U.S. patent application number 11/341238 was filed with the patent office on 2006-06-08 for compositions and methods for high-efficiency cleaning of semiconductor wafers.
Invention is credited to Thomas H. Baum, Eliodor G. Ghenciu, Michael B. Korzenski, David Minsek, Chongying Xu.
Application Number | 20060122085 11/341238 |
Document ID | / |
Family ID | 33539497 |
Filed Date | 2006-06-08 |
United States Patent
Application |
20060122085 |
Kind Code |
A1 |
Korzenski; Michael B. ; et
al. |
June 8, 2006 |
Compositions and methods for high-efficiency cleaning of
semiconductor wafers
Abstract
A composition including supercritical fluid and at least one
additive selected from fluoro species, and primary and/or secondary
amines, optionally with co-solvent, low k material
attack-inhibitor(s) and/or surfactant(s). The composition has
particular utility for cleaning of semiconductor wafers to remove
post-ashing residues therefrom.
Inventors: |
Korzenski; Michael B.;
(Danbury, CT) ; Xu; Chongying; (New Milford,
CT) ; Baum; Thomas H.; (New Fairfield, CT) ;
Minsek; David; (Pleasantville, NY) ; Ghenciu; Eliodor
G.; (King of Prussia, PA) |
Correspondence
Address: |
MOORE & VAN ALLEN PLLC
P.O. BOX 13706
Research Triangle Park
NC
27709
US
|
Family ID: |
33539497 |
Appl. No.: |
11/341238 |
Filed: |
January 27, 2006 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
10602172 |
Jun 24, 2003 |
|
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11341238 |
Jan 27, 2006 |
|
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Current U.S.
Class: |
510/175 ;
257/E21.255 |
Current CPC
Class: |
Y10S 438/906 20130101;
C11D 7/28 20130101; H01L 21/31133 20130101; C11D 7/5013 20130101;
G03F 7/425 20130101; C11D 11/0047 20130101; C11D 7/3209 20130101;
Y10S 134/902 20130101; H01L 21/02063 20130101; C11D 7/261
20130101 |
Class at
Publication: |
510/175 |
International
Class: |
C11D 7/32 20060101
C11D007/32 |
Claims
1.-96. (canceled)
97. A method of cleaning a semiconductor wafer having residue
thereon, said method comprising contacting the semiconductor wafer
with a cleaning composition for sufficient time to remove residue
from the semiconductor wafer having same thereon, wherein said
cleaning composition comprises at least one cleaning concentrate
and at least one supercritical fluid and said cleaning concentrate
comprises at least one fluoro species and boric acid.
98. The method of claim 97, further comprising forming said
cleaning composition by: (a) subjecting at least one source fluid
to pressure and temperature conditions wherein the source fluid
becomes said supercritical fluid; and (b) adding said cleaning
concentrate to the supercritical fluid to produce said cleaning
composition.
99. The method of claim 97, wherein the at least one source fluid
comprises a species selected from the group consisting of carbon
dioxide, oxygen, argon, krypton, xenon, ammonia, methane, methanol,
dimethyl ketone, hydrogen, forming gas, and sulfur
hexafluoride.
100. The method of claim 97, wherein the at least one source fluid
comprises carbon dioxide.
101. The method of claim 97, wherein the at least one fluoro
species comprises a fluorine-containing compound selected from the
group consisting of hydrogen fluoride (HF), ammonium fluoride
(NH.sub.4F), alkyl hydrogen fluoride (NRH.sub.3F), dialkylammonium
hydrogen fluoride (NR.sub.2H.sub.2F), trialkylammonium hydrogen
fluoride (NR.sub.3HF), trialkylammonium trihydrogen fluoride
(NR.sub.3(3HF)), tetraalkylammonium fluoride (NR.sub.4F), and xenon
difluoride (XeF.sub.2), wherein each R is independently selected
from C.sub.1-C.sub.8 alkyl and C.sub.6-C.sub.10 aryl.
102. The method of claim 97, wherein the at least one fluoro
species comprises triethylamine trihydrogen fluoride.
