U.S. patent application number 13/570033 was filed with the patent office on 2012-11-29 for microelectronic substrate cleaning systems with polyelectrolyte and associated methods.
This patent application is currently assigned to MICRON TECHNOLOGY, INC.. Invention is credited to Joseph N. Greeley, Lukasz Hupka, Timothy A. Quick, Prashant Raghu, Nishant Sinha.
Application Number | 20120298158 13/570033 |
Document ID | / |
Family ID | 41695182 |
Filed Date | 2012-11-29 |
United States Patent
Application |
20120298158 |
Kind Code |
A1 |
Greeley; Joseph N. ; et
al. |
November 29, 2012 |
MICROELECTRONIC SUBSTRATE CLEANING SYSTEMS WITH POLYELECTROLYTE AND
ASSOCIATED METHODS
Abstract
Several embodiments of cleaning systems using polyelectrolyte
and various associated methods for cleaning microelectronic
substrates are disclosed herein. One embodiment is directed to a
system that has a substrate support for holding the microelectronic
substrate, a dispenser positioned above the substrate support and
facing a surface of the microelectronic substrate, a reservoir in
fluid communication with the dispenser via a conduit, and a washing
solution contained in the reservoir. The washing solution includes
a polyelectrolyte.
Inventors: |
Greeley; Joseph N.; (Boise,
ID) ; Sinha; Nishant; (Boise, ID) ; Hupka;
Lukasz; (Salt Lake City, UT) ; Quick; Timothy A.;
(Boise, ID) ; Raghu; Prashant; (Boise,
ID) |
Assignee: |
MICRON TECHNOLOGY, INC.
Boise
ID
|
Family ID: |
41695182 |
Appl. No.: |
13/570033 |
Filed: |
August 8, 2012 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
12195003 |
Aug 20, 2008 |
8252119 |
|
|
13570033 |
|
|
|
|
Current U.S.
Class: |
134/58R ;
134/198; 510/175 |
Current CPC
Class: |
H01L 21/67057 20130101;
C11D 11/0047 20130101; H01L 21/67051 20130101; H01L 21/02057
20130101; B08B 3/08 20130101; C11D 3/37 20130101; C11D 7/06
20130101 |
Class at
Publication: |
134/58.R ;
134/198; 510/175 |
International
Class: |
B08B 3/12 20060101
B08B003/12; C11D 7/60 20060101 C11D007/60; C11D 3/60 20060101
C11D003/60; B08B 3/08 20060101 B08B003/08 |
Claims
1. A system for cleaning a microelectronic substrate, the system
comprising: a substrate support for holding the microelectronic
substrate; a dispenser positioned above the substrate support and
facing a surface of the microelectronic substrate; a reservoir in
fluid communication with the dispenser via a conduit; and a washing
solution contained in the reservoir, the washing solution including
a polyelectrolyte formed from monomers individually having an
electrolytic function group selected from the groups consisting of
a hydroxyl group (--OH), a carboxyl group (--COOH), a carboxamide
group (--CONH.sub.2), an amino group (--NH.sub.2), an imine group
(--C.dbd.NR), an imide group (RCONCOR', in which R is an alkyl
group different than R'), a vinyl pyrrolidone group ##STR00006## a
vinyl pyridine group ##STR00007## a nitro group (--NO.sub.2), a
sulfonate group (--HSO.sub.3), a sulfate group (--HSO.sub.4), and a
phosphate group (--HPO.sub.4).
2. The system of claim 1 wherein the washing solution includes
about 3 parts hydrogen peroxide and about 2 parts ammonium
hydroxide in 100 parts deionized water, and wherein the washing
solution further includes about 0.1% by weight of the
polyelectrolyte, and further wherein the polyelectrolyte includes a
polyacrylic acid having a molecular weight of about 50,000, and
further wherein the washing solution has a pH of about 10.0 to
about 10.3 and a temperature of about 30.degree. C. to about
75.degree. C.
3. The system of claim 1 wherein the polyelectrolyte includes a
polyacrylic acid or a polyacrylate salt having a molecular weight
of about 2,000 to about 450,000.
4. The system of claim 1 wherein the polyelectrolyte includes a
polyacrylic acid or a polyacrylate salt having a molecular weight
of about 2,000 to about 450,000, and wherein the washing solution
includes about 0.01% to about 5% by weight of the polyacrylic acid
or the polyacrylate salt.
