each disclose a polishing
solution not containing abrasive powder. The former is a chemical
polishing solution used for deburring of machine components made of
aluminum. It comprises an acid (including phosphoric acid) and
aluminum chelating agent of aromatic compound. A surface active
agent and hydrogen peroxide are added when necessary. The latter is
a chemical polishing solution for pretreatment in the plating of
brass, and it includes hydrogen peroxide, oxy-quinoline, a chemical
to form complex salt, and a surface active agent. Phosphoric acid
and sulfuric acid are added when necessary, and it is used for
adjusting luster or satin finish. The surface active agent is added
for the purposes of improving the wettability and of preventing
mist caused by bubbling. In any of these chemical polishing
solutions, the etching rate is 100 nm/min. or more, and these are
the polishing solutions for polishing (without scrubbing) based on
etching action. Therefore, these are not suitable for the use as
the polishing solutions to fabricate the buried Cu interconnect of
the present invention. As the polishing solution used for the
buried interconnect of LSI, it is necessary to provide surface
flatness on the level of nanometer. The required level of flatness
(i.e. luster) should be higher than the luster level achievable by
these polishing solutions.
[0026] A preferred etching rate for Cu of a polishing solution is
less than 10 nm/min. The reasons are as follows: The thickness of
the interconnect layer of a semiconductor device, to which the
polishing solution is applied, is generally 300-1000 nm. Where the
polishing is performed for several minutes, and where a polishing
solution with an etching rate of about 100 nm is applied, for
example, the Cu on the interconnect layer may be etched as deep as
several hundreds of nm. That is, dishing may reach several hundreds
of nm in depth. In order to suppress the dishing to several tens of
nm, the etching rate of the polishing solution is preferably
limited to less than 10 nm. Further, if over-polishing time is
taken into account, it is preferably less than 1 nm/min.
[0027] The addition of anti-corrosive agent to the polishing
solution has been already disclosed with the purpose of suppressing
the etching. A method to add an anti-corrosive agent such as BTA,
imidazole, or benzimidazole to the polishing solution for Cu is
disclosed in patent publications such as JP-A-11-21546,
JP-A-8-83780, and JP-A-10-116804. However, in all of these cases,
the method described is the addition of anti-corrosive agent to the
polishing solution containing abrasive powder. It has been asserted
that a sufficient polishing rate cannot be obtained if an
anti-corrosive agent is added to a polishing solution not
containing abrasive powder. JP-A-11-135466 disclosed that Cu could
be polished if BTA is added to an abrasive-free polishing solution.
However, it has been asserted that it is not practical to add an
anti-corrosive agent having higher anti-corrosive property than BTA
to a polishing solution, because the polishing rate, as well as the
etching rate, would be reduced or suppressed.
[0028] Therefore, the need exists for a polishing method and a
method for producing semiconductor devices, by which it is possible
to solve the problems (1) to (7) hereinabove in the process to
fabricate a buried metal interconnect, and to achieve high-speed
polishing rate (700 nm/min. or more) with improved etch rate
control.
SUMMARY OF THE INVENTION
[0029] To overcome the difficulties mentioned hereinabove, it is an
object of the present invention to provide a polishing method, and
a method for producing semiconductor devices, by which it is
possible to solve problems (1) to (7) hereinabove in the process to
fabricate a buried metal interconnect, and to achieve high-speed
polishing rate (700 nm/min. or more) with improved etch rate
control.
[0030] The above object is attained by the method for polishing a
metal film, comprising the steps of using a polishing solution
which contains an oxidizer, phosphoric acid, organic acid, a
chemical to form inhibition layer, and water, and of mechanically
scrubbing surface of the metal film.
[0031] Phosphoric acid has an effect to efficiently turn oxides (on
the surface of the metal film oxidized by an oxidizer) into
water-soluble state. A representative example of the phosphoric
acid used is orthophosphoric acid. Unless otherwise specified,
orthophosphoric acid is referred hereinafter as hosphoric acid. In
addition to orthophosphoric acid, the following substances may be
used: phosphorous acid (phosphonic acid), hypophosphorous acid
(phosphinic acid), metaphosphoric acid, polyphosphoric acid (e.g.
diphosphoric acid (pyrophosphoric acid)), or substances containing
the phosphoric acid group. Among these substances, orthophosphoric
acid and phosphorous acid have the highest effect to increase the
polishing rate. Also, orthophosphoric acid is advantageous in that
it is chemically stable and low in cost. Phosphorous acid and
hypophosphorous acid are advantageous in that each is less harmful
in the polishing solution as compared to orthophosphoric acid.
Orthophosphoric acid and phosphorous acid are advantageous in that
each is less stimulant and irritant as compared to hypophosphorous
acid or metaphosphoric acid. Phosphorous acid is advantageous in
that surface roughness is caused on the polishing surface less
frequently as compared to orthophosphoric acid.
[0032] Organic acid has an effect to act on the surface of the
metal film, together with phosphoric acid, and to efficiently turn
the metal oxides to water-soluble. Compared with the case wherein
the phosphoric acid or the organic acid as mentioned hereinabove is
added alone, polishing performance can be improved further if the
two are used together. Among the organic acids, carboxylic acid, or
hydrocarboxylic acid containing hydroxyl group or carboxyl group,
have the effect of increasing the polishing rate. For example, the
following substances may be used: organic acid, such as citric
acid, malic acid, malonic acid, succinic acid, tartaric acid,
phthalic acid, maleic acid, fumaric acid lactic acid
(.alpha.-hydroxypropionic acid or .beta.-hydroxypropionic acid),
pimelic acid, adipic acid, glutaric acid, oxalic acid, salicylic
acid, glycolic acid, tricarballylic acid, benzoic acid, formic
acid, acetic acid, propionic acid, butyric acid, valeric acid,
acrylic acid, and salts of these acids. The salt has an effect to
increase solubility. These chemicals may be used in combinations of
two or more.
[0033] Among these acids, it is preferable to use the following
substances as the organic acid added to the polishing solution of
the present invention to achieve high polishing rate and low
etching rate: malonic acid, tartaric acid, malic acid, citric acid,
succinic acid, maleic acid, fumaric acid, glycolic acid,
tricarballylic acid, lactic acid (.alpha.-hydroxypropionic acid or
.beta.-hydroxypropionic acid).
[0034] Among the above acids, lactic acid (.alpha.-hydroxypropionic
acid) is commonly used as a food additive. It has low toxicity, is
less harmful as a waste liquid, has no offensive odor, has high
solubility in water, and can be produced at low cost. Additionally,
lactic acid has a large effect to increase the polishing rate, and
serves as a solvent for the anti-corrosive agent discussed
hereinbelow. Thus, it is the most desirable substance to be used as
the organic acid in the polishing solution of the present
invention.
