U.S. patent application number 12/047970 was filed with the patent office on 2008-09-18 for reagent delivery using a membrane-mediated process.
Invention is credited to Stephen Mazur.
Application Number | 20080223826 12/047970 |
Document ID | / |
Family ID | 39761589 |
Filed Date | 2008-09-18 |
United States Patent
Application |
20080223826 |
Kind Code |
A1 |
Mazur; Stephen |
September 18, 2008 |
Reagent Delivery using a Membrane-Mediated Process
Abstract
Methods and apparatuses for using a semi-permeable membrane to
deliver a reagent to a surface in a topographically selective
manner are provided. The methods and apparatuses are particularly
useful for removing sulfur-containing electrocatalysts from copper
surfaces using a semi-permeable membrane to deliver an oxidizing
agent to a catalyst-coated surface.
Inventors: |
Mazur; Stephen; (Wilmington,
DE) |
Correspondence
Address: |
E I DU PONT DE NEMOURS AND COMPANY;LEGAL PATENT RECORDS CENTER
BARLEY MILL PLAZA 25/1122B, 4417 LANCASTER PIKE
WILMINGTON
DE
19805
US
|
Family ID: |
39761589 |
Appl. No.: |
12/047970 |
Filed: |
March 13, 2008 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
60894487 |
Mar 13, 2007 |
|
|
|
Current U.S.
Class: |
216/88 ;
156/345.11 |
Current CPC
Class: |
H01L 21/02068 20130101;
H01L 21/76877 20130101 |
Class at
Publication: |
216/88 ;
156/345.11 |
International
Class: |
C23F 1/02 20060101
C23F001/02; C23F 1/08 20060101 C23F001/08 |
Claims
1. An apparatus comprising: a) a fully or partially enclosed
container; b) a semi-permeable membrane having an internal surface
and an external surface, wherein the membrane forms a surface of
the fully or partially enclosed container; and c) a
reagent-containing fluid which at least partially fills the fully
or partially enclosed container, wherein the reagent-containing
fluid contacts at least a portion of the internal surface of the
membrane.
2. The apparatus of claim 1, wherein the reagent-containing fluid
comprises an oxidizing agent.
3. The apparatus of claim 1, wherein the semi-permeable membrane is
selected from the group consisting of perfluorosulfonate ionomer
membranes and perfluorocarboxylate ionomer membranes.
4. A process comprising: a) providing an apparatus comprising: i) a
fully or partially enclosed container; ii) a semi-permeable
membrane having an internal surface and an external surface,
wherein the membrane forms a surface of the fully or partially
enclosed container; and iii) a reagent-containing fluid which at
least partially fills the enclosed container, wherein the
reagent-containing fluid contacts at least a portion of the
internal surface of the membrane; b) providing a workpiece having a
surface and optionally an oxidizable or reducible compound adsorbed
onto the surface of the workpiece; c) contacting the surface of the
workpiece with the external surface of the membrane; and d)
allowing at least a portion of the reagent to diffuse through the
membrane to react with the workpiece surface or an oxidizable or
reducible compound adsorbed onto the surface of the workpiece.
5. The process of claim 4, wherein the reagent is an oxidizing
agent.
6. The process of claim 5, wherein the oxidizing agent is selected
from the group consisting of ozone, hydrogen peroxide, peracids,
Fe(NO.sub.3).sub.3, and Ce(NH.sub.4).sub.2(NO.sub.3).sub.6).
7. The process of claim 4, wherein the semi-permeable membrane is a
perfluorosulfonate ionomer membrane or a perfluorocarboxylate
ionomer membrane.
8. The process of claim 4, wherein the oxidizable compound is
3-mercapto-1-propane sulfonic acid.
9. The process of claim 4, further comprising coating the surface
of the workpiece with a fluid film of a hydrocarbon or a halocarbon
prior to contacting the workpiece with the external surface of the
membrane.
10. The process of claim 4, further comprising: e) contacting the
workpiece with water.
Description
CROSS-REFERENCE TO RELATED APPLICATION
[0001] This application claims priority under 35 U.S.C. .sctn.119
from U.S. Provisional Application Ser. No. 60/894,487, filed Mar.
13, 2007.
FIELD OF THE INVENTION
[0002] The invention is directed to methods and apparatuses for
using a semi-permeable membrane to deliver a reagent to a surface
in a topographically selective manner. The methods and apparatuses
are particularly useful for removing sulfur-containing
electrocatalysts from copper surfaces using a semi-permeable
membrane to deliver an oxidizing agent to a catalyst-coated
surface.