5. A system for cleaning a microelectronic substrate, the system
comprising: a vessel for holding the microelectronic substrate; a
transducer disposed within the vessel; a signal delivery device
operably coupled with the transducer, the signal delivery device is
configured to output an electrical signal that oscillates the
transducer; and a washing solution in the vessel, the washing
solution containing a polyelectrolyte having a plurality of ionic
functional groups on a carbon backbone, wherein the microelectronic
substrate is submerged in the washing solution.
6. The system of claim 5 wherein the ionic functional group
includes at least one of a hydroxyl group (--OH), a carboxyl group
(--COOH), a carboxamide group (--CONH.sub.2), an amino group
(--NH.sub.2), an imine group (--C.dbd.NR), an imide group
(RCONCOR', in which R is an alkyl group different than R'), a vinyl
pyrrolidone group ##STR00008## a vinyl pyridine group ##STR00009##
a nitro group (--NO.sub.2), a sulfonate group (--HSO.sub.3), a
sulfate group (--HSO.sub.4), and a phosphate group
(--HPO.sub.4).
7. The system of claim 5 wherein the ionic functional group
includes a carboxyl group, and wherein the polyelectrolyte is
configured to form an array of ionized carboxyl group (--COO.sup.-)
carried by a carbon backbone.
8. The system of claim 6 wherein the ionic functional group
includes a carboxyl group, and wherein the polyelectrolyte is
configured to form an array of ionized carboxyl groups
(--COO.sup.-) carried by a carbon backbone, and wherein the array
of ionized carboxyl groups has a sphere, a spiral, or a zigzag
arrangement.
9. A cleaning solution for cleaning a semiconductor substrate,
comprising: an oxidizer having a concentration of about 0.1% to
about 10% by volume; a base having a concentration of about 0.1% to
about 10% by volume; and a polyacrylic acid having a concentration
of about 0.01% to about 5% by weight, the polyacrylic acid having a
molecular weight of about 2,000 to about 450,000.
10. The cleaning solution of claim 9 wherein the polyacrylic acid
has a molecular weight of about 50,000, and wherein the cleaning
solution has a pH of about 10.0, and further wherein the oxidizer
includes hydrogen peroxide and the base includes ammonium
hydroxide.
11. The cleaning solution of claim 9, further comprising at least
one of a pH buffer, a chelating agent, a corrosion inhibitor, and a
surfactant.
Description
CROSS-REFERENCE TO RELATED APPLICATION
[0001] This application is a divisional of U.S. application Ser.
No. 12/195,003 filed Aug. 20, 2008, which is incorporated herein by
reference in its entirety.
TECHNICAL FIELD
[0002] The present disclosure is related to microelectronic
substrate cleaning systems with polyelectrolyte and associated
methods of cleaning microelectronic substrates.
BACKGROUND
[0003] Manufacturing microelectronic devices typically includes
physically and/or chemically processing microelectronic substrates.
For example, a layer of material can be added to microelectronic
substrates with physical vapor deposition (PVD), chemical vapor
deposition (CVD), or atomic layer deposition (ALD) processes. A
layer of material can also be removed from microelectronic
substrates with dry etching, wet etching, chemical-mechanical
polishing, or electrochemical-mechanical polishing processes. All
of these processes can leave solid particles adsorbed onto surfaces
of the microelectronic substrates. If not removed, the particles
can adversely impact subsequent processing and/or the performance
of microelectronic devices formed in the microelectronic
substrates.
[0004] One conventional cleaning technique includes washing
microelectronic substrates with an aqueous solution of hydrogen
peroxide (H.sub.2O.sub.2), ammonium hydroxide (NH.sub.4OH), and/or
hydrochloric acid (HCl) while applying physical energy (e.g.,
megasonic waves). However, as dimensions of microelectronic
features (e.g., trenches, apertures, etc.) decrease, the applied
physical energy may damage the ever smaller microelectronic
features. If physical energy is not applied in the cleaning
process, then the process tends to have low particle removal
efficiencies. Accordingly, there is a need for improved cleaning
systems and methods that can more effectively remove particles from
microelectronic substrates without damaging the microelectronic
features.