[0035] As a substance to suppress excessive oxidation or etching of
the metal film, it is effective to use a chemical to form an
inhibition layer. On order to form the inhibition layer, a chemical
is used that has an effect to decrease the etching rate of the
metal to be polished when it is added to the polishing solution,
thus making it possible to suppress the development of dishing on
Cu interconnect, which may occur after the interconnect
fabrication. Before the chemical to form inhibition layer is added
to the polishing solution of the present invention, the etching
rate is more than 50 nm/min. That is, it is a polishing solution
having essentially a high corrosive property. By adding the
chemical to form the inhibition layer to the polishing solution, an
anti-corrosive effect can be provided, and thus the present
invention is thereby made suitable for the use as the polishing
solution for CMP. More concretely, it is preferable to obtain an
etching rate of less than 10 nm/min.
[0036] As the chemical to form the inhibition layer, an
anti-corrosive agent to Cu alloy is the most preferable. The
following substances may be used: BTA, imidazole, benzimidazole,
naphthotriazole, benzothiazole, or a derivative of these
substances. Imidazole is suitable because it has high solubility in
water. Imidazole derivative is suitable because its solubility can
be increased by lactic acid and it can increase the polishing rate
for Cu. BTA derivative is suitable because it can suppress the
etching rate for Cu.
[0037] As the BTA derivative, the following substances may be used:
4-methyl-1.H-benzotriazole, tolyltriazole,
4-carboxyl-1.H-benzotriazole, 5-methyl-1.H-benzotriazole,
tolyltriazole, benzotriazole butyl ester,
5-chloro-1.H-benzotriazole, 1-chlorobenzotriazole, 1-hydroxybenzo-
triazole, 1-dihydroxybenzotriazole, 2,3-dicarboxylpropyl
benzotriazole, 4-hydroxybenzotriazole, 4-carboxyl-1.H-benzotriazole
methyl ester, 4-carboxyl-1.H-benzotriazole butyl ester,
4-carboxyl-1.H-benzotriazole octyl ester, 5-hexyl benzotriazole,
[1,2,3-benzotriazolyl-1-methyl][1,2,4-
-triazolyl-1-methyl][2-ethylhexyl]amine,
5,6-dimethyl-1.H-benzotriazole, etc.
[0038] As the imidazole derivative, the following substances may be
used: 4-methylimidazole, 4-methyl-5-hydroxymethyl- imidazole,
1-phenyl-4-methylimidazole, 1-(p-tolyl)-4-methylimidazole,
long-chain alkyl imidazole, etc.
[0039] As the benzimidazole derivative, the following substances
may be used: 2-mercapto benzimidazole,
2-(n-methylpropyl)-benzimidazole (n=1, 2),
2-(n-methylbutyl-benzimidazole (n=1, 2, 3),
2-(1-ethylpropyl)-benzimi- dazole,
2-(1-ethylpropyl)-methylbenzimidazole, 2-n-alkyl-methylbenzimidazo-
le, 2-(4-butylphenyl)-benzimidazole,
2-phenylmethyl-methylbenzimidazole, 2-cycloalkyl-benzimidazole,
etc.
[0040] As the benzthiazole derivative, 2-mercapto benzthiazole,
2,1,3-benzthiazole, etc. may be used.
[0041] As the other anti-corrosive agent, the following substances
may be used: benzofuroxan, o-phenylenediamine, M-phenylenediamine,
catechol, o-aminophenol, 2-mercapto benzooxazole, melamine,
thiourea, etc.
[0042] It is very effective to add a solvent for increasing
solubility of the chemical to form the inhibition layer in the
polishing solution. In a case wherein the temperature of the
polishing solution is decreased to nearly 0 degrees Celsius, or in
the case wherein the other additive is added, the solubility of the
chemical to form the inhibition layer is decreased to lower
than.the solubility in pure water, and thus it may be crystallized
and deposited in the polishing solution. Thus, it is preferable
that it is set to a solubility more than twice as high as the
solubility in pure water at room temperature. For example, in a
case wherein BTA is used as the chemical to form the inhibition
layer, the solubility of BTA is increased by more than two times by
adding methanol of about 1% to the polishing solution. The same
effect can be obtained by adding ethanol or isopropyl alcohol,
ethylene glycol, polyethylene glycol, methyl ethyl ketone, or
heptanol. Also, hydroxy acid such as lactic acid, citric acid, etc.
has an effect to increase the solubility. In particular, it is more
preferable to use lactic acid than citric acid because lactic acid
can provide a greater increase the polishing rate. However, in some
cases, citric acid is more preferable in view of the increase of
solubility.
[0043] As the other chemical to form inhibition layer, a surface
active agent or a thickener may be used. These polymers are
adsorbed on interface between the polishing solution and the metal
during CMP, and form a polymer inhibition film. This has an effect
to suppress the etching. Because these substances are not
selectively adsorbed.on Cu, it is suitable for general-purpose
application.
[0044] Among these polymers, it is more preferable to use the
polymer containing carboxyl group for the purpose of improving the
polishing rate on the metal. For example, polyacrylic acid,
polymethacrylic acid and ammonium salt of these acids,
triethanolamine salt, monoethanolamine salt, triethylamine salt,
diisopropanolamine salt, etc. may be used.
[0045] A polymer having higher molecular weight provides a greater
effect to form inhibition layer. In particular, a ladder polymer
having a high thickening effect has an effect to increase the
polishing rate. For example, crosslinking type polyacrylic acid,
and its salt, are suitable for this purpose.
[0046] Among the surface active agents are polymers having
anti-bacterial or anti-fungal effect. These polymers have the
effect to increase the polishing performance, and are useful to
prevent the growth of fungi or bacteria in the polishing solution
during storage, or in iste liquid. For example, cetyl pyridinium
chloride may be used for this purpose.
[0047] When two types of the chemicals to form the inhibition layer
are mixed and used, it is possible to increase the polishing rate
more than the case wherein these are separately used. For example,
anti-corrosive agent and surface active agent, or anti-corrosive
agent and thickener may be used in combination. More concretely, a
substance is selected from a first group, which comprises BTA,
imidazole and a derivative of these substances, and a substance is
selected from a second group, which comprises polyacrylic acid,
crosslinking type polyacrylic acid or ammonium salt and cetyl
pyridinium chloride. Then, these two types of substances are used
in combination.
[0048] The oxidizer is a substance having an effect to oxidize the
surface of the metal film to be polished. Hydrogen peroxide is the
most suitable, because it contains no metallic component. Also,
nitric acid, ferric nitrate, or potassium periodate may be used,
because these have sufficient oxidizing potency if the metal
components give no hindrance. These oxidizers may be used in
combination of two types or more.
