U.S. patent application number 10/979078 was filed with the patent office on 2005-06-23 for post rinse to improve selective deposition of electroless cobalt on copper for ulsi application.
Invention is credited to Dixit, Girish A., Gandikota, Srinivas, Padhi, Deenesh, Ramanathan, Sivakami.
Application Number | 20050136185 10/979078 |
Document ID | / |
Family ID | 32174995 |
Filed Date | 2005-06-23 |
United States Patent
Application |
20050136185 |
Kind Code |
A1 |
Ramanathan, Sivakami ; et
al. |
June 23, 2005 |
Post rinse to improve selective deposition of electroless cobalt on
copper for ULSI application
Abstract
A method for depositing a passivation layer on a substrate
surface using one or more electroplating techniques is provided.
Embodiments of the method include selectively depositing an
initiation layer on a conductive material by exposing the substrate
surface to a first electroless solution, depositing a passivating
material on the initiation layer by exposing the initiation layer
to a second electroless solution, and cleaning the substrate
surface with an acidic solution. In another aspect, the method
includes applying ultrasonic or megasonic energy to the substrate
surface during the application of the acidic solution. In still
another aspect, the method includes using the acidic solution to
remove between about 100 .ANG. and about 200 .ANG. of the
passivating material. In yet another aspect, the method includes
cleaning the substrate surface with a first acidic solution prior
to the deposition of the initiation layer.
Inventors: |
Ramanathan, Sivakami;
(Fremont, CA) ; Padhi, Deenesh; (Santa Clara,
CA) ; Gandikota, Srinivas; (Santa Clara, CA) ;
Dixit, Girish A.; (San Jose, CA) |
Correspondence
Address: |
MOSER, PATTERSON & SHERIDAN, LLP
APPLIED MATERIALS, INC.
3040 POST OAK BOULEVARD, SUITE 1500
HOUSTON
TX
77056
US
|
Family ID: |
32174995 |
Appl. No.: |
10/979078 |
Filed: |
October 29, 2004 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
10979078 |
Oct 29, 2004 |
|
|
|
10284855 |
Oct 30, 2002 |
|
|
|
6821909 |
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Current U.S.
Class: |
427/299 ;
257/E21.174; 257/E21.577; 257/E21.585; 427/331 |
Current CPC
Class: |
C23C 18/36 20130101;
C23C 18/1831 20130101; H01L 21/76873 20130101; C23C 18/1879
20130101; H01L 21/288 20130101; C23C 18/166 20130101; H01L 21/76877
20130101; C23C 18/50 20130101; H01L 21/76865 20130101; H01L
21/76874 20130101; H01L 21/76883 20130101; C23G 1/10 20130101; C23C
18/1834 20130101; H01L 21/76814 20130101; C23C 18/1882 20130101;
C23C 18/34 20130101; C23C 18/44 20130101; H01L 21/76849
20130101 |
Class at
Publication: |
427/299 ;
427/331 |
International
Class: |
B05D 003/00; B05D
001/40 |
Claims
1. A method of processing a substrate, comprising: polishing a
substrate surface to expose a conductive material disposed in a
dielectric material; cleaning the substrate surface with a first
acidic solution; selectively depositing an initiation layer on the
conductive material by exposing the substrate surface to an
initiation solution; depositing a passivating material comprising
cobalt or a cobalt alloy on the initiation layer by exposing the
substrate surface to an electroless solution; and cleaning the
substrate surface with a cleaning process.
2. The method of claim 1, wherein the first acidic solution
comprises a mixture selected from a group consisting of nitric acid
and deionized water at a ratio of about 1:2 to about 3:1, nitric
acid and hydrogen peroxide at a ratio of about 1:2 to about 3:1,
sulfuric acid and hydrogen peroxide at a ratio of about 2:1 to
about 4:1, or hydrochloric acid and hydrogen peroxide at a ratio of
about 2:1 to about 4:1.
3. The method of claim 2, wherein the initiation solution comprises
a noble metal source selected from the group consisting of
palladium, platinum or ruthenium.
4. The method of claim 2, wherein the initiation solution comprises
a borane reductant.
5. The method of claim 2, wherein the first acidic solution
comprises between about 0.2 wt % and about 5 wt % of hydrofluoric
acid and is applied to the substrate surface for about 300 seconds
or less at a temperature in a range from about 15.degree. C. to
about 60.degree. C.
6. The method of claim 5, wherein the electroless solution
comprises a cobalt source, a tungsten source, a hypophosphite
source, a borane reductant, a citrate source and a surfactant.
7. A method of processing a substrate, comprising: cleaning a
substrate surface with a first acidic solution; selectively
depositing a noble metal on the substrate surface by exposing the
substrate surface to an acidic electroless solution containing a
noble metal salt and an inorganic acid; electrolessly depositing
cobalt or a cobalt alloy on the noble metal; cleaning the substrate
surface with a second acidic solution selected from the group
consisting of nitric acid and deionized water at a ratio of about
1:2 to about 3:1, nitric acid and hydrogen peroxide at a ratio of
about 1:2 to about 3:1, sulfuric acid and hydrogen peroxide at a
ratio of about 2:1 to about 4:1, or hydrochloric acid and hydrogen
peroxide at a ratio of about 2:1 to about 4:1; and applying
ultrasonic or megasonic energy to the substrate surface while
cleaning the substrate surface with the second acidic solution.
8. The method of claim 7, wherein the first acidic solution
comprises between about 0.2 wt % and about 5 wt % of hydrofluoric
acid and is applied to the substrate surface for about 300 seconds
or less at a temperature in a range from about 15.degree. C. to
about 60.degree. C.