BRIEF DESCRIPTION OF THE DRAWINGS
[0005] FIG. 1 is a schematic view of a cleaning system configured
in accordance with an embodiment of the disclosure.
[0006] FIG. 2 is a schematic cross-sectional view of a cleaning
system configured in accordance with another embodiment of the
disclosure.
[0007] FIG. 3 is a plot of particle removal efficiency (PRE) of
various washing solutions in accordance with an embodiment of the
disclosure.
[0008] FIG. 4 is a plot of etch delta of various washing solutions
in accordance with an embodiment of the disclosure.
[0009] FIG. 5 is a plot of average zeta potential of various
washing solutions in accordance with an embodiment of the
disclosure.
DETAILED DESCRIPTION
[0010] Various embodiments of cleaning systems using a
polyelectrolyte and various methods of cleaning microelectronic
substrates with improved particle removal efficiencies are
described below. The term "microfeature substrate" is used
throughout to include substrates upon which and/or in which
microelectronic devices, micromechanical devices, data storage
elements, read/write components, and other features are fabricated.
Such a microelectronic substrate can include one or more conductive
and/or nonconductive layers (e.g., metallic, semi-conductive,
and/or dielectric materials) that are situated upon or within one
another. These conductive and/or nonconductive layers can also
include a wide variety of electrical elements, mechanical elements,
and/or systems of such elements in the conductive and/or
nonconductive layers (e.g., an integrated circuit, a memory, a
processor, a microelectromechanical system, etc.) The term
"surface" can encompass planar and nonplanar surfaces of a
microelectronic substrate with or without patterned and
non-patterned features. The term "polyelectrolyte" generally refers
to a polymeric compound formed from monomers individually having an
electrolytic functional group. The electrolytic functional group
can be either anionic or cationic. The electrolytic functional
group can also be either hydrophilic or hydrophobic. Particle
removal efficiency (PRE) generally refers to a percentage of
adsorbed solid particles removed from a microelectronic substrate.
In the following description, the PRE can be determined by (1)
counting a first number of the adsorbed particles using dark-light
inspection and/or other suitable inspection techniques; (2)
counting a second number of the adsorbed particles using dark-light
inspection after a cleaning process; (3) subtracting the second
number from the first number to derive a number of particles
removed; and (4) dividing the number of particles removed by the
first number to derive the PRE. A person skilled in the relevant
art will also understand that the disclosure may have additional
embodiments, and that the disclosure may be practiced without
several of the details of the embodiments described below with
reference to FIGS. 1-5.
[0011] FIG. 1 is a schematic view of an embodiment of a cleaning
system 100 for cleaning a microelectronic substrate 102 in
accordance with an embodiment of the disclosure. As shown in FIG.
1, the cleaning system 100 can include a dispensing assembly 104
positioned above a substrate supporting assembly 106. In several
embodiments, the cleaning system 100 can be configured as an
independent unit. In other embodiments, the dispensing assembly 104
and/or the substrate supporting assembly 106 can be incorporated
into a chemical-mechanical polishing (CMP) apparatus, an
electrochemical-mechanical polishing (ECMP) apparatus, and/or other
suitable microelectronic substrate processing equipment.
[0012] In the illustrated embodiment, the dispensing assembly 104
includes a dispenser 108, a first reservoir 110a holding a first
washing solution 109a, and a second reservoir 110b holding a second
washing solution 109b. The dispenser 108 can include a nozzle, an
atomizer, and/or other suitable delivery or dispensing component.
The first and second reservoirs 110a-b can be coupled to the
dispenser 108 in a parallel arrangement. A first branch 112a of a
conduit 112 couples the first reservoir 110a to the dispenser 108
via a first valve 111a, and a second branch 112b of the conduit 112
couples the second reservoir 110b to the dispenser 108 via a second
valve 111b. The first and second reservoirs 110a-b can individually
include a tank constructed from a metal, a polymeric material,
glass, and/or other material suitable for holding the first and
second washing solutions 109a-b, respectively. The first and second
valves 111a-b can individually include a ball valve, a butterfly
valve, a needle valve, and/or other suitable valve. In certain
embodiments, the conduit 112 can be flexible, and the dispensing
assembly 104 can optionally include an actuator (not shown)
configured to translate or otherwise move the dispenser 108
transversely across the microelectronic substrate 102 (as indicated
by arrow A). In other embodiments, the conduit 112 can be
substantially rigid, and the dispenser 108 can be fixed relative to
the microelectronic substrate 102. In further embodiments, the
dispensing assembly 104 can further include meters, mixers, valves,
and/or other fluid handling components.