BACKGROUND
[0003] Interconnections on integrated circuits are fabricated by
the Cu damascene process in which the interconnect circuit pattern
is lithographically etched into the surface of a dielectric layer
on the surface of the wafer. The etching creates "recessed areas"
in the dielectric layer that can be several nanometers to several
microns in depth. The remaining surface of the dielectric layer
forms "non-recessed areas" that surround the "recessed areas." The
pattern is then coated with thin conformal layers of a barrier
metal, such as Ta, followed by Cu. Additional Cu is then
electroplated over the entire surface of a wafer to fill completely
the recessed areas with Cu.
[0004] In order to assure complete filling of the smallest the
recessed areas, the electroplating chemistry incorporates an
electrocatalyst, most commonly 3-mercapto-1-propane sulfonic acid
(MPS), a salt of MPS, or a corresponding disulfide. These
electrocatalysts adsorb to the Cu surface and increase the rate of
Cu electrodeposition relative to areas of bare Cu lacking an
adsorbed electrocatalyst. This effect is amplified in very small
recessed areas because the surface concentration increases during
filling. Because the electrocatalyst is present on all surfaces of
the wafer, in the course of filling larger recessed areas, excess
Cu is deposited everywhere and must be removed. This is typically
achieved by chemical mechanical polishing, but may also be
accomplished by membrane-mediated electropolishing (MMEP) methods
disclosed by S. Mazur et al., (co-pending applications U.S. Ser.
No. 10/976,897; U.S. Ser. No. 10/986,048; and U.S. Ser. No.
11/291,697).
[0005] Removing excess Cu introduces significant expense, yield
loss and waste disposal problems for the fabrication of integrated
circuits. It is therefore desirable to minimize the amount of
excess Cu required to fill the circuit features.
[0006] One way to achieve this objective would be to interrupt
electrodeposition immediately after filling the small recessed
areas with Cu, and to then remove the electrocatalysts in a
topographically selective manner from the non-recessed areas, while
leaving the electrocatalysts in the recessed areas. In this way,
subsequent plating becomes concentrated in the recessed areas and
can be stopped with minimal accumulation of Cu on the non-recessed
areas.
[0007] MMEP has been shown to be highly effective for
topographically selective removal of MPS, but it is accompanied by
a significant amount of Cu removal. Typically, in order to
completely remove MPS from the surface of the non-recessed areas,
several nm of Cu must also be removed. It is therefore desirable to
improve the efficiency of MPS removal relative to Cu removal.
SUMMARY OF THE INVENTION
[0008] One aspect of this invention is an apparatus comprising:
[0009] a) a fully or partially enclosed container; [0010] b) a
semi-permeable membrane having an internal surface and an external
surface, wherein the membrane forms a surface of the fully or
partially enclosed container; and [0011] c) a reagent-containing
fluid which at least partially fills the fully or partially
enclosed container, wherein the reagent-containing fluid contacts
at least a portion of the internal surface of the membrane.
[0012] Another aspect of this invention is a process comprising:
[0013] a) providing an apparatus comprising: [0014] i) a fully or
partially enclosed container; [0015] ii) a semi-permeable membrane
having an internal surface and an external surface, wherein the
membrane forms a surface of the fully or partially enclosed
container; and [0016] iii) a reagent-containing fluid which at
least partially fills the fully or partially enclosed container,
wherein the reagent-containing fluid contacts at least a portion of
the internal surface of the membrane; [0017] b) providing a
workpiece having a surface and optionally an oxidizable or
reducible compound adsorbed onto the surface of the workpiece;
[0018] c) contacting the surface of the workpiece with the external
surface of the membrane; and [0019] d) allowing at least a portion
of the reagent to diffuse through the membrane to react with the
workpiece surface or an oxidizable or reducible compound adsorbed
onto the surface of the workpiece.
BRIEF DESCRIPTION OF THE FIGURES
[0020] FIG. 1 is a schematic cross-section of an apparatus.
DETAILED DESCRIPTION
[0021] One embodiment of the process of this invention can be used
to deliver reagents to the surface of a workpiece. The reagents can
react either with the surface of the workpiece, or with an
oxidizable or reducible compound that is adsorbed onto the surface
of the workpiece. If the surface of the workpiece has topographical
features, i.e., recessed areas and non-recessed areas, one
embodiment of the process of this invention can be used to deliver
reagents selectively to the non-recessed areas. In this way,
material can be removed from the non-recessed areas of the
workpiece without also removing material from the recessed
areas.