9. The method of claim 8, wherein the second acidic solution is
applied to the substrate surface at a flow rate between about 700
mL/min and about 900 mL/min for about 300 seconds or less at a
temperature in a range from about 15.degree. C. to about 35.degree.
C.
10. The method of claim 9, wherein the second acidic solution
removes between about 100 .ANG. and about 200 .ANG. of the cobalt
or cobalt alloy disposed on the substrate surface.
11. The method of claim 10, wherein the cobalt alloy comprises
cobalt and at least a second element selected from the group
consisting of tungsten, molybdenum, tin, phosphorous, boron and
combinations thereof.
12. The method of claim 11, wherein depositing the cobalt alloy
includes exposing the substrate surface to a cobalt electroless
solution comprising a cobalt source, a tungsten source, a
hypophosphite source, a borane reductant, a citrate source and a
surfactant.
13. A method of depositing a cobalt-containing layer on a
conductive material, comprising: exposing a substrate surface to a
first acidic solution to clean the conductive layer; exposing the
substrate surface to a water rinse process; exposing the substrate
surface to an initiation solution to form an initiation layer on
the conductive layer; exposing the substrate surface to the water
rinse process; and exposing the substrate surface to an electroless
solution to form the cobalt-containing layer on the initiation
layer, wherein the electroless solution comprises a cobalt source,
a tungsten source, a hypophosphite source, a borane reductant, a
citrate source, a surfactant and a pH adjusting agent in a
concentration such that the electroless solution has a pH at a
value in a range from about 9 to about 11.
14. The method of claim 13, wherein the conductive layer comprises
copper.
15. The method of claim 14, wherein the cobalt-containing layer
comprises cobalt and at least a second element selected from the
group consisting of tungsten, molybdenum, tin, phosphorous, boron
and combinations thereof.
16. The method of claim 15, wherein the first acidic solution
comprises nitric acid.
17. The method of claim 16, further comprises exposing the
substrate surface containing the cobalt-containing layer to a
second acidic solution.
18. The method of claim 17, wherein the second acidic solution
comprises nitric acid.
19. The method of claim 16, wherein the initiation solution
comprises a noble metal source selected from the group consisting
of palladium, platinum or ruthenium.
20. The method of claim 16, wherein the initiation solution
comprises a borane reductant.
Description
CROSS-REFERENCE TO RELATED APPLICATIONS
[0001] This application is a divisional of co-pending U.S. patent
application Ser. No. 10/284,855, filed Oct. 30, 2002, which is
herein incorporated by reference.
BACKGROUND OF THE INVENTION
[0002] 1. Field of the Invention
[0003] Embodiments of the invention relate to a method for
manufacturing integrated circuit devices. More particularly,
embodiments of the invention relate to a method for forming metal
interconnects.
[0004] 2. Description of the Related Art
[0005] Sub-quarter micron multilevel metallization is one of the
key technologies for the next generation of very large scale
integration (VLSI). The multilevel interconnects that lie at the
heart of this technology possess high aspect ratio features,
including contacts, vias, lines, or other apertures. Reliable
formation of these features is very important to the success of
VLSI and to the continued effort to increase quality and circuit
density on individual substrates. Therefore, there is a great
amount of ongoing effort being directed to the formation of
void-free features having high aspect ratios (height:width) of 4:1
or greater.
[0006] The presence of native oxides and other contaminants within
a feature causes problems during fabrication. For example, the
presence of native oxides and other contaminants within a feature
creates voids by promoting uneven distribution of a depositing
layer. The presence of native oxides and other contaminants can
also reduce the electromigration resistance of vias and small
features. Further, the presence of native oxides and other
contaminants can diffuse into the dielectric layer, the sublayer,
or the depositing layer and alter the performance of the device.
Typically, native oxides are formed when a substrate surface having
a nonconductive layer (silicon, silicon oxide) or a conductive
layer (aluminum, tungsten, titanium, tantalum, tungsten, copper)
disposed thereon, is exposed to oxygen in the atmosphere or is
damaged in a plasma etch step. The "other contaminants" may be
generated from sputtered material from an oxide over-etch, residual
photoresist from a stripping process, leftover polymer from a
previous oxide etch step, or redeposited material from a pre-clean
sputter etch process, for example.
[0007] A typical process for forming an interconnect on a substrate
includes depositing one or more layers, etching at least one of the
layer(s) to form one or more features, depositing a barrier layer
in the feature(s) and depositing one or more layers to fill the
feature. Copper and its alloys have become the metals of choice for
filling sub-micron interconnect technology because copper has a
lower resistivity than aluminum, (1.7 .mu..OMEGA.-cm compared to
3.1 .mu..OMEGA.-cm for aluminum), a higher current carrying
capacity, and a significantly higher electromigration resistance.
Copper also has good thermal conductivity and is available in a
highly pure state.
[0008] However, copper readily forms oxides when exposed to
atmospheric conditions. Copper oxides increase the resistance of
metal layers, become a source of particle problems, and reduce the
reliability of the overall circuit. Copper oxides may also
interfere with subsequent deposition processes.
[0009] One solution to prevent the formation of copper oxides is to
deposit a passivation layer or encapsulation layer over the copper
layer. A passivation layer isolates copper surfaces from ambient
oxygen. Cobalt and cobalt alloys have been observed as suitable
materials for passivating copper and may be deposited on copper by
electroless deposition techniques. However, copper does not
satisfactorily catalyze or initiate deposition of cobalt and cobalt
alloys from electroless solutions.