[0049] Regarding the abrasive powder, in a case wherein alumina
abrasive powder or silica abrasive powder is contained in the
polishing solution of the present invention, an effect to increase
the polishing rate is further obtained. However, the problems as
described hereinabove ((1) to (7)) may occur, and the abrasive
powder can be used when there is no such problem. The content of
the abrasive powder in the polishing solution varies according to
each individual purpose, as discussed hereinbelow. The purpose to
suppress the development of dishing and erosion can be attained by
setting the concentration of the abrasive powder to less than 0.05
weight %. For the purpose of decreasing the scratches on the
surface of the insulating film, the concentration of the abrasive
powder should be decreased to less than 0.5 weight %. For the
purpose of reducing the scratches on the surface of the metal film,
the concentration of the abrasive powder should be set to less than
0.1 weight %. For the purpose of decreasing delamination, the
concentration of the abrasive powder should be set to less than 0.3
weight %. For the purpose of improving ishability, the
concentration of the abrasive powder should be set to less than
0.01 weight %. For the purpose of decreasing the cost of the
polishing solution,. the concentration of the abrasive powder
should be set to less than 0.001 weight %. For the purpose of
solving the problem of the cost for the abrasive supply system or
iste liquid processing system, the concentration of the abrasive
should be set to less than 0.0001 weight %. For the purpose of
suppressing and reducing the dust in the clean room, the abrasive
powder should not be added.
[0050] In the fabrication of the buried Cu interconnect, if an
abrasive-free polishing solution is used for the polishing of the
Cu, and the polishing solution containing abrasive powder is used
for the polishing of the barrier metal, i.e. if two-step polishing
is performed, the problems (1), (2), (5) and (6) described
hereinabove can be extensively improved. A single. CMP system
provided with two or more polishing platens may be used, or two CMP
systems provided with a-polishing platen may be used. In this case,
using the abrasive-free polishing solution, the polishing can be
performed at higher rate compared with the polishing of the barrier
metal film, and difficulties such as polishing residues of Cu film
and barrier metal film in lower depression can be avoided. As to
the methods to supply the polishing solution, one method separately
supplies the solution to the polishing platen for Cu and the
polishing platen for the barrier metal. On the other hand, there is
also a method to supply the abrasive-free polishing solution to the
polishing platen for Cu and to the polishing platen for barrier
metal, and further, the solution containing abrasive powder is
supplied to the polishing platen for barrier metal.
[0051] Also, it is possible to use a polishing pad (stationary
abrasive pad) with abrasive powder buried in it, or to use a
grindstone. As a result, the content of the abrasive powder in the
polishing solution can be decreased, and this makes it easier to
solve the problem of iste liquid processing in (6) as described
hereinabove. In the case wherein a stationary abrasive pad or
grindstone is used instead of free abrasive, it is advantageous
because surface flatness can be improved even when CMP is performed
in one step, thus solving the problem (1) as described
hereinabove.
[0052] In the case wherein polishing is performed in two steps as
described hereinabove, a polishing selection ratio can be changed
between the first step and the second step. One effective method is
to decrease the polishing rate for Cu in the second step in order
to suppress the development of erosion and dishing. For this
purpose, it is recommended to increase the concentration of the
chemical to form inhibition layer in the polishing solution in the
second step, and to increase the polishing rate for barrier metal
film as compared with the polishing rate for Cu. For example, by
increasing the concentration of the anti-corrosive agent, it is
possible to increase the selection ratio for the barrier metal/Cu
by more than two times. Even when it is not added to the polishing
solution, if BTA aqueous solution of high concentration (about 1%).
is supplied to the polishing platen at the same time as the
polishing solution, the same effect can be provided.
[0053] When CMP is performed in two steps, a chemical exclusively
used for the barrier may be used. For example, an abrasive-free
polishing solution comprising hydrogen peroxide and aromatic nitro
compound may be used for TiN. The aromatic nitro compound has an
effect as an oxidizer to promote the etching of titanium compound.
When necessary, the above chemical to form the inhibition layer may
be-added. Compared with the polishing solution containing abrasive
powder, the polishing rate is low, but the process for fabricating
the Cu interconnect can be turned to a completely abrasive-free
process.
[0054] As the aromatic nitro compound as described above, the
following substances may be used: nitrobenzene sulfonic acid,
nitrophenol sulfonic acid, 1-nitronaphthalene-2-sulfonic acid,
sulfonic acid salt of these compounds, nitro-benzoic acid,
4-chlor-3-nitro-benzoic acid, nitro-phthalic acid,
isonitro-phthalic acid, nitro-terephthalic acid, 3-nitro-salicylic
acid, 3,5-dinitrosalicylic acid, picric acid, aminonitro-benzoic
acid, nitro-1-naphthoic acid, or carboxylic acid salt of these
compounds may be used. The salts as described hereinabove include
sodium salt, potassium salt, ammonium salt, etc. As the chemical to
be used for the semiconductor devices, it is most preferable to use
ammonium salt. Next, it is preferable to use potassium salt because
it has lower diffusion coefficient in semiconductor devices. These
chemicals may be used alone or in combinations of two or more.
Among these aromatic nitro compounds, nitrobenzene sulfonic acid
and its salt are most preferable because the polishing rate and the
etching rate for TiN are high. The aromatic nitro compound may be
used in the polishing solution and the etching solution of the
present invention at a concentration of 0.1-30 weight %, or more
preferably 1-20 weight %.
[0055] Instead of the two-step polishing as described hereinabove,
there is a complete abrasive-free process combined with drying
etching method. Specifically, the abrasive-free CMP is performed
for Cu in the first step, and barrier metal film is removed by dry
etching method in the second step, and a damascene Cu interconnect
can be fabricated. This makes it possible to solve the problems of
(1) to (7) as described hereinabove. As the gas to be used in the
dry etching method for barrier metal, sulfur hexafluoride
(SF.sub.6) is the most suitable. SF.sub.6 generates a large amount
of F radicals due to plasma dissociation, and it is advantageous to
use this for selectively removing TiN or TaN. Further, the
reactivity with Cu appears to be low. It is preferable that an
etching selection ratio of Cu to barrier metal is 3 or more. To
extend the process margin further, it is preferably 5 or more.
[0056] The polishing of the present invention can be applied for
the metal film to be polished such as Cu, Ti, TiN, Ta, TaN, WN,
WSiN, etc. In particular, Cu has high polishing rate when the
abrasive-free polishing solution is used, and it is the most
suitable as the metal to be polished by the method of the present
invention. In case of Ti, TiN, Ta, TaN, WN, or WSiN, the polishing
rate when the abrasive-free polishing solution is used is not as
high. as that of Cu, but the method can be applied by using the
polishing solution containing abrasive powder.
[0057] When CMP is performed using the polishing solution of the
present invention, which comprises oxidizer, phosphoric acid,
organic acid and the chemical to form the inhibition layer, the
surface of Cu film is first covered with and protected by the
chemical to form the inhibition layer. A projected portion 27 on
the surface of Cu film. as shown in FIG. 2 (a)., and is constantly
subjected to mechanical scrubbing of the abrasive cloth. The
inhibition or protective layer formed by the chemical to form the
inhibition layer is easily removed. The surface of Cu film exposed
to the polishing solution is oxidized by the oxidizer, and a thin
oxide layer is formed on the surface. Next, when phosphoric acid
and organic acid are supplied, the oxide layer is turned to aqueous
solution and is eluted. As a result, the thickness of the oxide
layer is reduced. The portion with thinner oxide layer is exposed
again to the oxidizer, and the thickness of the oxide layer is
increased. These reactions are repeated, and CMP process is
continued. Therefore, on the projected portion 27 on the surface of
Cu film, reaction products on the surface can be easily removed.