[0013] The supporting assembly 106 can include a substrate support
114 disposed in a basin 116. The substrate support 114 can include
a vacuum chuck, a mechanical chuck, and/or other suitable device
for holding the microelectronic substrate 102. The substrate
support 114 can also include a shaft 115 coupled to a motor (not
shown) for rotating substrate support 114 about an axis 117 (as
indicated by arrow R). The basin 116 can include an opening 118a
and an outlet 118b in a bottom portion of the basin 116 that is
coupled to a drain. The basin 116 can optionally include a
strainer, a filter, and/or other fluid handling component (not
shown).
[0014] In operation, after undergoing CMP or ECMP processing, the
microelectronic substrate 102 can be placed on the substrate
support 114 for cleaning. In one embodiment, the cleaning process
can include a first cleaning procedure with the first washing
solution 109a and followed by a second cleaning procedure with the
second washing solution 109b. During the first cleaning procedure,
an operator can open the first valve 111a to flow the first washing
solution 109a from the first reservoir 110a to the dispenser 108
via the conduit 112. The dispenser 108 then distributes the first
washing solution 109a onto a surface of the microelectronic
substrate 102 (as indicated by arrows 119). In certain embodiments,
the first washing solution 109a can have a pressure generally less
than about 1.0 psig. The pressure at the dispenser can be about 0.5
psig or about 0.2 psig. In other embodiments, the first washing
solution 109a can have other desired pressures at the dispenser 108
to apply physical energy to the surface of the microelectronic
substrate via spraying.
[0015] In certain embodiments, the dispenser 108 can be generally
stationary relative to the microelectronic substrate 102 during the
first cleaning procedure. In other embodiments, the dispenser 108
can translate transversely across the microelectronic substrate 102
while dispensing the first washing solution 109a onto the surface
of the microelectronic substrate 102. Optionally, in any of the
foregoing embodiments, the substrate support 114 can rotate about
the axis 117 and can force the first washing solution 109a to flow
on the surface of the microelectronic substrate 102 into the basin
116. The basin 116 then collects the spent first washing solution
109a and passes it to a drain via the outlet 118b.
[0016] The first washing solution 109a can include an oxidizer, a
base, and a polyelectrolyte. The oxidizer can include ozone
(O.sub.3), hydrogen peroxide (H.sub.2O.sub.2), a permanganate salt
(e.g., KMnO.sub.4), a chromate salt (e.g., NaCrO.sub.4), a
perchlorate salt (e.g., KClO.sub.4), hydroperoxide, and/or other
suitable oxidizer. In certain embodiments, the oxidizer can have a
concentration of about 0.1% to about 10% by volume. In other
embodiments, the oxidizer can have a concentration of about 1% to
about 5%, about 2% to about 4%, or about 3% by volume. The base can
include ammonium hydroxide (NH.sub.4OH), sodium hydroxide (NaOH),
potassium hydroxide (KOH), and/or other suitable basic composition.
In certain embodiments, the base can have a concentration of about
0.1% to about 10% by volume. In other embodiments, the base can
have a concentration of about 0.5% to about 8%, about 1% to about
6%, or about 2% to about 4% by volume. In further embodiments,
either the oxidizer or the base may be omitted from the first
washing solution 109a.
[0017] The polyelectrolyte can include a polymeric material formed
from monomers individually having an electrolytic function group.
Examples of the electrolytic function group include the hydroxyl
group (--OH), the carboxyl group (--COOH), the carboxamide group
(--CONH.sub.2), the amino group (--NH.sub.2), the imine group
(--C.dbd.NR), the imide group (RCONCOR', in which R is an alkyl
group different than R'), the vinyl pyrrolidone group
##STR00001##
the vinyl pyridine group
##STR00002##
the nitro group (--NO.sub.2), the sulfonate group (--HSO.sub.3),
the sulfate group (--HSO.sub.4), and the phosphate group
(--HPO.sub.4), and/or other suitable electrolytic functional
groups. In certain embodiments, the polyelectrolyte can have a
concentration of about 0.01% to about 5% by weight. In other
embodiments, the polyelectrolyte can have a concentration of about
0.05% to about 4%, about 0.1% to about 3%, or about 0.1% by weight.