[0010] To counteract this problem, a common approach has been to
activate the copper surface by first depositing a catalytic
material on the copper surface. The deposition of the catalytic
material typically requires multiple, time consuming steps and,
most times, the use of catalytic colloid compounds. Catalytic
colloid compounds can adhere to dielectric materials and produce
undesired, excessive, and non-selective deposition of passivating
material on the substrate surface. Non-selective deposition of
passivating material, such as deposition on dielectric materials,
may lead to surface contamination, unwanted diffusion of conductive
materials into dielectric materials, and even device failure from
short circuits and other device irregularities.
[0011] There is a need, therefore, for a method for selectively
depositing a passivation layer on a conductive substrate using one
or more electroplating techniques.
SUMMARY OF THE INVENTION
[0012] Embodiments of the invention provide a method for depositing
a passivation layer on a substrate surface using one or more
electroplating techniques. In one aspect, the method includes
selectively depositing an initiation layer on a conductive material
by exposing the substrate surface to a first electroless solution,
depositing a passivating material on the initiation layer by
exposing the initiation layer to a second electroless solution, and
cleaning the substrate surface with an acidic solution.
[0013] In another aspect, the method includes polishing a substrate
surface to expose a conductive material disposed in a dielectric
material, exposing the substrate surface to a first acidic
solution, selectively depositing an initiation layer on the
conductive material by exposing the substrate surface to a first
electroless solution, electrolessly depositing a passivating
material comprising cobalt or a cobalt alloy on the initiation
layer, and cleaning the substrate surface with a second acidic
solution.
[0014] In yet another aspect, the method includes cleaning a
substrate surface with a first acidic solution, selectively
depositing a noble metal selected from the group of palladium,
platinum, alloys thereof, and combinations thereof on the substrate
surface by exposing the substrate surface to an acidic electroless
solution containing a noble metal salt and an inorganic acid,
electrolessly depositing cobalt or a cobalt alloy on the noble
metal, cleaning the substrate surface with a second acidic
solution, and applying ultrasonic or megasonic energy to the
substrate surface while cleaning the substrate surface with the
second acidic solution.
BRIEF DESCRIPTION OF THE DRAWINGS
[0015] So that the manner in which the above recited aspects of the
invention are attained and can be understood in detail, a more
particular description of the invention, briefly summarized above,
may be had by reference to the embodiments thereof which are
illustrated in the appended drawings. It is to be noted, however,
that the appended drawings illustrate only typical embodiments of
this invention and are therefore not to be considered limiting of
its scope, for the invention may admit to other equally effective
embodiments.
[0016] FIG. 1 illustrates an exemplary processing sequence
according to embodiments of the invention described herein.
[0017] FIG. 2 illustrates an alternative processing sequence
according to embodiments of the invention described herein.
[0018] FIGS. 3A-3G are simplified, schematic sectional views of an
exemplary wafer at different stages of an interconnect fabrication
sequence according to embodiments.
DETAILED DESCRIPTION
[0019] FIG. 1 illustrates an exemplary processing sequence 100
according to embodiments of the invention. In step 110, a substrate
surface having one or more conductive materials at least partially
formed thereon, such as copper for example, is pre-rinsed/treated
to remove metal oxides or other contaminants from the substrate
surface. "Substrate surface" as used herein refers to a layer of
material that serves as a basis for subsequent processing
operations. For example, a substrate surface may contain one or
more conductive metals, such as aluminum, copper, tungsten, or
combinations thereof, for example, and may form part of an
interconnect feature such as a plug, via, contact, line, wire, and
may also form part of a metal gate electrode. A substrate surface
may also contain one or more nonconductive materials, such as
silicon, doped silicon, germanium, gallium arsenide, glass, and
sapphire, for example.
[0020] The pre-rinse/treatment process utilizes an acidic solution
to remove/etch a top portion of the substrate surface, such as
between about 10 .ANG. and about 50 .ANG., which may have
contaminating materials from a prior processing step. Such a prior
processing step may be a planarizing process, for example. The
acidic solution may contain an inorganic acid solution. For
example, the acidic solution may contain between about 0.2 weight
percent (wt %) to about 5 wt % of hydrofluoric acid (HF), such as
about 0.5 wt %. The acidic solution may also contain nitric acid
having a concentration between about 1 M and about 5 M.
Alternatively, the acidic solution may be a mixture of sulfuric
acid having a concentration between about 0.5 percent by volume
(vol %) and about 10 vol %, such as between about 1 vol % and about
5 vol %, and hydrogen peroxide having a concentration between about
5 vol % and about 40 vol %, such as about 20 vol %.
[0021] The pre-rinse solution is generally applied to the substrate
surface at a rate between about 50 mUmin and about 2,000 mL/min,
such as between about 700 mL/min and about 900 mL/min. The
pre-rinse solution is typically applied for about 5 seconds to
about 300 seconds, such as between about 30 seconds and about 60
seconds at a temperature between about 15.degree. C. and about
60.degree. C. The pre-rinse solution may be applied in the same
processing chamber or processing cell as any of the subsequent
deposition processes.
[0022] Optionally, a rinsing agent, such as deionized water for
example, is then applied to the substrate surface to remove any
remaining pre-rinse solution, any etched materials and particles,
and any by-products that may have formed during the pre-rinse (step
110). The rinsing agent is generally applied to the substrate
surface at a flow rate between about 50 mL/min and about 2,000
mL/min, such as between about 700 mL/min and about 900 mL/min. The
rinsing agent is typically applied for about 5 seconds to about 300
seconds, such as between about 30 seconds and about 60 seconds at a
temperature between about 15.degree. C. and about 80.degree. C. The
rinsing agent may be applied by a spraying method as well as by any
other method used for cleaning a substrate, such as by rinsing in
an enclosure containing a cleaning solution or bath.