Because of local heating, reaction is accelerated, and the repeated
reactions of oxidation and actions to turn to a water-soluble state
proceed more rapidly than on the recess 26, where the
anti-corrosive protective film is formed. That is, the polishing
rate is increased on the projected portion 27 and it is thereby
flattened.
[0058] The chemical to form inhibition layer is attached on the
surface of the metal film, and suppresses the reaction on the
recess 26, and further prevents the development of dishing. The
chemical to form inhibition layer commonly used as an
anti-corrosive agent, such as BTA derivative, forms a very firm
protective film on the surface of Cu film. Also, a polymer having a
surface active effect, such as polyacrylic acid, forms a polymer
film on the interface between the polishing solution and the Cu
surface, and provides an effect as the anti-corrosive agent.
[0059] Regarding the concentration of the chemical to form the
inhibition layer in the polishing solution, it is preferable that
the polishing rate should be maintained at 700 nm/min. or more, and
etching rate should be 10 nm/min. or less (Speed ratio: 70 or
more). More preferably, it is 1 nm/min. or less (speed ratio: 700
or more). If the chemical to form the inhibition layer is added at
a concentration higher than this, CPM rate may be decreased. If it
is added at a concentration lowerethan this, the etching rate is
increased. As a result of the lower concentration, CMP can be
carried out, but dishing would develop more frequently.
BRIEF DESCRIPTION OF THE DRAWINGS
[0060] For the present invention to be clearly understood and
readily practiced, the present invention will be described in
conjunction with the following figures, wherein like reference
characters designate the same or similar elements, which figures
are incorporated into and constitute a part of the specification,
wherein:
[0061] FIG. 1 is schematic drawing of the CMP (chemical-mechanical
polishing) system;
[0062] FIG. 2(a) shows cross-sectional structure of an interconnect
of a specimen before CMP, FIG. 2(b) shows cross-sectional structure
of an interconnect of a specimen after CMP, and FIG. 2(c) is a plan
view of the specimen after CMP, wherein the dotted line in FIG.
2(c) indicates position of the cross-section shown in FIG.
2(b);
[0063] FIG. 3(a) shows cross-sectional structure of a plug of a
specimen before CMP, FIG. 3(b) shows cross-sectional structure of
the plug unit of the specimen after CMP, and FIG. 3(c) is a plan
view of the specimen after CMP, wherein the dotted line indicates
position of the cross-section shown in FIG. 3(b);
[0064] FIG. 4 is a cross-sectional view of a specimen wherein a
plug and an interconnect are fabricated on a diffusion layer of a
substrate using a polishing solution of the present invention;
[0065] FIG. 5(a) shows cross-sectional structure of a specimen
wherein a multi-level interconnection is fabricated using a
polishing solution of the present invention, and FIG. 5(b) is a
plan view of the specimen, wherein the dotted line indicates
position of the cross-section shown in FIG. 5(a);
[0066] FIG. 6(a) shows cross-sectional structure of the specimen
wherein a multi-level interconnection is fabricated by dual
damascene method using the polishing solution of the present
invention, and FIG. 6(b) is a plan view of the specimen, wherein
the dotted line indicates position of the cross-section of FIG.
6(a);
[0067] FIG. 7(a) is a cross-sectional view of the specimen wherein
CMP is performed using a polishing solution with abrasive powder,
and FIG. 7(b) is a cross-sectional view of the specimen when CMP is
performed using the abrasive-free polishing solution;
[0068] FIG. 8 is a top view of a 2-step CMP system, to which the
present invention is applied;
[0069] FIG. 9 is a drawing to show cross-sectional structure of the
specimen wherein multi-level interconnection is fabricated using a
polishing solution of the present invention;
[0070] FIG. 10(a) is a drawing to show cross-sectional structure of
the specimen wherein a peripheral circuit and a LSI interconnect
layer with a memory array are fabricated by a conventional
polishing method, and FIG. 10(b) is a drawing to show
cross-sectional structure of the specimen wherein a peripheral
circuit and an LSI interconnect layer with a memory array are
fabricated by the method of the present invention;
[0071] FIG. 11(a) shows cross-sectional structure of an
interconnect of the specimen wherein the barrier metal remains
after Cu-CMP, and FIG. 11(b) is a plan view of the specimen,
wherein the dotted line indicates position of the cross-section
shown in FIG. 11(a);
[0072] FIG. 12(2) shows cross-sectional structure of a plug of the
specimen wherein the barrier metal remains after Cu-CMP, and FIG.
12(b) is a plan view of the specimen, wherein the dotted line
indicates position of the cross-section shown in FIG. 12(a);
[0073] FIGS. 13(a1) to 13(a5) each represent a cross-sectional
structure of the specimen formed by a conventional polishing
method, and FIGS. 13(b1) to 13(b4) each represent a cross-sectional
structure of the specimen formed by the polishing method of the
present invention;
[0074] FIG. 13(a1) shows the development of erosion in a first
interconnect layer, FIG. 13(a2) shows surface irregularities
(convex and concave portions) formed on an insulating film surface,
reflecting the erosion on the first interconnect layer after the
formation of the insulating film, FIG. 13(a3) shows the formation
of a Cu film to provide a second interconnect layer, FIG. 13(a4)
shows polishing residues generated when Cu-CMP is performed on the
second interconnect layer, FIG. 13(a5) shows how the polishing
residues are removed by over-CMP, wherein the arrows in FIG. 13(a1)
and FIG. 13(a5) show expansion of the erosion; and
[0075] FIG. 13(b1) shows he formation of the first interconnect
layer without developing erosion, and FIG. 13(b2) shows how the
insulating film is formed in flat shape. FIG. 13(b3) shows how Cu
film is formed to provide the second interconnect layer, and FIG.
13(b4) shows how the second interconnect layer is formed without
developing erosion.
DETAILED DESCRIPTION OF THE INVENTION
[0076] It is to be understood that the figures and descriptions of
the present invention have been simplified to illustrate elements
that are relevant for a clear understanding of the present
invention, while eliminating, for purposes of clarity, many other
elements found in a typical semiconductor application. Those of
ordinary skill in the art will recognize that other elements are
desirable and/or required in order to implement the present
invention. However, because such elements are well known in the
art, and because they do not facilitate a better understanding of
the present invention, a discussion of such elements is not
provided herein. The detailed description will be-provided
hereinbelow with reference to the attached drawings.