[0022] One aspect of this invention is an apparatus comprising:
[0023] a) a fully or partially enclosed container; [0024] b) a
semi-permeable membrane having an internal surface and an external
surface, wherein the membrane forms a surface of the fully or
partially enclosed container; and [0025] c) a reagent-containing
fluid which at least partially fills the fully or partially
enclosed container (which can also be referred to as a "vessel"),
wherein the reagent-containing fluid contacts at least a portion of
the internal surface of the membrane.
[0026] In some embodiments, the apparatus can be used in the
membrane-mediated delivery of a reagent to the non-recessed areas
of a workpiece having non-recessed areas. For example, in
integrated circuit (IC) interconnects, the recessed areas can be
about 0.5 micron below the surrounding non-recessed areas. In
printed wiring boards, the recessed areas may be 10 to 50 microns
below the surrounding areas.
[0027] Suitable reagents include oxidizing agents and reducing
agents. Suitable oxidizing agents include ozone, hydrogen peroxide,
peracids, and salts of high valent transition metal ions (e.g.,
Fe(NO.sub.3).sub.3 or Ce(NH.sub.4).sub.2(NO.sub.3).sub.6). Some
reagents, for example, hydrogen peroxide, can be used at
concentrations as high as 70%. The transition metal salts are more
typically used at concentrations of 0.01 M-1.0 M. Peracids can be
made in situ by combining a carboxylic acid with hydrogen
peroxide.
[0028] Preferably, the reagent-containing fluid is maintained at a
hydrostatic pressure greater than ambient atmospheric pressure, and
the membrane is sufficiently flexible to expand under the influence
of this pressure to establish a convex external surface (a "bulge"
or "blister") to contact the workpiece.
[0029] Suitable semi-permeable membranes for use with oxidizing
agents are those which are stable in the presence of the oxidizing
agent(s) and which are permeable to the oxidizing agent(s).
Suitable membranes include copolymers of fluorinated and/or
perfluorinated olefins and monomers containing strong acid groups.
Perfluorosulfonate ionomer membranes and perfluorocarboxylate
ionomer membranes are suitable. Other semi-permeable membranes can
also be used.
[0030] FIG. 1 shows a schematic of an apparatus in which A
represents a reagent-containing fluid, B represents a
semi-permeable membrane, C represents a workpiece, and D represents
recessed areas in a workpiece.
[0031] In the membrane-mediated processes of this invention, a
membrane is interposed between the reagent and the workpiece. In
some embodiments, the workpiece has small topographic features such
as recessed and non-recessed areas. By providing a membrane that is
thick and/or stiff enough that it does not conform to the small
topographic features of the workpiece, the membrane will not
contact the surfaces of the recessed areas. In this way, the
reagent is delivered selectively to the non-recessed areas, and the
process can selectively remove material that is adsorbed onto the
non-recessed areas of the workpiece, without removing material that
is in the recessed areas. In one embodiment, the workpiece is a
metal-coated substrate, e.g., a damascene wafer.
[0032] One aspect of this invention is a process comprising: [0033]
a) providing an apparatus comprising: [0034] i) a fully or
partially enclosed container; [0035] ii) a semi-permeable membrane
having an internal surface and an external surface, wherein the
membrane forms a surface of the fully or partially enclosed
container; and [0036] iii) a reagent-containing fluid which at
least partially fills the enclosed container, wherein the
reagent-containing fluid contacts at least a portion of the
internal surface of the membrane; [0037] b) providing a workpiece
having a surface and optionally an oxidizable or reducible compound
adsorbed onto the surface of the workpiece; [0038] c) contacting
the surface of the workpiece with the external surface of the
membrane; and [0039] d) allowing at least a portion of the reagent
to diffuse through the membrane to react with the workpiece surface
or an oxidizable or reducible compound adsorbed onto the surface of
the workpiece.
[0040] Suitable reaction temperatures are from 10-80.degree. C. In
one embodiment, the reaction temperature is within the range of
15-50.degree. C. Reaction times are from 0.1 sec to several
minutes, depending on the concentration and composition of the
reagent.
[0041] In one embodiment, a compound is adsorbed onto the workpiece
prior to contacting the surface of the workpiece with the external
surface of the membrane. In one embodiment, the workpiece has
adsorbed onto it a sulfur-containing electrocatalyst (e.g., MPS,
3-mercapto-1-propane sulfonic acid) and the reagent in the
reagent-containing fluid is an active oxidizing agent.