[0023] Following the pre-rinse process (step 110), an initiation
layer is deposited on the substrate surface, as shown at step 120.
In one aspect, the initiation layer is formed on the substrate
surface by selectively depositing a noble metal, such as palladium,
on the exposed conductive materials of the substrate surface (step
122). In another aspect, the initiation layer is formed on the
substrate surface by exposing/rinsing the substrate surface with
one or more boron-based reducing agents (step 124).
[0024] The initiation layer may be formed on the conductive
portions of the substrate surface by electrolessly depositing one
or more noble metals thereon. The electroless solution generally
provides for the deposition of a noble metal to a thickness of
about 50 .ANG. or less, such as about 10 .ANG. or less. The noble
metal may be palladium, platinum, gold, silver, iridium, rhenium,
rhodium, ruthenium, osmium, or any combination thereof. Preferably,
the noble metal is palladium or platinum.
[0025] In one aspect, the initiation layer is deposited from an
electroless solution containing at least one noble metal salt and
at least one acid (step 122). A concentration of the noble metal
salt within the electroless solution should be between about 20
parts per million (ppm) and about 20 grams per liter (g/L), such as
between about 80 ppm and about 300 ppm. Exemplary noble metal salts
include palladium chloride (PdCl.sub.2), palladium sulfate
(PdSO.sub.4), palladium ammonium chloride, and combinations
thereof.
[0026] The acid may be one or more inorganic acids, such as
hydrochloric acid (HCl), sulfuric acid (H.sub.2SO.sub.4),
hydrofluoric acid (HF), and combinations thereof, for example.
Alternatively, the acid may be one or more organic acids, such as a
carboxylic acid, including acetic acid (CH.sub.3COOH), for example.
A sufficient amount of acid is included to provide an electroless
solution having a pH of about 7 or less. Preferably, the pH of the
electroless solution is between about 1 and about 3.
[0027] In step 122, the electroless solution for forming the
initiation layer is generally applied to the substrate surface at a
rate between about 50 mL/min and about 2,000 mL/min, such as
between about 700 mL/min and about 900 mL/min. The electroless
solution is typically applied for about 1 second to about 300
seconds, such as between about 5 seconds and about 60 seconds, at a
temperature between about 15.degree. C. and about 80.degree. C.
[0028] In another aspect, the initiation layer is formed by rinsing
or exposing the substrate surface to a borane-containing
composition (step 124). The borane-containing composition forms a
metal boride layer selectively on the exposed conductive metals and
becomes a catalytic site for subsequent electroless deposition
processes. The borane-containing composition contains one or more
boron-based reducing agents, such as sodium borohydride,
dimethylamine borane (DMAB), trimethylamine borane, and
combinations thereof. Any alkali metal borohydrides and alkyl amine
boranes may also be used. The borane-containing composition has a
boron reducing agent concentration of about 0.25 grams per liter
(g/L) to about 6 g/L, such as between about 2 g/L and about 4 g/L.
The borane-containing composition may additionally include one or
more pH adjusting agents to adjust a pH of the composition to
between about 8 and about 13. Suitable pH adjusting agents include
potassium hydroxide (KOH), sodium hydroxide (NaOH), ammonium
hydroxide, ammonium hydroxide derivatives, such as tetramethyl
ammonium hydroxide, and combinations thereof.
[0029] In step 124, the underlying conductive material is exposed
to the borane-containing composition for about 30 seconds to about
180 seconds at a temperature between about 15.degree. C. and about
80.degree. C. The borane-containing composition may be applied at a
rate between about 50 mL/min and about 2,000 mL/min, such as
between about 700 mL/min and about 900 mL/min. In one aspect, the
borane-containing composition may include about 4 g/L of
dimethylamine borane (DMAB) and a sufficient amount of sodium
hydroxide to provide a pH of about 9.
[0030] Optionally, a rinsing agent, such as deionized water, for
example, is applied to the substrate surface to remove any solution
used in forming the initiation layer. The rinsing agent is
generally applied to the substrate surface at a rate between about
50 mL/min and about 2,000 mL/min, such as between about 700 mL/min
and about 900 mL/min. The rinsing agent is applied for about 5
seconds to about 300 seconds, such as between about 30 seconds and
about 60 seconds, at a temperature between about 15.degree. C. and
about 80.degree. C. The rinsing agent may be applied by a spraying
method as well as by any other method for cleaning a substrate,
such as by rinsing in an enclosure containing a cleaning solution
or bath.
[0031] A passivation layer is next deposited on the exposed
initiation layer by a selective electroless deposition process in
step 130. Preferably, the passivation layer includes cobalt or a
cobalt alloy. For example, useful cobalt alloys include
cobalt-tungsten alloys, cobalt-phosphorus alloys, cobalt-tin
alloys, cobalt-boron alloys, and ternary alloys, such as
cobalt-tungsten-phosphorus and cobalt-tungsten-boron. The
passivation layer may also include other metals and metal alloys,
such as nickel, tin, titanium, tantalum, tungsten, molybdenum,
platinum, iron, niobium, palladium, nickel cobalt alloys, doped
cobalt, doped nickel alloys, nickel iron alloys, and combinations
thereof. The passivation layer may be deposited to have a thickness
of about 500 .ANG. or less, such as between about 300 .ANG. and
about 500 .ANG.. The passivation layer isolates and protects an
underlying metal layer from exposure to oxygen, for example.
Accordingly, the passivation layer prevents the formation of metal
oxides.
[0032] Cobalt alloys, such as cobalt-tungsten, may be deposited by
adding tungstic acid or tungstate salts, such as sodium tungstate,
ammonium tungstate, and combinations thereof. Phosphorus for the
cobalt-tungsten-phosphorus deposition may be obtained by using
phosphorus-containing reducing agents, such as hypophosphite.