EXAMPLE 1
[0077] In the first exemplary embodiment, a description will be
given for a method of forming a Cu interconnect by performing
Cu-CMP. FIG. 1 is a schematic drawing of a cross-sectional view of
a CMP (chemical-mechanical polishing) system used in the present
invention. On a platen (surface plate) 11 where an abrasive cloth
17 is attached, a holder 12 supporting a wafer 14 by a backing pad
18 is rotated to perform CMP. A retainer ring 13 is preferably
provided to prevent the wafer from falling off during CMP.
Polishing load during CMP is adjusted by a load applied on the
holder 12. Standard polishing load is set to 220 g/cm.sup.2, the
number of revolutions of the platen is set to 60 rpm, and the
number of revolutions of the holder is set to 60 rpm. The polishing
load or the number of revolutions are not limited to these values,
as these values are exemplary only. An abrasive cloth, such as a
hard cloth IC1000 manufactured by Rodel Inc., may be used. If
necessary, an abrasive cloth with groove may be used. Similar
polishing rate (speed) may be attained when an abrasive-cloth
IC1400 of dual layer structure is used.
[0078] FIG. 8 is an external view wherein a CMP system is seen from
above. There are two platens (surface plates) for polishing, each
designed in the same structure. A first platen 84 is used for
polishing of Cu, and a second platen 85 is used for polishing of a
barrier metal. On both platens, abrasive cloth is attached. A
transport mechanism 83 carries a wafer 89 between these two
platens, and continuous polishing can be carried out (in two
steps). Reference numeral 81 denotes a wafer loader, and 82 is an
unloader. Further, three platens may be provided to perform buff
polishing.
[0079] The polishing solution of the present invention is dropped
down to perform CMP at a rate of about 200 cc/min. from a first
feeding outlet 15 provided above the platen 11 as shown in FIG. 1.
When CMP is completed, the first feeding outlet 15 is closed to
stop the supply of the polishing solution. From a second feeding
outlet 16, pure water is supplied at a rate of about 3000 cc/min,
and rinsing is performed for 30-60 seconds. CMP is performed at
room temperature. Then, the wafer is maintained in such condition
that it is not dried. The polishing solution is removed by brush
scrubbing, and the wafer is dried using a rinser dryer or a
spinner.
[0080] Using a wafer without an interconnect pattern, basic
polishing performance of the polishing solution of the present
invention may be evaluated. On a silicon wafer, a silicon oxide
film of 200 nm in thickness is prepared. As an adhesive layer, TaN
film of 30 nm in thickness, and Cu film of 2000 nm in thickness are
continuously formed under vacuum condition by sputtering method.
This may be used as the specimen. The wafer may be, for example, 5
inches in diameter.
[0081] The polishing solution used in the present embodiment is an
aqueous solution, which comprises hydrogen peroxide (30 weight %
H.sub.2O.sub.2 aqueous solution commercially available),
orthophosphoric acid (hereinafter referred as "phosphoric acid"),
.alpha.-hydroxypropionic acid (hereinafter referred as lactic
acid), BTA, and methanol, and the polishing solution does not
containing polishing abrasives. Its composition is as follows:
Hydrogen peroxide 30 weight %, phosphoric acid 0.2 weight %, lactic
acid 0.2 weight %, and imidazole 0.5 weight %. Using this
phosphoric acid type abrasive-free polishing solution, Cu film
polishing rate (speed) and etching rate (speed) may be determined.
The measurement of these values is made through conversion from the
changes of electric resistance values of the Cu film before and
after the polishing, and before and after the etching. Polishing
time may be set to 2 minutes, and etching time may be 10
minutes.
[0082] The resulting Cu polishing rate is controlled to less than
750 nm/min., and the etching rate to less than 1.0 nm/min., and
there is no problem of dishing. It is possible to attain a
polishing rate by more than 7 times as high as that of the
conventional citric acid type abrasive-free polishing solution as
disclosed in JP-A-11-135466 (e.g. a solution containing hydrogen
peroxide of 30 weight %, citric acid of 0.15 weight %, and BTA of
0.2 weight %). The polishing rate for SiO.sub.2 is less than 0.1
nm/min., and there is no problem of erosion.
[0083] When the above polishing solution contains no hydrogen
peroxide, it is difficult to polish Cu (polishing rate: less than
50 nm/min.). Polishing rate is about 500 nm/min. when the polishing
solution not containing lactic acid is used, and it is about 100
nm/min. when the polishing solution containing no phosphoric acid
is used. Polishing rate is about 200 nm/min. when the polishing
solution not containing imidazole is used. Etching rate is very
high (i.e. 100 nm/min.), and is not suitable as a polishing
solution for fabrication of a buried interconnect. In order to
attain polishing rate of less than 750 nm/min., and an etching rate
of less than 1.0 nm/min., the polishing solution preferably
includes hydrogen peroxide, phosphoric acid, lactic acid and
imidazole.
[0084] Using the above polishing solution, to which silica
abrasives were added by 1%, a barrier metal TaN is polished. The
may be performed by the same polishing procedure as the procedure
for Cu as described hereinabove, and a polishing rate of 60 nm/min.
may be attained. The polishing rate for TiN and Ta is 100 nm/min.
and 50 nm/min. respectively. In the experiment for fabricating the
buried interconnect as described hereinbelow, a description is
given for a case wherein TaN is used as barrier metal film. For TiN
and Ta, the experiment may be performed by the same procedure as
given hereinabove and by changing the polishing time. The polishing
rate for SiO.sub.2 is less than 1 nm/min.
[0085] Alternatively, a polishing solution may be prepared using
phosphorous acid, hypophosphorous acid, and metaphosphoric acid
instead of phosphoric acid, and a polishing rate for Cu may be
determined by the same procedure as hereinabove. The resulting
polishing rate are 750 nm/min., 720 nm/min. and 700 nm/min.
respectively. In each case, etching rate is suppressed to less than
1.0 nm/min. and there is no problem of dishing. Further, from the
results of microscopic examination of the polished surface, the
phosphorous acid has a higher effect to suppress or control surface
roughness of the polishing surface as compared with phosphoric
acid. In any of these polishing solutions, the polishing rate for
TiN is 100 nm/min., and the polishing rate for Ta and TaN is 50
nm/min. and 60 nm/min. respectively. The polishing rate for
SiO.sub.2 is less than 0.1 nm/min., and there is no problem of
erosion.
[0086] Where a buried interconnect is fabricated using a polishing
solution containing phosphoric acid, the same procedure as in the
cases of other phosphoric acid type polishing solution, such as
polishing solution containing phosphorous acid, hypophosphorous
acid, metaphosphoric acid, etc., is followed. FIG. 2(a) shows an
example of cross-sectional structure of the specimen before
polishing. On a silicon substrate 25 where an impurity doping layer
and an insulating film are formed, a BPSG film 24 (silicon oxide
film added with boron and phosphorus) of 500 nm in thickness, and a
silicon oxide film 23 of 500 nm in thickness, were formed. By a
lithography process and a dry etching process, a groove pattern of
500 nm in depth for an interconnect is prepared in the silicon
oxide film 23. A TaN layer 22 of 30 nm in thickness is formed as an
adhesive layer, and a Cu thin film 21 of 800 nm in thickness is
continuously formed under vacuum condition by sputtering methods.