103. The method of claim 97, wherein the cleaning concentrate
further comprises at least one co-solvent.
104. The method of claim 103, wherein the at least one co-solvent
comprises an organic species selected from the group consisting of
methanol, ethanol, isopropyl alcohol, N-alkylpyrrolidones,
N-arylpyrrolidones, dimethylsulfoxide, sulfolane, catechol, ethyl
lactate, acetone, butyl carbitol, monoethanolamine, butyrol
lactone, diglycol amine, .gamma.-butyrolactone, butylene carbonate,
ethylene carbonate, and propylene carbonate, wherein alkyl is
C.sub.1-C.sub.8 alkyl and aryl is C.sub.6-C.sub.10 aryl.
105. The method of claim 103, wherein the at least one co-solvent
comprises an organic species selected from the group consisting of
methanol, ethanol, and isopropyl alcohol.
106. The method of claim 97, wherein the supercritical fluid is
present in an amount of from about 80% by weight to about 99.01% by
weight, based on the total weight of the composition.
107. The method of claim 97, wherein the at least one fluoro
species is present in an amount of from about 0.01% by weight to
about 5% by weight, based on the total weight of the
composition.
108. The method of claim 97, wherein the boric acid is present in
an amount of up to about 5% by weight, based on the total weight of
the composition.
109. The method of claim 103, wherein the at least one co-solvent
is present in an amount of from about 1% to about 20% by weight,
based on the total weight of the composition.
110. The method of claim 97, wherein the contacting is carried out
at pressure in a range of from about 800 to about 10,000 psi.
111. The method of claim 97, wherein the contacting is carried out
at temperature in a range of from about 20 to about 150.degree.
C.
112. The method of claim 97, wherein the residue comprises material
selected from the group consisting of post-etch photoresist residue
and post-ash residue.
113. The method of claim 97, further comprising washing the
semiconductor wafer, at a region at which residue has been removed,
with a SCF-containing solution to remove post-removal residue and
fluoro species from said semiconductor wafer.
114. The method of claim 103, wherein the cleaning concentrate
comprises triethylamine trihydrogen fluoride, boric acid, and at
least one co-solvent, wherein the at least one co-solvent comprises
an alcohol selected from the group consisting of methanol, ethanol,
and isopropyl alcohol.
115. A kit comprising, in one or more containers, two or more of
the following reagents for forming a cleaning concentrate: at least
one fluoro species, boric acid, and optionally at least one
co-solvent, wherein the kit is adapted to form a cleaning
concentrate which is suitable for combination with at least
supercritical fluid.
116. A composition for cleaning semiconductor wafers, wherein the
composition comprises a supercritical fluid, at least one fluoro
species, boric acid, and at least one co-solvent.
117. The composition of claim 116, further comprising residue
material.
118. The composition of claim 117, wherein the residue comprises
material selected from the group consisting of post-etch
photoresist residue and post-ash residue.
Description
CROSS REFERENCE TO RELATED APPLICATIONS
[0001] This is a continuation of the U.S. patent application Ser.
No. 10/602,172 for "Compositions and Methods for High-Efficiency
Cleaning of Semiconductor Wafers" filed on Jun. 24, 2003 in the
name of Michael B. Korzenski et al., which is incorporated herein
in its entirety.
FIELD OF THE INVENTION
[0002] The present invention relates to compositions and methods
for high-efficiency cleaning of semiconductor wafers.
DESCRIPTION OF THE RELATED ART
[0003] The fabrication of multi-layer semiconductor circuits
requires the deposition of multiple patterned layers of
semiconductor, conductor and dielectric materials. Patterning is
conventionally carried out by optical imaging of a photoresist
layer formed from a composition containing a soluble polymer and a
photoactive compound. Following patterning, deposition, and
etching, the photoresist layer must be completely removed before
the next processing step.
[0004] Plasma ashing can remove photoresist but leaves a post-ash
residue on the substrate that must be removed. Typically, liquid
photoresist or post-ash residue removers are employed. Such
removers, however, generate a large amount of hazardous waste that
is harmful to the environment, and costly to dispose of, or
treat.