Cobalt alloys, such as cobalt-tin, may be deposited by adding
stannate salts including stannic sulfate, stannic chloride, and
combinations thereof. The metals salts may be in the electroless
solution at a concentration between about 0.5 g/L and about 30 g/L,
such as between about 2.5 g/L and about 25 g/L.
[0033] In one aspect, the passivation layer (step 130) is deposited
from a metallic electroless solution containing at least one metal
salt and at least one reducing agent. Suitable metal salts include
chlorides, sulfates, sulfamates, or combinations thereof. One
example of a metal salt is cobalt chloride. The metal salt may be
in the electroless solution at a concentration between about 0.5
g/L and about 30 g/L, such as between about 2.5 g/L and about 25
g/L.
[0034] Suitable reducing agents include sodium hypophosphite,
hydrazine, formaldehyde, and combinations thereof. The reducing
agents may also include borane-containing reducing agents, such as
dimethylamine borane and sodium borohydride. The reducing agents
have a concentration between about 1 g/L and about 30 g/L of the
electroless solution. For example, hypophosphite may be added to
the electroless solution at a concentration between about 15 g/L
and about 30 g/L of the electroless composition.
[0035] The electroless solution may further include between about
0.01 g/L and about 50 g/L of one or more additives to improve
deposition of the metal. Additives may include surfactants (RE
610), complexing agents (carboxylic acids, such as sodium citrate
and sodium succinate), pH adjusting agents (sodium hydroxide,
potassium hydroxide), stabilizers (thiourea, glycolic acid), and
combinations thereof.
[0036] The metallic electroless solution is applied to the
substrate surface at a rate between about 50 mL/min and about 2,000
mL/min, such as between about 700 mL/min and about 900 mL/min. The
metallic electroless solution is applied for about 30 seconds to
about 180 seconds, such as between about 60 seconds and about 120
seconds, at a temperature between about 60.degree. C. and about
90.degree. C.
[0037] In one aspect, a cobalt electroless composition for forming
the passivation layer may include about 20 g/L of cobalt sulfate,
about 50 g/L of sodium citrate, about 20 g/L of sodium
hypophosphite, and a sufficient amount of potassium hydroxide to
provide a pH of between about 9 and about 11. This electroless
composition may be applied to the substrate surface for about 120
seconds at a flow rate of about 750 mL/min and at a temperature of
about 80.degree. C. In another aspect, a cobalt-tungsten layer may
be deposited by the addition of about 10 g/L of sodium
tungstate.
[0038] Following the passivation layer deposition, the substrate
surface may be cleaned to remove unwanted portions of the
passivating material (step 140). In one aspect, the substrate
surface is rinsed with one or more oxidizing agents (step 142). In
another aspect, ultrasonic or megasonic energy is applied to the
substrate surface (step 144) during the rinse (step 142) to enhance
removal of the unwanted materials.
[0039] The post-deposition cleaning solution may include: (1) a
solution of nitric acid and deionized water; (2) a mixture of
nitric acid and hydrogen peroxide; (3) a mixture of sulfuric acid
and hydrogen peroxide; (4) a mixture of hydrochloric acid and
hydrogen peroxide; or (5) any combination thereof. The mixture of
nitric acid and deionized water has an acid to water ratio between
about 1:2 to about 3:1, such as about 1:1. The mixture of nitric
acid and hydrogen peroxide has an acid to peroxide ratio between
about 1:2 to about 3:1, such as about 2:1. The mixture of sulfuric
acid and hydrogen peroxide has an acid to peroxide ratio between
about 2:1 to about 4:1, such as about 3:1. The mixture of
hydrochloric acid and hydrogen peroxide has an acid to peroxide
ratio between about 2:1 to about 4:1, such as about 3:1. Typically,
the hydrogen peroxide is an aqueous solution comprising between
about 15% to about 40% hydrogen peroxide, such as 30% hydrogen
peroxide. Regardless of the specific cleaning composition, the
cleaning solution is generally applied to the substrate surface at
a rate between about 700 mL/min and about 900 mL/min, at a
temperature between about 15.degree. C. and about 35.degree. C.,
and at a pressure between about 0.5 atm and about 3 atm.
[0040] The post-deposition cleaning solutions are believed to clean
free cobalt particles, remove cobalt oxide, and remove reaction
by-products, such as Co(OH).sub.2 formed during deposition. The
cleaning solution is also believed to remove a layer of cobalt
material between about 1 .ANG. to about 400 .ANG. in thickness,
such as between about 100 .ANG. and about 200 .ANG., to remove any
random growth or lateral growth of cobalt materials on the
substrate surface and over the exposed conductive materials. Once
cleaned, the substrate can be transferred for additional
processing, such as annealing or subsequent deposition
processes.
[0041] In one aspect, the cleaning step (step 140) may be enhanced
using one or more sources of ultrasonic or megasonic energy applied
to the substrate support pedestal or substrate surface (step 144).
For example, ultrasonic energy may be applied at a power between
about 10 watts and about 250 watts, such as between about 10 watts
and about 100 watts to the substrate support pedestal. The
ultrasonic energy may have a frequency between about 25 kHz and
about 200 kHz, preferably greater than about 40 kHz. The ultrasonic
energy may be applied for between about 3 seconds and about 600
seconds, but longer time periods may be used depending upon the
application. If two or more sources of ultrasonic energy are used,
then simultaneous multiple frequencies may be used.