Further, in order to have better planarity of Cu film, vacuum heat
treatment is performed for 3 minutes at 450 degrees Celsius in a
sputtering system. On the silicon substrate 25, an impurity doping
layer is formed, such as a source, drain, etc., and a detailed
description of that formation will be apparent to those skilled in
the art.
[0087] For this specimen, CMP is performed on a first platen 84 as
shown in FIG. 8, using the phosphoric acid type abrasive-free
polishing solution as described above. As a result, the specimen
may be polished in such shape that dishing and erosion are less
than about 50 nm, as shown in FIGS. 11(a) and 11(b). Compared with
a case using the conventional organic acid type abrasive-free
polishing solution, the polishing may be completed in about
{fraction (1/7)} the conventional polishing time. Neither
delamination nor polishing scratches occur through the use of this
method.
[0088] The TaN is polished on a second platen 85 using a polishing
solution, which is prepared by adding silica abrasives by 1% to the
phosphoric acid type polishing solution as described hereinabove.
The duration of polishing is 30 seconds. As shown in FIG. 2(b) and
FIG. 2(c), polishing may be performed in such condition that
dishing and erosion are-less than about 50 nm. When both Cu and a
barrier metal were polished on a platen (polishing pad), erosion
occurred during abrasive-free polishing by the abrasive powder
remaining on the polishing pad. This suggests that a polishing pad
to be exclusively used for abrasive-free CMP should be
prepared.
[0089] By performing CMP in two steps for the specimen of FIG. 3(a)
according to the same procedure as that of the buried interconnect
as described hereinabove, a plug structure of Cu, as shown in FIG.
3(b) and FIG. 3(c), may be prepared. FIG. 12 shows a condition
wherein the barrier metal remains after Cu-CMP. In all of the
stages, polishing may be performed to such extent that dishing and
erosion are suppressed to less than about 50 nm. Neither
delamination nor scratches occurred in experimentation. For the
formation of the plug, Cu film is formed by an electroplating
method known in the art, in order to improve the property of the Cu
buried in the bore.
[0090] The concentration of imidazole in the polishing solution
used for the polishing of the barrier metal as described
hereinabove is 0.5 weight %, and the concentration may be the same
as the concentration of the polishing solution used for Cu
polishing. For the purposes of decreasing the polishing rate of Cu
by the polishing solution for the barrier metal, and of reducing
the dishing further, it is effective to increase the concentration
of imidazole in the polishing solution for the barrier metal. For
example, by increasing the concentration to 1.0 weight %, polishing
rate for Cu can be reduced to about one half. There are known
methods to add imidazole of this concentration into the polishing
solution and known methods to supply 2% imidazole water to the
platen at the same time as the polishing solution.
[0091] Electric resistivity of Cu interconnect prepared as shown in
FIG. 2 is 1.9 .mu..OMEGA. cm, including the portion of TaN layer.
Using a meander metal line pattern (line width 0.3-3 .mu.m; length
40 mm), or comb-type metal line pattern (line spacing 0.3-3 .mu.m;
length 40 mm), a conductivity/insulation test may be performed. As
a result, the yield is about 100%.
[0092] Also, as shown in FIG. 4, normal conductivity is achieved
from the impurity doping layer 45 to a tungsten plug 42, and LSI
operation is normal.
[0093] By repeatedly carrying out the processes to manufacture the
interconnect structure of FIG. 2, and the plug structure of FIG. 3,
a multi-level interconnection structure as shown in FIG. 5 may be
fabricated. The yield for plug conductivity achieved is nearly
100%, and normal operation of LSI is also achieved. The same
conductivity performance may be achieved when Cu is used as the
material for the plug, or when tungsten is used. In the case of
tungsten, film deposition by CVD is more advantageous from the
viewpoint of buried property, and there is no need to use an
adhesive metal film such as TiN or Ti.
[0094] Further, by similar polishing methods, it is also possible
to prepare a plug 41 formed by dual damascene method, as shown in
FIG. 6. This allows for a reduction in the number of processes of
multi-level interconnection. Normal operation of LSI is also
achieved in this method.
[0095] Using the interconnect-fabrication method shown in FIG. 5
and FIG. 6, and by the plug fabrication method, it is possible to
prepare an interconnect of LSI with three or more layers. As shown
in FIG. 13(a1) to 13(a5), when CMP is performed using the
conventional type polishing solution, more polishing residues are
generated on the upper layers, due to dishing and erosion that
occurs in the lower layers. FIG. 13(a4) shows how polishing
residues are generated. To remove these polishing residues,
over-CMP time is increased more in the upper layers, and this
further accelerates dishing and erosion. As a result, as shown in
FIG. 13(a5), dishing and erosion are increased in the upper layers.
When there are 3 or more interconnect layers, polishing residues
are increased further. When an attempt is made to remove these
residues, more than one-half of the interconnect in the dense
region may be eliminated due to erosion. Specifically, by the
conventional polishing method, it is difficult to reduce dishing
and erosion to less than 50 nm. Also, when interconnect layers are
produced up to 7 layers, it is naturally difficult to reduce them
to less than 100 nm.
[0096] By using the polishing method of the present invention, it
is possible to reduce and suppress dishing and erosion to less than
50 nm, even where no polishing residues are generated and the
interconnect layers are produced up to a third layer as shown in
FIG. 13(b4). Even where the layers are produced up to a seventh
layer as shown in FIG. 9, it is possible to suppress dishing and
erosion to less than 80 nm.
[0097] FIG. 9 shows a case wherein single damascene method is
adopted. CMP is repeatedly performed 14 times (M1-M7; P1-P7),
including the formation of the plug. When formation is by dual
damascene, it is possible to suppress dishing and erosion to less
than 80 nm.
[0098] FIG. 10 shows a memory array 102 and a peripheral circuit
101 in an LSI chip. In the memory array, metal lines are densely
arranged. The difference in pattern density is large in the memory
array as compared to the peripheral circuit. When conventional type
polishing methods are used, the time of over-CMP is longer on the
memory array. As shown in FIG. 10(a), erosion and dishing tend to
increase as compared to the logic unit. When this is carried out in
multi-layer arrangement, the problem explained in connection with
FIG. 13(a) occurs. When three layers or more are laminated, wiring
resistance extensively increases.
[0099] In contrast, according to the polishing method of the
present invention, the resistance to over-CMP is high. Thus, even
in the case wherein an LSI having portions with differences in
pattern density coexistent on the same chip, it is possible to
suppress dishing and erosion to less than 50 nm, as shown in FIG.