In further embodiments, the polyelectrolyte can have other suitable
concentrations.
[0018] The polyelectrolyte can form an array of repetitive ionized
functional groups carried on a carbon backbone in a solvent. For
example, in several embodiments, the polyelectrolyte can include a
polyacrylic acid (PAA) having the following chemical structure:
##STR00003##
The polyelectrolyte can also include an anionic salt (e.g., a
sodium salt as illustrated below) of the polyacrylic acid having
the following chemical structure:
##STR00004##
As a result, after dissolving in a solvent (e.g., deionized water),
the PAA can form a long chain molecule having an array of
repetitive ionized carboxyl groups (--COO.sup.-) carried by a
carbon backbone as follows:
##STR00005##
In certain embodiments, the array of ionized carboxyl groups can be
arranged generally linearly. In other embodiments, the array of
ionized carboxyl groups can form a sphere, a spiral, a zigzag,
and/or other suitable arrangement.
[0019] In a particular embodiment, the first washing solution 109a
can include 3 parts hydrogen peroxide by volume, 2 parts ammonium
hydroxide by volume, and about 0.1% by weight PAA in 100 parts
deionized water. The first washing solution 109a has a pH of about
10. In certain embodiments, the polyacrylic acid and/or the
polyacrylate salt can have a molecular weight of about 2,000 to
about 450,000. In other embodiments, the polyacrylic acid and/or
the polyacrylate salt can have a molecular weight of about 10,000
to about 300,000, about 30,000 to about 200,000, or about 50,000 to
about 100,000. In other embodiments, the first washing solution
109a can have other desired volume ratios and/or pH. In further
embodiments, the first washing solution 109a can also include a pH
buffer (e.g., the carbonic acid (H.sub.2CO.sub.3)), a chelating
agent (e.g., a dicarboxylic acid), a corrosion inhibitor (e.g.,
benzotriazole), a surfactant (e.g., ammonium dodecyl sulfate,
linear alkyl benzene, etc.), and/or other suitable composition. In
yet further embodiments, the first washing solution 109a can
include at least one of tetrabutylammonium perfluorooctanesulfonate
(PFOS), sorbitan monolaurate (SPAN20), and/or other suitable
surfactants in lieu of the polyelectrolyte.
[0020] The second washing solution 109b can include a composition
different than that of the first washing solution 109a. For
example, in certain embodiments, the second washing solution 109b
can include an oxidizer (e.g., hydrogen peroxide (H.sub.2O.sub.2)),
an acid (e.g., hydrochloric acid (HCl)), and optionally, an etchant
(e.g., hydrofluoric acid (HF)) in an aqueous solution. In other
embodiments, the second washing solution 109b can include a similar
composition in an organic solution. In further embodiments, the
second washing solution 109b can include a solvent (e.g., deionized
water) without other chemical compositions.
[0021] The polyelectrolyte has been observed to chemically improve
the PRE of the cleaning system 100 to reduce or eliminate the need
to also apply physical energy to the substrate. It has also been
observed that the addition of an organic additive (e.g., the
polyelectrolyte, an anionic surfactant (e.g., PFOS), or a non-ionic
surfactant (e.g., SPAN20)) can reduce material loss from the
surface of the microelectronic substrate 102. As a result, longer
washing periods (e.g., greater than about 2 minutes) may be used.
The following discussion proposes several possible mechanisms that
may improve the PRE, but it is understood that several embodiments
of the cleaning system 100 and associated methods for cleaning
microelectronic substrates can improve the PRE via a combination of
these mechanisms or other mechanisms in addition to or in lieu of
the mechanisms of action discussed below.