[0042] FIG. 2 illustrates an alternative processing sequence in
process 200 according to embodiments of the invention described
herein. Similar to the process 100 described above with reference
to FIG. 1, a substrate surface having one or more conductive
materials at least partially formed thereon, such as copper, for
example, is pre-rinsed/treated to remove metal oxides or other
contaminants from the substrate surface, in step 210. Next, a
passivation layer is deposited on the substrate surface using an
electroless solution containing at least one metal salt and at
least one borane-containing reducing agent, in step 220. Finally,
the substrate surface is cleaned in step 230, by rinsing with one
or more oxidizing agents and/or applying ultrasonic energy during
the rinse step.
[0043] The pre-rinse step 210 and the post-rinse step 230 are
similar to steps 110 and 140, respectively, which have been
described above. Step 220 forms a passivation layer on the
substrate surface using a mixture of metal salt(s) and
borane-reducing agent(s). Suitable metal salts include chlorides,
sulfates, sulfamates, or combinations thereof. The metal salt may
be in the electroless solution at a concentration between about 0.5
g/L and about 30 g/L, such as between about 2.5 g/L and about 25
g/L. Cobalt alloys, such as cobalt-tungsten may be deposited by
adding tungstic acid or tungstate salts, such as sodium tungstate,
ammonium tungstate, and combinations thereof. Suitable
borane-containing reducing agents include alkali metal
borohydrides, such as sodium borohydride, alkyl amine boranes, such
as dimethylamine borane (DMAB) and trimethylamine borane, and
combinations thereof. The borane-containing reducing agent contains
between about 0.25 g/L and about 6 g/L of the boron-containing
composition, such as between about 2 g/L and about 4 g/L. The
presence of the borane-containing reducing agents allow for the
formation of cobalt-boron alloys, such as cobalt-tungsten-boron and
cobalt-tin-boron among others.
[0044] In one aspect, a cobalt electroless composition for forming
the metal layer with a borane-containing reducing agent includes
about 20 g/L of cobalt sulfate, about 50 g/L of sodium citrate,
about 4 g/L of dimethylamine borane, and a sufficient amount of
potassium hydroxide to provide a pH of between about 10 and about
12. This electroless composition may be applied to the substrate
surface for about 120 seconds at a flow rate of about 750 mL/min
and at a temperature of about 80.degree. C. Optionally, a
cobalt-tungsten-boron layer may be deposited by the addition of
about 10 g/L of sodium tungstate.
[0045] The processing steps described above may be performed in an
integrated processing platform, such as the Electra.TM. ECP
processing platform, which is commercially available from Applied
Materials, Inc., located in Santa Clara, Calif. The Electra Cu.TM.
ECP platform generally includes one or more electroless deposition
processing (EDP) cells, pre-deposition cells, post-deposition
cells, such as spin-rinse-dry (SRD) cells, etch chambers, and
anneal chambers. The Electra.TM. ECP processing platform is more
fully described in U.S. Pat. No. 6,258,223, issued on Jul. 10,
2001, which is incorporated by reference herein.
[0046] FIGS. 3A-3G are schematic representations of an exemplary
interconnect structure 300 at different stages of fabrication in
accordance with embodiments of the invention described herein. FIG.
3A shows an underlying substrate surface 310 having a dielectric
layer 312 formed thereon. The dielectric layer 312 may be any
dielectric material including a low k dielectric material
(k.ltoreq.4.0), whether presently known or yet to be discovered.
For example, the dielectric layer 312 may be fluorinated silicon
glass (FSG), silicon dioxide, silicon carbide, or siloxy carbide
deposited using conventional deposition techniques, such as
physical vapor deposition and chemical vapor deposition. The
dielectric layer 312 is etched to form a feature 314 therein using
conventional and well-known techniques. The feature 314 may be a
plug, via, contact, line, wire, or any other interconnect
component. For simplicity and ease of description, however, the
feature 314 will be further described with reference to a via.
Typically, the feature 314 has vertical sidewalls 316 and a floor
318, having an aspect ratio of about 4:1 or greater, such as about
6:1. The floor 318 exposes at least a portion of the underlying
substrate surface 310. Although not shown, a wire definition may be
etched with the via as is commonly known to form a dual damascene
structure.
[0047] FIG. 3B shows a barrier layer 330 at least partially
deposited on the underlying metal layer 310. Prior to depositing
the barrier layer 330, the patterned or etched substrate dielectric
layer 312 may be cleaned to remove native oxides or other
contaminants from the surface thereof. For example, reactive gases
are excited into a plasma within a remote plasma source chamber
such as a Reactive Pre-Clean chamber available from Applied
Materials, Inc., located in Santa Clara, Calif. Pre-cleaning may
also be done within a metal CVD or PVD chamber by connecting the
remote plasma source thereto. Alternatively, metal deposition
chambers having gas delivery systems could be modified to deliver
the pre-cleaning gas plasma through existing gas inlets such as a
gas distribution showerhead positioned above the substrate.
[0048] In one aspect, the reactive pre-clean process forms radicals
from a plasma of one or more reactive gases, such as argon, helium,
hydrogen, nitrogen, fluorine-containing compounds, and combinations
thereof. For example, a reactive gas may include a mixture of
tetrafluorocarbon (CF.sub.4) and oxygen (O.sub.2), or a mixture of
helium (He) and nitrogen trifluoride (NF.sub.3). More preferably,
the reactive gas is a mixture of helium and nitrogen
trifluoride.
[0049] The plasma is typically generated by applying a power of
about 500 watts to 2,000 watts RF at a frequency of about 200 kHz
to 114 MHz. The flow of reactive gases ranges between about 100
sccm and about 1,000 sccm and the plasma treatment lasts for about
10 seconds to about 150 seconds. Preferably, the plasma is
generated in one or more treatment cycles and purged between
cycles. For example, four treatment cycles lasting 35 seconds each
is effective.