[0005] The art therefore has a continuing and critical need for
improved compositions for cleaning of residues, e.g., post-ashing
residues, from semiconductor wafers (such term herein including
wafer base or substrate articles per se, as well as such articles
having material deposited thereon or therein to form semiconductor
devices or precursor structures for such devices.
[0006] As a further and specific problem attendant the use of
conventional liquid-based cleaning and post-etch residue removal
compositions, the geometric scale of features in semiconductor
device architectures continues to diminish. At critical dimensions
(of high aspect ratio vias, deep trenches and other semiconductor
device or precursor structure features) below 0.1 .mu.m, the high
surface tension that is characteristic of aqueous compositions used
to clean wafers prevents the penetration of the composition into
the semiconductor wafer features.
[0007] Thus, although liquid-based cleaning and post-etch residue
removal integrated circuit processes are well-developed and
accepted for device manufacturing, their future utility is highly
questionable. Apart from problems attendant the high surface
tension of aqueous cleaning compositions, copper, porous, low-k
multi-layers may require special, non-aqueous cleaning to eliminate
aqueous contamination of the pores and consequent reduction of
device yields when pore contaminants cannot be removed.
Additionally, the dielectric constant of low k materials is
critical and aqueous contamination can negatively increase the
dielectric constant.
[0008] The foregoing highlights the need of the art for improved
cleaning compositions and methods for removal of post-etch
lithographic resist (polymer) residue, removal of chemical
mechanical planarization (CMP) particles in deep-trench, high
aspect ratio vias, removal of metal oxides, metal residues and
metal contaminants that remain on the wafer after etching, CMP and
interconnect processes (e.g., physical vapor deposition (PVD),
chemical vapor deposition (CVD) and plating) for metalization.
SUMMARY OF THE INVENTION
[0009] The present invention relates to compositions and methods
for high-efficiency cleaning of semiconductor wafers.
[0010] In one aspect, the invention relates to a composition for
cleaning semiconductor wafers, wherein the composition includes a
supercritical fluid and at least one additive selected from the
group consisting of:
[0011] a. fluoro-species; and
[0012] b. primary and/or secondary amine(s).
[0013] Another aspect of the invention relates to a method of
cleaning of a semiconductor wafer, wherein the method comprises
contacting the semiconductor wafer with a supercritical fluid-based
cleaning composition including supercritical fluid and at least one
additive selected from the group consisting of:
[0014] a. fluoro-species; and
[0015] b. primary and/or secondary amine(s).
[0016] Other aspects, features and embodiments of the invention
will be more fully apparent from the ensuing disclosure and
appended claims.
BRIEF DESCRIPTION OF THE DRAWINGS
[0017] FIG. 1 is a scanning electron microscope (SEM) micrograph of
a post-ashing trench structure in a two-layer coating on a silicon
substrate, wherein the two-layer coating includes a first (lower)
layer of low k dielectric material and a second (upper) layer of a
capping dielectric material, before cleaning.
[0018] FIG. 2 is an SEM micrograph of the trench structure of FIG.
1, after washing with a cleaning composition comprising SCCO.sub.2,
ethanol, (C.sub.2H.sub.5).sub.3N(3HF) and boric acid.
[0019] FIGS. 3A and 3B are scanning electron microscope (SEM)
micrographs of a post-ashing trench structure in a two-layer
coating on a silicon substrate, wherein the two-layer coating
includes a first (lower) layer of low k dielectric material and a
second (upper) layer of a capping dielectric material, before
cleaning.
[0020] FIG. 4 is an SEM micrograph of the trench structure of FIG.
1, after washing with a cleaning composition comprising SCCO.sub.2,
isopropanol, NH.sub.4F and non-ionic surfactant.