[0042] Removal of an adsorbed oxidizable compound is accomplished
by oxidizing it to form a soluble species. After the oxidizing
agent diffuses through the membrane, it reacts with the adsorbed
oxidizable compound, converting it to a form that has less affinity
for the workpiece surface and can be washed or rinsed or dissolved
away. The soluble species is then removed from the workpiece
surface by rinsing with a suitable or solution, i.e., a solvent or
solution that will dissolve the soluble species. For example, the
oxidized adsorbed oxidizable compound can be removed from the
workpiece surface by immersing the workpiece in a suitable solvent
(e.g., water) or by periodically rinsing the surface with a
suitable solvent.
[0043] Oxidation of the adsorbed oxidizable compound is
accomplished when a portion of the external surface of the membrane
contacts a portion of the non-recessed areas of the workpiece. As
used herein, "contact" (of the membrane and the workpiece) means
that preferably the workpiece and the membrane are within close
proximity, e.g., between 1 nm and 1 micron. Typically, the
apparatus is moved across the surface of workpiece, especially if
the area of the surface to be treated is larger than the contact
area of the membrane with the surface.
[0044] In one embodiment, the workpiece is coated with a thin layer
(less than 1 micron thick) of water-immiscible hydrocarbon or
halocarbon before being contacted with the membrane. Suitable
hydrocarbons include heptane and toluene. While it is not intended
that the invention be bound by any particular mechanism or theory,
it is believed the hydrocarbon or halocarbon lubricates the surface
and also improves the selectivity of the adsorbed oxidizable
compound removal by slowing or stopping diffusion of the oxidizing
agent into the recessed areas of the workpiece. In this way,
adsorbed oxidizable compound is removed preferentially, preferably
only, from those areas in direct contact with the membrane, leaving
the electrocatalyst in the recesses. This leads to more copper
plating out in the recesses than on the non-recessed areas of the
workpiece in a subsequent plating process.
[0045] Removal of an adsorbed reducible compound is carried out in
an analogous process, except that the reagent is a reducing agent,
for example sodium borohydride.
[0046] Selective oxidation of the adsorbed oxidizable compound can
also be accomplished by a membrane-mediated electrochemical
process. In such a process, the half-cell is configured as
described in U.S. Ser. No. 10/976,897.
[0047] The amount of adsorbed compound removed can be determined by
XPS and/or cyclic voltammetry.
EXAMPLES
Example 1
Preparation of MPS-Activated and MPS-Free Cu Surfaces
[0048] A 12'' silicon wafer pre-plated with approximately 150 nm of
Cu (Novellus Systems, Inc., Tualatin, Oreg.) was mounted on a
spin-coater (Headway Research, Inc., Garland, Tex., Model PWM32)
and treated at 300 rpm with reagents in the following sequence: DI
(de-ionized) water; 10 ml of 5% H.sub.2SO.sub.4; DI water; 10 ml
0.1% MPS (3-mercapto-1-propane sulfonic acid) in 5%
H.sub.2SO.sub.4; and DI water. The MPS-coated wafer was then dried
at 1000 rpm. By skipping the treatment with the 0.1% MPS solution,
the same procedure was used to prepare wafers free of MPS.
Example 2
Analysis of Cu Surfaces by Cyclic Voltammetry and XPS
[0049] Cyclic voltammetry measurements (EG&G PARC, Princeton,
N.J., Model 173 potentiostat and Model 175 programmer) were made at
a scan rate of 10 mV/sec, operating at potentials between -0.40V
and -1.00 V versus Hg/HgSO.sub.4. For this purpose, selected areas
of the wafer were masked by applications of a 2.5 cm square piece
of Teflon.RTM. tape with a round opening 1 cm in diameter (0.785
cm.sup.2). A pyrex flange joint 7 cm long with a 2 cm O-ring was
centered over the hole in the tape mask and clamped onto the wafer
to form a cylindrical cell with liquid-tight seal. 10 ml of
electrolyte solution (medium acid Cu plating solution, Novellus
Systems, Inc., Tualatin, Oreg.) was added to the cell. A
Hg/HgSO.sub.4 reference electrode (Radiometer Analytical SAS,
Villeurbanne, France, Model Ref 601) was inserted into the cell
along with a Cu foil counter electrode. An electrical connection
was made to the surface of the wafer outside the area of the cell
and connected to the potentiostat as the working electrode.
Measurements on wafers freshly prepared as in Example 1 exhibited
currents 20 to 30 mA higher than on MPS-free wafers at potentials
from -0.7 to -1.0 V versus Hg/HgSO.sub.4 (FIG. 1). This
demonstrates the catalytic effect of MPS on cathodic reaction of
the Cu surface and provides a means to detect the presence of MPS
on a Cu surface.