[0050] In another aspect, the patterned or etched dielectric layer
312 may be pre-cleaned first using an argon plasma and then a
hydrogen plasma. A processing gas having greater than about 50%
argon by number of atoms is introduced at a pressure of about 0.8
mTorr. A plasma is struck to subject the dielectric layer 312 to an
argon sputter cleaning environment. The argon plasma is preferably
generated by applying between about 50 watts and about 500 watts of
RF power. The argon plasma is maintained for between about 10
seconds and about 300 seconds to provide sufficient cleaning time
for the deposits that are not readily removed by a reactive
hydrogen plasma.
[0051] Following the argon plasma, the chamber pressure is
increased to about 140 mTorr, and a processing gas consisting
essentially of hydrogen and helium is introduced into the
processing region. Preferably, the processing gas comprises about
5% hydrogen and about 95% helium. The hydrogen plasma is generated
by applying between about 50 watts and about 500 watts power. The
hydrogen plasma is maintained for about 10 seconds to about 300
seconds.
[0052] The barrier layer 330 is conformally deposited on the floor
318 as well as the side walls 316 of the feature 314 using
conventional deposition techniques. The barrier layer 330 acts as a
diffusion barrier to prevent inter-diffusion of a copper metal to
be subsequently deposited into the via. Preferably, the barrier
layer 330 is a thin layer of a refractory metal having a thickness
between about 10 .ANG. and about 1,000 .ANG.. For example, the
barrier layer 330 may include tungsten (W), tantalum (Ta), titanium
(Ti), tantalum nitride (TaN), titanium nitride (TiN), or
combinations thereof. Preferably, the barrier layer contains
tantalum nitride deposited to a thickness of about 20 .ANG. or less
using atomic layer deposition or cyclical layer deposition
techniques, such as the cyclical layer deposition process shown and
described in co-pending U.S. patent application Ser. No.
10/199,415, filed on Jul. 18, 2002, entitled "Enhanced Copper
Growth With Ultrathin Barrier Layer For High Performance
Interconnects," which is incorporated by reference herein.
[0053] FIG. 3C shows a seed layer 340 at least partially deposited
on the barrier layer 330. The seed layer 340 is a copper or a
copper alloy material, which may be deposited using physical vapor
deposition, chemical vapor deposition, electroless plating, and
electroplating techniques. Preferably, the seed layer 340 is
deposited using a high density plasma physical vapor deposition
(HDP-PVD) process to enable good conformal coverage. One example of
a HDP-PVD chamber is the Self-Ionized Plasma SIP.TM. chamber,
available from Applied Materials, Inc. of Santa Clara, Calif.
[0054] FIG. 3D shows a bulk metal layer 350 at least partially
deposited on the seed layer 340. The bulk metal layer 350 is
deposited on the seed layer 340 to fill the via. The bulk metal
layer 350 may be deposited using CVD, PVD, electroplating, or
electroless techniques to a thickness between about 1,000 .ANG. and
about 2,000 .ANG.. The bulk metal layer 350 may include aluminum,
titanium, tungsten, copper, and combinations thereof. Preferably,
the bulk metal layer 350 contains copper deposited within an
electroplating cell, such as the Electra.TM. Cu ECP system,
available from Applied Materials, Inc. of Santa Clara, Calif.
[0055] A copper electrolyte solution and copper electroplating
technique is described in commonly assigned U.S. Pat. No.
6,113,771, entitled "Electro-deposition Chemistry," which is
incorporated by reference herein. Typically, the electroplating
bath has a copper concentration greater than about 0.7 M, for
example, a copper sulfate concentration of about 0.85 M, and a pH
of about 1.75. The electroplating bath may also contain various
additives as is well known in the art. The temperature of the bath
is between about 15.degree. C. and about 25.degree. C. The bias is
between about -15 volts to about 15 volts. In one aspect, the
positive bias ranges from about 0.1 volts to about 10 volts and the
negative bias ranges from about -0.1 volts to about -10 volts.
[0056] Optionally, an anneal treatment may be performed following
the metal layer 350 deposition whereby the wafer is subjected to a
temperature between about 100.degree. C. and about 400.degree. C.
for about 10 minutes to about 1 hour, preferably about 30 minutes.
A carrier/purge gas such as helium, hydrogen, nitrogen, or a
mixture thereof is introduced at a rate of about 100 sccm to about
10,000 sccm. The chamber pressure is maintained between about 2
Torr and about 10 Torr. The RF power is about 200 watts to about
1,000 watts at a frequency of about 13.56 MHz, and the preferable
substrate spacing is between about 300 mils and about 800 mils.
[0057] Following the bulk metal layer 350 deposition, the top
portion of the structure 300 may be planarized. A chemical
mechanical polishing (CMP) apparatus may be used, such as the
Mirra.TM. System available from Applied Materials, Inc., located in
Santa Clara, Calif. During the planarization process, portions of
the copper 340 and dielectric 312 are removed from the top of the
structure 300 leaving a fully planar surface. Optionally, the
intermediate surfaces of the structure 300 may be planarized
between the deposition of the subsequent layers described
above.
[0058] FIG. 3E shows a portion of the substrate surface subjected
to a pre-rinse/etch step to remove any unwanted contaminants
thereon. The substrate is rinsed or cleaned using an acidic
pre-clean solution to remove/etch at least a portion of the
substrate surface as indicated by the dashed line 360.
[0059] FIG. 3F shows an initiation layer 370 formed over the bulk
metal layer 350 as described above in step 120. The initiation
layer 370 may be deposited within an electroplating cell, such as
the Electra.TM. Cu ECP system, available from Applied Materials,
Inc. The initiation layer 370 may also be deposited within the same
cell as the bulk metal layer 350.