DETAILED DESCRIPTION OF THE INVENTION, AND PREFERRED EMBODIMENTS
THEREOF
[0021] The present invention relates to compositions and methods
for high-efficiency cleaning of semiconductor wafers. The
compositions include supercritical fluid and at least one additive
selected from the group consisting of (I) fluoro-species and (II)
primary and/or secondary amine(s). Such compositions optionally
further include co-solvent, low k material-attack-inhibitor, and/or
surfactant species, as variously employed in specific embodiments
of the invention.
[0022] In general, the compositions of the invention as variously
hereinafter described may alternatively "comprise," "consist" or
"consist essentially of" the ingredients specified for such
compositions. Additionally, compositions of the invention can
further include stabilizers, dispersants, etc., and other
ingredients, as appropriate to the formulation and use of such
compositions.
[0023] In one aspect, the invention provides wafer-cleaning
compositions utilizing a supercritical fluid (SCF) in combination
with hydrogen fluoride and/or a fluoride ion source.
[0024] The invention in such aspect utilizes a supercritical fluid
component having the viscosity and diffusivity of a gas, and
thereby capable of penetrating quickly into interstices, trenches,
high aspect ratio vias, and other finely-dimensioned features of
the wafer article. The supercritical fluid comprises a substantial
major fraction of the cleaning composition. The cleaning
composition also compensates for the polarity of the SCF by
inclusion of a component having a polarity that is opposite to that
of the SCF. For example, the non-polar character of a SCCO.sub.2
component is compensated by incorporation of a hydrogen fluoride
(HF) and/or fluoride ion
[0025] (F) component, hereafter referred to as "fluoro species," so
that the SCF's inherently low ability to solubilize polymer and/or
post-ash residues is obviated by the presence of the fluoro
species, which imparts to the composition the capability to
solubilize polar surface residues on the semiconductor wafer, and
to increase the etch rates of aqueous as well as non-aqueous
solutions.
[0026] It is indeed surprising that SCF and fluoro species in
combination would be an effective cleaning combination for
photoresist and post-ashing residues on the semiconductor wafer,
since fluoro species exhibit very low solubilities in SCF media,
and since it would be expected that the SCF would be such an
effective penetrant as to blanket the wafer surface preferentially
and produce only a low level, if any, of polymer and/or post-ashing
residue from the wafer surface, so that any removal action caused
by chemical (etching) attack on the wafer surface would be
negligible or energetically disfavored. This however, has been
discovered to not be the case. Contrariwise, the combination of SCF
and fluoro species has been demonstrated to be an effective
cleaning combination having superior ability to remove polymer
resist materials as well as post-ash residues from the wafer
surface.
[0027] SCF/fluoro species compositions of the invention are readily
formulated for use in cleaning of oxides and oxide-containing
residues, by subjecting the source fluid for the SCF to pressure
and temperature conditions above the critical point where the
source fluid becomes a supercritical fluid. Once the source fluid
is in the SCF state, the fluoro species and optional other
ingredients of the composition are added, e.g., under simple mixing
or blending conditions to produce a homogeneous cleaning
composition.
[0028] Such optional other ingredients include co-solvent media (to
enhance the solubility of the fluoro species in the SCF),
inhibitors (to prevent or at least minimize attack of the cleaning
composition on low k and other susceptible materials on the wafer
surface), surfactants (to increase the homogeneity of the
composition and the compatibility of its blended components), and
other additives, adjuvants and enhancers such as may be useful or
desirable in a given cleaning operation.
[0029] The SCF used in compositions of the invention can be of any
suitable type. Non-limiting examples of SCF species that can be
used in the broad practice of the invention include carbon dioxide,
oxygen, argon, krypton, xenon, ammonia, methane, methanol, dimethyl
ketone, hydrogen, forming gas, and sulfur hexafluoride. Carbon
dioxide is particularly preferred.