[0022] Without being bound by theory, it is believed that the
polyelectrolyte can improve the PRE by homogenizing an
electrokinetic potential (commonly referred to as a "zeta
potential") of particles adsorbed onto the surface of the
microelectronic substrate 102. Electrophoretic mobility measuring
devices are common tools for deriving a zeta potential of
particles. However, such measured zeta potential represents an
average value for the particles. Individual particles, instead, may
exhibit localized zeta potentials very different than the measured
value. For example, an individual particle may have a first region
with a zeta potential of about +10 mV, a second region with a zeta
potential of about -80 mV, and an average zeta potential of about
-50 mV. As a result, the first region of one particle may attract
the second region of another particle more (or repulse it less)
because of the different localized zeta potentials than if the
particles have a homogeneous -50 mV zeta potential. It is believed
that the polyelectrolyte with its array of ionized functional
groups (e.g., the carboxyl groups of PAA) can substantially
encapsulate particles inside a matrix of charge-conducting
electrolytic groups. As a result, substantially all regions of an
individual particle in the first washing solution 109a can be in
electrical communication with one another to at least reduce
regional differences in zeta potential, and thus increase the
repulsive force between the particles and the surface of the
microelectronic substrate.
[0023] Without being bound by theory, it is also or alternatively
believed that polyelectrolyte adsorbed on the particles can modify
the zeta potential of the particles because the matrix of ionized
functional groups can form a new surface double layer around the
particles suspended in the first washing solution 109a. It is also
believed that the zeta potential of the particles may be modified
by controlling the ionization characteristics of the
polyelectrolyte. In certain embodiments, controlling the ionization
characteristics of the polyelectrolyte can include varying the
molecular weight of the polyelectrolyte and/or controlling the pH
of the first washing solution 109a. In other embodiments,
controlling the ionization characteristics can include selecting a
suitable functional group for the polyelectrolyte based on a zeta
potential of the particles, an isoelectric point of the particles,
and/or other characteristics of the particles or the first washing
solution 109.
[0024] Without being bound by theory, it is also or alternatively
believed that the polyelectrolyte can improve the PRE by forming a
barrier layer that may sterically hinder the adsorption or
re-adsorption of the particles onto surface features (e.g.,
trenches) of the microelectronic substrate 102. For example, PAA
with a molecular weight of 15,000 is believed to form a barrier
layer with a thickness of about 2 nm on the particles containing
silicon nitride. PAA with a molecular weight of 30,000 is believed
to form a barrier layer with a thickness of about 3.5 nm on the
particles containing silicon nitride. For the particles with a
diameter of about 25 nm, the PAA barrier layer can substantially
increase the volume of the particles and thus reduce the chance of
being adsorbed in the trenches of the microelectronic substrate
102.
[0025] After flowing the first washing solution 109a for a first
period of time (e.g., 5 minutes for batch processes and 30-90
seconds for single wafer processes), the operator can close the
first valve 111a and end the first cleaning procedure. The operator
can then start the second cleaning procedure by opening the second
valve 111b to flow the second washing solution 109b from the second
reservoir 110b to the dispenser 108 via the conduit 112 for a
second period of time (e.g., about 1 to about 10 minutes for batch
processes and 30-90 seconds for single wafer processes). In certain
embodiments, the second washing solution 109b can include hydrogen
peroxide and hydrochloric acid in deionized water. In these
embodiments, it is believed that the second washing solution 109b
can remove metallic contamination (e.g., metallic chlorides) on the
surface of the microelectronic substrate 102. In other embodiments,
the second cleaning procedure can include rinsing the surface of
the microelectronic substrate 102 with only deionized water. In
further embodiments, the second cleaning procedure may be omitted.
In any of the foregoing embodiments, the operator can optionally
remove any remaining polyelectrolyte using oxygen plasma, wet
chemical treatments with sulfuric acid (H.sub.2SO.sub.4) and
hydrogen peroxide (H.sub.2O.sub.2) at a temperature of about
100.degree. C. to about 140.degree. C., and/or other suitable
techniques.
[0026] Several embodiments of the cleaning system 100 can more
efficiently remove adsorbed solid particles from the surface of the
microelectronic substrate 102 than conventional techniques. The
inventors have recognized that the addition of the polyelectrolyte
in the first washing solution 109a can statistically improve the
PRE over utilizing conventional cleaning solutions, e.g., an
aqueous solution of hydrogen peroxide (H.sub.2O.sub.2) and ammonium
hydroxide (NH.sub.4OH), commonly referred to as "SC1," with or
without the addition of anionic or non-ionic surfactants. As a
result, shorter cleaning periods may be utilized to increase
throughput.