[0050] X-ray photoelectron spectroscopy (XPS) was used to analyze
the surfaces. On an MPS-activated Cu surface, the signal from S (2p
electrons) represented 4% of all elements detected. In contrast, on
MPS-free wafers prepared as in Example 1, the signal from S
represented only 0.2% of all elements detected.
Example 3
Oxidation of MPS with Iron and Cerium Nitrates
[0051] A wafer fragment activated with MPS as in Example 1 was
immersed in a solution of 0.5M Fe(NO.sub.3).sub.3 for approximately
5 sec and immediately rinsed with DI water. Visual inspection
showed that all of the Cu had been removed exposing, the
silver-colored Ta sub-layer. One area of a second MPS-activated
wafer fragment was exposed to a solution of 0.05M
Fe(NO.sub.3).sub.6 for 15 sec and immediately rinsed with DI water.
Cyclic voltammetry indicated no detectable loss of MPS relative to
an un-treacted area of the same wafer fragment.
[0052] A third MPS-activated wafer fragment was exposed to a
solution of 0.05M Ce(NH.sub.4).sub.2(NO.sub.3).sub.6 for 10 sec.
Cyclic voltammetry indicated little if any MPS was removed. When
this experiment was repeated with 30 sec exposure the thickness of
Cu layer was reduced from 147 to 110 nm and cyclic voltammetry
showed more than 50% of the MPS had been removed.
Example 4
Oxidation with Aqueous Hydrogen Peroxide
[0053] A wafer fragment activated with MPS as in Example 1 was
immersed in a 50% solution of hydrogen peroxide in water (Aldrich)
for 15 sec and then rinsed with DI water. Discoloration on the
surface indicated the formation of copper oxides, but the thickness
of Cu was only reduced by 3.+-.2 nm. Cyclic voltammetry showed that
more than 50% of the MPS had been removed.
Example 5
Membrane-Mediated Oxidation with Aqueous Hydrogen Peroxide
[0054] A membrane cell with a window 1' in diameter was fitted with
a Nafion.RTM. PFSA membrane (N1110-H, E. I. du Pont de Nemours and
Company, Wilmington, Del.) and filled with a 50% solution of
hydrogen peroxide in water (Aldrich) adjusted to a hydrostatic
pressure of approximately 1 psi. An MPS-activated wafer was rinsed
with DI water, then brought into contact and gently stroked with
the external surface of the membrane for 30 sec, and then rinsed in
DI water. Cyclic voltammetry showed approximately 50% of the MPS
had been removed.
Example 6
Oxidation with Ozone
[0055] A wafer fragment activated with MPS as in Example 1 was
immersed in water saturated with ozone for 30 sec and then rinsed
with DI water. Cyclic voltammetry showed that virtually all of the
MPS had been removed. As second wafer fragment activated with MPS
as in Example 1 was exposed to a stream of gaseous ozone for 30 sec
and then rinsed with DI water. Cyclic voltammetry indicated
approximately 20% of the MPS had been removed.
Example 7
Membrane-Mediated Oxidation with Adipic Acid in H.sub.2O.sub.2
[0056] A wafer with 600 nm deep recessed features was activated
with MPS as in Example 1. A drop of heptane was placed on the wafer
surface. A membrane cell with a window 3'' in diameter was fitted
with a Nafion.RTM. PFSA membrane (N1110-H) and filled with a 20%
solution of hydrogen peroxide in water (Aldrich) and 0.1 wt %
adipic acid and adjusted to a hydrostatic pressure of approximately
1 psi. The membrane was brought down dry onto the surface of the
wafer and moved back and forth (2 cm/sec, 2 rpm) on the
heptane-wetted area for 60 sec. The heptane was then evaporated and
the wafer rinsed with 5% sulfuric acid in de-ionized water.
[0057] After rinsing with dilute sulfuric acid, the adipic
acid/H.sub.2O.sub.2-treated wafer was plated with an additional
layer of Cu (constant potential of -0.6 V vs. Hg/HgSO.sub.4;
area=12.5 cm.sup.2; 17 coulombs). Profilometry of the surface
indicated that the step height had been reduced from about 600 nm
to 200-400 nm.
[0058] This demonstrates that the membrane-mediated oxidation of
MPS is topographically selective, removing MPS selectively from the
non-recessed area, rather than from the recessed area.
* * * * *