[0030] Fluoro species usefully employed in the broad practice of
the invention include, without limitation, hydrogen fluoride (HF),
ammonium fluoride (NH.sub.4F), alkyl hydrogen fluoride
(NRH.sub.3F), dialkylammonium hydrogen fluoride (NR.sub.2H.sub.2F),
trialkylammonium hydrogen fluoride (NR.sub.3HF), trialkylammonium
trihydrogen fluoride (NR.sub.3(3HF)), tetraalkylammonium fluoride
(NR.sub.4F), and xenon difluoride (XeF.sub.2), wherein each R in
the aforementioned R-substituted species is independently selected
from C.sub.1-C.sub.8 alkyl and C.sub.6-C.sub.10 aryl. Triethylamine
trihydrogen fluoride is a preferred fluoro species due to its mild
fluorination properties and favorable solubility in CO.sub.2 when
supercritical carbon dioxide SCCO.sub.2 is employed as the SCF
species. Ammonium fluoride is another preferred fluoro species,
e.g., in compositions containing co-solvent media, due to its low
toxicity and ease of handling, as well as the acid-base buffering
action associated with the ammonia-HF combination.
[0031] Co-solvent species useful in the cleaning compositions of
the invention may be of any suitable type, including alcohols,
amides, ketones, esters, etc. Illustrative species include, but are
not limited to, methanol, ethanol, and higher alcohols,
N-alkylpyrrolidones or N-arylpyrrolidones, such as N-methyl-,
N-octyl-, or N-phenyl-pyrrolidones, dimethylsulfoxide, sulfolane,
catechol, ethyl lactate, acetone, butyl carbitol, monoethanolamine,
butyrol lactone, diglycol amine, .gamma.-butyrolactone, butylene
carbonate, ethylene carbonate, and propylene carbonate. Alcohols
such as methanol, ethanol and isopropyl alcohol (IPA) are
especially preferred.
[0032] Inhibitor additives may be used in the compositions of the
invention to inhibit attack of the cleaning composition on low
dielectric constant layers. Inhibitor species such as organic acids
and/or inorganic acids are usefully employed for such purpose.
Boric acid is a particularly preferred species.
[0033] The relative proportions of the above-described ingredients
of the cleaning compositions of the invention can be widely varied
to achieve a desired solvating and removal effect in application to
photoresist and post-ashing residue removal from semiconductor
wafers.
[0034] In general the SCF species comprises a substantial major
fraction of the cleaning composition, typically constituting from
about 75% by weight, based on the weight of the cleaning
composition, to about 99.9% by weight, on the same cleaning
composition weight basis. The fluoro species can be present in a
suitable amount in relation to the SCF species, and amounts of from
about 0.01% by weight to about 5% by weight, based on the weight of
the cleaning composition, are usefully employed in specific
embodiments of the invention. Low k material attack-inhibitors may
optionally be present in an amount of up to about 5% by weight,
based on the total weight of the composition. Co-solvent species
may optionally be employed in the compositions of the invention, at
concentrations of up to about 25% by weight, based on the total
weight of the composition, when employed to increase solubility of
the fluoro species in the particular SCF species employed.
Surfactants may optionally be utilized in compositions of the
invention at concentrations of up to 5% by weight, based on the
weight of the cleaning composition. In the compositions including
such species, the total weight percent of all ingredients is
100%.
[0035] In a specific illustrative embodiment, the cleaning
composition has the following formulation, wherein all percentages
are by weight:
[0036] a. Carbon dioxide: 80-99.01% (w/w)
[0037] b. Fluoride species: 0.01-5.0% (w/w)
[0038] c. Low-k material attack inhibitor: 0.0-5.0% (w/w)
[0039] d. Co-solvent: 0-20% (w/w)
[0040] e. TOTAL: 100% by weight
[0041] In another specific illustrative embodiment, the cleaning
composition has the following formulation, wherein all percentages
are by weight:
[0042] a. Carbon dioxide: 80-99% (w/w)
[0043] b. Fluoride species: 0.01-5.0% (w/w)
[0044] c. Co-solvent: 1-20% (w/w)
[0045] d. Surfactant: 0.0-5.0% (w/w)
[0046] e. TOTAL: 100% by weight
[0047] The pressure of the cleaning composition can be in a range
of from about 800 to about 10,000 psi, e.g., about 4000 psi, with
temperature of the composition being in a range of from about 20 to
about 150.degree. C., and more preferably in a range of from about
40 to about 100.degree. C., e.g., a temperature of about 50 to
about 80.degree. C.