[0027] Several embodiments of the cleaning system 100 can also
reduce or prevent material loss (commonly referred to as an
"undercut") caused by a washing solution. According to conventional
techniques, an etchant (e.g., hydrofluoric acid (HF)) is included
in a washing solution to overcome Van der Waals forces between
adsorbed particles and a microelectronic substrate. The etchant,
however, also removes material from the surface of the
microelectronic substrate and can generate surface defects
generally referred to as "HF defects." The HF defects are
considered destructive because they can render the microelectronic
substrate unacceptable for subsequent processing steps (e.g.,
component formation). As a result, such material loss at the
surface of the microelectronic substrate 102 caused by the washing
solution may not be tolerated. It is believed that the
polyelectrolyte additive, the anionic surfactant, or the non-ionic
surfactant can adsorb to the surface of the microelectronic
substrate, and thus passivate and protect the surface from material
loss.
[0028] Even though the cleaning system 100 illustrated in FIG. 1
has a first reservoir 110a and a second reservoir 110b, in certain
embodiments, the cleaning system 100 can include more or less
reservoirs holding the same or different washing solutions. For
example, the cleaning system 100 may also include a third reservoir
(not shown) holding deionized water for rinsing the microelectronic
substrate 102 after the first and/or second cleaning procedure. In
another example, the first washing solution 109a can contain a
first polyelectrolyte, and the second reservoir 110b can contain a
second polyelectrolyte that is different than the first
polyelectrolyte. The first and second polyelectrolytes can be
selected to remove different particles from the surface of the
microelectronic substrate 102.
[0029] FIG. 2 is schematic cross-sectional view of a cleaning
system 200 configured in accordance with another embodiment of the
disclosure. The cleaning system 200 includes a process tank or
vessel 210 and support elements 212 for carrying microelectronic
substrates 202. The process tank 210 can contain a washing solution
250 with a composition generally similar to that of the first
washing solution 109a discussed above with reference to FIG. 1. The
cleaning system 200 can also optionally include a transducer 220 in
the process tank 210 and a signal generator 240 operably coupled
with the transducer 220. The transducer 220 can include
piezoelectric or other mechanical elements that can be electrically
driven by the signal generator 240 to deliver sonic pressure waves
through the washing solution 250.
[0030] In operation, the support elements 212 can secure the
microelectronic substrates 202 in the washing solution 250. Then,
in certain embodiments, the optional signal generator 240 can
generate signals that energize the transducer 220 to produce
cavitation in the washing solution 250. Cavitation generally refers
to the creation and subsequent collapse of microscopic bubbles 204.
It is believed that the bubbles 204 can grow to a certain size and
then can partially collapse or completely implode. The collapse or
implosion of the bubbles 204 can impart energy to a surface of the
microelectronic substrates 202 to facilitate dislodging particles
from the microelectronic substrates 202. In other embodiments, the
microelectronic substrates 202 may be submerged in the washing
solution 250 for a period of time (e.g., 10 minutes) without
energizing the transducer 220 or otherwise imparting physical
energy onto the microelectronic substrates 202.
[0031] Several embodiments of the cleaning system 200 can
effectively clean microelectronic substrates 202 with reduced sonic
energy than conventional techniques. As discussed above, the
washing solution 250 having a polyelectrolyte can chemically
increase the repulsive forces between solid particles and/or the
microelectronic substrates 202 than conventional techniques. As a
result, less or no physical energy may be required to dislodge
adsorbed particles from the microelectronic substrates 202.
Accordingly, the risk of damaging surface features on the
microelectronic substrates 202 can be reduced.
[0032] Several experiments were conducted to determine the
effectiveness of cleaning solutions to remove adsorbed particles
from a surface of a microelectronic wafer. The surface containing a
thermal silicon oxide (SiO.sub.2) layer. In the experiments,
silicon nitride particles were first adsorbed onto the surface of
the microelectronic wafer. A dark-light inspection system (Model
No. Surfscan SP2) supplied by KLA-Tencor of San Jose, Calif., was
used to count the number of the adsorbed particles. The
microelectronic wafer was then transferred to a cleaning system
generally similar to that described above with reference to FIG. 1.