10(b). Also, it is possible to form three layers or more without
causing an increase in wiring resistance.
[0100] Also, in the case of a system LSI wherein the logic unit,
memory unit, etc. coexist, the polishing method of the present
invention can be applied.
[0101] By adding BTA by 0.2 weight % as a second chemical to form
the inhibition layer, it is possible to suppress Cu etching rate by
one-half. However, the polishing rate is decreased by about 50
nm/min. When methanol is added by 1% at the same time as BTA, it is
possible to increase the solubility of BTA.
EXAMPLE 2
[0102] The polishing solution for Cu used in a second embodiment is
an aqueous solution including hydrogen peroxide (30% H.sub.2O.sub.2
aqueous solution commercially available), phosphoric acid, lactic
acid, BTA, and ammonium salt of polyacrylic acid. The composition
is: hydrogen peroxide 30 weight %, phosphoric acid 0.2 weight %,
lactic acid 0.5 weight %, BTA 0.2 weight %, and ammonium salt of
polyacrylic acid 0.1 weight %. Using this polishing solution,
polishing rate and etching rate for a Cu film were determined.
Polishing performance is evaluated by the same procedure as in
Example 1 hereinabove. For the polishing of barrier metal film,
silica abrasive powder is added by 1% to the above polishing
solution.
[0103] As a result, polishing rate for Cu is suppressed to less
than 700 nm/min. and etching rate to less than 1.0 nm/min., and
there is no problem of dishing. Compared with the case of a
conventional organic acid type abrasive-free polishing solution,
the polishing rate is by about 7 times higher. Polishing rate for
SiO.sub.2 is less than 0.1 nm/min., and there is no problem of
erosion.
[0104] When silica abrasives are added by 1% to the polishing
solution, the polishing rate for TaN is 60 nm/min. The polishing
rates for TiN and Ta are 100 nm/min. and 50 nm/min., respectively.
In this embodiment, TaN is used. For TiN and Ta, polishing may be
achieved by the same procedure by changing the polishing time. The
polishing rate for SiO.sub.2 is less than 1 nm/min.
[0105] The specimen for fabricating the buried interconnect is
polished by CMP in two steps using the above polishing solution. As
a result, polishing may be performed with dishing and erosion
controlled to less than about 50 nm, as shown in FIG. 2(b) and FIG.
2(c). Cu polishing may be achieved in about {fraction (1/7)} of the
time required in the case wherein the conventional organic acid
type abrasive-free polishing solution is used. Neither delamination
nor polishing scratches occur using the present invention. As shown
in FIG. 3(b) and FIG. 3(c), the plug structure may also be
fabricated by controlling dishing and erosion to less than 50
nm.
[0106] When electric resistivity of a Cu interconnect thus formed
is measured, it is 1.9 .mu..OMEGA. cm, including the portion of TiN
layer. Using meander metal line pattern (line width 0.3-3 .mu.m;
length 40 mm) or comb-type metal line pattern (line spacing 0.3-3
.mu.m; length 40 mm), a conductivity/insulation test may be
performed. As a result, the yield is nearly 100%. It is also
possible to produce multi-level interconnection structures, as
shown in FIG. 5 and FIG. 6. LSI operation is normal in the present
invention.
[0107] In the present embodiment, ammonium salt of polyacrylic acid
is used. When cetyl pyridinium chloride of the same concentration
is used instead, it is possible to attain the above polishing rate
and to prevent mildew and bacteria in the polishing solution in
storage or in waste liquid.
[0108] The ammonium salt of polyacrylic acid used in the present
embodiment has a molecular weight of about 10,000. When a compound
with a molecular weight of about 100,000 is used, it is possible to
increase the polishing rate for Cu by 20%. Further, when
cross-linking type ammonium salt of polyacrylic acid with a
molecular weight of more than 1,000,000 is used, it is possible to
increase Cu polishing rate by 30%.
EXAMPLE 3
[0109] In the present embodiment, a Cu interconnect is compared in
the case wherein CMP is performed in one step on the specimen for
forming buried Cu interconnect using the polishing solution
containing silica abrasives, and in the case wherein polishing is
performed in two steps by the same procedure as in Example 1.
[0110] The polishing solution used in the present embodiment is an
aqueous solution, which includes hydrogen peroxide (30%
H.sub.2O.sub.2 aqueous solution commercially available), phosphoric
acid, lactic acid, and imidazole. The composition is: hydrogen
peroxide 30 weight %, phosphoric acid 0.2 weight %, lactic acid 0.2
weight %, and imidazole 0.5 weight %. Further, silica abrasives may
be added by 1% to this polishing solution. Using these two types of
polishing solutions, polishing rate and etching rate for Cu film
were determined. Polishing performance is evaluated by the same
procedure as in Example 1.
[0111] As a result, when the polishing solution containing silica
abrasive is used, the polishing rate of Cu is controlled to less
than 1000 nm/min., and the etching rate to less than 1.0 nm/min.,
and there is no problem of dishing. When the polishing solution not
containing silica abrasive is used, the polishing rate for Cu is
750 nm/min, which is similar to that of Example 1.
[0112] When the polishing solution containing silica abrasives is
used, the polishing rate for TiN is 100 nm/min., but when the
polishing solution not containing silica abrasives is used, the
polishing rate for Ta is 50 nm/min. (solution containing abrasives)
and 15 nm/min. (solution containing no abrasive), respectively. The
polishing rate for TaN is 60 nm/min. (solution containing
abrasives) and 15 nm/min. (solution containing nonabrasive),
respectively. In the experiment described hereinbelow, TiN is used
as the barrier metal film. For Ta and TaN, the experiment may also
be performed by the same procedure by changing the duration of
polishing.
[0113] A Cu interconnect is compared in the case wherein CMP is
performed in one step (on a single platen for Cu film and TiN film)
using the polishing solution containing silica abrasive on a
specimen for fabricating a buried Cu interconnect, and in the case
wherein polishing is performed in two steps (on two platens) by the
same procedure as in Example 1. When polishing is performed in one
step, the polished shape is as shown in FIG. 7(a), and erosion of
more than 50 nm occurred. Dishing is controlled to less then 50 nm.
FIG. 7(b) shows the result of the case wherein the same
interconnect structure of the specimen is polished by two-step CMP.
It is noted that the extent of the erosion differs dependent upon
whether the polishing solution contains abrasives. When polishing
scratches are examined using a surface particle counter, in the
case of one-step polishing, there are several tens to several
hundreds of polishing scratches. Despite these problems, in the
one-step CMP, polishing may be completed in about 1/4 of the time
required for the two-step CMP, when the polishing time for TiN is
included, thus improving throughput.
[0114] When the electric resistivity of a Cu interconnect polished
by one-step CMP is determined, it is 1.9 .mu..OMEGA. cm, including
TiN layer (thickness loss is taken into consideration). However,
wiring resistance is about 10% higher than the value obtained in
the two-step CMP. This may cause increased development of erosion.