[0048] In an illustrative cleaning process according to the present
invention, in one embodiment thereof, the substrate (wafer) to be
cleaned is placed in a sealed high-pressure chamber. The chamber
then is filled with the cleaning composition of the invention, and
the substrate is held under the cleaning solution for a
predetermined time, at predetermined pressure and temperature, as
appropriate to effect the desired cleaning of the substrate. The
specific contact time of the cleaning composition with the
substrate, and process (e.g., temperature and pressure) conditions
can be readily determined by simple experiment, based on the
disclosure herein, within the skill of the art.
[0049] After the substrate has been subjected to the cleaning
composition for sufficient time and at sufficient processing
conditions, the substrate may be rinsed with a solution containing
only the SCF species, or alternatively containing only the SCF
species and optional co-solvent(s), in order to remove the residue
and the fluoro species. After rinsing for a sufficient time to
effect appropriate removal of the residue and fluoro species, the
cleaning chamber may be vented and the substrate may be removed.
Appropriate rinsing conditions can readily be determined within the
skill of the art, based on the disclosure herein, to achieve a
specific removal character and extent.
[0050] In another aspect, the invention provides wafer cleaning
compositions utilizing supercritical fluid (SCF) in combination
with primary and/or secondary amine(s).
[0051] Such cleaning compositions, utilizing primary and/or
secondary amine(s) in the SCF-based cleaning composition,
optionally in combination with co-solvent(s), inhibitor(s) and/or
surfactant(s), are advantageous for cleaning of photoresists,
anti-reflective coatings, metal oxides and/or metal-containing
residues that are present on the semiconductor wafer after plasma
etching or ashing.
[0052] In such amine-containing SCF cleaning compositions,
co-solvent(s) and/or surfactant(s) are optionally employed to
enhance the compatibility of the primary and/or secondary amine(s)
with the SCF in the composition. The composition can comprise from
about 75% to about 99.9% by weight, based on the weight of the
cleaning composition, of the SCF, from about 0.01% to about 5.0% by
weight of the primary and/or secondary amine(s), from about 0% to
about 25% by weight of co-solvent(s), and up to about 5% by weight
of surfactant(s), on the same total composition weight basis, with
all ingredients of the composition totaling to 100 weight %.
Compositions of such type may further optionally comprise inhibitor
species to suppress attack on low k materials that may be present
on the wafer being cleaned.
[0053] Particularly preferred amine-containing SCF cleaning
compositions of above-described type include from about 80 to about
99.9% by weight of SCCO.sub.2, from about 0.01% to about 5.0% by
weight of primary or secondary amine, from about 0% to about 20% by
weight of co-solvent, and up to 5% by weight of surfactant, with
all ingredient weight percentages being based on the total weight
of the composition, and with all weight percentage amounts of such
ingredients totaling to 100 weight %.
[0054] The SCF in such composition can suitably include any of the
illustrative SCF species described hereinabove. SCCO.sub.2 is a
particularly preferred SCF species for such purpose. Suitable
amines include, without limitation, hydroxylamine (NH.sub.2OH),
ammonia (NH.sub.3), alkylamines (R--NH.sub.2) and dialkylamines
(R.sub.1R.sub.2NH), wherein R, R.sub.1 and R.sub.2 are each
independently selected from C.sub.1-C.sub.8 alkyl and
C.sub.6-C.sub.10 aryl. Co-solvents can be of any suitable type,
including alcohols, amides, ketones, esters, lactones, 1,3-diones,
etc., with alcohols such as isopropyl alcohol (IPA) being
particularly preferred. Surfactants likewise can be of any suitable
type, preferably including a non-ionic surfactant such as the
non-ionic surfactants commercially available from Air Products
& Chemicals, Inc. under the trademark Surfynol.RTM..
Inhibitor(s), when used, can be of a type as previously described
in connection with fluoro species-containing SCF cleaning
compositions of the invention.