[0060] FIG. 3G shows a passivation layer 380 formed over the
initiation layer 370 as described above in step 130. The
passivation layer 380 may also be deposited within its own
designated electroplating cell, such as the Electra.TM. Cu ECP
system. Alternatively, the passivation layer 380 may be deposited
within the same cell used to form the initiation layer 370 and/or
the bulk metal layer 350. The substrate surface is then exposed to
a post-deposition cleaning process as described above in step 140
shown in FIG. 1. The cleaning composition may be applied in-situ or
the substrate may be transferred to a different cell prior to
cleaning.
EXAMPLES
[0061] The following examples describe specific post-rinse
processes performed on a 200 mm substrate according to embodiments
of the invention. In each example, the 200 mm substrate surface had
been prepared as follows.
[0062] A patterned or etched wafer formed according to conventional
or well-known techniques was introduced into an integrated
Endura.RTM. processing system available from Applied Materials,
Inc., located in Santa Clara, Calif., which included a Pre-Clean II
chamber, an IMP PVD Ta/TaN chamber, and a PVD Cu chamber mounted
thereon, and was degassed at 350.degree. C. for about 40 seconds.
The wafer was first transferred to the Pre-Clean II chamber where
about 250 .ANG. were removed from the surface of the patterned
dielectric. A tantalum barrier layer was then deposited conformally
in the via having a thickness of about 250 .ANG. using the IMP PVD
Ta/TaN chamber. The wafer was then transferred to the PVD Cu
chamber where a 1,000 .ANG. thick conformal seed layer was
deposited in the via. Next, the wafer was transferred to an
Electra.TM. Cu ECP system also available from Applied Materials,
Inc., located in Santa Clara, Calif., where the via was filled with
copper. The wafer was then moved to a chemical mechanical polishing
system, such as the Mirra.TM. system also available from Applied
Materials, Inc., located in Santa Clara, Calif., to planarize the
upper surface of the wafer.
[0063] The wafer was then transferred back to the Electra.TM. Cu
ECP system, where an acidic pre-rinse solution was applied to the
substrate surface removing about 25 .ANG. of the top portion of the
substrate surface. The pre-rinse solution was a mixture of about
0.5 wt % of HF acid and 1 M nitric acid and was applied at a flow
rate of about 750 mL/min for about 60 seconds at a temperature of
about 25.degree. C. A rinsing agent (deionized water) was then
sprayed onto the substrate surface at a flow rate of about 750
mL/min for about 60 seconds. Next, an initiation layer was
deposited on the conductive portions of the substrate surface by
applying an electroless solution containing 3 vol % (320 ppm) of
palladium chloride and a sufficient amount of HCl to provide a pH
of about 1.5 to the substrate surface. A 500 .ANG. thick
passivation layer was then deposited on the initiation layer by
electroless deposition using a cobalt electroless solution
containing 20 g/L of cobalt sulfate, 50 g/L of sodium citrate, 20
g/L of sodium hypophosphite, and a sufficient amount of potassium
hydroxide to provide a pH of about 10.
Example 1
[0064] In this example, a first substrate surface, as prepared
above, was exposed to an ultrasonic post-rinse process, which
removed about 200 .ANG. of the passivation layer. The post-rinse
solution was a mixture of nitric acid and deionized water at a
ratio of 1:1 and was applied to the substrate surface at a flow
rate of about 750 mL/min for 45 seconds at a temperature of
25.degree. C. and a pressure of 1 atm. The post-rinse process was
enhanced by applying ultrasonic energy having a frequency of 100
kHz at 50 watts for 300 seconds to the substrate support
pedestal.
Example 2
[0065] In this example, a second substrate surface, as prepared
above, was exposed to an ultrasonic post-rinse process, which
removed about 200 .ANG. of the passivation layer. The post-rinse
solution was a mixture of nitric acid and hydrogen peroxide at a
ratio of 2:1 and was applied to the substrate surface at a flow
rate of about 750 mL/min for 45 seconds at a temperature of
25.degree. C. and a pressure of 1 atm. The post-rinse process was
enhanced by applying ultrasonic energy having a frequency of 100
kHz at 50 watts for 300 seconds to the substrate support
pedestal.
Example 3
[0066] In this example, a third substrate surface, as prepared
above, was exposed to an ultrasonic post-rinse process, which
removed about 200 .ANG. of the passivation layer. The post-rinse
solution included a mixture of sulfuric acid and hydrogen peroxide
at a ratio of 3:1 and was applied to the substrate surface at a
flow rate of about 750 mL/min for 45 seconds at a temperature of
25.degree. C. and a pressure of 1 atm. The post-rinse process was
enhanced by applying ultrasonic energy having a frequency of 100
kHz at 50 watts for 300 seconds to the substrate support
pedestal.
Example 4
[0067] In this example, a fourth substrate surface, as prepared
above, was exposed to an ultrasonic post-rinse process, which
removed about 200 .ANG. of the passivation layer. The post-rinse
solution included a mixture of hydrochloric acid and hydrogen
peroxide at a ratio of 3:1 and was applied to the substrate surface
at a flow rate of about 750 mL/min for 45 seconds at a temperature
of 25.degree. C. and a pressure of 1 atm. The post-rinse process
was enhanced by applying ultrasonic energy having a frequency of
100 kHz at 50 watts for 300 seconds to the substrate support
pedestal.
[0068] While the foregoing is directed to the preferred embodiments
of the present invention, other and further embodiments of the
invention may be devised without departing from the basic scope
thereof. The scope of the invention is determined by the claims
that follow.
* * * * *