A washing solution was then dispensed onto the surface of the
microelectronic wafer for about 30 seconds. Then, the
microelectronic wafer was rinsed with deionized water while
spinning for about 30 seconds and subsequently dried. The dried
microelectronic wafer was then inspected again using the dark-light
inspection system to determine the number of particles remaining on
the surface of the microelectronic wafer. Then, PRE was calculated
based on the number of particles before and after the cleaning
procedure as follows:
PRE = ( N 1 - N 2 ) N 1 .times. 100 % ##EQU00001##
where N.sub.1 is the number of particles before the cleaning
procedure, and N.sub.2 is the number of particles after the
cleaning procedure. The surface of the microelectronic wafer was
also inspected for zeta potential and material loss (as represented
by etch delta). Even though the experiments were conducted with a
silicon oxide layer on the surface of the microelectronic
substrate, it is believed that similar results can be achieved with
titanium nitride (TiN.sub.x) layers, tungsten (W) layers, and
polysilicon (Si) layers.
[0033] In a first set of experiments, the washing solution includes
a SC1 solution having 3 parts hydrogen peroxide (H.sub.2O.sub.2), 2
parts ammonium hydroxide (NH.sub.4OH), and 100 parts deionized
water by volume. In a second set of experiments, the washing
solution includes the SC1 solution with 0.1% weight addition of
tetrabutylammonium perfluorooctanesulfonate (PFOS). In a third set
of experiments, the washing solution includes the SC1 solution with
0.1% weight addition of sorbitan monolaurate (SPAN20). In a fourth
set of experiments, the washing solution includes the SC1 solution
with 0.1% weight addition of PAA with a molecular weight of about
50,000. All these washing solutions had a pH of about 10 to about
10.3 and were maintained at about 65.degree. C. Even though the
experiments were directed toward adding PAA to SC1, it is expected
that adding other polyelectrolyte compounds would yield similar
results.
[0034] The following table shows the PRE results from these
experiments using the foregoing washing solutions, and FIG. 3 is a
plot of these results in accordance with an embodiment of the
disclosure.
TABLE-US-00001 Washing Solution Number of Samples Mean PRE Standard
Error SC1 12 0.99958 0.01178 With PFOS 7 0.90700 0.01542 With
SPAN20 3 0.92000 0.02355 With PAA 5 1.07560 0.01824
As can be seen from the table above and FIG. 3, the washing
solutions with the anionic surfactant and the non-ionic surfactant
performed generally equivalent to or worse than SC1. The washing
solution with PAA, however, outperformed SC1 by about 2% to about
13% based on normalized PRE.
[0035] The following table shows the HF defect results from these
experiments as represented by etch delta, and FIG. 4 is a plot of
the etch delta of various washing solutions in accordance with an
embodiment of the disclosure.
TABLE-US-00002 Mean Etch Washing Solution Number of Samples Delta
(.ANG.) Standard Error SC1 6 0.331667 0.02261 With PFOS 7 0.095000
0.03917 With SPAN20 2 0.195000 0.03917 With PAA 4 0.085000
0.02770
As can be seen from the table above and FIG. 4, the solutions with
an organic additive (e.g., PAA, PFOS, or SPAN20) all had less etch
delta than the SC1 solution. The washing solution with PAA has the
least etch delta when compared to the SC1 solution and those
solutions with the anionic surfactant and the non-ionic surfactant.
As a result, the washing solution with PAA, the anionic surfactant,
or the non-ionic surfactant had reduced material loss from the
surface of the microelectronic substrate than SC1.
[0036] The following table shows the average zeta potential results
from these experiments, and FIG. 5 is a plot of the average zeta
potential of various washing solutions in accordance with an
embodiment of the disclosure.
TABLE-US-00003 Mean Zeta Washing Solution Number of Samples
Potential (mV) Standard Error SC1 6 -70.00 0.02261 With PFOS 2
-92.00 0.03917 With SPAN20 2 -50.00 0.03917 With PAA 4 -105.00
0.02770
As can be seen from the table above and FIG. 5, the washing
solutions with the anionic surfactant and the non-ionic surfactant
had a larger impact on the average zeta potential of the particles
than the washing solution with PAA. As a result, the improved PRE
performance of the washing solution with PAA is probably not due to
increased average electrostatic repulsion.
[0037] From the foregoing, it will be appreciated that specific
embodiments of the disclosure have been described herein for
purposes of illustration, but that various modifications may be
made without deviating from the disclosure. For example, many of
the elements of one embodiment may be combined with other
embodiments in addition to or in lieu of the elements of the other
embodiments. Accordingly, the disclosure is not limited except as
by the appended claims.
* * * * *