[0055] Amine-containing SCF cleaning compositions of the invention
can be deployed for cleaning at any appropriate supercritical fluid
conditions of temperature and pressure. Typically, such
compositions are utilized at pressure in a range of from about 800
and about 10,000 psi, e.g., about 4000 psi, and temperature in a
range of from about 20 to about 150.degree. C., e.g., and more
preferably from about 40 to about 100.degree. C. Specific process
conditions of temperature and pressure are readily determinable
within the skill of the art based on the disclosure herein, by
simple formulation, varying of process conditions, and
determination of the nature and extent of cleaning thereby
achieved, in a particular application of the cleaning
composition.
[0056] The features and advantages of the invention are more fully
illustrated by the following non-limiting examples.
[0057] FIG. 1 is a scanning electron microscope (SEM) micrograph of
a post-ashing trench structure in a two-layer coating on a silicon
substrate, wherein the two-layer coating includes a first (lower)
layer of low k dielectric material and a second (upper) layer of a
capping dielectric material, before cleaning.
[0058] FIG. 2 is an SEM micrograph of the trench structure of FIG.
1, after washing with a cleaning composition in accordance with one
embodiment of the present invention. In FIG. 1, the post-ashing
residue is visible as a continuous wall covering the trench
sidewall. FIG. 2 shows the same trench structure after cleaning for
approximately 2 minutes with a composition comprising a mixture of
about 10% by weight ethanol solution in SCCO.sub.2, wherein the
ethanol solution comprises about 0.5 wt %
(C.sub.2H.sub.5).sub.3N(3HF) and about 0.25 weight % boric acid. A
rinsing step follows after the cleaning step where the trench
structure is rinsed in SCCO.sub.2 solvent for approximately 5
minutes. Advantageously, the post-ashing (oxidizing or reducing)
sidewall residue has been removed, without attack on the dielectric
materials of the structure. Process conditions utilized in such
embodiment include pressure, temperature and flow rate of
approximately 4000 psi, 50.degree. C. and 50 mL/min.,
respectively.
[0059] FIGS. 3A and 3B are scanning electron microscope (SEM)
micrographs of a post-ashing trench structure in a two-layer
coating on a silicon substrate, wherein the two-layer coating
includes a first (lower) layer of low k dielectric material and a
second (upper) layer of a capping dielectric material, before
cleaning.
[0060] FIG. 4 is an SEM micrograph of the trench structure in the
two-layer coating on the silicon substrate of FIGS. 3A and 3B,
after washing with a cleaning composition in accordance with a
further embodiment of the present invention. FIG. 4 shows the same
trench structure after cleaning for approximately 2 minutes with a
composition comprising a mixture of about 10% by weight isopropanol
solution in SCCO.sub.2, wherein the isopropanol solution comprises
about 0.5 wt % NHF.sub.4, about 0.25 wt % boric acid, and 0.5 wt %
surfactant. A rinsing step follows after the cleaning step where
the trench structure is rinsed in SCCO.sub.2 solvent for
approximately 5 minutes. Process conditions utilized in such
embodiment include pressure, temperature and flow rate of
approximately 4000 psi, 50.degree. C. and 50 mL/min.,
respectively.
[0061] Post-ash residue is clearly visible on the surface of the
wafer in FIGS. 3A and 3B. FIG. 4 shows that after cleaning the
post-ash residue has been removed, with some etching of the
dielectric materials. An undercut is visible, which is due to
faster etching of the lower (low k) dielectric material.
[0062] The micrographs of FIGS. 1-4 thus evidence the efficacy of
the cleaning compositions of the invention, for high efficiency
cleaning of post-ashing residue on semiconductor wafers.
[0063] While the invention has been described herein in reference
to specific aspects, features and illustrative embodiments of the
invention, it will be appreciated that the utility of the invention
is not thus limited, but rather extends to and encompasses numerous
other aspects, features and embodiments. Accordingly, the claims
hereafter set forth are intended to be correspondingly broadly
construed, as including all such aspects, features and embodiments,
within their spirit and scope.
* * * * *