Further, using meander metal line pattern (line width 0.3-3 .mu.m;
length 40 mm) and comb-type metal line pattern (line spacing 0.3-3
.mu.m; length 40 mm), a conductivity/insulation test may be
performed. As a result, the yield is nearly 100%. When multi-level
interconnection is prepared and LSI operation is assessed, normal
LSI operation is achieved. There is no influence on the yield, even
when CMP is carried out in one step, but wiring resistance is
increased due to erosion.
EXAMPLE 4
[0115] In this embodiment, a complete abrasive-free process using
barrier metal removal by dry etching method is employed. For the
dry etching, SF.sub.6 (sulfur hexafluoride) is used. Gas flow rate
is 25 cc/min., processing pressure is 5 mmTorr, high frequency
output for plasma is 600 W, and high frequency output for bias is
0-100 W. Under these conditions, etching selection ratio is
determined between the barrier metal film and the SiO.sub.2 film.
The higher the bias power is, the more the etching rate is
increased, but the selection ratio is maximized when bias power is
not applied. When bias power is 0, TiN/SiO.sub.2 selection ratio is
15, and TaN(Ta)/SiO.sub.2 selection ratio is 11. In the case of TiN
or TaN, the etching effect due to F radicals is high. In the case
of SiO.sub.2, etching is difficult to achieve simply by F radicals,
and it is necessary to employ the acceleration effect of ions
caused by application of bias power. No etching is performed for Cu
under this condition. The dry etching rate is 320 nm/min. for TiN,
and 240 nm/min. for TaN.
[0116] A description is given hereinbelow of a Cu interconnect
formed using the above drying etching method. TaN is used as
barrier metal. The procedure is the same as was discussed-in the
case of TiN hereinabove. For Cu-CMP, the same procedure is
performed using phosphoric acid type abrasive-free polishing
solution as was described hereinabove. The wafer may be washed by
brush scrubbing and dried, and the TaN film is removed under the
above conditions using a dry etching system. Then, fabrication may
be performed wherein dishing and erosion are controlled to less
than about 50 nm/min. as shown in FIG. 2(b) and FIG. 2(c). The
structure, as shown in FIG. 3(b) and FIG. 3(c), may be prepared for
the plug. In this case, Cu film is formed by the electroplating
methods already known in the art to thereby improve the buried
property of Cu film. Dishing and erosion may be controlled to less
than about 50 nm. Neither delamination nor polishing scratches
occur.
[0117] When electric resistivity of a Cu interconnect produced by
the above method is determined, it is 1.9 .mu..OMEGA. cm, including
the portion of TaN layer. Using meander metal line pattern (line
width 0.3-3 .mu.m; length 40 mm) and comb-type metal line pattern
(line spacing 0.3-3 .mu.m; length 40 mm), a conductivity/insulation
test may be performed. As a result, the yield is nearly 100%.
[0118] Further, as shown in FIG. 4, normal conductivity is obtained
from the impurity doping layer 45 to the tungsten plug 42, and LSI
operation is also normal.
[0119] By repeatedly performing the process to manufacture the
interconnect structure of FIG. 2 and the plug structure of FIG. 3,
it is possible to build up a multi-level interconnection as shown
in FIG. 5. The yield of conductivity of the plug is nearly 100%,
and the LSI operates normally. Regardless of whether the material
for the plug is Cu or tungsten, the same conductivity may be
achieved. In case of tungsten, film deposition by CVD is more
advantageous for burying performance, and the boding metal may not
be used. In this case, tungsten CMP is performed.
[0120] Further, it is also possible to fabricate the plug 41 formed
by dual damascene as shown in FIG. 6. As a result, the number of
processes to manufacture multi-level interconnection may be
decreased.
EXAMPLE 5
[0121] In this embodiment, a complete abrasive-free process is
performed to remove the barrier metal by an abrasive-free CMP. TiN
is used as the barrier metal. Regarding Cu-CMP, the same procedure
is performed using phosphoric acid type abrasive-free polishing
solution, as described hereinabove. The polishing solution for TiN
is an aqueous solution, which includes hydrogen peroxide,
nitrobenzene sulfonic acid, and BTA. The composition is: hydrogen
peroxide 20 weight %, nitrobenzene sulfonic acid 10 weight %, and
BTA 0.3 weight %. When this polishing solution is used, the
polishing rate is less than 50 nm/min. for TiN, and less than 1
nm/min. for Cu. That is, the selection ratio is more than 50 times
higher than conventional methods.
[0122] Under the above condition, a two-step abrasive-free CMP is
carried out. As shown in FIG. 2(b) and FIG. 2(c), dishing and
erosion are controlled to less than about 50 nm. Regarding the
plug, it is also possible to fabricate the structure as shown in
FIG. 3(b) and FIG. 3(c). In this case, Cu film is formed by the
electroplating methods known in the art, in order to improve
burying performance. Also, in this case, the specimen is fabricated
such that dishing and erosion are less than about 50 nm. Neither
delamination nor polishing scratches occur.
[0123] When electric resistivity of Cu interconnect prepared by the
above method is determined, it is 1.9 .mu..OMEGA. cm, including the
portion of TiN layer. Using meander metal line pattern (line width
0.3-3 .mu.m; length 40 mm) and comb-type metal line pattern (line
spacing 0.3-3 .mu.m; length 40 mm), a conductivity/insulation test
may be performed. As a result, the yield is nearly 100%.
[0124] As shown in FIG. 4, normal conductivity is attained from the
impurity doping layer 45 to the tungsten plug 42, and LSI operation
is normal.
[0125] By repeatedly performing the process to manufacture the
interconnect structure of FIG. 2 and the plug structure of FIG. 3,
it is possible to build up multi-level interconnection as shown in
FIG. 5. The yield of conductivity of the plug is nearly 100%, and
normal operation of LSI is achieved. Regardless of whether the
material for the plug is Cu or tungsten, the same conductivity may
be achieved. In the case of tungsten, it is more advantageous to
form the film by CVD for burying performance, and bonding metal may
not be used. Also, tungsten CMP is performed in this case.
[0126] Further, the plug 41 may be prepared by dual damascene as
shown in FIG. 6. As a result, the number of processes to
manufacture multi-level interconnection may be decreased.
[0127] The method to perform CMP using a polishing solution
containing phosphoric acid and an organic acid reduces or
suppresses scratches and delamination, suppresses and controls the
development of dishing and erosion, and to carries out the
polishing operation at higher polishing rate. Other advantages and
benefits of the present invention will be apparent to those skilled
in the art.
[0128] The present invention is not limited in scope to the
embodiments discussed hereinabove. Various changes and
modifications will be apparent to those skilled in the art, and
such changes and modifications fall within the spirit and scope of
the present invention. Therefore, the present invention is to be
accorded the broadest scope consistent with the detailed
description, the skill in the art and the following claims.
* * * * *